James E. Huffman

Germanium blocked‐impurity‐band detector arrays: Unpassivated devices with bulk substrates

We have fabricated and characterized six‐element monolithic arrays of Ge:Ga blocked‐ impurity‐band detectors, with threshold wavelength 220 μm, peak quantum efficiency 14%, detective quantum efficiency 9%, dark current 300 e− s−1, and response uniformity better than 4%. The devices are described very well by the standard model of blocked‐impurity‐band detectors, and appear to satisfy many of the requirements of low‐background astronomical instruments.

Germanium blocked‐impurity‐band far‐infrared detectors

Ge:Ga blocked‐impurity‐band detectors having long‐wavelength thresholds of 190 μm and peak quantum efficiencies of 4% have been fabricated. This performance approaches that of state‐of‐the‐art discrete Ge:Ga photoconductors, with the additional benefit of good response at wavelengths longer than that obtained with unstressed photoconductors.

Growth methods for high purity Ge and Ge: Ga homoepitaxy

The intent of this article is to provide methods to prepare Ge and Ge: Ga homoepitaxy with residual group III and V impurity concentrations below 1013 cm-3. Methods for growing high purity Ge and Ge: Ga epitaxy have not been previously established. However, high purity layers of these types are required for fabricating a new type of far-infrared photon detector. The growth methods described here employ the halides of germanium (GeCl4) and of gallium (GaCl3) as sources in chemical vapor deposition. The undoped Ge epitaxy prepared contains residual impurity concentrations below our sensitivity limit of 2 X 1013 cm-3. The undoped growth method is modified to prepare Ge: Ga epitaxy with a measured residual donor concentration of 5 X 1012 cm-3.

Photoluminescence studies of ultrahigh‐purity epitaxial silicon

Photoluminescence has been used to identify bulk and interfacial contaminants in ultrahigh‐purity epitaxially grown silicon. When combined with depth profiling using spreading resistance analysis, it provides a powerful characterization technique which may be used for determining optimal layer growth parameters. Identification of impurities has been demonstrated at concentrations which are orders of magnitude below the sensitivity limit of other methods suitable for epitaxial layer characterization.

Large-format blocked-impurity-band focal plane arrays for long-wavelength infrared astronomy

Large-format, very-long-wavelength infrared (VLWIR) hybrid focal plane arrays (HFPAs) based on doped-silicon blocked-impurity-band (BIB) detectors have been developed and demonstrated for a variety of astronomy applications. An HFPA consists of a BIB detector array interfaced via indium column interconnects to a matching cryogenic signal processor/multiplexer. Arsenic-doped silicon (Si:As) BIB detector arrays with useful photon response out to nearly 30 micrometers are the most fully developed embodiment of this technology. HFPAs with Si:As BIB arrays have been optimized for low, moderate, and high infrared backgrounds in 128 X 128-pixel formats, and a high-flux 256 X 256-pixel version is under development. For high-flux applications, both the detector array and multiplexer are optimized to handle incident flux densities > 1016 photons cm-2s-1, providing high spatial uniformity, high pixel operability, and background-limited performance down to low frequencies (< 10 Hz). Antimony-doped silicon (Si:Sb) arrays and 128 X 128-pixel Si:Sb HFPAs having response to wavelengths > 40 micrometers have also been demonstrated, primarily for use at low and moderate backgrounds. BIB technology offers producible, low-cost, high-performance focal planes for astronomy in the VLWIR.

Infrared detectors for 2- to 220-μm astronomy

We present the performance characteristics of two examples from a special class of photon detector, based on the blocked impurity band (BIB) concept. Recent results are presented on Si:Sb BIB detectors covering the 2 to 50 micrometers wavelength range, and on Ge:Ga BIB detectors that are sensitive in the 50 to 220 micrometers range. The inherent properties of these BIB detectors make them a natural choice for infrared astronomy; minimal sensitivity to ionizing radiation, compatibility with large format (128 X 128) arrays, low dark currents and high detective quantum efficiencies, combined with a lack of anomalous behavior. The detector characteristics are discussed in terms of a standard BIB performance model. Both detector types appear to have unique potential for astronomy applications.

A new high purity doping source for CVD Si: Ga epitaxy

Abstract A new CVD growth chemistry has been developed for producing very pure and high crystalline-quality gallium-doped silicon epitaxy. Gallium trichloride, GaCl 3 , has been employed as an improved precursor to the currently accepted organometallic gallium source, trimethyl gallium, (CH 3 ) 3 Ga. In contrast to trimethyl gallium, this metal halide doping source does not cause carbon contamination of the epitaxial layer. Much more abrupt layer-to-layer transition regions have been demonstrated. Data on the electrical and crystalline characteristics of GaCl 3 -grown Si:Ga layers are presented. The current doping limit of 4X10 17 cm -3 obtained with this chemistry under normal CVD growth conditions is well below the solubility limit and is indicative of the unusual surface chemistry involved in doping. Results of experiments to elucidate the doping mechanism are discussed.

Epitaxy‐substrate discrimination in the photoluminescence characterization of epitaxial Si

We show that the difficulty in separating the epilayer and substrate contributions to the photoluminescence of epitaxial Si samples can be solved simply by growing test samples on a substrate which has no photoluminescence in the region of interest for impurity characterization. Lightly In‐doped Si is shown to be an ideal substrate material for the characterization of epitaxial layers of ultrahigh‐purity Si.

Float zone growth of high purity and high oxygen concentration silicon

Ultra-high purity silicon with high concentrations of interstitial oxygen has been prepared using the float-zone (FZ) technique. In this material, interstitial oxygen concentrations [O]∼ 9×1017 cm-3 have been achieved while maintaining good crystalline structure and a ratio of oxygen to shallow impurities greater than 105. This FZ method provides efficient oxygen “doping” by exposing only the melted zone during boule growth. Results of characterization using IR absorption, photoluminescence spectroscopy, transport and crystal quality measurements are presented. This material is of fundamental importance in the investigation of thermal donors (TDs) in silicon, where contamination from group-III and group-V impurities, and carbon, complicates the role of oxygen in the formation of TDs.