R.B. James

• Ph.D.
• Managing Director at Savannah River National Laboratory

The quaternary semiconductor Cd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.1</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-y</su...

We report the first‐time measurement of the electron‐hole pair (ehp) creation energy (Wehp) in novel Cd0.9Zn0.1Te0.98Se0.02 (CZTS) quaternary semiconductor. CZTS in single crystalline form is poised to be the future of large‐volume room‐temperature gamma‐ray detectors due to its excellent compositional homogeneity with highly reduced defects, high‐...

Diode structures, obtained by vacuum deposition of Al onto the surface of a p-Cd0.96Mn0.04Te0.96Se0.04 single crystals, have been manufactured and studied. Applying the Sah-Noyce–Shockley carrier generation-recombination model, a quantitative description of the electrical characteristics of diodes has been achieved. The resistivity of p-Cd0.96Mn0.0...

Cadmium zinc telluride (CdZnTe) with 10 atomic % Zn has been the material of choice for room-temperature semiconductor compact X- and gamma-ray detector applications for over three decades. Despite its commercial success as the most desirable room-temperature semiconductor radiation detection material, CdZnTe (CZT) suffers from a lack of compositio...

We have studied phase transformations in Cd0.96Mn0.04Te0.98Se0.02 solid solutions in the temperature range of 1080-1149 °C using differential thermal analysis (DTA). Following the "heating-dwell-cooling" procedure, we investigated the melt supercooling versus superheating, crystallization temperature versus dwell temperature, and crystallization ra...

2% of selenium was added to CdMnTe (CMT) to reveal the role of selenium in CMT material used as a gamma-ray detector. The average etch-pit density (EPD) in a typical 2-inch CdMnTeSe (CMTS) wafer was measured to be about 8.3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> cm <sup xmlns:mml="h...

In this work, we studied the free-carrier transport properties and space-charge formation/polarization in a CdZnTe bar-shaped radiation detector using the Laser-Induced Transient Current technique. We found out that a steady-state space charge ranging from 8 × 108 to 2.1 × 109 cm−3 is formed throughout the detector at about 0.5 s following biasing....

The performance of the state-of-the-art Cd1-xZnx Te1-ySey (CZTS) detectors, an emerging wide bandgap high-resolution room-temperature semiconductor radiation detector, is currently limited by the presence of various charge trapping centers including impurities and intrinsic point defects. In this article, we compare the performance of two CZTS sing...

Incorporation of Se into Cd1−xZnxTe (CZT) to form the quaternary compound semiconductor Cd1−xZnxTe1–ySey (CZTS) has proven to be an effective solution for compensating the major flaws associated with CZT, including poor homogeneity and high concentrations of electronically active deep levels that limit the performance of CZT detectors. In order to...

The quest for cost-effective, high performing room temperature semiconductor detector (RTSD) materials for high-energy gamma rays has been continuing for more than three decades. The requirements for RTSD materials, however, are more stringent as compared to other applications unrelated to detection of X- and gamma rays, mainly due to the requireme...

Nuclear detectors for x-ray and gamma-ray spectroscopy and imaging are a vital tool in many homeland security, medical imaging, astrophysics and other applications. Most of these applications require room-temperature operation due to the operational constraints imposed by a cryogenic cooling system. CdZnTe (CZT) has been the main material with the...

Because of its excellent opto-electronic properties, CdZnTe (CZT) has been the material of choice for x- and gamma-ray detectors operable at room temperature. CZT is the leading commercially available room-temperature radiation detector material today. Although much progress has been made over the past three decades, today's CZT crystals still face...

CdZnTe(CZT) detectors with more than 10% zinc content did not show any remarkable improvement in the detector performance due to the additional defects introduced by the higher zinc content. However, recent research showed that the formation of defects was suppressed effectively by adding a small amount of selenium (at. 2%) in CZT. On this basis, w...

The quest for cost-effective, high-performing radiation detector materials operable at ambient temperature has continued for more than three decades. One key to lower the overall detector cost of production is a high degree of compositional homogeneity. Spatial homogeneity of the charge-transport properties of the detector material is also essentia...

In this article, we report the growth of Cd0.9Zn0.1Te0.97Se0.03 (CZTS) wide bandgap semiconductor single crystals for room temperature gamma-ray detection using a modified vertical Bridgman method. Charge transport properties measured in the radiation detectors, fabricated from the grown CZTS crystals, indicated signs of hole trapping. Hole traps i...

We performed a gradual low-temperature annealing up to 360 K on a CdZnTeSe radiation detector equipped with gold and indium electrodes under bias at both polarities. We observed significant changes in the detector’s resistance and space-charge accumulation. This could potentially lead to the control and improvement of the electronic properties of t...

Quaternary Cd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.1</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-y</sub> Se <sub xmlns:m...

The electron- and hole-transport properties in cadmium zinc telluride selenide (CZTS) crystals are studied using a laser-induced transient-current technique with pulsed and dc bias. The internal electric field profile and velocity of surface recombination are determined by Monte Carlo simulations of electron and hole transient currents combined wit...

Both material quality and detector performance have been steadily improving over the past few years for the leading room temperature radiation detector material cadmium-zinc-telluride (CdZnTe). However, although tremendous progress being made, CdZnTe still suffers from high concentrations of performance-limiting defects, such as Te inclusions, netw...

Detection of X- and gamma-rays is essential to a wide range of applications from medical imaging to high energy physics, astronomy, and homeland security. Cadmium zinc telluride (CZT) is the most widely used material for room-temperature detector applications and has been fulfilling the requirements for growing detection demands over the last three...

X- and gamma-ray detectors are increasingly becoming an essential tool for science and technology in various fields, including homeland security, nonproliferation, nuclear security, medical imaging, astrophysics, and high energy physics. Cd1−xZnxTe1−ySey (CZTS) is emerging as a next-generation compound semiconductor for such applications. CZTS was...

We studied the spectral dependence of the Vickers microhardness HV0.025 of CdZnTe and CdZnTeSe samples upon illumination and found out that it increases over the entire applied spectral range of 1540–750 nm. We also found out that the photoconductivity and microhardness are correlated. We observed changes in the correlation diagram (change of slope...

This paper describes a new method for direct measurement and evaluation of the inhomogeneous electrostatic vector field with translational symmetry in electro-optic materials exhibiting the Pockels effect. It is based on the evaluation of maximum transmittance of low intensity light passing through a sample under a voltage bias. Here, the sample is...

The electrical and spectrometric characteristics of the Cr/cadmium telluride (CdTe)/Pt structure with a metal-semiconductor type rectifying contact, used in X/γ-ray detectors, are investigated. For the detectors fabrication, chlorine-doped CdTe crystals with a resistivity of (3-6) × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink...

An important area of modern electronics is creation of applied semiconductor structures with the use of laser technology. In particular, laser liquid-phase epitaxy of layers on а crystal substrate can be realized using laser radiation with a given critical energy density. This process is insufficiently studied for the CdTe and Cd1-xMnxTe crystals,...

Wide bandgap semiconductor materials capable of detecting X-rays and gamma-rays at room temperature without cryogenic cooling have great advantages that include portability and wide-area deployment in nuclear and radiological threat defense. Additional major applications include medical imaging, spectroscopy, and astrophysics. Most current room-tem...

We have characterized the structural quality of Cd0.9Zn0.1Te0.93Se0.07 ingot grown by the vertical Bridgman growth technique. The structural quality of Cd0.9Zn0.1Te0.93Se0.07 ingot along the length was investigated via X-ray topography in the reflection mode using a white beam synchrotron radiation source. The X-ray topography data revealed the pre...

CdZnTe (CZT) crystals with thicknesses up to 20 mm and diameters up to 75 mm have become available from Redlen Technologies, Inc. for making large-volume gamma-ray detectors. The modified growth and optimized annealing conditions allowed Redlen to minimize the dark current and improve the uniformity of CZT crystals. Two detector designs, pixelated...

CdZnTe (CZT) has been under continuous development as a room-temperature radiation detector for the past 2–3 decades. Due to its intrinsic defects, such as a high concentration subgrain boundary network, it has been very challenging to consistently produce high-quality CZT detectors with high yield, particularly for detector volumes exceeding a few...

The effect of selenium in CdZnTe was investigated by characterizing the Cd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.1</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:x...

Cadmium zinc telluride selenide (Cd1−xZnxTe1−ySey or CZTS) is one of the emerging CdTe-based semiconductor materials for detecting X- and gamma-ray radiation at or near room temperature (i.e., without cryogenic cooling). Potential applications of CZTS sensors include medical imaging, X-ray detection, and gamma-ray spectroscopy. Chemical passivation...

A study of deep levels in CdZnTeSe radiation-detection materials is presented. The approach relies on electrical methods that combine time and temperature evolution of the electric field and electric current after switching on the bias voltage. Two optical methods were also applied to study the deep levels. The first method utilizes the temperature...

X- and gamma-ray detectors are increasingly becoming essential tools for science and technology in various fields. These detectors offer broad applications such as homeland security, nonproliferation, nuclear security, medical imaging, astrophysics, and high energy physics. All these applications demand high-resolution detectors operable at room te...

X- and gamma-ray detectors have broad applications ranging from medical imaging to security, non-proliferation, high-energy physics and astrophysics. Detectors with high energy resolution, e.g. less than 1.5% resolution at 662 keV at room temperature, are critically important in most uses. The efficacy of adding selenium to the cadmium zinc telluri...

Because of its ideal band gap, high density and high electron mobility-lifetime product, cadmium zinc telluride (CdZnTe or CZT) is currently the best room-temperature compound-semiconductor X- and gamma-ray detector material. However, because of its innate poor thermo-physical properties and above unity segregation coefficient for Zn, the wide spre...

We present time-resolved nonequilibrium carrier and coherent acoustic phonon dynamics in (Cd, Mg)Te single crystals intended for detection of high-energy x-ray photons. Our (Cd, Mg)Te crystals were grown using a vertical Bridgman method and during the process were doped either with In (a shallow dopant) or Ge (a deep impurity). Next they were cut i...

We investigated the influence of deep levels on the electrical transport properties of CdZnTeSe (CZTS) radiation detectors by comparing experimental data with numerical simulations based on the simultaneous solution of drift-diffusion and Poisson equations, including the Shockley-Read-Hall model of the carrier trapping. We determined the Schottky b...

In this article, we report on the charge-transport characteristics of a new quaternary material Cd1-xZnxTe1-ySey (CZTS) grown by the Traveling Heater Method (THM). The as-grown CZTS material was found to possess fewer Te inclusions than CZT†. Moreover, high resistivity of ∼1-2x10¹⁰ ohm-cm was achieved, meeting the requirements of most gamma-ray det...

We grew Cd1-xMnxTe crystals with a nominal composition of 5% Mn and 95% Cd using the vertical Bridgman technique. We were able to grow crystals from as-received starting material that were free of secondary phases, such as Te inclusions with a size > 1-µm diameter, without adding compensating Cd to the initial charge. The Te precipitations (size <...

We grew Cd1-xMnxTe crystals with a nominal Mn concentration of 5% by the vertical Bridgman growth technique. The compositional variation along the length of the grown ingot was studied by powder X-ray diffraction. The composition was found to be uniform along the growth direction. The achieved resistivity was 1-2.5 x10¹⁰ ohm-cm with a mobility-life...

We investigated the influence of deep levels on the electrical transport properties of CdZnTeSe radiation detectors by comparing experimental data with numerical simulations based on simultaneous solution of drift-diffusion and Posisson equations, including the Shockley-Read-Hall model of the carrier trapping. We determined the Schottky barrier hei...

We present a study of deep levels in CdZnTeSe radiation-detection materials. The approach relies on electrical methods that combine time and temperature evolution of the electric field and electric current after switching on the bias voltage. We also applied two optical methods to study the deep levels. The first method utilizes the temperature and...