Time-resolved OBIC for probing current filamentation in GaAs/Al_xGa_1-xAs heterostructures

We developed a time-resolved optical beam induced current (TROBIC) technique to image current filamentation in a GaAs/Al_xGa_1-xAs heterostructures under high electric field conditions. The TROBIC method combines a laserscan microscope in the OBIC-mode with a sampling oscilloscope to time-resolve the OBIC signal and allowing to operate under high electric field conditions. We attribute the current patterns observed in the TROBIC images to the formation of current filaments in the Al_xGa_1-xAs layer, parallel to the two-dimensional electron gas (2DEG). We show that even in samples where the two-dimensional electron gas and the contacts to the 2DEG are perfectly ohmic and homogeneous, current filaments can still develop at high electric fields.