Microstructure of non-polar GaN on LiGaO2 grown by plasma-assisted MBE
We have investigated the structure of non-polar GaN, both on the M - and A-plane, grown on LiGaO2 by plasma-assisted molecular beam epitaxy. The epitaxial relationship and the microstructure of the GaN films are investigated by transmission electron microscopy (TEM). The already reported epi-taxial relationship and for M -plane GaN is confirmed. The main defects are threading dislocations and stacking faults in both samples. For the M -plane sample, the density of threading dislocations is around 1 × 1011 cm-2 and the stacking fault density amounts to approximately 2 × 105 cm-1. In the A-plane sample, a threading dislocation density in the same order was found, while the stacking fault density is much lower than in the M -plane sample.
Surface morphology evolution of m-plane (11¯00) GaN during molecular beam epitaxy growth: Impact of Ga/N ratio, miscut direction, and growth temperature
We present a systematic study of morphology evolution of [11¯00] m-plane GaN grown by plasma-assisted molecular beam epitaxy on free-standing m-plane substrates with small miscut angles towards the –c [0001¯] and +c [0001] directions under various gallium to nitrogen (Ga/N) ratios at substrate temperatures T = 720 °C and T = 740 °C. The miscut direction, Ga/N ratio, and growth temperature are all shown to have a dramatic impact on morphology. The observed dependence on miscut direction supports the notion of strong anisotropy in the gallium adatom diffusion barrier and growth kinetics. We demonstrate that precise control of Ga/N ratio and substrate temperature yields atomically smooth morphology on substrates oriented towards +c [0001] as well as the more commonly studied –c [0001¯] miscut substrates.
Low temperature epitaxial growth of GaN films on LiGaO2 substrates
GaN films have been grown on LiGaO2 {001} substrates at low substrate temperatures by pulsed laser deposition and their structural properties have been investigated. It is found that the metal-face LiGaO2 substrates are thermally more stable than O-face LiGaO2. It is also found that growth of GaN films proceeds epitaxially, even at room temperature (RT), on metal-face LiGaO2, but polycrystalline GaN films are formed on O-face LiGaO2 at RT. Reduction in growth temperature lessens the interface reactions that have previously been regarded as the most serious problem with this substrate have been revealed by x-ray reflectivity measurements.