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A series of sharp intense peaks was observed in the low-temperature photoluminescence spectrum of unintentionally doped GaN in the photon energy range between 3.0 and 3.46 eV. We attributed the majority of these peaks to excitons bound to unidentified structural and surface defects. Most of the structural- and surface-related peaks (at 3.21, 3.32, 3.34, 3.35, 3.38, and 3.42 eV) were observed in Ga polar films. In N polar GaN, we often observed the 3.45 eV peak attributed to excitons bound to the inversion domain interfaces. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have shown that external hydrostatic pressure leads to the creation of structural defects, mainly in the vicinity of the II-VI/GaAs interface in the CdTe/Cd[sub 1-x]Mg[sub x]Te heterostructures grown by the molecular beam epitaxy method on GaAs substrates. These defects propagating across the epilayer cause permanent damage to the samples from the point of view of their electrical properties. In contrast, photoluminescence spectra are only weakly influenced by pressure. Our results shed light on the degradation process observed even without pressure in II-VI-based heterostructures. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We studied optical manifestation of structural defects in unintentionally doped GaN. A series of sharp peaks (labeled as Yi with i=1,2,…,11) was observed in the low-temperature photoluminescence spectrum in the photon energy range between 2.6 and 3.46 eV. We attribute the majority of these peaks to excitons bound to yet unidentified structural defects. A preliminary transmission electron microscopy study in one of the samples exhibiting strong Yi lines revealed numerous inclusions, presumably inversion domains, which may be responsible for at least some of the Yi lines. [Copyright &y& Elsevier]

Results of a post-growth rapid thermal annealing (RTA) on GaAs proximity-capped structures with high density (∼1011 cm−2) of self-assembled InAs/GaAs quantum dots (QDs) are presented. Features due to the QDs, bi-dimensional platelets (2DP) and InAs wetting layer (WL) were identified in photoluminescence (PL) spectrum of the as-grown sample. It is shown, using transmission electron microscopy, that RTA at temperature up to 700 °C (for 30 s) results in an increase of QDs lateral sizes. After RTA at 800 °C or higher temperatures, no QDs can be distinguished and substantial thickening of the WL can be seen. The main PL peak blueshifts as a result of RTA in all investigated temperature ranges, which is accompanied by a quenching of the 2DP and WL PL. It is proposed that the main PL peak, which is due to the QDs in the as-grown sample, results from optical recombination in the modified WL in the samples, after RTA at 800 °C and higher temperatures. Laterally-enhanced Ga/In interdiffusion induced by strain is proposed to explain a relatively fast dissolution of QDs. [Copyright &y& Elsevier]

A free-standing GaN template grown by hydride vapor phase epitaxy has been characterized by transmission electron microscopy (TEM). The TEM investigation was augmented by x-ray diffraction, defect delineation etching process followed by imaging with atomic force microscopy and variable temperature photoluminescence. The density of dislocations near the N face was determined to be, in order, 3±1x10[sup 7], 4±1x10[sup 7], and about 1x10[sup 7] cm[sup -2] by cross-sectional TEM, plan-view TEM, and a defect revealing etch, respectively. The same methods on the Ga face revealed the defect concentration to be, in order, less than 1x10[sup 7] cm[sup -2] by plan-view TEM, less than 5x10[sup 6] cm[sup -2] by cross-sectional TEM, and 5x10[sup 5] cm[sup -2] by defect revealing hot H[sub 3]PO[sub 4] acid, respectively. The full width at half maximum of the symmetric (0002) x-ray diffraction peak was 69 and 160 arc sec for the Ga and N faces, respectively. That for the asymmetric (101_4) peak was 103 and 140 arc sec for Ga and N faces, respectively. The donor bound exciton linewidth was about 1 meV each at 10 K, and a green band centered at about 2.44 eV was observed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: A GaN layer was grown by molecular beam epitaxy on a freestanding GaN template prepared by hydride vapor-phase epitaxy. Two characteristic areas have been found in the overgrown layer: a region nearly free from dislocations and a region with the density of the edge dislocations of ∼5×109 cm−2, as determined by transmission electron microscopy. Low-temperature photoluminescence spectrum from the former contained only well-known exciton lines, whereas the spectrum of the defective area contained additional lines at 3.21 and 3.35eV. These lines are attributed to unidentified point defects trapped by the edge threading dislocations. [Copyright &y& Elsevier]