In Segregation Effects on Optical and Doping Properties of InAlGaN Quaternary for UV Emitting Devices
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In Segregation Effects on Optical and Doping Properties of InAlGaN Quaternary for UV Emitting Devices 1 12 Hideki Hirayama , Atsuhiro Kinoshita , Takuya Yamanaka12, Akira Hirata2 and Yoshinobu Aoyagi1 1 The Institute of Physical and Chemical Research (RIKEN), 2-1, Hirosawa, Wako-shi, Saitama, 351-0198, Japan, [email protected] 2 Department of Chemical Engineering, Waseda University, 3-4-1, Okubo, Shinjuku-ku, Tokyo, 169-8555, Japan
ABSTRACT We demonstrate room temperature intense ultraviolet (UV) emission wavelength ranging 300340 nm from InxAlyGa1-x-yN quaternary alloys grown by metal-organic vapor-phase-epitaxy (MOVPE). We found that the UV emission is drastically enhanced by introducing several percent of In into AlGaN. We fabricated single quantum well (SQW) consisting of InxAlyGa1-x-yN quaternary well and barrier, and clearly observed In segregation of sub-micron size from a cathode luminescence (CL) images. The intensity of 320nm-band emission from InAlGaN/InAlGaN QWs were as strong as those of 410nm-band emission from InGaN based QWs, at room temperature. The temperature dependence of photoluminescence (PL) emission for InAlGaN based QWs were much improved in comparison with GaN or AlGaN based QWs. We also grew Mg-doped InxAlyGa1-x-yN quaternary, and obtained hole concentration of 3×1017 cm-3 by Hall measurement for high Al content (more than 50 %) InxAlyGa1-x-yN quaternary. INTRODUCTION AlGaN alloy is expected to realize deep ultraviolet (UV) light emitting diodes (LEDs), laser diodes (LDs) or photo detectors, because it has large direct transition energy ranging between 6.2 eV (AlN) and 3.4 eV (GaN). However, there are two large problems for the use of AlGaN as UV emitting devices, i.e., the difficulty to obtain efficient UV emission, and the difficulty of p-type doping into high Al content (more than 30 %) AlGaN. We propose to use the In segregation effect in InAlGaN quaternary[1], in order to achieve room temperature bright UV emission and also high hole conductivity of wide bandgap InAlGaN. The emission intensity of wide bandgap InAlGaN should be much improved with In segregation effect, which is already observed in InGaN alloy [2]. Also the equivalent activation energy of acceptor should be decreased due to the effect of large Piezoelectric field applied in In segregated regions. The In segregation effects for the optical properties of InGaN have been studied carefully [3][4]. It was reported that the injected carrier is localized in quantum dot like region formed by In segregation in InGaN QWs, and nonradiative recombination is much suppressed due to electron localization, resulting that InGaN QWs emit well at room temperature. Dr. S. Nakamura in Nichia reported that the In compositional fluctuation more than 5 % is required for the high current injection devices such as LDs. In order to achieve 300 nm-band emitting InxAlyGa1-x-yN quaternary with 5 %-Inincorporation, high Al content ranging 30-60 % is necessary, because InAlGaN shows a large band bowing as a function of the I
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