© (2006) Elsevier

The semiconductor zinc telluride has attracted much attention as a promising material for fabricating compact terahertz emitters and detectors, and has already demonstrated efficient emission over a broad spectral range. A crucial factor when designing these devices is the thickness of the zinc telluride layer: in order to maximize the frequency bandwidth, it needs to be less than ten micrometres. The question is what is the best way to create such thin films? Polishing a block of zinc telluride is a common technique; however, it can be complex and, consequently, expensive. It also sets an upper limit on the size of the final film of about 20 millimetres.

Epitaxy — the growth of a crystalline material on a substrate one atomic layer at a time — offers an alternative and is now being investigated by a collaboration between Saga and Osaka universities1. In a controlled chamber, the team grew a zinc telluride film on sapphire. This robust substrate allows the fabrication of large films and control of layer thickness is relatively easy thanks to the constant growth rate. Using a laser to excite the sample, the team observe emission over a range of about 40 THz and a peak at 15 THz. After a thermal anneal to improve the crystal structure, the total emission intensity is very similar to that from films created by polishing.

This technique opens the way for creating thinner zinc telluride films that could find a use in free-space communications, sensitive detection of explosives and narcotics, as well as a whole host of medical applications.