HgCdTe/Si materials for long wavelength infrared detectors

Abstract

The heteroepitaxial growth of HgCdTe on large-area Si substrates is an enabling technology leading to the production of low-cost, large-format infrared focal plane arrays (FPAs). This approach will allow HgCdTe FPA technology to be scaled beyond the limitations of bulk CdZnTe substrates. We have already achieved excellent mid-wavelength infrared (MWIR) and short wavelength infrared (SWIR) detector and FPA results using HgCdTe grown on 4-in. Si substrates using molecular beam epitaxy (MBE), and this work was focused on extending these results into the long wavelength infrared (LWIR) spectral regime. A series of nine p-on-n LWIR HgCdTe double-layer heterojunction (DLHJ) detector structures were grown on 4-in. Si substrates. The HgCdTe composition uniformity was very good over the entire 4-in. wafer with a typical maximum nonuniformity of 2.2% at the very edge of the wafer; run-to-run composition reproducibility, realized with real-time feedback control using spectroscopic ellipsometry, was also very good. Both secondary ion mass spectrometry (SIMS) and Hall-effect measurements showed well-behaved doping and majority carrier properties, respectively. Preliminary detector results were promising for this initial work and good broad-band spectral response was demonstrated; 61% quantum efficiency was measured, which is very good compared to a maximum allowed value of 70% for a non-antireflection-coated Si surface. The R 0 A products for HgCdTe/Si detectors in the 9.6-µm and 12-µm cutoff range were at least one order of magnitude below typical results for detectors fabricated on bulk CdZnTe substrates. This lower performance was attributed to an elevated dislocation density, which is in the mid-10 6 cm Ϫ2 range. The dislocation density in HgCdTe/Si needs to be reduced to Ͻ10 6 cm Ϫ2 to make high-performance LWIR detectors, and multiple approaches are being tried across the infrared community to achieve this result because the technological payoff is significant.

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

“…The Everson etch is used to reveal dislocation density in bulk (211)B CdTe, CdZnTe, and CdTe/Si epilayers. 2,4,5,7,8,10,11,21 The Everson etch reveals the point of emergence of a dislocation as a pit. 21 The pits occur due to enhanced etch rate in the strained region around the dislocation core.…”

“…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.…”

Narrow-gap piezoelectric heterostructure as IR detector

“…The basic research is focused on the growth, doping and characterization of MCT on CdZnTe substrate with 4% zinc concentration for lattice matching, because the highest crystal perfection is realized only for this material compound [1]. The most attractive among alternative substrates, which have the advantages in comparison with CdZnTe substrates from the viewpoint of substrate dimensions and low cost, are those based on GaAs [2] and Si [2][3][4][5]. The disadvantage of these substrates is a large lattice mismatch of compound materials, which is equal to ~14.6% for CdTe/GaAs and ~19% for CdTe/Si at room temperatures (see Table 1).…”

Topography and Dislocations in (112)B HgCdTe/CdTe/Si

“…As-grown molecular beam epitaxy (MBE) (112)B CdTe/Si has a larger defect density and more disordered crystallinity than bulk (112)B CdZnTe substrates (see Table I and Refs. [1][2][3][4][5][6][7][8][9][10][11]. This results in MBE (112)B HgCdTe/CdTe/Si having a larger defect density and more disordered crystallinity than MBE (112)B HgCdTe/CdZnTe (Table I).…”