Field and carrier current density profiles in linearly graded silicon avalanche diodes

A detailed study for the d.c. field and carrier current density profiles of linearly graded double drift avalanche diodes is presented taking into account the effect of impurity and mobile charge density and the realistic field dependance of the ionization rates and drift velocities for the charge carriers. The study involves finding the location and magnitude of the electric field maximum by an iterative method. A small shift in the position of the electric field maximum towards the p-side of the metallurgical junction is observed which increases with increasing current density and decreasing doping gradient. The maximum field and the depletion layer width change sharply with doping gradient but very slightly with d.c. current density. Over a larger fraction of the depletion layer, hole current density exceeds electron current density and hole dominance increases with decreasing doping gradient. The avalanche centre where J_p = J_n is found to be always on the n-side of the junction.     

The transition layer in TiB2-GaAs and Au-TiB2-GaAs Schottky contacts

Spectral characteristics of the transverse bulk photovoltage in the TiB₂-GaAs and Au-TiB₂-GaAs Schottky contacts for starting samples (unannealed) and samples annealed at 400, 600, and 800°C were measured. The concentration of the dopant for the n-GaAs substrate was 10¹⁶ cm^?3. It was found that the transition layer is formed in the TiB₂-GaAs structures owing to the diffusion of boron atoms into the GaAs substrate. Thermal annealing leads to an increase in the doping level of the layer. For the Au-TiB₂-GaAs structure, the transition layer is formed, with the doping level of this layer being weakly affected by thermal annealing. The spectral position of the bulk-photovoltage peaks indicates that the tails of the density of states are formed in the band gap of the semiconductor transition layer owing to an increase in the dopant concentration to 10¹⁷–10¹⁸ cm^?3.     

Physicochemical properties of the surface and near-surface region of epitaxial n-GaAs layers modified by atomic hydrogen

Changes in the static electrical parameters of the Au-GaAs Schottky barriers in the (n-n ⁺)-GaAs structures treated with atomic hydrogen are closely related to modification of the chemical properties of the surface layers in these structures, including changes in the rate of n-GaAs etching in a DMF-monoethanol amine (1:3) solution, in the electrochemical deposition rate and the structure of the resulting Au layer, and in the degree of passivation of linear defects emerging on the surface. The unprotected surface of epitaxial n-GaAs(100) layer exhibited virtually no etch pits upon the treatment in atomic hydrogen at 100°C. For n-GaAs protected with a 50-Å-thick SiO₂ film, a drop in the etching rate and a considerable decrease in the number of etch pits, as well as a decrease in the thickness of electrochemically deposited gold layer and a change in is structure, were observed for the samples treated in atomic hydrogen at all temperatures in the range studied (100–400°C).     

Lifetime estimation of SiC MOSFETs under high temperature reverse bias test

Reliability physics of silicon carbide (SiC) metal-oxide semiconductor field-effect transistor (MOSFET) is not sufficiently clear; therefore an accurate estimation method of lifetime has been strongly required. The relationship between the failure time of 4H-SiC double implanted MOSFETs under high temperature reverse bias test and the doping concentration in a drift layer was studied to clarify the failure physics. The failure time of the device showed dependence on the doping concentration in the 150 mm wafer. The breakdown occurred at the gate oxide over the threading dislocation in the JFET region. The electric field simulation indicated that the oxide electric field linearly depends on the doping concentration, which means the failure time depends on the oxide electric field. According to these results, the electric field acceleration tests were conducted with the samples in the uniform area of the doping concentration so as to exclude the distribution of the oxide electric field in each sample. The lifetime showed dependence on the oxide electric field varied by the drain bias intentionally. These results revealed the importance of the doping concentration uniformity of the epitaxial layer and we established the method to estimate the lifetime accurately.     

Hot-hole lateral transport in a two-dimensional GaAs/Al0.3Ga0.7As structure

A narrow peak at the leading edge of the current pulse was found in samples of p-GaAs/Al_0.3Ga_0.7As structures subjected to a high electric field. An analysis of the shape and height of the peak as a function of the electric field, as well as the field redistribution along the sample, allows us to conclude that domain instability exists under these conditions. It is also shown that the energy of holes heated in moderate electric fields can significantly exceed the optical phonon energy.     

A computer method for the characterization of surface-layer ohmic contacts

The paper presents a general computer model for the calculation of the specific resistance of ohmic contacts with a heavily doped surface layer. A computer program is developed for the calculation. The theoretical model makes use of the depletion approximation. Two distinct cases are considered: the space-charge region extends beyond the surface layer and the space-charge region is contained in the surface layer, respectively. Curves, illustrating the specific resistance dependence on the bulk doping, with the surface layer doping and thickness as parameters are numerically computed. By fitting the theoretical curves with published experimental data the surface layer parameters are determined for Al/p-Si, Ni/n-Si and Au/n-GaAs contacts.     

砷化镓气相外延中Zn的行为和微光材料的制备

在Ga-AsCl_3-H_2系统中用金属Zn为掺杂剂,研究了气相外延GaAs时Zn的掺入和行为。GaAs中Zn的分配系数和空穴浓度分别为10和大于10~(20)cm~(-3),它们都比掺Cd的GaAs大2—3个数量级。这保证了用以制备光阴极材料所需的高空穴浓度的P-GaAs。结合掺Zn和掺s,已重复制得界面良好的P-n结构材料。     

Formation of the low-resistivity compound Cu<Subscript>3</Subscript>Ge by low-temperature treatment in an atomic hydrogen flux

The systematic features of the formation of the low-resistivity compound Cu₃Ge by low-temperature treatment of a Cu/Ge two-layer system in an atomic hydrogen flux are studied. The Cu/Ge two-layer system is deposited onto an i-GaAs substrate. Treatment of the Cu/Ge/i-GaAs system, in which the layer thicknesses are, correspondingly, 122 and 78 nm, in atomic hydrogen with a flux density of 10¹⁵ at cm² s^–1 for 2.5–10 min at room temperature induces the interdiffusion of Cu and Ge, with the formation of a polycrystalline film containing the stoichiometric Cu₃Ge phase. The film consists of vertically oriented grains 100–150 nm in size and exhibits a minimum resistivity of 4.5 µΩ cm. Variations in the time of treatment of the Cu/Ge/i-GaAs samples in atomic hydrogen affect the Cu and Ge depth distribution, the phase composition of the films, and their resistivity. Experimental observation of the synthesis of the Cu₃Ge compound at room temperature suggests that treatment in atomic hydrogen has a stimulating effect on both the diffusion of Cu and Ge and the chemical reaction of Cu₃Ge-compound formation. These processes can be activated by the energy released upon the recombination of hydrogen atoms adsorbed at the surface of the Cu/Ge/i-GaAs sample.     

Effect of surface stoichiometry on Be doping in GaAs by intermittent supply of AsH3 and TEG in an ultra-high vacuum

The effects of surface stoichiometry on Be doping in GaAs grown by molecular layer epitaxy have experimentally been investigated. Be-doped p⁺-GaAs layers were grown on (0 0 1)-oriented GaAs substrates by intermittent supply of AsH₃ and triethylgallium (TEG) in an ultra-high vacuum. Be(MeCp)₂ was used as a p-type dopant gas. The surface stoichiometry before introducing the dopant gas was controlled by changing the AsH₃ and TEG injection sequence and supply time. The doping characteristics were evaluated by secondary ion mass spectroscopy analysis. It was found that doping characteristics of Be-doped GaAs are strongly dependent on the doping sequence and surface stoichiometry. This experimental result and the Be doping mechanism are discussed on the basis of rate law of the surface chemical reaction.     

Alteration of diffusion profiles in semiconductors due to p-n junctions

Concentration profiles of diffusing species in semiconductors are calculated including the effects of the electric fields at p-n junctions. The junction electric field can significantly alter diffusion behavior near the junction at the growth temperature, and thus affect dopant uniformity and junction placement for some commonly occurring epitaxial growth conditions. The junction electric field affects diffusion in the same manner as the internal electric field that results from a dopant concentration gradient. The field can produce diffusion profiles with either enhanced or retarded diffusion rates at the junction and pile-up or depletion of the diffusing species near the junction. Several experimental examples for diffusion of Mg across a p-n junction in (Al, Ga). As during growth by liquid phase epitaxy are presented.     

Amorphization of the surface region in epitaxial <Emphasis Type="Italic">n</Emphasis>-GaAs treated with atomic hydrogen

It was found that the atomic-hydrogen treatment of n-GaAs epitaxial samples having initially high-quality surfaces both with a SiO₂ protective film on the n-layer surface and without it can lead to the amorphization of these surfaces and a thin (≈7 nm) surface layer, which is accompanied by the formation of a hydride phase. The lack of a hydrogen sublattice in the near-surface layer can imply that the main driving forces in the amorphization of epitaxial n-GaAs are short-range chemical interactions between hydrogen atoms and also between hydrogen atoms and atoms of the basic matrix of the crystal.     

Effect of substrate orientation on Zn-doping of AIGalnP grown by atmospheric pressure orgamometallic vapor phase epitaxy

Dependence of hole concentration ofp(Zn) — (Al_0.6Ga_0.4In_0.5P on substrate orientation was examined. It increases with tilting the substrate from (100) towards (511)A. Addition of ann-GaAs cap layer on top of the quaternary increases hole concentration while ap-GaAs cap shows little effect.     

Accumulation of electrons in GaAs layers grown at low temperatures and containing arsenic clusters

Capacitance spectroscopy was used to investigate the properties of Au/GaAs Schottky barriers in structures in which a thin layer of gallium arsenide grown at low temperature (LT-GaAs) and containing As clusters was sandwiched between two uniformly copper-doped layers of n-GaAs grown at standard temperatures. We detected electron accumulation in the LT-GaAs layer surrounded by two depletion regions in the adjacent n-GaAs layers. Emission of electrons from the LT-GaAs layer at 300 K results in an extended plateau in the capacitance-voltage characteristic. It is found that the presence of the 0.1 μm thick LT-GaAs layer sandwiched between the two much thicker n-GaAs layers results in an increase in the breakdown electric field to values as high as 230 kV/cm, which is much higher than typical values for standard Au/n-GaAs structures. Fiz. Tekh. Poluprovodn. 32, 1170–1174 (October 1998)     

Determination of the electron concentration and mobility in the vicinity of a quantum well and δ-doped layer in InGaAs/GaAs heterostructures

Comparative admittance measurements in mesadiodes on an n ⁺-GaAs substrate and in ring planar diode structures on an i-GaAs substrate, which contain a Si ??-doped layer and an InGaAs quantum well in the GaAs epitaxial layer are performed. The possibility of determining the concentration profile and electron mobility in the vicinity of the ??-doped layer and the InGaAs quantum well is shown based on an analysis of the simultaneously measured capacitance-voltage and conductance-voltage characteristics of the mesadiodes. By performing such measurements for i-GaAs-based ring diode structures with the given geometry, it is possible to reliably determine only the concentration profile. The influence of the relative location of the quantum well and ??-doped layer on the concentration profile and mobility is revealed. The phenomenon of Maxwell relaxation in i-GaAs-based ring diode structures is discussed.     

Influence of SiO2 protective films on the diffusion of atomic hydrogen during the hydrogenation of epitaxial n-GaAs

The surface relief of SiO₂ films and the influence of these films on the in-diffusion of atomic hydrogen in a semiconductor in the course of hydrogenation were investigated by atomic-force microscopy and scanning tunneling microscopy. The mesostructures appearing as a corrugation on the semiconductor surface are shown to be formed during the deposition of the SiO₂ film. This fact causes an increase in the amount of hydrogen penetrating into a semiconductor in the course of hydrogenation. The deposition of the dielectric film on the n-GaAs surface results in its reconstruction consisting in forming a quasi-periodic relief. The treatment of the n-GaAs surface covered with the SiO₂ protective film in atomic hydrogen modifies the surface relief of the epitaxial layer.     

Influence of the screening effect on passivation of <Emphasis Type="Italic">p</Emphasis>-type silicon by hydrogen

Passivation of p-Si by hydrogen through its diffusion was simulated by solving diffusion-kinetic equations with allowance made for hydrogen-acceptor-pair formation, internal electric field, and the screening effect. Screening of hydrogen and acceptor ions by free carriers leads to a decrease in the radius of interaction between the ions and to the weakening of the concentration dependence of hydrogen diffusivity in heavily doped Si. At a binding energy of the pairs of 0.70–0.79 eV, calculated and experimental concentration profiles of holes and the hydrogen-acceptor pairs are in agreement over a wide range of boron concentrations, from 4×10¹⁴ to 1.2×10²⁰ cm^?3. The radius of the Coulomb interaction of hydrogen and boron ions is 35 Å in lightly doped Si and decreases as the dopant concentration increases.     

Influence of the electron-hole equilibrium shift on transition-metal diffusion in GaAs

Diffusion of impurities of transition metals Fe, Cu, and Cr in heavily doped p ⁺-, n ⁺-, and intrinsic (at diffusion temperature) GaAs is studied. A technique in which impurity diffuses into GaAs-based structures with heavily doped layers (p ⁺-n or n ⁺-n) was used. It is shown that the impurity diffusivity values in p ⁺-GaAs and n ⁺-GaAs are significantly higher and lower, respectively, than for i-GaAs. The results obtained are discussed taking into account the effect of the electron-hole equilibrium shift in semiconductors on the diffusion of impurities migrating according to the dissociative mechanism. The interstitial-component concentration for Fe, Cu, and Cr impurities in GaAs was determined at the diffusion temperature.     

The spectral response and efficiency of heavily doped emitters in silicon photovoltaic devices

An analytical model of the spectral response and efficiency of an emitter is developed. The model is valid for an emitter of any thickness or any doping concentration and profiles. Explicit expression for the spectral response and efficiency of the emitter are derived. They take into account the space dependent mobility μ_p, band gap narrowing ΔE_g, lifetime and electric field. The expression reduces to simpler forms for quasi-transparent and transparent emitters. It is found that unlike a dark emitter, the effect of electric field on the behavior of the illuminated emitter is not negligible. The effect of change in ΔE_g and μ_p models on the spectral response and efficiency of the emitter is discussed. An increase in ΔE_g degrades the performance of the emitter. An increase in μ_p at high doping also degrades the behavior but only if the surface recombination velocity S_p is large. If S_p is very small, an increase of μ_p improves the spectral response and the efficiency of the emitter. The results calculated theoretically are in good agreement with the experimental results of Ref. [25] both for thin and thick emitters except for λ ≤ 0.4 μm and λ > 1.0μm. This discrepancy is attributed to the uncertainties in the experimental values of α at these wavelengths. It is shown that the value of μ_p at high dopings can be determined from the spectral response measurements provided that the value of S_p can be determined accurately from other independent measurements.     

Influence of the nonequilibrium-carrier concentration on the hall voltage in a p-type semiconductor

The dependence of the Hall voltage on the external electric field in a p-type semiconductor sample placed in a weak magnetic field is investigated. It is shown that the Hall voltage depends nonlinearly on the electric field in a sample whose thickness is comparable to the diffusion length and surface-recombination velocity is rather small. The Hall-voltage sign is opposite to that in a bulk sample in a certain range of electricfield strengths. The theoretical model describes well the experimental data for a p-type Ge sample.     

Characteristics of nuclear radiation detectors based on semi-insulating gallium arsenide

The characteristics of detectors based on bulk semi-insulating GaAs (SI-GaAs) have been studied by α particle detection and spectrometry. A distinctive feature of these detectors is the dependence of the width of the space charge region W on reverse bias voltage U. The rate of increase in W(U) is ∼1 μm/V, which permits formation of a sensitive region a few millimeters thick. The main obstacle to applying kilovolt-range bias voltages U is the reverse current noise. The characteristics of diode structures in which a rectifying barrier to SI-GaAs was formed by metal deposition (Schottky diodes) and by growing heterostructures with heavily doped AlGaAs or GaAsSb epitaxial layers were compared. Nonequilibrium carrier transport in epitaxial structures capable of sustaining bias voltages above 1 kV was investigated in both weak (below 1 kV/cm) and strong (10–30 kV/cm) electric fields. In both cases, the carrier lifetimes were found to be about a few nanoseconds. Such low values are due to the high concentration of trapping centers (EL2-type native defects), which limits the carrier transport. An analysis of the spectral line shape revealed that the lifetime is almost constant throughout the detector volume. The charge introduced by a particle was found to be enhanced in fields of ∼30 kV/cm. This effect can be qualitatively explained by focusing the electric field lines at the vertex of the α-particle track, which leads to an increase in the local field strength to ∼10⁻⁵ V/cm and impact ionization by nonequilibrium electrons. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 4, 2004, pp. 490–497. Original Russian Text Copyright ? 2004 by Verbitskaya, Eremin, Ivanov, Strokan, Vasil'ev, Gavrin, Veretenkin, Kozlova, Kulikov, Markov, Polyakov.