Molecular beam epitaxy (MBE) growth of HgCdTe on large-size Si (211) and CdZnTe (211)B substrates is critical to meet the demands of extremely uniform and highly functional third-generation infrared (IR) focal-panel arrays (FPAs). We have described here the importance of wafer maps of HgCdTe thickness, composition, and the macrodefects across the wafer not only to qualify material properties against design specifications but also to diagnose and classify the MBE-growth-related issues on large-area wafers. The paper presents HgCdTe growth with exceptionally uniform composition and thickness and record low macrodefect density on large Si wafers up to 6-in in diameter for the detection of short-wave (SW), mid-wave (MW), and long-wave (LW) IR radiation. We have also proposed a cost-effective approach to use the growth of HgCdTe on low-cost Si substrates to isolate the growth-and substrate-related problems that one occasionally comes across with the CdZnTe substrates and tune the growth parameters such as growth rate, cutoff wavelength (k cutoff ) and doping parameters before proceeding with the growth on costly large-area CdZnTe substrates. In this way, we demonstrated HgCdTe growth on large CdZnTe substrates of size 7 cm · 7 cm with excellent uniformity and low macrodefect density.
This paper presents the status of HgCdTe growth on large-area Si and CdZnTe substrates at Raytheon Vision Systems (RVS). The different technological tools that were used to scale up the growth from 4 inch to 6 inch diameter on Si and from 4 cm 9 4 cm to 8 cm 9 8 cm on CdZnTe without sacrificing the quality of the layers are described. Extremely high compositional uniformity and low macrodefect density were achieved for single-and two-color HgCdTe layers on both Si and CdZnTe substrates. Finally, a few examples of detector and focal-plane array results are included to highlight the importance of high compositional uniformity and uniformly low macrodefect density of the epitaxial layers in obtaining high operability and low cluster outages in single-and two-color focal-plane arrays (FPAs).
Small 15 lm unit-cell mid-wavelength infrared (MWIR) detectors have been fabricated and characterized at Raytheon Vision Systems (RVS) to enable the development of high resolution, large format, infrared imaging systems. The detectors are fabricated using molecular beam epitaxy (MBE) grown 4-in. HgCdTe-on-Si wafers with a p-on-n double layer heterojunction (DLHJ) device architecture. Advanced fabrication processes, such as inductively coupled plasma (ICP) etching, developed for large format MBE-on-Si wafers and 20 lm unit-cell two-color triple layer heterojunction (TLHJ) focal plane arrays (FPAs) have been successfully extended and applied to yield high performance 15 lm unit-cell single color detectors that compare favorably with state-of-theart detectors with larger pitch. The measured 78 K MWIR cut-off wavelength for the fabricated detectors is near 5.5 lm, and the current-voltage characteristics of these devices exhibit strong reverse breakdown and RoA performance as a function of temperature with diffusion limited performance extending to temperatures down to 120 K.
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