Capacitance-voltage Measurements Research Articles

Demonstration of non-negligible oxygen exchange in the thermal oxidation of silicon carbide

Oxygen incorporation mechanism with various temperatures during the thermal oxidation of 4H–SiC in dry O2 has been investigated by the isotopic tracing technique. The results suggest that the oxygen exchange is the main incorporation mechanisms of oxygen for SiC oxidation. The temperature and locations of oxygen exchange are different from those in Si oxidation. In SiC thermal oxidation, oxygen exchange occurs even for extremely low oxidation rate at low temperature, and it is not confined to the surface region but throughout the oxide layer. The rate of oxygen exchange increases as temperature increases. This is the direct evidence that oxygen exchange in SiC oxidation cannot be negligible. By analysing the results of X-ray photoelectron spectroscopy and capacitance-voltage measurements, it is found that such significant oxygen exchange is not caused by a large number of defects. Moreover, based on the fitting of refractive index and extinction coefficient, the number of defects in the oxide layer decreases with the increase of temperature, which indicates that oxygen exchange contributes to reducing defects in the oxide layer during high-temperature oxidation and low-temperature post-oxidation annealing.

Investigation of structural, kinetics and electrical properties of CuAlMnZn shape memory alloy – p-type silicon Schottky diode

SEM (scanning electron microscopy) and DSC (differential scanning calorimetry) measurements were done to characterize the microstructure and transformation temperature properties of the materials. The CuAlMnZn shape memory alloy (SMA) was used as a Schottky contact in Schottky diode fabricating. The electrical behavior of the diode was investigated using current and admittance experiments. Current-voltage (I–V), capacitance-voltage (C–V) and conductivity voltage (G/ω-V) measurements of the produced diode were carried out at room temperature, dark, light and at different frequencies. For the diode we obtained, basic diode parameters such as ideality factor (n), barrier height (Φb), shunt resistance (Rsh) and series resistance (Rs) were calculated. The current-voltage (I–V) measurements showed that the produced diode exhibits a good rectification in dark conditions. The frequency and potential dependence of the C–V and G/ω-V characteristics of this diod were investigated. It was observed that the C–V and G/ω-V characteristics changed significantly with frequency. The increase in capacitance, especially at low frequencies, was attributed to the presence of interfacial states at the metal/semiconductor interface. The Rsh and Rs values were observed to decrease with illumination. The experimental observations showed that the CuAlMnZn/p-Si Schottky diode can be used as a photodiode for optoelectronic applications.

Bilayer of zirconium oxide/lanthanum oxide high-κ dielectric fabricated for metal-oxide-semiconductor nano-electronic device applications

This study reports the fabrication of zirconium oxide (ZrO2)/lanthanum oxide (La2O3) bilayer on silicon substrates using the ions generated in a modified dense plasma focus device. Both ZrO2 and La2O3 are fabricated using one burst of focused plasma each on substrates kept at a distance of 4.0 cm from top of the anode. The as-deposited bilayer is further annealed to study the effect of annealing on the characteristics of the bilayer. The bilayer is found to have uniform morphology as obtained in scanning electron microscopy and atomic force microscopy results. The uniformity of bilayer is found to improve upon annealing. These as-deposited and annealed bilayers are electrically characterized through current-voltage and capacitance-voltage measurements in a metal–oxide-semiconductor (MOS) capacitor configuration. The leakage current density and capacitance density of MOS capacitors fabricated on as-deposited and annealed bilayers, respectively are ~2.89 × 10−10 A/cm2 and ~7.23 × 10−12 A/cm2 at 1 V and ~2.18 µF/cm2 and ~2.72 µF/cm2. Conduction mechanism of MOS capacitor is field/tunnel emission and Schottky emission at low and high electric field, respectively. The annealed bilayers are found to possess improved morphological and electrical properties making them suitable candidate for future nano-electronic device applications.

The role of SiO2 in semiconducting BaTiO3-based ceramics: Extension of the Jonker model and effect on the electrical properties

BaTiO3-based ceramics with positive temperature coefficient of resistance (PTCR) recently gained in significance due to their application as cabin heaters in electrical vehicles. Although used as a sintering aid in BaTiO3 ceramics for decades, the effect of SiO2 on the electrical properties as well as the underlying physical mechanisms have not been investigated in detail. Here, we systematically study the influence of SiO2 on PTCR properties, but also on the resistance development at temperatures below the PTC regime, which has hardly been given attention to so far. Using capacitance-voltage measurements, we determine temperature dependent grain boundary potential barrier parameters. By combining these results with x-ray diffraction measurements and resistance-temperature properties, we propose a model describing the resistance evolution throughout the whole temperature range from room-temperature up to the PTCR regime. Further, we show that electrical field strength increases with higher SiO2 content, accompanied by a reduced voltage sensitivity of resistance.

Schottky junction devices by using bio-molecule DNA template-based one dimensional CdS-nanostructures

Creating a well-defined nanostructure through de-oxyribo nucleic acid (DNA)-nanotechnology, and specifically the development of metal/inorganic semiconductor junctions on DNA-assembled nanostructures, is an emerging research area. Herein, we investigate the electrical properties of biomolecule DNA-template based one-dimensional nanowires (NWs)-CdS/Au and without-template based nanoparticles (NPs)-CdS/Au devices grown on the Indium Tin Oxide (ITO) glass substrates. More importantly, the NWs-CdS/Au device displays a dramatic augmentation of current flow and also a striking change in threshold voltage (~55 mV) in comparison to NPs (~190 mV) and reported bulk-CdS/Au (~680 mV) devices. Albeit the manifestation of non-linear/asymmetric current-voltage (I–V) characteristic establishes the CdS/Au junction as Schottky device, but captivatingly, the large ideality factor of about 24 found in NWs-CdS/Au device could be due to the DNA-assembled based organic process CdS-semiconductor. Capacitance-voltage (C–V) measurements of the NWs-CdS/Au divulge a remarkable hump-like feature at lower frequency owing to the frequency dispersion effect. In contrast, the effect appears to be enfeebled with increasing frequency. We conjecture that the density of surface/interface traps materialises at the interface of nanostructures-CdS/metal-Au results in the changes in underlying electrical properties. The observation of significant differences in the electrical properties of DNA-assembled NWs-based Schottky junctions could possibly be helpful for the fabrication of more sophisticated and higher multispecificity biosensors for medical applications.

Characteristics of HfO2 Thin Film Capacitor Deposited by RF Magnetron Sputtering

High-k HfO2 thin films were assessed as a gate dielectric for possible oxide thin-film transistor applications. A HfO2 gate dielectric layer was deposited by radio frequency magnetron sputtering (RF-MS) of a sintered ceramic target at the working pressure of 5 mTorr and annealed at various annealing conditions. X-ray diffraction (XRD) and UV-Vis transmission spectroscopy were carried out to determine the structure and optical transparency of the sputtered HfO2 films, respectively. The electrical characteristics of the HfO2 films were evaluated using the metal-oxide-semiconductor (MOS) capacitor structure of Ti/HfO2/n++-Si. The capacitance-voltage (C-V) and current-voltage (I-V) measurements were taken using an impedance analyzer (Keysight, E4990A) and semiconductor parameter analyzer (Keithley, 4200-SCS), respectively. A dielectric constant of up to 8 with a leakage current as low as 1.0 × 10−9 A/cm2 at 2.0 V were observed.

Capacitance and Current Deep-Level Transient Fourier Spectroscopy (DLTFS) for the Characterization of Defect States in Mg-Doped GaN-on-Si p+n Diodes

GaN is a promising semiconductor for high power and high frequency devices such as pn diodes [1] and high electron mobility transistors (HEMTs). Moreover, GaN grown on silicon substrates allow the study of new technologies [2]. However, many defects can degrade the performance of the GaN based devices and occur in the form of native point defects, impurities and extended defects. Few defect states were found, such as nitrogen vacancies, Mg dopants or C impurities but they are not well explained. Therefore, in this work we investigated the defect characteristics of Mg-doped GaN-on-Si p+n diodes using the Deep-Level Transient Fourier Spectroscopy (DLTFS). This technique is based on the measurement of capacitance (C-DLTFS) or current (I-DLTFS) transients during charge release from filled traps. It is an electrical characterization technique used to determine and calculate the density N T, the energy position and the capture cross-section σ T of defect states.The p+n diodes were grown by MOCVD on Si substrates. The p+n structure was composed of a 400 nm thick Mg-doped p +-GaN layer at 6x1019 cm-3 and of a 750 nm thick Si-doped n-GaN layer at 3x1016 cm-3. The DLTFS measurements have been performed between 100 K and 425 K with a dynamic signal of frequency of 1 MHz for various reverse voltages U R and pulse voltages U P = -0.5 V for C-DLTFS and U P = 3 V for I-DLTFS. Capacitance-voltage measurements (not shown) evidenced a graded and non-linear p + n junction.The C-DLTFS spectrum (fig 1.a) shows two positive peaks (T1 and T2) respectively at 130 K and at 330 K and the I-DLTFS spectrum (fig 1.b) shows a positive peak at 390 K. For the peaks at high temperature on C-DLTFS and I-DLTFS spectra, average E A values of about 0.83 eV and 0.81 eV were extracted for both spectra respectively (fig 1.c). So, these two peaks are related to the same defect state. Besides, shifts to high temperature values (opposite as for the Poole-Frenkel effect) were observed on both spectra and this could indicate interface traps. Also, when increasing U P to positive values (not shown), the T1 amplitude increases while the T2 amplitude decreases [3]. This defect state might be associated with hole traps at the interface of the p+n junction on the p+ -side of the junction and are tentatively assigned to CN states [4]. For the peak at low temperature (T1), no temperature shift with U R was observed indicating bulk traps in the n-region and an activation energy (E A) of about 0.23 eV was extracted (fig 1.c). This defect is commonly assigned to dislocations related to VN defects or to VN-VG complexes. Moreover, Mg dopants (p-type) for this doping level have an E A value of about 0.25 eV very close to the T1 E A value. So, the graded and non-linear p + n junction could be explained by the Mg dopants diffusion into the n-type region along dislocations, as previously observed [5].[1] Y. Zhang et al., “High-Performance 500 V Quasi- and Fully-Vertical GaN-on-Si pn Diodes,” IEEE Electron Device Lett., vol. 38, no. 2, pp. 248–251, Feb. 2017.[2] M. Ishida et al., “GaN on Si Technologies for Power Switching Devices,” IEEE Trans. Electron Devices, vol. 60, no. 10, pp. 3053–3059, Oct. 2013.[3] Y. Lechaux et al., “Characterization of defect states in Mg-doped GaN-on-Si pn diodes using deep-level transient Fourier spectroscopy,” Semicond. Sci. Technol., vol. 36, no. 2, p. 024002, Dec. 2020.[4] T. Narita et al., “The origin of carbon-related carrier compensation in p-type GaN layers grown by MOVPE,” J. Appl. Phys., vol. 124, no. 21, p. 215701, Dec. 2018.[5] S. Usami et al., “Direct evidence of Mg diffusion through threading mixed dislocations in GaN p–n diodes and its effect on reverse leakage current,” Appl. Phys. Lett., vol. 114, no. 23, p. 232105, Jun. 2019. Figure 1

Effect of the native oxide on the surface passivation of Si by Al2O3

The effect of the native silicon oxide layer on the passivation properties of Al2O3 on p-type Si surfaces has been investigated. This was done by comparing effective carrier lifetime, surface saturation current density, fixed charge, and density of interface states of samples, where the native oxide was not removed prior to Al2O3 passivation, with samples subjected to a 3 min HF-dip. The sample with the native oxide exhibits excellent surface passivation post-annealing, with a surface saturation current density of 13 fA/cm2 and significantly longer effective lifetime compared to the sample, where the native oxide was removed. Capacitance–voltage measurements of a sample with the native oxide revealed a remarkably low density of interface states (1010 eV−1 cm−2), almost three times lower than a sample where the native oxide was removed prior to Al2O3 deposition. The results indicate that a thin layer of native oxide improves the Al2O3 surface passivation of silicon.

Improved performance on multi-crystalline silicon solar cells by optimizing aluminum back surface field process

Traditional aluminum back surface field (Al-BSF) multi-crystalline silicon (mc-Si) solar cells have been favored by the market for a long time due to their low cost. However, the Al-BSF formed after Al screen printing and firing restrict the doping profile and the passivation effect. Here we report a scheme to produce the Al-BSF in advance (before phosphorus diffusion) by using the additional preparation processes consisting of three successive steps, namely Al screen printing, annealing and Al removing. The Al removing process helps optimize the depth of Al-BSF, while the annealing process and the subsequent diffusion process helps improve the doping profiles. As a result, the passivation performance of such improved Al-BSF is greatly improved in terms of electrochemical capacitance voltage measurements (ECV) and minority carrier lifetime characterizations. Also the average conversion efficiency for such mc-Si cells with improved Al-BSF reaches 18.73%, which is 0.27% higher than that of the same batch of traditional Al-BSF solar cells. This approach represents an efficient method for further improving mc-Si solar cells.

Extraction of the Trench Sidewall Capacitances in an n-Type 4H-SiC Trench Metal– Oxide–Semiconductor Structure

In this work, a method was investigated to extract trench sidewall and trench bottom capacitances of a SiC trench metal-oxide-semiconductor (MOS) structure. Five groups of 4H-SiC trench MOS capacitors were designed and fabricated, with various trench bottom widths and trench mesa widths. High-frequency capacitance-voltage (HFCV) measurements at 100 kHz were performed on these trench MOS structures. The relationships between trench MOS capacitances and the widths of trench bottom as well as trench mesa were studied. As expected, under the same bias voltage, the measured trench MOS capacitances were proportional to the trench bottom widths and trench mesa widths. Based on this, the contributions of capacitances from the bottom, mesa, and sidewall of trench in trench MOS structure were studied systematically. The oxide thicknesses at different locations in trench were extracted. The C-V characteristics of the MOS capacitors from trench sidewall and trench bottom could also be deduced, from which the flat-band voltage and the charges in oxide of these two MOS capacitors could be subsequently calculated and analyzed. This method provides a convenient and precise technology to monitor process control in SiC trench MOSFETs manufacturing.

Dislocations introduced in n-GaN at room temperature cause conductivity inversion

Dislocations were introduced by scratching at room temperature of the surface of n-GaN films grown by Metalorganic Chemical Vapor Deposition (MOCVD) on basal plane sapphire. The dislocations were observed to propagate from the scratch along the<11–20> directions along several slip systems and form a region with high dislocation density extending by 30–40 µm on each side of the scratch. The regions with enhanced dislocation density were characterized by a strong decrease of intensity of bandedge cathodoluminescence (CL) band at 368 nm, an emergence of the dislocation-related band at 400 nm wavelength, and a strong increase in intensity of the yellow CL band related to defects. Capacitance-voltage and current-voltage measurements in the dark and under illumination performed as a function of temperature indicates that the region with enhanced dislocation density is converted to p-type. Measurements of current versus temperature, admittance spectra, and Deep Level Transient Spectroscopy (DLTS) allowed for the first time to determine the energy position of dislocation-related acceptors level near Ev+ 0.35 eV and to estimate their concentration.

Observation of Divacancy Formation for ZnON Thin-Film Transistors With Excessive N Content

This study proposes a model of mobility and negative bias stress stability degradation mechanism of zinc oxynitride (ZnON) thin-film transistors (TFTs) with various anion compositions. The subgap density of states (DOS) for ZnON TFTs were extracted using monochromatic photonic capacitance–voltage measurement. The extracted subgap DOS indicated an additional nitrogen-related subgap peak was observed in ZnON TFTs with an excessive nitrogen condition, which might originate from a nitrogen divacancy formation. Furthermore, the shifted threshold voltage components after the bias stress test were quantitatively divided as subgap DOS and interface trapping.

Digital switch boards for IV and CV measurements of large-array Low Gain Avalanche Detectors

The High-Granularity Timing Detector (HGTD), with a time resolution of approximately 30 ps, is proposed for the ATLAS Phase II upgrade to address the challenge of greatly increased pile-up interactions. The HGTD is based on the technology of Low Gain Avalanche Detectors (LGADs). The current–voltage (IV) and capacitance–voltage (CV) measurements are important methods to study the main characteristics that can be exploited for quality controlling LGADs during production. A single probe can be controlled via computer to switch channels when using an automatic probe station, but this leaves the remaining, adjacent channels floating and results in inaccurate measurements due to the punch-through effect. We designed the digital switch boards for the IV and CV measurements of 5 × 5 and 15 × 15 LGADs arrays. With the digital switch board and probe cards, channels on a large-array LGADs can be scanned automatically during the measurement, which greatly improves the measurement efficiency. The results show that the leakage currents and noise of all channels induced by the two digital switch boards are lower than 10 pA. We show the IV and CV curves of all channels on two LGADs from Hamamatsu Photonics K. K. (HPK) with our digital switch boards. Compared with the results measured by HPK with an automatic probe station, the IV and CV curves that we measured have better uniformity and accuracy, demonstrating that the quality control of the large-array LGADs can be conducted well with our digital switch board.

Improving light-sensing behavior of Cu/n-Si photodiode with Human Serum Albumin: Microelectronic and dielectric characterization

This research was mainly focused on the investigation of the effect of Human Serum Albumin (HSA) on the electrical features of Cu/n-Si device. To do this, HSA layer was grown as an interfacial layer between Cu and n-Si to create Cu/HSA/n-Si device. To investigate the performance of the obtained device architecture in optoelectronic applications, the electrical and photo-response properties of the device were evaluated by current-voltage measurements at different light power intensities. The results show that as well as the device showed a good rectification characteristic in the dark, it also showed that it exhibits a good photodiode property at different light intensities. Besides, main diode parameters such as ideality factor, effective barrier height, and series resistance were evaluated by thermionic emission theory and Cheung approximation. Obtained results from both calculation methods revealed that diode parameters highly depend on the light power intensity. This variation in the diode parameter is explained in detail taking electron-hole formation in the HSA and n-Si into consideration. Besides, the capacitive properties of the device were investigated with capacitance-voltage measurements in the frequency range of 200 and 1000 kHz and it was observed that the device exhibits capacitive properties in this range. Furthermore, main dielectric parameters such as dielectric constant, dielectric loss, and loss tangent were also evaluated by using impedance spectroscopy in the different frequency range and results showed that all-dielectric parameters highly depend on frequency. All obtained results have been discussed in detail.

Characterization of magnetic Czochralski silicon devices with aluminium oxide field insulator: effect of oxygen precursor on electrical properties and radiation hardness

Aluminium oxide (Al2O3) has been proposed as an alternative to thermal silicon dioxide (SiO2) as field insulator and surface passivation for silicon detectors, where it could substitute p-stop/p-spray insulation implants between pixels due to its negative oxide charge, and enable capacitive coupling of segments by means of its higher dielectric constant.Al2O3 is commonly grown by atomic layer deposition (ALD), which allows the deposition of thin layers with excellent precision.In this work, we report the electrical characterization of single pad detectors (diodes) and MOS capacitors fabricated on magnetic Czochralski silicon substrates and using Al2O3 as field insulator. Devices are studied by capacitance-voltage, current-voltage, and transient current technique measurements. We evaluate the influence of the oxygen precursors in the ALD process, as well as the effect of gamma irradiation, on the properties of these devices. We observe that leakage currents in diodes before the onset of breakdown are low for all studied ALD processes. Charge collection as measured by transient current technique (TCT) is also independent of the choice of oxygen precursor. The Al2O3 films deposited with O3 possess a higher negative oxide charge than films deposited by H2O, However, in diodes a higher oxide charge is linked to earlier breakdown, as has been predicted by simulation studies. A combination of H2and O3 precursors results in a good compromise between the beneficial properties provided by the respective individual precursors.

A Low Program Voltage Enabled Flash like AlGaN/GaN Stack Layered MIS-HEMTs Using Trap Assisted Technique

In this paper, a flash like Al2O3/SiO2 stacked layer AlGaN/GaN-based metal insulator semiconductor high electron mobility transistor (MIS-HEMT) was fabricated using trap assisted technique. The MIS-HEMT showed a large positive shifting of threshold voltage (∆VTH) of 4.6 V after applying a low program voltage (VP) of 3 V, resulting in a very low threshold voltage of −0.3 V with a decent maximum drain current (IDMAX) of 575 mA mm−1. A ultraviolet-ozone (UV/O3) surface treatment was done prior to gate dielectric deposition to produce a thin gallium oxynitride (GaOXNY) layer at GaN/oxide interface, which correspondingly acts as a charge trapping layer, resulting in the reduction in VP. The capacitance-voltage (C–V) measurements revealed that the traps contributing to the significant positive shifting of VTH had a density of 5.7 × 1012 cm−2. These traps were attributed to the border or oxide defects. A significant reduction in gate leakage current (IG) of more than three orders of magnitude was found in MIS-HEMT, due to the high quality Al2O3/SiO2 stack gate dielectric layer compared to conventional HEMT. The flash like stack layered programmed MIS-HEMT exhibited a GMMAX of 123 mS mm−1, on-off ratio of 1.7 × 107, subthreshold slope of 121 mV dec−1 with a reduced gate leakage current of 7.5 × 10−9 A mm−1.

Investigation of abnormal forming process current caused by copper diffusion in Cu/GeSO/TiN resistance random access memory

Understanding its resistance switching (RS) properties is beneficial to the development of resistance random access memory (RRAM). In this work, a RRAM device with a Cu/GeSO/TiN structure (from top to bottom) is investigated. Before forming, the device can operate with a small ratio (<10) of high resistance state (HRS) to low resistance state (LRS). The distribution of this ratio is dependent on device cell size, and is a result of oxygen accumulation. By applying a positive bias during forming process, an abnormal relatively flat current is observed. These observations are confirmed by testing devices of different cell sizes. Bias stresses and capacitance-voltage (C–V) measurements are also used to confirm the changes in film characteristics. In addition, material analyses of transmission electron microscopy (TEM) images are also applied to examine the diffusion of Cu ions that affect the forming process of this Cu/GeSO/TiN device.

Precision defect engineering of metal/insulator/metal diodes using atomic layer deposition to localize Ni impurities in Al2O3 tunnel barriers

Extrinsic impurity defect engineering is demonstrated to increase the maximum asymmetry of metal/insulator/metal (MIM) tunnel diodes. Using atomic layer deposition, transition metal Ni impurities are inserted at precise physical locations within the thickness of the insulating tunnel barrier in asymmetric electrode TiN/Al2O3/Al MIM diodes. The presence of Ni in Al2O3 is found to suppress the onset of Fowler–Nordheim tunneling from the Al electrode without changing the relative dielectric constant or refractive index of the insulator. Current–voltage asymmetry, a performance metric for MIM diodes, is reversed in Al2O3(Ni) devices and is increased over the control Al2O3 device (without Ni impurities) when the Ni impurities are placed close to the Al electrode. Capacitance–voltage measurements on MIM and metal/oxide/semiconductor devices along with Fowler–Nordheim derivative analysis all indicate the introduction of negative charge highly correlated with the position of the Ni defect layer within the Al2O3. Internal photoemission measurements show little change in zero-field energy barrier heights at the electrode interfaces, but varying field dependencies with respect to the position of the Ni defect layer. Combined results suggest that the level of the deep states introduced by the Ni atoms in Al2O3 is consistent with DFT predictions for the corundum Al2O3 system. Overall, this work demonstrates the possibility of improving MIM diode performance using precisely placed extrinsic defects.

Nanoscale Dopant Profiling of Individual Semiconductor Wires by Capacitance-Voltage Measurement.

Developing nanoscale electrical characterization techniques adapted to three-dimensional (3D) geometry is essential for optimization of the epitaxial structure and doping process of nano- and microwires. In this paper, we demonstrate the assessment of the depletion width as well as the doping profile at the nanoscale of individual microwire core-shell light-emitting devices by capacitance-voltage measurements. A statistical study carried out on single wires shows the consistency of the doping profile values measured for individual microwires compared to assemblies of hundreds of wires processed on the same sample. The robustness of this method is then demonstrated on four epitaxial structures with different growth and doping conditions. Finally, electron-beam-induced current and secondary electron profiles are used to validate the depletion region width and the position in the core-shell structure.

Determination of Schottky barrier height of graphene electrode on AlGaN/GaN heterostructure

A graphene Schottky contact was fabricated on an AlGaN/GaN heterostructure and subsequently analyzed. The calculated and experimentally measured Schottky barrier heights (SBHs) determined using the theoretical Schottky–Mott model, the thermionic emission model, the temperature-dependent current–voltage measurement, and the capacitance–voltage measurement were observed to be inconsistent, which was attributed to the ambiguities in both the Schottky contact area and the Richardson constant. While excluding the effects of these two factors, an SBH of 0.15 eV was determined by the temperature-dependent Richardson plot. This result was confirmed by calculating the inverse of the square of the measured capacitance with consideration of the threshold voltage required to deplete the two-dimensional electron gas under the Schottky contact.