Picosecond OMVPE GaAs/SiO2photoconductive devices and applications in materials characterization

Preliminary experiments utilizing thin polycrystalline OMVPE GaAs/SiO2films have resulted in photoconductive detectors with sampling oscilloscope limited responses of 35 ps (FWHM), and signal levels exceeding 1.0 V into a 50 Ω load. To our knowledge these are the largest sampling oscilloscope limited responses ever reported for thin film polycrystalline semiconductor photodetectors. This photoconductor was then utilized as a pulsed electrical bias to neutralize the effects of dielectric relaxation evident in simple evaporated metal contacts on crystalline semiconductors. This approach was successfully taken with the more difficult case of low dark resistivity (3000 Ω . cm), low dislocation density (0-5 cm^-2) Si, which is expected to have a dielectric relaxation time in the picosecond time scale. This opens up the use of picosecond time resolved photoconductivity as a sensitive probe of dislocations present in OMVPE and MBE single crystal semiconductor films deposited on lattice mismatched substrates, without special metallization processing.