256x256 HgCdTe MWIR array grown on Ge substrates

Abstract

A 256 x 256 IRCMOS array with a 35 micron pitch operating at 77 K in the MWIR range, has been developed using HgCdTe and CdTe layers grown by Molecular Beam Epitaxy (MBE) on a germanium (Ge) heterosubstrate. The CdTe(21 1)B layer is first grown on a 2 inch diameter (2! 1) oriented Ge wafer with a smooth surface morphology and good crystalline quality. The HgCdTe(211)B layer is also grown by M.B.E. on this CdTe/Ge heterosubstrate with the same quality. The material characteristics are detailed. The 256 x 256 photodiode array is made using the standard LETI/LIR planar n-on-p ion implanted technology. At 80 K, photodiodes exhibited an RoA figure of merit higher than 106 Q2 for a cut-off wavelength of 4.8 urn. An NEDT of 6 mK at 80 K was also obtained on the IRCMOS. The electro-optical characteristics of the component are presented and we show that the 256 x 256 component performances using HgCdTe grown on Ge heterosubstrate are comparable for MWIR applications to those obtained on 256 x 256 component using HgCdTe grown on CdZnTe homosubstrate.