Optical absorption edge of semi-insulating GaAs and InP at high temperatures

The temperature dependences of the optical absorption edges of semi-insulating GaAs and InP have been measured from room temperature to 905 °C and 748 °C, respectively, with accuracies of ±1 °C at room temperature and ±5 °C at 900 °C. The temperature dependence of the optical absorption edge is adequately reproduced by an Einstein model although the Varshni model gives an improved fit to the band gap. Finally, the widths of the absorption edges are correlated with ionicity.