A. A. Lavrent’ev

Electronic band structure of In2S3 and CdIn2S4 semiconductor spinels from the data of x-ray spectroscopy and theoretical calculations

The electronic band structure of the chalcogenide spinels In2S3 and CdIn2S4 has been studied using the FEFF8 program. It is shown that the valence band top is formed by the S p states mixed with the In s and In p states for In2S3 or with the Cd s, Cd p, In s, and In p states for CdIn2S4. Compared to In2S3, the presence of Cd atoms in the nearest environment of S atoms in CdIn2S4 does not considerably affect the electronic band structure. In CdIn2S4 the Cd 4d states, as well as the In 4d states, form a narrow localized band shifted deep into the valence band. The theoretical results are in good agreement with the experimental x-ray photoelectron and x-ray spectra.

Formation of Periodic Steps on 6H-SiC (0001) Surface by Annealing in a High Vacuum

Influence of high-vacuum annealing at temperatures in the range 1300-1400°C and residual pressure of ~10-6 Torr on the surface of 6H-SiC (0001) wafers has been studied. Auger spectroscopy and RHEED data show that the annealing conditions do not lead to any surface reconstruction of the wafers. Atomic force microscopy reveals atomically flat surface terraces separated by steps of unit-cell height (h = 1.5 nm).

Formation of nanocarbon films on the SiC surface through sublimation in vacuum

The possibility of forming nanocarbon films on the SiC surface with the use of the technology employed in sublimation epitaxy of silicon carbide has been demonstrated. The temperature range in which nanocarbon films four to five lattice-cells thick form is found. The presence in films of two-dimensional graphite crystals is revealed.

Semi-insulating silicon carbide layers obtained by diffusion of vanadium into porous 4H-SiC

Semi-insulating silicon carbide layers have been obtained by diffusion of vanadium into porous 4H-SiC. The diffusion was performed from a film deposited by cosputtering of silicon and vanadium, with the content of the latter equal to 20%. The diffusion profile of vanadium in porous silicon carbide has a complex structure with a fast diffusion coefficient of 7×10−15 cm2/s. The activation energy of the resistivity of vanadium-diffusion-doped porous SiC layers is 1.45 eV. The resistivity of vanadium-doped semi-insulating layers is 5×1011 Ω cm at 500 K, which exceeds the resistivity of undoped porous SiC by two orders of magnitude. The results obtained indicate that porous SiC is a promising material for semi-insulating substrates in device structures based on wide-bandgap semiconductors.

High-temperature diffusion doping of porous silicon carbide

The results of experiments on high-temperature (2000–2200°C) diffusion doping of porous silicon carbide (PSC) by vanadium and erbium are reported. It is established that the specific features of diffusion processes in PSC at these temperatures are determined by modification of the porous structure due to the transport of vacancies. Based on a comparison of these results to available data on the low-temperature (900–1000°C) diffusion, it is concluded that the mechanisms of diffusion in PSC at low and high temperatures are different and that SiC with a porous structure is an effective medium particularly for low-temperature diffusion.

Diffusion of interstitial magnesium in dislocation-free silicon

The diffusion of magnesium impurity in the temperature range T = 600–800°C in dislocation-free single-crystal silicon wafers of p-type conductivity is studied. The surface layer of the wafer doped with magnesium by the ion implantation technique serves as the diffusion source. Implantation is carried out at an ion energy of 150 keV at doses of 5 × 1014 and 2 × 1015 cm–2. The diffusion coefficient of interstitial magnesium donor centers (Di) is determined by measuring the depth of the p–n junction, which is formed in the sample due to annealing during the time t at a given T. As a result of the study, the dependence Di(T) is found for the first time. The data show that the diffusion process occurs mainly by the interstitial mechanism.

Formation of graphite/sic structures by the thermal decomposition of silicon carbide

The conditions in which carbon layers are synthesized on the surface of silicon carbide (SiC) wafers by thermal decomposition are studied. The effect of temperature and composition of the gas atmosphere on the structural properties of the layers being synthesized is analyzed. The conditions in which continuous graphite films with both single-crystal and polycrystalline structure can be obtained are determined.

Specific features of the hydride vapor-phase epitaxy of nitride materials on a silicon substrate

Specific features of the growth of the GaN/AlN/Si heterocomposite in which layers of Group-III element nitrides are grown on a silicon substrate by hydride vapor-phase epitaxy are studied. The effect of the temperature at which the AlN buffer layer is grown on diffusion processes at the heterointerfaces and on the quality of the epitaxial layers being grown is considered. It is shown that, with the epitaxial technique used, the buffer layer should be grown at high temperatures (1080°C) because the thickness of the component-mixing region is minimized in this case and abrupt interfaces are formed in the GaN/AlN/Si heterocomposite. The double-stage growth of gallium nitride on the high-temperature AlN buffer layer with a thickness of 300–400 nm makes it possible to obtain GaN layers with thicknesses of up to 0.3 μm without crack formation.

Magnesium outdiffusion from porous silicon carbide substrates during autodoping of gallium nitride epilayers

We have studied the outdiffusion of magnesium from silicon carbide substrates during autodoping of gallium nitride epilayers. The autodoping effect was observed in the case of porous substrates obtained by surface anodization of 6H-SiC wafers. It is established that the magnesium distribution profiles can be controlled by post-growth annealing. The fact of doping is confirmed by the results of photoluminescence measurements at 77 K.

Evaluation of band gaps in CuGa(SxSe1−x)2 solid solutions from calculated total densities of states

The local partial and total densities of states in CuGa(SxSe1−x)2 (x=0, 0.17, 0.33, 0.50, 0.67, 0.83, and 1.0) solid solutions are calculated by the local coherent potential method within the virtual crystal approximation. The lattice parameters of the chalcopyrite solid solutions under investigation are determined in the framework of the Jaffe-Zunger theory with the use of the Pauling tetrahedral radii. It is revealed that the band gap Eg linearly depends on the sulfur concentration x in the anionic sublattice. This result is in agreement with the experimental data, but the theoretical band gaps Eg are found to be approximately 0.5 eV less than the experimental values.