ABSTRACT
There has been much interest in light-emitting diodes (LEDs), which emit from ultraviolet (UV) to red wavelengths, fabricated from III-V nitride compound semiconductors. Major developments in wide-bandgap III-V nitride semiconductors have recently led to the commercial production of high-efficiency UV/blue/green!amber LEDs (Nakamura et al., 1995a; 1995b; Mukai et al., 1998a; 1998b). All of these light-emitting devices use an InGaN active layer instead of a GaN active layer because of the difficulty in fabricating highly efficient lightemitting devices using a GaN active layer (Morko~ et al., 1994; Ponce and Bour, 1997; Mukai et al., 1998b) Several groups recently reported that the dislocations are nonradiative recombination centers in GaN (Rosner et al., 1997; Sugahara eta/., 1998). In InGaN, however, the role of dislocations has not yet been clarified. Highly efficient blue/green InGaN single-quantum-well (SQW) or multi-quantumwell (MQW) structure LEDs and LDs have been fabricated directly on a sapphire substrate in spite of a high dislocation density of l-10 x l010cm2 originating from a large lattice mismatch between GaN and the sapphire substrate (Nakamura et al., 1995b; Nakamura and Fasol, 1997; Mukai et al., 1998a). Due to the high efficiency of the LEDs gro\\n on the sapphire substrates, the dislocations in InGaN do not appear to work as a nonradiative recombination center (Lester et al., 1995). Here, the present performance of UV/blue/green!amber LEDs and the role of the dislocations in the InGaN are described.
