Fabrication and properties of GaN-based lasers P. Perlin a,b,Ã , T. S ´ wietlik a , L. Marona a , R. Czernecki a,b , T. Suski a , M. Leszczyn ´ ski a,b , I. Grzegory a,b , S. Krukowski a , G. Nowak a , G. Kamler a , A. Czerwinski c , M. Plusa c , M. Bednarek d , J. Rybin ´ ski d , S. Porowski a a Institute of High Pressure Physics, "UNIPRESS", Sokolowska 29/37, 01-142 Warsaw, Poland b TopGaN Ltd., Warsaw, Poland c Institute of Electron Technology, Warsaw, Poland d Firefighting School, Warsaw, Poland article info Available online 7 June 2008 PACS: 73.40.Kp 61.72.Ff 42.55.Ah 42.55.Px 42.60.By 42.60.Lh Keywords: A3. Metal organic chemic vapor deposition B2. Semiconducting III–V materials B3. Laser diodes abstract In this paper we will discuss the application of almost dislocation-free, high-pressure grown gallium nitride bulk crystals as a substrate for the epitaxy of GaN/InGaN/AlGaN laser diode structures. We show that these laser diodes may have very low dislocation densities (even down to 8  10 4 cm 2 ). These dislocations appear during the growth of the laser structure as a result of the combined effect of strain and perturbation of the atomic step flow. We show also that the lifetime of these devices seems to be dependent on operating current via the increasing junction temperature. & 2008 Elsevier B.V. All rights reserved. 1. Introduction Ten years after the first demonstration of the InGaN laser diode (LD) by Nakamura [1], the Japanese industry finally succeeded in launching a mass production of violet, 405 nm, LDs for optical data storage applications (BlueRay and HD DVD). It is also envisioned that nitride devices may become a base for a new branch of consumer electronics—laser TV. For these devices a longer emission wave- length, 450–460 nm, is required. The production volume necessary to meet the total demand of these two markets can be estimated at hundreds of millions of LDs per year. In order to meet this demand, the further development of the production of bulk GaN substrate crystals must be achieved. As for today, the dominating method of GaN substrate production is the hydride vapor-phase epitaxy–dislo- cation elimination by epitaxial growth with inverse-pyramidal pits (HVPE–DEEP) method introduced by Sumitomo Electronic [2,3]. The GaN crystals obtained by this method have an average density of dislocations in the order of 10 5 –10 6 cm 2 . Though the DEEP method obviously dominates in the mass production of GaN substrates, alternative methods like the amonothermal [4] method or the high- pressure synthesis method [5] may offer advantages for nitride lasers industry, especially in terms of higher wafer quality. Indeed, the density of dislocations of the high-pressure grown crystals is lower than 100 cm 2 [5]. In this paper we would like to give the reader a short review of the challenges related to the production of laser structures on very low dislocation density, high-pressure grown bulk GaN crystals. We will discuss the quality of GaN/ InGaN/AlGaN LDs grown on such crystals, demonstrating typical defects and their distribution. The final part of the paper is devoted to reliability studies of these devices. We will show the mechanisms which may influence the lifetime of nitride LDs, focusing on the high operating temperature of the junction as the driving force for device degradation. 2. Substrate crystals We synthesized our crystals using the high nitrogen pressure solution [5] method, which is a temperature gradient growth method based on the direct reaction between gallium and nitrogen at high-temperature and high-nitrogen pressure. The dominating morphological form of GaN crystals grown by the high-pressure method is a thin hexagonal platelet (Fig. 1). The large hexagonal surfaces of the platelets always corresponds ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2008.06.010 Ã Corresponding author at: Institute of High Pressure Physics, "UNIPRESS", Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland. Tel.: +48 22 888 00 76; fax: +48 22 877 3598. E-mail address: piotr@unipress.waw.pl (P. Perlin). Journal of Crystal Growth 310 (2008) 3979– 3982