Making cheaper supercrystals

Semiconducting crystals at the heart of next-generation high-resolution scanning and imaging devices could be produced more cheaply and efficiently thanks to a new process introduced by a Durham University spin-out company.

Cadmium Telluride and Cadmium Zinc Telluride crystals at the heart of next-generation high-resolution scanning and imaging devices could be produced more cheaply and efficiently thanks to a new process introduced by a Durham University spin-out company.

Arnab Basu, managing director of Durham Scientific Crystals, explained that the semiconducting crystals, or ‘super’ crystals, are becoming an increasingly important component in a variety of imaging and scanning devices but that the processes currently used to produce these crystals are both expensive and inefficient. It is partly due to the high cost of the process that the current market value of super crystals is nearly 10 times that of gold.

Conventional liquid-phase techniques, in which crystals are grown through evaporation, produce relatively low volumes of good-quality material, said Basu. But the new process, which uses a novel multi-tube physical vapour transport method, produces crystals from the vapour phase of growth – using condensation rather than evaporation. This, claimed Basu, results in bigger crystals with better mechanical properties and fewer defects. It therefore makes the production of super crystals more cost-effective and potentially opens up the technology to a wider range of applications.

Basu was keen to stress, though, that while the Durham process will make the crystals more cost-effective, super crystals produced using conventional methods are already used in a variety of applications. One particularly promising area he identified was in the development of digital radiography equipment, where the use of semi-conducting crystals can effectively halve the time taken to produce an X-ray image.

He explained that rather than converting radiation into light and then into an electrical signal, semiconducting crystals make it possible to convert the X-ray directly into an electrical signal and therefore produce a much higher- resolution image. He said that, aside from medical imaging applications, the crystal also has potential use in gamma ray detectors used in space exploration and in the security market for scanning equipment used in baggage scanners.

Basu said that while the basic principles behind the process are relatively simple, the Durham team has added a number of innovative steps that enable precise control of temperature throughout the process.

The team has also developed a method for preventing the crystal from coming in contact with the quartz structure in which it is grown, leading to further improvements in the quality of the crystals. The company expects to become one of the first to move into NetPark, a major new science park in the north-east.

Once there it hopes to be able to produce 28,000cm2 of semiconducting crystal per year. Basu said the crystals should be making their first commercial appearance early next year, with a number of customers lined up in the space and security industries.

Basu is optimistic about the technology’s potential. Within three years he expects the company to be serving around 10 per cent of a global market estimated to be worth $50-70m.

A basic description of the process can be found <link>here=http://www.dur.ac.uk/scientific.enterprise/Crystal%20Growth%20page.htm</link>.