Structural defects in GaN-based materials and their relation to GaN-based laser diodes
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1195-B01-05
Structural defects in GaN-based materials and their relation to GaN-based laser diodes S. Tomiya1, M. Ikeda1, S. Tanaka1, Y. Kanitani1, T. Ohkubo2 and K. Hono2 1 Advanced Materials Laboratory, Sony Corporation, Atsugi, Kanagawa 243-0021, Japan. 2 National Institute for Materials Science, Tsukuba, 305-0047, Japan.
ABSTRACT Reduction of structural defects in III-nitride based optical devices is of critical importance for high efficient and high reliable optoelectronic performance. Here, three different types of structural defects such as threading dislocations, Mg-related pyramidal defects and columnar defects, observed in GaN-related epitaxial films are described and their relation to reliability of GaN-based LDs is discussed. Composition fluctuations of GaInN MQWs with different In concentrations by analyzed by a laser assisted 3D atom probe are also described. INTRODUCTION Many efforts have been paid in the development of GaN-based laser diodes (LDs) since the first demonstration of a continuous-wave (cw) laser in 1996 [1], since GaN-based LDs are strongly desired for many optoelectronic applications such as optical data storage, color displays, photochemical processing, and environmental monitoring [2]. Near-UV emission GaN-based LDs already realized to be mass-market products with application in Blu-ray for optical data storage. Blue emission LDs are appearing in applications such as laser projection display systems. In addition, recently there have been increaseing requirement to improve the emission efficiency of green light emitting diodes (LED) and to realize green LDs. Under such a circumstance, it is very important to know structural defects in the GaNbased LDs since reduction of the defects in the devices is of critical importance for obtaining high efficient and high reliable optical performance. Since their crystal structure is different from that of conventional zinc-blende-based III-V materials such as GaAs, many different kinds of structural defects are nucleated in the epitaxial films of GaN-based LDs. In this paper, we describe various kinds of structural defects observed in these epitaxial films and discuss their correlation with the reliability of GaN-based LDs. In addition, we have also described the atom probe analysis results of composition fluctuation of GaInN MQWs with different In concentrations. THREADING DISLOCATIONS In the early development stage of GaN-based LDs, a high density of threading dislocations (typically 108-1010/cm2) was inevitable, since samples were grown on sapphire substrates. It is known that one single dislocation in the optical device is very harmful [3]. Therefore, the dislocation density should be minimized to 103-104/cm2, which means that there are essentially no dislocations in the stripe region. Using the dislocation reduction technique such as epitaxial lateral overgrowth (ELO) technique [4], the dislocation density can be minimized to 106/cm2, which is ten orders of magnitude smaller than that in the stripe region. However, our previous transmission
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