GaN1−xSbx highly mismatched alloys grown by low temperature molecular beam epitaxy under Ga-rich conditions

The electronic structure of the conduction and valence bands of highly mismatched alloys (HMAs) such as GaN1−xSbx are well described by the band anticrossing model. The properties of this alloy, which has a large band gap range and controllable valence band positions, make it a candidate material for efficient solar energy conversion devices. We have examined the growth and structural properties of amorphous and crystalline GaN1−xSbx. These HMAs were grown by low temperature molecular beam epitaxy (MBE) under Ga-rich conditions. While there is a monotonic linear increase of Sb incorporation with Sb overpressure, there was no obvious dependence of Sb incorporation with growth temperature for the range of 10-470 °C. At growth temperatures lower than 100 °C, GaN1−xSbx HMAs lose crystallinity and become amorphous for Sb compositions at or exceeding ~5%. Ga-rich growth resulted in strong absorption at energies as low as 1 eV for GaN1−xSbx alloys of all compositions. The strong low energy absorption may arise from a Ga-related defect band.