Microscopic defects on MBE grown LWIR Hg_1−xCd_xTe material and their impact on device performance

Abstract

Long wavelength infrared molecular beam epitaxy (MBE) grown p-on-n Hg_1−xCd_xTe 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 10⁵ per cm² 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 10⁶ cm⁻²) zero bias resistance (R₀) at 40K decreases as roughly as the square of the EPD. At 78K, however, measured R₀ is not affected by the EPD up to densities as high as mid-10⁶ cm⁻². Visual defects greater than 2–3 µm than ∼2 µm 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 R₀. 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.