Transient photocapacitance measurement for characterization of deep defects in B-doped (001) and (111) diamond films

Diamond which is expected as a potential material for high-performance electronic devices has several interesting physical properties, such as a large bandgap, high thermal conductivity, and high breakdown field strength. To realize diamond high-performance devices, it is essential to investigate the nonradiative defects of the diamond films which have not been clarified in detail. In this study, we have developed an evaluation system for nonradiative defects by means of transient photocapacitance method, and characterized the boron-doped CVD diamond films. Using a high-power MWPCVD apparatus, undoped buffer and B-doped diamond layers were homoepitaxially grown on mechanically polished high-pressure/high-temperature-synthesized Ib (001) and (111) diamond substrates with an off angle of 5° tilted from the [001] and [111] direction, respectively. As a Schottky electrode, some semi-transparent Au electrodes (15 nm in thickness) were fabricated by an electron beam evaporator. Ohmic electrodes was fabricated by depositing Ti (30 nm)/ Pt (20 nm)/ Au (50 nm) films, followed by a subsequent annealing in vacuum at 460 °C. The system developed in this study for the transient photocapacitance measurements allowed the Schottky diodes to be illuminated by monochromatized light in the energy range of 0.8-2.4 eV with a constant photon flux density.  We clearly observed a steep increase in photocapacitance, due to hole emissions from hole trap states in the depletion layer of the (001) diamond Schottky diode. Signal intensity was increased by the photon irradiation in the energy range above 1.2 eV, indicating the presence of an acceptor-type defect around 1.2 eV above the valence-band edge. On the other hand, (111) diamond Schottky diode had a poor rectification ratio of less than 103. We observed deep defects with a continuous energy distribution in the energy range of 0.8-2.4 eV.

Dr. Osamu Maida is an engineer specializing in semiconductor crystal growth and its defect characterization. He received his PhD in Engineering from Osaka University. Dr. Maida is working to increase the size and quality of heteroepitaxial diamond crystals. He is currently a researcher at the Graduate School of Engineering at Osaka University.