A proposed mechanism for radiative recombination through surface states on InP

Recombination involving radiative surface states on InP has been studied in detail by low-temperature photoluminescence. A variety of surface treatments, including etching in HF-based solutions, is found to give rise to a luminescence band located between 1.1 and 1.4 eV, depending on bulk properties of the sample. A model is presented which attributes this emission band to recombination from the bulk conduction band and bulk neutral donors to surface states distributed from the valence band to at least 300 meV into the band gap. The peak emission energy depends on the occupancy of these surface states and is governed by the position of the quasi-Fermi level for holes at the surface. This model is shown to account for the properties of this luminescence band as a function of temperature, excitation power density, and substrate doping type.