Electrical properties of isotype and anisotype ZnO/4H-SiC heterojunction diodes

Abstract

Electrical properties of isotype n-ZnO/n-4H-SiC and anisotype n-ZnO/p-4H-SiC heterojunction diodes have been investigated and compared. The influence of the electron concentration in ZnO on diode parameters has been also examined. ZnO/4H-SiC heterojunctions fabricated by atomic layer deposition of ZnO on bulk 4H-SiC substrates show highly rectifying behaviour with leakage current values lower than 10−11A. The isotype heterojunction diodes demonstrate better electrical properties than anisotype heterojunction diodes, in particular lower values of ideality factors (1.13–1.2 as compared to 1.36–1.52), series resistance (5–7 Ω as compared to 66–80 Ω), capacitance (2 times lower, at 0 V), and built-in voltage (1.13–1.42 V as compared to 1.78–1.87 V). Diodes with higher doped ZnO layers show lower series resistance and built-in voltage as compared to diodes with lower doped ZnO layers. Isotype as well as anisotype heterojunction diodes demonstrate a strong influence of UV-light illumination on reverse current-voltage characteristics; however, isotype structures with n-4H-SiC show lower reverse current under cyan (λ = 488 nm) light illumination as to anisotype structures with p-type 4H-SiC, due to the lack of donor-acceptor pair absorption. This makes ZnO/4H-SiC isotype heterojunction diodes more suitable for visible-blind UV photodetectors than the anisotype ones.