Photoluminescence study on GaN homoepitaxial layers grown by molecular beam epitaxy
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Internet Journal o f
Nitride S emiconductor Research
Volume 1, Article 13
Photoluminescence study on GaN homoepitaxial layers grown by molecular beam epitaxy H. Teisseyre, G. Nowak, M. Leszczynski, I. Grzegory, M. Bockowski, S. Krukowski, S. Porowski High Pressure Research Center M. Mayer, A. Pelzmann, Markus Kamp , K. J. Ebeling Abteilung Optoelektronik, Universität Ulm G. Karczewski Institute of Physics, Polish Academy of Sciences This article was received on June 4, 1996 and accepted on September 24, 1996.
Abstract GaN epitaxial layers on GaN single crystals were grown using molecular beam epitaxy with an NH3 source. The deposited layers were examined by high resolution x-ray diffraction and photoluminescence (PL) spectroscopy. We observed strong and extremely narrow (half-widths of 0.5 meV) lines related to the bound excitons. In the higher energy range we observed three strong lines. Two of them are commonly attributed to free exciton transitions A (3.4785 eV) and B (3.483 eV). Their energetic positions are characteristic of strain-free GaN material.
1. Introduction The MOVPE (metalorganic vapor phase epitaxy) technique has dominated research activity in GaN and related materials. This is mainly due to difficulties in supplying atomic nitrogen and achieving high growth rates in the MBE environment, and the improved physical properties of heteroepitaxial layers realized by MOVPE on Al2O3 and SiC substrates. The aim of our work was to grow GaN film on GaN single crystals by using the MBE technique, and to compare our samples to homoepitaxial layers grown by MOVPE. To overcome the problem of damage introduced to the epitaxial layer during growth by plasma MBE, we employed the technique of On Surface Cracking (OSC) where uncracked ammonia molecules are injected on to the GaN growth surface. A detailed description of this technique and cracking process which takes place on the sample surface is given in [1]. In this work we report first MBE grown homoepitaxial GaN film. As a substrate we used single GaN crystals grown at about 15 kbar and 1800 K [2]. The measured x-ray rocking curve full width at half maximum (FWHM) of smallest (about 1 mm) substrate crystals used is very close (~25 arcsec) to the theoretical value for a perfect crystals. Larger crystals become slightly mosaic and have small angle boundaries. Photoluminescence (PL) from substrate crystals is influenced by the high free electron concentration (~5 x 1019 cm-3). The ultraviolet peaks are very weak and broadened with a characteristic "shark fin" shaped high energy cut-off corresponding to the position of the Fermi energy (Burstein-Moss effect) [3]. Additionally, a strong yellow luminescence is always observed. The detailed description of physical properties of these crystals is published elsewhere [4]
2. Experimental results For our investigation we used a Riber 32 MBE system adapted for group V gas sources. The system is turbopumped and the attached gas control and handling system is home made. The MBE system is equipped with Knudsen cells used
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