Direct growth of CdZnTe/Si substrates for large-area HgCdTe infrared focal plane arrays

CdTe buffer layers which were grown on (211)B GaAs by molecular beam epitaxy were subjected to two different etch treatments to quantify the crystal quality and dislocation density. The optical properties and thicknesses of the samples were obtained by ex situ spectroscopic ellipsometry. The surface morphologies of the CdTe epilayers were analyzed by atomic force microscopy, scanning electron microscopy, and Nomarski microscopy before and after chemical etching. We compare the triangle-and trapezoid-shaped etch pits due to the Everson and Nakagawa etch solutions, respectively. Measured etch pit density (EPD) values of triangle etch pits were found in the 8 9 10 7 cm À2 to 2 9 10 8 cm À2 range, and trapezoid-shaped etch pits were found in the 1 9 10 7 cm À2 to 7 9 10 7 cm À2 range for samples with thicknesses <2 lm.

Section: à2mentioning

confidence: 99%

Characterization of CdTe Growth on GaAs Using Different Etching Techniques

Bilgilisoy

Özden

Bakali

et al. 2015

“…The CdTe is used as a buffer layer rather than CdZnTe because our earlier work with CdZnTe grown by either MOCVD or MBE showed that the material properties, such as x-ray rocking curve full-width at half-maximum (FWHM), degrade as Zn is added to form the ternary alloy. 2,5 This appears to be particular to CdZnTe grown by vapor-phase techniques because the properties of bulk-grown CdZnTe are superior to those of CdTe for the alloy range used for lattice matching to HgCdTe. Currently, MBE-grown CdSeTe is being explored as a potentially better material for buffer layers on Si substrates.…”

Section: Materials Growth and Characterizationmentioning

confidence: 99%

HgCdTe/Si materials for long wavelength infrared detectors

Johnson

Buell

Vilela

et al. 2004

Self Cite

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.

“…Recent developments in molecular beam epitaxy (MBE) chalcogenide bufferlayer growth technology on Si substrates have offered a new dimension to HgCdTe-based infrared (IR) technology. [2][3][4][5][6][7] Si substrates provide advantages in terms of their relatively large area (3 inch to 8 inch diameter is easily obtained) compared with CZT substrate materials; durability during processing; reliability during thermal cycling; and more importantly, reduced cost as compared with CZT. This innovation in Si-based composite substrates has made it possible to fabricate very large-format IR arrays that offer higher-resolution low-cost arrays and more dies per wafer.…”

Section: Introductionmentioning

confidence: 99%

“…This progress in CdTe/Si(211) has laid the foundation for large-format, low-cost HgCdTe IRFPAs. 4,5 Raytheon Vision Systems (RVS) has reported the ability to grow/fabricate HgCdTe IRFPAs on 6-inch CdTe/Si(211) substrates. 8 On a 6-inchdiameter CdTe/Si(211) substrate, nonuniformity results of 0.1-lm variation of the cutoff wavelength across the entire diameter have been demonstrated in MW/SW with extremely low surface defect densities (below 100 cm À2 ).…”

Section: Introductionmentioning

confidence: 99%

Analysis of Current–Voltage Measurements on Long-Wavelength HgCdTe Photodiodes Fabricated on Si Composite Substrates

Wijewarnasuriya

Chen

Brill

et al. 2010

We have performed a detailed study of dark current versus voltage to understand existing limitations in dark current and address the nonuniformity of dark current in devices fabricated on HgCdTe grown on silicon substrates. One interesting observation is that trap-assisted tunneling, g-r currents, are not found close to zero bias in certain devices. Devices from the low end of the R 0 A distribution show heavy shunting paths close to zero bias. We believe that these shunting paths may be the limiting cause of tail distributions in fabricated focal plane array tail distributions. Possible causes for these shunting paths are surface charges associated with dislocation cores and impurity gettering at dislocation cores. The measured non-anti-reflection (AR)-coated quantum efficiency (QE) was 0.576 at 78 K and displays the classical response versus wavelength. The measured QE on isolated single devices is consistent with the 256 9 256 focal-plane array mean QE. Obtained average dark currents are on the order of mid 10 À5 A cm -2 , which is one order of magnitude higher than dark currents obtained from arrays on latticematched substrates. On average, arrays on lattice-mismatched substrates show performance characteristics inferior to those of arrays fabricated on lattice-matched substrates. This inferior performance is due to array pixel operability, as can be seen from the tail of the distribution and the average dark currents, which are one order of magnitude higher than those obtained on lattice-matched substrates.