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