Observation of Optical Orientation of Equilibrium Electrons in N-Type Semiconductors

Abstract

The first experiments on optical orientation of free carriers in semiconductors were performed recently [1– 5]. Since holes usually do not become oriented in the valence band, owing to rapid relaxation of their spins [6], most experiments were performed on p-type materials and the oriented carriers were the electrons propelled into the conduction band by circularly polarized light. Thus, only the spins of non-equilibrium carriers were oriented, a phenomenon analogous to the optical orientation of excited gas atoms [7]. However, we have previously observed [3] optical orientation also in n-type material. We show in the present paper that this phenomenon is due to optical orientation of equilibrium electrons, i.e., the orientation is realized in the ground state, in analogy with “optical pumping” of atoms [7].