Photoluminescence Intensity Enhancement of GaAs by Vapor-Deposited GaS: a Rational Approach to Surface Passivation
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PHOTOLUMINESCENCE INTENSITY ENHANCEMENT OF GaAs BY VAPORDEPOSITED GaS: A RATIONAL APPROACH TO SURFACE PASSIVATION PHILLIP P. JENKINSt ALOYSIUS F. HEPP,t* MICHAEL B. POWER,tt, ANDREW N. MACINNES,tt,tt AND ANDREW R. BARRONtt,* tSverdrup Technology, Inc., Lewis Research Center Group, 2001 Aerospace Parkway, Brook Park, OH 44142 tNational Aeronautics and Space Administration, Lewis Research Center, MS 302-1, Cleveland, OH 44135. ttDepartment of Chemistry and Materials Research Laboratory, Harvard University, Cambridge, MA 02138. ttGallia, Inc., 53 Beaver Rd., Weston, MA 02193
ABSTRACT A two order-of-magnitude enhancement of photoluminescence intensity relative to untreated GaAs has been observed for GaAs surfaces coated with chemical vapor-deposited GaS. The increase in photoluminescence intensity can be viewed as an effective reduction in surface recombination velocity and/or band bending. The gallium cluster [(t-Bu)GaS]4 was used as a single-source precursor for the deposition of GaS thin films. The cubane core of the structurally-characterized precursor is retained in the deposited film producing a cubic phase. Furthermore, a near-epitaxial growth is observed for the GaS passivating layer. Films were characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectron and Rutherford backscattering spectroscopies.
INTRODUCTION Gallium arsenide and related III-V compound semiconductors have the potential to be widely used in high-speed electronics and optoelectronics due to their direct bandgap and high electron mobility. However, nonradiative recombination due to surface states considerably reduce the efficiency of II-V materials as charge carrier devices. Control of surface chemistry is critical for the realization of commercial GaAs devices. Chemical and photochemical passivation of GaAs by group VI compounds has been an area of intense activity. 1-13 3 2 Solution- or gas-phase reactions with compounds such as H2 S,l Na 2 S, (NH 4 ) 2 S, 5 6 7 8 Na 2 Se,a P 2S 5 , As 2 S3, organothiols, and elemental Se and Te have all been shown to generate passivating layers on GaAs surfaces. Other techniques include deposition of GaSe by molecular beam epitaxy 9 and of sulfide layers by electrodeposition.10 The passivating effects of these sulfurizing and related treatments are often attributed to the formation of either Ga-S or As-S bonds terminating at the GaAs surface." Although these passivating effects are often comparable to an ideal AIGaAs/GaAs interface, 7 they are unstable under normal laboratory conditions presumably due to oxygen 2adsorption and/or atmospheric hydrolysis and subsequent degradation of the sulfur layer.' Several workers have concluded that a chemical vapor deposition (CVD) route to gallium sulfide should be the ideal solution to the passivation of GaAs surfaces. 15 With this goal in mind, several of us recently reported' 4 the deposition of GaS thin films by metal organic chemical vapor deposition (MOCVD) using the single-source precursor, [(t-Bu)GaS] 4 , [(t-Bu) = C(CH
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