A. M. Strel’chuk

Electrical characteristics of p-3C-SiC/n-6H-SiC heterojunctions grown by sublimation epitaxy on 6H-SiC substrates

Abstract Sublimation epitaxy in a vacuum (SEV) has been used to obtain p-3C–SiC/n-6H–SiC heteroepitaxial structures. Results of a study of epilayers (X-ray diffraction analysis, scanning electron microscopy involving secondary electrons and electron beam induced current modes) and diode structures on their base ( I – V and C – V characteristics, electroluminescence spectra, DLTS) are presented. Band discontinuities are determined and a band diagram of the p-3C–SiC/n-6H–SiC heterostructure is constructed.

Radiation hardness of wide-gap semiconductors (using the example of silicon carbide)

Results obtained in studying the effect of ionizing radiation on epitaxial layers and devices based on silicon carbide (SiC) are considered. It is shown that, in investigations of wide-gap semiconductors (WGS), account should be taken of how the rate of removal of mobile charge carriers—the standard parameter in determining the radiation hardness of a material—depends on temperature. The use of data obtained only at room temperature may lead to an incorrect assessment of the radiation hardness of WGS. A conclusion is made that the WGS properties combine, on the one hand, high radiation hardness of high-temperature devices based on these semiconductors and, on the other, the possibility of effective radiation-induced doping (e.g., for obtaining semi-insulating local regions in a material at room temperature).

Radiation defects in n-4H-SiC irradiated with 8-MeV protons

Capacitance methods and electron spin resonance (ESR) were applied to study deep centers in n-6H-SiC irradiated with 8 MeV protons. Schottky diodes and p-n structures grown by sublimation epitaxy or commercially produced by CREE Inc. (United States) were used. The type of the irradiation-induced centers is independent of the material fabrication technology and the kind of charged particles used. Irradiation results in an increase in the total concentration of donor centers. The possible structure of the centers is suggested on the basis of data on defect annealing and ESR.

Effect of irradiation with fast neutrons on electrical characteristics of devices based on CVD 4H-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.

Low-temperature transport properties of multigraphene films grown on the SiC surface by sublimation

Multigraphene films grown by sublimation on the surface of a semi-insulating 6H-SiC substrate have been studied. It is shown that pregrowth annealing of the substrate in a quasiclosed growth cell improves the structural quality of a multigraphene film. Ohmic contacts to the film have been fabricated, and the Hall effect has been studied at low temperatures. It is found that a 2D electron gas exists in the films. It is concluded that the conductivity of the film is determined by defects existing within the graphene layer or at the interface between the graphene film and a SiC substrate.

Electrical characteristics of (p)3C-SiC-(n)6H-SiC heterojunctions

The electrical characteristics of (p)3C-SiC-(n)6H-SiC epitaxial heterostructures obtained by sublimation epitaxy in vacuum are studied. The band discontinuities are determined and the energy band diagram of the heterojunction is constructed. It is shown that the obtained heterostructure offers a promising material for high electron mobility transistors.

Optical and electrical properties of 4H-SiC irradiated with Xe ions

Structures with aluminum-ion-implanted p+-n junctions formed in 26-μm-thick chemicalvapor-deposited-epitaxial 4H-SiC layers with an uncompensated donor concentration Nd−Na = (1–3) × 1015 cm−3 are irradiated with 167-MeV Xe ions at fluences of 4 × 109 to 1 × 1011 cm−2 and temperatures of 25 and 500°C. Then as-grown and irradiated structures are thermally annealed at a temperature of 500°C for 30 min. The as-grown, irradiated, and annealed samples are analyzed by means of cathodoluminescence, including the cross-sectional local cathodoluminescence technique, and electrical methods. According to the experimental data, radiation defects penetrate to a depth in excess of several tens of times the range of Xe ions. Irradiation of the structures at 500°C is accompanied by “dynamic annealing” of some low-temperature radiation defects, which increases the radiation resource of 4H-SiC devices operating at elevated temperatures.

3C-SiC p-n structures grown by sublimation on 6H-SiC substrates

Sublimation epitaxy in a vacuum has been employed to grow n-and p-type 3C-SiC layers on 6H-SiC substrates. Diodes have been fabricated on the basis of the p-n structure obtained, and their parameters have been studied by measuring their current-voltage and capacitance-voltage characteristics and by applying the DLTS and electroluminescence methods. It is shown that the characteristics of the diodes studied are close to those of diodes based on bulk 3C-SiC. A conclusion is made that sublimation epitaxy can be used to fabricate 3C-SiC p-n structures on substrates of other silicon carbide polytypes.

Electrical characteristics of multigraphene films grown on high-resistivity silicon carbide substrates

Multigraphene films grown by sublimation of the surface of semi-insulating 6H-SiC substrates in a vacuum have been studied. The films exhibit a semiconductor-type conductivity. A conclusion is made that this type of conduction is supposedly determined by defects present between separate graphene crystals constituting the carbon layers under study.

Investigation of the p−-3C-SiC/n+-6H-SiC heterostructures with modulated doping

A heterostructure of the p−-3C-SiC/n+-6H-SiC type with modulated doping was synthesized by sublimation epitaxy in vacuum. Features of the current-voltage characteristics and the electroluminescence spectra show evidence of quantum confinement effects in a triangular quantum well at the heterojunction. The results indicate that the proposed technology employing sublimation epitaxy in vacuum can be used to obtain quantum-confined structures based on silicon carbide.