⁴He and ³He Calorimetric Absorption Spectroscopy: Principles and Results on InGaAs/AlInAs Quantum Wells and Fe in InP and GaAs

Abstract

A novel absorption technique, Calorimetric Absorption Spectroscopy (CAS), is compared to other photothermally based spectroscopic methods. CAS is more sensitive than any other low-temperature absorption technique reported hitherto and it is quantitative. The method is based on the integral detection of phonons emitted during nonradiative recombination processes. A low-temperature resistance thermometer acts as phonon detector. The sensitivity of CAS increases drastically with decreasing temperature. An increase in sensitivity by an order of magnitude to 10 pW is reached by decreasing the base temperature from 1.3 K (⁴He-temperatures) to 0.5 K (³He-temperatures). Depending on the excitation density, αd products down to 10⁻¹⁰ can be detected. The experimental set-up to perform CAS measurements at ³He temperatures is described and modeled in detail. A direct determination of quantum efficiencies, obtained by combining CAS with calorimetric transmission spectroscopy (CTS), is demonstrated. Recent applications of CAS for the characterization of thin InGaAs/AlInAs quantum wells as well as for the study of the fine structure of deep traps like Fe centers in InP and GaAs are presented.