Microscopic defects on MBE grown LWIR Hg1−xCdxTe material and their impact on device performance

We present a detailed study on the surface morphologies and chemical composition of growth pits in lead selenide (PbSe) epilayers grown by molecular-beam epitaxy. Various growth pits were investigated by scanning electron microscopy and energy-dispersive x-ray analysis. The vast majority of growth pits within the PbSe epilayers contained either single or multiple PbSe microcrystals with a distinct cuboid shape. Based on the observed structures and morphologies of the PbSe microcrystals, the formation mechanism of the cuboid structures was considered to be (100) preferential crystal growth originating from PbSe polycrystalline seeds.

Section: Resultsmentioning

confidence: 65%

Nature of Growth Pits in Lead Salt Epilayers Grown by Molecular Beam Epitaxy

et al. 2008

“…The model diode current can be written as (1) where d is the absorber layer thickness, N d is the base-layer donor concentration, τ p is the minority carrier lifetime, and n is an ideality factor. 11 Figure 5 shows a fit of Eq. 1 to the I-V characteristic of a small diameter (10-µm) diode from layer 3-971.…”

Section: Lwir Hgcdte On Cdte Buffer Layersmentioning

confidence: 99%

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

Carmody

Pasko

Edwall

et al. 2004

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.

“…CdHgTe is an important material for infrared detectors 1,2 as the direct band gap can be compositionally tuned from -0.26 eV to 1.61 eV at 77 K. 3 Defects in CdHgTe can be detrimental to detector performance, 4,5 and it is therefore important to optimize the growth conditions to reduce their density. To this end we have performed a study of defects in the CdHgTe material system to determine how the different defects relate to the growth conditions.…”

Section: Introductionmentioning

confidence: 99%

Defects in HgTe and CdHgTe Grown by Molecular Beam Epitaxy

Selvig

Tonheim

Lorentzen

et al. 2008

The defect morphology in HgTe and CdHgTe was studied in (211)B-oriented layers grown in a 20°C temperature range around the optimal growth temperature. The density of defects varies strongly with the growth temperature. In HgTe, the shape of the microvoid defects is very sensitive to the growth temperature and can be used to determine the deviation from the optimal growth temperature. Using thermodynamical modeling, the optimal growth temperature for CdHgTe can then be calculated. We describe a mechanism for the formation of microvoids and needles which involves preferential surface diffusion of Te combined with an impurity or defect on the substrate. Microvoids on (111)B-oriented partially twinned HgTe layers were also studied. The microvoids in the twinned parts of the layer were found to be rotated 180 deg relative to the untwinned parts of the layer.