Studies of GaAs - oxide interfaces with and without Si interlayer

We have studied the properties of metal-oxide-semiconductor structures fabricated by plasma enhanced 'chemical vapor deposition of Si02 upon GaAs substrates. We have characterized the dependence of these properties upon the presence of a silicon interlayer, the type and the degree of misorientation of the substrate, and the type of plasma enhancement. We conclude that the presence of a silicon interlayer is beneficial for n-type GaAs if the oxide is deposited by a remote plasma technique. For such oxides on n-type GaAs coated with silicon, integration of the quasistatic capacitance curve suggests a band-bending range of 0.6-0.9 V. Also for these samples, we observe a hysteresis of order 0.6 V, and shifts of only 0.2 V in the midpoint of the rise from minimum to maximum capacitance upon changing frequency from 10 to 200 kHz. The benefits of using a silicon interlayer with a direct plasma deposited Si02 film are less evident. It is assumed that much of the improvement of these results arises not from a large reduction of the interface density but rather from a shift of the spectrum towards the conduction band edge. This appears evident from the improvement on n-type samples coincident with a degradation on p-type samples. The total band bending change derived from the integral from the quasi-static capcitance-voltage curves is less sensitive to this interlayer than is the frequency dispersion.