Shi-Jong Leem

Reduction in crystallographic tilting of lateral epitaxial overgrown GaN by removal of oxide mask

The lateral overgrowth of GaN was carried out by low-pressure metalorganic chemical vapor deposition. SiO2 mask was removed just before coalescence and a subsequent lateral overgrowth was carried out to complete the fabrication of a SiO2-removed lateral epitaxial overgrown (LEO) GaN layer. The crystallographic tilting of (0002) plane, that was apparent in our standard LEO GaN layers, was absent in SiO2-removed LEO layer and x-ray diffraction measurement indicated a superior crystallinity for the SiO2-removed LEO layer. These results are attributed to the elimination of the interface between oxide mask and laterally grown GaN layer. The reduced crystallographic tilting in SiO2-removed LEO GaN layer also enhanced the quality of the coalesced fronts, as determined from cathodoluminescence images.

Improvement of Structural Properties of GaN Pendeo‐Epitaxial Layers

The effects of growth parameters on growth behavior of Pendeo-epitaxial GaN layers in (1100) patterned GaN seed stripes on sapphire were systematically investigated to improve the structural properties of the overgrown layers. It was found that the ratio of lateral to vertical growth rate (y) is strongly affected by changes in growth temperature, reactor pressure, and V/III ratio, which have an effect on the distribution of crystallographic tilt among the wing regions. Also, the crystallographic anisotropy, which was determined from the results of (0002) X-ray diffraction rocking curves taken perpendicular and parallel to the seed stripe direction, can be improved with relatively high V/III ratio.

Structural properties of GaN grown by pendeo-epitaxy with In-doping

We have studied the effect of isoelectronic In-doping on the structural properties of GaN grown by pendeo-epitaxy. From an analysis of cross-sectional transmission electron microscopy (TEM) images, the threading dislocation originating from the (0001) facet of GaN seed layer, thereafter propagating onto the top surface of regrown GaN layer, were reduced due to isoelectronic In-doping, which could enhance vacancy trapping. In addition, threading dislocations in the coalescence region were not observable. These results indicate that these dislocations are bent or terminated in the boundary of coalesced region. Also, the crystalline quality was improved from the results of high resolution X-ray diffraction and TEM measurements.

Correlation between the type of threading dislocations and photoluminescence characteristics at different doping concentrations of Si in GaN films

At various doping concentrations of Si in GaN films, the correlation between the type of dislocations and photoluminescence (PL) characteristics was investigated. A different broadening behavior of symmetric and asymmetric Bragg peaks as a function of carrier concentration provided qualitative evidence that the type of threading dislocations generated in GaN layers was strongly dependent on the doping levels of Si. PL spectra in conjunction with x-ray rocking curve measurements suggested that the yellow luminescence associated with deep levels was more strongly related with edge dislocations than screw or mixed ones.

Inversion domains triggering recovery of luminescence uniformity in epitaxially lateral overgrown thick GaN film

A 150 μm-thick GaN layer was grown by halide vapor phase epitaxy utilizing selective lateral overgrowth on a SiO2-prepatterned sapphire substrate. A series of optically active regions above the SiO2 mask was observed in cross sectional monochromatic cathodoluminescence images taken at 367 nm. These bright regions were, however, consistently terminated by triangular shaped domains at 60 to 80 μm thickness, leaving no sign of luminescence nonuniformity beyond the thickness. In conjunction with the recent results on the characteristics of inversion domains in GaN, we proposed that these triangular regions might be inversion domains.