Curing Quantum Dots using Inductively Coupled Argon Plasma T. Mei * , D. Nie * , H. S. Djie ** , and B. S. Ooi ** * School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore, etmei@ntu.edu.sg ** Center for Optical Technology, Department of Electrical and Computer Engineering, Lehigh University, Bethlehem, PA 18015, USA ABSTRACT The crystal quality of InGaAs/GaAs quantum dots (QDs) is substantially improved without redistribution of composition using inductively coupled Ar plasma exposure. An increase in photoluminescence intensity by 1.7 times is observed in the plasma-treated QDs with the peak wavelength unshifted. The bandgap blue-shift subject to the rapid thermal annealing is also suppressed, denoting improved thermal stability. The PL excitation-dependent experiment shows more prominent state-filling phenomenon in the plasma-treated QDs due to higher carrier density by defect density reduction. Keywords: quantum dot, intermixing, thermal annealing, argon plasma, photoluminescence 1 INTRODUCTION Great advancement achieved in QD growth using molecular beam epitaxy and metal-organic vapor phase epitaxy (MOVPE) allows QD-based devices to demonstrate superior performances.[1] However, QD structures are highly-strained material systems grown under low temperature such that appreciable amount of defects exist in the materials inherently. Defects may affect device performance such as threshold current due non-radiative recombination and the material’s thermal stability [2] as well such that bandgap shift is enhanced in annealing process. In order to eliminate the grown-in defects and improve QD performances, thermal treatment has been used during overgrowth and at postgrowth level with the penalty of notable bandgap blue-shift. [3-5] In the previous study of argon inductively coupled plasma (ICP) process for quantum well (QW) intermixing, we have observed significant photoluminescence (PL) enhancement in InGaAsP/InP QW samples [6]. It is further and more clearly evidenced in an experiment using an AlGaAs/GaAs 5-QW structure [7], where the PL peak of a defect-rich QW was recovered in contrast to the PL peaks of the rest QWs. In this paper, we report the effect of the inductively coupled Ar plasma exposure on the crystal quality of an In 0.5 Ga 0.5 As/GaAs QD structure fabricated by cycled monolayer deposition. The reduction of low temperature grown-in defects using inductively coupled argon plasma process in the InGaAs/GaAs samples is demonstrated. The optical property and the thermal stability are investigated in samples processed by plasma exposure and rapid thermal annealing (RTA). Low temperature photoluminescence (PL) is used to study the modification of QD optical properties and the change in QD thermal stability. 2 EXPERIMENTS The InGaAs/GaAs QDs structure [8] shown in Fig. 1 is a QD infrared photodetector structure grown by molecular beam epitaxy on a Si-doped n+ (100)-oriented GaAs substrate. A 300-nm-thick undoped GaAs buffer layer was first grown and subsequently a 1000-nm-thick, Si doped (n=2×10 18 cm -3 ) GaAs bottom contact layer. 20-stacks of InGaAs QD layers were then consecutively grown, separated by 50-nm-thick GaAs layers which were doped with Si (n=1×10 18 cm -3 ) within a thickness of 10 nm in the center of each layer. On the top is a 600-nm-thick, Si doped (n=2×10 18 cm -3 ) GaAs contact layer. For each QD layer, five pairs of alternating InAs and GaAs monolayers were grown under a constant As flux with interruption after each monolayer in order to stabilize the surface. The growth temperature was 515°C for QD layers and 600°C for other layers. Figure 1: The growth structure of experimental samples 244 NSTI-Nanotech 2006, www.nsti.org, ISBN 0-9767985-6-5 Vol. 1, 2006