Heterobarrier photodiode MSM structures with subpicosecond temporal resolution

Interdigital heterobarrier metal–semiconductor–metal (MSM) structures are proposed as ultrafast photodetectors of visible radiation. Vertical photocarrier drift in MSM diode structures provides the simplest way of reducing the active region of a detector to a submicron size and of considerably shortening the response time without a significant loss of the radiation coupling efficiency. External electrooptic sampling was used to determine the subpicosecond (half-amplitude duration 0.6 ps) electrical response of a detector built into a coplanar microwave transmission line. Under a bias voltage of 1 V and for an optical excitation energy of 10 pJ per pulse the change in the photodiode voltage amounted to 40% of the bias voltage, which makes these diode structures sufficiently efficient and extremely fast detectors of optical radiation.