Laser Stimulated Deposition of GaAs, GaAsP and GaAsP-GaAs Superlattices
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LASER STIMULATED DEPOSITION of GaAs, GaAsP and GaAsP-GaAs SUPERLATTICES
N.H. KARAM*, S.M. BEDAIR*, N.A. EL-MASRY** AND D. GRIFFIS** * Dept. of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695-7911 "**Dept. of Materials Engineering, North Carolina State University Raleigh, North Carolina 27695
ABSTRACT
An Ar+ ion laser has been used for direct writing of GaAs and GaAsP single crystal films on thermally biased GaAs substrates. Multiple scanning of the laser beam at speeds in the range 100-200 urm/s at carefully selected growth conditions resulted in single crystalline selectively deposited films. Photoluminescence indicates that these deposited films have optical properties that are comparable with the conventionally (MOCVD) grown material. Laser beam irradiation has been used to form a superlattice (SL) structure which has been demonstrated in the GaAsP-GaAs system. When a GaAs substrate is exposed to fluxes of AsH 3, PH3 and TMG at 500'C, only GaAs will be deposited because of the insufficient cracking of PH 3 . However, localized laser heating results in GaAsP deposition. A GaAsP-GaAs superlattice with a period of about 400 X&has been synthesized. This laser induced technique can thus have potential applications in the generation of abrupt interfaces without the use of shutters as in MBE or gas switching as in MOCVD.
INTRODUCTION
Laser chemical vapor deposition (LCVD) is a powerful tool that has promising potential in selective epitaxy of optical and electronic devices. Infrared (IR) and visible lasers have been used to induce pyrolytic deposition [1-7]. In this case the focused laser beam creates a hot spot on the substrate where deposition occurs. Direct-writing is achieved by scanning the laser beam relative to the substrate. Recently, successful deposition of GaAs on GaAs and Si wafers has been reported [2-7] using an Ar+ ion laser. Unlike pyrolytic LCVD, photolytic deposition may be induced by UV lasers (8-10] where the reactants are absorbent to the laser power. An ArF excimer laser has been used to deposit InP on GaAs, InP and quartz substrates [8].
Mat. Res. Soc. Symp. Proc. Vol. 75. 11987 Matenals Research Society
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Recently, the first direct-writing of single crystalline GaAs and its alloys with P has been reported by the authors [4,6] using an Ar+ ion laser. In this paper we demonstrate the potential of the multi-scan technique introduced earlier [4,6], in producing better GaAs and GaAsP LCVD on GaAs substrates. We also report preliminary results of the first laser beam induced strained layer superlattice demonstrated in the GaAs-GaAsP system.
EXPERIMENTAL
The experimental set-up for LCVD is illustrated schematically in Figure 1. The experiment was carried out in a specially designed vertical MOCVD system operated at atmospheric pressure and has been previously described [5, 6]. GaAs substrates
Figure 1. Schematic diagram of a laser chemical vapor deposition apparatus.
oriented 2' off the towards were irradiated with an Ar+ laser. The las
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