InGaN Laser Diodes Grown on SiC Substrate Using Low-Pressure Metal-Organic Vapor Phase Epitaxy
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ABSTRACT We report the crystal growth and the characteristics of InGaN multiple quantum well (MQW) laser diodes grown on a 6H-SiC substrate using a low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). We discuss the buffer layer, the control of InGaN and AlGaN alloy composition, the magnesium doping of GaN and AlGaN, and the characteristics of the MQW structure. We also demonstrate the room-temperature pulsed operation of the laser diode. The threshold voltage was reduced to 15 V by improving the p-contact resistance. The threshold current was reduced to 500 mA by changing the MQW structure and employing high reflection coating. INTRODUCTION Sapphire is the substrate which is most widely used for GaN growth. Room-temperature pulsed [1-7] and continuous wave (CW) operation [8] of InGaN quantum well laser diodes (LDs) fabricated on a sapphire substrate have been reported. However, there are some intrinsic problems in the use of a sapphire substrate concerning the cavity mirror fabrication and electrode process. The use of a SiC substrate may solve these problems because SiC is cleavable and electrically conductive. Furthermore, SiC has small lattice mismatch to GaN and very large thermal conductivity, which are expected to benefit the laser charactersistics. Room-temperature pulsed operation [9-11] and CW operation [12] of InGaN multiple quantum well (MQW) LDs fabricated on a SiC substrate have been reported. The issue of growth pressure for metalorganic vapor phase epitaxy (MOVPE) is important in a different way. Historically, the atmospheric-pressure growth has been mainly used for the growth of GaN. This is probably because people believe that high source gas pressure is indispensable for the growth of GaN. Meanwhile, low-pressure growth has been used for the growth of the other III-V compounds. Low pressure growth has two merits. The first is that we can easily control the gas flow pattern. This means that it is suitable for multiple and large wafer growth. The second is that we can easily suppress the prereaction between group Ill and group V sources. This is especially important for the growth of AlGaN. We considered that lowpressure growth must supply sufficient source gas pressure on the surface. Therefore, we selected the low-pressure growth which is best suited for mass production. We applied the LPMOVPE for the fabrication of GaN LDs and succeeded in demonstrating pulsed operation [9]. There have been several reports on the LP-MOVPE growth of GaN based materials on SiC substrates [13-22]. However, some important issues for fabricating InGaN MQW LDs using the LP-MOVPE on the SiC substrate have not been sufficiently investigated. In this paper, we report the crystal growth and the characteristics of InGaN MQW LDs grown on SiC substrate using LP-MOVPE. We discuss the buffer layer, the control of InGaN and A1GaN alloy composition, the magnesium doping of GaN and A1GaN, and the characteristics of the MQW structure. We also show the room temperature pulsed operation of the LDs. The method for reducing the t
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