Photoluminescence Excitation Dependence in Three-dimensional Si/SiGe Nanostructures
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0958-L03-05
Photoluminescence Excitation Dependence in Three-Dimensional Si/SiGe Nanostructures Eun-Kyu Lee1, Boris V. Kamenev1, Theodore I. Kamins2, Jean-Marc Baribeau3, David J. Lockwood3, and Leonid Tsybeskov1 1 Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, NJ, 07102 2 Quantum Science Research, Hewlett-Packard Laboratories, Palo Alto, CA, 94304 3 Instutute for Microstructural Sciences, National Research Council, Ottawa, K1A 0R6, Canada ABSTRACT We find that in SiGe clusters grown on Si using Stranski-Krastanov (S-K) growth mode, (i) photoluminescence (PL) spectra, (ii) PL lifetime and (iii) PL thermal quench activation energies exhibit strong dependence on the excitation intensity. Under PL excitation intensity increasing from 1 to 104 W/cm2, the PL spectra exhibit blue shift from below Ge bandgap up to ~970 meV. The PL lifetime shows strong dependence on the detection wavelength, decreasing from 20 µs at ~0.8 eV to 200 ns at ~ 0.9 eV. The process of PL thermal quench has two clearly distinguished activation energies. At low temperature, small (~15 meV) and excitationindependent activation energy is attributed to exciton thermal dissociation. At higher temperature, excitation-dependent PL thermal quench activation energy (increasing from ~ 120 to 340 meV as excitation intensity increases) is found, and it is attributed to hole redistribution via tunneling and/or thermal ionization over the Si/SiGe valence band energy barrier. INTRODUCTION Three-dimensional (3D) Si/SiGe nanostructures grown in Stranski-Krastanov (S-K) growth mode have attracted significant attention for the potential application in CMOScompatible light emitters operating at 1.3-1.6 µm spectral range [1-4]. The fabrication of Ge-rich SiGe cluster embedded in Si matrix is expected to enhance photoluminescence (PL) efficiency at elevated temperatures by localizing carriers within the confinement barriers [3, 5]. However, the radiative recombination in these structures remains extremely slow due to the spatially indirect confinement of electrons and holes, i.e., type-II band alignment at the interface [3, 6]. In this work, we report exciation dependence in the spectra, lifetime and thermal quenching activation energies of PL originating from S-K SiGe clusters. We find correlation between the observed PL spectra blue shift as excitation intensity increases and lifetime shortening at high detection energies. Our results from temperature dependent PL measurements can be understood by considering excitation dependent competition between carrier phononassisted tunneling and thermionic emission over the valence band confinement barrier. EXPERIMENTAL DETAILS The samples investigated in this work were prepared in a load-locked, single-wafer, lamp-heated chemical vapor deposition (CVD) reactor in a H2 ambient. The Si substrates were 15–25 Ω•cm Si (100) wafers, on which an undoped, 400-nm-thick Si buffer layer was grown.
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using GeH4 in H2, with a total reactor pressure of 1.33 The Ge clusters were grown at 600 kPa. The Si
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