Abstract
In this study, we compared the device performance of GaInN-based green LEDs grown on c-plane sapphire substrates with a conventional low temperature GaN buffer layer to those with a sputtered-AlN buffer layer. The light output power and leakage current characteristics were significantly improved by just replacing the buffer layer with a sputtered-AlN layer. To understand the origin of the improvement in performance, the electrical and optical properties were compared by means of electro-reflectance spectroscopy, I–V curves, electroluminescence spectra, L–I curves, and internal quantum efficiencies. From the analysis of the results, we concluded that the improvement is mainly due to the mitigation of strain and reduction of the piezoelectric field in the multiple quantum wells active region.
Highlights
Technological progress in III-nitride based wide bandgap semiconductors has been greatly encouraged because of a continuous demand for energy saving, long lifetime, and environmentally friendly devices [1,2,3]
We reported that less strain in the u-GaN template layer can be achieved by replacing a conventional low temperature GaN buffer layer with a sputtered-AlN buffer layer on a c-plane sapphire substrate, where the crystalline quality of both samples was comparable [20]
Since the strain in the epitaxial layer after cooling down is greatly impacted by the strain of an adjacent layer during growth, one can infer that the strain and piezoelectric field in the MQWs active region is significantly influenced by the strain of the underlying layer [21,22,23]
Summary
Technological progress in III-nitride based wide bandgap semiconductors has been greatly encouraged because of a continuous demand for energy saving, long lifetime, and environmentally friendly devices [1,2,3]. III-nitride based semiconductors are typically grown on sapphire substrates by using metal-organic chemical vapor deposition (MOCVD) because homo-epitaxial substrates are still expensive due to a difficulty in mass production. The direct growth of a GaN film on a sapphire substrate leads to very poor crystal quality due to a large difference in the lattice constant and thermal expansion coefficients of the. Amano et al, who were the first to demonstrate that crystal quality and surface morphology can be remarkably improved by the introduction of a thin buffer layer [1,8]
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