Noncontact Observation of Microdefects in N-GaAs Wafers by Photo-Thermal-Radiation and Photoluminescence Microscopy

Correlation between the distributions of nonradiative microdefects and dislocations in a Si-doped n-GaAs wafer has been investigated with a photothermal-radiation (PTR) microscope. We measured the PTR image with the wavelength of excitation light fixed at 895nm, and compared the PTR image with the dislocation-density distribution. The PTR image shows negative correlation with the dislocation-density profile. The PTR signal apparently originates from the nonradiative microdefects generated dominantly in the low-dislocation-density regions. The effect of annealing on the microdefects in the Si-doped n-GaAs wafers has been investigated with the PTR and photolurninescence(P1) microscope. We found that the PTR intensity decreases after annealing, while the PL intensity increases. Upon etching of the surface, the PL intensity decreases but the PTR intensity shows no appreciable change.