Pulsed laser deposition and processing of wide band gap semiconductors and related materials |
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Authors: | R D Vispute S Choopun R Enck A Patel V Talyansky R P Sharma T Venkatesan W L Sarney L Salamancariba S N Andronescu A A Iliadis K A Jones |
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Affiliation: | (1) CSR, Department of Physics, University of Maryland, 20742 College Park, MD;(2) Department of Materials and Nuclear Engineering, University of Maryland, 20742 College Park, MD;(3) Department of Electrical Engineering, University of Maryland, 20742 College Park, MD;(4) Army Research Laboratory, AMSRL-PS-DS, 07703 Fort Monmouth, NJ |
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Abstract: | The present work describes the novel, relatively simple, and efficient technique of pulsed laser deposition for rapid prototyping
of thin films and multi-layer heterostructures of wide band gap semiconductors and related materials. In this method, a KrF
pulsed excimer laser is used for ablation of polycrystalline, stoichiometric targets of wide band gap materials. Upon laser
absorption by the target surface, a strong plasm a plume is produced which then condenses onto the substrate, kept at a suitable
distance from the target surface. We have optimized the processing parameters such as laser fluence, substrate temperature,
background gas pressure, target to substrate distance, and pulse repetition rate for the growth of high quality crstalline
thin films and heterostructures. The films have been characterized by x-ray diffraction, Rutherford backscattering and ion
channeling spectrometry, high resolution transmission electron microscopy, atomic force microscopy, ultraviolet (UV)-visible
spectroscopy, cathodoluminescence, and electrical transport measurements. We show that high quality AlN and GaN thin films
can be grown by pulsed laser deposition at relatively lower substrate temperatures (750–800°C) than those employed in metal
organic chemical vapor deposition (MOCVD), (1000–1100°C), an alternative growth method. The pulsed laser deposited GaN films
(∼0.5 μm thick), grown on AlN buffered sapphire (0001), shows an x-ray diffraction rocking curve full width at half maximum
(FWHM) of 5–7 arc-min. The ion channeling minimum yield in the surface region for AlN and GaN is ∼3%, indicating a high degree
of crystallinity. The optical band gap for AlN and GaN is found to be 6.2 and 3.4 eV, respectively. These epitaxial films
are shiny, and the surface root mean square roughness is ∼5–15 nm. The electrical resistivity of the GaN films is in the range
of 10−2–102 Θ-cm with a mobility in excess of 80 cm2V−1s−1 and a carrier concentration of 1017–1019 cm−3, depending upon the buffer layers and growth conditions. We have also demonstrated the application of the pulsed laser deposition
technique for integration of technologically important materials with the III–V nitrides. The examples include pulsed laser
deposition of ZnO/GaN heterostructures for UV-blue lasers and epitaxial growth of TiN on GaN and SiC for low resistance ohmic
contact metallization. Employing the pulsed laser, we also demonstrate a dry etching process for GaN and AlN films. |
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Keywords: | AlN deposition epitaxy GaN pulsed-laser |
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