Transient picosecond/subpicosecond Raman scattering studies of nonequilibrium electron distributions and phonons in CdTe

Grann, E. D.; Chen, Y.; Tsen, Kong-Thon; Ferry, D. K.; Almeida, Tatiana das Chagas; Chen, Y. P.; Faurie, J. P.; Sivananthan, S.

doi:10.1063/1.363338

Cited by 11 publications

(3 citation statements)

References 14 publications

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“…The population of electrons and holes around the zone center Γ across the direct band gap results in a negative Δ n by the FC and BF effects and a positive Δ n by the BGR at 1030 nm (Figure A), leading to a negative total contribution when the density is larger than 1.4 × 10 18 cm –3 , which is consistent with the experimental observation (Figure ). The LT-induced effect is estimated by considering the transfer of the carriers’ excess energy to the lattice in a few picoseconds (generation of multiple optical phonons and their relaxation; also, the time when the TR data reach minimum in Figures A and ), given by where N peak is the peak value of the deduced carrier density, ρ is the density of CdTe, C latt is the specific heat of CdTe, and E F c and E F v are the Fermi energies of the electrons and holes in the conduction and valence bands, respectively. At the present fluence, Δ T is less than 1 deg and therefore Δ n LT only affects slightly the asymptotic value of N ( t ) after hundreds of picoseconds.…”

Section: Resultsmentioning

confidence: 99%

Ultrafast Carrier Dynamics of CdTe: Surface Effects

Punpongjareorn

et al. 2016

J. Phys. Chem. C

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Cadmium telluride has been an important absorber material used in solar cells for decades given its near-optimum band gap and lower cost for device fabrication. However, the overall efficiency has been low compared to the theoretical limit. One major contributor to the problem of the relatively low open-circuit voltage is the high surface recombination of photogenerated carriers. In this contribution, time-resolved pump–probe reflectivity was used to study the carrier dynamics of CdTe(111) under the influence of selected surface conditions. It was found that surfaces after the processes of chemical etching and thermal oxidation for short durations exhibit bulk-like transient reflectivity and a clearly reduced surface recombination velocity, according to a model calculation. The comparative study indicates that the origins of carrier traps include the midgap defect states that are associated with the uncapped Te surface atoms, namely the Te antisites and Te interstitials, and subsurface damages resulting from polishing and ion sputtering. The present results suggest that the formation of a thin oxide layer through annealing after chemical etching may be beneficial for surface improvement for CdTe-based solar cells.

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Section: Resultsmentioning

confidence: 99%

Ultrafast Carrier Dynamics of CdTe: Surface Effects

Punpongjareorn

et al. 2016

J. Phys. Chem. C

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“…Other techniques such as photoreflectance [10,11], reflectance-difference [12], Raman spectroscopy [13,14], Raman spectroscopy using transient subpicosecond/picosecond [15], reflectivity and picosecond time-resolved photoluminescence [16], transmission, modulated transmission [17] and resonant spin-flip Raman scattering [18] have also been applied to study the II-VI semiconductors.…”

Section: Introductionmentioning

confidence: 99%

Surface dependent behaviour of CdS LO-phonon mode

Molina-Contreras

Medina-Gutiérrez

Frausto-Reyes

et al. 2007

J. Phys. D: Appl. Phys.

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In this paper, we develop a sensitive optical method to monitor the surface roughness in the investigation of surfaces. By applying this method to measure the RMS surface roughness of various surfaces, we found RMS values which are comparable to those obtained by atomic force microscopy measurements. In addition, we present a simple empirical model to calculate the RMS surface roughness which shows very good agreement with the surface roughness measurements taken by the method reported in this paper. Finally, the application of our method to the study of the LO-phonon mode of CdS suggests that its intensity is dominated by the surface roughness. This roughness dependent behaviour of the CdS LO-phonon mode is experimentally confirmed by using an excitation wavelength near its E0 transition.

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“…Techniques as Photoreflectance(PR) [9,10], Reflectance-Difference(RD) [11], Raman spectroscopy [12,13], Raman spectroscopy using transient subpicosecond/picosecond [14], reflectivity and picosecond time-resolved photoluminescence [15], transmission, modulated transmission [16], and resonant spinflip Raman scattering [17] also have been used to investigated the II-VI semiconductors.…”

Section: Introductionmentioning

confidence: 99%

CdS Roughness by Anti-Stokes Raman Spectroscopy

et al. 2006

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A Raman system, with the 514.5 and 632.8 nm excitations wavelengths, was used to qualitatively detect the surface roughness of a CdS wafer sample. Anti-Stokes Raman spectra were obtained from several sample zones with different mean roughness levels, previously measured with Atomic Force Microscopy. Our results show that there is a spectrum profile which can be related to the sample roughness, which shows a better definition with the 514.5 nm excitation wavelength.

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Transient picosecond/subpicosecond Raman scattering studies of nonequilibrium electron distributions and phonons in CdTe

Cited by 11 publications

References 14 publications

Ultrafast Carrier Dynamics of CdTe: Surface Effects

Ultrafast Carrier Dynamics of CdTe: Surface Effects

Surface dependent behaviour of CdS LO-phonon mode

CdS Roughness by Anti-Stokes Raman Spectroscopy

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