Mechanisms of Optical Gain in Cubic GaN and Ingan
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Cite this article as: MRS Internet J. Nitride Semicond. Res. 4S1, G2.3 (1999)
ABSTRACT The epitaxial growth of zinc-blende (cubic) GaN and InGaN on GaAs with a common cleavage plane and readily high-quality, low-cost wafers may be considered as an alternative approach for the future realization of cleaved laser cavities. To obtain detailed information about the potential of cubic GaN and InGaN for device applications we performed optical gain spectroscopy accompanied by time-integrated and time-dependent photoluminescence measurements at 2 K and 300 K. From intensity-dependent gain measurements, the identification of the gain processes was possible. For moderate excitation levels, the biexciton decay is likely to be responsible for a gain structure at 3.265 eV in cubic GaN [10]. For the highest pump intensities, the electron- hole-plasma is the dominant gain process, providing gain values up to 200 cm -'. Furthermore cubic GaN samples with different cavity lengths from 250 to 600 mim were cleaved to investigate the influence of the sample geometry on the gain mechanisms. In these samples increased gain values up to 150 cm -1as well as lower threshold excitation densities were observed, indicating the potential of cubic GaN for device applications. The results of GaN will be compared with intensity-dependent gain measurements on InGaN samples, grown on GaAs with varying In-content. The observed gain mechanisms in cubic InGaN will be discussed in detail. INTRODUCTION The epitaxy of metastable, cubic GaN on GaAs (001) substrates has attracted some interest recently since c-GaN layers and the GaAs substrate have a common cleavage plane, they are considered to be well suited for the fabrication of laser cavities with cleaved facets [1-8]. Because of this application, high optical excitation experiments have been used to measure the gain in c-GaN/GaAs (001) grown by MBE [2] revealing some insight into involved recombination mechanisms 13]. The stimulated emission from c-GaN has been reported for MOCVD [4] and
MOVPE [5] grown epilayers. In our previous work [10] we studied the gain spectra of c-GaN at 2 K and found that excitonic processes add to the gain at moderate excitation densities and many particle processes are effective for increased excitation intensities. The purpose of the present
paper is to analyze the mechanisms of optical amplification and the efficiency of the stimulated emission in cubic GaN and InGaN layers.
G 2.3 Mat. Res. Soc. Symp. Proc. Vol. 537 0 1999 Materials Research Society
EXPERIMENTAL Cubic GaN films with a phase purity better than 99.9% were grown on semi-insulating GaAs (001) substrates by RF-plasma assisted molecular beam epitaxy (MBE) at a substrate temperature of 720'C. Undoped epitaxial layers were grown under carefully controlled stoichiometric growth conditions[6]. Details of the growth procedure were reported in Ref.13. The optical properties of the c-GaN layers investigated under low and high excitation intensities are reported in Ref. 10. By cleaving we obtained c-GaN samples
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