Photoluminescence intensity of GaN films with widely varying dislocation density
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investigated the impact of the presence of dislocations on room-temperature photoluminescence intensity in GaN films grown by molecular beam epitaxy. To determine both screw and edge dislocation densities, we employed x-ray diffraction in conjunction with a geometrical model, which relate the width of the respective reflections to the polar and azimuthal orientational spread. There is no direct dependence of the emission efficiency on the density of either type of dislocation in the samples under investigation. We conclude that dislocations are not the dominant nonradiative recombination centers for GaN grown by molecular beam epitaxy.
Dislocations often act as efficient nonradiative recombination centers in most III–V semiconductors, such as GaAs and InP. However, the role of dislocations for the quantum efficiency in GaN is still a controversial issue. Commercial high-brightness GaN-based light-emitting diodes (LEDs) with an overall dislocation density up to 1010 cm−2 seem to be unaffected by such extremely high defect densities.1 The output power of two LEDs, one grown on epitaxially laterally overgrown GaN with an average dislocation density of 7 × 106 cm−2 and one grown on sapphire with four orders of magnitude higher dislocation density, is virtually identical, indicating that dislocations do not govern nonradiative recombination in these structures.2 However, Hino et al.3 concluded that dislocations with a screw-component Burgers vector are predominant nonradiative centers in their Si-doped GaN layers but not edge dislocations. This conclusion is consistent with theoretical work which predicts that edge dislocations are electrically inactive, whereas full-core screw dislocations induce deep states in the gap.4 Contradictorily, in previous calculations,5 the same group pointed out that screw dislocations in GaN are energetically favored to exist in an open-core configuration which is electrically inactive in GaN. In contrast, Cherns et al.6 recently correlated cathodoluminescence maps and transmission electron micrographs of (In,Ga)N/GaN quantum wells and reported that edge dislocations quench the luminescence rather than screw and mixed dislocations. More recently, Shi et al.7 suggested that both edge and screw dislocations act as dominant nonradiative centers in GaN.
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Address all correspondence to this author. e-mail: [email protected]. J. Mater. Res., Vol. 18, No. 5, May 2003
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In this letter, we address this puzzling issue by investigating GaN layers with widely varying dislocation density by x-ray diffraction (XRD) and room-temperature photoluminescence (PL). To extract both the screw- and edge-dislocation densities from the x-ray measurements, we employ a geometrical model which relates the width of the respective reflections to the polar and azimuthal orientational spread. We found no apparent correlation between dislocation density and PL intensity, suggesting that neither screw nor edge dislocations are the dominant nonradiative centers in
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