Performance characteristics of cw InGaN multiple-quantum-well laser diodes
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Performance characteristics of cw InGaN multiple-quantum-well laser diodes Michael Kneissl*, William S. Wong, Chris. G. Van de Walle, John E. Northrup, David W. Treat, Mark Teepe, Naoko Miyashita, Peter Kiesel, Noble M. Johnson Electronic Materials Laboratory, XEROX Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304, U.S.A. ABSTRACT The performance characteristics are reported for continuous-wave (cw) InGaN multiple-quantum-well laser diodes grown on epitaxially laterally overgrown GaN on sapphire substrates by metalorganic chemical vapor deposition. Room-temperature cw threshold currents as low as 41mA with operating voltages of 6.0V were obtained. The emission wavelength was near 400 nm with output powers greater than 20 mW per facet. Under cw conditions laser oscillation was observed up to 90°C. A significant reduction in thermal resistance was observed for laser diodes transferred from sapphire onto Cu substrates by excimer laser lift-off, resulting in increased cw output power of more than 100mW.
INTRODUCTION Since the first demonstration of an InGaN multiple-quantum-well (MQW) laser diode in 1995 [1] enormous progress has been made with the currently most advanced devices operating under cw conditions and lifetimes greater than 15000 hours [2,3,4]. The commercialization of violet laser diodes was recently announced [5], targeting a wide range of applications particularly high-density optical data storage and printing. In order to improve the performance and lifetime of group III-nitride laser diodes, the reduction of the dislocation density in the material has shown to be a pivotal step. As Nakamura and co-workers have demonstrated by employing an epitaxial lateral overgrowth technique [2,3], the dislocation density in GaN films grown on sapphire can be reduced from ~1010cm-2 to ~106cm-2, thus greatly enhance the performance of laser diodes. In the meantime a number of other groups have realized room-temperature cw operation of InGaAlN laser diodes [6,7,8,9] using a variety of techniques to reduce the dislocation density in GaN materials [10,11,12]. In this paper we report on the performance characteristics of InGaN MQW laser diodes grown on low-dislocation density epitaxially laterally overgrown (ELOG) GaN on sapphire substrates and compare these to results obtained on laser diodes directly grown on sapphire substrates. We also discuss the effect of the substrate thickness and material on the thermal impedance of laser diodes and demonstrate improved thermal resistance for laser diodes transferred from the sapphire substrate onto Cu using excimer laser-lift-off.
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Electronic mail: [email protected] G10.6.1
EXPERIMENTAL RESULTS A schematic of a laser diode structure is shown in Fig. 1. The InGaAlN heterostructure was grown by metalorganic chemical vapor deposition (MOCVD) on (0001) c-face sapphire substrates. First a 4µm thick GaN film was deposited on the sapphire substrate followed by a 100 nm thick layer of silicon dioxide (SiO2). The SiO2 film was subsequently patterned to form
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