Arthur Monroe Turner

Electrical effects of subgrain boundaries, twins, dislocations, and Te precipitation on long-wavelength IR HgCdTe photodiode arrays

HgCdTe crystals have a high density of intrinsic material defects generated either during the growth process itself or subsequent annealing steps. An understanding of the relationships between these material imperfections and the electrical performance of long-wavelength infrared (LWIR) HgCdTe photodiodes provides guidance in the choice of the growth technique and subsequent processing to minimize electrically detrimental defects. It also sets limits of material perfection required to achieve a specified performance level. Understandings of these relationships have been gained for subgrain boundaries, twins, dislocations, and Te precipitation in LWIR HgCdTe n-on-p photodiodes. Measurements of bias dependent dark current, responsivity, and noise as functions of defect density were performed on both arrays and test structures. This paper emphasizes the direct relationship between material defects and array performance. Wherever possible, the reader is referred to more detailed discussions. All the diodes reported in this study were planar, ion implanted structures using vacancy doped material. All reported measurements were taken at 77 K.

Producibility of Vertically Integrated Photodiode (VIP)tm scanning focal plane arrays

Vertically integrated photodiode, VIPTM, technology is now being used to produce second generation infrared focal plane arrays with high yields and performance. The VIPTM process employs planar, ion implanted, n on p diodes in HgCdTe which is epoxy hybridized directly to the read out integrated circuits on 100 mm Si wafers. The process parameters that are critical for high performance and yield include: HgCdTe dislocation density and thickness, backside passivation, frontside passivation, and junction formation. Producibility of infrared focal plane arrays (IRFPAs) is also significantly enhanced by read out integrated circuits (ROICs) which have the ability to deselect defective pixels. Cold probe screening before lab dewar assembly reduces costs and improves cycle times. The 240 X 1 and 240 X 2 scanning array formats are used to demonstrate the effect of process optimization, deselect, and cold probe screening on yield and cycle time. The versatility of the VIPTM technology and its extension to large area arrays is demonstrated using 240/288 X 4 and 480 X 5 TDI formats. Finally, the high performance of VIPTM IRFPAs is demonstrated by comparing data from a 480 X 5 to the SADA-II specification.