Surface and optical property modifications of self-assembled CdTe/ZnTe quantum dots caused by thermal treatment
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T.W. Kima) Advanced Semiconductor Research Center, Division of Electronics and Computer Engineering, Hanyang University, Seongdong-gu, Seoul 133-791, Korea (Received 27 November 2007; accepted 18 January 2008)
Atomic force microscopy images showed that the size of the CdTe quantum dots (QDs) slightly increased with increasing annealing temperature up to 350 °C. Photoluminescence spectra showed that the excitonic peak corresponding to the interband transition from the ground electronic subband to the ground heavy-hole band (E1–HH1) in the CdTe/ZnTe QDs annealed at 350 °C was shifted to lower energy compared with that in as-grown CdTe/ZnTe QDs. The full width at half-maximum of the E1–HH1 transition peak in the CdTe/ZnTe QDs annealed at 350 °C decreased resulting from the improvement of the crystallinity for the annealed CdTe QDs.
I. INTRODUCTION
Self-assembled semiconductor quantum dots (QDs) formed by the Stranski–Krastanov (SK) growth mode have become particularly attractive because of their promising applications in electronic and optoelectronic devices, such as single electron transistors,1 capacitance spectroscopy,2 QD lasers,3,4 and QD infrared photodetectors5,6 operating at lower currents and higher temperatures. Defect-free QDs in highly lattice-matched heterostructures can be generated using SK growth mode.7,8 However, the random size distribution of the QDs leads to inhomogeneous broadening of the photoluminescence (PL) emission of QDs.9 Since the nonuniformity of the size distribution of QDs negates the advantages of QD lasers and comprises an inherent technical problem in the fabrication of the QD lasers, the size control of QDs is necessary for achieving high-efficiency devices. Among the various kinds of QDs, III–V/III–V QDs have been the most extensively studied systems.10 However, relatively little work has been performed on II–VI/II–VI QDs compared with III–V/III–V QDs because of the delicate problems encountered in the growth process.11 Even though some studies on the structural and the optical properties of self-assembled InAs/GaAs QDs due to rapid thermal annealing (RTA) have been performed to improve the quality of QDs,12–15 few studies concerning thermal annealing effects on the optical properties of self-
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0157 J. Mater. Res., Vol. 23, No. 5, May 2008
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assembled CdTe/ZnTe QDs have been conducted.16–18 Recently, studies on a strong dependence of the exciton spin relaxation in CdTe/ZnTe QDs on the average dot size and the depth of the confining potential have been reported.17 Because the optical properties of CdTe/ZnTe QDs are significantly affected by the surface properties of the QDs, correlation studies of the microstructural and the optical properties of these QDs are very important for improving the efficiencies of electronic and optoelectronic devices. Furthermore, studies on surface and optical property modifications of self-assembled Cd
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