CdZnTe substrate producibility and its impact on IRFPA yield

The need for cost effective production of HgCdTe infrared detectors and foc al plane assemblies has led to increased attention to the availability of h igh quality large-area CdZnTe substrates. Reasonable yield of large-area su bstrates (greater than or equal to 4 cm x 6 cm format) is necessary for fab rication of focal plane assemblies (FPAs) now in production, and for future infrared (IR) detectors which are growing in size and complexity. Raytheon 's infrared materials producibility (IRMP) program has addressed this issue , after identifying critical drivers of FPA yield coming from substrates, a nd targeted certain improvements in substrate process steps for highest imp act on large-area substrate yield. Three specific areas of improvements in the substrate process were addressed: (1) compounding of a large 6 kg charg e of CdTe; (2) vertical Bridgman growth of 92 mm diameter CdZnTe boules in both quartz and pyrolytic boron nitride (PBN) crucibles; and (3) optimized Cd overpressure control during growth and cool-down of the boule. It was sh own that the Cd overpressure and the cooling schedule had the strongest eff ects on defect populations. The resulting improvements include a 33% increa se in wafer yield per unit starting weight, an estimated 50% reduction in s ubstrate cost per cm(2), better morphology of epitaxial HgCdTe layers, and improved yield of satisfactory IR detectors. The criteria for selecting sub strates have also improved as a result of this work. In addition, photovolt aic detectors were fabricated on wafers from a variety of sources, and test ed. Results compare favorably with those on baseline (earlier process) subs trates.