Improvement of ZnO/Si Heterojunctions with a Coaxial Circular Transmission Line Model Applicable to both Ohmic and Schottky

Investigating heterointerfaces with test structures is crucial for fabricating electronic and photonic devices. Recently, we proposed and developed a PbS colloidal quantum dot/ZnO/Si hybrid infrared detector for infrared-sensitive optoelectronic devices on silicon-based large-scale integrated circuits. The conventional circular transfer length method (CTLM) is commonly used for evaluating Ohmic contact. To apply the CTLM to a heterointerface junction, we propose a coaxial CTLM (CCTLM) that includes a circular electrode in the middle and doughnut-shaped outer contact electrodes. The proposed test structure can be identified and quantitatively analyzed for the junction type (Ohmic or Schottky) by changing the electrode area. By using the CCTLM test structure for n-type ZnO/n-type Si heterojunctions and X-ray photoemission spectroscopy measurements, we identified the heterojunction as the Schottky type via the CCTLM and estimated the band diagram of the heterojunction.