Miroslaw Wroblewski

Luminescence and reflectivity in the exciton region of homoepitaxial GaN layers grown on GaN substrates

Abstract In this work we report results of photoluminescence (PL) and reflectivity measurements in the exciton region of GaN homoepitaxial layers grown by metalorganic chemical vapour deposition on GaN substrates. At low temperature (4.2K), very narrow (FWHM = 1.0meV) PL lines related to excitons bound to neutral acceptor (3.4666eV) and neutral donor (3.4719eV) were observed. The energies of free excitons from reflectivity and PL measurements were found to be: E A = 3.4780eV, E B = 3.4835eV and E C = 3.502eV.

Exciton region reflectance of homoepitaxial GaN layers

Reflection measurements in the exciton region of GaN homoepitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) on GaN single crystals are reported. At low temperature (4.2 K) three free exciton lines have been found with energies; EA=3.4776 eV, EB=3.4827 eV, and EC=3.502 eV. The spin‐orbit parameter Δso=19.7±1.5 meV and the crystal field parameter Δcr=9.3±0.3 meV have been obtained. From temperature dependence of exciton spectra the energy gap dependence has been found: E(T)=E(0)−λ/[exp(β/T)−1] (λ=0.121 eV, β=316 K).

Thermal properties of indium nitride

Abstract Indium nitride single crystals, grown by the nitrogen microwave plasma method have been used in the determination of thermal properties of InN. Specific heat of InN was measured in the temperature interval between 150 and 300 K. InN Debye temperature and Gruneisen parameter calculated from these data are: Θ = 660 K and γ = 0.77. Thermal conductivity of InN has been measured by the laser-flash method. The InN thermal conductivity, obtained from measurement of InN ceramics, was 45 W/(m·K) This is much below 176 W/(m·K), the ideal lattice estimate based on phonon-phonon inelastic scattering, indicating a large contribution from point defects and grain boundaries to phonon scattering. InN vs. In + N 2 stability has been studied by ultra-high-pressure X-ray measurements: for nitrogen pressure p = 60 kbar, InN has been found to be stable up to T = 710 ± 10 °C. It has been also demonstrated that the decomposition of InN at temperatures below 660 °C is kinetically controlled.

High-pressure direct synthesis of aluminium nitride

We report the results of direct synthesis of aluminium nitride (AlN) under high nitrogen pressure up to 1 GPa and temperatures up to 2000 K. At pressure from 10 to 650 MPa we observe the combustion synthesis of AlN. As the result of the combustion process one can obtain the AlN sintered powder or AlN/Al metal matrix composites. For N2 pressure higher than 650 MPa the crystal growth of AlN from the solution of atomic nitrogen in aluminium is possible. Both needle-like and bulk AlN single crystals, up to 1 cm and 1 mm, respectively, have been obtained.