Optical Properties of in GaAs/InP Quantum Wires Defined by High Voltage Electron Beam Lithography at 200 kV
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OPTICAL PROPERTIES OF InGaAs/InP QUANTUM WIRES DEFINED BY HIGH VOLTAGE ELECTRON BEAM LITHOGRAPHY AT 200 kV P.ILS, M.MICHEL, A.FORCHEL* AND I.GYURO, P.SPEIER, E.ZIELINSKI** * Lehrstuhl ffir Technische Physik, Universitit Wiirzburg, D-8700 WMirzburg, Germany; ** Alcatel-SEL Research Center, D-7000 Stuttgart, Germany.
ABSTRACT We have fabricated and analyzed high quality InGaAs/InP quantum wires by electron beam lithography and wet chemical etching. In order to optimize the shape of the wetetched wires different wire orientationswere investigated. As results of the lithography process we obtain wire masks with widths down to 15 nm and etched wires with widths of the InGaAs layer of 18 nm. The wires were studied optically by means of photoluminescence spectroscopy. In contrast to dry etched wire structures the wet chemically etched wires show strong optical emission even for geometrical widths less than 25 nm. The weak decrease of the quantum efficiency with decreasing wire width indicates that there are no dead layers at the side walls of the wires, which is in contrast to previous studies on dry-etched structures. The photoluminescence energy of the InGaAs/InP wires is independent of the wire dimension down to widths of 50 nm. This indicates that a steep lateral potential in our structures is obtained due to the confinement by the semiconductor/vacuum transition at the etched surfaces. For wires with smaller widths an increasing blue shift of photoluminescence energy up to more than 30 meV is observed.
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INTRODUCTION
In the last few years the fabrication and analysis of the optical properties of semiconductor wire structures with dimensions below 100 nm have been subject of intense investigations because many novel properties are expected on the basis of theory and because these structures are promising for optoelectronic device applications. Electron beam lithography is a widely used technique for creating ultrafine masks necessary for fabricating such wire structures. High acceleration voltages for electron beam lithography offer several advantages over conventional beam voltages of typically 20 to 50 kV. For high electron energies up to 200 keV the forward scattering of the electrons by the resist is negligible. The backscattering distribution is largely broadened at high energies. Hence the contribution of the backscattered electrons to the exposure dose is significantly diminished compared to the dose of the primary electron beam and thus uncritical for the exposure [3]. The corresponding large reduction of the proximity effect allows the fabrication of ultrasmall wire structures with small period.
Mat. Res. Soc. Symp. Proc. Vol. 283. @1993 Materials Research Society
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In order to minimize damage at the sidewalls of the wire structures, which leads to a significant degradation of the optical properties of the wires, deep wet chemical etching is used for transferring the created mask pattern into the semiconductor structure.
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TECHNOLOGY
Starting material for the structuring process are metal organic
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