Nonuniform Morphology and Luminescence Properties of a Molecular Beam Epitaxy GaN Film from Atomic Force Microscopy, Sca
- PDF / 1,741,289 Bytes
- 15 Pages / 612 x 792 pts (letter) Page_size
- 99 Downloads / 137 Views
Internet Journal o f
Nitride S emiconductor Research
Volume 2, Article 7
Nonuniform Morphology and Luminescence Properties of a Molecular Beam Epitaxy GaN Film from Atomic Force Microscopy, Scanning Electron Microscopy and Cathodoluminescence L.-L. Chao, G. S. Cargill III, C. Kothandaraman Department of Chemical Engineering, Materials Science, and Mining Engineering, Columbia University D. Cyr, G. Flynn Department of Chemistry, Columbia University E. S. Hellman, D. Wiesmann, D. N. E. Buchanan, I. Brener Bell Laboratories, Lucent Technologies This article was received on December 30, 1996 and accepted on May 23, 1997.
Abstract Complex faceted features of micrometer sizes and with intense luminescence rise 200-300 nm above the surface of a GaN thin film grown by molecular beam epitaxy on (0001) sapphire. Cathodoluminescence measurements at room temperature and at 8K were used to investigate the luminescence properties of these microfeatures in comparison with those of the background GaN material. The morphology of the micro-features was studied by scanning electron microscopy and by atomic force microscopy. GaN and related compounds have been considered as promising materials for light emitting devices in the short wavelength visible and UV spectral regions because of their direct, wide band gaps and high luminescence efficiency. Remarkable, rapid success has been achieved in developing devices based on III-V nitrides, which allows these material systems to rival other systems under development [1]. Blue-green LEDs fabricated from InGaN/AlGaN double-heterostructure layers on sapphire substrates by Nichia Chemical Industries in Japan are commercially available, despite the presence of high extended defect densities in the 1010 /cm2 range [2]. In December 1995, an important milestone in the development of nitride lasers was reached; Nakamura et al. in Nichia demonstrated the first nitride-based laser diode which operated at 417 nm under pulsed conditions at room temperature [3]. The morphology and spatial distribution of luminescence in GaN thin films have been investigated by several research groups [4], [5], [6], although most efforts have been directed to developing appropriate growth conditions for improved film quality. From observations by scanning electron microscopy (SEM) and atomic force microscopy (AFM), Trager-Cowan et al. described an MBE-grown GaN film which contained an assembly of oriented hexagonal crystallites rising above a background of polycrystalline or amorphous material [4]. All the crystallites, oriented in a similar fashion, had roughly the same sizes, 1 or 2 µm across a hexagonal face and about 1 µm high. These crystallites were much brighter than the surrounding background material in panchromatic low-temperature cathodoluminescence (CL) images. Trager-Cowan et al. concluded that the crystallites were of better quality than the background material. They also observed a green emission band, attributed to impurities, which became weaker for higher electron beam voltages, generating luminesc
Data Loading...
