Density of states and relaxation spectra of etched, H-terminated and naturally oxidized Si-surfaces and the accompanied defects

A new contactless method, the modulation CV-technique, is described which allows a very sensitive determination of surface and interface state densities as well as the complete dispersion behaviour of these states. With chemical H-termination surface state distributions may be achieved which are comparable to the best thermally oxidized surfaces. The comparison of these two surfaces shows: Though these surfaces have the same distribution of interface traps Dit, they have a remarkable difference in the relaxation behaviour. The characteristic relaxation times are one to two orders of magnitude lower for thermally oxidized surfaces than for H-terminated ones. This is a hint that the matrix elements which determine the interaction with the bands are different in the two different cases. The natural oxidation of H-terminated surfaces shows a quite different behaviour than thermal oxidation: Peaked defect groups which are related to O-back-bonded Si-dangling-bonds grow and disappear during the first stages of oxidation. This is a hint to ordering processes during oxidation in addition to defect creation during growth. These results supplement the general understanding of growth mechanisms. The appearing defects during all treatments may be put into three categories: (1) normally distributed defects (Gaussian distribution); (2) reconstruction defects; (3) Boltzmann-distributed defects.