| Abstract Scope |
The band gap of In<SUB>x</SUB>Ga<SUB>(1-x)</SUB>N spans the entire visible spectrum. Progress in understanding the growth of this material has resulted in the production of blue LEDs and laser diodes. Increasing the composition of indium is necessary in order to produce devices that emit in the green spectral region, as well as for the development of high efficiency solar cells. Ammonia molecular beam epitaxy (MBE) provides an attractive method of growth due to ultra high vacuum (UHV) growth conditions as well as high purity group III elemental source materials. Growth on orientations of GaN other than the conventional c plane (0001) are also of interest due to the reduction (semipolar) or elimination (nonpolar) of spontaneous and piezoelectric polarization in the growth direction, as well as increased indium uptake on certain orientations. Presented in this work is a growth study of InGaN films on nonpolar m-plane GaN (10-10), semipolar GaN( (11-22) and (20-21)), as well as on conventional c-plane GaN templates on sapphire. Indium incorporation, impurity incorporation, and surface morphology were studied for the growth of InGaN on all 4 orientations. Growths were performed coloaded so that direct comparisons between orientations could be made as growth conditions were systematically varied. Growths consisted of 100nm of a high temperature GaN buffer (750˚C) followed by a low temperature (560-630˚C) InGaN growth (50-200nm) , and finally a thin (3nm) GaN cap to protect the films. Various substrate temperatures, growth rates, and thicknesses were examined to investigate the effect of each on the properties of the films. Indium composition was analyzed using high resolution x-ray diffraction measurements (HRXRD), while surface morphology was characterized with atomic force microscopy (AFM) images. Secondary ion mass spectrometry (SIMS) was performed to determine impurity concentration levels. It was observed that the (20-21) orientation had the greatest propensity for indium incorporation into the films, whereas (11-22) had the least for identical growth conditions. It was also observed that indium incorporation was strongly affected by substrate temperature during growth, as higher temperatures resulted in less indium for all orientations. For instance, the indium composition on (20-21) decreased from 13.9% to 6.4% when the growth temperature was increased from 575˚C to 630˚C. Finally SIMS analysis indicates higher impurity (O, C, H) incorporation for non-basal plane than for c-plane similar to MOCVD growth of GaN. |