Developments in MOVPE HgCdTe arrays for passive and active infrared imaging

Abstract

SELEX Galileo Infrared Ltd has developed a range of 3 rd Generation infrared detectors based on HgCdTe grown by Metal Organic Vapour Phase Epitaxy (MOVPE) on low cost GaAs substrates. There have been four key development aims: reducing the cost especially for large arrays, extending the wavelength range, improving the operating temperature for lower power, size and weight cameras and increasing the functionality. Despite a 14% lattice mismatch between GaAs and HgCdTe MOVPE arrays show few symptoms of misfit dislocations even in longwave detectors. The key factors in the growth and device technology are described in this paper to explain at a scientific level the radiometric quality of MOVPE arrays. A feature of the past few years has been the increasingly sophisticated products that are emerging thanks to custom designed silicon readout devices. Three devices are described as examples: a multifunctional device that can operate as an active or passive imager with built-in range finder, a 3-side buttable megapixel array and an ultra-low noise device designed for scientific applications.

LWIR Lateral Effect Position Sensitive HgCdTe Photodetector at 205 K

“…Exemplary 1/f noise calculations for HgCdTe photodiodes were performed, based on McWhorter’s theory [ 29 , 43 , 44 , 45 ] or taking into account carrier mobility/scattering fluctuations [ 38 , 46 ]. The dislocations intercepting the junction were found to induce TAT and 1/f noise and are supposed to cause bandgap narrowing and getter impurities that can act as active trap centers [ 30 , 32 , 38 , 42 , 46 , 47 , 48 ].…”

“…Then, the 1/f noise can be greatly reduced, providing the heteropassivation is applied by interdiffusion between the HgCdTe and the CdTe passivation layer during the high-temperature annealing. High-temperature annealing was also found to inactivate defects and dislocations in the active volume of the detector [ 47 ].…”

Study of HgCdTe (100) and HgCdTe (111)B Heterostructures Grown by MOCVD and Their Potential Application to APDs Operating in the IR Range up to 8 µm

“…As-grown HgCdTe is often limited by the mercury vacancies [ 16 , 17 ], whose concentration can be effectively reduced by the thermal annealing during the controlled cooling after the growth. However, the reverse-bias characteristics of HgCdTe diodes are strongly dependent on dislocations intercepting the junction [ 18 ]. The high dislocation density in HgCdTe alloys grown on GaAs is due to the large lattice mismatch (14%) between CdTe and GaAs.…”