Optical Characterization of Buried Ingaas/GaAs Wires Overgrown by MBE
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ABSTRACT We have prepared buried InGaAs/GaAs wires by high resolution electron beam lithography, wet chemical etching and subsequent MBE overgrowth. Wires with lateral widths of less than 40nm have been realized. For optimized regrowth conditions such as growth temperature, growth rate, III/V ratio, and arsenic flux a smooth surface morphology of the I00nm thick overgrown (Al)GaAs layer is obtained. Etched only ultra narrow wires show a decrease of radiative recombination due to process induced defects and surface recombination at the open sidewalls. Optical investigations of narrow overgrown wires show a significant enhancement (up to two orders of magnitude) of the photoluminescence intensity. This is due to the disappearance of the open sidewalls and carrier capture from the overgrown barrier. From studies of the influence of the crystallographic orientation on the quantum efficiency we find, that B surfaces of the wires offer the best conditions for MBE overgrowth.
INTRODUCTION The fabrication of low dimensional semiconductor structures is of increasing interest for future device applications as e.g. quantum wire lasers. These narrow structures can be achieved by direct epitaxial growth on patterned substrates [1-2], by implantation induced intermixing [3] or by dry or wet chemical etching of two dimensional substrates, coated with an appropriate etch mask [4-7]usually defined by high resolution electron beam lithography. In the case of the various etch techniques open surfaces are created, which often degrade the radiative quantum efficiency because of nonradiative surface states and defect recombination. [8]. Especially ultra narrow structures show a significant decrease of the normalized photoluminescence intensity with decreasing lateral width. In this work we describe results on etched only and etched and MBE overgrown InGaAs/GaAs wires. We obtain a significant improvement of the wire emission intensities for narrow wires.
519 Mat. Res. Soc. Symp. Proc. Vol. 318. @1994 Materials Research Society
MBE GROWTH OF QUANTUM WELLS FOR WIRE FABRICATION We have fabricated InGaAs/GaAs single quantum wells (SQW) by growing an AIGaAs buffer on oriented semiinsulating substrate, followed by an GaAs barrier, InGaAs and the GaAs cap-layer. The indium content of the quantum wells was varied between 10% and 18%. The appropriate GaAs top layer thickness is influenced by three different effects: i) Wet chemical etching of and oriented wires on substrate using the H 2 S0 4 system as an etchant creates sidewalls [9]. This implies a broadening of the etched structure for increasing etch depth. Therefore low etch depths and small cap layer thicknesses are required. i) As reported elsewhere [10] tunnelling effects of the SQW-carriers through the cap layer to surface states are observed for a cap layer thickness below 12nm. In order to achieve a high radiative recombination rate the cap layer thickness should be greater than 12nm. iii) The MBE overgrowth process contains high temperature steps (e.g. annealing of the sample in t
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