Status of the MBE technology at Leti LIR for the manufacturing of HgCdTe focal plane arrays

This paper presents recent developments that have been made in Leti Infrared Laboratory in the field of molecular beam epitaxy (MBE) growth and fabrication of medium wavelength and long wavelength infrared (MWIR and LWIR) HgCdTe devices. The techniques that lead to growth temperature and flux control are presented. Run to run composition reproducibility is investigated on runs of more than 15 consecutively grown layers. Etch pit density in the low 10(5) cm(-2) and void density lower than 10(3) cm(-2) are obtained routinely on CdZnTe substrates. The samples exhibit low n-type carrier concentration in the 10(14) to 10(15) cm(-3) range and mobility in excess of 10(5) cm(2)/Vs at 77 K for epilayers with 9.5 mu m cut-off wavelength. LWIR diodes, fabricated with a n-on-p homojunction process present dynamic resistance area products which reach values of 8 10(3) Ohm cm(2) for a biased voltage of -50 mV and a cutoff wavelength of 9.5 mu m at 77 K. A 320 x 240 plane array with a 30 mu m pitch operating at 77 K in the MWIR range has been developed using HgCdTe and CdTe layers MBE grown on a Germanium substrate. Mean NEDT value of 8.8 mK together with an operability of 99.94% is obtained. We fabricated MWIR two-color detectors by the superposition of layers of HgCdTe with different compositions and a mixed MESA and planar technology. These detectors are spatially coherent and can be independently addressed. Current voltage curves of 60 x 60 mu m(2) photodiodes have breakdown voltage exceeding 800 mV for each diode. The cutoff wavelength at 77 K is 3.1 mu m for the MWIR-1 and 5 mu m for the MWIR-2.