GaAs Quantum Dots by MOCVD
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GaAs QUANTUM DOTS BY MOCVD
Takashi Fukui and Seigo Ando* Research Center for Interface Quantum Electronics, Hokkaido University, N 13, W 8, Sappro 060, Japan *NTT Basic Research Laboratories, Musashino-shi, Tokyo 180, Japan ABSTRACT New GaAs quantum dots called tetrahedral quantum dots (TQDs) were fabricated using selective area metalorganic chemical vapor deposition (MOCVD). GaAs sub-micron crystals were completely buried in AIGaAs with single growth run without any processing damage at heterojunction interface. The substrates were Si0 2 masked (11)B GaAs, which are partially etched free of SiO2 over triangular area using electron beam lithograpy and reactive ion First, truncated tetrahedral AIGaAs buffer layers with etching techniques. Next, GaAs TQDs were {110} facet sidewalls were grown in triangular area. Finally, AlGaAs layers were sequentially grown on the top of AlGaAs. The shape of GaAs overgrown on the resulting tetrahedral structures. The size of tetrahedron was measured by an atomic force microscope(AFM). The size bottom triangle of GaAs TQDs were estimated to be 20 nm. fluctuation was about 2%, which means that uniformity of selective area Photoluminescence of GaAs TQDs buried in AlGaAs was growth is excellent. A clear emission peak from GaAs TQDs was observed at 810 measured at 8.5K. The energy shift from the GaAs emission peak is 19meV, which agrees nm. The results suggest that the selective area well with the calculation. MOCVD method is very promising to fabricate GaAs quantum dots. I.
INTRODUCTION
Semiconductor quantum well dot structures are attractive new materials because the energy band structure changes to an energy sub-level structure A sharp luminescence spectrum with 0-dimensional electron-hole systems. and very low threshold current were expected for quantum well box lasers [1]. However, these properties are only varied if the size of quantum dots it is very difficult to On the other hand, are extremely uniform. fabricate uniform quantum dots with nanometer scale. There have been several attempts to fabricate quantum dot structures and electron using interference photolithography and plasma etching [2], Zero-dimensional sub-level beam lithography and reactive ion etching [3,4]. These structures were observed in optical or transport properties. processing technologies, however, have several disadvantages, such as Another fabrication damage to the etched surface and non-uniform shapes. fabrication method is to modify AlGaAs/GaAs quantum well physical properties This method makes use of the Al/Ga using focused ion beam implantation [5]. interdiffusion between well and barrier regions in the partial implantation As a result, the region to produce 0-dimensional carrier confinement. hetero-interfaces are not sharp. In previous reports, we proposed novel quantum dot fabrication method using selective area metalorganic chemical vapor deposition(MOCVD), in which GaAs dots were perfectly buried by AlGaAs without processing damage [6]. The electron structure and fundamental fabrication experiment
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