Selective GaAs Quantum Dot Array Growth using Dielectric and AlGaAs Masks Pattern-Transferred from Diblock Copolymer
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1014-AA07-15
Selective GaAs Quantum Dot Array Growth using Dielectric and AlGaAs Masks PatternTransferred from Diblock Copolymer Joo Hyung Park1, Anish Khandekar2, Sang-Min Park2, Luke Mawst1, Thomas Kuech2, and Paul Nealey2 1 Electrical and Computer Engineering, University of Wisconsin - Madison, 1415 Engineering Dr., Madison, WI, 53706 2 Chemical and Biological Engineering, University of Wisconsin - Madison, 1415 Engineering Dr., Madison, WI, 53706 ABSTRACT To take the full advantage of ideal Quantum Dots (QDs) for diode lasers and photodetectors, the selective growth of QDs on a patterned substrate was investigated. The substrate nanopatterning and QD formation was realized with diblock copolymers combined with selective MOCVD growth. Two methods are employed to achieve selective growth; 1) a nanopatterned SiO2 mask, and 2) a native oxidized AlGaAs nanopatterned mask. Using a SiO2 mask, the surface geometry and size distribution of GaAs QDs are studied. The selective growth on nanopatterned SiO2/GaAs substrate achieved a QD density of 5◊1010/cm2, comparable to SK growth mode with a QD size distribution peak at a 12nm diameter. The diblock copolymer nanopatterning was applied to Al0.7Ga0.3As/GaAs substrate and the patterned substrate was subject to growth of GaAs/InGaAs/GaAs QDs. The photoluminescence (PL) properties of the patterned QDs are reported in this investigation.
INTRODUCTION To reach the full theoretical potential advantages of ideal Quantum Dots (QDs) for diode lasers and photodetectors, elimination of the wetting layer, which is inherent to self-assembled QDs of the Stranski-Krastnow (SK) growth mode, and achieving a uniform mono-modal QD size distribution are needed. The SK QD approach is complicated by the randomness of the QD size distribution and inherent presence of the wetting layer. These factors have been experimentally identified as one of the underlying causes for low optical gain and high temperature sensitivity in diode lasers which result from carrier leakage out of the QDs into the wetting layer [1-3]. An alternate approach to QD formation is the use of nanopatterning with diblock copolymers combined with selective MOCVD growth [4-5]. We utilize cylinder-forming PS-bPMMA which have the ability of preserving the hole size through the pattern transfer procedures [5-6]. The combination of diblock copolymer lithography with selective MOCVD growth of the QDs could lead to a higher degree of control over QD shape, size uniformity, and composition over the self-assembly process [7]. Since the SK self-assembly process is not employed, the problematic wetting layer states are eliminated and improved optical gain can be expected. Control over the QD height, shape, and strain, also allows for the design of increased energy spacing between ground and excited QD states and hence a wider control or selection of the emission wavelengths. Since the QD strain is decoupled from the size, the process also has potential for achieving longer wavelength emission compared with SK QDs.
On a GaAs substrate,
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