MOVPE에 의한 3차원 마이크로 GaN 구조의 선택적 결정 성장에 관한 연구

Abstract

The majority of GaN-based structures are grown along the [0001] c-axis of the wurtzite crystal structure. However, the optoelectronic devices grown along this direction suffer from strong undesirable spontaneous and piezoelectric polarization fields, which give rise to internal electrical fields. These fields can cause significant separation of the electron and hole carrier wave functions and a resultant red shift of the recombination energy. The internal electric field caused by spontaneous polarization and piezo effects can be eliminated by growing the devices on non- or semi-polar facets of GaN crystals using the selective area growth (SAG) of III-nitrides.

In this work, we propose a novel technique for selective growth only on the apex areas of hexagonal GaN pyramids. Well-aligned micro-pyramidal GaN structures with semi-polar {1-101} facets were formed only on the apexes of hexagonal GaN pyramids by metal organic vapor phase epitaxy (MOVPE). With a very small contact area for selective regrowth, a significant relaxation of the strain and a corresponding reduction in threading dislocation can be expected. We also expect an increase of the radiation efficiency with this approach to light-emitting diode (LED) structures because the selective growth on the {1-101} facets should reduce spontaneous and piezoelectric polarization. In this study, we mainly focused on the fabrication process of the microstructures on the apexes of hexagonal GaN pyramids. The distribution of crystalline defects was analyzed by transmission electron microscopy (TEM) and room temperature cathodoluminescence (CL).

We also fabricated three dimensional GaN stripes only on top of the triangular shaped GaN stripes. This approach can be effective growth method to realize literally three dimensional structures which available for many applications. The evolution of well aligned selectively grown GaN stripes which including {11-22} facets was realized only on top of the lower GaN stripes by selective epitaxial MOVPE growth. Reduction of threading dislocation and relaxation of strain can be expected because of small window area for the selective growth. Distribution of crystalline defects was evaluated by transmission electron microscopy (TEM) and room temperature cathodoluminescence (CL).