Pyrolysis Studies of Single-Source Precursors to Gallium Phosphide
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PYROLYSIS STUDIES OF SINGLE-SOURCE PRECURSORS TO GALLIUM PHOSPHIDE KENNETH E. LEE*, CHARLOTTE K. LOWE-MA, AND KELVIN T. HIGA Research Department, Chemistry Division, Naval Air Warfare Center, Weapons Division, China Lake, California 93555
ABSTRACT
New dialkylgallium dialkylphosphide compounds having the formula [(tBu)(R)GaPR' 2 ]n (R = t-Bu, Me 3 SiC=C; R' = t-Bu, i-Pr, Et; n = 1, 2) were recently prepared and characterized. When R = R' = t-Bu, the compound is a low melting, monomeric solid. The other compounds are dimeric solids with the unsymmetrical acetylides occurring as cis and trans isomers. Polycrystalline gallium phosphide was deposited from these sources on silicon at low pressure (0.05-0.1 Torr) and low temperature (350-600 'C) in a horizontal OMVPE reactor. The film growth was monitored by a residual gas analyzer and the by-products were trapped (N 2 (0)) to be later analyzed by 1H and 13 C NMR. The deposited films were characterized by Raman spectroscopy, X-ray powder diffraction, and Auger emission spectroscopy.
INTRODUCTION Gallium phosphide (GaP) semiconducting films have important applicadevices', highly efficient solar cells 2 , multicolor light tions in power conversion emitting diodes 3 , optical window materials 4 a, near UV photodetectors', and infrared detector materials. 4 b,5 Interest in developing different source compounds for the metalorganic chemical vapor deposition (MOCVD) of GaP films has been driven by the desire for higher purity films, a reduction in risk of exposure to toxic precursors, a reduction of the air-sensitivity of sources, and lowered deposition temperatures. 6 To address these concerns, dialkylgallium dialkylphosphide (R2 GaPR 2 ) single-source precursors have been proposed in which a covalent Ga-P bond is already present.6 ,7 It has been demonstrated that lower film growth temperatures can be achieved with precursors having p-hydrogens which facilitate hydrocarbon elimination. 6 Efficient hydrocarbon elimination during the film growth process provides deposited materials that are low in carbon contamination. Thus, source compounds featuring Et, i-Pr, and t-Bu alkyl groups are of interest. For example, epitaxial films of gallium arsenide (GaAs) have been deposited at low temperature (475-550 'C) from the dimeric singlesource precursor [Me 2 GaAs(t-Bu) 21 2.8 Attempts at depositing films of GaP from single-source precursors have also been reported. 7 a,9 In this paper, we report the deposition of polycrystalline gallium phosphide films from the single-source precursors [(t-Bu)(R)GaPR' 2]n (R= t-Bu, Me 3 SiC-C; R' = t-Bu, i-Pr, Et; n = 1, 2). 1 The depositions were monitored by a residual gas analyzer and the hydrocarbon by-products were determined by 1H and 13 C NMR. The deposited films were characterized by Raman spectroscopy, X-ray powder diffraction, and Auger emission spectroscopy (AES). Mat. Res. Soc. Symp. Proc. Vol. 282. 01993 Materials Research Society
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EXPERIMENTAL
A schematic of the CVD apparatus used for the depositions is shown in Figure 1. The mass
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