Electronic properties of selenium-doped silicon

Abstract

Two dominant selenium-related defects in silicon have been studied by transient capacitance and current techniques. For one of the centers, the A center, Arrhenius plots of thermal emission rates for electrons and holes (log et−1/T) give ’’thermal activation energies’’ of EC −ET =0.52 eV and ET −EV =0.62 eV, respectively. Although the electron-capture cross section of the center is too large to be measured with our equipment, a conservative estimate gives a value larger than 10−14 cm2. The electron-capture cross section σtnB of the other center, the B center, showed a T−3.2 temperature dependence and has a value of 3×10−15 cm2 at 100 K. From the measured data for σtnB and etnB a value of 0.30 eV for the Gibbs free energy of the B center is obtained. This energy value is constant and equal to the enthalpy in the temperature range investigated. Plotting log T2σtnB versus 1/T, an activation energy of 14 meV is obtained. This is interpreted as the energy separation between the lowest state accessible in a cascade capture process and the conduction band. In all samples, the concentrations of the A and B centers are found to be equal.