Yu. V. Zhilyaev

Phonon spectrum of wurtzite GaN and AlN Experiment and theory

We present the results of a detailed study of the first and second-order Raman scattering in wurtzite GaN and AIN at room and liquid helium temperatures. A complete group-theory analysis of phonon symmetry and optical selection rules permitted us to assign the observed features in the second-order Raman spectra to combinations of phonons at the Γ, K. and M points of the Brillouin zone. The joint treatment of these results with lattice dynamical calculations based on phenomenological interatomic potential model allowed us to obtain the reliable data on phonon dispersion curves in bulk GaN and AIN.

Raman spectroscopy of GaN nucleation and free-standing layers grown by hydride vapor phase epitaxy on oxidized silicon

GaN nucleation layers (NL-GaN) and GaN free-standing (FS-GaN) layers are studied using Raman spectroscopy and atomic force microscopy. The layers are deposited onto oxidized silicon substrates by hydride vapor phase epitaxy at 520 °C (NL layers) and 970 °C (FS layers). The effect of high-temperature annealing (1010 °C) on the properties of FS-GaN layers is investigated. The average height of the islands in the NL-GaN layers is found to increase from 15 to 400 nm when the growth time is increased from 10 to 200 min. The average growth rate of NLs is found to be very low, namely, ≈1×10−2 nm/s. E2 (566 cm−1) and A1 (longitudinal optical) (730 cm−1) peaks are observed on NL-GaN layers when the average size of the islands increases to 400 nm, scattering by E2 (567.3 cm−1) and E1 [transverse optical (TO)] (558.3 cm−1) modes is detected on FS-GaN layers. High-temperature annealing of the FS-GaN layers results in an increase of the intensity of E2 and E1(TO) peaks detected from the front side whereas no effect is...

Sulfide passivation of III-V semiconductor surfaces: role of the sulfur ionic charge and of the reaction potential of the solution

A model is proposed for describing the effect of a solution on the electronic properties of sulfided surfaces of III-V semiconductors which treats the adsorption of sulfur in terms of a Lewis oxide-base interaction. According to this model, the density of states on a sulfided surface, which pin the Fermi level, decreases as the global hardness of the electron shell of the adsorbed sulfide ions is increased. The Thomas-Fermi-Dirac method is used to calculate the global hardness of sulfide ions with different charges as a function of the dielectric constant of the medium. It is shown that the hardness of a sulfur ion is greater when its charge is lower and the dielectric constant of the solvent is lower.

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.

The dislocation origin and model of excess tunnel current in GaP p-n structures

An excess tunnel current in GaP epitaxial nondegenerate p-n junctions on GaP and Si substrates was studied. An important experimental result is that the slope of exponential current-voltage (I–V) characteristic (in lnI–V coordinates) is independent of the width of the space-charge region, i.e., on n-and p-region doping levels. This fact is unexplained by existing models. A dislocation shunt model based on multihop tunneling through a dislocation line, which may be considered as a chain of parabolic potential barriers, is proposed. The density of dislocations predicted by this model is in agreement with the transmission electron microscopy (TEM) observations.

Determination of the Free Carrier Concentration in Ultra-Pure GaAs Epilayers by a Photoreflectance Technique

A new method for the diagnostics of high-quality n-GaAs epilayers grown by vapor phase epitaxy in an open chloride system has been developed and implemented. As the free carrier concentration in the material decreases from 1015 to 1011 cm−3 and the quality of epilayers increases, the photoreflectance spectra of GaAs exhibit a change from the traditional Franz-Keldysh (FK) oscillations (enhanced by the exciton effects) to a weak oscillatory structure observed in the region of exciton transition energies. It is shown that the periods of this structure are close to that of the FK oscillations.

Tunnel excess current in nondegenerate barrier (p-n and m-s) silicon-containing III–V structures

Data are scaled from a study of the forward current in three types of barrier structure: p-n homostructures p-n-GaP/n-Si, p-n-GaAs-n-GaP/n-Si, and p-n-GaAs-n-GaAs/n-Si; heterostructures n-GaP/p-Si, p-GaP/n-Si, n-GaAsP/p-Si, and n-GaAs/p-Si; and Au-n-GaP/ n-Si surface-barrier structures. Epitaxial layers of GaP and GaAs were created on Si-substrates by gaseous phase epitaxy in a chloride system. Temperature measurements show that the forward current has a tunnel character, although the width of the space charge region greatly exceeds the tunneling length. A model is proposed for nonuniform tunneling along dislocations that intersect the space charge region. This type of tunneling is taken into account by introducing a phenomenological “dilution” factor for the barrier. The model makes it possible to calculate the dislocation density in device structures from the current-voltage characteristic.

Aluminum nitride on silicon: Role of silicon carbide interlayer and chloride vapor-phase epitaxy technology

A new approach to the deposition of aluminum nitride (AlN) layers with thicknesses ranging within ∼0.1–10 μm on silicon single crystal substrates by hydride-chloride vapor-phase epitaxy (HVPE) has been developed and implemented, which involves the formation of thin (∼100-nm-thick) intermediate silicon carbide (3C-SiC) interlayers. It is established that wavy convex bands with a height of about 40 nm are present on the surface of as-grown AlN layers, which are situated at the boundaries of blocks in the layer structure. It is suggested that the formation of these wavy structures is related to morphological instability that develops due to accelerated growth of AlN at the block boundaries. Experiments show that, at low deposition rates, AlN layers grow according to a layer (quasi-two-dimensional) mechanism, which allows AlN layers characterized by half-widths (FWHM) of the X-ray rocking curves of (0002) reflections about ωθ = 2100 arc sec to be obtained.

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.