Calorimetric Absorption Spectroscopy of Deep Defects and Quantum Dots |
R. Heitz, L. Podlowski, J. Böhrer, A. Hoffmann, I. Broser and D. Bimberg Technische Universität Berlin, Institut für Festkörperphysik, 10623 Berlin, Germany |
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In recent years calorimetric absorption spectroscopy has been developed to a powerful tool of semiconductor spectroscopy based on the detection of nonradiative relaxation processes. Calorimetric absorption spectroscopy is an ultrasensitive quantitative absorption technique. Recent investigations of Fe in III-V semiconductors and of InAs/GaAs quantum dots are presented here to illustrate the potential of the method. Sharp absorption lines are observed at the low energy onset of the Fe3+/2+ charge transfer band in III-V semiconductors. Calorimetric absorption spectroscopy measurements in the mK range reveal a strong temperature dependence of their absorption strength identifying unambiguously Fe3+(6A1(S)) as a ground state. The excited state is attributed to (Fe2+,h). The importance of exchange interaction for the observed fine structure is pointed out and binding energies are determined. The quantum yield of the intracenter 5Τ2-5E transition of F2+ is determined to be below 50% at 2 K. A correlation between the nonradiative relaxation rate and the isotope splitting of the 5Τ2-5E transition is observed, demonstrating the crucial role of the dynamical Jahn-Teller coupling of the 5Τ2 state to local Τ2 modes for the multiphonon relaxation process. Quantum dots having a d-function density of states should exhibit no Stokes shift between absorption and emission as observed for one- and two-dimensional systems. Calorimetric absorption spectroscopy demonstrates ground state absorption coinciding in energy with the luminescence for self- organized InAs/GaAs quantum dot structures grown by MBE. Transitions into excited hole states are resolved and a comparison to photoluminescence excitation spectroscopy is presented. |
DOI: 10.12693/APhysPolA.88.619 PACS numbers: 71.55.Eq, 71.70.Gm, 73.20.Dx |