Investigation of the Optimum Growth Conditions of Wide-Bandgap Quaternary InAlGaN for UV-LEDs
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Investigation of the Optimum Growth Conditions of Wide-Bandgap Quaternary InAlGaN for UV-LEDs T. Yamabi1 2, A. Kinoshita1 2, H. Hirayama1, M. Ainoya1 2, A. Hirata2, T. Araki3, Y. Nanishi3 and Y. Aoyagi1 1 The Institute of Physical and Chemical Research (RIKEN), Hirosawa 2-1, Wako-shi, Saitama, 351-0198, Japan 2 Department of Chemical Engineering, Waseda University, Okubo 3-4-1, Shinjuku-ku, Tokyo, 169-8555, Japan 3 Department of Photonics, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu-shi, Shiga, 525-8577, Japan ABSTRACT We systematically investigated the optimum growth condition of wide-bandgap quaternary InAlGaN for ultraviolet (UV) light-emitting diodes (LEDs) grown on SiC by metal organic vapor phase epitaxy (MOVPE). We obtained intense UV emission in the wavelength of 315-370 nm from quaternary InAlGaN, which was as high as blue emission from InGaN. We found that the optimized growth temperature of quaternary InAlGaN is shifted from 790 to 870 °C as the emission peak wavelength is changed from 370-315 nm. The strongest PL was obtained with the wavelength around 330 nm. The growth condition for intense PL is found to be decided by two factors, i.e., the carrier confinement in In segregation region and crystalline quality. We also found that the small In mole fraction of 2-5 % is enough to obtain maximally PL intensity for InAlGaN, which is much smaller value than that for InGaN, due to the large carrier confinement with small In fluctuation.
INTRODUCTION GaN and related compound semiconductors are attracting considerable attention as candidate materials for the realization of visible or ultraviolet (UV) laser diodes (LDs) and light emitting diodes (LEDs), because wide-bandgap direct transitions can be adjusted between 6.2 eV (AlN) and 2.0 eV (InN). Quaternary InxAlyGa1-x-yN is considered to be particularly important for the realization of 300-nm UV emitters, because the room temperature (R.T.) intense UV emission and hole conductivity can be obtained using wide bandgap InAlGaN [1-3]. UV LDs or LEDs are expected to realize high efficient and low driving cost emitting devices in comparison with the conventional UV light sources such as excimer lasers, He-Cd lasers, mercury lamps or excimer lamps. They are expected to be used for white-light emitting devices, high-density optical storage or chemical processes [4]. The purpose of our work is to develop high-intensity UV-LEDs or LDs operating in the wavelength of 250-350 nm range. Recently, several research groups have been studying AlGaN or GaN based emitters to obtain high-intensity UV emission with wavelength below 360 nm [5-8]. However, there are some large problems in achieving AlGaN-based UV emitters, i.e., the difficulty in obtaining efficient UV emission from AlGaN-quantum wells (QWs) at R.T., or the I3.42.1
difficulty to obtain hole conductivity in p-type AlGaN. Recently, we obtained intense emission in the wavelength of 280-400 nm from InAlGaN / In(Al)GaN QWs at R.T.[9]. The intensity of UV emission from InAlGaN-based QWs was as large as that of blu
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