We have used differential reflectance (DR) spectroscopy, an optical modulation technique which does not require external modulation, to characterise bulk semiconductors and semiconductor microstructures. DR signals are the result of inhomogeneities on or below the semiconductor surface. They may be intrinsic, such as alloy fluctuations or layer thickness variations, or externally induced, such as ion implantation, hydrogenation, etc. The DR spectra are similar to spectra measured by other modulation techniques, exhibiting sharp derivative�like lineshapes at photon energies corresponding to the critical point transitions. The magnitude of the DR signal, its position and linewidth can all be used to identify and characterise fluctuations in semiconductor parameters, for example surface electric field, alloy composition, layer thicknesses, etc. It can also be used to monitor surface damage caused by different techniques, such as hydrogenation, reactive ion etching and ion implantation.
Characterisation of Semiconductors by Differential Reflectance Spectroscopy
