Efficient Sub-Bandgap Photodetection via Two-Dimensional Electron Gas in ZnO Based Heterojunction

Sub-bandgap photodetection with two-dimensional electron-confinement in CdZnO-MgZnO heterojunction is realized. The reported photodetection is based on metal-less internal photoemission via optical excitation in 2D electron gas (2DEG) present at the bottom of the conduction band offset in the heterojunction. A physical model is also employed to explain the underlying mechanism of transmission of electrons across the heterojunction. The rib structure of CdZnO waveguide provides strong optical confinement which leads to an improved electro-optic coupling. A high density of 2DEG, uniform momentum distribution across heterojunction and improved electro-optic coupling result in a responsivity of 8.5 mA/W at a wavelength of 532 nm.