A diffraction analysis in the transmission electron microscope was carried out on InxGa1−xN layers grown on (0001) sapphire by metalorganic vapor phase epitaxy on top of thick GaN buffer layers. It is found that the ternary InxGa1−xN layers can be chemically ordered. The In and Ga atoms occupy, respectively, the two simple hexagonal sublattice sites related by the glide mirrors and helicoidal axes of the P63 mc symmetry group of the wurtzite GaN. The symmetry of the ordered ternary is subsequently lowered by the disappearance of these operations, and it is shown to agree with the P3ml space group.
The composition dependence of the Fermi-level pinning at the oxidized ͑0001͒ surfaces of n-type In x Ga 1−x N films ͑0 ഛ x ഛ 1͒ is investigated using x-ray photoemission spectroscopy. The surface Fermi-level position varies from high above the conduction band minimum ͑CBM͒ at InN surfaces to significantly below the CBM at GaN surfaces, with the transition from electron accumulation to depletion occurring at approximately x = 0.3. The results are consistent with the composition dependence of the band edges with respect to the charge neutrality level.
The integrated photoluminescence (PL) intensities of both ordered and disordered epilayers of InGaP grown on GaAs have been measured as a function of temperature. The highest PL efficiency occurs in the most disordered sample. We find that the PL intensities can drop from 2 to almost 4 orders of magnitude between 12 and 280 K. The samples show an Arrhenius behavior characterized by two activation energies. Below 100 K the activation energies lie in the region of 10–20 meV. Above 100 K the activation energy is approximately 50 meV except in the most disordered sample where it increases to 260 meV. We conclude that the low-temperature PL efficiency is most likely controlled by carrier thermalization from spatial fluctuations of the band edges followed by nonradiative recombination. At higher temperatures the PL efficiency is dominated by a nonradiative path whose characteristic activation energy and transition probability depend upon the degree of sublattice ordering.
The photoluminescence (PL) of an Ino 486ap 52P/(Ala 26ao 8 )p 52Inp 48P multiple-quantum-well sample composed of wells of various widths has been measured as a function of temperature. The presence of LO-phonon replicas at low temperature for the largest well indicates that the PL is dominated by localized excitons. This is further con6rmed by the variation of the PL peak energies and PL linewidths as the temperature is increased above 4.2 K. The temperature dependence of the integrated PL intensities shows that the major loss mechanism is thermal activation of electron-hole pairs out of the wells followed by nonradiative recombination in the barriers. The experimental data substantiate the proposition that the poor thermal characteristics of visible lasers is caused by carrier 1eakage out of relatively shallow wells.
In this paper growth of high quality InGaN films on (0001) sapphire substrates by atmospheric pressure organometallic vapour phase epitaxy in a vertical rotating disk reactor is investigated. The InGaN layers grown above 800 °C are transparent and show no In-droplets on the surface. The In-content varies between 56 and 9 % for growth temperatures between 700 and 850 °C. The DC X-ray rocking curve of InGaN typically shows a FWHM between 8 and 15 arcmin. Room temperature PL shows an intense band edge emission with a FWHM between 100 and 200 meV for an In-content of 9 and 56 %. The initial efforts on QW growth are discussed.
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