Nitride Laser Diodes With InGaN Based MQW Structures
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ABSTRACT Advantages of applying III-V nitride materials for short wavelength light-emitting devices despite their extremely high dislocation density are discussed from the viewpoint of dislocation motion. There are also difficulties proper to these materials, which make it difficult to fabricate laser diodes. We present recent works to realize high performance laser diodes. We introduce the nitrogen ambient metalorganic chemical vapor deposition (MOCVD) growth which realizes the highly p-typed GaN films without any post-treatments. Some of our results respecting the room temperature pulsed operation of the conventional laser diode and the advanced inner stripe (IS) laser diode with InGaN based multi-quantum-well (MQW) grown by MOCVD are reported. INTRODUCTION III-V nitride compound semiconductors are promising for shortening the wavelength of laser diodes owing to their wide direct band-gap energies which extend into the far ultraviolet region. Recent drastic improvements in the MOCVD growth technique have led to the
commercial production of high-brightness blue/green light-emitting diodes (LEDs) [1,2] and the room temperature lasing operation, under pulsed current, of nitride based lasers [3-5]. More recently, room temperature continuous operation of nitride based lasers was also realized [6,7]. Nitride based light-emitting devices are highly efficient and have long lifetime [8] despite their extremely high dislocation density (108-10"cm 3). This fact is surprising and anomalous in view of experience with light-emitting devices constructed from other material systems. First, to clarify the cause of this fact, the relationship between dislocation motion and the reliability of the major light-emitting devices constructed from Ill-arsenides (GaA1As/GaAs), Ill-phosphides (lnGaAsP/InP) and Ill-nitrides material systems are discussed on the basis of dislocation theory [9]. Second, we introduce the nitrogen ambient MOCVD growth which allows the production of highly p-type doped GaN films without any post-treatments [10]. Third, a result respecting the room temperature pulsed operation of InGaN based multi-quantum-well (MQW) laser diodes grown by MOCVD is reported [5]. Formation of cleaved facets, used to achieve lasing in most semiconductor systems, has been believed to be difficult for C-face sapphire substrate used in nitride compounds. For this reason, dry etching, scribing, or cleavage of A-face sapphire substrates has been employed to form the facets for the laser cavities [3,4]. We have fabricated the laser diodes with simple cleaved mirror facets on conventional C-face sapphire substrates, and obtained room temperature pulsed operation [5]. We also introduce the advanced inner stripe (IS) laser diodes using dry etching and overgrowth (OG) techniques [11]. 1157 Vol. 482 © 1998 Materials Research Society Mat. Res. Soc. Symp. Proc.
Effect of dislocations on device lifetime Transmission electron microscopy (TEM) observation of GaN-based materials grown on sapphire by MOCVD revealed that straight threading dislocati
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