Abstract
We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 108 cm−2 at 750 °C) than that of the low temperature grown sample (1.1 × 109 cm−2 at 730 °C). A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.
Highlights
The GaN-based semiconductor materials have been attracting immense interest due to their importance in many applied fields such as ultraviolet light emitting diodes, high electron mobility transistors, optical data storage and related devices.[1,2,3,4,5,6] The minimization of the defects and obtaining the smooth film with high structural quality of GaN surface are the key factors for realization of high performance GaN based devices
We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001) substrates using plasma assisted molecular beam epitaxy
The GaN film grown at 750 ◦C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films
Summary
The GaN-based semiconductor materials have been attracting immense interest due to their importance in many applied fields such as ultraviolet light emitting diodes, high electron mobility transistors, optical data storage and related devices.[1,2,3,4,5,6] The minimization of the defects and obtaining the smooth film with high structural quality of GaN surface are the key factors for realization of high performance GaN based devices. In GaN epilayers, these defects are expected to affect the electronic structure and optical properties. There are a number of reports related to the studies of quantitative analysis of defects concentration.[7,8] the influence of growth temperature on defect concentration and the nature of the mid-gap defect states are less explored.[9,10]. Properties using PL which show that the PL spectra are sensitive to the changes in the mid-gap defect states. We report the effect of growth temperature on the defects in the epitaxial GaN films grown using plasma assisted molecular beam epitaxy (PAMBE). The PL spectra were measured for indentifying the nature of the defect states contributing to the band gap region. The variation of deep level defect distribution at different growth temperature and its correlation with defects density has been discussed
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