Factors affecting the properties of thermally grown oxides on gallium arsenide.

This thesis concerns the growth mechanisms and the physical and electrical properties of dielectric films grown on gallium arsenide in dry oxygen between 350° C and 760° C for times up to 3 hours. Rutherford backscattering of 1.5 MeV helium ions was used to measure the thickness and composition of the films and to ascertain and compare their growth mechanisms on (110) and (100) surfaces of n and p-type bulk and epitaxial material. Metal-oxide-semiconductor (MOS) devices were fabricated from oxidised n-type bulk material and their a. c. and d. c. electrical characteristics were measured at room temperature by capacitance- voltage, capacitance-frequency and voltage-current techniques. Investigations were carried out, also, into the effect on the oxidation rate of implanting foreign ions into the surfaces prior to oxidation. Thirteen species of ions were implanted and, as a result, significant increases and probable reductions in the oxidation rate were obtained. It is shown by the results that native oxides formed thermally on gallium arsenide appear to grow because of indiffusing oxygen reacting with gallium at the substrate-oxide interface. The resulting films consist essentially of but they contain small quantities of arsenic when grown at high temperatures. The growth characteristics of bulk and epitaxial material are similar and do not appear to be affected by the dopant species at the concentrations used in conventional semiconducting material. However, differences between the oxidation rate on (110) and (100) surfaces were observed and are attributed to arsenic outdiffusion and to Strains within the films caused by mismatch between the oxide and substrate lattices. The electrical measurements show that the MOS devices possess field induced hysteresis and small flat band voltages. Their oxide films have breakdown field strengths and dielectric constants which are lower than those of films grown by other methods and which render them unsuitable for use as gate insulators of MOS devices