Properties of the Biexciton and the Electron-Hole-Plasma in Highly Excited GaN
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Internet Journal o f
Nitride S emiconductor Research
Volume 2, Article 25
Properties of the Biexciton and the Electron-Hole-Plasma in Highly Excited GaN J.-Chr. Holst, L. Eckey, A. Hoffmann, I. Broser Institut fuer Festkoeperphysik, Technische Universitaet Berlin H. Amano, I. Akasaki Department of Electrical and Electronic Engineering, Meijo University This article was received on June 23, 1997 and accepted on September 10, 1997.
Abstract High-excitation processes like biexciton decay and recombination of an electron-hole-plasma are discussed as efficient mechanisms for lasing in blue laser diodes [1]. Therefore, the investigation of these processes is of fundamental importance to the understanding of the properties of GaN as a basic material for optoelectronical applications. We report on comprehensive photoluminescence and gain measurements of highly excited GaN epilayers grown by metal-organic chemical vapor deposition (MOCVD) over a wide range of excitation densities and temperatures. For low temperatures the decay of biexcitons and the electron-hole-plasma dominate the spontaneous-emission and gain spectra. A spectral analysis of the lineshape of these emissions is performed and the properties of the biexciton and the electron-hole-plasma in GaN will be disscused in comparison to other wide-gap materials. At increased temperatures up to 300 K exciton-exciton-scattering and band-to-band recombination are the most efficient processes in the gain spectra beside the electron-hole-plasma.
1. Introduction Tremendous success in the growth and processing technologies of group-III nitrides have recently led to a first GaN-based laser structure operating in the ultraviolet spectral range [1]. For this structure the decay of localized biexcitons [2] and the recombination of an electron-hole-plasma are discussed as possible mechanisms responsible for lasing [3]. This indicates the need for a basic understanding of their properties in GaN. We therefore performed photoluminescence and gain spectroscopy at high excitation densities on GaN-epilayers grown by metal organic chemical vapor phase deposition (MOCVD).
2. Experimental The sample used for this study was grown on a 6H-SiC substrate [4] with an epilayer thickness of 3µm. To obtain the high excitation (HE) density necessary for our investigations we used a dye laser pumped by an excimer laser, providing pulses at a rate of 30Hz with a typical duration of 15ns and an energy of up to 20µJ at 340nm. The sample was kept in a cryostat at temperatures varied between 2 K and 300 K. Gain measurements were performed using the stripe length method [5].
3. Results 3.1. Photoluminescence at High Excitation Levels At low excitation densities the MOCVD sample investigated exhibits a very strong emission I2 at 3.461 eV caused by the annihilation of excitons bound to neutral donors. This luminescence has a linewidth of 5 meV in the sample presented here. The energy of the free A-exciton in this sample is 3.467 eV as determined in Downloaded from https://www.cambridge.org/core. I
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