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The program is intended to develop the metalorganic chemical vapor deposition (MO-CVD) process for growth of InP films using triethylindium (TEI) and phosphine (PH/sub 3/) reactants in a H/sub 2/ carrier gas, and then to prepare such films on inexpensive substrate materials for subsequent fabrication of heterojunction polycrystalline solar cells by deposition of CdS (or other semiconductor) on the InP. Minor changes in reactor design have permitted achievement of InP film growth rates up to four times larger than those previously obtained. Deposition conditions have been established for obtaining good-quality undoped n-type epitaxial InP films on single-crystal (111A) and (111B) InP substrates, and p-type Zn-doped epitaxial InP films have been produced on both GaAs and InP single-crystal substrates, with doping concentrations in the 10/sup 16/-10/sup 18/ cm/sup -3/ range. Experiments have continued on the growth of polycrystalline InP films on various low-cost substrates, including several glasses, metals and metal alloys, and intermediate layers of metals and semiconductors previously deposited on glass substrates; a wide range of InP film properties has been obtained in these studies, results of which are summarized. Experimental Schottky-barrier device structures, employing thin Au barrier layers, have been fabricated on p-type InP films prepared in various single- and multiple-layer configurations. Detailed characterization of the transport properties in both undoped n-type epitaxial InP films on GaAs : Cr and InP : Fe semi-insulating substrates and Zn-doped p-type epitaxial films on GaAs : Cr substrates is presented and discussed. The first heterojunction photovoltaic solar cell employing a vacuum-deposited n-type CdS film and an epitaxial p-type InP film grown by MO-CVD has been fabricated and characterized.
Plans for the six main technical tasks of this 12-month program are discussed and the activities of the first three months are summarized. A new reactor system for growing thin films of InP by the metallorganic-hydride chemical vapor deposition (MO-CVD) process has been completed. Experiments using triethylindium (TEI) and phosphine (PH/sub 3/) reactants in a H/sub 2/ carrier gas have shown that InP films can be successfully grown over a range of deposition temperatures. Epitaxial growth of single-crystal films has been obtained on at least two different crystallographic orientations of single-crystal GaAs at temperatures as low as approximately 525/sup 0/C, and there is evidence that the process can be utilized at even lower temperatures--perhaps below approximately 475/sup 0/C. Films not intentionally doped are n type, with measured carrier concentrations in the 10/sup 16/ cm/sup -3/ range and electron mobilities up to approximately 2000 cm/sup 2//V-sec (room temperature). Initial investigations involve single-crystal substrates (GaAs, sapphire, InP) but various low-cost materials--glasses, alumina ceramics, metals, and certain composites of these--are being selected and evaluated for subsequent use in the program. Specific candidate materials are discussed. The program also involves the formation and evaluation of heterojunction photovoltaic device structures using the InP layers formed by MO-CVD and deposited films of CdS, ZnCdS, and similar II-VI compounds and alloys; this work is done at Stanford University. During the first quarter, two techniques for producing ohmic contacts of Au/Zn/Au on p-type InP were successfully developed, with low contact resistances being achieved following annealing in H/sub 2/ at temperatures up to 475/sup 0/C. Planned work for the next quarter is outlined.