Studies on Spin Orbit Splitting and Dual Mode Phonon Vibrations in ZnS x Se1−x Ternary Alloys Films with Varying Se Concentration

Abstract

ZnS x Se 1Àx (x = 0, 0.41, 0.51, 0.91, 1) ternary alloy thin films with variable structural, optical and vibrational properties were prepared by thermal evaporation of solvothermally synthesized ZnS-ZnSe nanocomposite powders. The deposited films were uniform and have zinc-blende structure with (111) orientation. Variation of lattice parameter with composition was slightly nonlinear with a bowing parameter of 0.12 Å . Spin orbit (SO) splitting of the valence band was observed in binary ZnSe and ternary samples with large Se atomic concentration such as ZnS 0.41 Se 0.59 and ZnS 0.51 Se 0.49 . The SO splitting energy decreases as the Se atomic concentration in the alloy decreases. Two phonon modes (corresponding to ZnS and ZnSe bonds) behavior were observed in the Raman spectra of the ternary alloys. The observed phonon mode frequencies shifted with changes in Se atomic concentration in agreement with theroretical predictions. Gap mode vibration of Se in ZnS lattice was also observed at 221 cm À1 in the ternary sample with small Se atomic concentration (ZnS 0.91 Se 0.09 ), which also matches closely with theoretically calculated values.

Strain Engineering in InP/(Zn,Cd)Se Core/Shell Quantum Dots

“…The Raman spectrum of these InP/ZnSe core/shell QDs features both the InP Raman bands, with the LO phonon shifted to 354 cm –1 , and a new band at around 200–240 cm –1 , that again consists of multiple sub-bands (see Figure c). Since the most pronounced contribution at 247 cm –1 almost coincides with the 249 cm –1 reported for the LO phonon of bulk ZnSe, we assign this additional band to ZnSe phonons. Possibly, the low-energy shoulder contains contributions of ZnSe TO phonon or surface phonon modes, which should be retrieved at 205 and 226 cm –1 , respectively …”

“…Since the most pronounced contribution at 247 cm –1 almost coincides with the 249 cm –1 reported for the LO phonon of bulk ZnSe, we assign this additional band to ZnSe phonons. Possibly, the low-energy shoulder contains contributions of ZnSe TO phonon or surface phonon modes, which should be retrieved at 205 and 226 cm –1 , respectively …”

“…(a) Lorentzian functions used to fit the shell-related LO Raman bands and (b) shell-related LO phonon frequencies versus relative cadmium amount in the alloy. The bulk values for zinc blende ZnSe and wurtzite CdSe are displayed as lines. , The solid line is a fit according to Bouamama et al …”