Inductively coupled plasma etch damage in 4H−SiC investigated by Schottky diode characterization

Ti Schottky diodes have been used to investigate the damage caused by inductively coupled plasma (ICP) etching of silicon carbide. The Schottky diodes were characterized using IV and CV measurements. An oxidation approach was tested in order to anneal the damage, and the diode characterization was used to determine the success of the annealing. The barrier height, leakage current, and ideality factor changed significantly on the sample exposed to the etch. When the etched samples were oxidized the electrical properties were recovered and were similar to the unetched reference sample (with oxidation temperatures ranging from 900°C up to 1250°C). Annealing in nitrogen at 1050°C did not improve the electrical characteristics. A low energy etch showed little influence on the electrical characteristics, but since the etch rate was very low the etched depth may not be sufficient in order to reach a steady state condition for the surface damage.     

Electrical properties of Au–Sb/p-GaSe:Gd Schottky barrier diode

Experimental results of the fabricated Schottky barrier diode on a GaSe:Gd substrate are presented. The electrical analysis of Au–Sb/p-GaSe:Gd structure has been investigated by means of current–voltage (I–V) and capacitance–voltage (C–V) measurements at 296 K temperature. The diode ideality factor and the barrier height have been obtained to be 1.07 and 0.85 eV, respectively, by applying a thermionic emission theory. At high currents in the forward direction, the series resistance effect has been observed. The series resistance has been determined from I–V measurements using Cheung's method.     

Effect of hydrogen on interface of metal–semiconductor Schottky diode

The effect of hydrogen on p-type Si/Mn and Si/Co Schottky diode has been investigated in present studies. The variations of I–V characteristics suggested that the rectifying act of these diodes change with variation of hydrogen pressure, which is due to the diffusion of hydrogen through the Mn and Co metal films up to Si surface or a creation of surface states at the interface. It is also observed that the effect of hydrogen found to be reverse in order for forward as well as reverse direction of current in Mn and Co deposited films on Si substrate, corresponding to anionic and protonic model of hydrogen interaction with metals. One can say that hydrogen plays an amphoteric role to neutralize either donors or acceptors level in semiconductors and metals. The Raman spectra of Si/Mn and Si/Co are taken and stoke lines link with the presence of hydrogen is observed. In this paper, we are presenting the role of hydrogen pressure on I–V characteristics at the interface of metal–semiconductor structure.     

Comparison of 3C–SiC, 6H–SiC and 4H–SiC MESFETs performances

A comparative analysis of the main DC and microwave performances of MESFETs made of the commercially available silicon carbide polytypes 3C–SiC, 6H–SiC and 4H–SiC is presented. In this purpose, we have developed an analytical model that takes into account the basic material properties such as field dependent mobility, critical electric field, ionization grade of impurities, and saturation of the charge carrier velocity. For a better precision in appreciating device characteristics in the case of a short gate device, the influences of the gate length and parasitic elements of the structure, e.g. source and drain resistances, are considered too. Cut-off frequency f_T, the corresponding output power P_m and the thermal stability are also evaluated and compared with the available experimental data, revealing the specific electrical performances of MESFETs, when any of the three polytypes is used in device fabrication.     

Influence of growth conditions of oxide on electrical properties of AlGaN/GaN metal–insulator–semiconductor transistors

AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors(MIS-HEMTs) on a silicon substrate were fabricated with silicon oxide as a gate dielectric by sputtering deposition and electron-beam(EB) evaporation. It was found that the oxide deposition method and conditions have great influences on the electrical properties of HEMTs. The low sputtering temperature or oxygen introduction at higher temperature results in a positive equivalent charge density at the oxide/AlGaN interface(Nequ), which induces a negative shift of threshold voltage and an increase in both sheet electron density(ns) and drain current density(ID). Contrarily, EB deposition makes a negative Nequ, resulting in reduced ns and ID. Besides, the maximum transconductance(gm-max) decreases and the off-state gate current density(I_G-off) increases for oxides at lower sputtering temperature compared with that at higher temperature, possibly due to a more serious sputter-induced damage and much larger Nequ at lower sputtering temperature. At high sputtering temperature, I_G-off decreases by two orders of magnitude compared to that without oxygen, which indicates that oxygen introduction and partial pressure depression of argon decreases the sputter-induced damage significantly. I_G-off for EB-evaporated samples is lower by orders of magnitude than that of sputtered ones, possibly attributed to the lower damage of EB evaporation to the barrier layer surface.     

Current–voltage characteristics of Schottky diode simulated using semiconductor device equations

The Poisson's equation and the drift diffusion equations have been used to simulate the current–voltage characteristics of Schottky diode. The potential variation inside the bulk semiconductor near the metal–semiconductor contact was estimated first and then the current as a function of bias through the Schottky diode using silicon parameters were calculated over a wide temperature range. From the simulated current–voltage characteristics the diode parameters were extracted by fitting of current–voltage data into thermionic emission diffusion current equation. The derived barrier parameters are analysed to study the effect of various parameters, e.g. semiconductor thickness, doping concentration, temperature dependence of carrier mobility and energy band gap, on the current–voltage characteristics of Schottky diode in view of the thermionic emission diffusion current equations.     

4H–SiC BJTs with current gain of 110

4H–SiC BJTs with a common emitter current gain of 110 have been demonstrated. The high current gain was attributed to a thin base of 0.25 μm which reduces the carrier recombination in the base region. The device open base breakdown voltage (BV_CEO) of 270 V was much less than the open emitter breakdown voltage (BV_CBO) of 1560 V due to the emitter leakage current multiplication from the high current gain by “transistor action” of BJTs. The device has shown minimal gain degradation after electrical stress at high current density of >200 A/cm²up to 25 h.     

Microstructure and electrical properties of nitrogen doped 3C–SiC thin films deposited using methyltrichlorosilane

The growth, microstructure and electrical properties of in-situ nitrogen doped 3C–SiC (111) thin films for sensor applications are presented in this paper. These thin films are deposited at a pressure of 2.5 mbar and temperature of 1040 °C on thermally oxidized Si (100) substrates from methyltrichlorosilane (MTS) precursor using a hot wall vertical low pressure chemical vapor deposition (LPCVD) reactor. Ammonia (NH₃) is used as the nitrogen doping gas. The sensor response depends on chemical composition, structure, morphology and operating temperature. The above properties are investigated for all in situ nitrogen doped (0, 9, 17 and 30 at% of nitrogen) 3C–SiC thin films using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and four probe method. The XRD patterns of the 3C–SiC thin films show a decrease in the crystallinity and intensity of the peak with increase in dopant concentration from 0 to 17 at%. AFM investigations show an improvement in the grain size of the nitrogen doped 3C–SiC thin films with increase in nitrogen concentration from 0 to 17 at%. The sheet resistance of nitrogen doped 3C–SiC thin films is measured by the four probe technique and it is found to decrease with increase in temperature in the range of 40–550 °C. The resistivity and average temperature coefficient of resistance (TCR) of doped 3C–SiC thin film deposited with 17 at% of nitrogen concentration are found to be 0.14 Ω cm and −103 ppm/°C, respectively and this can be used as a sensing material for high temperature applications.     

Impact of defect on I(V) instabilities observed on Ti/4H–SiC high voltage Schottky diodes

Anomaly in current at low forward bias is observed for large-area Ti Schottky diodes on n type 4H–SiC. Random telegraph signal (RTS) measurements, carried out on these defective devices, show discrete time switching of the current. Thermal activation of RTS signal gives two related trap signature (activation energy and cross section). Frequency analysis, using power spectral densities (PSDs) numerically calculated, confirms the presence of an extended defect which presents different charge states (i.e. an extended defect decorated by punctual traps). PSDs show two cut-off frequencies proving the individual response of two traps. Simulations of the I–V characteristics using two barrier heights modulated by a Gaussian function which represents the defect distribution show a good agreement with the experimental results. Finally we note that there's a strong correlation between traps observed by telegraph noise techniques and excess current.     

Control of electrical properties in Heusler-alloy/Ge Schottky tunnel contacts by using phosphorous δ-doping with Si-layer insertion

We experimentally demonstrate the control of electrical properties of Heusler-alloy/Ge contacts by phosphorous (P) δ-doping techniques with Si-layer insertion. Low-temperature molecular beam epitaxy methods enable us to obtain the high quality Heusler-alloy/Ge heterointerfaces with P δ-doped layers. Although the resistance area product (RA) values are scattered in the Heusler-alloy/Ge interfaces with conventional δ-doping techniques, we precisely adjust the RA values in the newly developed interface with Si-layer insertion. This method will open a way for developing source and drain structures in Ge-based spintronics devices.     

High temperature Hall effect measurements of semi-insulating 4H–SiC substrates

High temperature Hall effect and resistivity measurements have been made on semi-insulating 4H–SiC samples. Both vanadium doped and undoped materials have been studied. Resistivity measurements before and after annealing up to 1800 °C are also reported. The thermal activation energy of the resistivity in vanadium doped samples has one of two values, 1.5 and 1.1 eV, due, respectively, to the vanadium donor level and an as yet unidentified defect. The activation energies for high purity semi-insulating material (HPSI) varied from 0.9 to 1.5 eV. Hall effect measurements were made on several HPSI and 1.1 eV V-doped samples. In all cases the material was found to be n-type. Mixed conduction analysis of the data suggests that the hole concentration is negligible in all samples studied. This suggests that the defects responsible for the semi-insulating properties have deep levels located in the upper half of the bandgap. The resistivity of V-doped samples were unaffected by anneals up to 1800 °C. The annealing results for HPSI samples were mixed.     

Phosphorous passivation of the SiO2/4H–SiC interface

We describe experimental and theoretical studies to determine the effects of phosphorous as a passivating agent for the SiO₂/4H–SiC interface. Annealing in a P₂O₅ ambient converts the SiO₂ layer to PSG (phosphosilicate glass) which is known to be a polar material. Higher mobility (approximately twice the value of 30–40 cm²/V s obtained using nitrogen introduced with an anneal in nitric oxide) and lower threshold voltage are compatible with a lower interface defect density. Trap density, current–voltage and bias-temperature stress (BTS) measurements for MOS capacitors are also discussed. The BTS measurements point to the possibility of an unstable MOSFET threshold voltage caused by PSG polarization charge at the O–S interface. Theoretical considerations suggest that threefold carbon atoms at the interface can be passivated by phosphorous which leads to a lower interface trap density and a higher effective mobility for electrons in the channel. The roles of phosphorous in the passivation of correlated carbon dangling bonds, for SiC counter-doping, for interface band-tail state suppression, for Na-like impurity band formation and for substrate trap passivation are also discussed briefly.     

Numerical simulation study of current–voltage characteristics of a Schottky diode with inverse doped surface layer

The Poisson’s equation and drift–diffusion equations are used to simulate the current–voltage characteristics of Schottky diode with an inverse doped surface layer. The potential inside the bulk semiconductor near the metal–semiconductor contact is estimated by simultaneously solving these equations, and current as a function of bias through the Schottky diode is calculated for various inverse layer thicknesses and doping concentrations. The Schottky diode parameters are then extracted by fitting of simulated current–voltage data into thermionic emission diffusion equation. The obtained diode parameters are analyzed to study the effect of inverse layer thickness and doping concentration on the Schottky diode parameters and its behavior at low temperatures. It is shown that increase in inverse layer thickness and its doping concentration give rise to Schottky barrier height enhancement and a change in the ideality factor. The temperature dependences of Schottky barrier height and ideality factor are studied. The effect of temperature dependence of carrier mobility on the Schottky diode characteristics is also discussed.     

Lateral polarity control of Ⅲ-nitride thin film and application in GaN Schottky barrier diode

N-polar and Ⅲ-polar GaN and AIN epitaxial thin films grown side by side on single sapphire substrate was reported.Surface morphology,wet etching susceptibility and bi-axial strain conditions were investigated and the polarity control scheme was utilized in the fabrication of Schottky barrier diode where ohmic contact and Schottky contact were deposited on N-polar domains and Ga-polar domains,respectively.The influence of N-polarity on on-state resistivity and I-V characteristic was discussed,demonstrating that lateral polarity structure of GaN and A1N can be widely used in new designs of optoelectronic and electronic devices.     

Influence of air gaps on the thermal–electrical–mechanical behavior of a copper metallization

Shrinking the IC dimensions the dielectric insulation between metal interconnects has become one of the major limits on increasing circuit speed. A lot of possible new low-k materials failed to meet specifications: too leaky, too soft, too unstable, and too expensive. Due to this air gaps beside the metallization are one solution. The reliability of ULSI multilevel copper metallizations under electro- and stress migration stress test conditions is investigated here with finite element analysis. A determination of the electrical and mechanical stress in a 3D copper metallization model based on the 45 nm technology node is carried out and the impact of a variation of the applied current density as well as geometrical parameters on the thermal–electrical and mechanical behavior is investigated. For a determination of the reliability the mass flux and mass flux divergence are separately calculated by a user routine. The influence of air gaps on single via structures and structures with a chain of four vias on the thermal–electrical–mechanical behavior is determined.     

Temperature-dependent electrical properties of β-Ga2O3 Schottky barrier diodes on highly doped single-crystal substrates

Beta-phase gallium oxide(β-Ga_2O_3) Schottky barrier diodes were fabricated on highly doped single-crystal substrates,where their temperature-dependent electrical properties were comprehensively investigated by forward and reverse current density – voltage and capacitance – voltage characterization. Both the Schottky barrier height and the ideality factor showed a temperature-dependence behavior, revealing the inhomogeneous nature of the Schottky barrier interface caused by the interfacial defects. With a voltage-dependent Schottky barrier incorporated into thermionic emission theory, the inhomogeneous barrier model can be further examined. Furthermore, the reverse leakage current was found to be dominated by the bulk leakage currents due to the good material and surface quality. Leakage current per distance was also obtained. These results can serve as important references for designing efficient β-Ga_2O_3 electronic and optoelectronic devices on highly doped substrates or epitaxial layers.     

Study of electrophysical properties of metal–semiconductor contact by the theory of complex systems

The purpose of this work is to analyze the electrical properties of the metal–semiconductor contact (MSC) in the framework of the theory of complex systems. The effect of inhomogeneity of the different microstructures: polycrystalline, monocrystalline, amorphous metal–semiconductor contact surface is investigated, considering a Schottky diode (SD) as a parallel connection of numerous subdiodes. It has been shown that the polycrystallinity of the metal translates a homogeneous contact into a complex system, which consists of parallel connected numerous elementary contacts having different properties and parameters.     

Defects annealing in 4H–SiC epitaxial layer probed by low temperature photoluminescence

The thermal evolution of defects induced in 4H–SiC by multiple implantation of C ions was investigated by Low Temperature Photoluminescence in the temperature range 450–1000 K. The photoluminescence spectra show sharp luminescent lines (alphabet lines) in the wavelength range 426–440 nm upon irradiation and thermal treatment at 450 K induces the appearance of a new line at 427 nm (D_I centre). The trend shown by the luminescence lines as a function of the temperature is quite complex. The alphabet lines intensity increases up to 850 K, whereas at higher temperature decreases with an activation energy of 2.0 eV, suggesting that the defect, responsible for these lines, is the Si-vacancy. The luminescence yield of D_I centre is always increasing as a function of the temperature, with a higher slope from 750 K, suggesting a correlation to the reconfiguration and to the annealing of point defects.     

Carrier lifetime investigation in 4H–SiC grown by CVD and sublimation epitaxy

Depth-resolved carrier lifetime measurements were performed in low-doped epitaxial layers of 4H silicon carbide samples. The technique used was a pump-and-probe technique where carriers are excited by an above-bandgap laser pulse and probed by free carrier absorption. Results from chemical vapour deposition samples show that lifetimes as high as 2 μs may be observed in the mid-region of 40 μm thick epilayers. For epilayers grown by the sublimation method decay transients were characterised by a fast (few nanoseconds) initial recombination, tentatively assigned to the ‘true’ lifetime, whereas a slow tail of several hundred microsecond decay time was assigned to trapping centres. From the saturation of this level at increased pumping we could derive the trapping concentration and their depth distribution peaking at the epilayer/substrate interface.     

Band structure anisotropy effects on the hole transport transient in 4H–SiC

We study the role of band structure anisotropy on the hole transport in 4H–SiC during the transient regime. For the same strength of the applied electric field, the drift velocity overshoot of the hole is stronger and reaches steady state later when the field is applied perpendicular to the c-axis, than when the field is in the c-axis direction. In both cases, the time for the hole drift velocity and mean energy to reach steady state is under 50 fs, depending on the electric field strength, and are one order of magnitude shorter than the time for the electron drift velocity and mean energy to attain the steady state.