P-type Si Substrates Research Articles

The formation of porous silicon (PSi) on p-type Si (100) substrate via the electrochemical anodization method with varying current density

The porous silicon (PSi) has been successfully formed on the surface of p-type Si (100) using the electrochemical anodization method in which Si was as an anode and Pt was as a cathode etched in the HF ethanoic solution for 12 min. The current densities applied during the anodization process varied from 60 mA/cm2, 70 mA/cm2, 80 mA/cm2, and 90 mA/cm2 to observe its effects on the morphological and optical properties of PSi. The morphology of PSi was tested via AFM instrument while its reflectance was measured using UV-Vis Spectrometry. The AFM images of the surface PSi reveals the pores’ depth, the pores’ size, and the surface roughness of the PSi. The results demonstrate that the increase in the current densities results in the deeper pores’ depth and the bigger pores’ size so that lifts the surface roughness values as well. On the other hand, the increase in the current densities tends to decrease the reflectance intensities of the PSi.

Ir/Ni/W/Ni Ohmic contacts for n-type 3C-SiC grown on p-type silicon substrate

In this work, Ohmic contacts to n-type 3C-SiC grown on p-type Si substrate employing Ni layer and Ir/Ni/W/Ni multilayers were investigated. Specific contact resistances of 2.57 × 10–4 Ω · cm2 and 2.74 × 10–5 Ω · cm2 were achieved with Ni layer and Ir/Ni/W/Ni multilayers, respectively, at an annealing temperature of 1050 °C. Samples were characterized using XRD, AFM and SEM. The result indicates the W is effective as a carbon absorbing and stabilizing layer and the presence of Ir cap layer facilitates lowering the surface roughness. As a result, the thermal stability and contact surface morphology of Ir/Ni/W/Ni/3C-SiC is greatly improved compared with Ni/SiC contact.

Band-to-band tunneling mechanism observed at room temperature in lateral non-degenerately doped nanoscale p-n and p-i-n silicon devices

Non-degenerately doped lateral nanoscale p-n and p-i-n silicon-on-insulator devices have been fabricated and characterized at room temperature (297 K). In both types of devices, p-type Si substrate is used as a backgate to modify the potential in the top Si layer in both forward- and reverse-bias regimes. In the forward-bias regime, both types of devices exhibit negative differential transconductance (NDT), with the current peak position and level controlled by the backgate and anode voltage. In the reverse-bias regime, the devices exhibit a sharp current increase as a function of the backgate voltage, which is a signature of the band-to-band tunneling (BTBT) mechanism. These findings suggest that NDT and the sharp increase of current, induced by the contribution of the BTBT mechanism, can be achieved even in non-degenerately doped backgated diodes, which opens new possibilities for BTBT-based functionalities, benefiting from a simple design and CMOS compatibility.

Formation of a double-layer Pb reconstruction on the B-segregated Si(111) surface

A novel low-dimensional structure of Pb is found to form on the B-segregated heavily doped p-type Si(111) substrate. The hole doping changes the growth mode of the Pb/Si(111) layer resulting in the formation of a double-layer film, which structure drastically differs from the typical single-layer hexagonal incommensurate (HIC) or striped incommensurate (SIC) phases in the Pb/Si(111) system. Using scanning tunneling microscopy, angle-resolved photoelectron spectroscopy, and density functional theory calculations, the atomic arrangement and electronic band structure of this surface reconstruction were examined. Two possible models were proposed both being constructed from the similar Pb bilayer (ΘPb = 2 ML) with 3×3 periodicity, but having different orientations relative to the B-segregated Si(111) substrate. Both models produce a similar electronic band structure consistent with an experimentally obtained ARPES spectrum.

Electrical properties of InGaN nanostructures with branched morphology synthesized via MBE on p-type Si(111)

The work is devoted to the study of electrical properties of InGaN nanostructures with branched morphology (NSs) on p-type Si substrates. It was found that the IV curves between InGaN NSs and p-Si are close to linear, which could indicate a tunneling conductivity. Such unique structures as InGaN NSs on p-Si can be used as building blocks for water splitting devices and tandem solar cells.

Strong Room-Temperature Electroluminescence from Ge-on-Si by Precise in-situ Doping Control

Germanium (Ge) has been considered as a promising material for optoelectronic integrated circuit (OEIC) on a silicon (Si) platform [1-3]. Although Ge is an indirect-band-gap semiconductor, the energy difference between its direct and indirect band gaps is rather small and it has been shown that introduction of tensile strain can reduce this difference and significantly enhance the direct-gap light emission [4]. For realization of high efficiency electroluminescence from the tensile strained Ge, high quality diode structures with low leakage current should be formed. In this study, a p-i-n junction is formed within the epitaxial Ge by the precise in-situ doping method and additionally high density P delta doping is performed in the vicinity of the surface to create a low resistivity Ohmic contact. After the growth, a mesa-defined vertical diode is fabricated to reduce the leakage current. As a result, an excellent diode property with very large on-off ratio is observed and strong room temperature electroluminescence is observed owing to the very low leakage current.Solid-source molecular beam epitaxy was used for the growth of the Ge-on-Si (GOS) structure. First, an undoped Ge buffer layer of 40 nm was grown on a p-type Si (100) substrate at a temperature of 350°C. Subsequently, a B-doped (5×1018 cm-3) Ge layer of 500 nm, an undoped Ge layer of 90 nm and a P-doped (1×1019 cm-3) Ge layer of 500 nm were grown at 300°C. For p and n-type in-situ doping, B and GaP effusion cells were used, respectively. After the growth of the p-i-n structure, a growth of an ultra-thin (UT) Si layer (2 monolayers), P delta doping (2×1014 cm-2) and 7 nm Ge capping were performed to obtain a low resistivity Ohmic contact [5]. As top and back metal contacts, Au and AuGa were deposited, respectively, where the top metal contact area (90μm×40μm) was defined by lift-off process. An optical active area (125μm×75μm) were mesa-defined by the photo-lithography and following reactive ion etching (RIE) process.SIMS depth profiles of B and P in the Ge epilayer are shown in Fig. 1(a). It is found that uniform and abrupt doping can be realized for both B and P. Current-voltage characteristic shown in Fig. 1(b) reveal a good diode rectifying property with an on/off ratio of over 105. We can say that the leak current is highly suppressed by the mesa etching. A current injected light emission was measured by micro-photoluminescence (PL) system equipped with a cooled InGaAs detector, a detection limit of which was 1600 nm. Room temperature EL spectra at various continuous injected currents are shown in Fig. 1(c). The EL spectrum appears at around 200 mA injected current, and the EL intensity drastically increases with the injection current increase. As shown in the inset of Fig.1 (c), the EL intensity against the injected current shows a behavior with a threshold around 260 mA.In summary, a GOS mesa structure p-i-n vertical diode was fabricated by the in-situ doping method. We observed excellent I-V characteristic with an on/off ratio of over 105. As a result, strong EL spectra were observed with injection currents over 260 mA, indicating that the Ge-on-Si p-i-n structure has high potential to realize high efficiency Ge lasers monolithically integrated on the Si platform.[1] J. Liu et al, Semicond. Sci. Technol. 27. 094006 (2012)[2] P. Boucaud et al, Photo. Res. 1, 102 (2013)[3] J. Liu et al, Opt. Express. 15. 11272 (2007)[4] X. Sun et al, Appl. Phys. Lett. 95. 011911 (2009)[5] M.Yamada et al, Appl. Phys. Lett. 107. 132101 (2015) Figure 1

The effect of indium oxide (In2O3) dopant on the electrical properties of LiTaO3 thin film-based sensor

The effect of the indium oxide (In2O3) dopant on the electrical properties of the lithium tantalate (LiTaO3) thin film-based sensor was investigated in this study. LiTaO3 thin film was made on p-type Si (100) substrates by applying the chemical solution deposition (CSD) method. The LiTaO3 thin film was annealed at the temperature of 850 °C for 15 h. Surface morphology and elemental characterization analysis were obtained by using SEM-EDX (scanning electron microscopy–energy-dispersive X-ray spectroscopy). Then, the dielectric constant value and the photoresistive characteristic of LiTaO3 thin film were measured to determine the effect of the In2O3 dopant on the electrical properties of the thin film. From the SEM-EDX measurement, it is observed that the surface of the thin film is still non-homogeneous; therefore, the electron flow will be obstructed. Based on the elemental atomic composition analysis, it appears that the Indium atoms have appeared in the LiTaO3 thin films doped by In2O3 2%, 4%, and 6%. From the results of thin film dielectric constant calculation, it can be seen that the dielectric constant value between undoped and In2O3-doped LiTaO3 thin film does not change, which is 2.44. The photoresistive value shows that the Indium dopant decreases the resistivity but increases the conductivity of the thin film. Based on the photoresistive characteristic measurement results, it can be concluded that the LiTaO3 thin film can be used as a light sensor, and In2O3dopant can increase the conductivity of the LiTaO3 thin film.

Investigation and Fabrication of p-Si/N-Mg0.3Zn0.7O:In Self-Powered Heterojunction Photodiodes by Mist Atmospheric Pressure Chemical Vapor Deposition

In this study, the N-Mg0.3Zn0.7O:In thin films with 1% and 5% In doping concentration are deposited on the p-type Si substrate using mist atmospheric pressure chemical vapor deposition to form p-Si/N-Mg0.3Zn0.7O:In heterojunction. X-ray diffraction and X-ray photoelectron spectroscopy are used to estimate how In doping concentration affects the crystallinity and oxygen deficiency in the Mg0.3Zn0.7O:In thin films. The electrical and photoresponse characteristics of p-Si/N-Mg0.3Zn0.7O:In heterojunction photodiodes with 1% and 5% In doping in N-Mg0.3Zn0.7O:In are investigated. The photodiode with 5% In doping improves the responsivity, but the response time, rejection ratio, and specific detectivity are inferior to that with 1% In-doping. Moreover, the present p-Si/N-Mg0.3Zn0.7O:In heterojunction photodiodes are operated as self-powered photodiodes since the built-in potential is formed at the p-Si/N- Mg0.3Zn0.7O:In junction.

The temperature induced current transport characteristics in the orthoferrite YbFeO3− δ thin film/p-type Si structure

The perovskite ytterbium ferrite is a new ferroelectric semiconductor material. We presented the temperature induced current–voltage (I–V) characteristics of the Al/YbFeO3−δ /p-Si/Al hetero-junction. The orthoferrite YbFeO3−δ thin films were deposited on a single crystal p-type Si substrate by a radio frequency magnetron sputtering system. The potential barrier height (BH) and ideality factor n of the heterojunction were obtained by thermionic emission current method based on the recommendations in the literature. The fact that the calculated slopes of I–V curves become temperature independent implying that the field emission current mechanism takes place across the device, which has been explained by the presence of the spatial inhomogeneity of BHs or potential fluctuations. Moreover, a tunneling transmission coefficient value of 26.67 was obtained for the ferroelectric YbFeO3−δ layer at the Al/p-Si interface.

Nanoflower ZnO thin-film grown by hydrothermal technique based Schottky diode

This paper reports the realization of planar Schottky diodes based on nanorod ZnO thin film. The nanorod ZnO thin film was fabricated by hydrothermal technique on boron doped p-type Si (100) substrate. The Ag//ZnO/Al planar diode operating with voltage bias from –3 to 3 V. The I–V characteristics clearly indicate that the devices have rectifying performance. The thermionic emission theory governs the current across the studied Schottky diode. The device achieved a turn-on voltage of 0.9 V, barrier height 0.69 eV and saturation current of 1.2 × 10–6 A. The diode shows a very large ideality factor (n > > 2) which is attributed to high interface trap concentration. The surface topology was investigated by scanning electron microscope (SEM). The structural properties of the nanostructured ZnO thin film were characterized by X-ray diffraction (XRD). The SEM images reveal that the ZnO nanorods grow perpendicular to the substrate with uniformity and high density. The XRD pattern illustrates the dominant peak appearing at (002). This intense peak indicates the c-axis orientated phase of the wurtzite ZnO structure. It demonstrates that the crystals grow uniformly perpendicular to the substrate surface in good agreement with the SEM images.

Enhancement in structural, morphological and optical features of thermally annealed zinc oxide nanofilm

This paper presents the study of surface morphological, optical and microstructural features of zinc oxide (ZnO) nanofilm layered upon p-type Si substrate of <100> orientation by employing conventional RF magnetron sputtering system at different annealing temperatures. The effect of annealing on the nano-film is examined using different characterization techniques such as Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), FTIR (Fourier Transform Infrared Spectroscopy), UV-vis spectroscopy and Raman spectroscopy. The sharp diffraction peak at (002) orientation is seen by the XRD spectra which signifies a better growth of single crystalline thin film along the z-axis with the hexagonal wurtzite crystal structure. The surface morphological study shows that the grain size of the thin film intensifies from 22.06 nm to 36.77 nm when the annealing temperature is increased whereas there is a decrease in the values of lattice constants (a=b, c), FWHM (full width at half maximum), residual stress, lattice strain and dislocation density by increasing annealing temperature. The enhancement in the grain size makes the thin film appropriate for MEMS device applications including piezoelectric energy harvesters, gas sensors, etc. The optical bandgap of the ZnO thin film is estimated using Kubelka-Munk (KM) approach and it decreases from 3.23 to 3.16 eV for As-deposited, 400 °C, 600 °C and 800 °C respectively which makes the annealed thin film apposite for optoelectronic device applications. The intensity of the Raman peaks strengthens with the annealing temperature. These results prove that the annealing extensively enhances the crystallinity, structural, morphological and optical features of ZnO thin film and hence becomes suitable for nanoelectronic device applications.

Superconductivity in a Hole-Doped Mott-Insulating Triangular Adatom Layer on a Silicon Surface.

Adsorption of one-third monolayer of Sn on an atomically clean Si(111) substrate produces a two-dimensional triangular adatom lattice with one unpaired electron per site. This dilute adatom reconstruction is an antiferromagnetic Mott insulator; however, the system can be modulation doped and metallized using heavily doped p-type Si(111) substrates. Here, we show that the hole-doped dilute adatom layer on a degenerately doped p-type Si(111) wafer is superconducting with a critical temperature of 4.7±0.3 K. While a phonon-mediated coupling scenario would be consistent with the observed T_{c}, Mott correlations in the Sn-derived dangling-bond surface state could suppress the s-wave pairing channel. The latter suggests that the superconductivity in this triangular adatom lattice may be unconventional.

Influence of Vertical and Radial Distances of Nano-Resistors in SSI-LEDs on Light Intensity Distributions

Two- and three-dimensional light intensity distributions from nano-resistor based solid-state incandescent light emitting devices, made of MOS capacitors with a high-k gate dielectric deposited on the p-type Si substrate, has been simulated using physics-based analytical calculations. The inter-nano-resistor distance affected the resolvability of individual nano-resistor light sources. Formation of clusters of nano-resistors and the presence of few large-sized nano-resistors resulted in bright radiation spots observed at higher magnifications. Light from individual nano-resistors could not be resolved at lower magnifications. The device’s center region was brightest, with light intensity diminishing uniformly in the radially outwards direction.

Investigation of the Nanomechanical Properties of Crystalline Anatase Titanium Dioxide Films Synthesized Using Atomic Layer Deposition

Crystalline titanium dioxide (TiO2) polycrystalline films of 500 nm thickness were synthesized using atomic layer deposition (ALD) on p-type Si (100) substrates. The crystal structure, phase purity, film thickness and morphology were characterized using x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The nanomechanical properties were measured using nanoindentation. Due to low temperature ALD deposition, XRD revealed a single anatase phase growth. FE-SEM images indicate columnar grain structure growth primarily in the vertical directions. The hardness was measured as 5 GPa at 24% film thickness, which is considerably softer compared to the reported benchmark values of the well-known rutile phase of ~ 12 GPa. The elastic moduli were estimated as 138 and 145 GPa for samples A and B, respectively. Samples A and B are identical except that sample A is slightly thicker; the slight difference in thickness has no influence on the results.

Improved rectification and transport properties of hybrid PEDOT:PSS/Ge/Si heterojunctions with Ge nanoclusters

The electrical characteristics and deep-level transient spectroscopy of a hybrid poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/GeNCs/Si heterojunction with Ge nanoclusters grown by molecular beam epitaxy on a p-type Si(001) substrate are investigated. The heterostructure shows good rectifying J–V characteristics, the dark current exhibits an activation energies of 280 meV and 550 meV, while the reverse bias leakage current is suppressed due to the coating of Ge nanoclusters with PEDOT:PSS. We show that recombination via deep hole states close to grain boundaries can be partly suppressed by the PEDOT:PSS thin films, leading to a decrease in the saturation current and an improvement of the rectification without deterioration of forward current.

Gallium-doped zinc oxide films with diverse nanomorphologies grown via sol–gel united spin coating technique

Some gallium-doped zinc oxide nanofilms (GZONFs) with diverse morphologies were produced on the p-type Si (100) substrate by the sol–gel united spin coating. The thermally annealed nanofilms were characterized using different techniques to determine the influence of various Ga contents (0–5%) on their structures, morphologies, optical and electrical characteristics. The XRD patterns of the as-prepared nanofilms displayed the existence of the single-phase polycrystalline particles with varying sizes (55–36 nm). The band gap values of these GZONFs were ranged from 3.227–3.269 eV. The nanofilm produced with 1% of Ga exhibited the minimal electrical resistivity ≈ 4.6429 × 10–3 Ω cm, highest carrier density ≈ 1.37648 × 1020 cm−3 and Hall mobility ≈ 9.779 cm2/V s. It was shown that the overall properties of the proposed GZONFs can be customized by adjusting the concentration of Ga doping.

Optical, structural and electrical characterization of pure ZnO films grown on p-type Si substrates by radiofrequency magnetron sputtering in different atmospheres

ZnO films were grown on p-type Si substrates by radio-frequency magnetron sputtering of ZnO target in pure argon or mixed argon-oxygen plasma and were investigated using atomic force microscopy, spectroscopic ellipsometry, Fourier-transformed infrared spectroscopy and electrical methods. It was observed that the films grown in argon plasma had large surface roughness which increases with the rise of deposition time. The lateral size of ZnO columns showed similar dependence on deposition parameters as the roughness. Contrary to this, the films produced in argon-oxygen plasma were found to be smoother and denser having thinner ZnO columns. These films also demonstrated an abrupt absorption band-gap edge that is the evidence of better crystalline quality of these films (the lower number of native point and elongated defects). Plasmon-phonon interaction in ZnO films as well as the effect of the plasmon system of Si substrate on this interaction was considered. The theoretical approach used for the fitting of specular infrared reflection spectra allowed determining concentration and mobility of free carriers as well as conductivity of ZnO films. It was found that the films grown in pure argon plasma demonstrated a higher concentration and a smaller mobility of free carriers in the comparison with the corresponding parameters of the films grown in argon-oxygen mixed plasma. The direct resistivity measurements show the essentially higher values compared with the values estimated from IR reflection spectra. The possible reasons of this difference are discussed. The utility of infrared reflection spectroscopy for the non-destructive analysis of electro-physical properties of polycrystalline films was shown.

Impedance spectroscopy analysis of n-type (nitrogen-doped) ultrananocrystalline diamond/p-type Si heterojunction diodes

Heterojunction diodes are constructed by growing n-type (nitrogen-doped) ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite films onto p-type Si substrates in nitrogen and hydrogen mixed-gases by coaxial arc plasma deposition. The fabricated heterojunctions are analyzed regarding their film morphology and electrical properties. The complex structure of UNCD/a-C:H films, which consists of nano-sized-sp3 diamond grains and sp2-grain boundaries (GBs), makes it difficult to separate their contribution to electrical conductivity of the films using conventional characterization methods. In this paper we characterize the n-type UNCD/p-type Si heterojunction diode by employing impedance spectroscopy method, which can isolate the differing components that contribute to the overall conductivity of the film. The impedance spectroscopy is measured in the frequency range of 100 Hz to 2 MHz, with AC small signal superimpose on DC bias voltage in the range of 0–1 V. The influence of the bias on UNCD grains and GBs contribution to resistance and capacitance of UNCD/a-C:H film and n-UNCD/p-Si heterojunction is investigated by equivalent circuit model using fitting of the impedance data. The results revealed that the electrical conductivity is mainly controlled by the GBs rather than the UNCD grains. Furthermore, the extracted value of dielectric constant of N-doped UNCD/a-C:H film is found to be comparable with that of microcrystalline diamond, which indicates the capacitance contribution in the device is mainly originated from the UNCD grains. This study demonstrates capability of impedance spectroscopy to provide an obvious separated contribution of sp3 and sp2 bonded carbons to the electrical conductivity in their coexistence materials.

Improved power conversion efficiency in n-MoS2/AlN/p-Si (SIS) heterojunction based solar cells

In the present work, MoS2/Si (n-p) and MoS2/AlN/Si (Semiconductor-Insulator-Semiconductor (SIS)) heterojunctions based solar cells have been fabricated by depositing ultrathin layers of MoS2 and AlN on p-type Si substrate by DC magnetron sputtering technique. The SIS heterojunction exhibits higher current and large threshold voltage as compared to conventional p-n junction in Current-Voltage (I-V) characteristics. It suggests that the tunnelling of charge carriers can be a better transport mechanism for solar cell applications. With the AlN layer insertion, the power conversion efficiency of the device increases from 2.92% to 3.53%. The insertion of ultrathin insulating AlN layer in between the n-MoS2/p-Si heterojunction lowers the static charge transfer and makes more effective tuning of the Fermi level. The obtained results demonstrate a novel route for the fabrication of efficient photovoltaic devices for next-generation energy harvesting applications.

Analysis of Electrical Characteristics of Pd/n-Nanocarbon/p-Si Heterojunction Diodes: By C-V-f and G/w-V-f

Diamond films are candidate for a wide range of applications, due to their wide band gap, high thermal conductivity, and chemical stability. In this report, diamond-based heterojunction diodes (HJDs) were fabricated by growing n-type nanocarbon composite in the form of nitrogen-doped ultrananocrystalline diamond/amorphous carbon (UNCD/a-C:H:N) films onto p-type Si substrates. X-ray photoemission and the Fourier transform infrared spectroscopies were employed to examine the contribution of nitrogen atoms from the gas phase into the deposited films. The results indicate the incorporation of nitrogen atoms into the grain boundaries of UNCD/a-C:H film by replacing hydrogen atoms. The capacitance- (C-V-f), conductance- (G/ω-V-f), and series resistance-voltage characteristics of the fabricated Pd/n-(UNCD/a-C:H:N)/p-Si HJDs were studied in the frequency range of 40 kHz-2 MHz. The existence of interface states (Nss) and series resistance (Rs) were attributed to the interruption of the periodic lattice structure at the surface of the fabricated junction as well as the defects on the (UNCD/a-C:H:N)/Si interface. By increasing the frequency (≥500 kHz), the Nss reveals an almost frequency-independent behavior, which indicates that the charges at the interface states cannot follow ac signal at higher frequency. The obtained results demonstrated that the UNCD/a-C:H:N is a promising n-type semiconductor for diamond-based heterostructure diodes.