Native cation vacancies in Si-doped AlGaN studied by monoenergetic positron beams

Abstract

Native defects in Si-doped AlGaN grown by metalorganic vapor phase epitaxy were probed by monoenergetic positron beams. Doppler broadening spectra of the annihilation radiation and positron lifetimes were measured, and these were compared with results obtained using first-principles calculation. For Si-doped AlxGa1−xN (4 × 1017 Si/cm3), the vacancy-type defects were introduced at above x = 0.54, and this was attributed to the transition of the growth mode to the Stranski-Krastanov mechanism from the Frank-van der Merwe mechanism. For Si-doped Al0.6Ga0.4N, the vacancy concentration increased with increasing Si concentration, and the major defect species was identified as Al vacancies. A clear correlation between the suppression of cathodoluminescence and the defect concentration was obtained, suggesting the cation vacancies act as nonradiative centers in AlGaN.

Inhomogeneous distribution of defect-related emission in Si-doped AlGaN epitaxial layers with different Al content and Si concentration

“…2) at room temperature. It is well known that Si doping into an Al x Ga 1-x N epitaxial layer drastically changes its structural, electrical, and optical properties through phenomena, such as dislocation inclination, 3 nano-mask effect, 4,5 changes in electric conductivity, 6,7 cathodoluminescence (CL) intensity enhancement, 8 introduction of point defects, 9 and changes in optical polarization along with variation in strain state. 10,11 For the fabrication of high-efficiency devices, it is important to investigate in detail the effects of Si doping on AlGaN ternary alloys.…”

Si concentration dependence of structural inhomogeneities in Si-doped AlxGa1−xN/AlyGa1−yN multiple quantum well structures (x = 0.6) and its relationship with internal quantum efficiency

“…18 However, the changes in energy fluctuation with the Si concentration were very small in the AlGaN MQWs, and it is difficult to explain the change in the IQE by the interface quality and composition fluctuation. Thus, the variation of the defect complex concentration with Si concentration reported by Uedono et al 16 explains the change in the IQE of AlGaN MQWs with Si concentration in the well layers. The defect complexes composed of cation vacancies and impurities may contribute directly to the IQE of AlGaN MQWs.…”

“…The emission energy distribution arising from the inhomogeneity of the relative Al content and the well layer thickness was estimated by monochromatic CL measurements; however, the distribution was not affected by the Si concentration. Therefore, the variation of the defect complex concentration with Si concentration reported by Uedono et al 16 is mainly reflected in the IQE of Si-doped AlGaN MQWs. Defect complexes composed of cation vacancies and impurities, rather than dislocations and interfacial quality, are the major contributors to the IQE of the Si-doped AlGaN MQWs with different Si concentrations.…”

“…In an alternative approach, electron-beam-pumped UV light sources have been demonstrated that use hundreds of Al-rich AlGaN multiple quantum wells (MQWs) as targets and do not require ptype AlGaN. 7,8 Si doping of an Al x Ga 1Àx N epitaxial layer changes its structural, electrical, and optical properties, including strain state, 9,10 surface morphology, 10-13 dislocation inclination, 2,13 electrical conduction, 14 luminescence intensity, 15 point defects, 16 and optical polarization. 17 The relationship between these changes is complicated, and the effects of Si doping in III-nitrides are not fully understood.…”

Enhanced damage buildup in C+-implanted GaN film studied by a monoenergetic positron beam

“…In the previous studies, ion-bombardment-produced defects have been studied in and also other group-III nitrides such as InGaN, AlGaN, and AlN. 12,13 Carbon is a common amphoteric impurity in GaN which affects their technologically important electrical and optical properties. It is reported to contribute p-type conductivity 14 and is expected to be also related to the yellow emission.…”