The electronic structure of indium phosphide surfaces

Indium phosphide (InP) is a member of a group of compounds known as III-V semiconductors. InP's direct band gap and high carrier mobility, approximately twice that of Si, makes it the ideal candidate for the manufacture of electronic devices such as field effect transistors. However, the wide spread use of InP has been restricted by the lack of a suitable compound or native oxide that could be used to form a passivating film on the surface. To date such films have been shown to contain defects within the film or at the overlayer-substrate interface. These defects trap the charge carriers and inhibit the device performance. The trapping states are also known to be formed by the deposition of metals. The main objective of the work described in this thesis was to monitor the change in the electronic structure of n and p-InP under a variety of conditions in order to elucidate the physicochemical origin of the extrinsic surface states. In addition, the properties of some inorganic and organic sulphur compounds were investigated for use as passivating agents with which to form an inert and insulating film on the surface. Some of these compounds were found to have potential for use in the construction of electronic devices. Electrochemical and ultra high vacuum techniques were utilised to monitor the electronic characteristics of the surfaces as a function of oxygen exposure. A simplex curve fitting algorithm was used to fit a model of the electronic structure of the surface to the surface photovoltage spectra. The results are expressed as surface potential curves. In addition to the states tailing into the band gap from the band edges, three midgap states were identified at approximately 0.25, 0.50 and 0.75 of the gap energy. The origin of these surface states was attributed to a disordered surface layer generated by the adsorption processes. A model of the origin and distribution of the surface states is discussed