InGaN Laser Diode Degradation. Surface and Bulk Processes
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1195-B01-04
InGaN Laser Diode Degradation. Surface and Bulk Processes Piotr Perlin1,2, Łucja Marona1, , Przemek Wisniewski1,2, Mike Leszczynski1,2, Pawel Prystawko1,2, Michał Boćkowski1,2, Robert Czernecki1,2, Irina Makarowa2, Bogdan Kowalski3 and Tadek Suski1 1. Institute of High Pressure Physics, Sokolowska 29/37, 01-142 Warsaw, Poland; 2. TopGaN Ltd, Sokolowska 29/37, 01-142 Warsaw, Poland; 3. Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland.
ABSTRACT We discuss main degradation mechanisms present in nitride based laser diodes operating in 400-440 nm spectral range. We can clearly divide the aging processes into these occurring on the facets of the device and the bulk phenomena. Surface processes are predominantly connected with photochemical reactions on the laser mirrors and manifest by the formation of the carbon deposits. The nature of these photochemical reactions resembles very closely the mechanism known as Package Induced Failure observed previously in case of 980 nm laser diodes. Degradation involving bulk like effects is much less understood. The existing experimental results seem mot to be sufficient for proposing an unambiguous model of the physical effects involved. In particular, magnesium diffusion from the p-type layers into the active layer was proposed as a possible degradation path. However, our study of SIMS profiles in the device subjected to over 8 000 h of electrical stress reveals no visible modification in the Mg profile. The same holds for the hydrogen spatial distribution thus substantially limiting candidates for the diffusion processes. Nevertheless, it seems that the diffusion mechanism is involved in bulk degradation. The claim is supported by two facts: well confirmed stability of the extended defects network in nitride emitters and characteristic square-root time-dependence of the degradation rate.
INTRODUCTION Since the first appearance of nitride optoelectronic devices on the market, the problem of identification of the degradation mechanism has been the central issue of the development of this technology. However, the degradation of nitride laser diode emitters turned out to be a process escaping from the direct identification, esoteric and changeable. The lifetime of the first InGaN laser diodes fabricated on the sapphire substrate and containing between 109-1010 dislocation per square centimeter was very short. For example the first CW operated laser demonstrated by Nakamura lived only one second [1]. The improvement introduced by ELOG technology and the use of free standing GaN substrates was quoted responsible for the increased lifetime of nitride laser diodes which soon was reported to reach 10 000 hours [2,3]. This course of the technology development focused the attention of researchers on the dislocations as a main cause of the laser diode degradation. However, dislocations in the GaN, AlGaN and InGaN do not
multiply or move [4] and even heavily degraded devices did not contain usually new extended defects. In that situati
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