ZnO is a compound semiconductor from II-VI family which has been studied for more than fifty years because of versatile properties like wide direct band gap (3.37 eV), high optical transmittance in visible region (400-800 nm), high exciton binding energy (60 meV) and good electrical conductivity (~10-4 Ω-1.cm-1). Owing to these interesting properties, ZnO is a promising material for applications in different fields like optoelectronics for UV or blue LED’s, laser diodes, in optics as optical windows, anti-reflection coatings and in electronics for thin film transistors. ZnO is n-type semiconductor because of native defects, therefore, less solubility of acceptor impurities in ZnO and deep acceptor levels generated by p-type impurities like nitrogen and lithium, which increases the work function is reported as a reason behind unstable p-type conductivity of ZnO. Besides, a defect free epitaxial growth in form of thin films is also an important issue regarding use of ZnO in device fabrication, specifically LED’s and laser diodes. These issues provided basic initiative of this research project. Co-doping of ZnO with an acceptordonor impurity or acceptor-acceptor impurity can be effective for resolving conductivity-related issues. We have chosen rare-earths as donor impurity and group-I elements as acceptor impurity in ZnO to observe the p-type character whereas the epitaxial relationships are studied by depositing films on two single crystal substrates i.e. silicon and strontium titanate (STO). Apart from material being deposited, the thin film deposition process itself plays a critical role for determining the physical properties of as-deposited films. Pulsed laser deposition is selected in this project to deposit undoped and doped ZnO thin films on different substrates i.e. borosilicate glass, silicon and STO because of its uniqueness and variety of available parameters significantly affecting thin film characteristics. Laser pulses in two different time regimes: long pulse ~ nanoseconds and ultrashort pulse ~ femtoseconds are used for crystalline and nanocrystalline thin films respectively. Owing to scarcity of available literature on ultrashort laser deposition of ZnO, important PLD parameters for femto-pld are optimized using Ti: sapphire laser (wavelength = 800 nm, pulse repetition rate =1 kHz and pulse length = 100 femtoseconds). Three series of experiments are performed to deposit undoped ZnO thin films on borosilicate glass substrates varying like targetsubstrate distance, laser pulse energy, substrate temperature and deposition time. Highly c-axis iii oriented nanocrystalline ZnO thin films showing optical transmittance > 90% are obtained using these PLD conditions: dT-S =80 mm, El =180 μJ, PO2 =1 mTorr and TS = 100 °C. Three sets of rare-earth doped ZnO thin films are prepared. Set-I is deposited using 0, 2, 3, 4 and 5 wt.% yttrium doped ZnO (YZO) on (0 0 4) silicon substrates using nano-PLD. Microstructural analysis (XRD and Raman spectroscopy) shows films prefer c-axis growth under high interfacial stress. Very small amount of yttrium is doped at lattice sites and phase segregation is observed at higher concentrations. SE analysis revealed light absorption at lower wavelengths ≤ 370 nm and light transmission at higher wavelengths ≥ 400 nm. Set-II and set-III comprise yttrium and samarium doped ZnO respectively, deposited on glass employing optimized femto-PLD. Microstructural analysis (XRD and AFM) of both sets confirm nanocrystalline growth of films, supporting phase segregation at low (1 wt.%) and compound phase growth at high (10 wt.%) doping concentrations. Hetero-epitaxial Ag-Dy: ZnO (ADZO) and Li-Gd: ZnO (LGZO) thin films are deposited on (1 0 0) STO substrates employing optimized femto-PLD and nano-PLD respectively. Microstructural analysis indicates complete incorporation of silver atoms at lattice sites of zinc. Structural and optical analysis of LGZO thin films demonstrates significant modification in crystallinity and optical transmittance which indicates defect states lying within the energy gap of ZnO.It is concluded from rare-earth co-doped with Group-I element in ZnO leads to variety of defect generation caused by presence of metal oxides in their crystalline or non-crystalline phase and compound phases. Defects created by high concentration of rare-earth can increase the solubility limit of Group-I elements like silver and lithium, in ZnO. These dopants are capable of making acceptor levels in energy gap along with high (> 80%) optical transmittance. Heteroepitaxial growth of ZnO on (1 0 0) STO can be improved by co-doping ZnO with Ag and Dy.