Showing papers on "Mercury cadmium telluride published in 1986"
TL;DR: In this article, the authors present data on the deposition of MCT films by a simple electroplating technique and report on the highest efficiency polycrystalline MCT thin-film solar cell to date.
Abstract: Cd‐rich mercury cadmium telluride (MCT) is a promising material for thin‐film solar cell applications. In this letter we present data on the deposition of MCT films by a simple electroplating technique and report on the highest efficiency polycrystalline MCT thin‐film solar cell to date, which has an efficiency of 10.6% under AM1.5 illumination.
76 citations
TL;DR: In this paper, the photolysis of dimethylmercury, dimethylcadmium, and dimethyltelluride using an ArF excimer laser operating at 193 nm as the radiation source is described.
Abstract: Mercury cadmium telluride has been successfully grown by the photolysis of dimethylmercury, dimethylcadmium, and dimethyltelluride, using an ArF excimer laser operating at 193 nm as the radiation source. Growths were accomplished on CdTe substrates at a temperature of 150 °C, with a growth rate of 4 μm per hour. Films are shiny, and x‐ray diffraction indicates epitaxial growth. Secondary ion mass spectroscopy and infrared transmission measurements indicate that the composition of the initial films is Hg0.2Cd0.8Te. Details of the growth apparatus and additional data is presented.
46 citations
Patent•
31 Oct 1986
TL;DR: In this article, a three-layer photovoltaic structure with polycrystalline semiconductor layers disposed in series optically and in sequential touching contact is proposed, which includes a relatively wide optical bandgap energy window layer, a light-absorbing layer and a third, relatively wide band gap energy layer that forms a minority carrier mirror with the light absorbing layer.
Abstract: A three layer, photovoltaic structure having polycrystalline semiconductor layers disposed in series optically and in sequential touching contact includes a relatively wide optical bandgap energy window layer, a light-absorbing layer and a third, relatively wide bandgap energy layer that forms a minority carrier mirror with the light-absorbing layer. All three layers have different compositions so that the structure includes two heterojunctions. The light-absorbing layer and third layer are of the same conductivity type. The structure is conveniently realized using II-VI semiconductor compounds such as a cadmium sulfide or zinc sulfide window layer, a mercury cadmium telluride, cadmium telluride, zinc cadmium telluride or mercury zinc telluride light-absorbing layer and a third layer of cadmium telluride, zinc telluride, zinc cadmium telluride, mercury cadmium telluride or cadmium manganese telluride. Cadmium is present in at least two of the three layers of the novel structures. Tellurium is present in two of the three layers. Structures according to the invention may be conveniently formed by electrodeposition and may employ opaque or transparent substrates depending on the particular semiconductor materials used and their relative positions.
28 citations
TL;DR: In this paper, Hg1−xCdxTe was grown on CdTe substrates using dimethylcadmium, diethyltelluride and mercury in a horizontal reactor.
26 citations
TL;DR: The interdiffused multilayer process (IMP) has been implemented on a computer controlled metal-organic chemical vapor deposition (MOCVD) system to improve the compositional uniformity of epitaxial films grown by this technique.
Abstract: The interdiffused multilayer process (IMP) has been implemented on a computer controlled metal–organic chemical vapor deposition (MOCVD) system to improve the compositional uniformity of epitaxial films grown by this technique. Currently, this process is giving compositional uniformity of ≂3% over 1 cm2 on CdTe substrates. Full temperature Hall measurements have been performed to show that as‐grown mercury cadmium telluride (MCT) (x∼0.2 and 0.3 epilayers have consistent p‐type conductivity with carrier levels in the range of 2.5×1016 cm−3 to 1.7×1017 cm−3 at 77 K. For MCT with composition in the range x=0.2 to 0.3, the acceptor levels increased as an alkyl source was exhausted, but improved when a new source was introduced. The as‐grown MCT layers have mobilities typically of 350 cm2 V−1 s−1 at 77 K, consistent with p‐type material, and the mobility shows a high degree of reproducibility. Preliminary mercury annealing experiments to identify residual impurity levels were performed. A 15 μm MOCVD layer of ...
23 citations
TL;DR: In this paper, electrical characterizations of n and p-type mercury cadmium telluride epitaxial layers intentionally doped during their growth by the molecular beam epitaxy technique are reported.
Abstract: Electrical characterizations of n‐ and p‐type mercury cadmium telluride epitaxial layers intentionally doped during their growth by the molecular beam epitaxy technique are reported The doping by stoichiometry adjustment can produce good mobility material of both n or p semiconductor types However, p‐type material is feasible only for cadmium fraction (x) greater than 02, whereas the n‐type conduction is possible only for x less than 03 For the first time in situ doping of HgCdTe by indium is reported It is incorporated in the material during the growth and behaves as a n‐type dopant Carrier concentrations up to 1018 cm−3 have been obtained An indium doped layer having a cadmium fraction of 055 was also found to be n‐type
19 citations
TL;DR: Growth of epitaxial mercury cadmium telluride (Hg1−xCdxTe) on (100) GaAs substrates by organometallic vapor phase epitaxy is described in this paper.
Abstract: Growth of epitaxial mercury cadmium telluride (Hg1−xCdxTe) on (100) GaAs substrates by organometallic vapor‐phase epitaxy is described. Transport measurements made on these layers at 80 K indicate an electron mobility greater than 2×105 cm2/ V s for layers of composition x≂0.2. An intervening CdTe buffer layer was used to accommodate the large (14%) lattice mismatch between these systems, and HgCdTe layers have been grown with CdTe buffer layer thicknesses from 1000 A to 3 μm. It is shown that a CdTe buffer layer of 2–3 μm is necessary to accommodate the misfit dislocations at the CdTe‐GaAs interface.
19 citations
TL;DR: In this paper, the authors investigated the dependence of the quality of the layers on the combined thickness of the CdTe and HgTe layers, e.g., the homogeneity in depth of the composition of the layer is of the order of ± 0.005, and the interface region is quite abrupt.
Abstract: The interdiffused multilayer process (IMP), in which alternate submicron layers of CdTe and HgTe are grown by metal–organic vapor‐phase epitaxy (MOVPE) and are allowed to interdiffuse during the deposition of subsequent layers, has been used to grow mercury cadmium telluride epitaxially on CdTe substrates. A thorough investigation by electrolyte electroreflectance (EER) shows that epilayers of 1×1 cm grown by this method have a reasonable lateral homogeneity with lateral fluctuations in the alloy composition being less than ±0.008. The homogeneity in depth of the composition of the layer is of the order of ±0.005, and the interface region is quite abrupt (less than 3000 A in thickness). These characteristics are quite attractive and compare well with state of the art liquid‐phase epitaxy (LPE) materials. In order to understand better the potential of this relatively novel growth method we have investigated the dependence of the quality of the layers on the combined thickness of the CdTe and HgTe layers, e...
11 citations
Patent•
09 Jun 1986TL;DR: In a covered graphite slider for the liquid phase epitaxial growth of mercury cadmium telluride, the authors showed the addition of an improved wipe-off arrangement positioned in tandem with the CdTe substrate for preventing residual growth solution from migrating back onto the substrate which has just been wiped-off by the LPE slider.
Abstract: In a covered graphite slider apparatus for the liquid phase epitaxial growth of mercury cadmium telluride, this invention shows the addition of an improved wipe-off arrangement positioned in tandem with the CdTe substrate upon which the HgCdTe epitaxial layer is grown. This arrangement includes the providing of a discardable CdTe drainage apron adjacent the substrate for preventing residual growth solution from migrating back onto the substrate which has just been wiped-off by the LPE slider.
6 citations
TL;DR: In this paper, a liquid phase epitaxial (LPE) growth technique was used to lower the growth temperature through the use of a solvent, and allow the deposition of thin films on large foreign substrates that are grown without any Hg.
Abstract: Mercury cadmium telluride (Hg1-x Cdx Te) is an important material for infrared detector applications due to tde variable bandgap obtained through simply varying the mercury/cadmium ratio. Thus IR sensing systems with various wavelength requirements, typically from 2 to 12 μm, can potentially all be supplied by one materials technology. Bulk crystal growth technology was originally pursued for these applications. However, large, high quality crystals are difficult to grow because of the high melting point of HgCdTe and the resulting high Hg vapor pressure. Liquid phase epitaxial (LPE) growth techniques can lower the growth temperature through the use of a solvent, and allow the deposition of thin films on large foreign substrates that are grown without any Hg.
6 citations
TL;DR: The intrinsic semiconductor mercury cadmium telluride (Hg 1−x Cd x Te), a solid solution of HgTe and CdTe, has assumed an ever increasing role in the fabrication of infrared (IR) detectors because its energy gap (0-1.5 eV) can be tailored to match the specific needs of IR detection and fiber optic systems.
Abstract: The intrinsic semiconductor mercury cadmium telluride (Hg 1−x Cd x Te), a solid solution of HgTe and CdTe, has assumed an ever increasing role in the fabrication of infrared (IR) detectors because its energy gap (0-1.5 eV) can be tailored to match the specific needs of IR detection and fiber optic systems. In photovoltaic focal plane array (FPA) applications, low power consumption, as well as excellent sensitivity at elevated temperatures, have made Hg 1−x Cd x Te the material of choice for both the midwave IR (MWIR) and longwave IR (LWIR) region.
TL;DR: The growth of thin films of mercury-based materials by molecular beam epitaxy (MBE) presents significant experimental problems which must be overcome in order to successfully grow infrared detector materials such as mercury cadmium telluride (MCT).
Abstract: The growth of thin films of mercury-based materials by molecular beam epitaxy (MBE) presents significant experimental problems which must be overcome in order to successfully grow infrared detector materials such as mercury cadmium telluride (MCT) Many of the problems associated with the use of Hg in MBE arise from its high room temperature vapor pressure (2 mTorr) and its low sticking coefficient The MBE system must be designed for Hg usage by considering such things as the ultra high vacuum pumping system, the Hg source, Hg containment, and Hg removal In addition, Hg is a toxic heavy metal and must be handled appropriately Other problems involved with the growth of MCT are associated with the design of the MBE furnaces which are used to evaporate cadmium telluride and tellurium
22 Nov 1986
TL;DR: The main objective of the Infrared Detector Materials Research Program inthe Defence Sciences Office (DSO) of DARPA has been to develop a fundamental science base for the growth and processing of infrared detector materials as mentioned in this paper.
Abstract: The goal of DARPA's research program in Infrared Detector Materials is todevelop a science base for production of affordable large area high performance focalplane arrays. Intrinsic materials (HgCdTe and related Hg -based alloys) are preferred,principally because of their large absorption coefficient. A summary of progress andissues in bulk and epitaxial growth of II -VI materials, II -VI superlattices, contacts,ion implantation, and low frequency noise is given.IntroductionThe principal objective of the Infrared Detector Materials Research Program inthe Defence Sciences Office (DSO) of DARPA has been to develop a fundamental sciencebase for the growth and processing of infrared detector materials. This is motivatedby the judgement that the cost of high performance large area infrared focal planearrays will not be reduced without such a base of understanding. The program hassupported the development of various detector technologies including silicon Schottkybarrier. The major emphasis is on mercury cadmium telluride (HgCdTe) and related II -VImaterials. The basic challenge is to devise materials and processing techniques whichcan make feasible silicon -like whole wafer (3 -inch or larger) processing in II -VIsemiconductors. The hope is for eventual monolithic integration of detectors and allancillary focal plane circuitry with concomitant benefits in cost, performance, andreliability.HgCdTe was discovered by Lawson et al. at RSRE in 1958 and much of thefundamental work in this and other II -VI semiconductors has been carried out inEurope. To cite but a few notable firsts, p -n junction development at CNRS,metalorganic chemical vapor deposition (MOCVD) at RSRE, molecular beam epitaxy (MBE)at Grenoble, wide bandgap optoelectronic devices It SAT, and the pioneering work ofPolish scientists in semimagnetic semiconductors. In the United States, while therehas been extensive industrial activity, the university 9ommunity until recently hashad relatively little involvement in HgCdTe technology. DARPA /DSO has recognized theimportance of increasing the degree of university participation and a major portion ofthe program's research funds has supported university and joint university /industryresearch projects.Intrinsic vs Extrinsic Detector MaterialsImportant criteria for IR detector materials are based on making the electricalnoise in the detector element generated by the background photon flux of the IR scenedominant over all other noise sources. In most instances this can be expressed asPB % PTH
06 Oct 1986
TL;DR: In this paper, the authors describe data on long wave infrared photodiode detectors for use in 10.6 μm heterodyne laser receivers which operate at 78 K with bandwidths up to 1 GHz.
Abstract: The use of Mercury Cadmium Tellurium photodetectors in CO2 laser radar systems has been of interest for many years. In this paper we will describe data on our long wave infrared photodiode detectors for use in 10.6 μm heterodyne laser receivers which operate at 78 K with bandwidths up to 1 GHz. Performance data on these diodes at 78 K will be presented. Typical measured dc characteristics are quantum efficiencies greater than 60% at 10.6 μm a spectral response optimized for CO2 laser radiation, RA products greater than 120 Ω-cm2 at 50 mV reverse bias and breakdown voltages greater than 1.5 volt. The frequency response of these devices is limited by the dewar and preamp characteristics and is typically greater than 1 GHz. The heterodyne NEP is within a factor 1.5 of the quantum limit. Heterodyne NEP data as a function of local oscillator power, bias voltage and frequency are presented. These data will be compared with a heterodyne device/equivalent circuit model. Device model predictions of junction resistance and capacitance are made and the relevance to heterodyne operation is discussed. Theoretical predictions are compared to measured data and the implied device physics is discussed.
22 Nov 1986
TL;DR: In this article, two vertical infinite melt liquid phase epitaxy dipping furnaces are used to produce epitaxial layers of cadmium telluride and CdHgTe.
Abstract: Epitaxial layers of cadmium telluride and cadmium mercury telluride are currently being grown by use of two vertical 'infinite melt' liquid phase epitaxy dipping furnaces. In one system, CdTe is being grown from mercury solvent at 250-300°C under an atmosphere of pure hydrogen at one bar pressure. In the second furnace, CdHgTe layers are produced from a mercury-rich melt at 460-500°C under a hydrogen atmosphere at up to fifteen bar pressure. Both furnaces are remotely controlled and feature extremely accurate and sensitive pressure control systems. The combination of a dipping furnace and large (10 kg) mercury-rich melt offers many potential advantages over more conventional small scale LPF systems employing tellurium-rich melts. For example - 1) Melt wipe-off problems are drastically reduced. 2) Impurity levels can be cut since mercury is readily available in an extremely pure form. 3) Etch-back of CdTe substrates is much slower and more easily controlled, giving good interfaces. 4) Both n- or p-type layers can, in principle, be grown without recourse to annealing. 5) The melt is maintained at temperature over many months aiding both run-to-run uniformity and a high through-put of material. The design of the furnaces will be described, and results obtained from measurements of the layers produced will be presented and discussed.© (1986) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
22 Nov 1986
TL;DR: In this article, preliminary experimental results of epitaxial growth of CdZnTe on sapphire, silicon and single crystal CdznTe via a low pressure chemical vapor deposition process are reported.
Abstract: Preliminary experimental results of epitaxial growth of CdZnTe on sapphire, silicon and single crystal CdZnTe via a low pressure chemical vapor deposition process are reported. The CdZnTe layers grown were smooth and specular in appearance. The infrared transmission trace of CdZnTe grown on silicon and sapphire showed good transmission through the film. The X-ray diffraction scan of CdZnTe on silicon showed that the film is epitaxial with a lattice constant of 6.45 A.
07 Jul 1986
TL;DR: Wilson et al. as mentioned in this paper used a cadmium mercury telluride photodiode operating at 77K as a widebandwidth, high sensitivity detector of CO laser radiation, and they described results on a practical detector, cooled to193K on a thermoelectric cooler.
Abstract: D. J. Wilson, R.S.R.E., Malvern, U.K.IntroductionHeterodyne systems operating in the infrared have been developed for rangefinding,velocity measurement and anemometry. More recently such systems have been extended tocover vibration detection and active imagery (ref. 1). These advanced systems havefrequently used a cadmium mercury telluride photodiode operating at 77K as a widebandwidth, high sensitivity detector of CO laser radiation. In practical systems thistype of detector may be disadvantageous because of the requirement for high pressureair to achieve the operating temperature.It has been shown that useful performance can be achieved at intermediatetemperatures (ref. 2). Here we describe results on a practical detector, cooled to193K on a thermoelectric cooler.
13 Oct 1986
TL;DR: In this paper, the authors measured the dark current as a function of temperature in both isolated HgCdTe diode arrays and arrays which have been bump-bonded to silicon multiplexers.
Abstract: Mercury cadmium telluride is a promising detector material for low background astronomical imaging and spectroscopy in the near infrared. We have begun a program to measure dark current as a function of temperature in both isolated HgCdTe diode arrays and arrays which have been bump-bonded to silicon multiplexers. In this paper, we describe measurements of 2.5 μm cutoff diode material and a hybrid array with a CCD readout. Measurements of 52 μm x 52 μm detectors indicate that id may be less than 50-100 e-/sec at 87 K.
01 May 1986
TL;DR: In this article, a simple positive-feedback circuit varies bias voltage as necessary for linearizing mercury cadmium telluride infrared detectors in Fourier transform spectrometers and other spectral and imaging instruments.
Abstract: Simple positive-feedback circuit varies bias voltage as necessary. Ideal detector biased with constant voltage, detector current proportional to photon flux plus constant offset. Detector connected between inverting input and ground, and feedback from operational amplifier through feedback resistor Rf make voltage at inverting input equal to noninverting input. Bias voltage held constant. Principle applied to linearizing mercury cadmium telluride infrared detectors in Fourier-transform spectrometers and other spectral and imaging instruments.
07 Jul 1986
TL;DR: Theoretical analysis of high band gap Hgl-xCdxTe infrared absorption and consideration of the available metallurgical processes show the ability of this material to give rise to optical waveguides exhibiting characteristics equivalent or better than classical III V in-frared waveguide at 10.6 μm.
Abstract: Theoritical analysis of high band gap Hgl-xCdxTe infrared absorption and consideration of the available metallurgical processes show the ability of this material to give rise to optical waveguides exhibiting characteristics equivalent or better than classical III V in-frared waveguides at 10.6 μm. The E.D.R.I. process (Isothermal Evaporation Diffusion) has been used to grow HgCdTe layer on CdTe substrates. The Hgl-xCdxTe (x = 0.5) source material has been obtained by the Travelling Heater Method. Exceptionally transparent material at 10.6 pm is obtained for Cd composition x greater than 0.5. The E.D.R.I. process produces graded composition layer ranging from x = 0.55 at the surface to x = 1 in the substrate, giving rise to highly transparent graded index waveguides. When a 10.6 μm beam is coupled by a high index Germanium prism with the waveguide modes, the totally reflected light exhibits m-lines at specific angles from which the effective indices of the waveguide modes are deduced. Then an inverse W.K.B. computation leads to the refractive index profile of the structure. The comparison with the Cadmium ratio obtained with the electron microprobe gives the relation between refractive index and Cadmium concentration. The propagation of a 10.6 μm wave exhibits an exceptionnally low attenuation (< 0.5 dB/cm) on all TE modes, even those of high order.
06 Oct 1986
TL;DR: In this article, the authors describe the design of a Cadmium, Mercury Telluride p-type photoconductive detector with its associated thermo-electric cooler, bias supply and amplifier.
Abstract: CO2 laser rangefinders have been used for some years to complement the operation of 8 to 12um thermal imaging systems. Being wavelength compatible they can range on to any point in the thermal scene, and have the added advantage of being eye safe.' Using coherent detection and operating the laser in a CW mode the rangefinder can also provide information on target movement in the form of Doppler shifts which produce frequency modulation of the carrier. This enables acquisition of velocity and vibration data. Other options can include active imaging by use of an add on scanner and anemometry for air turbulence studies.2 Systems of this type normally use a low power, (up to 10 watts) frequency stable CO2 laser, a modulator to superimpose any carrier frequency code on the laser beam and a cooled detector, normally a Cadmium Mercury Telluride photo-diode operating at 77K. These detectors have a high quantum efficiency, and a frequency response which can be well in excess of 1GHz.
One disadvantage is that the detectors require Joule-Thompson or engine cooling; this results in added bulk due to high pressure gas cylinders or compressor, with consequent extra capital and running costs. These systems would be more attractive and versatile if this inconvenience could be avoided by running at higher temperatures. With direct detection, higher temperatures result in a rapid degradation of performance due to reduction in detectivity. Heterodyne detectors, thermoelectrically cooled to about 190K, offer convenience without as large a penalty, due to their greater dependance on quantum efficiency. This paper describes the design of a Cadmium, Mercury Telluride p-type photoconductive detector with its associated thermo-electric cooler, bias supply and amplifier in a complete package. Performance under both laboratory conditions and in a laser rangefinder is discussed and results are compared, with a photo-voltaic detector,operating at 77K using a joule-Thompson cooler.
22 Nov 1986
TL;DR: Hall and resistivity data for epitaxial mercury cadmium telluride layers grown by the MOVPE IMP technique are presented in this paper. But the authors focus on the effect of variation of substrate material and its orientation upon the Hall characteristics of the layers, and a correlation between substrate orientation and anomalous p-character is reported.
Abstract: Hall and resistivity data are presented for epitaxial mercury cadmium telluride layers grown by the MOVPE IMP technique The effect of variation of substrate material and its orientation upon the Hall characteristics of the layers is discussed and a correlation between substrate orientation and anomalous p-character is reported This correlation is explained in terms of a skin effect, which may be present as a surface or an interfacial layer The effect of such a skin when annealing material from p-type to n-type has been investigated The conditions favouring the observation of skin effect have been considered The Hall parameters presented for CMT grown on sapphire indicate layers with low carrier concentration (n ~ 2 x 10 14 cm -3 ) can be grown by this MOVPE process Parameters on both n and p type material are reported
26 Sep 1986
TL;DR: In this paper, the authors proposed a new solution for pyroelectric arrays with 64 elements, which is the state-of-the-art in the current state of the art.
Abstract: Pyroelectric vidicons and newly developped Pyroelectric arrays give a NETD around 0.5 K for 25 Hz chopping frequency. However while Pyroelectric vidicons operate with 200 TV lines, pyroelectric arrays are limited to 64 elements in the present state of the art. This number of elements will probably increase dramatically in the next few years, and new solutions are proposed.