Deposition Of PbO Thin Films And Its X-ray Photoconductivity

In the past century, X-ray imaging technology was developed from film-screen imagingtechnology, computer radiography imaging technology and digital radiography iamgingtechnology, and it plays an important part in the fields of medical, nondestructive test,industrial detection and others. With the rapid development of digital information, digitalimaging technology is currently of great interest compared to traditional imaging system. Mostof the existing X-ray detectors rely on indirect conversion where a scintillator converts X-rayquanta into visible light, which is detected by an array of photodiodes. An alternativeconversion principle is called direct conversion, where X-rays are absorbed in aphotoconductor and directly generate electron hole pairs, which are subsequently separated bya bias field to generate a signal on the external electrodes. The benefits inherent of directconversion are high spatial resolution and higher signal-to-noise ratio due to the higher chargegeneration yield of some materials. In addition, photodiodes production during platefabrication is obviated.Lead oxide (PbO), a traditional n-type semiconductor material, is one of the possiblecandidates to be used as a direct conversion material for X-ray imaging. It shows a lowoperating electric field of1V/μm and a low electron-hole pair creation energy of5-6eV. Theproperties of PbO as a X-ray detector are also characterized by high average atomic number,wide energy band gap and low substrate temperature. PbO is a kind of traditionalsemiconductor photoelectric material which is sensitive to X-ray, and has high photoelectriccharacteristic in the range of the entire wavelength, which suppresses additional noise andachieve excellent spectral and spatial resolution. As a direct X-ray converter, PbO is apromising candidate for static as well as for dynamic application.In this paper, the development history of X-ray detectors and X-ray photoconductivematerials and preparation methods and characterization technique of metallic oxide arediscussed. High resistance lead oxide thin films are prepared by direct current magnetronsputtering. The optical properties, crystalline structure, X-ray photoconductivity, surfacemorphology and elemental composition of the lead oxide thin films prepared by differenttechnological parameters are also studied.The results show that the oxygen flow rate has great effect on the PbO thin films by dcmagnetron sputtering. We can get tetragonal PbO and orthorhombic PbO, both of them findphotoconductivity. Moreover, it is also found that tetragonal PbO is superiors for X-ray detection than orthorhombic PbO. Annealing makes the native carrier concentration of thinfilm decreased and it is benefit to improve the photoconductive effect. In addition, with theincrease of oxygen flow rate, the surface morphology of thin films become flat and smooth.Annealing makes the grain size larger and increases the film crystallinity.