The Influence of Substrate Polarity on the Blue Emission from As-doped GaN Layers Grown by Molecular Beam Epitaxy
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The Influence of Substrate Polarity on the Blue Emission from As-doped GaN Layers Grown by Molecular Beam Epitaxy S.V. Novikov1,4, L.X. Zhao1, C.T. Foxon1, I. Harrison2, R.P. Campion1, C.R. Staddon1, S.W. Kang3, O. Kryliouk3 and T. Anderson3 1 School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK 2 School of Electrical and Electronic Engineering, University of Nottingham, Nottingham, NG7 2RD, UK 3 Chemical Engineering Department, University of Florida, Gainesville, FL 32611, USA 4 On leave from the Ioffe Physical-Technical Institute, St.Petersburg, Russia
ABSTRACT
The influence of sample orientation and polarity on the blue emission from As-doped GaN layers grown by plasma-assisted molecular beam epitaxy (PA-MBE) was investigated. Arsenic doped GaN layers were grown under identical PA-MBE conditions on several types of substrates including c-plane (0001) sapphire and polar and non-polar GaN templates grown by metalorganic vapour phase epitaxy (MOVPE). Non-polar GaN MOVPE templates were grown on aplane (11-20) sapphire and LiAlO2 (100). The orientation and polarity have a strong influence on the morphology and the optical properties of As-doped GaN layers. Strong blue emission from As-doped GaN was observed only in the case of (000-1) oriented N-polarity layers.
INTRODUCTION
The group III-nitrides have been actively investigated for the past decade, because of their importance in short-wavelength photonics and high temperature, high frequency electronic device structures. To date most of the group III-nitride based device structures were grown parallel to the (0001) c-axis of their wurtzite structure. The unique feature of wurtzite group IIInitrides in comparison with the standard III-V compounds is the existence of the strong polarity effects inside the crystal layer structure. For wurtzite group III-Nitrides, the built-in electric fields arising due to the piezo- and spontaneous polarizations are very significant [1 and references therein]. The existence of the built-in electric fields inside the group III-nitrides structures are an advantage for some device applications, but play a very negative role for the others. For example, high density two-dimensional electron gas can be achieved at GaN/AlGaN interfaces without any doping, which is now strongly explored for high mobility transistors [2]. A strong red shift of the photo-emission is observed in GaN/AlGaN and GaN/InGaN quantum well structures due to quantum confined Stark effect, which allows one to change and control the emission wave-length [3]. However, quantum confined Stark effect significantly reduces the optical emission intensity due to charge separation within the quantum wells [4] and the resulting red shift is undesirable in UV emitters. The strong piezoelectric and spontaneous polarization effects led to current instabilities and charge trapping in GaN/AlGaN double barrier resonant
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tunnelling structures [5]. All the above led to highly active studies of non-polar growth of group III-nitride laye
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