E. N. Mokhov

On mechanisms of sublimation growth of AlN bulk crystals

A novel model of bulk AlN crystal growth by the sublimation technique is developed. The model takes into account both di!usive and convective transport of gaseous Al and N 2 , and the kinetic limitation of nitrogen adsorption/desorption on AlN surfaces. The maximum growth rate is found to be controlled by joint e!ect of enhancement of the convective species transport in a nearly stoichiometric vapor phase and of the suppression of nitrogen incorporation into the crystal due to low N 2 sticking probability. The interplay of these e!ects provides nonmonotonic dependence of the growth rate on pressure. The theoretical predictions agree well with experimental data reported in literature and obtained in this work. ( 2000 Published by Elsevier Science B.V. All rights reserved.

GaN epitaxial layers grown on 6H‐SiC by the sublimation sandwich technique

We report on the structural and optical properties of GaN epitaxial layers grown on 6H‐SiC. We employed the sublimation sandwich method to grow single crystal layers at high growth rates with free carrier concentrations of 2×1017 cm−3. Very narrow x‐ray diffraction peaks of the GaN (0002) plane are obtained indicating the high quality of this system. These findings are directly reflected in the optical properties. The photoluminescence shows a single sharp exciton line with a half width of 4 meV. Impurity related donor acceptor transitions are seen with very weak intensities. However, at lower energies the internal luminescence transitions of the 3d transition metal ions Fe and V are observed.

Analysis of sublimation growth of bulk SiC crystals in tantalum container

Abstract Sublimation growth of SiC bulk crystals in tantalum container is studied both experimentally and theoretically. The model of heterogeneous processes occurred on the side wall of the tantalum container proposed recently in Ramm et al. (Mat. Sci. Eng. B 61–62 (1999) 107) is extended to take into account the process of carbon gettering by the container side wall. We formulate a quasi-steady approach for modeling of the bulk crystal growth. Using this concept we predict evolution of the crystal shape and study processes which govern SiC bulk crystal growth. We apply anisotropic thermal elastic analysis to predict stress distribution in the growing crystal. For the first time a model of dislocation formation is applied for SiC bulk growth to compute dislocation density field in highly stressed areas of the growing crystal.

High rate GaN epitaxial growth by sublimation sandwich method

Abstract Thick GaN epitaxial layers were grown by the sublimation “sandwich method” (SSM) on SiC substrates at temperatures from 1100°C to 1250°C in ammonia flow. Metallic Ga or GaN powder was used as the vapor source. The possibility of growing of monocrystalline GaN layers with growth rates as high as 1 mm/h was demonstrated. The dependence of the growth kinetics on temperature, source to substrate distance and input ammonia flow rate was studied. Various characterization techniques show the high quality of the GaN layers.

On the microscopic structures of shallow donors in 6H SiC: studies with EPR and ENDOR

Abstract Nitrogen and phosphorus in 6H-SiC were investigated with electron paramagnetic resonance (EPR) at 10 GHz and at 140 GHz and with electron nuclear double resonance (ENDOR). The phosphorus defects were prepared by neutron transmutation of 30 Si in 6H-SiC. We observed two sets of EPR spectra due to two different phosphorus-related defects. Both EPR spectra exhibit a strong temperature dependence. It is proposed, that one of these EPR spectra is due to the isolated shallow phosphorus donor on Si sites and the other due to a P-vacancy-pair defect. The electronic structures of the shallow donors P and N are discussed using effective mass theory. It is shown that the shallow P donor on the hexagonal site has not yet been observed.

Zeeman spectroscopy of the Fe3+ center in GaN

We report an optical investigation of the Zeeman behavior of the deep iron acceptor in GaN grown on 6H–SiC. The characteristic ground state splitting of the near‐infrared luminescence transition at 1.2988 eV allows for an unambiguous assignment to Fe3+previously proposed on the basis of ODMR results. The observed luminescence lifetime of 8 ms as well as the fine structure of the excited state are consistent with a 4T1(G)–6A1(S) transition. The 4T1(G) state is found to couple only weakly to e‐type phonon modes.

Sublimation Growth of AlN in Vacuum and in a Gas Atmosphere

The growth of AlN crystals by sublimation technique is investigated. Two mechanisms of Al and N2 transport from the source to the seed are distinguished — occurring predominantly via diffusion or via drift of the reactive species. Drift transport provides considerably higher growth rates compared to diffusive transport. The interplay of these mechanisms depends on temperature and gas pressure in the growth system. A theoretical model of AlN sublimation growth is developed allowing one to estimate the growth rate as a function of gas pressure and temperature. The theoretical predictions agree well with experimental observations obtained while growing AlN in the nitrogen atmosphere and in vacuum.

Growth of silicon carbide by sublimation sandwich method in the atmosphere of inert gas

Silicon carbide growth by sublimation sandwich method in the atmosphere of an inert gas is studied both experimentally and theoretically. An analytical description of diffusion transport of gaseous reactive species, coupled with quasi-equilibrium heterogeneous reactions at the source-wafer and substrate surfaces is derived. The species transport inside the sandwich cell is shown to be essentially determined by conditions in the ambience. The growth rate is studied as a function of process parameters (substrate temperature, temperature difference between the source-wafer and the substrate, and others). The developed approach is extended to the transient from the diffusion to the collisionless regime of the species transport. The theoretical results are in good agreement with the experimental data obtained.

Identification of iron transition group trace impurities in GaN bulk crystals by electron paramagnetic resonance

Abstract We report on the observation of electron paramagnetic resonance of iron, manganese and nickel trace impurities in bulk GaN crystals grown by the sublimation sandwich method. The resolved hyperfine structure due to interaction with 55Mn ( I = 5 2 ) nuclei has been observed in GaN, allowing unambiguous identification of the impurity. Manganese and nickel exist in Mn2+ (3d5) and Ni3+ (3d7) charge states with electron spin S = 5 2 and S = 3 2 , respectively, and occupy gallium sites in the GaN lattice. For Mn2+ we found g = 1.999, hyperfine structure constant A = 70.10−4 cm−1 and fine structure parameter /D/ = 240.10−4 cm−1. The EPR spectrum of Ni3+ in GaN had the characteristic anisotropy of an S = 3 2 system in a strong axial crystalline field. The effective g-factor values were found to be g′∥ = 2.10 and g′⊥ ≅ 4.20 for a system with an effective spin S′ = 1 2 . An analogy was revealed between the parameters of Mn2+ and Ni3+ in GaN and ZnO crystals. The zero-phonon line at 1.047 eV seems to belong to transition 4T2(F)-4A2(F) within 3d levels of Ni3+ ion with a 3d7 electronic configuration.

Identification of manganese trace impurity in GaN crystals by electron paramagnetic resonance

We report on the first observation of electron paramagnetic resonance of manganese trace impurity in GaN crystals. The resolved hyperfine structure due to interaction with nuclei has been observed in GaN for the first time, allowing unambiguous identification of the impurity. Manganese exists in the charge state with electron spin S = 5/2 and occupies gallium sites in the GaN lattice. We found g = 1.999, and the fine structure parameter .