Effects of Surface Treatments on Optical Properties of GaN
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0955-I15-08
Effects of Surface Treatments on Optical Properties of GaN Gakuyo Fujimoto1, Katsushi Fujii1, Tsutomu Minegishi1, Hiroki Goto1, Takenari Goto1, and Takafumi Yao1,2 1 Center for Interdisciplinary Research, Tohoku University, Aramaki aza Aoba 6-3. Aoba-ku, Sendai, Miyagi, 980-8578, Japan 2 Institute of Materials Research, Tohoku University, 2-1-1 katahira, Aoba-ku, Sendai, Miyagi, 980-8577, Japan
ABSTRACT Removing artificial oxide layer is important for fabrication process of semiconductor devices. We employed photoluminescence for optical, reflection high energy electron diffraction, atomic force microscope, and Nomarski microscope for surface analysis. We found that it is more difficult to remove the oxide layer made by O-plasma such as in O-plasma asher than that of native one. Our result reached that HF etching is effective for removal of the artificial oxide layer without changing surface morphology. In addition, (NH4)2Sx treatment after HF etching reduces donor bound exciton drastically which is dominant luminescence near the band edge at low temperature. INTRODUCTION GaN, has direct wide band-gap, and related nitrides have attractive properties for ecological light emitting devices such as super bright light emitting diodes [1,2] and short wavelength laser diodes [1] and high power and/or high-temperature electric devices [1]. It is also known as a material which has very high stability [3-5]. To improve the device performance, surface treatments are key technologies to reduce the surface and/or interface defects. From this point of view, it is important to control the surface state of GaN after a removal of artificial oxide layer, since we have occasions to make oxide layer necessarily such as ashing photo-resist by O-plasma in a process. Surface passivation and chemical wet etching are effective ways to reduce surface state, and are well studied about GaN especially on chemical bonding and surface band bending [6,7]. HF aqueous solution is one of the effective etchant for surface oxide layer and (NH4)2Sx solution is one of the well known solutions for surface passivation with sulfur atoms of GaN [6,7], and also GaAs [8]. HF is often used to remove surface oxide layer of silicon substrates [9]. However, there are few reports on oxide layer removing of artificial oxide layer on GaN and surface passivation of GaN. In this study we focused to removing of artificial oxide layers on GaN grown by metal organic chemical vapor deposition (MOCVD) and observed how surface states of GaN changed when an artificial oxide layer was etched. The (NH4)2Sx treatment was also performed the asgrown sample and after the etching. The characteristics changes were observed by optically and morphologically.
EXPERIMENTS The thickness of GaN templates grown on c-plane sapphire substrates by MOCVD was 4 µm. GaN templates were handled in six ways, including as-grown (As sample), (NH4)2Sx treated (S sample), Oxidized (O sample), (NH4)2Sx treated after Oxidized (O-S sample), HF etched after Oxidized (O-HF sample), (NH4)2Sx t
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