Relaxation Time of Surface States on Germanium

Abstract

Two types of state exist at the surface of single crystal germanium; the first type, which is assumed to be at the semiconductor-oxide interface, is chiefly responsible for the carrier recombination process, while the second type, associated with the oxide structure and adsorbed ions, is believed to control the position of the Fermi level at the surface with respect to the electron band energy. The latter type of state has been studied by means of the "field-effect," or change in conductance with an applied field perpendicular to the surface. The results indicate that the relaxation or capture time of these states is much longer than that of the interface states, and is also extremely sensitive to surface treatment and ambient gas. In addition, some surface treatments lead to a distribution of time constants on the same surface over a range as large as six decades. Possible physical models for this behavior are discussed as well as its connection with excess or $\frac{1}{f}$ noise.