In 1959, Lawson and co-workers publication triggered development of variable band gap Hg1−xCdxTe (HgCdTe) alloys providing an unprecedented degree of freedom in infrared detector design. Over the five decades, this material system has successfully fought off major challenges from different material systems, but despite that it has more competitors today than ever before. It is interesting however, that none of these competitors can compete in terms of fundamental properties. They may promise to be more manufacturable, but never to provide higher performance or, with the exception of thermal detectors, to operate at higher temperatures.

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Barrier infrared detectors

InAsSb-based XBnn bariodes grown by molecular beam epitaxy on GaAs

The paper presents progress in infrared (IR) detector technologies during 200 history of their development. Classification of two types of IR detectors (photon detectors and thermal detectors) is done on the basis of their principle of operation. The overview of IR systems and detectors is presented. Also recent progress in different IR technologies is described. Discussion is focused mainly on current and the most rapidly developing detectors: HgCdTe heterostructure photodiodes, quantum well AlGaAs/GaAs photoresistors, and thermal detectors. The outlook for near-future trends in IR technologies is also presented.

Infrared detectors: an overview

Within a very few years, InAs/GaSb superlattice technology has proven its suitability for high-performance infrared imaging detector arrays. At the Fraunhofer Institute for Applied Solid State Physics (IAF) and AIM Infrarot-Module GmbH, efforts have been focused on developing mature fabrication technology for dual-color InAs/GaSb superlattice focal-plane arrays for simultaneous, colocated detection at 3 μm to 4 μm and 4 μm to 5 μm in the mid-wavelength infrared atmospheric transmission window. Integrated into a wide-field-of-view missile approach warning system for an airborne platform, a very low number of pixel outages and cluster defects is mandatory for bispectral detector arrays. Process refinements, intense root-cause analysis, and specific test methodologies employed at various stages during the process have proven to be the key for yield enhancements.

Dual-Color InAs/GaSb Superlattice Focal-Plane Array Technology

The InAs/InAsSb (Gallium-free) type-II strained-layer superlattice (T2SLS) has emerged in the last decade as a viable infrared detector material with a continuously adjustable band gap capable of accommodating detector cutoff wavelengths ranging from 4 to 15 µm and beyond. When coupled with the unipolar barrier infrared detector architecture, the InAs/InAsSb T2SLS mid-wavelength infrared (MWIR) focal plane array (FPA) has demonstrated a significantly higher operating temperature than InSb FPA, a major incumbent technology. In this brief review paper, we describe the emergence of the InAs/InAsSb T2SLS infrared photodetector technology, point out its advantages and disadvantages, and survey its recent development.

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InAs/InAsSb Type-II Strained-Layer Superlattice Infrared Photodetectors

In this paper we describe the crystal growth and surface characterisation of ultra-flat 4" GaSb substrates suitable for the
epitaxial deposition of advanced infrared detectors. Results will be presented on the production of single crystal 4"
GaSb ingots grown by a modified version of the liquid encapsulated Czochralski (LEC) technique , supported by the
analysis of bulk material quality by dislocation Etch Pit Density (EPD) and X-Ray topography (XRT) assessments. This
study will also describe how various techniques were used to characterize the quality of the bare substrate. Surface oxide
properties of the GaSb substrates will be characterized by spectroscopic ellipsometry (SE). Bow, Warp and Total
Thickness Variation (TTV) data will be presented for 4" wafers processed on a multiwafer-type polishing platform. This
study will conclude with a 'blueprint' for the manufacture of large diameter GaSb substrates, this defining the
requirements for the production use of GaSb within a commercial epitaxial wafer foundry.

Multiwafer production of epitaxy ready 4" GaSb substrates: requirements for epitaxially growth infrared detectors

In this work newly developed 4" GaSb substrates are investigated for their suitability in the epitaxial growth of type II
InAs/GaInSb superlattice detectors. The Czochralski technique was used to grow 4" GaSb crystals with etch pit
densities in the range of 1.5-2.5E3 cm-2. Bulk crystal structure was investigated by X-ray topography and revealed large
central areas of zero or low dislocation density. Epitaxy-ready substrate surfaces were characterized by low levels of
surface roughness and uniform oxide coverage. The material quality of superlattice detector structures grown on 2" and
4" GaSb substrates has been compared. Surface morphology evaluations of a 4" GaSb epiwafer reveal very low haze
surface and defect density level that is similar to a 2" epiwafer. An rms surface roughness of 4.4 A was measured by
AFM which is only 1-2 A larger than seen on 2" diameter SLS epiwafers. High resolution X-Ray measurements of the
epitaxial layer structure indicate high structural quality and reproducible SL periodicity. Good layer thickness
uniformity with a center-to-edge variation just over 2% has been achieved.

Epitaxy ready 4" GaSb substrates: requirements for MBE grown type-II superlattice infrared detectors

In this paper we describe the crystal growth and surface characterisation of 'ultra-flat' 4" GaSb substrates suitable for the
epitaxial deposition of advanced infrared detectors. Results will be presented on the production of single crystal 4"
GaSb ingots grown by a modified version of the liquid encapsulated Czochralski (LEC) technique, supported by the
analysis of bulk material quality by dislocation etch pit density assessments. This study will also describe how various
techniques were used to characterize the quality of the bare substrate. Surface properties of the GaSb substrates will be
characterized by spectroscopic ellipsometry, white light interferometry and haze/particle defect mapping. Bow, Warp
and Total Thickness Variation (TTV) data will be presented for batches of 4" wafers processed on a volume multiwafer-type
polishing platform. This study will conclude with a 'blueprint' for the manufacture of large diameter GaSb
substrates, this defining the requirements for the production use of GaSb within a commercial epitaxial wafer foundry.

Large diameter 'ultra-flat' epitaxy ready GaSb substrates: requirements for MBE grown advanced infrared detectors

In this paper we describe the growth and characterization of antimonide based compound semiconductor substrates. The
Czochralski technique has been used to grow single crystals of 4" InSb and 4" GaSb with dislocation densities of
<20/cm2 and <100/cm2, respectively. Epitaxy ready wafer surfaces have been characterized by surface microscopy and
spectroscopic ellipsometry, revealing sub-nanometer levels of surface roughness (rms) and oxide coverage in the 10-50
Angstrom range. GaSb wafers with thinner oxides (<20 Angstroms) have been developed and quality assessments made
by epitaxial growth testing. Surface morphology evaluations indicate high levels of surface quality, comparable to pretreated
variants of the same substrate type. We also illustrate current crystal growth systems and ingot forms, and
discuss the challenges associated with scaling present InSb and GaSb technologies to deliver larger substrate formats.

Scaling up antimonide wafer production: innovation and challenges for epitaxy ready GaSb and InSb substrates

The GaSb-based 6.1 A lattice constant family of materials and heterostructures provides rich bandgap engineering possibilities and have received considerable attention for their potential and demonstrated performance in infrared (IR) detection and imaging applications. Mid-wave and long-wave IR photodetectors are progressing toward commercial manufacturing applications. To succeed, they must move from research laboratory settings to general semiconductor production, and high-quality GaSb-based epitaxial wafers with diameter larger than the current standard 3-inch are highly desirable. 4-inch GaSb substrates have been in production for a couple of years and are now commercially available. Recently, epi-ready GaSb substrates with diameter in excess of 6-inch were successfully produced. In this work, we report on the MBE (Molecular Beam Epitaxy) growth of generic MWIR bulk nBn photodetectors on 6-inch diameter GaSb substrates. The surface morphology, optical and structural quality of the epiwafers as evaluated by atomic force microscopy (AFM), Nomarski microscopy, low temperature photoluminescence (PL) spectroscopy, and high-resolution x-ray diffraction (XRD) will be discussed. Current density versus voltage (J-V) and photoresponsivity measurements from large-area mesa diode fabricated will also be reported. Material and device properties of these 6-inch epiwafers will be compared to similar structures grown on commercially available 4-inch diameter GaSb substrates.

Mark J. Furlong

Papers

Multiwafer production of epitaxy ready 4" GaSb substrates: requirements for epitaxially growth infrared detectors

Epitaxy ready 4" GaSb substrates: requirements for MBE grown type-II superlattice infrared detectors

Large diameter 'ultra-flat' epitaxy ready GaSb substrates: requirements for MBE grown advanced infrared detectors

Scaling up antimonide wafer production: innovation and challenges for epitaxy ready GaSb and InSb substrates

MBE growth of Sb-based bulk nBn infrared photodetector structures on 6-inch GaSb substrates