Investigation of Pd/MoO_x/n-Si diodes for bipolar transistor and light-emitting device applications

Sub-stoichiometric molybdenum oxide (MoO x) has recently been investigated for application in high efficiency Si solar cells as a "hole selective"contact. In this paper, we investigate the electrical and light-emitting properties of MoO x-based contacts on Si from the viewpoint of realizing functional bipolar devices such as light-emitting diodes (LEDs) and transistors without any impurity doping of the Si surface. We realized diodes on n-type Si substrates using e-beam physical vapor deposition of Pd/MoO x contacts and compared their behavior to implanted p +n-Si diodes as a reference. In contrast to majority-carrier dominated conduction that occurs in conventional Schottky diodes, Pd/MoO x/n-Si diodes show minority-carrier dominated charge transport with I-V, C-V, and light-emitting characteristics comparable to implanted counterparts. Utilizing such MoO x-based contacts, we also demonstrate a lateral bipolar transistor concept without employing any doped junctions. A detailed C-V analysis confirmed the excessive band-bending in Si corresponding to a high potential barrier (> - > 0.90 V) at the MoO x/n-Si interface which, along with the observed amorphous SiO x(Mo) interlayer, plays a role in suppressing the majority-carrier current. An inversion layer at the n-Si surface was also identified comprising a sheet carrier density greater than 8.6 × 10 11 cm - 2, and the MoO x layer was found to be conductive though with a very high resistivity in the 10 4 ω-cm range. We refer to these diodes as metal/non-insulator/semiconductor diodes and show with our device simulations that they can be mimicked as high-barrier Schottky diodes with an induced inversion layer at the interface.