Metal-induced growth of crystal Si for low-cost Al:ZnO/Si heterojunction thin film photodetectors

Quality crystal silicon (Si) thin films were grown via the metal-induced growth (MIG) method, which is a low-cost and metal-silicide assisted technique. The metal catalysts of Ni, Pd and Co were first deposited onto substrates for silicide template layer formation. Then, crystal Si thin films with a thickness of ~ 5 µm were epitaxially deposited on the silicide seeds via DC magnetron sputtering. The crystallinity of the Si films was confirmed and investigated by X-ray diffraction (XRD). These Si thin films were then used to fabricate Al doped ZnO (AZO)/MIG Si heterojunction photodetectors. The device achieved a saturation photocurrent of 23.2 mA/cm2 at − 5 V. This photocurrent level is comparable with that of previous reported AZO/bulk-Si devices. Current transport mechanisms and defect distributions were also studied. By analyzing the dark current-voltage (I - V) characteristics, the space charge limited (SCL) current dominated junction behaviors with an exponential defect level distribution were determined. In the bias range of 0.25 V < V < 1.0 V, SCL current transported in the mobility regime based on I ∝ Vβ, where β > 3. For 0 < V < 0.25 V, tunneling and SCL current in ballistic regime were implied due to I ∝ V1.5. In the reverse bias, the device exhibited SCL current in saturation regime or tunneling, suggested by the unity I-V relation. The fabricated devices with the theoretical understanding of the defect and carrier transport mechanisms provided new design insights for low-cost ZnO/MIG-Si thin film optoelectronics.