Long wavelength infrared, molecular beam epitaxy, HgCdTe-on-Si diode performance

Abstract

In the past several years, we have made significant progress in the growth of CdTe buffer layers on Si wafers using molecular beam epitaxy (MBE) as well as the growth of HgCdTe onto this substrate as an alternative to the growth of HgCdTe on bulk CdZnTe wafers. These developments have focused primarily on mid-wavelength infrared (MWIR) HgCdTe and have led to successful demonstrations of high-performance 1024 ϫ 1024 focal plane arrays (FPAs) using Rockwell Scientific's double-layer planar heterostructure (DLPH) architecture. We are currently attempting to extend the HgCdTe-on-Si technology to the long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) regimes. This is made difficult because the large lattice-parameter mismatch between Si and CdTe/HgCdTe results in a high density of threading dislocations (typically, Ͼ5E6 cm Ϫ2 ), and these dislocations act as conductive pathways for tunneling currents that reduce the R o A and increase the dark current of the diodes. To assess the current state of the LWIR art, we fabricated a set of test diodes from LWIR HgCdTe grown on Si. Silicon wafers with either CdTe or CdSeTe buffer layers were used. Test results at both 78 K and 40 K are presented and discussed in terms of threading dislocation density. Diode characteristics are compared with LWIR HgCdTe grown on bulk CdZnTe.

Structural Analysis of CdTe Hetero-epitaxy on (211) Si

“…1 In Table I the best reported values of X-ray diffraction (XRD) full-width at half-maximum (FWHM) and etch pit density (EPD) from molecular-beam epitaxy (MBE) (211)B HgCdTe/CdZnTe, HgCdTe/CdTe/Si, CdZnTe, and CdTe/Si have been compiled. [2][3][4][5][6][7][8][9][10][11] As-grown MBE (211)B CdTe/Si has a larger defect density and more disordered crystallinity than bulk (211)B CdZnTe substrates. This results in MBE (211)B HgCdTe/CdTe/Si having a larger defect density and more disordered crystallinity than MBE (211)B HgCdTe/CdZnTe.…”

High Performance Long-Wave Infrared (LWIR) HgCdTe on Silicon

“…It is interesting to note that some HgCdTe/CdTe/Si layers grown at EPIR Technologies and U. Illinois at Chicago have shown lifetimes comparable to those grown on CdZnTe. Indeed, a recent work [13] also reports the recombination lifetimes of two samples of LWIR HgCdTe on Si to be comparable to those grown on CdZnTe, even though the dislocation densities are greater.…”

“…The authors of [13] conjecture that this may be a consequence of not all dislocations being active as recombination centers. The reproducibility of these results and the lifetime uniformity over the area of the wafers is not clear.…”

Characterization of Smooth CdTe(111) Films by the Conventional Close-Spaced Sublimation Technique

“…10 The highest quality epitaxial HgCdTe films have been grown on bulk grown CdZnTe substrates with dislocation densities between 10 4 /cm 2 and mid-10 5 /cm 2 . [10][11][12][13][14] The problem with bulk grown CdZnTe substrates is that properties are not uniform across the surface (composition and lattice constant) and they are not available in large sizes. 10,14 In addition, CdZnTe has a large difference in thermal expansion coefficient with flip-chip bonded complementary metal-oxide semiconductor (CMOS) readout circuits.…”