InAs Quantum Dots for Optoelectronic Device Applications
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InAs Quantum Dots for Optoelectronic Device Applications K. Stewart, S. Barik, M. Buda, H.H. Tan and C. Jagadish Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, The Australian National University, Canberra ACT 0200, AUSTRALIA ABSTRACT In this paper we discuss the growth of self-assembled InAs quantum dots (QDs) on both GaAs and InP substrates by low pressure Metal Organic Chemical Vapor Deposition. The influence of various growth parameters, such as the deposition time, the QD overlayer growth temperature, the V/III ratio and the group III and/or group V interdiffusion on QD formation are discussed and compared for the two systems. Stacking issues and preliminary results for an InAs/GaAs QD laser are also presented. INTRODUCTION Self-assembled semiconductor quantum dots (QDs) grown in the Stranski-Krastanov growth mode have found application in a multitude of optoelectronic devices such as lasers, modulators and photodetectors. Improved characteristics are predicted for these devices due to the unique electrical and optical properties provided by the quantum dots as a result of their 3dimensional carrier confinement and delta function like density of states [1]. However, there are still many challenges associated with the growth of these QDs, especially by Metal-Organic Chemical Vapor Deposition (MOCVD). Self assembled growth of quantum dots has advanced rapidly by Molecular Beam Epitaxy (MBE) with the fabrication of QD lasers emitting at 1.3 µm with low threshold currents and reasonable differential efficiencies [2-3]. Compared with MBE, higher growth temperatures are typically required by MOCVD to ensure proper cracking of the precursor gases. This has a number of implications for QD growth including increased growth kinetics, island coalescence and indium evaporation which can lead to highly non uniform arrays of large QDs. In this paper, we will highlight some of the key parameters associated with MOCVD growth of InAs QDs onto both GaAs and InP substrates. While both systems involve the deposition of InAs to form the QDs, they each have their individual advantages and challenges. The emission wavelength of InAs/GaAs QDs falls just short of 1.3 µm, whereas that for InAs QDs deposited on InP can easily extend beyond 1.5 µm for telecommunication applications. InAs/GaAs QDs are highly strained (~7.2% lattice mismatch) compared to the InAs/InP system (~3.2% lattice mismatch). This narrows the window of growth parameters and growth flexibility for formation of high density, defect/dislocation free QDs and makes stacking of multiple QD layers more difficult. While the InAs/InP system is less strained, InAs QDs deposited onto InP substrates tend to form dashes rather than dots and also suffers from the effect of As/P interdiffusion. These issues and preliminary results from a laser incorporating 3-stacked layers of InAs/GaAs QDs will be presented. EXPERIMENTAL DETAILS The InAs QD structures used in this study were grown on (100) GaAs or InP substrates by low-
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