Calorimetric Absorption Spectroscopy of Deep Defects and Quantum Dots

Abstract

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 absorptioii 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 Fe 3 +/2 + charge transfer band in Ill-V semiconductors. Calorimetric absorption spectroscopy measurements in the mK range reveal a strong temperature dependence of their absorption strength identifying unambiguously Fe3+ ( 6 Α1 (S)) as a ground state. The excited state is attributed to (Fe2+ ,h). The importance of exchange interactioii for the observed fine structure is pointed out and binding energies are determined. The quantum yield of the intracenter 5 Τ2 -5E transition of Fee+ is determined to be below 50% at 2 K. Α correlatioii 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 5 Τ2 state to local T2 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 absorptioii 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.