Temperature dependence of Optical Transitions of One Dimensional InGaAs/GaAs Quantum Structures
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0959-M19-03
Temperature dependence of Optical Transitions of One Dimensional InGaAs/GaAs Quantum Structures Zhixun Ma1,2, Todd Holden3, Zhiming Wang4, Samuel S. Mao1, and Gregory J. Salomo4 1 Lawrence Berkeley National Lab, Berkeley, CA, 94720 2 Physics Department, Untrafast Photonic Materials and Applications, Brooklyn College of CUNY, Brooklyn, NY, 11210 3 Physics Department, Queensborough Community College of CUNY, Bayside, NY, 11364 4 Department of Physics, University of Arkansas, Fayetteville, AR, 72701 One dimensional semiconductor structures such as quantum wires (QWRs) and quantum dot chains (QDCs) are of interest because their applications in lasing, photon detecting and sensing [1]. These structures are artificially grown via alternating layers in molecular beam epitaxy growth chamber [2]. One believes in general that the quantum well material is strained while the barrier material is free of strain. But in quantum dot (QD) structures, the barrier material around QDs is deformed by strain relaxation of QDs. The lattice deformation will be severe in one dimensional structure along a certain direction [3]. These accommodated strains may lead to the state splitting of heavy hole (hh) and light hole (lh) and to a change in band gap as well as confinement potentials. In addition, piezoelectric effect [4] may appear if shear strain exists, and thus band structure and carrier distribution will be affected. The samples used in this study were grown on semi-insulating GaAs (001) substrates with a miscut angle smaller than 0.05o, using solid source molecular beam epitaxy. The QWR and QDC samples consist of 17 layers of In0.3Ga0.7As/GaAs and In0.45Ga0.55As/GaAs, respectively. The samples were mounted in cryostat to measure the contactless elecroreflectance (CER) at various temperatures. For the bulk materials (unbound electronic states) and low filed modulation, the relative change of the reflectivity is given by the third derivative Lorentzian function, ∆R / R = Re[ Ae iΦ ( E − E 0 + iΓ) − m ] , [5] where A is amplitude, the phase angle, the broadening factor, E0 the transition energy and m=2.5 (3D), 3 (2D), 3.5 (1D). For bound state transitions such as excitonic and quantum confinement states, however, the change of reflectivity is of first derivative with either Lorentzian or Guassian lineshape depending on the broadening mechanism. The transition energy E0 can be obtained by fitting experimental data with the third or the first 12 derivative function. Although this study is focused Bulk GaAs (001) 1.510 eV 10 experimental on investigation of the quantum confinement states Fitting 8 of the layered quantum wire system, we measured 17K 6 the CER of a bare GaAs (001) substrate (as shown 4 in Fig. 1) for clarity because some bound state 2 300K transitions are closely located at band-gap of the 0 bulk GaAs substrate. Obviously, the experimental -2 1.421 data obtained at low and room temperatures show a -4 1.2 1.3 1.4 1.5 1.6 Photon Energy (eV) simple derivative-like lineshape, which can be well fitted with the third d
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