Light emitters fabricated on bulk GaN substrates. Challenges and achievements.
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Light emitters fabricated on bulk GaN substrates. Challenges and achievements. Piotr Perlin1, M. Leszczyński1, P. Prystawko1 , R. Czernecki1, G. Nowak1 P. Wisniewski1, L. Dmowski1, H. Teisseyre, E. Litwin- Staszewska1, T. Suski1, I. Grzegory1, S.Porowski1, V.Yu. Ivanov2, M. Godlewski2, J, Holst3, A. Hoffman3 1
High Pressure Research Center, “Unipress” , ul. Sokolowska 29/37 , 01-142 Warsaw, Poland Institute of Physics, Polish Academy of Sciences, Warsaw, Poland 3 Technische Universitaet Berlin, Germany 2
ABSTRACT We used high-pressure grown GaN single crystal substrates to fabricate dislocation free optoelectronic devices like light emitting diodes and laser diodes structures. The latter ones demonstrated laser action under optical pumping condition with the threshold of about 200 kW/cm2 at room temperature. In the present paper we would focus on the specific aspects of the homoepitaxial growth by MOVPE method including epi-ready substrate preparation and surface polarity choice. We believe that our results demonstrate clearly the feasibility of device fabrication based on high-pressure grown GaN bulk crystals.
INTRODUCTION Close observation of the development of GaN based technology in the last few years makes a clear impression that heteroepitaxial techniques, used up to date, have already reached their limits [1]. Sapphire or SiC substrates enable growers to prepare structures with concentration of misfit dislocations in the range of 108 cm-2. While it is true that the use of modern growth methods such as lateral overgrowth techniques brought a huge improvement of epitaxial layer quality, it is still very difficult to lower the concentration of extended defects below 106 cm-2 and to reduce harmful strain fluctuations. In this situation to make a further progress, we need indeed a new technological breakthrough. It particularly applies to higher power optoelectronic and electronic devices. In case of the light emitters all attempts to construct shorter wavelength devices have to face a dramatic sensitivity to the number of dislocations [2]. Homoepitaxial growth of GaN layers and InGaN/AlGaN quantum structures can offer a solution. Unfortunately, bulk GaN substrates are of scarce availability One of the potential ways is to use large area HVPE GaN substrates. However, concentration of dislocations in such material is not lower than 5x105 cm-2. There is a number of applications which require even farther reduction of dislocation density. For example, a satisfactory performance of high-power laser diodes critically relies on the reduction of nonradiative recombination channels i.e. charged dislocations [1]. In this paper we report on the progress in development of epitaxial growth techniques using bulk GaN substrates obtained by means of high-pressure synthesis [3]. In next sections we repeat the basic information concerning high pressure growth method of highly conducting GaN crystals. Then some procedures leading to preparation of epi-ready GaN substrates are given. This part is I4.7.1
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