Details of the improvement of crystalline quality of a-plane GaN using one-step lateral growth
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0955-I04-02
Details of the improvement of crystalline quality of a-plane GaN using one-step lateral growth Daisuke Iida, Tetsuya Nagai, Takeshi Kawashima, Aya Miura, Yoshizane Okadome, Yosuke Tsuchiya, Motoaki Iwaya, Satoshi Kamiyama, Hiroshi Amano, and Isamu Akasaki Materials Science and Engineering, Faculty of Science and Technology, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, 468-8502, Japan ABSTRACT Low defect density a-plane GaN films were successfully grown by sidewall epitaxial lateral overgrowth (SELO) technique. Control of V/III ratio during the growth of GaN by metalorganic vapor phase epitaxy (MOVPE) was found to be very important to achieve a complete overgrowth on the SiO2 mask regions and atomically flat surface. The threading dislocation and stacking fault densities in the overgrown regions were lower than 106 cm−2 and 103 cm−1, respectively. The root mean square roughness was 0.09 nm. We also fabricated and characterized a-plane-GaN-based-light-emitting diodes (LEDs) using SELO technique. The light output power of the blue-green LED steeply increased with the decrease of threading dislocation density from 1010 cm-2 to 108 cm-2 and tended to saturate at lower dislocation densities. INTRODUCTION Recently, high-brightness violet, blue and green LEDs and violet laser diodes (LDs) using c-plane group III nitrides have been commercialized and widely used all over the world. They have been developed as a result of outstanding breakthroughs such as the improvement in crystalline quality using a low-temperature-deposited buffer layer [1] and the realization of the conductivity control of nitrides [2-4]. However, the performance of these LEDs and LDs in longer-wavelength regions, such as green regions, is still insufficient. Heterojuction of these devices are perpendicular to direction. Band bending and charge separation in QWs by spontaneous and piezoelectric polarizations lead to poor internal quantum efficiency and red-shift in emission wavelength. This is a major obstacle to achieving high-efficiency green and/or longer-wavelength LEDs and LDs [5]. The use of non-polar nitrides potentially solves these problems, because no piezoelectric field is expected in the a-plane heterostructure [6]. Therefore, the growth of GaN on r-plane sapphire, which results in a-plane GaN (a-GaN), has attracted considerable attention. The characterization of optical properties of MQWs [7] and the performance of LEDs [8] have already been reported. Therefore, by using a-GaN, it is in principle possible to achieve high efficiency and high performance light-emitting devices.
However, growing non-polar a-GaN of high crystalline quality on r-plane sapphire is known to be very difficult. A-GaN grown on r-plane sapphire has a threading dislocation density of ~3 × 1010 cm-2 and stacking fault density of ~3.5 × 105 cm-1 [9]. There are several reports on the reduction of defect density in a-GaN using lateral overgrowth techniques [10, 11]. In particular, one-step lateral growth using grooved GaN with a SiO2 mask on terr
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