Development of a charge-carrier drift velocity measurement system in diamonds by using a UV pulse laser

There are continuing efforts of developing faster FETs and diamond is one of the strong candidates as a base semiconductor. Since the upper-limit-frequency of diamond FETs determines saturated drift velocities of charge-carriers, we need to first characterize diamond to develop better FETs. It is, however, not easy to measure the velocities with response time of less than 20 ns. Therefore, we developed a drift velocity measurement system using a time-of-flight (TOF) technique with a UV laser with 100 ps pulse width. In order to realize response times faster than 20 ns, we employed a 50 Ω coaxial cable as a load, with which we could effectively reduce the stray capacitance and inductance, and also, suppress reflections in the signal which gives false signals. As a result, we can measure carrier-transit times shorter than 10 ns.