Recombination Mechanisms in a Type II GaAs/AlGaAs Superlattice

Abstract

A variety of experiments^{1, 2, 3} have shown that the GaAs/GaA1As band offset can be determined optically, with potentially meV resolution, provided type II recombination can be observed. Type II, or cross-interface recombination, can be induced in a GaAs/A1GaAs superlattice of arbitrary composition and periodicity by the application of hydrostatic pressure¹. Figure 1 depicts schematically the band structure of such a superlattice at ambient pressure and at a non-zero pressure above the crossing point to type II behaviour. A typical above-crossing spectrum is displayed in Fig. 2. For pressures larger than the composition and periodicity dependent crossing point the X valley of the AlGaAs, rather than the Γ valley of the GaAs, is the lowest energy conduction-band minimum. The electrons will thus transfer to the AlGaAs while the holes remain in the GaAs. The oscillator strength of the optical recombination of these electrons and holes is very small since the k-space and real space overlaps of these electron and hole wavefunctions are both small. This qualitative arguement is in agreement with the results of a pseudopotential calculation⁴ which predicts a small oscillator strength for the optical type II recombination. Experiments investigating the time-decay and recombination mechanisms of these processes are described below.

Supported in part by ONR under contract N00014-85-C-0868.