Measurement of charge-separation potentials in GaAs1−xNx

Abstract

The ternary alloy GaAs1−xNx is interesting as a semiconductor that can be grown epitaxially on GaAs. As is well known, the band gap can be reduced by as much as 0.4 eV by changing the nitrogen concentration from 0% to 3%. We measured the spectral response and photoconductive lifetime of the alloys as a function of temperature. In this work, the films were grown by gas-source molecular-beam epitaxy on semi-insulating GaAs substrates. All measurements were made using the contactless, resonant-coupled photoconductive decay method. Our data show that the spectral response of GaAs1−xNx alloys consists of photoconductive band tails that extend well into the infrared (beyond the nominal band gap). For example, the photoconductive band tails extend to about 1900 nm for GaAs0.967N0.033 at room temperature. The primary photoconductive decay times are in the range of 200–300 ns at room temperature. At temperatures below about 200 K, the decay rate decreases substantially. By plotting the decay rate values on an Arrhenius plot, we calculate activation energies of 70–80 meV for GaAs1−xNx samples with x=1.1%–3.3%. These energies represent potential barriers that inhibit recombination.