Diffuse optical reflectivity measurements on GaAs during molecular-beam epitaxy processing

In situ measurements of the diffuse and specular reflectivity of GaAs substrates in molecular-beam epitaxy show that the GaAs surface roughens during thermal desorption of the oxide and smooths during the growth of a buffer layer. The diffuse reflectivity increases abruptly over a temperature interval smaller than 0.4 °C as the oxide desorbs. This provides a convenient optical signature for determining when the substrate is clean. The oxide desorption temperature and the amount of surface roughening both increase with the thickness of the oxide. The decrease in the diffuse reflectivity during the growth of the buffer layer is not monotonic, showing instead an oscillatory behavior.