Investigation of defects influencing performance of type-II InAs/GaInSb superlattice based infrared PIN type photodetectors

We report on an investigation of dark current contributions from common microscale crystallographic defects in type-II InAs/GaInSb superlattice infrared PIN type photodiode structures grown on (100) GaSb substrates and have identified three general classifications. Defects on several wafers of varying design were examined from multiple perspectives to correlate electrical activity with structural properties, to develop the identification and classification scheme. Active defects were first identified by current density vs voltage (J-V) measurements and electron beam induced current (EBIC) scans of individual diodes with micrometer resolution. The EBIC scans were then correlated with plan-view optical and atomic force microscopy images, both before and after anisotropic etch-pit analysis using a newly developed etchant. The atomic scale structure of active and inactive defects was then compared using cross-sectional transmission electron microscopy (TEM) on vertical slices of defects extracted using focused ion beam milling. Analysis of the TEM images yielded important clues as to the structure and root causes of benign and active defects, in which only significant disruptions at the epi-substrate interface appear to play a key role in producing microscale defects that efficiently promote dark current.