S. N. Rodin

Chloride vapor-phase epitaxy of gallium nitride on silicon: Effect of a silicon carbide interlayer

A new approach is described, according to which the use of a thin silicon carbide (SiC) interlayer ensures the suppression of cracking and the simultaneous release of elastic strain in gallium nitride (GaN) epilayers grown by hydride-chloride vapor-phase epitaxy (HVPE) on 1.5-inch Si(111) substrates. Using this method, 20-μm-thick GaN epilayers have been grown by HVPE on Si substrates with AlN (300 nm) and SiC (100 nm) interlayers. A high quality of the obtained GaN epilayers is confirmed by the photoluminescence spectra, where an exciton band with hvmax = 3.45 eV and a half-width (FWHM) of 68 meV is observed at 77 K, as well as by the X-ray rocking curves exhibiting GaN(0002) reflections with a half-width of ωϑ = 600 arc sec.

Chloride vapor-phase epitaxy of gallium nitride at a reduced source temperature

Gallium nitride (GaN) layers on sapphire substrates have been grown by hydride-chloride vaporphase epitaxy (HVPE) at a Ga-source temperature reduced from 890°C (standard value) to 600°C. All epilayers are transparent and have smooth surfaces. The structural quality of layers was evaluated by measuring the X-ray rocking curve width (FWHM) using a triple-crystal X-ray diffractometer. For the best samples, this quantity amounted to 8 arc min. Analysis of the dependence of the crystal structure quality and photoluminescent properties of GaN layers on the Ga-source temperature showed that a decrease in this parameter to 600°C did not significantly affect the HVPE growth of GaN despite a considerable change in the vapor phase composition (ratio of GaCl and GaCl3 concentrations).

Gan films grown by vapor-phase epitaxy in a hydride-chloride system on Si(111) substrates with AlN buffer sublayers

Oriented GaN layers with a thickness of about 10 μm have been grown by hydride-chloride vaporphase epitaxy (HVPE) on Si(111) substrates with AlN buffer layers. The best samples are characterized by a halfwidth (FWHM) of the X-ray rocking curve of ωθ = 3–4 mrad. The level of residual mechanical stresses in AlN buffer layers decreases with increasing temperature of epitaxial growth. The growth at 1080°C is accompanied by virtually complete relaxation of stresses caused by the lattice mismatch between AlN and Si.

Epitaxy of semipolar GaN on a Si(001) substrate with a SiC buffer layer

A new method of synthesis of semipolar gallium nitride on a silicon substrate using the technology of solid-phase epitaxy of 3C-SiC nanocrystals has been suggested. It has been demonstrated that application of buffer layers of 3C-SiC and AlN enables one to form epitaxial layers of semipolar gallium nitride with layer deviation from the polar position of the c axis of a wurtzite crystal by an angle of 48°–51° at the minimal half-width of the X-ray diffraction rocking curve (ωθ) ∼ 24′. The observed bend of a cylindrical character in the structure of GaN/AlN/3C-SiC(001) is explained by the anisotropic deformation of semipolar GaN on silicon.

The effect of surfactants on epitaxial growth of gallium nitride from gas phase in the Ga-HCl-NH3-H2-Ar system

We have studied epitaxial layers of gallium nitride (GaN) in a template composition grown by surfactant-mediated hydride-chloride vapor phase epitaxy. The surfactant component was provided by 5 mass % additives of antimony and indium to the source of gallium. Comparative analysis of the obtained results shows evidence of the positive influence of surfactants on the morphology of epitaxial GaN layers.

Chloride vapor-phase epitaxy of gallium nitride on silicon: Structural and luminescent characteristics of epilayers

The structure and luminescent properties of gallium nitride (GaN) epilayers grown by hydride-chloride vapor-phase epitaxy (HVPE) in a hydrogen or argon atmosphere on 2-inch Si(111) substrates with AlN buffer layers have been studied. The replacement of hydrogen atmosphere by argon for the HVPE growth of GaN leads to a decrease in the epilayer surface roughness. The ratio of intensities of the donor-acceptor and exciton bands in the luminescence spectrum decreases with decreasing growth temperature. For the best samples of GaN epilayers, the halfwidth (FWHM) of the X-ray rocking curve for the (0002) reflection was 420 sec of arc, and the FWHM of the band of exciton emission at 77 K was 48 meV.

Growth of single-crystalline GaN layers in a horizontal reactor by chloride epitaxy

Chloride epitaxy of GaN layers in a horizontal reactor is studied numerically. The steady 3D fluxes of the gas mixture in the reactor are simulated with allowance for heterogeneous reactions on the substrate (growth of epitaxial GaN layers) and on the reactor walls (growth of a polycrystalline GaN deposit). Experimental data on the growth rate distribution for polycrystalline and epitaxial GaN layers are explained. It is shown that, if the diameter of the reactor is not large enough, the growth of the deposit on the walls makes the GaN growth rate distribution over the substrate more nonuniform due to the parasitic diffusion of reagents from the gas phase to the reactor walls.

Impurity centers of rare-earth ions (Eu, Sm, Er) in GaN wurtzite crystals

Gallium nitride (GaN) was doped with Eu, Sm, and Er impurities using the diffusion method. The behavior of rare-earth impurities (the formation of donor or acceptor levels in the GaN band gap) correlates with the total concentration of defects, which is determined from optical measurements, and with the position of the Fermi level in starting and doped crystals. The intensity of emission lines, which are characteristic of the intracenter f-f transition of rare-earth ions, is controlled by the total defect concentration in the starting semiconductor matrix.

Bulk large-area GaN layers

Mirror-smooth, transparent bulk GaN layers with an area of 2×3 cm2 and a thickness of up to 1 mm were grown by hydrochloride vapor-phase epitaxy. Cracking of the material was eliminated by using a two-stage growth process; separation from a substrate was provided by a low-temperature buffer layer of preset thickness. For the best samples, FWHM of the X-ray rocking curve was ωθ=3.5′ and the dislocation density amounted to 107–108 cm−2.