Gallium nitride (GaN) is one of important functional materials for optoelectronics and electronics. GaN exists both in equilibrium wurtzite and metastable zinc-blende structural phases. The zinc-blende GaN has superior electronic and optical properties over wurtzite one. In this report, GaN nanodots can be fabricated by Ga metal droplets in ultra-high vacuum and then nitridation by nitrogen plasma. The size, shape, density, and crystal structure of GaN nanodots can be characterized by transmission electron microscopy. The growth parameters, such as pre-nitridation treatment on Si surface, substrate temperature, and plasma nitridation time, affect the crystal structure of GaN nanodots. Higher thermal energy could provide the driving force for the phase transformation of GaN nanodots from zinc-blende to wurtzite structures. Metastable zinc-blende GaN nanodots can be synthesized by the surface modification of Si (111) by nitrogen plasma, i.e., the pre-nitridation treatment is done at a lower growth temperature. This is because the pre-nitridation process can provide a nitrogen-terminal surface for the following Ga droplet formation and a nitrogen-rich condition for the formation of GaN nanodots during droplet epitaxy. The pre-nitridation of Si substrates, the formation of a thin SiN x layer, could inhibit the phase transformation of GaN nanodots from zinc-blende to wurtzite phases. The pre-nitridation treatment also affects the dot size, density, and surface roughness of samples.
In this paper we present the first report of the study of the characteristics of In0.53Gs0.47As/InP modulation-doped heterostructures grown by liquid-phase epitaxy. Electrical properties were studied by Hall and Shubnikov-de Haas Measurements. A series of doping levels in the InP layer was used to investigate the dependences of mobility and sub-band configuration on sheet carrier density. Mobility enhancements were observed at low temperatures according to Hall measurements. Enhanced electron mobilities were as high as 62000, 60200 and 7410 cm2/Vs at 10, 77 and 300 K, respectively. These are comparable to those obtained by other epitaxial techniques, which indicates that liquid-phase epitaxy is capable of growing high-quality In0.53Ga0.47As/InP heterojunctions.
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