Electrically Pumped Random Lasing From ZnO Films Prepared By Pulsed Laser Deposition

ZnO is a direct wide band gap (3.37eV) semiconductor material with a high exciton binding energy (60meV). Owing to these characteristics and its high optical gain coefficient and refractive index, ZnO is considered to be an ideal material for ultraviolet (UV) random lasers. Optically pumped ZnO random lasing (RL) was reported in1998. Until recent years electrically pumped RL from ZnO materials have been achieved. In the case of realizing the electrically pumped RL using the metal-insulator-semiconductor (MIS) structures device, the random laser actions are related to the properties of the light-emitting semiconductor layer and the insulator layer. While, the properties of these layers strongly rely on the deposition method. In this thesis, the ZnO films as the light-emitting layers and the Si3N4/MgO films as the insulator layers are deposited by pulse laser depositon (PLD). Meanwhile, the MIS structured devices based on these films are also fabricated. The electrically pumped ultraviolet random laser actions of these devices have been investigated systematically. The primarily results achieved in this thesis are summarized as follows.(1) ZnO films on silicon substrates were prepared by PLD under different conditions. The effects of laser wavelength, substrate temperature and oxygen partial pressure on the morphology and photoluminescence of ZnO films has been investigated. It is found that the ZnO films are of the best surface morphology when using the355nm Nd:YAG laser. Moreover, the defects in ZnO film are substantially decreased with the increase of the substrate temperature and the partial pressure of oxygen during depositon.(2) ZnO films on Si were prepared by magnetron sputtering and PLD, respectively. Furthermore, the MIS structured devices based on these ZnO films were prepared. It is found that the device using the PLD ZnO film possesses the lowest threshold current for RL and highest output optical powers. This is due to that the PLD ZnO film has much fewer defects, leading to remarkably lower optical loss during the multiple scattering within such ZnO film.(3) The ZnO-based MIS structured devices using the PLD Si3N4film as the insulator layer were prepared. It is shown that the increase of substrate temperature for depositon of Si3N4film facilitate to decrease the threshold current for RL and to enhance the optical output. (4) The ZnO-based MIS structured devices using the PLD MgO film as the insulator layer were prepared. Such devices exhibit electrically pumped UV random laser action under sufficiently high forward bias. The device made by successive depositon of ZnO and MgO films on Si by PLD featured a relatively lower threshold current for RL.