Tunable and abrupt thermal quenching of photoluminescence by increasing temperature has been observed for the blue band in high-resistivity Zn-doped GaN. The photoluminescence intensity dropped by several orders of magnitude within a few Kelvins, and the temperature at which that drop occurred could be tuned by changing the incident light intensity. Modeling the system with rate equations for competing electron-hole recombination flows through three defect species, one of which is a nonradiative deep donor, gives results consistent with these observations.

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We comprehensively examine the importance of phonons on the optical properties of GaN. Using Raman and photoluminescence (PL) spectroscopies, the energies and linewidths of optic phonons, excitons, and discrete phonon sidebands (PSBs) are studied between 20 and 325 K. The temperature dependence of the A1 (LO) phonon energy and linewidth are described by a combined two- and three-phonon decay process. The narrow E22 phonon decays by the three-phonon emission process. Three band-edge excitons are observed in PL with linewidths between 2.8 and 5.3 meV at temperature 22 K. The energy gap shrinkage and exciton linewidths are completely interpreted based on electron-phonon interactions. The shift, broadening, and asymmetry of the PSBs are explained by incorporating the decay mechanism of A1 (LO) phonon and the exciton broadening from electron-phonon interactions.

Time-resolved free-carrier absorption and transient grating techniques were applied to determine carrier lifetimes and diffusion coefficients in a set of hydride vapor phase epitaxy GaN layers of various thickness (from 10 to 145 μm). A linear increase in nonradiative carrier lifetime in 80–800 K range found to be in a correlation with decrease of the bipolar carrier diffusion coefficient. This correlation confirmed that recombination rate is governed by carrier diffusive flow to the grain boundaries of columnar defects. A model of diffusion-governed nonradiative lifetime was proposed for fitting the measured lifetime values in the layers of different thickness as well as lifetime dependence on temperature or threading dislocation density.

In this paper we report 3‐7 μm thick p‐GaN growth by hydride vapor phase epitaxy (HVPE) on sapphire substrates. Mg impurity was used for doping. As‐grown GaN layers had p‐type conductivity with concentration NA‐ND up to 3×1019 cm–3. Mg atom concentration was varied from 1017 to 1020 cm–3. Hydrogen concentration was about 10 times less than that for Mg, which may explain effective p‐type doping for as‐grown GaN layers. Micro‐cathodoluminescence revealed a columnar‐like structure of the GaN layers with a non‐uniform distribution of material regions having dominant 362 nm or 430 nm luminescence. Use of these thick p‐GaN layers to grow InGaN‐based blue and green LEDs by the HVPE is demonstrated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)