Transparent process [13-15] etc. Compared to other

Transparent conducting films have a wide
range of applications in optoelectronic devices. Low resistivity, high
transmittance in the visible range and high stability against heat are the
peculiar properties of transparent conducting films.  Most of the transparent conducting oxides such
as Indium Tin Oxide (ITO), Fluorine-doped Tin Oxide (FTO) etc. have a high
cost, low stability to H2 plasma and toxicity. On the other hand,
Zinc Oxide (ZnO) is a highly transparent, low cost and comparatively stable material
ZnO is a wide direct band gap semiconductor which finds application in thin
film transistors 2,
 light emitting diodes 3,
solar cells 45,
sensors 6,
photodetectors 7
etc. Most of the optoelectronic applications require high carrier mobility and
as a consequence, doping of ZnO becomes essential.  ZnO thin films are prepared by various
deposition techniques such as sputtering 8,
chemical vapor deposition (CVD) 9,
pulsed laser deposition (PLD) 10,
molecular beam epitaxy (MBE) 11,
spray pyrolysis 12,
sol-gel process 13-15
etc. Compared to other methods sol gel process is a simple, low cost, and effective
method to produce high-quality thin films. Also, it is easy to control the
composition and to produce large area thin films. Although sol-gel process is an
easier technique for producing thin films, there are certain factors affecting
the physical, optical and electrical properties of ZnO thin films. These
factors include pre-annealing temperature, post-annealing temperature, thickness
and so on. Since intrinsically ZnO is an n-type semiconductor, one of the major
challenges in the development of ZnO-based optoelectronic devices is to get an
efficient p-type ZnO 14.
Recently researchers have been working on p-type ZnO by doping different
elements (N, P, As, Sb. Na, Li, and K) with various techniques since it has a
lot of applications in diodes and transistors 15.
Because of the nitrogen’s low ionization energy and similar ionic radius
compared with oxygen, ease of handling, low toxicity and source abundance, it
can be considered as the most promising dopant 1617.
Solution processing is an easy and simple technique for p-type doping compared
to other techniques.