The Design, Fabrication And Characteristics Of ZnO Based Laser Devices

Znic Oxide (ZnO) featured by its large exiton binding energy (60meV) and itsexcellent optoelectronic properties is one of the best materials for high efficientultraviolet (UV) light emitting devices and low-threshold lasers. Aiming at theshortage and the key problems in the current development of ZnO based electricallypumped lasers, in this dissertation, ZnO based electrically pumped lasers have beendesigned and fabricated via plasma assisted molecular beam epitaxy and radiofrequency magnetron sputtering, and their characteristics have been studied. It isproved that both the performance and the output characteristics of this kind of laserscan be greatly improved by properly designing the device structure as well as bystudying the injecting mechanism of the non-equilibrium carriers. The researchresults are achieved as follows:(1) In view of the problems of the presently reported ZnO MIS random lasingstructures, such as high threshold current and voltage, uncontrolled output modes,we have improved the performance of this kind of lasers by enhanceing the opticalfeedback mechanism and mode coupling as well as by introducing the confinementof both the optical field and the electric filed. We firstly prove that introducing theFP cavity into the MIS structure, which can enhance the optical feedback in thevertical direction, will lower the threshold and reduce the number of the random patterns in this direction. Moreover, we also prove that since the ZnO stripewaveguide arrays can introduce the confinement of both the optical field and theelectric filed as well as mode coupling into the MIS structure, it can effectivelyincrease its lasing efficiency, reduce the threshold and improve the outputcharacteristics.(2) In view of the fact that presently it is very difficult to effectively injectnon-equilibrium holes into the ZnO active layer and that the impact ionizationprocess in the MIS structures requires high working voltage, we make use of theaccelerated electrons which are obtained in solid structure to pump the ZnO activelayer. In this way, both non-equilibrium holes and electrons can be generated in thislayer. Based on this idea, we have realized UV emissions and lasing from manystructures and confirmed its feasiblity. In order to further improve the random lasingcharacteristics, ZnO stripe waveguide arrays have been introduced which canenhance the confinement of both the optical field and the electric filed as well asbring about modes coupleing. As a result, the threshold has been reduced and theoutput characteristics have been improved. Moveover, we have proved that it isrequired much less voltage to generated holes in ZnO layer under the excitation ofaccelerated electrons than that through the impact ionization process.(3) In view of the difficulties of both p-type and n-type doping of MgZnO, wemake use of the accelerated electrons obtained in solid structure to pump the MgZnOfor UV emissions and UV lasing, which can generate both non-equilibrium holes andelectrons simultaneously in this layer. Based on this idea, UV light emitting devicesat around328nm and DUV light emitting devices at around285nm have beenobtained. Moreover, UV lasing at330nm has been achieved at high voltage. In orderto reduce the working votage and improve the performance, MgZnO films with lowresistivity have been fabricated under Zn-rich conditions, and UV lasing at360nmhas been obtained at low voltage.