Determination of homogeneous and inhomogeneous broadening in semiconductor nanostructures by two-dimensional Fourier-transform optical spectroscopy

Abstract

The imaginary part of two-dimensional Fourier-transform spectra in the rephasing and nonrephasing modes is used to analyze the homogeneous and inhomogeneous broadening of excitonic resonances in semiconductor nanostructures. Microscopic calculations that include heavy-and light-hole excitons as well as coherent biexcitonic many-body correlations reveal distinct differences between the rephasing and nonrephasing spectra. A procedure is proposed that allows separation of disorder-induced broadening in complex systems that show several coupled resonances.In the past decades, various optical techniques have been used to investigate and unravel the structure of electronic states in semiconductor nanostructures and other material systems. 1-5 Spatially resolved linear optical measurements give information about homogeneous and inhomogeneous broadening separately. Typically, however, they provide only general information, e.g., the total linewidth. On the other hand, nonlinear experiments have been applied successfully to obtain much more detailed information about the nature of excited states, the coupling among them, and many-body effects. In addition, different nonlinear optical techniques were used to investigate the amounts of homogeneous and inhomogeneous broadening ͑see Ref. 5 and references therein͒.Pump-probe measurements provide one-dimensional spectral information that cannot distinguish between homogeneous and inhomogeneous broadening. Hole burning can find the homogeneous contribution to the optical linewidth and, by comparing to the linear spectrum, provides an estimate of the inhomogeneous contribution. Four-wave-mixing ͑FWM͒ experiments show photon echoes in the timeresolved ͑TR͒ traces. 5,6 Their temporal width is determined by the inhomogeneous linewidth. However, for systems where more than a single resonance is simultaneously excited, the width of the echo is ill defined due to beating, 5,7,8 in particular, for small inhomogeneous broadening see ͑Fig.1͒. The time-integrated ͑TI͒ trace yields the homogeneous width, i.e., the dephasing rate. However, in the presence of more than just a single optical resonance, the decay parameter cannot uniquely be determined and a fitting procedure is needed.In semiconductor nanostructures, many-body Coulomb interaction strongly alters the nonlinear optical response. [3][4][5]9,10 Even at the Hartree-Fock level, e.g., the line shape of time-resolved FWM is significantly modified and signals for the wrong time ordering appear. [3][4][5]11,12 Additionally, already in the low-intensity third-order ͓ ͑3͒ ͔ limit, characteristic dependencies of the nonlinear transients and spectra on the polarization directions of the incident pulses and couplings among optically isolated resonances appear due to many-body correlations. [3][4][5]9,[13][14][15][16][17] A detailed microscopic description of interacting excitons in the presence of disorder is a formidable task. Thus, wellestablished knowledge is lacking on this topic. It was, however, shown that Hartree-Fock renormalizations...

Coherent two-exciton dynamics measured using two-quantum rephasing two-dimensional electronic spectroscopy

“…FTOPT spectra of MBIs among excitons in semiconductor quantum wells have been simulated using phenomenological [11,17] and microscopic first-principles [12,28,29] calculations. The former treat the quantum well as a simple few-level system (meaning that it begins with the same isolated states used in the sum-over-states approach) and then includes phenomenological terms to represent the MBIs, including any required binding energies, while the latter considers only the band structure of the semiconductor quantum well and the Coulomb coupling to generate the excitons, the multiexcitons, and the MBIs.…”

Polarized Optical Two-dimensional Fourier Transform Spectroscopy of Semiconductors

“…However, echo peak is not well defined due to the interplay between disorder and many-body interactions when disorder-induced broadening is small. In addition, the echo peak can be distorted by beating when more than one resonance is excited [119]. The retrieval of homogeneous width from TI FWM signal with beating requires careful fits to a sophisticated model in general.…”

“…In microscopic calculations of 2D spectra with the inclusion of many-body interactions of HH and LH excitons as well as biexcitons [119], inhomogeneous broadening demonstrates different behaviors in non-rephasing and rephasing pathways, making it possible to separate disorder-induced broadening. Experimental studies towards this goal are still on the way.…”

Electrical Properties of InP Crystals with Inhomogeneities Regions

“…It has been concluded [1] that large-sized structure imperfections have an effect on the properties of high-resistant materials, but in low-resistant materials inhomogeneities on the distribution of impurities have a principal influence. Though such crystals are considered as unsuitable material for production of many electronic devices, in some extent these disordered materials are used in special solid-state devices of microelectronics [2][3][4].…”