Cathodoluminescence and Micro-Structure of Polycrystalline GaN Grown on ZnO/Si
- PDF / 503,660 Bytes
- 6 Pages / 596 x 842 pts (A4) Page_size
- 114 Downloads / 165 Views
Cathodoluminescence and Micro-Structure of Polycrystalline GaN Grown on ZnO/Si Tsutomu Araki, Hidetaka Kagatsume, HiroakiAono and YasushiNanishi Dept. of Photonics, Ritsumeikan University 1-1-1 Noji-Higashi, Kusatsu 525-8577, Japan
ABSTRACT We have investigated relationships between microscopic structure and cathodoluminescence (CL) property of polycrystalline (poly-) GaN grown by electron-cyclotron-resonance plasma-excited molecular beam epitaxy (ECR-MBE) on ZnO/Si substrates. Very strong CL with a peak of 3.45 eV was observed from the poly-GaN, which mainly showed a columnar structure with a size of 50-100 nm. On the other hand, the intensity of CL from the poly-GaN with few columnar domains was weaker than that of the poly-GaN with the columnar structure. The CL image from the poly-GaN, in which the columnar domains were locally observed, showed a strong contrast between bright domains and a dark background. It is confirmed that these bright regions in the CL images are corresponding to the columnar domains of the poly-GaN, by comparing with the SEM images. These results suggest that the columnar domains are responsible for the strong CL from the poly-GaN grown on the ZnO/Si substrates. Cross-sectional transmission electron microscope (TEM) observation revealed that the columnar domains had high quality crystallinity with few defects.
INTRODUCTION III-nitrides and its related alloys have been excellent candidates for optoelectronic application to cover a wide spectral range from red to ultra-violet. Recently, the successful syntheses of high quality GaN and its alloys have resulted in the commercialization of blue lasers (LDs), light emitting diodes (LEDs) and ultraviolet photodetectors. However the fabrication of devices is still encountering problems that are motivating a worldwide research. Especially, a significant amount of efforts has been devoted to the development for growth of high quality films of III-nitrides. Since bulk nitride crystal growth is difficult due to the high melting temperatures and high dissociation pressure of III -N compounds, GaN related materials are typically grown on SiC, which is expensive, or on Sapphire, which is cheaper but has a large lattice mismatch with the nitride films. The nitride films grown on these substrates usually have a large dislocation density of 109-10 /cm2 . In this context, the major efforts have been put into the development of growth techniques in order to limit the defect density in the GaN films. Recently novel growth techniques such as epitaxial lateral overgrowth (ELO) [1], PENDEO [2], low-temperature-deposited (LT-) interlayer [3], mass transport [4] and anti-surfactant [5] have successfully demonstrated the high quality epitaxial growth. On the other hand, polycrystalline (poly-) GaN including ma ny grain boundaries grown on a variety of substrate have been of particular interest. In 1997, Iwata et al reported the growth of poly-GaN on a silica glass by gas source molecular beam epitaxy, which showed strong photoluminescence (PL) [6]. We have also i
Data Loading...
