P-N Junction of NiO Thin Film for Photonic Devices

The development of a short-wavelength p-n junction device is essentially important for the realization of transparent electronics for next-generation optoelectronics. Nickel oxide (NiO) thin films with a tunable electrical conductivity of both p-type and n-type under the optimized growth conditions using RF sputtering technique with high optical transmission in the visible region have been fabricated. The room-temperature conductivities for n-type and p-type NiO thin films were about 5.91 × 10¹ and 1.9 ×10^-2 S·cm^-1, respectively. A p-n junction of NiO thin film has been realized, successfully exhibiting good rectifying behavior with efficient UV photodiode characteristics, providing suitable solution for low-cost visible blind UV photodetector application.

I. Introduction

With the increasing demand of short-wavelength high-speed transparent electronic devices, the research community is continuously focusing on the development of an efficient p-n junction where, specifically, homojunctions based on wide-bandgap oxides are of utmost importance. Although the realization of homojunction is attractive, it imposes stringent conditions on the material development. The fabrication of an oxide material exhibiting p-type as well as n-type conductivity is a challenging task where only zinc oxide (ZnO) is reported to exhibit both types of conductivities, and hence, its homojunctions have been attempted. ZnO is a naturally occurring n-type semiconducting material which can exhibit p-type conductivity when deposited under special conditions or doped with certain impurities like N, Sb, As, etc. [1]–[4]. Unfortunately, the reliability and reproducibility of p-type ZnO film is still questionable due to the high ionization energy of acceptor impurities, low solubility of dopants, and self-compensation effect [5]. Hence, efforts are continuing in search of other possible oxide materials for the realization of an efficient homojunction. Nickel oxide (NiO) is a well-known wide-bandgap (bulk value is 4.0 eV) p-type semiconductor which is one of the most promising candidates for the next-generation blue and UV LEDs and lasing devices [6], [7]. Recently, there has been a report on the transformation of conductivity from p-type to n-type in NiO thin films by UV laser irradiation followed by postdeposition annealing [8].