Dependence of the diode characteristics of n-ZnO/p-Si (111) on the Si substrate doping

We report on the dependence of the diode characteristics of n-ZnO on p-type Si (111) on the dopant concentration in the Si (111) substrate. Silicon substrates were used with a high resistivity (p) (∼1 - 20 Ω·cm) and a low resistivity (p+) (∼0.004 - 0.0055 Ω· cm). Zinc-oxide films were deposited using a radio-frequency sputtering system on the p and p+-Si (111) substrates at room temperature. The films were subsequently annealed at 800 .deg. C in air and in N2 in a horizontal thermal furnace to change the electron carrier concentration. By investigating the current and the voltage characteristics of the diodes, we discovered that the diode characteristics depended on the carrier concentration. We discuss the relationship between the carrier concentration and the emission properties of n-ZnO/p-Si diodes. The devices exhibited excellent rectification behavior and diode characteristics, having a turn-on voltage of about 2.3 - 2.7 V and a series resistance between 215 and 330 Ω. The diode characteristics were modified by thermal annealing in an ambient, and n-ZnO/p+-Si (111) heterojunction diodes emitted yellowish light at voltages over 10 V.