A new optical temperature measurement technique for semiconductor substrates in molecular beam epitaxy

A new optical temperature measurement technique for use in molecular beam epitaxy is demonstrated with GaAs substrates. The temperature of the semiconductor is inferred from its band gap, which is measured by the diffuse reflectivity of the substrate that is textured on the back surface. The method has a sensitivity of better than 2 °C, and an absolute accuracy limited by the accuracy with which the band gap is known as a function of temperature. It was found to be necessary to calibrate the measurement technique with a thermocouple in contact with the sample in order to achieve satisfactory accuracy at high temperatures. Measurements of the optical absorption edge of GaAs, show that the slope of the Urbach edge is independent of temperature from room temperature to 450 °C.