Piezoelectric exciton acoustic-phonon coupling in single quantum dots

Abstract

Microphotoluminescence spectroscopy at variable temperature, excitation intensity, and energy was performed on a single InAs/AlAs self-assembled quantum dot. The exciton emission line ͓zero-phonon line ͑ZPL͔͒ exhibits a broad sideband due to exciton acoustic-phonon coupling by the deformation-potential mechanism. Additionally, narrow low-energy sidebands at about 0.25 meV of the ZPL are attributed to exciton acoustic-phonon piezoelectric coupling. In lowering the excitation energy or intensity these bands gradually dominate the emission spectrum of the quantum dot while the ZPL disappears. At high excitation intensity the sidebands due to piezoelectric coupling decrease strongly and the ZPL dominates the spectrum as a consequence of screening of the piezoelectric coupling by the photocreated free carriers. DOI: 10.1103/PhysRevB.78.241305 PACS number͑s͒: 78.55.Cr, 78.67.Hc, 73.21.La, 63.20.kk Semiconductor quantum dots ͑QDs͒ are promising candidates for optical devices, both for traditional and for quantum information applications. The knowledge of interactions of confined carriers with the environment is of fundamental importance for the device operation because they determine the optical efficiency on one hand and the coherence properties on the other. Phase coherence can be lost either by relaxation processes, namely, radiative and phonon-assisted recombination, or by coupling to acoustic phonons ͑pure dephasing͒. The former produces a broadening of the Lorentzian zero-phonon line ͑ZPL͒. Coupling to acoustic phonons gives rise to non-Lorentzian sidebands. 1Temperature induced broadening of the ZPL associated to exciton-phonon scattering was reported for natural QDs in a GaAs quantum well 2 and CdSe/ZnCdSe QDs. 3 Acousticphonon sidebands were observed in CdTe/ZnTe QDs, 1,4 InAs/GaAs QDs, 5 GaAs monolayer fluctuation QDs, 6 and CdSe QDs. Exciton acoustic-phonon interactions have been treated theoretically considering both the deformation potential ͑DP͒ and piezoelectric ͑PZ͒ coupling mechanisms. 1,8,9 It was pointed out theoretically 10 and experimentally 1 that in small QDs the DP coupling mechanism dominates over PZ coupling. However, effects related to piezoelectricity in QDs are still under investigation, as they are very sensible to QD geometry, size, and composition. [11][12][13][14] In this work we performed microphotoluminescence ͑micro-PL͒ spectroscopy on a single InAs/AlAs QD and measured the influence of temperature, excitation power, and excitation energy on the emission spectra. Besides a broad acoustic-phonon sideband, similar to previously reported ones originating from DP coupling 1,4-7 we observe a narrow low-energy sideband and show that it originates from the PZ exciton coupling to long-wavelength acoustic phonons. This interpretation is supported by the strong reduction in the PZ sidebands observed on increasing excitation power, as a consequence of screening by the photocreated carriers.The sample was grown by molecular-beam epitaxy and self-assembly of InAs dots between 20 nm thick AlAs...

Single-photon emission by semiconductor quantum rings in a photonic crystal

“…The X and XX line shapes change significantly upon decreasing excitation power: they broaden and slightly red-shift. This behavior has been reported for InAs/ AlAs QDs and explained in terms of sidebands due to acoustic phonon emission [19]. Increasing the excitation power screens out the piezoelectric coupling of X and XX to acoustic phonons, leading to a transition from broad spectra dominated by low-energy phonon sidebands to narrower lines corresponding to the zero-phonon-line exciton emission.…”

Magneto-photoluminescence spectroscopy of single InAs/AlAs quantum dots

“…The high AlAs barrier strongly localizes the wavefunction, thereby giving rise to very low diamagnetic shifts. Low-energy sidebands which have been investigated previously are now studied in magnetic field [7]. Their energy shifts with increasing field support the proposed mechanism of piezoelectric exciton-acoustic phonon interaction.…”

“…Single self-assembled semiconductor quantum dots (QDs) [1][2][3][4][5][6][7][8][9] are of great interest for their possible use in quantum information processing. For qubit operations using spin degrees of freedom the knowledge of electron and hole g-factors and their control are important.…”

Exciton-phonon coupling in individual ZnTe nanorods studied by resonant Raman spectroscopy

“…A similar high-frequency shoulder was recently observed for CdSe NPs and CdTe NPs in room temperature, which was assigned to contribution of acoustic phonons. 8,[72][73][74][75] Acoustic phonons are involved in most of the electronic processes via deformation potential and piezoelectric potential. 76,77 The exciton-acoustic phonon coupling decides the homogenous exciton linewidth of semiconductor in low temperature and exciton dephasing times.…”