Subnanosecond 4<Emphasis Type="Italic">H</Emphasis>-SiC diode current breakers

Mesa epitaxial 4H-SiC-based p ⁺-p-n ₀-n ⁺ diodes have been fabricated and their reverse recovery characteristics have been measured in modes typical of fast semiconductor current breakers, drift step recovery diodes, and SOS diodes. It has been found that, after the short (～10 ns) pulsed injection of nonequilibrium carriers by a forward current with a density of 200–400 A cm^?2 and the subsequent application of a reverse voltage pulse (with a rise time of 2 ns), diodes can break a reverse current with a density of 5–40 kA cm^?2 in a time of about (or less than) 0.3 ns. A possible mechanism for ultrafast current breaking is discussed.     

Effect of irradiation with fast neutrons on electrical characteristics of devices based on CVD 4<Emphasis Type="Italic">H</Emphasis>-SiC epitaxial layers

The effect of irradiation with 1-MeV neutrons on electrical properties of Al-based Schottky barriers and p⁺-n-n⁺ diodes doped by ion-implantation with Al was studied; the devices were formed on the basis of high-resistivity, pure 4H-SiC epitaxial layers possessing n-type conductivity and grown by vapor-transport epitaxy. The use of such structures made it possible to study the radiation defects in the epitaxial layer at temperatures as high as 700 K. Rectifying properties of the diode structures were no longer observed after irradiation of the samples with neutrons with a dose of 6×10¹⁴ cm^?2; this effect is caused by high (up to 50 GΩ) resistance of the layer damaged by neutron radiation. However, the diode characteristics of irradiated p⁺-n-n⁺ structures were partially recovered after an annealing at 650 K.     

Control over carrier lifetime in high-voltage <Emphasis Type="Italic">p-i-n</Emphasis> diodes based on In<Subscript>x</Subscript>Ga<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>As/GaAs heterostructures

The possibility of controlling the effective lifetime of nonequilibrium carriers by varying the lattice mismatch between the interfaced materials of a heterostructure has been studied on the example of InGaAs/GaAs heterostructures. It was found that, at a given composition (thickness) of a lightly doped layer of the InGaAs alloy, the nonequilibrium carrier lifetime depends on its thickness (composition), which enables variation of the nonequilibrium carrier lifetime from several nanoseconds to a microsecond without any significant change in the concentration of mobile carriers. The results obtained were used to fabricate pulse p ⁺-p ⁰-π-n ⁰-n ⁺ diodes with blocking voltages of up to 500 V, which can switch currents of ≥10 A and have recovery times no longer than 10 ns.     

Modification of Au-Ti(W,Cr, TiB<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)-GaAs contacts properties caused by external influences

In this paper it is considered an influence of gamma-radiation ⁶⁰Co, microwave and ultrasonic processing on electro-physical properties and relaxation of internal stresses in Au-Ti(W, Cr, TiB _x )-GaAs contacts, based on GaAs plate, containing n-n ⁺ structures of GaAs. Correlation between radius of curvature of GaAs plates and contact parameters is detected. It is shown experimentally, that modification of electro-physical parameters of diodes with Schottky barrier, based on GaAs is specified by internal stresses relaxation in gallium arsenide structures with contacts.     

Effect of the fabrication conditions of SiGe LEDs on their luminescence and electrical properties

SiGe-based n⁺–p–p⁺ light-emitting diodes (LEDs) with heavily doped layers fabricated by the diffusion (of boron and phosphorus) and CVD (chemical-vapor deposition of polycrystalline silicon layers doped with boron and phosphorus) techniques are studied. The electroluminescence spectra of both kinds of LEDs are identical, but the emission intensity of CVD diodes is ～20 times lower. The reverse and forward currents in the CVD diodes are substantially higher than those in diffusion-grown diodes. The poorer luminescence and electrical properties of the CVD diodes are due to the formation of defects at the interface between the emitter and base layers.     

<Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript>-Si-<Emphasis Type="Italic">n</Emphasis>-CdF<Subscript>2</Subscript> heterojunctions

Boron diffusion and the vapor-phase deposition of silicon layers are used to prepare ultrashallow p⁺-n junctions and p⁺-Si-n-CdF₂ heterostructures on an n-CdF₂ crystal surface. Forward portions of the I–V characteristics of the p⁺-n junctions and p⁺-Si-n-CdF₂ heterojunctions reveal the CdF₂ band gap (7.8 eV), as well as allow the identification of the valence-band structure of cadmium fluoride crystals. Under conditions in which forward bias is applied to the p⁺-Si-n-CdF₂ heterojunctions, electroluminescence spectra are measured for the first time in the visible spectral region.     

“Ideal” static breakdown in high-voltage (1 kV) 4<Emphasis Type="Italic">H</Emphasis>-SiC<Emphasis Type="Italic">p-n</Emphasis> junction diodes with guard ring termination

Nearly “ideal” static high-voltage breakdown (1060 V) in 4H-SiC p⁺-n-n⁺ diodes with guard ring termination is observed. At the doping level of 1.9 × 10¹⁶ cm^?3 in the n-type base, the diode breakdown field is 2.7 × 10⁶ V/cm. At the reverse bias as high as 1000 V, the leakage-current density does not exceed 5 × 10^?5 A/cm². The diodes withstand without degradation an avalanche-current density of 1 A/cm², which corresponds to the dissipated power of 1 kW/cm².     

Solution of the problem of charge-carrier injection into an insulating layer under self-consistent boundary conditions at contacts

The problem of charge carrier injection into a finite-length insulating layer is analytically solved in the drift-diffusion approximation, taking into account self-consistent boundary conditions. The main assumption is the neglect of intrinsic doping of the i-type layer. The solution allows calculation of the potential, electric field, and current-voltage characteristics of various structures, i.e., metal-i-n ⁺ (or p ⁺)-semiconductor, metal-i-layer-metal, and n ⁺(p ⁺)-i-n ⁺(p ⁺) structures. The solution allows generalization for structures having heterobarriers at semiconductor layer interfaces. The proposed approach considers contact phenomena and volume effects associated with the space-charge-limited current in the i-type layer. The solution is valid in both extreme cases and intermediate conditions.     

Self-Action of Intense Millimeter Waves in Waveguides with Integrated P-I-N Structures

The nonlinear interaction of high power millimeter (mm) electromagnetic waves with silicon integral p-i-n structures placed in a metal waveguide is theoretically investigated. The level of double injection of charge carriers due to detection of high intensity millimeter wave electric field in p-i-n structures is estimated. A mathematical model of the mutual influence of electromagnetic waves and injected charge carriers in the active region of p-i-n structures is formulated. A numerical solution of the nonlinear Helmholtz equation supplemented by proper boundary conditions on the active region boundary is obtained. The effect of high-power electromagnetic waves leads to an excessive injection of carriers into the active region of the semiconductor between p⁺-i, n⁺-i injection junctions and redistribution of the electric field in the structure. The reflection and transmission coefficients vary rapidly with the change in the input amplitude of the electromagnetic wave. This leads to bistability of these coefficients. The bistability is more pronounced in the low-frequency part of the mm range.     

Optical and electrical properties of 4<Emphasis Type="Italic">H</Emphasis>-SiC irradiated with fast neutrons and high-energy heavy ions

Photoluminescence and deep-level transient spectroscopy are used to study the effect of irradiation with fast neutrons and high-energy Kr (235 MeV) and Bi (710 MeV) ions on the optical and electrical properties of high-resistivity high-purity n-type 4H-SiC epitaxial layers grown by chemical vapor deposition. Electrical characteristics were studied using the barrier structures based on these epitaxial layers: Schottky barriers with Al and Cr contacts and p⁺-n-n⁺ diodes fabricated by Al ion implantation. According to the experimental data obtained, neutrons and high-energy ions give rise to the same defect-related centers. The results show that, even for the extremely high ionization density (34 keV/nm) characteristic of Bi ions, the formation of the defect structure in SiC single crystals is governed by energy losses of particles due to elastic collisions.     

Investigation of the ZnS-CdHgTe interface

The ZnS-Cd_xHg_1?xTe interface was investigated using the capacitance-voltage characteristics of MIS structures in experimental samples. During fabrication of the n⁺-p junctions based on p-Cd_xHg_1?xTe, the density of states within the range N _ss =(1–6)×10¹¹ cm^?2 eV^?1 at T=78 K was obtained. The experiments showed that the conditions in which n⁺-p junctions are fabricated only slightly affect the state of the ZnS-CdHgTe interface. The negative voltages of the at bands V _FB , even if immediately after deposition of the ZnS films V _FB >0, point to the enrichment of the ZnS-p-CdHgTe near-surface layer with majority carriers, specifically, holes. This led to a decrease in the leakage current over the surface. During long-term storage (as long as ～15 years) in air at room temperature, no degradation of differential resistance R _d , current sensitivity S _i , and detectivity D* of such n⁺-p junctions with a ZnS protection film was observed.     

Study of deep levels in GaAs <Emphasis Type="Italic">p–i–n</Emphasis> structures

An experimental study of the capacitance–voltage (C–V) characteristics and deep-level transient spectroscopy (DLTS) of p⁺–p⁰–i–n⁰ structures based on undoped GaAs, grown by liquid-phase epitaxy at two crystallization-onset temperatures T_o (950 and 850°C), with optical illumination switched off and on, are performed. It is shown that the p⁰, i, and n⁰ layers of epitaxial structures are characterized by the presence of defects with deep donor- and acceptor-type levels in concentrations comparable with those of shallow donors and acceptors. Interface states are found, which manifest themselves in the C–V characteristics at different measurement temperatures and optical illumination; these states form an additive constant. A distinct temperature dependence of the steady-state capacitance of the structures is revealed. It is found that the injection of minority carriers under an applied positive filling pulse and optical recharging lead to modification of the structure and, correspondingly, the DLTS spectra of the p⁺–p⁰–i–n⁰ structures. It is revealed that the p⁺–p⁰–i–n⁰ GaAs structures grown at T_o = 850°C are characterized by a lack of interface states and that the recharging of acceptor-type deep traps under illumination does not change the C–V characteristics. The conventionally measured DLTS spectra reveal the presence of two hole traps: HL5 and HL2, which are typical of GaAs layers.     

Diamond Diode Structures Based on Homoepitaxial Films

(m–i–p)-Structures with high-resistance epitaxial i-layers are fabricated on heavily doped p⁺-type substrates with platinum contacts. The structures are studied using several methods: optical and electron microscopy and luminescence, and electrophysical (C–V and I–V characteristics) methods and tested as detectors of ionizing radiation. It is shown that the (m–i–p)-structures are promising for development of several electronic devices (high-voltage diodes, detectors of ionizing radiation, and photovoltaic devices).     

Effect of Dislocation-related Deep Levels in Heteroepitaxial InGaAs/GaAs and GaAsSb/GaAs <Emphasis Type="Italic">p</Emphasis>–<Emphasis Type="Italic">i</Emphasis>–<Emphasis Type="Italic">n</Emphasis> Structures on the Relaxation time of Nonequilibrium Carriers

The results of an experimental study of the capacitance–voltage (C–V) characteristics and deep-level transient spectroscopy (DLTS) spectra of p⁺–p⁰–i–n⁰ homostructures based on undoped dislocationfree GaAs layers and InGaAs/GaAs and GaAsSb/GaAs heterostructures with homogeneous networks of misfit dislocations, all grown by liquid-phase epitaxy (LPE), are presented. Deep-level acceptor defects identified as HL2 and HL5 are found in the epitaxial p⁰ and n⁰ layers of the GaAs-based structure. The electron and hole dislocation-related deep levels, designated as, respectively, ED1 and HD3, are detected in InGaAs/GaAs and GaAsSb/GaAs heterostructures. The following hole trap parameters: thermal activation energies (E _t ), capture cross sections (σ _p ), and concentrations (N _t ) are calculated from the Arrhenius dependences to be E _t = 845 meV, σ _p = 1.33 × 10^–12 cm², N _t = 3.80 × 10¹⁴ cm^–3 for InGaAs/GaAs and E _t = 848 meV, σ _p = 2.73 × 10^–12 cm², N _t = 2.40 × 10¹⁴ cm^–3 for GaAsSb/GaAs heterostructures. The concentration relaxation times of nonequilibrium carriers are estimated for the case in which dislocation-related deep acceptor traps are involved in this process. These are 2 × 10^–10 s and 1.5 × 10^–10 s for, respectively, the InGaAs/GaAs and GaAsSb/GaAs heterostructures and 1.6 × 10^–6 s for the GaAs homostructures.     

Oscillations of induced photopleochroism in ZnO/GaAs heterojunctions

Anisotype and isotype ZnO/GaAs heterojunctions were formed by magnetron sputtering of thin n-ZnO:Al films on epitaxial layers of n-and p-GaAs. It is shown that the heterostructures obtained have a high photosensitivity (～5×10³ V/W at 300 K) in a wide spectral range (1.5–3.2 eV), which oscillates due to the radiation interference in thin ZnO films. Under oblique incidence of linearly polarized radiation on a ZnO film, photopleochroism is induced in a heterojunction, whose value oscillates within ～1–55% at θ=85°. The photopleochroism oscillations are also due to the radiation interference in the ZnO film. It is concluded that the heterojunctions obtained are promising candidates for selective photodetectors of linearly polarized radiation.     

Hydrogen-containing donors in silicon: Centers with negative effective correlation energy

The reconstruction of shallow-level hydrogen-containing donors in Si is studied. The donors are formed by implantation of low-energy (300 keV) hydrogen ions into the experimental samples and subsequent heat treatment at 450°C. The experiments are carried out for Ag-Mo-Si Schottky diodes and diodes with a shallow (～1 μm) p⁺-n junction. The concentration and distribution of the donors are determined by applying the method of C–V characteristics at a frequency of 1.2 MHz. An analysis of the temperature dependence of the equilibrium electron concentration shows that the reconstruction of the hydrogen-containing donors can be described under the assumption of recharging of a center with negative effective correlation energy (U < 0). The transformation between two equilibrium configurations of a double hydrogen donor (D _B ⁺⁺ ? D _A ⁰ ) proceeds with the Fermi level position E_F = E _c ? 0.30 eV. The reconstruction of the donors from a neutral to a doubly charged state (D _A ⁰ → D _B ⁺⁺ ) which is stimulated by the capture of minority carriers, is observed at room temperature.     

A new type of high-efficiency bifacial silicon solar cell with external busbars and a current-collecting wire grid

Results regarding bifacial silicon solar cells with external busbars are presented. The cells consist of [n⁺p(n)p⁺] Cz-Si structures with a current-collecting system of new design: a laminated grid of wire external busbars (LGWEB). A LGWEB consists of a transparent conducting oxide film deposited onto a Si structure, busbars adjacent to the Si structure, and a contact wire grid attached simultaneously to the oxide and busbars using the low-temperature lamination method. Bifacial LGWEB solar cells demonstrate record high efficiency for similar devices: 17.7%(n-Si)/17.3%(p-Si) with 74–82% bifaciality for the smooth back surface and 16.3%(n-Si)/16.4%(p-Si) with 89% bifaciality for the textured back surface. It is shown that the LGWEB technology can provide an efficiency exceeding 21%.     

A 4<Emphasis Type="Italic">H</Emphasis>-SiC<Emphasis Type="Italic">p-i-n</Emphasis> diode fabricated by a combination of sublimation epitaxy and CVD

The possibility of fabricating heavily doped (N _a ?N _d ≥ 1 × 10¹⁹ cm_?3) p⁺-4H-SiC layers on CVD-grown lightly doped n-4H-SiC layers by sublimation epitaxy has been demonstrated. It is shown that a Au/Pd/Ti/Pd contact, which combines a low specific contact resistance (～2 × 10^?5 Ω cm²) with high thermal stability (up to 700°C), is the optimal contact to p-4H-SiC. The p-n structures obtained are used to fabricate packaged diodes with a breakdown voltage of up to 1400 V.     

Giant burst of impact ionization in a <Emphasis Type="Italic">p-n</Emphasis> junction of the 6<Emphasis Type="Italic">H</Emphasis>-SiC polytype

A study of the electron component of impact ionization in the p ⁺-n ^?-n ⁺ junction in the 6HSiC polytype made it possible to detect a giant burst of impact ionization and origination of an extra early avalanche breakdown. The electric field of this breakdown is lower by ～20% than the electric field of the breakdown arising as a result of a steady development of the impact ionization. It is of interest that this phenomenon occurs abruptly, without any apparent causes, in particular, without an increase in the dark current characteristic of a prebreakdown state of the p-n junction. Conditions for origination of an unusual breakdown and its properties made it possible to assume that there are nonlinear processes that give rise to a streamer. In the p-n junction plane, the anomalous breakdown is seen as a narrow glowing track with a width of ≈10 μm. This effect takes place in the conditions of the Wannier-Stark ladder of states. The latter can stimulate a local accumulation of charge and formation of a streamer structure.