The objective of this task is to evaluate and characterize laser induced processing of semiconductor materials and devices, with emphasis on the III-V compound series. Laser processing comprises three principal phenomena photon absorption, conversion of absorbed photon energy to heat, and material response to the thermal stimulus. We are examining each of these phenomena in detail both theoretically and experimentally. We have developed a model that includes, in addition to normal band-to-band absorption, absorption due to laser generated free carriers. The model assumes that the two effects are additive, and that the band-to-band absorption coefficient is constant and equal to its small signalvalue. We have found that, under these conditions, band-to-band absorption predominates when the laser wavelength is shorter than the bandgap wavelength. We regard the use of the small signal absorption coefficient, however, to be suspect, especially when the laser wavelength is close to the bandgap wavelength.
Semi-annual technical rept. 1 Jun 1978-31 Jul 1979