Polarization effect on time-of-flight measurements performed on a CVD diamond single crystal

Abstract

Time-of-flight experiments have been performed on a freestanding CVD diamond sample with Ti–Au contacts. Electron–hole pairs are generated with alpha rays from an 241Am source. A low-field mobility of 2972 cm2/Vs and a saturation velocity of 12.3 × 106 cm/s have been extracted from the hole current pulses. However, the obtained electrons pulse shapes do not allow a clear determination of the mobility. The electrons appear to be slowed down by space-charges located near the contacts. This clear polarization effect is attributed to negative charges trapped at the metal/diamond interface. Its influence has been investigated by comparing the current pulses obtained when applying a negative or positive bias. This bias influences the electric field inside the sample. Two competitive effects can be identified: a bulk effect and a contact effect. Time-of-flight can thus be used to identify the presence of defects in diamond crystals for electronic applications.