Mid-Infrared Spectral Photoresponse of Semi-Insulating GaAs

Abstract

AbstractWe have developed a characterization technique using spectral photoconductivity that is capable of identifying deep energy levels in gallium arsenide. Our technique requires less sample processing than deep level transient spectroscopy (DLTS) and can be used on semi-insulating (si) gallium arsenide. The technique uses a mid-infrared fourier transform spectrometer for rapid photoresponse versus wavelength measurements. Using this technique we have observed evidence of several below mid-gap energy levels in undoped si gallium arsenide by the spectral PC technique. Spectral PC measurements were made on si GaAs before and after illuminating the cooled samples with high intensity white light at 8K. The PC spectrum typically showed a broad photoresponse that was attributed to multiple energy levels being present in the material. The observed energy levels were: 0.54 eV, 0.44 eV, 0.25 eV, 0.17 eV, 0.14 eV and ~0.10 eV. The shallow photoresponse from the carbon acceptor was not observed. The most striking spectral feature was a sharp ionization edge at about 0.44 eV in all of the samples studied. This energy level correlates to the 0.43 eV intrinsic defect level that has been observed by temperature dependent Hall effect measurements. The 0.44 eV level was also observed in our PC spectrum of a n-type Bridgman grown sample that had shown the 0.43 Hall effect level. The presence of additional deep levels in concentrations comparable to those of EL2 and carbon indicates that the simple model for compensation in si GaAs which invokes only EL2 and shallow impurities needs revision.