Memory Switching Effects in a-Si/c-Si Heterojunction Bipolar Structures

We report a three-terminal undoped amorphous silicon (a-Si) / p-n crystalline silicon (c-Si) structure, which exhibits off and on states. An offstate is characterized by a current in the structure in the low nanoampere range due to the large resistance of the undoped a-Si layer, while in the on state the structure exhibits a large conductance and its current is determined in practice by the load resistance. Reversible switching between the two states with a rise time of about 40 ns and a fall time of about 200 ns was achieved by applying appropriate positive or negative current pulses to the base of the c-Si p-n junction. The structure can be integrated into a standard bipolar process, and, being of a size suitable for VLSI applications, may be useful as a basic three-terminal memory cell.