Preparation And Characterization Of High Quality Cu₂O Films And Related Functional Devices

As a p-type semiconductor,cuprous oxide(Cu2O)has been considered as a promising candidate for application in solar cell and thin film transistors(TFTs)due to its large optical absorption coefficient,high hole mobility,abundance and nontoxicity.Because the film crystal orientation and microstructure as well as the electrical properties could not be well controlled in most of the previously reported Cu2O films,Cu2O-based functional devices have not shown good performance.It is therefore necessary to obtain high quality Cu2O films with good electrical properties(high Hall mobility,proper resistivity)in order to further improve the performance of Cu2O-based functional devices.In this background,this paper carried out the research on high quality Cu2O and Cu2O TFTs deposited by pulsed laser deposition(PLD)method.The main research work and results are as follows:(1)Basal process parameter study of PLD-deposited Cu2OThe transmission mode of plume plasma and liquid drops among PLD process were studied.liquid drops are more restrained in the normal direction of target than plume plasma,so liquid drops on substrate could be decreased effectively by put substrate on a different axis location.Furthermore,transmission length of plume plasma is longer than liquid drops,so liquid drops could be decreased by increasing the distance between substrate and target.At the last,films deposited under higher laser energy have better quality confirmed by scanning electron microscope and electrical test.(2)Formation of high quality single crystal Cu2O film and study of its properties.Low-resistivity,single-crystalline Cu2O films were realized on MgO(110)substrates through manipulating the oxygen pressure(PO2)of pulsed-laser deposition.X-ray diffraction and high resolution transmission electron microscopy measurements revealed that the films deposited at PO2 of 0.06 and 0.09 Pa were single phase Cu2O and the 0.09-Pa-deposited film exhibited the best crystallinity with an epitaxial relationship of Cu2O(110)//MgO(110)with Cu2O[111]//MgO[111].The pure phase Cu2O films exhibited higher transmittances and larger band gaps with an optical band gap of 2.56 eV obtained for the 0.09 Pa-deposited film.Hall-effect measurements demonstrated that the Cu2O film deposited at 0.09 Pa had the lowest resistivity of 6.67 ?·cm and highest Hall mobility of 23.75 cm2·v-1·s-1.(3)Formation of CU2O film with domain structure and study of its properties.Copper oxide films have been deposited on the Y-stabilized ZrO2(YSZ)(100)substrates by pulsed laser deposition and the effect of oxygen pressure(PO2)on the film properties was investigated in detail.The phase,crystallinity,and surface morphology of the films were strongly influenced by PO2 and the film prepared at 0.09 Pa was pure cuprous oxide(Cu2O)having the best film crystallinity.An out-of-plane epitaxial relationship of Cu2O(110)//YSZ(100)with six different kinds of domain structure were observed for the 0.09 Pa-deposited sample and the corresponding in-plane epitaxial relationships were deduced.The lowest resistivity of 13.4 ?·cm and highest Hall mobility of 16.3 cm2·v-1·s-1 were also obtained for the film deposited at 0.09 Pa.The optical band gap of the as-prepared copper oxide films varied from 2.37 to 2.57 eV.(4)Formation and performance of Cu2O-based TFTs.Cu2O-based TFTs consist of 50 nm PLD-deposited Cu2O active layer,100 nm thermal oxidized SiO2 dielectric layer and 50 nm Au electrode.Proper N2 plasma process could adjust carrier concertration of active layer,to a certain extent improve on/off ratio of devices.However,due to bombardment impact of N2 plasma crystalline structure was damaged and defects were introduced,resulting in the decrease of mobility of Cu2O devices.