Growth and Characterization of InGaN/GaN Multiple Quantum Wells on Ga-Polarity GaN by Plasma-Assisted Molecular Beam Epitaxy

Abstract

InGaN/GaN multiple quantum-wells (MQWs) on Ga-polarity GaN by plasma-assisted molecularbeam epitaxy were grown and characterized. In-situ reflection high-energy-electron diffraction observations and high-resolution X-ray diffraction results indicated that a flat interface and a good periodicity of the InGaN/GaN heterostructures were achieved. Photoluminescence measurements revealed the superior optical properties of InGaN/GaN MQWs emitting from ultraviolet (388 nm) to green-yellow (528 nm) range with the In composition varying from 0.04 to 0.30. Stimulated-emission features by optical pumping were demonstrated, which implied the high-quality of the MBE-grown InGaN/GaN MQWs.Introduction GaN and its related alloys (AlGaN, InGaN) have attracted a great deal of attention due to its potential applications in optical and electronic devices [1][2][3][4]. At present, the InGaN-based heterostructures are mainly fabricated by the metalorganic chemical vapor deposition (MOCVD) technique. Although molecular-beam epitaxy (MBE) has many advantages over MOCVD, such as low temperature growth and p-type doping without post-annealing [5], there are only limited research works reported on the InGaN-based single and multiple quantum wells (MQWs) fabrication by the MBE technique [6,7]. We have pointed out that the quality of MBE-grown GaN films on c-face sapphire substrates can be greatly improved by controlling the lattice-polarity of the GaN films during the growth [8], to which Ga-polarity GaN films are preferred. It is well accepted that Ga-polarity GaN films are usually obtained by MOCVD growth, while the lattice orientation of MBE films grown on c-face sapphire substrates is known to be mainly N-polarity or a mixed one [9]. Recently, excellent electron mobility values of MBE-grown GaN films and AlGaN/GaN heterostructures applying the growth on the Ga-polarity mode have been reported [10][11][12]. We speculate that lattice-polarity control in MBE technique is a key point to approach the high-quality GaN films and try to extend this opinion to InGaN-based heterostructures.In this paper, we report the growth and characterizations of InGaN/GaN MQWs grown on a Ga-polarity GaN by rf-MBE. In-situ reflection high-energy-electron diffrac-