The OTFTs with both p type and n type channel layers were fabricated using the inverted-staggered (top contact) structure by thermal vapour deposition on Si/SiO<sub>2</sub> substrate. Pentacene and N,N’-Dioctyl- 3,4,9,10-
perylenedicarboximide (PTCDI-C8) were used as channel layer for the fabrications of p type and n type OTFTs respectively. A comparative study on the degradation and density of states (DOS) of p type and n type organic semiconductors have been carried out. In order to compare the stability and degradation of pentacene and PTCDI-C8 OTFTs, the devices were exposed to air for 2 h before performing electrical measurements in air. The DOS
measurements revealed that a level with defect density of 10<sup>20</sup> cm<sup>-3</sup> was formed only in PTCDI C8 layer on exposure to air. The oxygen adsorption into the PTCDI-C8 active layer can be attributed to the formation of this level at 0.15 eV
above the LUMO level. The electrical charge transport is strongly affected by the oxygen traps and hence n type organic
materials are less stable than p type organic materials.
Transparent conducting indiuim galium zinc oxide (IGZO) films were successfully grown on glass substrates at room temperature by rf magnetron sputtering. Structural, optical, morphological and electrical properties of IGZO films deposited at different rf power were investigated. Composition of the film was analysed by EDAX measurement which shows that percentage of Zn increased with the rf power. Surface morphology of the IGZO film measured from AFM analysis showed that the roughness of the film was increased with increase in RF power. The average transmission in the visible range was greater than 80% and the transmission in the higher wavelength region decreased with increase in RF power. The carrier concentration in IGZO films could be controlled by controlling rf power due to the increase of Zn/(Ga+In+Zn) ratio. Nonlinear properties of IGZO thin films were measured using z-scan technique. Increase in free electron concentration of IGZO thin films lead to a decrease of the corresponding nonlinear optical absorption response.