Preparation And Optoelectronic Performance Of N-ZnO Nanorods/p-GaN Heterojunction Devices

Wurtzite structure ZnO is a direct wide bandgap (3.37eV) semiconductor material with aexciton binding energy reach up to60mev. It can achieve a stable light emission with highefficiency when working in the environment higher than room temperature. However, it isstill difficult to obtain a high quality, controllable p-ZnO because of the constraints of p-typedoping technology, this limited the development of ZnO based homojunction devices greatly.Therefore, many groups used other p-type semiconductor materials with n-ZnO to fabricateheterojunction LED. Wurtzite structure GaN has similar photoelectric properties and smalllattice mismatch (only1.8%) comparing with ZnO and the p-type doping technology of GaNis simple. Thus, p-GaN is regarded as the most promising candidate to constractheterojunction devices with n-ZnO. In this paper, we grew ZnO nanorods arrays on p-GaNsubstrate by hydrothermal method and fabricated the heterojunction LEDs successfully. Weused Anderson energy band diagram and the photoluminescence (PL) spectra to discusse theorigin of the EL emission in detail.The major findings of this thesis are as follows:1. According to the optimal growth conditions, we grew n-ZnO nanorod array on thep-GaN substrate by the hydrothermal method. To construct the heterojunction LED device,using the pulsed laser deposition (PLD) technology, Pt/Ti and Pt/Ni alloy-electrodes weredeposited on the surface of n-ZnO nanorods and p-GaN, respectively. Relevant tests show that,carrier concentration and mobility of n-ZnO nanorods are much higher than p-GaN film. Theheterojunction device has a good diode rectifier effect and the ohmic contact is formedbetween the metal electrode and semiconductor. The electroluminescence spectrum of thedevice working at forward biased display a blue light emission with the wavelength centeredat430nm under room temperature. Although the energy barrier height of electrons and holescaused by p-n junction are almost equal, carrier concentration and Hall mobility of n-ZnO arehigher than p-GaN, when the device working, much electrons in n-ZnO acrossed the p-njunction and injected into the p-GaN region occurred radiative recombination with holequickly. Thus, for n-ZnO nanorods/p-GaN heterostructure LED, electroluminescence mainlyorigin from p-GaN side and there is no obvious light emission from n-ZnO region.2. In order to realize the electroluminescence of n-ZnO，in this paper, we insert some wide band-gap semiconductor interface layer (AlN, ZnS, Ga2O3) with suitable thickness betweenn-ZnO nanorods and p-GaN to block the rapid injection of electrons and suppress the lightemission of p-GaN side effectively. Calculation shows that, the energy barrier for electrons(EC) is much higher than holes (EV) in the interface of p-n junction, block the electronsinject into p-GaN side. Electroluminescent tests showed that, all the LEDs based on n-ZnOnanorods/p-GaN PIN heterostructure devices can achieve a better near ultraviolet lightemission under the forward voltage, that is the near band edge emission of n-ZnO.