The extension and morphological dependence of dislocations on degradation of electrical properties of HgCdTe/CdZnTe detectors
摘要
In small-scale infrared focal plane array (IRFPA) development, material defects, particularly those at the HgCdTe/CdZnTe interface, are major contributors to dead pixels and overall device degradation. This study examines the structural and electrical impacts of these defects, focusing on their extent, density, and morphological variation across HgCdTe epilayers using nanoscale and microscale characterization techniques. Dislocation density at the top surface ranged from 105 to 106 cm−2 across all epilayer types. Near the interface, this increased to 106 in Type I, 5 × 106 cm−2 in Type II, and exceeded 107 cm−2 in Type III. Dislocations' core size was less than or equal to 1 μm in Type I and Type III, and greater than 1 μm in Type II. Electrical properties, including sheet resistivity and carrier concentration, were measured layer by layer at 77 K using the Van der Pauw and Hall Effect methods. A model was developed to illustrate the impact of dislocation density and morphology on electrical and strain properties of the epilayers. Sheet resistivity increased moderately from surface to interface in Type I and Type II (0.8–2 KΩ/square) and more significantly in Type III (4–8KΩ/square). Type I epilayers maintained stable carrier concentrations from 5 × 1015 cm−3–5 × 1016 cm−3, while Type II ranged from 5 × 1015 cm−3–1 × 1018 cm−3 and showed mixed carrier behavior near the interface. Trap density in Type III was 5 × 1015 cm−3, determined by dark current fitting of 50 × 50 µm2 diodes, while Type I and Type II had trap densities of 5 × 1011 cm−3. Diode quality declined when smaller core dislocations, with a density 1 × 107 cm−2 extended up to 5 µm from the interface.