A Study Of The Photocurrent Spectra Of ZnO Based Nano Porous Films And The Photocurrent Spectra Testing System

The Metal Oxide Semiconductors (MOS) are functional materials with remarkablephotoresponse, which have been widely used in the fields of photocatalysis,photoconductivity, light activated gas sensors and solar cells. Two dominant applicationsfor MOS are photocatalysis and gas sensor. In these applications, the most critical issue arephotoelectrical response process and mechanics of material in gas phase conditions. Theresearch of the photoinduced carrier’s generation, recombination and transport of MOSunder some atmosphere with the existence of Volatile Organic Compounds (VOCs) makesgreat importance to the research of photocatalysis and the light activated gas sensors. Butmost of the conventional work were performed under the illumination of light with certainwavelength. So far, just a few researchers have made spectroscopy a primary tool of theirwork. We have offered the photocurrent spectrum measurement to testing the photoresponseof MOS under different atmosphere. This in situ measurement can be used to study thematerial’s traps, photogenerated charge separation and photoresponse mechanism.Following the instruction of high throughout screening, we developed the photocurrentspectra testing system, which can be used for the testing of16devices’ photocurrent,photocurrent spectra and volt-ampere characteristics at different speed and atmosphere.There are two kinds of devices, one is the material chip and the other is the Fluorine dopedTin Oxide (FTO) device. The repeatability measurement shows that our system hasoutstanding stabilization.In this paper, we have studied the influence of sintering process to the photocurrentspectra. Our results show that the ZnO sintered at550in air has much higher response at380nm and quicker decrease than ZnO sintered at550in vacuum. We owed this resultsto oxygen vacancy (VO) and the surface morphology of ZnO. We used the screen printingtechnique to fabricate the material chip of porous ZnO films. The ZnO films were bysensitized by metal chloride solutions. The SEM image of ZnO film sensitized by AlCl3andSnCl4solutions shows that the Al2O3and SnO2exist on the surface of ZnO nanoparticleswith much smaller nanoparticles. We observed two peaks in the photocurrent spectrum ofZnO film sensitized by AlCl3and SnCl4. Each peak represents a photoresponse progress. The peak at380nm is assigned to the exciton transition. Compared with pure ZnO film, thepeak at480nm of ZnO film sensitized by AlCl3and SnCl4are owed to surface states and wefound VZnplaying an important role on this phenomenon. In100ppm formaldehyde gas,the peaks at480nm of ZnO film sensitized by AlCl3and SnCl4appear more obvious thanthe peaks in dry air. It is suggested that formaldehyde gas act as the multiplicator for thecontribution of VZnto photocurrent.We used the sol-gel method to prepare the ZnO doping with Al and Sn for the materialchip and FTO device. The SEM figures show different morphologies have been attained onthe surface of ZnO material chip. And the photocurrent spectra shows that the ZnO dopingSn has much higher response at380nm than the ZnO doping Al and doping nothing. Weowed this to the different surface morphologies and surface states. And the photocurrentspectra results obtained from the FTO device have good consistency with ZnO material chip.