Characterization of Excimer Laser Deposited Gaas Films From the Photolysis of Trimethylgallium and Trimethylarsine At 19
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CHARACTERIZATION OF EXCIMER LASER DEPOSITED GaAs FILMS FROM THE PHOTOLYSIS OF TRIMETHYLGALLIUM AND TRIMETHYLARSINE AT 193 nm V. R. MCCRARY, V. M. DONNELLY, D. BRASEN, A. APPELBAUM AND R. C. FARROW. AT&T Bell Laboratories, Murray Hill, New Jersey 07974 ABSTRACT The growth of GaAs thin films from the excimer laser photolysis of trimethylarsine (TMAs) and trimethylgallium (TMGa) at 193 nm is reported. Scanning electron microscopy (SEM), electron channeling, Rutherford backscattering spectroscopy (RBS), transmission electron microscopy (TEM), and Auger electron spectroscopy (AES) were used to characterize the films. Incident laser fluences on the surface of 0.096-0.115 J/cm 2 lead to carbon desorption, adatom mobility, transient annealing and hence epitaxial growth. However, TEM micrographs also revealed the growth of GaAs twins along the direction in a novel periodic fashion, with a spacing equal to that of the ArF excimer laser wavelength (193 nm). Time-resolved mass spectrometry, used to determine gas-phase photolysis products created during the deposition process, showed that AsCH3 and higher gallium-alkyls are significant products which transport As and Ga to the surface. INTRODUCTION Previously, we reported the growth of polycrystalline GaAs thin films from the excimer laser photolysis of trimethylarsine (TMAs) and trimethylgallium (TMGa) at 193 nm [1]. Layers were deposited on (100) silicon and GaAs substrates with estimated laser fluences at the surface ranging between 0.052-0.084 J/cm2 (N.B. The fluences reported in previous studies [1,2], have been multiplied by 1.28 to reflect a more accurate absolute calibration obtained in the current study). Though the films were stoichiometric, they did contain 1-3 atomic percent carbon contamination. However, the laser fluences mentioned above were insufficient to reduce carbon levels in the film to below 1% and were not adequate to promote epitaxial growth. This is contrary to what was observed in the excimer laser deposition in InP, where carbon levels were well below 1% and epitaxial films were grown at incident fluences of -0.13 J/cm2 [2]. Based on the InP results, we attributed the lack of epitaxy and high carbon levels in our early GaAs films to insufficient laser fluences at the surface [1]. In the present work, we have broadened the scope of the previous investigation and present preliminary characterization of epitaxial GaAs films grown by this combined photochemical and photothermal technique.
EXPERIMENTAL PROCEDURE The deposition system has been described in detail elsewhere [1]. Briefly, the reactor was an all-stainless steel, multiport chamber which was evacuated by a liquid nitrogen-trapped diffusion pump to a base pressure of 1 x 10-7 torr. During the deposition process, the diffusion pump was valved
off and the reactive carrier gases were pumped away by a mechanical pump.
Welded stainless steel lines transported TMGa and TMAs through a manifold where they were mixed with a helium carrier, and directed onward to the reactor. Hydrogen was flowed over th
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