Growth and properties of transparent p-NiO/n-ITO (In 2 O 3 :Sn) p–n junction thin ﬁlm diode B.V. Mistry a , P. Bhatt b , K.H. Bhavsar a , S.J. Trivedi a , U.N. Trivedi b , U.S. Joshi a, ⁎ a Department of Physics, University School of Sciences, Gujarat University, Ahmedabad-380 009, India b Department of Instrumentation and Control, Vishwakarma Government Engineering College, Chandkheda, Gandhinagar-382 424, India abstract article info Article history: Received 7 June 2010 Received in revised form 13 January 2011 Accepted 14 January 2011 Available online 28 January 2011 Keywords: Transparent conducting oxide p–n junction Current–voltage characteristics Chemical solution deposition We have grown “all oxide” transparent p–n junction thin ﬁlm nanostructure device by using chemical solution deposition and E-beam evaporation onto SiO 2 substrate. Combined grazing incidence X-ray diffraction and atomic force microscopy conﬁrm phase pure, mono-disperse 30 nm NiO and 2 at. wt.% Sn doped In 2 O 3 (ITO) nanocrystallites. Better than 70% optical transparency, at a wavelength of 600 nm, is achieved across 160 nm thick p–n junction. The optical band gap across the junction was found to decrease as compared to the intrinsic ITO and NiO. The current–voltage (I–V) characteristics show rectifying nature with dynamic transfer resistance ratio of the order of 10 3 in the forward bias condition. Very small reverse leakage current with appreciable breakdown was observed under the reverse bias condition. The observed optical and electrical properties of oxide transparent diode are attributed to the heteroepitaxial nature and carrier diffusion at the junction interface. © 2011 Elsevier B.V. All rights reserved. 1. Introduction “Transparent electronics” is an emerging technology that employs wide band-gap semiconductors for the realization of invisible circuits for next generation optoelectronic devices [1–5]. Wide band gap transparent conducting oxides (TCO) are interesting materials because of their tenability to efﬁciently combine the high/low conductivity with high visual transparency. TCO materials exhibiting high optical transparency and electrical conductivity that can be grown as efﬁciently as thin ﬁlms are used extensively for a variety of applications including architectural windows, thin ﬁlm photovoltaics, other optoelectronic devices [6,7], solar cells [8], ion-storage [9], ﬂat panel displays (FPD) [10], defrosting windows in refrigerators and airplanes [11], gas sensors [12], etc. Transparent conducting oxides, such as cadmium oxide (CdO) [13], tin oxide (SnO 2 ) [14], zinc oxide (ZnO) [15], indium tin oxide (ITO), [16] etc., have great technological potential due to their right combination of electrical and optical properties. Most of the well-known and widely used transparent conducting oxide thin ﬁlms such as ZnO, SnO 2 , ITO, etc. are n-type material, but their corresponding p-type counterpart of transparent conducting oxides were surprisingly missing for a long time. There are a number of reports available on p-type transparent conducting oxides such as CuAlO 2 , LaCuO 2 , SrCu 2 O 2 , etc. [17–19]. On the other hand, in parallel, there is an effort to ﬁnd an effective way to achieve p-type conduction in the generally n-type oxides such as ZnO [20]. This has opened up a new ﬁeld in optoelectronics device technology, the so-called “transparent electronics,” where a combination of the two types of transparent conducting oxides in the form of a p–n junction could lead to a “functional” window, which transmits visible portion of the solar radiation yet generates electricity by the absorption of the UV part of it. Most of the presently known TCO ﬁlms, for example, indium tin oxide (ITO), impurity doped tin oxides, and impurity doped zinc oxides, are n-type semicon- ductors due to the free electrons resulting from extrinsic donors as well as intrinsic donors. However, for large scale optoelectronic device applica- tions, transparent conducting p-type semiconductors are required. NiO is an interesting candidate in this class with a wide band gap of 3.6–4.0 eV and exhibits very low p-type conductivity due to presence of Ni 3+ or oxygen vacancies. We have already shown optimized p-type conductivity and high transparency in Li doped NiO epitaxial ﬁlms grown by pulsed laser deposition [21]. In the present paper, we report on the simple fabrication technique and properties of a transparent all oxide thin ﬁlm diode consisting of p-type NiO and n-type ITO p–n junction. 2. Experimental procedure Nominal 2 at. wt% Sn doped In 2 O 3 ﬁlms were synthesized by chemical solution deposition (CSD) technique on double side polished SiO 2 (quartz) substrates [22]. High purity (N 99.9%; Sigma-Aldrich) hydrated SnCl 2 ·2H 2 O and In(C 2 H 3 O 2 ) 2 4H 2 O were dissolved in 2-mithoxyethanol and monoethanolamine to yield clear and trans- parent 0.3 M solution, which was spin coated on sonicated SiO 2 substrates at 4000 rpm using a spin coating unit (Apex Instruments, India; model SCU 2005). Deposited ﬁlms were annealed in air in temperature range of 400–650 °C. Typical ﬁlm thickness was controlled to be ~80 nm. The top layer of p-type semiconductor, NiO, was Thin Solid Films 519 (2011) 3840–3843 ⁎ Corresponding author. Tel.: +91 79 26303041; fax: +91 79 2630 6194. E-mail address: usjoshi@gmail.com (U.S. Joshi). 0040-6090/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2011.01.255 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf