<title>Advanced LWIR HgCdTe detectors for strategic applications</title>

Abstract

The demand for high detectivity LWIR JR focal plane arrays that operate at low backgrounds is shown to drive the HgCdTe technology toward increased detector performance. Reduced operating temperature together with advanced material technology and detector design are presented as solutions. High performance MWIR, MLWJR and LWJR HgCdTe detector test arrays and variable area test structures were recently demonstrated through the joint collaboration of Aerojet Electronic Systems Division and RockwellInternational. These devices are based on the innovative buried planar heterostructure (BPH) detector architecture grown by liquid phase epitaxy of HgCdTe on JI-VI substrates. The major features of the BPH design include planar geometry, heterostructure wide gap p-type on narrow gap n-type HgCdTe and a buried LWJR electrical junction. Excellent 78K median R0A performance across the JR spectrum from 5.2 tm to 12 p.m is reported and shown to follow the diffusion trend line. Excellent 40K median RA performance for devices with cutoffs ranging from 9 im to 19 im are also presented. LWIR RA statistical performance data at both 78K and 40K from fanout test arrays are presented with median RA values of 100 ohm-cm2 at 78K and > 106 ohm-cm2 at 40K for cutoffs of 10.4 .tm and 1 1.4 p.m respectively. The 90% test array operability was found to exceed 5 x iO ohm-cm2 at 40K. Devices with median RAs of 20 ohm-cm2 at 78K and 7 x i05 ohm-cm2 at 40K were measured for cutoffs of 12 jim and 13 im respectively. Uniform and high quantum efficiencies were measured at 40K with a median of 70%. INTRODUCTIONRecent improvements in HgCdTe material and detector technologies have sparked increased interest in the use of high performance HgCdTe photovoltaic detector arrays for both tactical and strategic surveillance systems. HgCdTe focal plane arrays (FPAs) have evolved from small linear photoconductors arrays to relatively large two-dimensional photovoltaic mosaics. Both scanning and staring HgCdTe focal plane configurations with response in the 3-5 or the 8-1 2 tm spectral bands have been demonstrated.Modem HgCdTe FPAs offer significant advantages in such applications as missile seekers, target acquisition sights, infrared search and track, threat warning and surveillance as a result of increased sensitivity, resolution and reduction in system complexity. For tactical arrays that operate at higher JR backgrounds, emphasis on improved performance is being supplanted by emphasis on material parameter repeatability and reduction of manufacturing costs.1 Strategic requirements, however, continue to drive the HgCdTe technology toward extremely high sensitivity and operability to maintain near background limited infrared photodetector (BLIP) for the very low background flux levels encountered in these missions.Infrared strategic surveillance systems have a variety of spectral requirements that span the JR spectrum. Many of the system scenarios desire longer wavelength detectors to maximize signals received from cold targets. Low background applications i...