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

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.