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Studies toward the development of stable InP insulated gate field-effect transistors Backhouse, Christopher James


Studies of the InP substrate, of dielectrics, and of the dielectric/substrate interfaces were undertaken in order to contribute to the development of stable insulated-gate field-effect transistors (IGFETs). Optical transient current spectroscopy (OTCS) was applied to semi-insulating InP substrates to obtain information on deep levels. A new "isothermal" method of analysis was developed which allowed, for the transient at each temperature, the determination of the parameters describing the transient without needing to use data from transients at other temperatures. This avoided the need for making some assumptions which have been made in previous work. Nine deep levels were found, eight of which had not previously been detected in semi-insulating material. Evidence was found that gold in electrodes reacts with the substrate and introduces deep levels which contribute to instability in the operation of InP IGFETs. Negative transients, where the photocurrent transient increases with time, were observed for the first time in InP. A level associated with Fe was found to exhibit field-enhanced trapping behaviour. Semi-insulating InP was found to be like GaAs in that under high electric fields it exhibits low frequency oscillations due to propagating high-field domains. In previous work with GaAs the temperature dependence of the frequency of these oscillations has been shown to provide information about deep levels. In the present work a modified version of this technique was applied to InP, resulting in the detection of 14 spectral peaks whose activation energies fell into five groups centred at 0.30, 0.39, 0.41, 0.44 and 0.49 eV. It is suggested that these five groups were the contributions of five deep levels, where one level with field-enhanced trapping gave rise to propagating high-field domains, and the occupancies of the remaining four levels were perturbed by the passage of the domains. The strongest spectral peak was found to have an activation energy similar to that found for the Fe level detected in the OTCS analysis, a level which exhibited field-enhanced trapping. Evidence was found that the Fe level may play a role in the instability of IGFETs on semi-insulating InP. Dielectric layers of silicon nitride deposited on InP using a "remote plasma" method were characterised by current and capacitance vs voltage measurements. Although deposited in a manner designed to prevent substrate damage, excessive slow trapping states were observed. Native oxide layers on InP were investigated using ellipsometry and current vs voltage measurements. The native oxide films were produced by furnace oxidation, oxidation under high pressures of oxygen and oxidation under ultraviolet illumination. The ultraviolet oxidations appear to produce an oxide composed of indium phosphate, which has dielectric and interfacial properties that are promising for use in an IGFET. Some of the techniques used in the present work were tested and improved by applying them first to GaAs. Finally, a report is given of some preliminary trials of methods using optical reflectivity and transmission measurements to characterize the IIIV surface and bulk.

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