High-quality diamond grown by chemical-vapor deposition: Improved collection efficiency in α-particle detection

Abstract

Diamond films were grown on silicon by microwave chemical-vapor deposition using a ${\mathrm{CH}}_4–{\mathrm{H}}_2$ gas mixture. The crystalline quality of the films was assessed through their $\alpha$ -particle detection performance, a property highly sensitive to film quality, by using a 5.5 MeV ${}^{241}\mathrm{Am}$ source. A maximum collection efficiency $\eta$ of 70%, 50% being the average value, was obtained in a 115-μm-thick sample after $\beta$ -particle irradiation (“priming effect”). Unprimed efficiency $\eta$ =50% maximum, 30% average, was also obtained on other samples. The dependence of the efficiency and the resolving power on the external electric field was studied as well. The results are interpreted by means of a Monte Carlo analysis of the $\alpha$ -particle detection process. It is concluded that, in the priming process, a saturation occurs of deep defects limiting the as-grown detector performance, and charge collection distance is only limited by grain boundaries located close to the substrate side. Therefore, there is indication that further improvement can be reasonably obtained by increasing film thickness.