The Growth Of Arsenic-doped P-type ZnO Thin Films And The Study Of Electroluminescence Emission From ZnO/GaAs Heterojunctions

ZnO is aⅡ-Ⅵwide band gap(Eg=3.34eV) semiconductor. Because its large exciton bound energy, about 60meV at RT, it can be used to fabricate many useful devices, such as emitting diode, lasers and high-speed optical switch. Therefore, it also has great uses in both civil and military fields.Many methods have been used to deposit ZnO films such as Molecure Beam Epitaxy (MBE), Metal Organic Chemical Vapor Deposition (MOC- -VD),Pulsed Large Deposition(PLD),Sputter and Thermal Evaporation. Among them, high quality ZnO films can be obtained by MBE and MOCVD , but only MOCVD provides high growth efficiency.Previous research had established that ZnO was always n-type, because it was also known that the crystal growth was typically Zn-rich, the dominant donor was almost always identified as either the O vacancy VO or the Zn interstitial ZnI. This model was strongly challenged in the year 2000 when Kohan et al. showed theoretically that both VO and ZnI have high formation energies in n-type ZnO and that furthermore, both are deep, not shallow, donors. Also in the year 2000, the defect-donor model was further challenged by Van de Walle's theoretical result that H is always a donor in ZnO, that it is easily ionized, and that it has a low enough formation energy to be abundant. However, no matter which model is dominant in ZnO films, the self-compensation of the donor is the key point to prevent the formation of the p-type conductivity. Now, high quality p-type ZnO films have formatted in many groups, but the state of the acceptor impurity has not conformed. Take As atoms for example, some person suggests that the Aso impurity is the reason of the p-type conductivity in ZnO films, then on the country, other person suggests that the compound AsZn-2VZn impurity is the dominant acceptor. So make sure the state of the acceptor-like dopant is important.Recent years, researchers have successfully earned P-type ZnO thin films grown on GaAs substrate by thermal annealing. But only few of them have observed the ZnO-based EL spectra on both UV-Blue and infrared range. In my opinion, the quality of the ZnO film grown by Sputter, which is used commonly to deposit acceptor-like impurity, is not good enough to show the high single orientation character and high uniform surface conditions. So it is difficult to cause the emission by means of the electron integrating with the hole.In this paper, the formation of the p-type ZnO films on GaAs substrates would be mainly due to As diffusion, which was in agreement with the results of X-ray photoelectroscopy (XPS). Compared with the original values, the binding energy of As3d was shifted to the lower binding energy side (41.6 eV) after annealing. We found that As-O band is broken and the arsenic exists in the state of AsZn-2VZn acceptor complex after annealing. Meanwhile, no peak related to Ga band level is detected in the XPS spectra for all the films in our work.We deposit Zinc oxide film by MOCVD on the Si substrate which is sputtering a thin GaAs film. The crystal quality and optical properties of ZnO films were investigated with X-ray diffraction (XRD) and the room temperature photoluminescence (PL) spectra. The result of the X-ray diffraction shows a strong peak around 2?=34.4°and photo- luminescence(PL) spectra shows a strong uv-peak around 375nm. All of this indicates that the quality of ZnO film grown by MOCVD on such substrate is good. X-ray photoelectroscopy (XPS) shows that As atoms have already diffused into ZnO film, and the hall-measurement has indicated that the ZnO film is P-type.We also draw the I-V curves of the ZnO/n-GaAs,ZnO/p-GaAs structure, and analysis them in detail to confirm the ZnO film's P-type conductivity, again. And blue-violet and infrared EL emission from p-ZnO/n-GaAs heterojunction has been reported. The p-ZnO films have been formed by the doping As atoms diffused into ZnO film from GaAs substrate. The p-ZnO/n-GaAs heterojunction showed a diode I-V characteristic and a threshold voltage of ~2.5V under forward bias. In addition, we use the Au/Zn metal as the P-type ZnO film's electrode. By comparing the differences in the I-V curves, we educe the conclusion that the Au/Zn metal is suitable as the P-type ZnO electrode to form Ohmic contact.