Abstract
Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500–750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-300 nm was obtained for the film grown at 720 °C. The micro-Raman spectroscopy studies also exhibited the high-quality wurtzite nature of GaN film grown on sapphire at 720 °C. The SIMS measurements revealed a non-traceable amount of background oxygen impurity in the grown GaN films. The results show that the growth temperature strongly influences the surface morphology and crystalline quality of the epitaxial GaN films on sapphire grown by LMBE.
Highlights
Group III-nitride compounds have attracted much attention for their emerging applications in optoelectronic devices such as light-emitting diode (LED), laser diodes (LD) and ultra-violet detectors, due to their direct band gap semiconducting nature and good thermal conductivity.1–3 The surface morphology and crystalline quality of GaN templates are the key factors for the realization of high performance GaN based devices
The results show that the growth temperature strongly influences the surface morphology and crystalline quality of the epitaxial GaN films on sapphire grown by laser molecular beam epitaxy (LMBE)
We report on the growth of high crystalline quality GaN films on pre-nitridated sapphire (0001) substrates by employing a hydride vapor phase epitaxy (HVPE) grown high pure GaN bulk target in an ultrahigh vacuum (UHV) LMBE system and discuss the effect of growth temperature on the structural properties of the grown GaN layers
Summary
Group III-nitride compounds have attracted much attention for their emerging applications in optoelectronic devices such as light-emitting diode (LED), laser diodes (LD) and ultra-violet detectors, due to their direct band gap semiconducting nature and good thermal conductivity. The surface morphology and crystalline quality of GaN templates are the key factors for the realization of high performance GaN based devices. GaN is heteroepitaxially grown on different substrates like SiC, Si [111],6,7 sapphire (0001), etc.13–15 Among these substrates, sapphire is commonly used for fabricating GaN based LED and LD devices due to its low cost, superior material quality and availability in large-sized wafers. For most of the device applications, a sharp or abrupt interface at the substrate-overlayer is essential In this respect, a low temperature growth will minimize the formation of thick interfacial compounds or alloys. We report on the growth of high crystalline quality GaN films on pre-nitridated sapphire (0001) substrates by employing a HVPE grown high pure GaN bulk target in an ultrahigh vacuum (UHV) LMBE system and discuss the effect of growth temperature on the structural properties of the grown GaN layers.
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