DETECT DENSITY-MEASUREMENTS OF LOW-TEMPERATURE-GROWN MOLECULAR-BEAM EPITAXIAL GAAS BY PHOTOTHERMAL DEFECTION SPECTROSCOPY

The subgap optical absorption of GaAs layers grown by low temperature molecular beam epitaxy is measured by photothermal deflection spectros copy (PDS). The absorption increases as the growth temperature decreas es at a fixed wavelength. Defect densities evaluated from the absorpti on spectra and the known absorption cross sections are between 10(18) and 10(19) cm(-3). It is shown that complementary PDS phase spectra ca n be used to separate the absorption of the epitaxial layers from the bulk. (C) 1995 American Institute of Physics.