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Abstract
GaN/AlN quantum wells (QWs) with varied nominal thickness of 0.5-4 monolayers have been studied by time-resolved photoluminescence (PL) spectroscopy. The structures demonstrate an emission peak with the thickness-dependent wavelength in the range 225-320 nm. The observed temporal behavior of PL between 225 and 280 nm can be described as a superposition of fast and slow decaying components with characteristic decay time constants of the order of 0.1-0.7 ns and 7-30 ns, respectively. The fast PL component with the decay time smaller than 1 ns dominates in the thicker GaN insertions and tends to vanish in the thinnest ones, where the slow PL component becomes progressively longer. These observations imply formation in the GaN/AlN monolayer-thick layers of an inhomogeneous excitonic system involving both direct and indirect in space excitons.
Highlights
GaN/AlN quantum wells (QWs) have been recently considered as a promising active region of light-emitting devices operating in mid- and deep-ultraviolet regions [1, 2]
The samples were grown on c-sapphire by plasma-assisted molecular beam epitaxy (PA MBE) using a Compact 21T Riber setup
Metal-rich conditions and a maximum substrate temperature TS=780°C were used for the growth of a 65 nm thick AlN nucleation layer by migration enhanced epitaxy and a 1.5-μm-thick AlN buffer layer by metal-modulated epitaxy
Summary
GaN/AlN (or GaN/AlGaN) quantum wells (QWs) have been recently considered as a promising active region of light-emitting devices operating in mid- and deep-ultraviolet regions [1, 2]. More conventional AlGaN-based QWs with the thickness of several nanometers, grown on c-sapphire, usually suffer from intrinsic electrostatic fields, which reduce an electron-hole overlapping as a result of the quantumconfined Stark effect (QCSE).
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