Geoffrey Alan Scarsbrook

Properties of bulk polycrystalline CVD diamond

Abstract Properties are reported of bulk polycrystalline diamond synthesized by chemical vapour deposition (BPCVD diamond). It is shown that this material exhibits optical and thermal properties similar to those of high purity natural Type IIa diamond. The mechanical strength and elastic properties of this material have been measured by a disc-bursting technique and values of bursting strength of up to 1138 MPa and Youngs modulus values of 986–1079 GPa have been observed. Indentation measurements indicate a value for fracture toughness K 1c of 6MP a m 1/2 . The dielectric constant and dielectric loss have been measured by an open resonator technique at frequencies of 36, 72 and 144 GHz. Bulk values of dielectric loss tangent as low as 73 × 10 −6 have been observed, the lowest so far reported for CVD diamond. The threshold to laser damage has been tested at laser wavelengths of 10.6, 1.06 and 0.532 μm. Damage thresholds are found to be influenced by bulk absorption. However, the best values measured in BPCVD diamond at 10.6 μm approach that of natural Type IIa diamond.

Thermal properties of bulk polycrystalline CVD diamond

Abstract The thermal properties of bulk polycrystalline CVD diamond are presented and correlated with measured optical properties. A technique for measuring thermal diffusivity is described, and measurements of thermal conductivity as a function of temperature are reported. UV, visible, Fourier transform IR (FTIR) and Raman spectroscopies were used to assess the quality of bulk polycrystalline diamond plates produced by chemical vapour deposition (CVD), which is compared with that of type IIa natural diamond. The refractive index at a wavelength of 10.0 μm was measured as 2.375 ± −0.014, which is in good agreement with the value of 2.3756 accepted for type IIa natural diamond. For colourless, transparent CVD diamond plates, the absorption coefficient in the 8–14 μm wavelength region is between 0.1 and 0.3 cm−1. The data presented show that the thermal and optical properties of CVD diamond with thermal conductivities between 4 and 16.5 W cm K−1 are dictated by the quantity of impurity phases. However, other mechanisms dominate in the very highest quality polycrystalline CVD diamond plates. In these, values of thermal conductivity (up to 21 W cm−1 K−1 at 300 K) and optical transmission (71.3% in the IR and 68% in the visible) approaching those of natural type IIa diamond are achieved.

Development of high quality single crystal diamond for novel laser applications

The extreme properties of diamond make it an exceptional material for a range of demanding optical applications. However, the use of single crystal diamond in lasers has been limited by the availability of suitably-sized crystals with low absorption, and the relatively high levels of strain-related birefringence present. We present recent progress in CVD diamond synthesis which addresses these properties, and show how this new high quality, engineered diamond is enabling novel laser technologies such as mid-IR semiconductor disk lasers and high efficiency diamond Raman lasers.

Unlocking diamond's potential as an electronic material

In this paper, we review the suitability of diamond as a semiconductor material for high-performance electronic applications. The current status of the manufacture of synthetic diamond is reviewed and assessed. In particular, we consider the quality of intrinsic material now available and the challenges in making doped structures suitable for practical devices. Two practical applications are considered in detail. First, the development of high-voltage switches capable of switching voltages in excess of 10 kV. Second, the development of diamond MESFETs for high-frequency and high-power applications. Here device data are reported showing a current density of more than 30 mA mm−1 along with small-signal RF measurements demonstrating gigahertz operation. We conclude by considering the remaining challenges which will need to be overcome if commercially attractive diamond electronic devices are to be manufactured.

Mechanical property measurements of bulk polycrystalline CVD diamond

Abstract This paper reports the bursting strength and Youngs modulus values for bulk polycrystalline chemical vapour deposited (BP CVD) diamond using a differential pressure technique. The pressure-deflection data have a linear relationship and are analysed using plate theory. The results are presented for BP CVD diamond discs (14 and 25 mm in diameter and 179–319 μm thick), silicon, gallium arsenide and sapphire. Youngs modulus values with a range of 986–1079 GPa and bursting strengths of 746–1138 MPa were calculated for BP CVD diamond.

Laser damage testing of CVD-grown diamond windows☆

Abstract Laser-induced damage threshold (LIDT) measurements have been made on bulk polycrystalline (BP) CVD diamond plates using 0.532, 1.06 and 10.6 μm radiation and compared with measurements on natural type IIa diamond samples. Using 10.6 μm radiation, damage thresholds for BP CVD diamond have been measured as 5.6–12.7 MW mm−2 (29–66 J cm−2) using a 50 ns laser spike. These values compare with measurements in type IIa diamond of 12.5–18.5 MW mm−2 made in this study, and values of 3.5–40 MW mm−2 reported elsewhere. The LIDTs measured show a strong correlation with bulk absorption, which is significant at 0.532 μm, and with sample surface finish, but poor correlation with the carbonaceous inclusions found in the samples. Extrapolation from the d.c. dielectric breakdown threshold to the time domain of interest would suggest that, in both current CVD diamond and type IIa single-crystal natural diamond, the damage threshold is being substantially reduced by material or sample imperfections.