Optical Studies of Free and Bound Excitonic States in GaSb Evidence for Deep A⁺‐Complexes

The energies of the free exciton and of four excitons bound to neutral acceptors (A°, X) are determined by either reflection, absorption, or emission with high purity p‐type GaSb. The data give evidence that bound excitons may be described alternatively as an electron bound by a donor‐like A + ‐centre. For one particular deep A + ‐centre, transitions from neutral donor states to that A + ‐centre are observed besides the bound exciton decay. p‐GaSb is especially favourable for observing deep A + ‐centres, because of the position of the Fermilevel. Conditions under which they may be observable for other III–V compounds are discussed.