Calculational analysis of different scattering mechanisms of two-dimensional electron gas in AlGaN/(AlN)/GaN and InAlN/(AlN)/GaN high-electron mobility transistors was carried out. It was found that ...the mobility of AlGaN-based structures at room temperature is mainly limited by inherent scattering mechanisms (namely, optical and acoustic phonon scattering), while the mobility in our InAlN-based structures is limited by the interface roughness scattering. The low-temperature mobility is found to be limited by the interface roughness scattering for both AlGaN- and InAlN-based structures.
The results of experimental and theoretical studies of phonon modes in short-period (GaN)m(AlN)n superlattices (SLs) grown by MOVPE and PA MBE on the (0001) Al2O3 substrate are reported. Using a ...comprehensive group-theoretical analysis, the genesis of the SL vibrational modes from the modes of bulk AlN and GaN crystals has been established, which is important for interpreting the SL Raman spectrum. In the framework of Density Functional Theory, the lattice dynamics and the structural properties of (GaN)m(AlN)n SLs (m+n⩽12) were studied. An analysis of the eigenvectors of the phonon modes made it possible to reveal their microscopic nature. We established that the E(TO) modes are localized in the layers constituting the SL. It is shown that the localized nature of this mode is kept even in the SLs with the thinnest layers (m+n=4). In turn, the A1(TO) mode demonstrates a delocalized nature and reflects the averaged characteristics of the SL as a whole. A combined analysis of the ab initio calculations and Raman data was performed. Thus, the above studies open new possibilities for analyzing the structural properties of GaN/AlN SLs by Raman and IR spectroscopy.
Optical and structural properties of thick InGaN layers grown by MOCVD and MBE were studied by photoluminescence, optical transmission and Raman spectroscopies and X-ray diffraction analysis. Optical ...bandgap, Urbach energy, and full widths at half maximum (FWHM) of photoluminescence and Raman spectra depending on the InGaN alloy composition were determined experimentally. Minimal theoretical linewidth of photoluminescence spectra resulted from random distribution of In and Ga atoms in cation sublattice was calculated.
Simulation analysis of III-N two-dimensional electron gas-based structures that could be used for stable monolithically integrated enhancement/depletion-mode circuits was carried out. Three different ...designs were proposed and analysed, including a novel p-GaN/AlN-GaN SPSL/GaN, which is expected to have lower ON-state resistance and higher transconductance than conventional normally-off GaN-based transistors.
Two buffer structures based on Al
x
Ga
1 –
x
N solutions with silicon doping and without it have been studied by transmission electron microscopy. The structures have been grown on silicon substrates ...with the (111) orientation by metalorganic vapor-phase epitaxy with consistently decreasing Al content. A significant threading dislocation density reduction in the region of intermediate layers has been found at a change in the Al content from 32 to 23%. Phase decay and the phenomenon of compositional self-modulation in the Al
x
Ga
1 –
x
N layers in the direction of growth have been detected at an Al content equal to 32, 23, 12, and 4%. A model of the structure of layers in the region of composition modulation has been proposed.
InAlN/AlN/GaN semiconductor heterostructures with a barrier thickness of 5–13 nm have been grown by metalorganic vapor phase epitaxy (MOVPE) on sapphire and SiC substrates. Optimization of GaN buffer ...and InAlN layers allows fabricating structures with sheet conductivity values below 210 Ohm/sq. High electron mobility transistors (HEMTs) fabricated from such structures show drain current value exceeding 1.25 A/mm with maximum transconductance of 450 mS/mm. Use of thin in situ Si
3
N
4
capping allows to fabricate and compare HEMT and MIS-HEMTs.
AlN/GaN superlattices (SL) grown by metalorganic vapor-phase epitaxy with the period of SLs varied from 20 nm to 140 nm, and the thickness of the structures ranged from 0.7 to 1 µm were studied by ...polarized Raman spectroscopy technique. The peaks within a complex spectral feature of the symmetry A1(TO) observed at about 580 cm−1, were assigned to the interface and quasi-confined phonons. Frequency splitting between the peaks was found monotonously increasing along with the SL period. This dependence was explained using the dielectric continuum model. A method based on this finding was proposed for estimating the period SL using Raman spectroscopy. This method extends the traditional approach based on the studies of folded acoustic phonons in the short-period SLs.
Possibility of AlN growth by MOVPE in a planetary reactor with high growth rate was investigated. Growth was performed on (0001) Al2O3 substrates at the reactor pressure of 100mbar. It was shown that ...deposition rate is close to diffusion limit at low NH3 flows and reduces abruptly above a certain threshold value of NH3 due to gas-phase parasitic reactions. At constant V/III ratio of 1.5–2, AlN growth rate dependence on TMAl flow was linear and a maximum growth rate of 8.6μm/h was achieved. Process modeling allowed predicting and explaining the trends related to the onset of parasitic chemistry for various V/III ratios and other growth conditions. Surface morphology planarization was achieved by either (1) NH3 flow rate reduction or (2) TMGa injection after the layer with thickness of 75–300nm was grown. The second approach looks more fruitful resulting in atomically flat Al(Ga)N layers with a 2μm/h growth rate. For the conditions (high temperature, low NH3 and high H2 concentration) used Ga acts mostly as surfactant (Ga content in Al(Ga)N is about 3–5%).
► AlN MOVPE with growth rate exceeding 8μm/h in planetary reactor is demonstrated. ► Surface morphology is improved by (1) NH3 supply reduction or (2) TMGa injection. ► Atomically flat Al(Ga)N layers growth with 2μm/h growth rate is demonstrated.
In situ growth of an ultra-thin (up to 2.5 nm) Si3N4 film on the top of n-GaN is shown to reduce remarkably the height of the barrier formed by deposition of Ni-based Schottky contact. The reduction ...is interpreted in terms of polarization dipole induced at the Si3N4/n-GaN interface and Fermi level pinning at the Ni/Si3N4 interface. Detailed study of temperature-dependent current-voltage characteristics enables identification of the electron transport mechanism in such Schottky diodes under forward bias: thermal/field electron emission over the barrier formed in n-GaN followed by tunneling through the Si3N4 film. At reverse bias and room temperature, the charge transfer is likely controlled by Poole-Frenkel ionization of deep traps in n-GaN. Tunneling exponents at forward and reverse biases and the height of the Ni/Si3N4 Schottky barrier are evaluated experimentally and compared with theoretical predictions.
The work presents experimental data of Ga
+
focused ion beam etching of disc and ring patterns in Si
3
N
4
/GaN structure. The reasons for the difference in etching depth between the discs and the ...rings are described.
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