Stable Li-N Codoped P-type ZnO Films And Their Application In Optoelectronic Devices

Znic Oxide (ZnO), as a semiconductor material, has a direct and wide band gap(3.37eV). Moreover, the room temperature exiciton binding energy of ZnO is60meV. With the characters above, ZnO may achieve a wide range of applications inultraviolet (UV) light-emitting devices (LEDs), UV detectors, low threshold lasers,etc. And for these reasons, ZnO become the international frontier and hot spot ofsemiconductor optoelectronic research field in recent years. After a decade ofexploration, the research on ZnO has made a series of landmark achievements. Butthe problem in the p-type doping ZnO has not been solved completely until now.Stable p-type ZnO is still hard to obtain. The present work is focused on the keyissue that hinder the development of ZnO, and the following results are obtained:1. Li-N codoped ZnO:(Li,N) films have been obtained by the plasma-assistedmolecular beam epitaxy technique. The ZnO:(Li,N) films show p-type conduction asmeasured by Hall measurement, and the hole concentration is of the order ofmagnitude of1016cm3. The p-type conduction can maintain for over200days. Theformation mechanism of the p-type ZnO and why the p-type conduction can last forsuch a long time have also been investigated by XPS and temperature-dependent PLand supported bySynchrotron-based x-ray absorption fine structure(XAFS) technique.The results above indicating the good stability of the p-type ZnO can be obtained viathe Li-N codoping method. 2. On the basis of the prepared stable p-type ZnO films, some ZnO homojunctionLEDs have been constructed and the electroluminescence (EL) at room temperaturehas been observed from the ZnO homojunction. The LEDs fabricated from the ZnOhomojunctions have been measured intermittently for over half a year and show thegood stability of EL. In order to increase the EL emission of ZnO homo pn junctionLEDs, the Ag nanoparticles (NPs) were spin-coated onto the ZnO homojunctionLEDs by using the principle that surface plasmons can be employed to increase theemission of luminescent materials and devices. And the EL emission of the ZnOhomojunction LEDs can be enhanced significantly by Ag NPs. This is the first reporton surface plasmon enhanced ZnO homojunction LEDs to the best of our knowledge.The surface plasmon enhanced LEDs also show the good stability after measuringintermittently for three months. Note that no report on the stability of surfaceplasmon enhanced devices can be found before.3. The applicability of the ZnO pn homojunction in self-powered UV photodetectorshas been explored. The photoresponse spectrum of the ZnO pn homojunctiondevices without any external power source only shows a dominant peak at around380nm, whose full width at half maximum is only9nm. The above characters of thedevices demonstrate the potential applications in self-powered highlyspectrum-selective UV photodetectors. In order to evaluate the reliability of theself-powered highly spectrum-selective UV photodetectors, the response spectrum ofthe device without any external power source has been recorded intermittently. Theresponse spectrum of the device degrades little after five months. Reliableself-powered highly spectrum-selective ZnO homojunction UV photodetectors havebeen realized for the first time.