Enhancement of intrinsic emission from ultrathin ZnO films using Si nanopillar template
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NANO EXPRESS
Open Access
Enhancement of intrinsic emission from ultrathin ZnO films using Si nanopillar template Tun-Yuan Chiang1,2 and Ching-Liang Dai1*
Abstract Highly efficient room-temperature ultraviolet (UV) luminescence is obtained in heterostructures consisting of 10-nm-thick ultrathin ZnO films grown on Si nanopillars fabricated using self-assembled silver nanoislands as a natural metal nanomask during a subsequent dry etching process. Atomic layer deposition was applied for depositing the ZnO films on the Si nanopillars under an ambient temperature of 200°C. Based on measurements of photoluminescence (PL), an intensive UV emission corresponding to free-exciton recombination (approximately 3.31 eV) was observed with a nearly complete suppression of the defect-associated, broad-range visible emission peak. As compared to the ZnO/Si substrate, the almost five-times-of-magnitude enhancement in the intensity of PL, which peaked around 3.31 eV in the present ultrathin ZnO/Si nanopillars, is presumably attributed to the high surface/volume ratio inherent to the Si nanopillars. This allowed considerably more amount of ZnO material to be grown on the template and led to markedly more efficient intrinsic emission. Keywords: Ultrathin films, ZnO, Nanopillars, Atomic layer deposition, Photoluminescence
Background Due to the wide application of, for instance, transistors [1,2], ultraviolet photodetectors [3], and piezoelectric transducers [4,5] in the industry, all of which need to use ZnO thin film, which is regarded as a promising material for optoelectronic applications. In particular, the wide bandgap of 3.37 eV and large exciton binding energy of 60 meV (much higher than that of ZnSe (40 meV) and GaN (25 meV)) inherent to ZnO have been demonstrated to exhibit efficient excitonic emission at room temperature. Consequently, considerable efforts have been devoted to this particular material in order to harvest efficient ultraviolet (UV) emission from ZnO [6-8]. These approaches, however, required not only the thickness of 100 nm or more for ZnO thin film, but also much more time in fabricating processes. Thus, ultrathin ZnO film (
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