Fabrication and characteristics of double heterojunction bipolar transistor based on p-CuO/n-Si heterojunction

Oxide-based electronics have found applications ranging from medical implantable devices to low-cost solar panels and large area displays; however, fabricated circuits and devices have been limited to passive elements and at most PN junctions for sensor and photovoltaic applications. Fabricating active elements, i.e., transistors, with the same materials and techniques would usher in considerable advancement in capabilities and usage. Here the successful fabrication of a metal oxide double heterojunction bipolar transistor (DHBT) using p-CuO/n-Si/p-CuO hetero-structure is reported as the first step toward all oxide transistors in the future. CuO was deposited by sputtering on both sides of a 15 mu m thick n-type Si layer and connections were made to three layers separately. IV characteristics of the PNP transistor were then obtained which exhibited a current amplification factor of about 30. A relatively large leakage current at the base-collector junction was present and was consequently remedied by annealing. The leakage was dependent on the deposition conditions of CuO over Si. Oxide semiconductors are either p or n-type making fabrication devoid of doping steps and ion implantation, which greatly simplifies the manufacturing process.