Characterization of Al doped MgxZn1-xO thin film and theirscontact to AlGaN application

Autor: Ting-Yao Chen, 陳鼎堯
Rok vydání: 2008
Druh dokumentu: 學位論文 ; thesis
Popis: 96
Transparent conducting oxides(TCO’s) are characterized by a unique combination of low electrical resistivity and high optical transparency. Zinc oxide has recently gained much interest because of its potential use in many applications, ranging from transparent electrodes in light emitting diodes, solar cells, photodetectors, thin film gas sensors, spintronic devices, surface acoustic wave devices, and flat-panel display devices, attributed to its wide direct band gap,excellent chemical and thermal stability, and specific electrical and optoelectronic property with a large exciton binding energy. A TCO with a wider band gap can improve the efficiency of UV or blue light emitting devices when used as a transparent electrode.The band gap of ZnO can be controlled by alloying with MgO.In this work, we propose the use of band-gap modified Zn1−xMgxO as transparent conducting films. In this study, the characteristics of MgxZn1-xO and MgxZn1-xO:Al thin films were deposited by using radio frequency magnetron co-sputtering system have been investigated. The performances of the transparent conductive thin film contacted with semiconductors were also investigated. This thesis was divided into two parts, first part, MgxZn1-xO (x=0, 0.1, 0.2 and 0.3) thin films were deposited and MgxZn1-xO:Al thin film by co-sputtering system with MgxZn1-xO and aluminum targets on sapphire substrates at room temperature. Second part, MgxZn1-xO:Al thin films contacted with GaN and AlGaN. First part, the effect of post-annealing on photoelectric and material haracteristics of MgxZn1-xO thin films was investigated. The detailed deposition conditions were base pressure 4×10-6 torr, sputtering gas ambient Ar 10sccm,sputtering pressure 10mtorr, RF power supplied to MgxZn1-xO(x=0~0.3) targets 100W, thin film thickness fixed 200nm. The electrical characteristics, opticalproperties, Crystallization and chemical composition of the thin films were analyzed by Hall measurement, ultraviolet visible spectrometer (UV-VIS spectrometer), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS), respectively. The minimum resistivity of MgxZn1-xO thin films were obtained by annealing at 900oC for 1min in nitrogen atmosphere by using rapid thermal annealing (RTA) system. MgxZn1-xO thin films were doped suitable aluminum atom in order to increase conductivity. The optimization RF power of 100 W was supplied to MgxZn1-xO target, and RF power of 20W (x=0), 25W (x=0.1), 30W (x=0.2), 35W (x=0.3) was supplied to aluminum target, respectively. The resistivity of MgxZn1-xO:Al(x=0~0.3) thin film were 1.55×10-3 Ωcm (x=0) to 3.34×10-2 Ωcm (x=0.3), respectively, through the aluminum atoms doped MgxZn1-xO thin film can increase conductive effective.The transmittance of MgxZn1-xO:Al film has over 80 % in visible light region. The optical band gap were also determined by the transmittance spectra, which increased from 3.55 eV at (x=0) to 4.59 eV at (x=0.3). Second part, the structures of MgxZn1-xO:Al/n-GaN and MgxZn1-xO:Al/n-AlGaN were deposited to form the ohmic contact, that were achieved with thermal annealing. We will explore TCO with semiconductor contact characteristics. The current-voltage (I-V) characteristics were measured using an HP4156 semiconductor parameter analyzer. Specific contact resistance, ρc, was calculated by measuring the resistance versus the distance between TLM pattern.In present research, MgxZn1-xO:Al thin film could obtained the width optical energy bandgap by Mg content adjustment, the suitable aluminum atom doping also promotion thin film electric conduction characteristic effectively. A transparent conducting oxide with a wider band gap can improve the efficiency of UV or blue light emitting devices, so MgxZn1-xO:Al thin films will application in LED in the future.
Databáze: Networked Digital Library of Theses & Dissertations
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