T. E. Schlesinger

Cadmium zinc telluride and its use as a nuclear radiation detector material

We present a comprehensive review of the material properties of cadmium zinc telluride (CZT, Cd1ˇxZnxTe) with zinc content xa 0:1‐0.2. Particular emphasis is placed on those aspects of this material related to room temperature nuclear detectors. A review of the structural properties, charge transport, and contacting issues and how these are related to detector and spectrometer performance is presented. A comprehensive literature survey and bibliography are also included. # 2001 Elsevier Science B.V. All rights reserved.

Determination of the interdiffusion of Al and Ga in undoped (Al,Ga)As/GaAs quantum wells

We have employed photoluminescence spectroscopy to determine the temperature dependence of the interdiffusion coefficient of Al and Ga in GaAs/Al0.3Ga0.7As quantum wells. The position of the photoluminescence peaks, due to the n=1 electron to heavy‐hole transition, was measured before and after annealing the samples. A variational calculation was employed to determine the expected position of these photoluminescence peaks and from this a value of the interdiffusion coefficient was extracted. The interdiffusion process is characterized by an activation energy of about 6 eV leading to an interdiffusion coefficient at 850 °C of 4×10−19 cm2/s. This technique allows for the measurement of small diffusion coefficients in a wide variety of material systems.

Evidence for EL6 (Ec―0.35 eV) acting as a dominant recombination center in n-type horizontal Bridgman GaAs

Horizontal Bridgman grown n‐type GaAs is shown to contain two important electron traps EL6 (0.35 eV) and EL2 (0.80 eV) in the 1015 cm−3 concentration range. A heat treatment at 800 °C for 1 h results in the reduction of EL6 to about 1013 cm−3 to a depth of at least 10 μm and an increase in EL2 by an amount about equal to the reduction of EL6. Measurement of the minority‐carrier (hole) diffusion lengths in this depth range by an electron beam induced current (EBIC) technique shows an inverse correlation with the concentration of the EL6 trap. The results may be explained if EL6 is assumed to be VGa‐VAs, EL2 to be AsGa‐VAs, and the interaction between the two traps to involve Asi.

CHAPTER 9 - Cd1−xZnxTe Spectrometers for Gamma and X-Ray Applications

Most of the efforts on Cd 1- x Zn x Te (CZT) gamma ray spectrometers have been motivated by the benefits and commercial success of cadmium-tellurium (CdTe) devices and the possibility of manufacturing relatively large homogeneous CZT crystals at an acceptable cost. CdTe detectors have been shown to operate at room temperature, have good stopping power for energetic photons, produce reliable spectra, and be rugged in field applications. CdTe devices and instruments are sold today for environmental monitoring, waste remediation, industrial gauging, monitoring nuclear materials, and medical instrumentation. This chapter focuses on CZT detector technology. It discusses CdTe and growth of CZT crystals. The chapter reviews the properties of the material, particularly those properties that pertain to detector performance. A review of the performance of CZT gamma and x-ray spectrometers and imaging arrays are also presented. The chapter concludes with a brief discussion of future work needed to advance the technology.

Imaging of optical field confinement in ridge waveguides fabricated on very-small aperture laser

Optical field confinement in a ridge waveguide nanostructure (“C” aperture) designed for ultrahigh-density recording was observed using an apertureless near-field scanning optical microscope. The aperture was fabricated on a commercial edge-emitting semiconductor laser as the light source. High-contrast near-field images at both 1× and 2× lock-in detection frequencies were obtained. The emission patterns are in agreement with theoretical simulation of such structures. A 90 nm×70 nm full width half maximum spot size was measured and is comparable to the ridge width of the aperture.

Guided-wave electro-optic beam deflector using domain reversal in LiTaO/sub 3/

We have fabricated and demonstrated the operation of electro-optic beam deflectors using domain reversal in planar waveguides fabricated on LiTaO/sub 3/ substrates. The planar waveguides were made using proton exchange on z-cut substrates, and proton exchange with subsequent rapid thermal annealing was used to form the inverted domains. The deflection sensitivity of the device was measured to be about 6.7 mrad/kV. Calculations indicate that the deflection sensitivity should be increased by a factor of 25 to 30 with improvements in device geometry. >

Study of impurity segregation, crystallinity, and detector performance of melt-grown cadmium zinc telluride crystals

A review of growth methods used to produce Cd 1-x Zn x Te (CZT) (0.0<x<0.20) crystals for radiation detector applications is presented. Most of the results emphasize the high-pressure Bridgman (HPB) method. For selected melt-grown HPB ingots, the liquid/solid segregation coefficients of some impurities were measured. The correlation of the impurity content and nuclear detector performance will be discussed. Extended defects and surface and bulk crystallinity were measured using triple and double axis X-ray diffraction techniques (TAD and DAD-XRD), X-ray topography, and infrared microscopy. X-ray diffraction maps and IR images were generated and compared to gamma-ray detector tests to correlate macroscopic defects with the nuclear detector responses. Defects states of CZT were also investigated using low-temperature photoluminescence spectroscopy. Comparisons between the material and detector properties for different CZT growth methods will be discussed.

Ridge waveguide as a near-field optical source

We investigate the feasibility of using a ridge waveguide at optical frequencies as a near-field optical transducer, using the finite difference time domain method. The complete electromagnetic field picture of the ridge waveguide, in the absence and presence of the irradiated medium, is presented. A power efficiency of 7% and an optical spot with full width half maximum of 50 nm×80 nm is obtained in the medium. We show that impedance considerations play a major role in the transducer-medium optical coupling.

An Integrated Read/Write Head for Hybrid Recording

A proposed integrated read/write head for hybrid recording is described. This design features a thin film waveguide to deliver light to an aperture. This aperture is described in terms of the propagating modes of a ridge waveguide with a reduced cutoff frequency. Also included in this integrated head is a geometry that maintains the necessary coincidence of the optical and magnetic fields. The essential features of this design are very compatible with existing fabrication methods.

Study of defects in LEC-grown undoped SI-GaAs by thermally stimulated current spectroscopy

Abstract Thermally stimulated current spectroscopy (TSC) reveals at least six traps in LEC semi-insulating GaAs. The relative concentrations of the traps are related to the native defect complexes expected from growth stoichiometry and subsequent annealing conditions. Variations of the sample conditions prior to the TSC scan are found to provide some evidence as to nature of the traps observed and also appear to cause photo-induced defect reactions.