PROGRESS IN CDZNTE SUBSTRATE PRODUCIBILITY AND CRITICAL DRIVERS OF IRFPA YIELD ORIGINATING WITH CDZNTE SUBSTRATES

With the goal of maximizing the yield of infrared focal plane arrays ( IRFPAs), Santa Barbara Research Center's (SBRC) Infrared Materials Pro ducibility Program (IRMP) has focused on assessing and improving the q uality, yield, and throughput of CdZnTe substrates. A baseline detecto r lot was fabricated to identify the critical drivers of IRFPA yield c oming from the substrates and to evaluate the quality and yield of the current vendor base for CdZnTe substrates. Substrate induced defects and impurities that call potentially affect device performance and ope rability were carefully mapped out in detail on 44 x 67 mm(2) size sub strates, received fi om IRMP substrate vendors as well as SBRC. This p aper will report on the correlations found between this substrate char acterization data base and the IRFPA level defect distributions. Key r esults from these correlation studies are: (1) extended defects found on the substrates with the Nakagawa etch correlated well with responsi vity reduction in the final IRFPA; (2) cross-hatch patterns that were evident in the responsivity map correlated well with similar features seen by x-ray topography on LPE double layers; and (3) a possible corr elation of device performance (leakage current at 78K) with copper and lithium impurities in the substrate. Recent initiatives toward improv ing the quality and yield of the substrate growth process have focused on improving purity in the pre-growth charge preparation, modificatio n of growth parameters to reduce defects and scaling up of the vertica l Bridgman growth process from its current 67 mm diameter boule size t o 92 mm diameter boules. Promising initial results from the large diam eter boule growth process will be shown. The 92 mm diameter CdZnTe bou le (6 kg charge) shows two predominant single crystal grains encompass ing 75% of boule volume. Defect characterization of boules grown under baseline and modified conditions is discussed.