Effects of radiation damage in semiconductors using picosecond compressional waves

Coherent acoustic phonon (CAP) interferometery is an ultrafast pump-probe optical technique wherein a traveling nano-acoustic wave samples, layer by layer, the properties of thin film heterostrucutres or nanostructured materials. Here we use sensitivity of the CAP technique to analyze the effects of extended ion irradiation in GaAs wafers. During ion irradiation multiple defects are created per ion, resulting in a continuous Gaussian-like damage profiles with full widths on the order of 500nm. The presence of such defects acts to modify local wavefunctions, resulting in degradation of the optoelectronic properties. We present results wherein (a) quantitative defect concentration profiles are measured as a function of depth, and (b) the severity of the electronic structure modifications in GaAs are measured as a function of defect concentration. The former represents a novel characterization technique with sensitivity and depth limits surpassing current techniques, while the latter represents unique measurements of the band structure in radiation damaged GaAs.