Key performance-limiting defects in P-on-N HgCdTe LPE heterojunction infrared photodiodes

The operability of long-wavelength p-on-n double layer heterojunction arrays for 40K low-background applications has long been limited by the wide variation in pixel-to-pixel zero bias resistance (R 0 ) values. Diodes on test structures showing lower performance, with R 0 values below 7 x 106 ohm at 40K, usually contained gross metallurgical defects such as dislocation clusters and loops, pin holes, striations, Te inclusions, and heavy terracing. However, diodes with R 0 values between 7 x 106 and 1 x 109 ohm at 40K contained no visible defects. To study the "invisible" performance-limiting defects (i.e. defects that cannot be revealed by etching), a good correlation between the dynamic resistance at 50 mV reverse bias (R50) value at 77K and the R 0 value at 40K was first established, and then used as a tool. The correlation allowed measurements of a large number of devices at 77K, rather than relying exclusively on time-consuming measurements at 40K. Interesting results regarding R 0 values at 40K, such as insensitivity to low-density dislocations, mild degradation from Hg vacancies, severe degradation from Hg interstitials, and correlation with junction positioning, were obtained from specially designed experiments.