Andrey Bolshakov

Surface Channel MESFETs on Hydrogenated Diamond

Metal–semiconductor field effect transistors (MESFETs) based on hydrogen terminated diamond were fabricated according to different layouts. Aluminum gates were used on single crystal and low-roughness polycrystalline diamond substrates while gold was used for ohmic contacts. Hydrogen terminated layers were deeply investigated by means of Hall bars and transfer length structures. Room temperature Hall and field effect mobility values in excess of 100 cm2 V⁻¹ s⁻¹ were measured on commercial and single crystal epitaxial growth (100) plates by using the same hydrogenation process. Hydrogen induced two-dimensional hole gas resulted in sheet resistances essentially stable and repeatable depending on the substrate quality. Self-aligned 400 nm gate length FETs on single crystal substrates showed current density and transconductance values>100 mA mm⁻¹ and >40 mS mm⁻¹, respectively. Devices with gate length LG=200 nm showed fMax=26.4 GHz and fT=13.2 GHz whereas those fabricated on polycrystalline diamond, with the same gate geometry, exceeded fMax=23 GHz and fT=7 GHz. This work focused on the optimization of a self-aligned gate structure with respect to the fixed drain-to-source structure with which we observed higher frequency values; the new structure resulted in improvement of DC characteristics, better impedance matching and a reduction in the fMax/fT ratio.

Diamond device architectures for UV laser monitoring

The paper reviews the status of diamond detectors for UV laser monitoring and imaging. Single pixel detectors, position sensitive architectures, optically activated switches and sensor arrays for beam positioning and imaging are analyzed. The performances of natural diamond and synthetic diamond produced by chemical vapor deposition are compared to evaluate the suitability of such an outstanding material for the described applications.

Laser-driven plasma CVD of thin films

A novel technique for CVD synthesis of materials, that does not demand a vacuum chamber and provides high deposition rates, have been developed. It is based on CW CO2-laser maintenance of a stationary optical discharge in a gas stream, exhausting over a substrate into the air. Nano- and polycrystalline diamond films were deposited on tungsten substrates from atmospherics pressure Xe(Ar):H2:CH4 gas mixtures at flow rates 2 1/min. 2,5 kW CO2-laser focused beam produced plasma. Deposition area was about 1 cm2 and growth rates up to 30-50 micrometers /hour. Peculiarities and advantages of laser plasmatrons are discussed.