Highly c-axis oriented growth of GaN film on sapphire (0001) by laser molecular beam epitaxy using HVPE grown GaN bulk target

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

Laser Molecular Beam Epitaxy Growth of GaN Layer on Sapphire (0001) Under Various Process Conditions

“…Further increase in growth temperature above 720 C dramatically reduced the growth rate due to desorption of GaN or Ga from the growing surface. 9 Fig . 5 shows a typical room temperature PL spectrum of 240 nm thin LMBE grown GaN film on nitridated sapphire.…”

“…The secondary ion mass spectroscopy measurements revealed a non-traceable level of oxygen background impurity in the GaN film mainly due to use of high pure HVPE grown GaN bulk target and UHV environment. 9 …”

“…11 The HR-XRD and micro-Raman analysis shows that our GaN film grown on sapphire using LMBE technique has hexagonal phase. 9 The band edge emission is different for GaN films grown by different growth techniques, kind of substrate, substrate temperature and buffer layers on substrates. For example, a band edge emission for MOCVD grown GaN sample is 3.51 eV whereas it is 3.42 eV for MBE grown samples.…”

“…The phi-scan XRD data also confirmed the hexagonal structure of GaN on sapphire with 30° rotation of GaN unit cell with respect to sapphire. 9 The x-ray rocking curves of GaN films were measured for (0002) GaN plane. The FWHM of GaN (0002) peak decreases from 1582 arc sec to 102 arc sec with increase of growth temperature from 500 to 720 °C.…”

“…The details of sapphire cleaning and nitridation in laser MBE system has been discussed previously. 9 A high purity polycrystalline HVPE grown GaN target (99.9999%) was ablated using a KrF excimer laser (248-nm wavelength, 25 ns pulse) with an energy density of ~ 5 J/cm 2 at different repetition rates ( 5 Hz and 10 Hz). Generally, laser ablated GaN plume consists the energetic species such as GaN, nitrogen deficient GaN 1-x and Ga and the grown GaN samples have deficiency in nitrogen.…”