Photocurrent Cancelation Due to Barrier Asymmetry in GaAs / Al(x)Ga(1-x)As Heterostructure Photodetectors
Bi-directional photocurrent cancellation in 30 period GaAs/AlxGa1-xAs split-off band photodetectors will be discussed. This cancellation results in a distinctive zero-response “notch” in spectral responsivity curves that can be controlled over the entire response range of the detector by using applied bias voltage. This phenomenon occurs at low negative bias, indicating a built-in potential offset in the AlxGa1-xAs barriers, with higher potential occurring at GaAs-on-AlGaAs interfaces. This asymmetry is also shown in threshold wavelength difference between negative and positive applied bias, and shows increasing potential offset with increasing aluminum fraction of the AlxGa1-xAs barriers. This barrier asymmetry is a major contributor to the photovoltaic operation in otherwise symmetric device structures, and a thorough understanding of this characteristic could lead to better operating and design parameters used for multi-junction photodetectors.