Optical Properties of Nearly Lattice-matched AlInN/GaN Single Quantum Wells with Varying Well-widths
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0955-I12-06
Optical Properties of Nearly Lattice-matched AlInN/GaN Single Quantum Wells with Varying Well-widths Lay-Theng Tan1, Robert W Martin1, Ian M Watson2, and Kevin P O'Donnell1 1 Physics, University of Strathclyde, Glasgow, G4 0NG, United Kingdom 2 Institue of Photonics, University of Strathclyde, Glasgow, G4 0NW, United Kingdom
ABSTRACT Single GaN quantum wells in the nearly lattice-matched GaN/Al1-xInxN system have been studied using photoluminescence (PL) and PL excitation (PLE) spectroscopy. The structures were grown on free-standing GaN and sapphire substrates. Selectively excited PL is able to distinguish luminescence originating from the wells, barriers and underlying GaN buffer layers. The PL spectra show the quantum well transition energy decreases as the well-width increases. This manifestation of the quantum confined Stark effect (QCSE) results from intense built-in electric fields. Power dependent PL measurements provide information on the screening of the internal fields. PLE data provide an estimation of the band-gap of nearly lattice-matched Al1x InxN layer. INTRODUCTION Ternary III-nitride material Al1-xInxN opens up a range of useful applications as it covers an extremely large variation in energy-gap, ranging from 0.7 to 6.2 eV. Most importantly, it can be lattice-matched to GaN with an InN fraction of ~ 17 % [1-2]. Improvements in the quality of Al1-xInxN have led to the development of lattice-matched III-N dielectric Bragg mirrors [1] and insertion layers for in situ growth monitoring by reflectometry [2]. With the commercial availability of free-standing GaN (FS-GaN) substrates, Al1-xInxN can be deployed in strain free GaN-based devices with reduced defect densities. In this work, we describe the study of a set of near lattice-matched GaN/Al1-xInxN single quantum well (SQW) samples with various GaN well widths using photoluminescence (PL) and PL excitation (PLE) spectroscopy. EXPERIMENTAL DETAILS GaN/Al1-xInxN SQW samples were grown by metal organic chemical vapour deposition (MOCVD) in an Aixtron 200-series reactor. The samples consisted of an undoped GaN buffer, approximately 1.5 or 0.5 µm thick, followed by a near-lattice-matched Al1-xInxN barrier with a nominal thickness of 100 or 10 nm, then a GaN SQW and a 10 nm near-lattice-matched Al1xInxN cap. The structures were grown on c-plane sapphire and FS-GaN (0001) substrates. GaN wells, with thickness from 1.5 to 4 nm were grown at ~ 815 °C, the same growth temperature used for the Al1-xInxN layers. PL was excited using a 1000 W short arc xenon (Xe) lamp with a monochromator or the 244 nm line of a frequency-doubled cw Ar+ laser with spot size of 10 µm. The samples were maintained at ~ 17 K in a closed-cycle helium cryostat for the lamp excitation
and at room temperature for the laser excitation. PLE spectra were obtained by scanning the monochromator on the excitation side.
RESULTS AND DISCUSSION
1.5nm
LT PL Int (a.u.)
2.8
3.2
3.4
3.6
3.8
3.0
3.2
3.4
3.6
3.8
3.2
3.4
3.6
3.8
3nm
2.8 LT PL Int (a.u.)
3.0
F S- Ga
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