Spatially Resolved Study of Magnesium Incorporation in Zn 1-x Mg x O Nanostructures
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0957-K03-07
Spatially Resolved Study of Magnesium Incorporation in Zn1-xMgxO Nanostructures Martin Schirra, Anton Reiser, Günther Michael Prinz, Raoul Schneider, Rolf Sauer, and Klaus Thonke Institut für Halbleiterphysik, Universität Ulm, Ulm, 89069, Germany
ABSTRACT We report on the growth of Zn1-xMgxO nanopillars on a-plane sapphire by the vaporliquid-solid process. The as-grown nanostructures are characterized by scanning electron microscopy, spatially resolved cathodoluminescence, and integral photoluminescence. Microscopic investigation with different secondary electron detectors confirms that the pillars really grew by the vapor-liquid-solid process. Photoluminescence line shifts suggest that an average value of 7% Mg was incorporated in the Zn1-xMgxO nanostructures. Both ZnO- and Zn1-xMgxO– related luminescence features are observed. The incorporation of Mg into single pillars is demonstrated by spatially resolved cathodoluminescence, and different Mg concentrations are found in individual pillars. Preliminary annealing experiments at 850°C lead to an almost complete disappearance of the ZnO- and Zn1-xMgxO– related band edge luminescence, whereas the morphological structure of the sample remains nearly unchanged.
INTRODUCTION Modern optoelectronic devices like light emitting diodes (LED) rely on the potential of band gap engineering. When ZnO with a band gap of 3.37eV (at room temperature) is considered as a candidate for LEDs in the blue and ultraviolet spectral region alloying with magnesium (Mg) to the ternary system Zn1-xMgxO pushes the band gap further into the UV region. In the literature [1] a maximum Mg concentration of approximately 33% is reported, however, recent work [2] suggests a maximum Mg concentration up to 44%. Novel approaches exploit nanopillars as light emitting devices [3,4]. To realize such structures a couple of difficulties have to be overcome. A major challenge is to control the selective incorporation of Mg into the ZnO nanopillars. In this paper successful growth of Zn1-xMgxO nanopillars by the vapor-liquid-solid process is described, and structural and optical properties of such pillars are discussed. To characterize our ZnO pillars on the nanometer scale, scanning electron microscopy and spatially resolved cathodoluminescence are applied. The band edge luminescence observed by spatially resolved CL and integral photoluminescence are compared. The annealing behavior of Zn1-xMgxO nanostructures is studied and first results are reported.
EXPERIMENTAL
The investigated sample was grown by the vapor-liquid-solid (VLS) process [5] in a horizontal tube furnace with three heating zones. As source material, a mixture of high purity zinc oxide (ZnO) and graphite powder in an alumina boat and an additional Mg source were used. The substrate was a-plane sapphire covered with a 5nm thick gold film. The Au film was melted at 1070°C, subsequently the sample temperature was lowered to a temperature of 940°C. Melting the Au film leads to a statistical size distribution of the Au droplets ser
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