Effects of Laser Irradiation on Growth and Doping Characteristics of GaAs in Chemical Beam Epitaxy
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ABSTRACT In this paper, we report laser-assisted chemical beam epitaxy (CBE) of GaAs using triethylgallium (TEGa), tris-dimethylaminoarsenic (TDMAAs), and an Ar ion laser operating at visible or ultraviolet (UV) wavelength. The laser-assisted growth with TDMAAs, compared to As 4 or AsH 3 , shows a wider range of growth enhancement at low substrate temperatures. Unlike CBE of GaAs without laser irradiation, laser-enhanced GaAs growth rate was found to be constant as the V/III incorporation ratio changes. By using diiodomethane (C12 H2 ) as a dopant gas, the GaAs films with laser irradiation show a much higher hole concentration than those grown simultaneously without laser irradiation at substrate temperatures from 460-530'C. Laser irradiation was also found to enhance silicon incorporation at low temperatures. Photothermal effects are responsible for laser-enhanced growth and silicon doping, but the wider temperature window in laser-enhanced growth and the laser-enhanced carbon incorporation are caused by additional photocatalytic or photochemical effects.
INTRODUCTION Chemical beam epitaxy (CBE), or metallorganic molecular beam epitaxy (MOMBE), has been under active development to exploit the advantages of conventional solid-source molecular beam epitaxy (MBE) and metal-organic vapor phase epitaxy (MOVPE). One of the important issues in CBE is the selective-area growth by direct writing with an external energy source, e.g., an argon ion laser. Studies have shown that laser-assisted CBE has the potential for selective-area growth, etching, doping and compositional change, which could enable us to integrate different materials and structures on the same chip and develop novel devices, e.g., multiple-wavelength lasers [1]. Many studies have reported the selective-area growth of GaAs by laser-assisted CBE or MOMBE using triethylgallium (TEGa) and AsH 3 or As4 [2-7]. However, the temperature window for the selective-area growth is very narrow using AsH 3 or As 4, and hence limits the application. A novel source which could provide a wider temperature window would be desirable. Another issue of great interest is replacing the highly toxic and highly-pressurized AsH 3 with novel organometallic arsenic sources. Trisdimethylaminoarsenic (TDMAAs, As[N(CH 3)2]3), with As directly bonded to N, is a promising substitute to the highly toxic and highly pressurized AsH 3 because of its low but reasonable vapor pressure and low cracking temperature. Since there are no As-H and As-C bonds, one can expect TDMAAs to have lower toxicity and lower carbon incorporation. TDMAAs has also been successfully used in CBE/MOMBE of GaAs [8-11], and AlGaAs [8]. In this paper, we report argon ion laser-assisted CBE of GaAs using TDMAAs. Laser processing also allows selective-area doping without prepatterning. So far, only laserenhanced Si doping into GaAs using Sill4 [12,13] and trimethylsilane [14] has been investigated, but no laser-modified p-type doping has been studied. In this paper we also discuss the laser373 Mat. Res. Soc. Symp. Proc. V
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