Confocal Micro-PL Mapping of Defects in CdTe Epilayers Grown on Si (211) Substrates with Different Annealing Cycles

Abstract

We have applied confocal microphotoluminescence (μ-PL) microscopy to investigate the effects of extended defects in CdTe epilayers grown on (211) Si substrates with different numbers of annealing cycles N. Our results show that the PL dark spot density (PL-DSD) decreases while the spatially averaged PL intensity increases with increasing number of annealing cycles. This is consistent with the general trend that an increase in the number of annealing cycles leads to a reduction of the x-ray diffraction linewidth and etch pit density (EPD). However, direct comparison between the etch pits, imaged by scanning electron microscopy, and PL dark spots on the same sample area results in two important observations: (1) the PL-DSD is substantially higher than the EPD, and (2) not all etch pits appear as dark spots in PL maps. These findings suggest that PL mapping is a more sensitive technique for revealing the extended defects that are actually detrimental to photogenerated carriers, in addition to the apparent advantages of being noninvasive and more efficient.