H. J. Kim

Critical evaluation of the status of the areas for future research regarding the wide band gap semiconductors diamond, gallium nitride and silicon carbide

Abstract The extreme thermal and electronic properties of diamond and of silicon carbide, and the direct band gap of gallium nitride, provide multiplicative combinations of attributes which lead to the highest figures of merit for any semiconductor materials for possible use in high power, high speed, high temperature and high frequency applications. The deposition of monocrystalline diamond, at or below 1 atm total pressure and at a temperature T , has been achieved on diamond substrates; the deposited film has been polycrystalline on all other substrates but the achievement is no less significant. For electronic applications, heteroepitaxy of single-crystal films of diamond, an understanding of mechanisms of nucleation and growth, methods of impurity introduction and activation, and further device development must be achieved. Stoichiometric gallium nitride free of nitrogen vacancies has apparently not been obtained. Thus, knowledge of the defect chemistry of this material, the growth of semiconducting films on foreign substrates, and the development of insulating layers and of their low temperature deposition as well as device fabrication procedures must be achieved. By contrast, all of these problems have already been solved for silicon carbide, including the operation of a MOSFET at 923 K — the highest operating temperature ever reported for a field-effect device. However, considerable research remains to be done regarding the development of large silicon carbide substrates, of ohmic and rectifying contacts, of new types of devices, and of low temperature techniques for the deposition of insulating layers. Fugitive donor and acceptor species in unintentionally doped samples must also be identified and controlled.

Interface structures in beta-silicon carbide thin films

Interface structures in monocrystalline beta‐silicon carbide thin films grown on (001) silicon substrates have been studied by high‐resolution electron microscopy of cross‐sectional specimens. Despite a large lattice mismatch, there is a periodic registry of {111} atom planes across the SiC‐Si interface. Planar defects on SiC {111} planes are grown‐in and arise primarily from lattice and thermal expansion mismatch. Thermal oxidation in wet atmospheres results in preferential attack of the SiC film at sites where planar defects intersect the film surface, whereas oxidation in dry atmospheres does not.

Extrinsic Gettering Via the Controlled Introduction of Misfit Dislocations

As an alternative to existing gettering techniques, extrinsic gettering by misfit dislocations is described and gettering efficiency evaluated. Uniform arrays of misfit dislocations were generated at epitaxial Si interfaces by incorporation of 0.1–1% of Ge. The dislocations were shown to be confined to the interface by means of optical and electron microscopies. The misfit dislocations were used as extrinsic gettering sinks for metallic impurities deliberately introduced and diffused towards the dislocations. Transmission electron microscopy and secondary ion mass spectrometry analyses showed the preferential precipitation of Cu and Au at the misfit dislocations.

The effects of thermal annealing on the microstructural, optical and electrical properties of beta silicon carbide films implanted with boron or nitrogen

The effects of annealing of B or N dual implanted regions in 15-20 Μm thick monocrystalline Β-SiC films has been investigated using cross-sectional TEM, SIMS, Raman spectroscopy, C-V and sheet resistance measurements. Implantation resulted in buried amorphous regions (in the B films) or highly disordered regions (in the N films) and residually strained regions. Annealing for 300 s at selected temperatures between 1173 and 2073 K caused structural reordering, precipitation (in the B samples) and dopant diffusion, as the temperature was progressively increased. Only slight changes were noted in the sheet resistance of either type of sample as a result of annealing to 1973 K. However, the values of this parameter decreased markedly atT > 1973 K in both implanted and as-grown samples. Thus, this phenomenon was most probably caused by the formation of additionaln-type defects in the bulk of the materials.

Monocrystalline beta -SiC semiconductor thin films: epitaxial growth, doping, and FET device development

High-purity, single-crystal beta -SiC thin films have been epitaxially grown by means of chemical vapor deposition. The defect nature of these films has been characterized, and antiphase boundaries, one of the major defects observed, were eliminated through utilization of off-axis Si-substrates. Doping of these films was possible through in-situ incorporation during growth or through ion implantation. The use of elevated temperatures during ion implantation resulted in damage-free material suitable for device fabrication. MESFETs constructed from these films showed good transistor action up to temperature of 523 K. Depletion-mode MOSFETs fabricated on beta -SiC

Extrinsic Gettering with Epitaxial Misfit Dislocations

New results are presented on Ge doped Si epitaxial layers which contain interfacial misfit dislocations. Microscopic and chemical analyses showed the preferential gettering of several metallic species (Au, Cu, Ni, and Fe) at the misfit dislocations with semiquantitative correlation between dislocation density and the captured impurity concentration. Wafer curvature was measured and shown to be less than that for typical Si 3 N 4 and SiO 2 layers used in IC fabrication. The reduction of Schottky diode leakage current has been clearly demonstrated and attributed to gettering of residual impurities, as well as signifying that, the active surface device region is not deleteriously affected by spurious defect reactions at the buried epitaxial interface.