High resolution x-ray diffraction analyses of GaN/LiGaO₂

Abstract

Lithium gallate (LiGaO2) is gaining increasing attention as a potential substrate for the growth of the important semiconductor GaN. In order to better understand this material we have performed high-resolution double- and triple-axis x-ray diffraction analyses of both the starting LiGaO2 and GaN/LiGaO2 following epitaxial growth. A high-resolution triple-axis reciprocal space map of the substrate showed a sharp, well-defined crystal truncation rod and a symmetric streak of intensity perpendicular to q002, suggesting high structural quality with mosaic spread. Triple-axis scans following GaN growth showed (1) the development of isotropic diffuse scatter around the LiGaO2 (002) reflection, (2) the presence of a semi-continuous intensity streak between the LiGaO2 (002) and GaN (0002) reflections, and (3) a compact pattern of diffuse scatter around the GaN (0002) reflection that becomes increasingly anisotropic as the growth temperature is increased. These results suggest that LiGaO2 permits the epitaxial growth of GaN with structural quality that may be superior to that observed when growth is performed on SiC or Al2O3.

Characterization of AlGaN/GaN structures on various substrates grown by radio frequency-plasma assisted molecular beam epitaxy

“…The orientation relationship between the hexagonal GaN layer and orthorhombic LGO is (0001) GaN || (001) LGO and [ ] 1210 GaN || [010]LGO. This observation confirms the relationship examined by Matyi et al 7 Figure 4a is a cross-sectional HRTEM image displaying the interface between GaN and LGO. Typically, low dislocation density material grown by MOCVD is produced by nucleating small crystallites, often of cubic structure.…”

“…Additionally, AlGaN can be lattice matched to LGO at growth temperature or room temperature by appropriate selection of Al composition. [3][4][5][6][7][8][9] Employing LGO as a substrate, we recently reported the electrical characteristics of the first demonstration of a twodimensional electron gas (2DEG) produced at an AlGaN/GaN heterostructure on LGO. The electron mobility was 731 cm 2 /Vs and sheet electron concentration was 1.3 × 10 13 cm -2 at room temperature measured on 1 cm × 1 cm sample without any patterning performed on the sample.…”

The growth of GaN on lithium gallate (LiGaO2) substrates for material integration

“…One such substrate, lithium gallate (LGO), LiGaO 2 , has been the focus of much interest in recent years. Our results [9][10][11][12][13][14] have shown that the structural quality, as determined by x-ray diffraction, is very good. We have also, recently, been able to demonstrate device-quality electrical properties.…”

“…This asymmetry leads to a slight, in plane rotation on the order of 3 degrees about the c-axis. 13 No mosaic structure results from this pure rotation. Al can be added to the GaN to equalize the magnitude of the a and b axis mismatch.…”

“…The critical thickness may be estimated from other observations. Matyi et al 13 performed reciprocal space x-ray mapping of GaN on…”