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.

In high-purity GaN grown by hydride vapor phase epitaxy, the commonly observed yellow luminescence (YL) band gives way to a green luminescence (GL) band at high excitation intensity. We propose that the GL band with a maximum at 2.4 eV is caused by transitions of electrons from the conduction band to the 0/+ level of the isolated C N defect. The YL band, related to transitions via the −/0 level of the same defect, has a maximum at 2.1 eV and can be observed only for some high-purity samples. However, in less pure GaN samples, where no GL band is observed, another YL band with a maximum at 2.2 eV dominates the photoluminescence spectrum. The latter is attributed to the C N O N complex.

This paper reviews semi-polar GaN surfaces, of interest for light emitting devices, from both theoretical and experimental perspectives. Theoretical results on polarization charges at InGaN/GaN heterointerfaces and In incorporation into InGaN films are presented for polar (0001), semi-polar (1122) and nonpolar (1100) surfaces. Specific features of semi-polar InGaN/ GaN structures are emphasized which can be beneficial for improving optical and transport properties of quantum-wellbased light emitting devices. The analysis favours semi-polar surfaces such as the (1122) surface as growth plane for longwavelength light emitters. Therefore, the experimental sections emphasize progress towards long-wavelength LEDs and lasers by growth of InGaN/AlGaN/GaN(1122) heterostructures on large-area GaN(1122)/m-sapphire templates. The current status of such templates as grown by hydride vapour phase epitaxy is presented. The implementation of an epitaxial lateral overgrowth method on such templates to improve device performances is demonstrated.

Point defects in high-purity GaN layers grown by hydride vapor phase epitaxy are studied by steady-state and time-resolved photoluminescence (PL). The electron-capture coefficients for defects responsible for the dominant defect-related PL bands in this material are found. The capture coefficients for all the defects, except for the green luminescence (GL1) band, are independent of temperature. The electron-capture coefficient for the GL1 band significantly changes with temperature because the GL1 band is caused by an internal transition in the related defect, involving an excited state acting as a giant trap for electrons. By using the determined electron-capture coefficients, the concentration of free electrons can be found at different temperatures by a contactless method. A new classification system is suggested for defect-related PL bands in undoped GaN.

The yellow luminescence band was studied in undoped and Si-doped GaN samples by steady-state and time-resolved photoluminescence. At low temperature (18 K), the zerophonon line (ZPL) for the yellow band is observed at 2.57 eV and attributed to electron transitions from a shallow donor to a deep-level defect. At higher temperatures, the ZPL at 2.59 eV emerges, which is attributed to electron transitions from the conduction band to the same defect. In addition to the ZPL, a set of phonon replicas is observed, which is caused by the emission of phonons with energies of 39.5 meV and 91.5 meV. The defect is called the YL1 center. The possible identity of the YL1 center is discussed. The results indicate that the same defect is responsible for the strong YL1 band in undoped and Si-doped GaN samples.