Effects of core size and shell thickness on phonon modes in GaAs/AlAs shell quantum dots

Abstract

Phonon modes in spherical GaAs quantum dots (QDs) embedded in spherical AlAs shells with up to 11 855 atoms (about 8.0 nm in diameter) are calculated by using a valence force field model. All the vibration frequencies and vibration amplitudes of these shell QDs are calculated directly from the lattice dynamic matrix by employing the projection operators of the irreducible representations of the group theory. The effects of the size of GaAs cores and the thickness of AlAs shells on the phonon modes are investigated. The quantum confinement effects of both the vibration frequencies and vibration strengths are investigated. The microscopic interface modes, which can only be revealed by the microscopic model, are identified and discussed.

Calculations on the size effects of Raman intensities of silicon quantum dots

“…From the data listed in Table I, we see that when the size of Si QD's decreases from 75.79 Å to 14.11 Å, the frequency of the first Raman peak of A 1 modes shifts from 28.6 cm Ϫ1 to 129.8 cm Ϫ1 , the first Raman peak of E modes shifts from 8.6 cm Ϫ1 to 46.7 cm Ϫ1 , and the first Raman peak with T 2 symmetry shifts from 12.4 cm Ϫ1 to 58.8 cm Ϫ1 . The size effects of lowest frequencies of phonon modes in QD's have been discussed in detail in our previous studies, [12][13][14][15] and again this is shown in the calculated Raman spectra. Furthermore, we notice that even though the frequencies of the lowest-frequency peak increase in all these three figures, they increase at a different rate.…”

“…These investigations lead to many interesting physics that otherwise cannot be revealed. [12][13][14][15] With this model, we have studied the size effects of phonon modes in semiconductor quantum dots, including QD's of one material, such as GaAs or InAs, as well as QD's with a core of one material embedded in a shell of another material, such as GaAs cores embedded in AlAs shells. To further develop our theoretical model in investigations of properties of QD's, in this paper, we have studied the size effects of Raman intensity in semiconductor QD's with the same model.…”

Interatomic potentials for the vibrational properties of III-V semiconductor nanostructures

“…An additional long range Coulomb potential was soon introduced into the VFF model [24]. However, within this model, the parameters which fit the elastic properties do not reproduce phonons well [23] and vice versa [27], [28]. Another type of very popular potentials are based on the parametrization given by Stillinger and Weber [29].…”

Comparison of three empirical force fields for phonon calculations in CdSe quantum dots

“…These have been employed chiefly in molecular dynamics simulations of processes such as surface reconstruction and phase transitions, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] but there has also been interest in using empirical potentials to calculate the geometries and vibrations of semiconductor nanocrystals ("quantum dots" when nearly spherical). [20][21][22][23][24][25][26][27][28] Our group has been using quantitative resonance Raman intensity analysis to probe electron-phonon coupling in 4 CdSe-containing quantum dots (QDs), [29][30][31][32][33] and full interpretation of these data requires knowledge of the phonon frequencies and modes. While the vibrational properties of molecules and nanomaterials are determined largely by the masses and connectivities of the atoms, the details can be quite dependent upon the specific force field used.…”