Picosecond Measurement of Interband Saturation, Intervalence Band Absorption, and Surface Recombination in Germanium
Description: The picosecond optical response of five thin germanium samples was measured following intense optical excitation using two variations of the excitation and probe technique. Seven-picosecond laser pulses of wavelength 1.054 um were used to measure the optical transmission of the samples for a variety of probe delays, excitation fluences, and sample temperatures. These parametric experiments were performed in an effort to determine if carrier cooling, carrier diffusion, or carrier recombination dominates the carrier dynamics immediately following excitation. The studies of a 5.7 um thick sample indicated that Auger recombination does not dominate the carrier dynamics, but that the carriers most likely cool immediately to within a few optical phonons of the lattice temperature. Lattice heating may also occur depending on excitation level. Neither cooling nor diffusion was ruled out as a major contributor to the transient optical response. A numerical analysis indicated that, although diffusion may be minimized in the thinner samples, the importance of surface recombination increases as the sample thickness decreases. The lattice temperature dependence of the optical transmission was found not to be in disagreement with the known temperature dependence of the low-density diffusion coefficient. Finally, new structure was observed in the data which is consistent with an increased intervalence band absorption at the highest excitation levels.
Date: August 1984
Creator: Perryman, Gary Paul