Sandia National Laboratories

Other

Sandia Corporation

Ralph B James

Arnold Burger

Douglas A Chinn

Gomez W Wright

Tuviah E Schlesinger

Haim Hermon

Mark J Mescher

Edwin Y Lee

Henry S Chang

John M Van Scyoc, Iii

Kuo-Tong Chen

H Walter Yao

A method for treatment of the surface of a CdZnTe (CZT) crystal that provides a native dielectric coating to reduce surface leakage currents and thereby, improve the resolution of instruments incorporating detectors using CZT crystals. A two step process is disclosed, etching the surface of a CZT crystal with a solution of the conventional bromine/methanol etch treatment, and after attachment of electrical contacts, passivating the CZT crystal surface with a solution of 10 w/o NHF and 10 w/o HOin water.

Surface treatment and protection method for cadmium zinc telluride crystals

A photolithographic process forms patterns on HgI surfaces and defines metal sublimation masks and electrodes to substantially improve device performance by increasing the realizable design space. Techniques for smoothing HgI surfaces and for producing trenches in HgI are provided. A sublimation process is described which produces etched-trench devices with enhanced electron-transport-only behavior.

Lithography process for patterning HgI2 photonic devices

A CdZnTe (CZT) crystal provided with a native CdO dielectric coating to reduce surface leakage currents and thereby, improve the resolution of instruments incorporating detectors using CZT crystals is disclosed. A two step process is provided for forming the dielectric coating which includes etching the surface of a CZT crystal with a solution of the conventional bromine/methanol etch treatment, and passivating the CZT crystal surface with a solution of 10 w/o NH F and 10 w/o H O in water after attaching electrical contacts to the crystal surface.

Ionizing radiation detector

A method for treatment of the surface of a CdZnTe (CZT) crystal that provides a native dielectric coating to reduce surface leakage currents and thereby, improve the resolution of instruments incorporating detectors using CZT crystals. A two step process is disclosed, etching the surface of a CZT crystal with a solution of the conventional bromine/methanol etch treatment, and after attachment of electrical contacts, passivating the CZT crystal surface with a solution of 10 w/o NH F and 10 w/o H O in water.

An improved semiconductor radiation detector which involves engineering the internal electrical field through an external infrared light source. A planar semiconductor radiation detector is applied with a bias voltage, and an optical light beam with a selected photon energy is used to illuminate the detector and engineer the internal electric field. Different light beam intensities or photon energies produce different distributions of the internal electric field. The width of the electric field can be fine-tuned by changing the optical beam intensity and wavelength, so that the radiation detector performance can be optimized. The detector is portable, small in size, and operates at room temperature.

Semiconductor radiation spectrometer

Wafer-fused semiconductor radiation detector useful for gamma-ray and x-ray spectrometers and imaging systems. The detector is fabricated using wafer fusion to insert an electrically conductive grid, typically comprising a metal, between two solid semiconductor pieces, one having a cathode (negative electrode) and the other having an anode (positive electrode). The wafer fused semiconductor radiation detector functions like the commonly used Frisch grid radiation detector, in which an electrically conductive grid is inserted in high vacuum between the cathode and the anode. The wafer-fused semiconductor radiation detector can be fabricated using the same or two different semiconductor materials of different sizes and of the same or different thicknesses; and it may utilize a wide range of metals, or other electrically conducting materials, to form the grid, to optimize the detector performance, without being constrained by structural dissimilarity of the individual parts. The wafer-fused detector is basically formed, for example, by etching spaced grooves across one end of one of two pieces of semiconductor materials, partially filling the grooves with a selected electrical conductor which forms a grid electrode, and then fusing the grooved end of the one semiconductor piece to an end of the other semiconductor piece with a cathode and an anode being formed on opposite ends of the semiconductor pieces.

Wafer-fused semiconductor radiation detector

An electron gas grid semiconductor radiation detector (EGGSRAD) useful for gamma-ray and x-ray spectrometers and imaging systems is described. The radiation detector employs doping of the semiconductor and variation of the semiconductor detector material to form a two-dimensional electron gas, and to allow transistor action within the detector. This radiation detector provides superior energy resolution and radiation detection sensitivity over the conventional semiconductor radiation detector and the &ldquo;electron-only&rdquo; semiconductor radiation detectors which utilize a grid electrode near the anode. In a first embodiment, the EGGSRAD incorporates delta-doped layers adjacent the anode which produce an internal free electron grid well to which an external grid electrode can be attached. In a second embodiment, a quantum well is formed between two of the delta-doped layers, and the quantum well forms the internal free electron gas grid to which an external grid electrode can be attached. Two other embodiments which are similar to the first and second embodiment involve a graded bandgap formed by changing the composition of the semiconductor material near the first and last of the delta-doped layers to increase or decrease the conduction band energy adjacent to the delta-doped layers.

Electron gas grid semiconductor radiation detectors

A method for reducing the leakage current in CZT crystals, particularly Cd.sub.1-x Zn.sub.x Te crystals (where x is greater than equal to zero and less than or equal to 0.5), and preferably Cd.sub.0.9 Zn.sub.0.1 Te crystals, thereby enhancing the ability of these crystal to spectrally resolve radiological emissions from a wide variety of radionuclides. Two processes are disclosed. The first method provides for depositing, via reactive sputtering, a silicon nitride hard-coat overlayer which provides significant reduction in surface leakage currents. The second method enhances the passivation by oxidizing the CZT surface with an oxygen plasma prior to silicon nitride deposition without breaking the vacuum state.

Method for surface passivation and protection of cadmium zinc telluride

A method for treatment of the surface of a CdZnTe (CZT) crystal that reduces surface roughness (increases surface planarity) and provides an oxide coating to reduce surface leakage currents and thereby, improve resolution. A two step process is disclosed, etching the surface of a CZT crystal with a solution of lactic acid and bromine in ethylene glycol, following the conventional bromine/methanol etch treatment, and after attachment of electrical contacts, oxidizing the CZT crystal surface.

Method for surface treatment of a cadmium zinc telluride crystal

A method of purifying nonmetallic, crystalline semiconducting materials useful for room temperature radiation detecting devices by applying an electric field across the material. The present invention discloses a simple technology for producing purified ionic semiconducting materials, in particular PbI.sub.2 and preferably HgI.sub.2, which produces high yields of purified product, requires minimal handling of the material thereby reducing the possibility of introducing or reintroducing impurities into the material, is easy to control, is highly selective for impurities, retains the stoichiometry of the material and employs neither high temperatures nor hazardous materials such as solvents or liquid metals. An electric field is applied to a bulk sample of the material causing impurities present in the sample to drift in a preferred direction. After all of the impurities have been transported to the ends of the sample the current flowing through the sample, a measure of the rate of transport of mobile impurities, falls to a low, steady state value, at which time the end sections of the sample where the impurities have concentrated are removed leaving a bulk sample of higher purity material. Because the method disclosed here only acts on the electrically active impurities, the stoichiometry of the host material remains substantially unaffected.

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Livermore, CA, United States of America

Ralph B James