Microscopic defects on MBE grown LWIR Hg1-xCdxTe material and their impact on device performance

Long wavelength infrared molecular beam epitaxy (MBE) grown p-on-n Hg1-xCdxTe double layer planar heterostructure (DLPH) detectors have been characterized to determine the dominant mechanisms limiting their performance. Material defects have been identified as critical factors that limit 40K performance operability. This effort has concentrated on identifying microscopic defects, etch pit density (EPD) and relating these defects to the device performance. Visual inspection indicates defect densities as high as 10(5) per cm(2) with a spatial extent as observed by atomic force microscope in the range of micrometers extending several micrometers beneath the surface. At high EPD values (greater than low 10(6) cm(-2)) zero bias resistance (R-o) at 40K decreases as roughly as the square of the EPD. At 78K, however, measured R-o is not affected by the EPD up to densities as high as mid-10(6) cm(-2). Visual defects greater than 2-3 mu m in size (void defects) always result in a cluster of etch pits. Visual defects less than similar to 2 mu m in size (micro-void defects) result in either a single etch pit or a cluster of etch pits. Large variations in a cross-wafer etch pit distribution are most likely a major contributor to the observed large spreads in 40K R-o. This study gives some insight to the present limitation to achieve higher performance and high operability for low temperature infrared applications on MBE grown HgCdTe material.