Cadmium Telluride

Cadmium Telluride
Name	Cadmium telluride
Category	Semiconductor; II-VI compound
Formula	CdTe
Crystal system	Cubic (zincblende)
Color	Grey to black (polycrystalline); brownish (single crystal)
Hardness	~2.5 (Mohs)
Density	6.2 g/cm³
Melting point	1092 °C
Band gap	~1.44 eV (room temperature)

Cadmium Telluride Cadmium telluride is a II-VI compound semiconductor used primarily in photovoltaic devices, radiation detectors, and infrared optics, with a zincblende crystal structure and a direct band gap near 1.44 eV. It combines cadmium and tellurium in a 1:1 stoichiometry and is notable for its near-optimal band gap for single-junction solar cells, high absorption coefficient, and established thin-film manufacturing pathways.

Introduction

Cadmium telluride figures in the histories of Bell Labs, General Electric, Bell Telephone Laboratories, RCA, and Westinghouse Electric Corporation laboratories where early II-VI semiconductor research advanced; it later became central to commercialization attempts by First Solar, GE Energy, Shell Solar, BP Solar, and Sharp Corporation. The material's development intersects with institutions such as Massachusetts Institute of Technology, Stanford University, University of Cambridge, Imperial College London, and California Institute of Technology that contributed to characterization methods; it has been the subject of patents held by Texas Instruments, Hitachi, Mitsubishi Electric, Samsung, and Panasonic Corporation. Strategic initiatives by governments including the United States Department of Energy, the European Commission, the Japan Science and Technology Agency, and the National Renewable Energy Laboratory influenced deployment of cadmium telluride photovoltaics.

Properties

Cadmium telluride exhibits optical and electronic properties exploited in devices; its direct band gap around 1.44 eV yields strong absorption used in thin films by manufacturers like First Solar and researchers at NREL and Fraunhofer ISE, while semiconductor physics developed at AT&T Bell Labs and IBM provided foundational models. Crystallographic and defect studies conducted at Oxford University, ETH Zurich, University of Tokyo, and Seoul National University describe its zincblende lattice, excitonic features, and point defects, with characterization techniques from Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, and Argonne National Laboratory used to probe vacancies and doping. Thermal, mechanical, and electrical research linked to NASA, European Space Agency, CERN, and Los Alamos National Laboratory address radiation hardness and carrier lifetimes important to detector applications.

Synthesis and Growth

Growth methods for cadmium telluride span bulk and thin-film techniques developed and refined by companies such as First Solar, research groups at MIT, Stanford, Kyoto University, and process vendors including Applied Materials, Veeco Instruments, and Oxford Instruments. Techniques include Bridgman growth used historically by Bell Labs and RCA for single crystals, molecular beam epitaxy explored at IBM Research and Hitachi, metal-organic chemical vapor deposition advanced at Epistar, close-spaced sublimation used by First Solar, and sputtering adapted by Sharp and Panasonic. Doping and alloying with zinc, selenium, or mercury to produce CdZnTe, CdTeSe, or HgCdTe were investigated at Princeton University, University of Illinois Urbana–Champaign, University of Manchester, and University of California, Berkeley to tailor band gaps and transport.

Applications

Photovoltaics are the largest application, where commercial modules from First Solar, regionally deployed projects backed by Iberdrola, Enel, EDF Renewables, NextEra Energy and utilities like PG&E and National Grid use CdTe thin films for utility-scale solar plants. Radiation detectors employing CdTe and CdZnTe are used in instruments at CERN, Fermilab, European Synchrotron Radiation Facility, and medical imaging systems by companies such as Siemens Healthineers, GE Healthcare, and Philips; infrared detectors based on HgCdTe trace development to Bell Labs and Raytheon Technologies. Research into tandem cells and integration with perovskite absorbers has involved partnerships among Oxford PV, University of Oxford, EPFL, and Heliatek to boost efficiency. Niche uses include electro-optic devices studied at Bell Labs and MIT Lincoln Laboratory.

Environmental and Health Impacts

Cadmium is a toxic heavy metal whose risks have been addressed by environmental agencies like the United States Environmental Protection Agency, the European Chemicals Agency, and the World Health Organization; occupational exposure standards are set by OSHA and NIOSH. Tellurium compounds have been evaluated by EPA and public health bodies across Canada, Australia, and Japan for environmental fate and toxicity, with life-cycle analyses by IEA and IRENA informing policy. Incidents and remediation efforts involving cadmium compounds have engaged organizations such as Superfund programs in the United States and regional regulators in the European Union, while hazardous waste management standards reference guidance from UNEP and WHO.

Recycling and Disposal

Recycling programs and technology development involving cadmium telluride modules have been pursued by manufacturers like First Solar and recycling firms such as Umicore and Sims Metal Management, with regulatory frameworks influenced by the Waste Electrical and Electronic Equipment Directive in the European Union and extended producer responsibility laws in Japan and South Korea. Demonstration recycling plants and pilot projects funded by DOE programs, the European Commission Horizon 2020 initiative, and private partnerships with Veolia address recovery of cadmium and tellurium, while lifecycle assessments from NREL and Fraunhofer ISE compare environmental impacts to crystalline silicon supply chains involving firms like Trina Solar and JinkoSolar.

Regulatory and Economic Aspects

Trade, subsidies, and market adoption have involved multinational corporations such as First Solar, SunPower, JinkoSolar, Canadian Solar, and policy actions by governments and agencies including the United States Department of Commerce, the European Commission, China Ministry of Commerce, and India Ministry of New and Renewable Energy. International standards and safety regulations from IEC, ISO, and national standards bodies guide module testing and transport overseen by organizations like IATA for shipping, while economic analyses by IEA, World Bank, and BloombergNEF evaluate levelized costs, supply chain risks for tellurium and cadmium, and market forecasts.

Category:Semiconductor materials