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

Long wavelength infrared molecular beam epitaxy (MBE) grown p-on-n Hg1-xCdx Te double layer planar heterostructure (DLPH) detectors have been character ized to determine the dominant mechanisms limiting their performance. Mater ial defects have been identified as critical factors that limit 40K perform ance operability. This effort has concentrated on identifying microscopic d efects, etch pit density (EPD) and relating these defects to the device per formance. 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, meas ured 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 re sult 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 cluste r 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 p erformance and high operability for low temperature infrared applications o n MBE grown HgCdTe material.