Conductance-voltage Characteristics Research Articles

Impact of Oxide Charges on The Minority Carrier Response in MOS(p) Devices With Al2O3/SiO2 Gate Stacks under Strong Inversion Condition

Admittance measurement, including capacitance and conductance, is very useful to analyze the electrical characteristics of metal-oxide-semiconductor (MOS) systems. These techniques offer insights into various device properties, including interface trap density and minority carrier lifetime in the substrate. It is essential to note that, apart from the gate area, the oxide region beyond the device could significantly influence measurement results [1]-[2]. In this work, a compact model proposed in [3] was used to clarify an unusual minority carrier response time observed in experimental data. The results proved the heightened sensitivity of device alternating current (AC) characteristics to oxide charges in the outer region. Additionally, the dependencies of oxide thickness and quality on the transition frequency (ωm) of devices were explored.The MOS (Al/AlOx/SiO2/p-Si) structure illustrated in Fig. 1 was employed in this study. Aluminum oxide region is under the gate electrode, while silicon oxide (SiO2) covers the entire wafer. Table 1 summarizes samples (S1 to S5) with consistent aluminum oxide thickness but diverse SiO2 thickness. Fig 2. shows the process flow and the anodic oxidation (ANO) system. By tilting the wafer at a specific angle during ANO, a high-quality SiO2 layer with different thicknesses on a single wafer could be obtained. Fig 3(a) to (d) illustrate the capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of devices with varying SiO2 thicknesses. All devices exhibit low-frequency capacitance characteristics in strong inversion regions with thickness-dependent minority carrier response, particularly at 10kHz. Additionally, devices show different thicknesses depending on G-V characteristics at 1MHz and 10kHz. Fig 4(a) and (b) illustrate the Cinv/Cox ratio for varied oxide thicknesses and Gm/ω characteristics under strong inversion bias (VG = +3V). Gm means the measurement conductance. Following established research [3], peak Gm/ω magnitudes would occur at ωm. Table 2 reveals microsecond-range response times (τR) at ωm, considerably faster than conventional silicon minority carrier lifetimes (usually 1 ms to 100 ms). Moreover, decreasing oxide thickness shifts the ωm toward lower values.To explain this observed phenomenon, the environment outside the devices should be taken into consideration. Fig 5(a) and (b) show the schematic diagram and AC signal model proposed in [1] and [2]. Oxide charges in the outer region would deplete majority carriers and invert the p-type silicon surface to an n-type inversion layer. As a result, the lateral depletion region (Cd, out) and conductive channel (Rs) are formed outside the device, which are functions of substrate doping concentration and the effective oxide charges. The detailed model derivation is discussed in [2]. For this reason, an AC signal applied on the gate would extend outside the device for about a millimeter to a micrometer, affecting measuring results. Based on the model, the effective charges in the SiO2 could be extracted by measuring results. The thicker oxide has more oxide charges, as shown in Fig 6(a). Fig 6(b) and (c) show the modeling results of the Cinv/Cox ratio versus different oxide thicknesses and the Gm/ω-ω plot, which are very close to the experimental results. By simplifying the conductance formula (Gm), Gm reveals an inverse proportional to lateral effective conductance (GLeff) at low frequency (e.g., 10 kHz) and a direct proportional at high frequency (e.g., 1 MHz). Thicker SiO2 devices possess more oxide charges, leading to a greater lateral coupling effect, resulting in a greater GLeff compared to thinner devices. This elucidates the observed variations in Gm-V characteristics at 1 MHz and 10 kHz. Figures 7(a) and (b) display TCAD-simulated C-V and ωm for devices with varying oxide charge densities, confirming that minor changes in oxide charges result in noticeable differences in minority carrier responses in the strong inversion region. Fig 8(a) and (b) show the TCAD simulated results for devices with low doping substrate. For low doping substrates, oxide charges play a much more important role under AC operation.In summary, the study established a correlation between oxide charge densities and thicknesses. The origin of the faster minority carrier response and the peak shift in Gm/ω- ω plot were thoroughly explained and validated by TCAD simulation. Oxide charges were found to play a crucial role, especially in low-doping substrates, offering insights for advanced IC fabrication.[1] E. H. Nicollian and A. Goetzberger, IEEE Transactions on Electron Devices, vol. 12, no. 3, pp. 108-117, 1965.[2] K. C. Chen, K. W. Lin, S. W. Huang, J. Y. Lin, and J. G. Hwu, IEEE Journal of the Electron Devices Society, vol. 10, pp. 960-969, 2022.[3] S. Monaghan et al., IEEE Transactions on Electron Devices, vol. 61, no. 12, pp. 4176-4185, 2014. Figure 1

The electrical and dielectric features of Al/YbFeO3/p-Si/Al and Al/YbFe0.90Co0.10O3/p-Si/Al structures with interfacial perovskite-oxide layer depending on bias voltage and frequency

In this investigation, thin films of YbFeO3, both in its pure form and doped with 10% Co, were fabricated on a p-Si substrate at 500 °C through the radio-frequency magnetron sputtering method. Examination via Scanning Electron Microscopy demonstrated a porous texture for the pure sample, contrasting with a smooth and crack-free surface post-Co doping. Analysis via X-ray photoelectron spectroscopy unveiled Yb’s 3 + oxidation state, alongside the presence of lattice oxygen, oxygen vacancies, and adsorbed oxygen evident in Gaussian fitting curves. Photoluminescence spectroscopy revealed an augmented emission intensity, likely attributed to increased defect initiation in the Co-doped specimen. Moreover, Raman spectroscopy was employed to identify vibration modes in the examined samples, demonstrating shifts in Raman peaks indicative of Co substitution and subsequent distortion in the crystal structure of YbFeO3. Electrical assessments were conducted at room temperature (300 K) under ambient conditions, employing voltage and frequency as variables. Capacitance–voltage measurements illustrated the emergence of an accumulation, with depletion and inversion regions manifesting at different frequencies based on the applied voltage, attributed to the YbFeO3 interfacial layer at the Al and p-Si interface. The conductance-voltage characteristics indicated that the structure exhibited maximum conductance in the accumulation region. Series resistance for these configurations was deduced from capacitance-conductance-voltage measurements, indicating a dependence on both bias voltage and frequency. The doping process led to a reduction in capacitance and series resistance, accompanied by an increase in conductance values. After obtaining corrected capacitance and conductance parameters, it became evident that series resistance significantly influences both parameters. Interface state density (Nss), determined through the Hill-Coleman relation demonstrated a decreasing trend with increasing frequency. The pure sample exhibited higher interface state density compared to the Co-doped sample at each frequency, highlighting that the 10% Co-doped YbFeO3 thin film enhances the quality of the metal–semiconductor interface properties compared to the pure contact.

Sol-Gel Multilayered Niobium (Vanadium)-Doped TiO2 for CO Sensing and Photocatalytic Degradation of Methylene Blue.

Multilayered TiO2 films doped either with Niobium or Vanadium (1.2 at. %) were deposited by the sol-gel dip coating method on c-Si and glass substrates. The films on glass substrates were tested for CO sensing and photocatalytic degradation of methylene blue. X-ray diffraction data analysis showed that all the TiO2:Nb(V) films were nanocrystalline in the anatase phase, with a uniform and compact microstructure and a homogeneous superficial structure of small grains with diameters in the range of 13-19 nm. For the electrical characterization, the TiO2:Nb(V) films were incorporated in Metal-Insulator-Semiconductor (MIS) structures. The specific resistivity is of the order of 104 Ωcm and its value decreases with increasing the electrical field, which testifies to the injection of electrons into these layers. From the analysis of the current-voltage curves taken at different temperature- and frequency-dependent capacitance-voltage and conductance-voltage characteristics, the density and parameters of deep levels in these TiO2 films are evaluated and the electron charge transport mechanism is established. It was shown that the current in these TiO2:Nb(V)-Si MIS structures is mainly carried out by inter-trap tunneling via deep levels energetically distributed in the TiO2 bandgap. Testing these sol-gel TiO2:Nb(V) layers for gas sensing and photocatalytic capabilities proved that they could serve such purposes. In particular, the results of the V-doped sol-gel TiO2 film confirm its CO detection capability, which is rarely reported in the literature. For the photodegradation of methylene blue, the Nb-doped TiO2 samples were superior, with nearly double the photocatalytic efficiency of undoped TiO2.

A numerical modeling of the frequency dependence of the capacitance–voltage and conductance–voltage characteristics of GaN MIS structures

The capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics of GaN metal–insulator–semiconductor (MIS) structures have a frequency dependence due to the capture and emission of electrons by the high density of the interface states. However, the details of how an interface state affects C–V and G–V characteristics is still not well understood. In this paper, we report a numerical modeling method that can simulate the frequency dependent C–V and G–V characteristics of GaN MIS structures.

Solar and infrared light sensing comparison of Yb/CIGS photodiode

Glass/Mo/CIGS/Yb Schottky photodiodes were fabricated by the physical vapor deposition method. The structural and morphological characterization of the CIGS layer on Mo was carried out. The current-voltage ( I-V ) characteristics were investigated in the dark, under solar light, and infrared. The diodes' ideality factor and zero bias barrier height were calculated as 1.55 and 0.84 eV in the dark, respectively. When the time-dependent current plots are examined, it is seen that the rise and decay times are lower for solar light than infrared. As the intensity of solar light increases, the rise and decay times decrease. The responsivity value for 100 mW/cm 2 solar light was found to be 8.5 mA/W and the detectivity value was 1.7 × 10 7 Jones. For infrared light, the same parameters were calculated as 3.4 mA/W and 7.1 × 10 6 Jones. Furthermore, capacitance-voltage and conductance-voltage characteristics were evaluated for different frequencies. • Yb/CIGS photosensor was produced on bi-layer Mo layer. • Switch ON−OFF time was maintained at 5 s • I-t and C-t measurements taken at different solar light intesities (from 20 to 100 mW/cm 2 ) and infrared (100 mW/cm 2 ). • Responsivity and detectivity parameters were calculated. • Frequency−dependent C-V and G-V characteristics investigated.

Ionizing radiation response of bismuth titanate-based metal-ferroelectric-semiconductor (MFS) type capacitor

In this study, the ionizing radiation (gamma-irradiation) response of the metal-ferroelectric-semiconductor (MFS) type capacitors whose interfacial layer is bismuth titanate (Bi4Ti3O12), which is from the Aurivillius family, was investigated. The capacitance-voltage (CV) and conductance-voltage (G/ω-V) characteristics and the device parameters derived from these characteristics provide essential information about the radiation response. Therefore, MFS-type capacitors in which their Schottky/rectifier contacts Au and interfacial layer Bi4Ti3O12 (BTO) were prepared and exposed to various doses of gamma-rays. The voltage-dependent C and G/ω data were obtained before irradiation and after some irradiation doses using the Hewlett Packard Impedance Analyzer. Experimental results showed that the CV curves exhibited multilayer capacitor behavior before and after radiation rather than conventional Schottky structures due to the very thin Silicon dioxide (SiO2) interlayer at the BTO/Si interface, which was assumed to form during the annealing of BTO films in air ambient. On the other hand, the C-G/ω-V curves exhibited asymmetric and hysteretic behavior because of the different electrical properties at the bottom and top interfaces and the natural ferroelectric behavior of the BTO. On the other hand, considering the radiation effects, the C-G/ω-V characteristics and other device parameters did not show any significant changes at the 5 kGy irradiation dose, but significant differences were observed in all parameters at the 22 kGy dose. Therefore, it can be concluded that these MFS-type structures with the BTO interlayer can be used as a capacitor or radiation sensor at doses around 5 kGy and below 22 kGy. However, it is not recommended to use them as capacitors at doses close to 22 kGy due to the large capacitive change (approximately tenfold decrease) at this dose. Besides, the tendency of the device to deteriorate at 22 kGy doses indicates that it is not suitable for use as a capacitor or radiation sensor above 22 kGy gamma-irradiation doses.

Si-based photosensitive diode with novel Zn-doped nicotinate/nicotinamide mixed complex interlayer

Al/Zn-complex/p-Si/Al metal-polymer-semiconductor (MPS) diode is deposited by using thermal evaporation technique for metal layers and spin-coating technique for polymer interface layer. Zn(C6H6N2O)2(C6H4NO2)2(H2O)].1/2(H2O) is prepared as a precursor material and different spin-coating solutions in terms of Zn-complex contribution (0.5, 1.0, 2.0 and 3.0 mg) are used in the film deposition process. The characterization of this precursor is provided by TEM imaging. In addition, deposited interface layers in different amount of Zn-complex in solution are investigated by AFM. Current-voltage (I−V), capacitance-voltage (C−V) and conductance-voltage (G−V) characteristics of the MPS diode are evaluated as a function of compositional change at the interface under dark and illumination conditions. Main diode parameters as barrier height, ideality factor and parasitic resistances are extracted from dark I−V curves and also they are discussed for the measurements under different illumination intensity. Capacitive behavior of these MPS diodes are observed by dark C−V and G−V measurements, and resistance values are also calculated from these results. The on/off illumination switching response of the diodes are observed from transient photo-current, photo-capacitance and photo-conductance plots.

Low-temperature growth of CdTe thin films as passivation layers for IR and THz functional elements

Low-temperature modes of growing thin (dCdTe = 80–360 nm) CdTe layers by the “hot-wall” method with a high degree of adhesion to CdHgTe epitaxial layers were implemented. Growth parameters (source and substrate temperatures 650 K and 373 K, respectively, deposition time 60 min), at which the film is optimal when used as a protective passivation coating for the functional elements of the IR and THz photoelectronics were selected. The study of morphology, chemical composition and electrical properties of CdTe thin films depending on temperature and growth time were carried out. It is shown that the CdTe semiconductor film on the CdHgTe surface grows in columns that aggregate with increasing deposition time. The study of capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of CdTe/p-Si structures demonstrated the controllability of the space charge region in silicon by the voltage applied to CdTe, which indicates good dielectric properties of CdTe with low surface density at the CdTe/p-Si boundary (4.5 × 1010 сm−2) and small leakage currents through the dielectric.

Effectiveness of UV-Ozone Treatment and Alneal Process for Si Surface Passivation with Sol-Gel Spray-Coated SiO2 Film

Passivated Emitter and Rear Contact (PERC) cell is dominating solar market over conventional Aluminum-Back Surface Field cells [1]. PERC structure uses dielectric passivation layer at the rear to overcome optical and electrical losses, enhancing the cell performance. Silicon dioxide (SiO2) film passivates both n- and p-type silicon (Si). Thermal oxidation provides excellent Si passivation but adds to the thermal budget. An alternative, spray-coating, is a low-temperature deposition technique which is industrially viable and has high throughput and therefore, substantiates its potential for implementation in solar industry.We achieved low surface recombination velocity (Seff) of 8.07 cmsec-1 with spray-coated SiO2 film on p-type Si and anticipated that good passivation is due to UV-Ozone treatment and alneal [2]. In this work, a thorough investigation is performed in terms of interface state density (Dit) and fixed oxide charge density (Qf), extracted from capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of metal-oxide-semiconductor (MOS) capacitor.In this work, p-type Si wafers were RCA cleaned without final 2% HF dip. For MOS capacitor fabrication, samples were bifurcated into two sets. One set was processed as it is and another set was dipped in 2% HF and was UV-Ozone treated for 5 min. Sol-gel prepared using tetraethyl orthosilicate, iso-propyl alcohol, deionized water, and nitric acid was sprayed over these wafers using custom-designed spray-coater tool. Subsequently, wafers were baked at 150oC and subjected to Post Deposition Annealing (PDA) in O2 ambient for 30 min. Front and rear contacts were created by depositing Aluminum (Al) dots over the film and Al blanket at the back of Si, respectively. These were further divided into two. One set of each was not treated further and the other was subjected to Post Metallization Annealing (PMA) in Forming gas annealing (FGA; 4% H2 and 96% N2) ambient for 30 min. Lifetime structures were fabricated for RCA oxide and UV-Ozone treated samples with SiO2 deposited on both sides of wafer following the sequence discussed above and were subjected to PDA. Al was blanket deposited on both sides of the wafer. These structures were subjected to PMA in FG ambient for 30 min. Later, Al was etched.Effectiveness of UV-Ozone treatment is demonstrated by comparing Dit and Qf with RCA-oxide. Thickness of spray-coated SiO2 film is ∼17 nm and of RCA oxide and UV-Ozone oxide is ∼1.5 nm. Dit of 1.4-1.6×1012 cm-2eV-1 is obtained for RCA oxide and 3.0-4.1×1011 cm-2eV-1 for UV-Ozone oxide after PDA without PMA (Fig. 1(a)). Dit is an order of magnitude less for UV-Ozone oxide, providing better chemical passivation in comparison to the RCA oxide. UV-Ozone oxide gives lower Qf in comparison to the RCA oxide (Fig 1(b)). Qf values are 2.3-2.8×1012 and 0.92-1.5×1012 cm-2 for RCA oxide and UV-Ozone oxide, respectively. Therefore, UV-Ozone treatment prior to film deposition gives better interface quality than RCA oxide. This can be attributed to surface cleaning in addition to oxide formation during UV-Ozone treatment [3].Efficacy of alneal was studied by comparing PMA effect on films over RCA oxide and UV-Ozone oxide. Dit for film on RCA oxide and UV-Ozone oxide are 0.84-1.1×1011 cm-2eV-1 and 2.0-6.0×1010 cm-2eV-1, respectively after PDA and PMA. Dit has reduced by an order of magnitude after PMA. This is attributed to hydrogen passivation provided by PMA in FG ambient [4]. Process of annealing after Al deposition is termed as alneal. Qf has also reduced after alneal. Qf values are 6.2-7.0 × 1011 cm-2 and 3.8-6.5 × 1011 cm-2 for RCA oxide and UV-Ozone oxide, respectively. The trends in Qf and Dit can be correlated to the shift in C-V characteristics and G-V peak value, respectively (Fig. 2 (a) and (b)).Lifetime of 118.66 µsec and 459.52 µsec was measured using Sinton lifetime tester and corresponding Seff was calculated as 95.59 cms-1 and 8.07 cms-1 for film over RCA oxide and UV-Ozone oxide, respectively (Fig. 3). UV-Ozone oxide provides better passivation in comparison to the RCA oxide. Low Seff in case of UV-Ozone oxide is attributed to low Dit, as both these oxides show similar Qf.Therefore, it can be concluded that good passivation with low Seff for spray-coated SiO2 film is attributed to UV-Ozone treatment as well to the alneal process.

Investigation on the effect of interface state density and series resistance in Ag/Ge-NW/Si (MS) device synthesized by glancing angle deposition technique

Catalyst-free Ge-nanowire (NW) was synthesized using the glancing angle deposition (GLAD) technique integrated into an electron beam evaporator. The study is mainly focussed on the analysis of frequency and voltage dependence of the capacitance–voltage (C-V) and conductance-voltage (G/ω-V) characteristics of Ag/Ge-NW/Si device over a wide range of frequency (200 kHz−2 MHz) and voltage (−5 V to +5 V) at room temperature. FEG-SEM image confirmed the successful growth of vertically oriented Ge-NW on Si substrate. Both C-V and G/ω -V values showed wide dispersion in the depletion, inversion, and accumulation region due to interface state density (Dit) and series resistance (Rs). The voltage and frequency-dependent Dit and Rs were calculated from the Hill-Coleman and Nicollian-Brews methods, respectively. It is observed that the overall Dit and Rs for the device decrease with an increase in the frequency at different voltages.

The photosensitive activity of organic/inorganic hybrid devices based on Aniline Blue dye: Au nanoparticles (AB@Au NPs)

In this study, Aniline Blue (AB) synthetic triarylmethane dye and AB:Au NPs mixture films were deposited on n-Si by spin coating technique to form an organic/inorganic hybrid electro-optic device. Thus, Co/AB/n-Si (named D1) and Co/AB:Au NPs (1%)/n-Si (named D2) photoactive devices were fabricated, and current-voltage (I–V) measurements were performed on both devices to investigate electrical properties under dark and various light illumination intensities changes from 100 to 400 mW/cm2. Sensitivity and responsivity as well as specific detectivity of both devices were obtained depending on the reverse bias voltage for various light intensities. The main device parameters such as ideality factor (n), barrier height (Фb), series resistance (Rs) and experimental interface states density (Nss) were calculated and discussed in details. The light intensity-dependent I–V measurements revealed that the reverse bias current increased with the increasing of the light intensity and confirmed photodiode behaviors. The illumination coefficient (m) values were also extracted from the light-intensity dependent I–V characteristics and obtained as 0.87 and 1.28 for D1 and D2, respectively. Furthermore, the D2 device exhibited a higher response to the light than D1 due to the surface plasmon resonance effect of Au NPs. The capacitance-voltage (C–V) and conductance-voltage (G-V) characteristics of both devices were also studied in details under dark at 500 kHz applied frequency. As a result, the experimental results highlight that the D1 and D2 devices can be used in various optical applications such as photodiodes, photodetector and carrier storage devices.

3D structures for silicon carbide transistors utilising Al[formula omitted]O[formula omitted] as a gate dielectric

This paper reports on the first investigation of the characteristics of 3D structures formed in silicon carbide for the realisation of ultra-high performance nanoscale transistors, based on the FINFET topology. Capacitance–voltage characteristics show evidence of a second flatband voltage, located at a higher bias than that seen for purely planar devices. Two distinct peaks in the conductance–voltage characteristics are observed, centred at the flatband voltages, where the amplitude of the high voltage peak correlates with the sidewall area. This suggests that the chemical behaviour of the sidewalls differ from those of the (0001) wafer surface. The breakdown electric field of the dielectric film grown on the 3D structure is in excess of 3 MV cm−1. It is demonstrated that 3D transistors (FINFETs) do not utilise the gate voltage range where the abnormal characteristics exist and so this work reports for the first time the possibility of high performance nanoscale transistors in silicon carbide that can operate at high temperatures.

The response of high barrier Schottky diodes to light illumination

We have investigated the illumination effect on electrical characteristics of nearly ideal Yb/p-Si Schottky diodes with a high zero-bias barrier height (Φbo). The value of reverse bias current increased as the illumination level increased for these diodes. The electrical parameters such as ideality factor (n) and Φbo were obtained as 1.09 and 0.80 eV in dark, respectively. n increases with increasing illumination level whereas Φbo decreases. The series resistance calculated using Cheung functions almost did not change with the illumination level. The characteristics of capacitance–voltage and conductance-voltage were obtained as a function of illumination level, applied bias voltage and frequency. The effect of illumination on the capacitance–voltage and conductance-voltage characteristics was clearly observed for 10 kHz frequency whereas the illumination did not affect the characteristics for 1 MHz frequency, significantly. The photovoltaic parameters such as open circuit voltage of 0.21 V, short circuit current of 1.60 × 10–5 A, and fill factor of 62% were obtained for 1040 W/m2. These values have changed with increasing illumination level. The effect of illumination on the density of the interfacial states was observed. The experimental findings have showed that the diodes are sensitive to illumination and have photovoltaic behavior. The Yb/p-Si Schottky diodes are promising for photodiode applications.

Capacitance-Voltage Measurements on MBE-Grown Ge-SixGe1-x-ySny Heterojunction pn-Diodes for Material Characterisation

In recent years, there has been an increased interest in the ternary Group-IV semiconductor alloy SixGe1-x-ySny [1–4]. Since it allows the decoupling of its bandgap and its lattice-constant, SixGe1-x-ySny is predestined for the realisation of lattice-matched heterojunctions on Ge(Sn) virtual substrates on the Si platform. Furthermore, SixGe1-x-ySny is a predicted direct bandgap semiconductor at higher Sn concentrations, which makes it attractive for optoelectronic applications. An exemplary heterojunction optoelectronic device would be the single confinement heterostructure laser diode, the still missing key component for the monolithic integration of the optical on-chip communication on Si.However, the design and dimensioning of heterojunction devices requires detailed knowledge of the electrical properties of the alloy semiconductor over composition, where currently much less is known about SixGe1-x-ySny. Although, previous investigations have focused mostly on the growth conditions and the optical properties of SixGe1-x-ySny bulk alloys [1,2,4].In this work, we will concentrate on the growth and electrical characterisation of Ge-SixGe1-x-ySny heterojunction diodes. In detail, we will highlight the possibilities of current-voltage (I-V) and capacitance-voltage (C-V) measurements on Ge-SixGe1-x-ySny heterojunction pn-diodes as a useful tool for material characterisation. For this purpose, we grew a series of four samples with different composition of the SixGe1-x-ySny layer, but the SixGe1-x-ySny composition fulfilling lattice-matching on Ge (see Fig 1 (a)). Afterwards, we fabricated single mesa diodes to enable the subsequent electrical characterisation of the grown heterostructure diodes.The growth process was performed in a 6” molecular beam epitaxy (MBE) system, where Si, Ge and Sn are used as matrix materials and B and Sb as dopants, respectively. Since the condition of lattice matched growth of SixGe1-x-ySny requires a fixed ratio of Si/Sn = 3.66, the Si and Sn fluxes were kept constant for all samples. Thus, we varied the Ge flux to achieve different SixGe1-x-ySny compositions, resulting in a varying SixGe1-x-ySny growth rate. This method enables better control of the lattice matching but also requires a highly precise calibration of the evaporation cells of the alloy compound fluxes. The Sn concentration of the SixGe1-x-ySny layers was varied between 5 % and 12.5 %. Since the most critical growth parameter is the substrate temperature, it is therefore measured and controlled in-situ by a thermocouple as well as an infrared pyrometer. Especially, the infrared pyrometer allows us to observe the dynamic processes on the sample surface during growth. For the growth of the SixGe1-x-ySny layer, we chose to keep the substrate temperature at TSub = 200 °C, which is mainly based on our previous SixGe1-x-ySny growth studies.The heterojunction pn-diode (see Fig 1 (a)) is formed by a p-doped Ge layer with an acceptor concentration of NA = 1018 cm-3 and the n-doped SixGe1-x-ySny layer with a donor concentration of ND = 5·1019 cm-3. In order to achieve a good ohmic contact to the p-Ge, a highly p-doped Ge layer forms the underlying bottom contact of the diode. The whole diode structure is grown on our standard Ge virtual substrate (VS) on Si(100) [5].A detailed material characterisation was performed to achieve information of the composition as well as the crystal quality using X-ray diffraction (XRD) and Raman spectroscopy.After MBE growth, the samples were processed to diodes in a single mesa process. For the subsequent I-V and C-V measurements, we used a Keithley 4200 semiconductor characterisation system using the bottom as signal and the top as ground contact (Fig 1 (b)). For the C-V measurements, a parallel capacitance (C) and conductance (G) model was applied. The maximum measurement frequency was f = 100 kHz. Fig. 1 (c) shows a comparison of the current density-voltage (J-V) characteristics of diodes with a mesa radius of 80 µm for all four compositions. As can be seen, good diode behaviour is achieved even for high Sn concentrations. An exemplary capacitance-voltage and conductance-voltage (C-V and G-V) characteristics of the sample with 10 % Sn is shown in Fig 1 (d). The C-V characteristics shows good agreement with the theoretical curve in the range of -0.6 V ≤ vDC ≤ 0 V. Further calculations in this range allowed us the extraction of the built-in-voltage of the heterojunction diode, an important parameter of a pn-heterojunction. We present detailed results of the C-V measurements of our diodes and the applied methods for material characterisation.Our results show that C-V measurement of SixGe1-x-ySny heterojunction pn-diodes is a useful tool for the determination of electrical parameters of this novel ternary alloy semiconductor SixGe1-x-ySny. These parameters are crucial for the further design of SixGe1-x-ySny heterojunction devices. Figure 1

Photodiode based on Al-doped SnO2: Fabrication, current-voltage and capacitance-conductance-voltage measurements

Al doped tin oxide (Al:SnO2)11Diodes. are fabricated onto silicon substrate by easy spray pyrolysis route. The room temperature current-voltage (I–V) measurements of Ag/Al:SnO2/n-Si/Au junction are taken under dark and various illumination level. The reverse and forward current increase with the increasing of illumination intensity, gradually. The device exhibits good photodiode properties but a photovoltaic behavior is not observed. Ideality factor values is found to be 7.54 and 5.41 two distinct linear region of the I–V curve of the junction under dark. Its value varies between 4.87 and 5.80 under light. The zero-bias barrier height decreases with increasing illumination level. The value of series resistance obtained from generalized Norde plot have showed a strong dependence on illumination level. Its value is calculated as 1.83 kΩ and 0.91 kΩ under dark and illumination level of 190 mW/cm2, respectively. The space limited current (SCLC) conduction mechanism is investigated under dark and light conditions. The frequency dependence of capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of the junction are analyzed in a wide range of applied voltage (from -8 V to + 8 V). The thickness of Al:SnO2 thin film is obtained as 360 nm by using C and G data at 1 MHz and 8 V.

Photovoltaic, capacitance-voltage, conductance-voltage, and electrical impedance characteristics of p-type silicon/intrinsic-silicon/n-type semiconducting iron disilicide heterostructures built via facing target direct-current sputtering

p-Type silicon (Si)/intrinsic Si/n-type semiconducting iron disilicide heterostructures were built via facing target direct-current sputtering. To assess the photovoltaic properties, the current density-voltage characteristic curves were recorded in conditions of dark and under irradiation via an Air Mass 1.5 solar simulator (100 mW/cm2). The built heterostructures demonstrated effective rectifying behavior along with a rather substantial leakage current. The open-circuit voltage and the short-circuit photocurrent density values were 178.00 mV and 10.08 mA/cm2, respectively. The assessed energy conversion efficiency was approximately 0.75%. The series resistance (Rs) values at 0 V appraised by the Nicollian-Goetzberger technique were 60.28 Ω at 2 MHz, and 4.13 × 103 Ω at 10 kHz. Their interface state density values evaluated through the Hill-Coleman method were 1.38 × 1012 cm−2/eV at 10 kHz and 1.31 × 1011 cm−2/eV at 2 MHz. The Rs and interface states occurring in the heterostructure interface zone should be the potential determinant of the degeneration of the photovoltaic properties. The characteristics of the real (Z’) and imaginary components of impedance under the changing voltages manifested a shape of one semicircle having a semicircular midpoint beneath the Z’ coordinate. An equivalent circuit model that was related with the heterostructure behavior should be assembled from the parallel association of resistance and constant phase element connected with Rs.

Effects of surface passivation on capacitance-voltage and conductance-voltage characteristics of Al/p-type Si/Al and Al/V2O5/p-type Si/Al diodes

Electrical properties of Al/p-type Si/Al metal-semiconductor and Al/V2O5/p-type Si/Al metal–interfacial layer–semiconductor diodes with and without anodic surface passivation are investigated by the capacitance-voltage (C-V) and conductance-voltage (G/ω−V) characteristics. The measurements were performed at various voltages from −2 V to 2 V in the frequency range from 50 kHz to 1 MHz at room temperature and in the dark. The barrier height, concentration of acceptor atoms, and diffusion potential of these diodes were determined from the linear C−2-V plots. The barrier heights increase for the MS and MIS diodes with anodic surface passivation. Furthermore, the series resistance and interface state density of the diodes were obtained by the Hill-Coleman method and the Nicollian-Goetzberger method, respectively. It is found that the anodic passivation process has a positive effect on these parameters.

Negative capacitance within forward biasing voltage of organic device at higher frequencies

The fabricated structure based on organic magnesium phthalocyanine material for solar cells is investigated. Such device is fabricated by a facile spin coating route. It is observed that negative values of capacitance (NC) and dielectric constant are exhibited within the forward voltage at adjustable frequencies ranges of 500 KHz-1 MHz. In order to understand the mechanism and the behaviour of such device, the capacitance voltage and conductance voltage characteristics in terms of frequency are studied. Based on impedance spectroscopy measurements, the real and imaginary parts of impedance are frequency dependent. The electrical conductivity in terms of voltage of organic diode is investigated within −2 V, +5 V bias voltage range at 500 kHz and 1 MHz. The average of conductivity about 2μ S/cm is then recorded. Many parameters causes the negative capacitance and dielectric constant.

Break-junction tunneling spectra of Bi2212 superconducting ceramics: Influence of inhomogeneous d-wave-Cooper-pairing and charge-density-wave order parameters

Conductance-voltage characteristics (CVCs) of tunnel break junctions made of Bi2Sr2CaCu2O8+δ crystals were measured. It was demonstrated that the CVCs have a V-shaped inner gap region, similar to those typical of CVCs for tunnel junctions between d-wave superconductors. The CVCs have different forms for different junctions, but all of them reveal weak dip-hump structures outside the inner gap region. Calculations of the tunnel current in the ab plane of the break junctions were carried out in the model of the inhomogeneous d-wave superconductor partially gapped by charge density waves (CDWs). The averaging of the tunnel current over the statistical distributions of both the superconducting and CDW order parameters was carried out. The theoretical results qualitatively reproduce the behavior of experimental curves. A conclusion was made that tunnel directionality and the statistical distributions of both order parameters are crucial factors governing the observed CVC shapes for break junctions made of high-Tc oxides.

A comprehensive investigation on Ag-doped ZnO based photodiodes with nanofibers

The morphological, optical and electrical properties of undoped Zinc Oxide (ZnO) and 0.5% and 2% Ag-doped ZnO based Photodiodes were investigated. ZnO samples, which were deposited on p-type Si semiconductor substrates using spin a coating method, were produced by sol–gel method. The morphological properties of the ZnO films were investigated by atomic force microscopy. The results revealed that thin films are in nanofiber like structure that nanofiber spread homogeneously on the substrate. Additionally, the permittivity, absorbance, reflectivity and bandgap energy values were calculated by using the UV measurement results. The optic bandgaps of the films were also calculated by the optical absorption method. Each sample shows permittivity properties in the visible region; samples show absorption properties in the region where the applied wavelength is smaller than 400 nm. Reflecting boundaries were shift to higher boundaries with increased dopant effect. The transmittance of samples was found low in the UV region, but it shows higher characteristics which are between 78 and 88% in the visible region. To investigate the electrical properties of produced thin films, Current–Voltage, Capacitance–Voltage, Conductance–Voltage characteristics and Current–Time measurements were obtained in different illumination intensities. It was seen that the samples show photoconductive performance.