Process Makes Single-Crystal Diamond a Reality

R. Winn Hardin

LMA Inc. has developed a process that grows single-crystal diamond that has performed significantly better than conventional polycrystalline diamond in tests, enabling a host of photonic applications from advanced diode lasers to UV-transmissive windows and boron-doped UV photodetectors.
"Our thrust is to allow people to think of diamond in a very different way," LMA President Robert Linares said. The proprietary chemical vapor-deposition growth method has produced single crystals that are 0.8 cm² and 600 µm thick. Linares hopes to deliver diamond materials measuring 1 cm² and 1 mm thick by the end of the year, and up to 25mm thick by the turn of the century.

Optics' best friend
Diamond is a versatile photonic material, whether it be a heat transfer interface for high-power semiconductor lasers in the telecom industry, a window for a UV to IR spectrometer, a UV photodetector, a single-point diamond-turning machine or an optical component in corrosive or high-temperature environments.
According to Linares, companies have tried to attach conventional polycrystalline diamond films to sensitive optics -- such as germanium and cadmium tellurium -- to protect the windows and lenses from corrosive gases, heat and liquids.
The results have been far from perfect, even with high-grade polycrystalline material, he said. (Low-grade or black polycrystalline material does not transmit visible light, and the highest-quality material contains grain boundaries that scatter light, causing transmission to drop significantly below 500 nm.)
In tests, Linares said, the single-crystal diamond material showed approximately twice the thermal conductivity of black polycrystalline diamond. Despite the comparisons, however, he said single-crystal diamond will enable more applications rather than steal from polycrystalline diamond.
Today LMA is trying to raise capital to expand production of the material, which is undergoing beta tests. Linares expects a finished optic to cost slightly more initially than the same component made from polycrystalline diamond.
Although the raw crystal will cost more, he said the single crystal costs considerably less to polish and finish.