SR-MOCVD Deposition Of ZnO Films And Their Charicterization

Zinc Oxide (ZnO) is one of the most important compound semiconductor optoelectronic materials. It has plenty of favorable natures, such as a wide bandgap of 3.37eV at room temperature and large exciton energy of 60meV, which provide an attractive prospect to highly efficient UV light emitters, light emitting diodes (LEDs) and low-threshold excitonic laser diodes (LDs). In this paper we studied the SR-MOCVD (Synchrotron Radiation assistant MOCVD) deposition of ZnO film, and the film properties were studied as well. The main results are as follwing.1. The SR-MOCVD system is designed and constructed at the synchrotron radiation facility of NSRL. To make sure this system can work, the ZnO film is deposited with DEZn and O2 as sources to debug the equipment, until the films can be deposited uniformly.2. To understand the deposition mechanism of SR-MOCVD ZnO film, the photoionization and photodissociation of diethylzinc (ZnC4H10) are performed using vacuum ultraviolet (VUV) synchrotron radiation and a time-of-flight mass spectrometer (TOF-MS). The photoionization mass spectrums of all the observed ions from diethylzinc and their photoionization efficiency (PIE) curves with the photon energy from 8 to 22 eV are measured. From their PIE curves, the ionization potential of ZnC4H10 (IP = 8.20±0.05 eV) and appearance potentials of fragment ions (ZnC2H5+, ZnH+, Zn+, C2H5+, C2H3+ etc.) are obtained. According to the gas phase energetic data from references, the formation enthalpies of chief ions are evaluated and their possible channels of dissociative photoionization as well as their branch rates are discussed. The results indicate that the chief channels are the simple cleavage of the Zn-C bond in the parent ions to form fragmental ions C2H5+ and ZnC2H5+ which further dissociated to Zn+ ion. More than 75% of the total production ions belong to Zn-containing ions.3. The SR-MOCVD and MOCVD deposition of ZnO films on Si (001) substrate at different temperature are carried out with DEZn and CO2 as sources. The XRD, SEM, XPS and PL spectra are used to characterize their crystal quality, surface morphology and optical property. The property dependence of ZnO film to the substrate temperature is also discussed. In the meantime, we compare the property difference between the SR-MOCVD ZnO films and the MOCVD ones. It is indicated that with the SR assistance the ZnO films can grown even at room temperature, and the deposited ZnO film has no C contamination with a higher crystal quality, compared with those of the MOCVD films. The SR-MOCVD ZnO film has a less intensity of green peak in the PL spectra, which indicates that the SR assistance can decrease the density of some kinds of defects in the films.4. The growth mechanism of SR-MOCVD is discussed primarily, campared with MOCVD. For the MOCVD method, after the thermodynamic reaction between the absorpted DEZn and CO2 on the substrate surface, the outcome dissociated into ZnO and some other organic ions at a high temperature which discharged out of the chamber. But with the assistance of SR, after the photoionization and photodissociation of DEZn and CO2, the ZnO films grow with the reaction of the outcomes: Zn atoms,ions and Zinc containing ions with O atoms,ions on the surface of substrates. Thus, the ZnO film can grow at a low temperature with the help of SR photoionization and photodissociation to the sources. And the SR can decrease C contamination, which can improve the crystal quality.