Growth and Characterization of Mg0.15Zn0.85O Thin Films by Pulsed Laser Deposition
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Growth and Characterization of Mg0.15Zn0.85O Thin Films by Pulsed Laser Deposition Wei Wei1, Chunming Jin1, Anand Doraiswamy2, Roger J Narayan2, and Jagdish Narayan1 1 Materials Science and Engineering, North Carolina State University, 3030 Engineering Building I, 911 Partners Way, Raleigh, NC, 27695-7907 2 Biomedical Engineering, University of North Carolina, 152 MacNider Hall, Chapel Hill, NC, 27599-7575 Abstract Mg0.15Zn0.85O thin films were grown on fused silica substrates at different substrate temperatures using pulsed laser deposition. X-ray diffraction and transmission electron microscopy were used to investigate the structure of the films. High resolution transmission electron microscopy showed that the film contained small grains with low angle boundaries. The optical properties of the films were investigated using absorption spectra. The bandgap energy values of the films were determined by fitting the absorption data. Introduction As a wide bandgap II-VI semiconductor, ZnO has been considered as a promising candidate for the applications of optoelectronic devices such as light emitting diodes and laser diodes because of its distinguished electrical and optical properties, as well as the facts that it has a variety of source and it is a nontoxic material. MgxZn1-xO is a compound semiconductor, formed by randomly substituting Zn2+ with Mg2+. Although phase diagram shows that the solubility of face-centered MgO in hexagonal ZnO is as low as 4 atomic percent [1], it was shown that the nonequilibrium nature of thin film processes such as pulsed laser deposition (PLD) could elevate the solubility even larger than 34 atomic percent [2]. As the magnesium content increases, the bandgap of MgxZn1-xO could increase from 3.39 eV for unalloyed ZnO (x=0) to 4.42 eV for Mg0.34Zn0.66O. MgxZn1-xO also plays an important role in ZnO-based optoelectronic devices. The variable bandgap energy provides the ability to adjust the operating wavelength of the devices. It is also the key barrier material for constructing MgxZn1-xO/ZnO/ MgxZn1-xO superlattice heterostructures [3], similar to AlGaN and AlGaAs used for III-V semiconductor heterostructures [4]. MgxZn1-xO was usually grown on sapphire (0001) substrates at relatively high substrate temperature in a temperature range from 650-750 oC. High growth temperature is detrimental for developing MgxZn1-xO/ZnO/ MgxZn1-xO heterostructures since magnesium may diffuse into the ZnO-well layer during the growth processes. In this work, we report the growth and characterization of Mg0.15Zn0.85O thin films by pulse laser deposition. Mg0.15Zn0.85O thin films were deposited on fused silica substrates at different substrate temperatures in range from room temperature to 750 oC. The crystalline structure of the films was characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The optical properties of the films were also studied with the measurement of absorption spectra.
Experimental A KrF excimer laser (Lambda Physik, Fort Lauderedale, FL) was
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