The structure and the optical-electrical properties of the ZnO films and the Al:ZnO/N: ZnO homojunction photodiode

Abstract

In this article, Al or N-doped ZnO films are prepared by wet chemical deposition method, and then the Al-ZnO/N-ZnO homojunction photodiode is structured. The influence of triethanolamine (TEA) content and deposition temperature on the structure, phase, and optical-electrical properties of N-ZnO films is investigated. The results of X-ray Diffraction (XRD) measurement show that the N-ZnO films have a hexagonal wurtzite structure with a preferred growth orientation along (002) crystal plane. The obvious Raman peak appeared at 436 cm−1 should be assigned to non-polar high-frequency E2H mode, which indicates the good crystallinity of N-ZnO film. The results of low temperature photoluminescence (LT-PL) measurement exhibit that the peak of UV emission, which shifts from 386 to 390 nm with the increase in measurement temperature from 50 to 250 K, may be mainly the exciton emission, coming from shallow donor Zni to valence band (Zni →VB: ΔE~3.15 eV) or conduction band to the shallow acceptor No (CB→No: ΔE~3.215 eV). Two visible emissions peaks may be attributed to the electron transitions from the single charged oxygen vacancies Vo+ and the double charged oxygen vacancies Vo++ defects, respectively. Three infrared emission peaks may be related to the electron transitions from the transition from deep donor level (Vo, Zni) to deep acceptor level (OZn) or the intra band transition between two states of Vo and Zni. For the response times of Al-ZnO/N-ZnO homojunction photodiode, the rise time (τr) is <2 ms and the decay time (τd) is about 22 ms. The value of responsivity (R) is calculated to be about 0.274 mA/W.