Improved operability in Hg1-xCdxTe detector arrays

As liquid phase epitaxial (LPE) growth and array fabrication processes have matured to give excellent wafer average performance, the yield limiter for infrared focal plane arrays (IRFPAs), especially large ones, have become o utages. In this work, significant progress has been made in identifying the source and eliminating outages from LPE grown Hg1-xCdxTe P-on-n structures . Historically, studies of the sources of outages have employed defect etch es to look for dislocations and other crystalline defects, and secondary io n mass spectroscopy (SIMS), imaging SIMS, and sputter initiated resonance i on spectrometry (SIRIS) to look for impurities at critical interfaces. Usin g these techniques, trends were established, but direct correlation with ou tages have been observed. In LPE grown materials, where the dislocation den sities are always below 5 x 10(5) cm(-2), and often below 1 x 10(5) cm(-2) on CdZnTe substrates, dislocations only account for a few outages. In order to understand the source(s) of outages, a failure analysis was performed o n several long wavelength IRFPAs. Using a dilute etchant, the metals and th en cap layers of some 64 x 64 pixel IRFPAs which had excellent average perf ormance, but suffered from a high density of pixels with excessive leakage current, were removed. Using a scanning electron microscope with energy dis persive spectroscopy capability, the presence of carbon particles was corre lated with excessive leakage current on a 1:1 pixel basis. A series of expe riments was then conducted which isolated the source of the particles to th e cap layer growth process, which was consequently changed to eliminate the m. The process improvements have reduced the particle density to below the measurement limit of the optical measurement technique implemented to monit or the density of particles on witness wafers. These improvements are resul ting in IRFPAs with significantly improved operability.