Title

Theoretical and materials chemistry of some group III and V elements

Date of Award

1993

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

James T. Spencer

Keywords

Chemical vapor deposition, phosphapentaboranes, aluminum, thin films

Subject Categories

Materials Chemistry

Abstract

The theoretical and material aspects of some group III and V compounds have been investigated. Phosphaborane clusters were investigated by modified neglect of differential overlap semi-empirical molecular orbital calculations (MNDO-SCF) to better understand important structural, electronic, and thermodynamic properties of these experimentally difficult species. The structural, thermodynamic and electronic properties of 111 phosphapentaborane cluster compounds have been calculated via MNDO-SCF. The geometry-optimized, minimum energy structures for all of the known and structurally characterized phosphaborane systems have been calculated. In each case, exceptionally good agreement was observed between the experimentally determined and the calculated structural parameters. Calculations for five classes of phosphapentaborane clusters have been completed and have been related to experimentally proposed structural types. Predictions concerning structural and chemical reactivities for unknown and known phosphapentaborane compounds have been made based on these MO calculations.

Production of important thin film materials was discussed relative to chemical vapor deposition (CVD). Advantages of CVD over older thermodynamic deposition techniques were described. The CVD process has been briefly reviewed through seven primary steps. The importance of new source materials which meet stringent industrial requirements have been detailed relative to environmental, occupational safety, and contaminations considerations.

Thin films of pure aluminum, aluminum boride and aluminum oxide have been prepared from the chemical vapor deposition (CVD) of $\rm Al(BH\sb4)\sb3,$ and $\rm AlH\sb2(BH\sb4)\cdot N(CH\sb3)\sb3,$ on both single crystals and thermally sensitive substrates. Films were characterized by EDX, AES, SEM, XRD, and resistivity measurements and ranged in thickness from 500 A to 2 $\mu$m. Each type of film was shown by AES to be compositionally uniform in the bulk sample with only very shallow surface contaminations of oxygen and carbon. Both source compounds were, in general, relatively thermally stable, volatile, air-sensitive liquids, thus providing nearly ideal precursor properties for chemical vapor deposition.

Organophosphorus sources for the chemical vapor deposition (CVD) of indium phosphide have been examined with MNDO-SCF theoretical calculations in order to predict important depositional parameters such as decomposition temperature and temperature selectivities. Decomposition temperatures and temperature selectivities for the three known organophosphorus sources, t-butyl phosphine (TBP), i-butyl phosphine (IBP) and bisphosphinoethane (BPE), have been shown to match MNDO's predicted values, indicating that MNDO can be used as a first test for the suitability of organophosphorus compounds. Optimized depositional parameters for TBP, IBP and BPE were presented. Alternative phosphorus sources with enhanced depositional properties have been identified and analyzed in terms of decomposition temperature and optimized deposition conditions. Cyclohexyl phosphine (PCH) has been used in conjunction with trimethyl indium (TMI) to deposit polycrystalline indium phosphide with no carbon incorporation. Attempted indium phosphide depositions using dichloro-t-butyl phosphine (DCTBP) and TMI yielded both an etching of the InP(100) surface (73.4 A/sec) and polycrystalline $\rm Cu\sb3P.$

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