Abstract
A high Al-content (y > 0.4) multi-quantum-well (MQW) structure with a quaternary InxAlyGa(1-x-y)N active layer was synthesized using plasma-assisted molecular beam epitaxy. The MQW structure exhibits strong carrier confinement and room temperature ultraviolet-B (UVB) photoluminescence an order of magnitude stronger than that of a reference InxAlyGa(1-x-y)N thin film with comparable composition and thickness. The samples were characterized using spectroscopic ellipsometry, atomic force microscopy, and high-resolution X-ray diffraction. Numerical simulations suggest that the UVB emission efficiency is limited by dislocation-related non-radiative recombination centers in the MQW and at the MQW - buffer interface. Emission efficiency can be significantly improved by reducing the dislocation density from 109cm−2 to 107cm−2 and by optimizing the width and depth of the quantum wells.
Highlights
InAlGaN has emerged as a promising alternative because it is known to be less sensitive to dislocations than AlGaN is.[6,7,8,9,10,11]
Molecular beam epitaxy (MBE) has been used recently to demonstrate p-type AlxGa(1-x)N with a hole concentration up to 2 × 1019cm−3 for x = 0.27.12 there are no reports on the molecular beam epitaxy (MBE) growth of high Al-content (y > 0.4), low In content (x
Well and barrier compositions can be maintained throughout the MQW; due to differing strain and strain relaxation in the multilayered structure, absorption and emission wavelengths are expected to shift compared to the thin films of similar compositions
Summary
(Received 13 August 2016; accepted 22 December 2016; published online 7 March 2017) The relaxation of the MQW is similar to that of the Al0.5Ga0.5N reference sample, with slightly higher Al and In content in the QW barrier and well layers, respectively, than in the corresponding thin films.
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