Role In Carrier Dynamics Research Articles

Effect of Nanostructure on Carrier Transport Mechanism of III-Nitride and Kesterite Solar Cells: A Computational Analysis

In this work, the computational analysis on use of nanostructures to both III-Nitride and Kesterite solar cell are presented and compared. The scope behind the comparative analysis of III-nitride and kesterite material based solar cells is due to their excellent material properties, which made them suitable as an absorber for solar cells. In III-nitride based solar cells, stress induced polarization charges play an important role in carrier dynamics of cell, whereas, kesterite based cells suffer from detrimental effect due to its in-house defects. Here, an analysis is carried out to understand the above mentioned important effects, i.e., carrier transport mechanisms under the influence of polarization charges in III-nitride materials and in presence of defects in kesterite materials with nanostructures. It is anticipated that, nanostructures provide lots of advantages over bulk layer in order to overcome the detrimental effects in solar cells. A detailed comparative analysis of both type of solar cells are carried out. Finally, quantum efficiency measurement is carried out in order to observe the range of light absorption in each structures. It is quite interesting to observe that nanostructure doesn’t boost the performance of the solar cell unless until the device is engineered properly. It is purely depends on carrier recovery and transport from the nanostructures.

Strong carrier localization effect in carrier dynamics of 585 nm InGaN amber light-emitting diodes

Temperature dependence and time-resolved photoluminescence (TRPL) have been carried out to study carrier dynamics for 585 nm InGaN amber light-emitting diodes (LEDs). It is found that in InGaN amber LEDs, peak emission energy only shows a slight blueshift from 588 to 575 nm, as temperature increased from 10 K to 300 K. Moreover, radiative recombination lifetime has demonstrated independent of temperature based TRPL results. These two features indicate that a strong carrier localization effect plays a dominant role in carrier dynamics for InGaN amber LEDs. Also, activation energy of 40.3 meV is obtained through Arrhenius plot of PL intensity versus temperature.

Towards highly efficient photoanodes: the role of carrier dynamics on the photoelectrochemical performance of InGaN/GaN multiple quantum well coaxial nanowires

The carrier dynamics in highly active InGaN/GaN coaxial nanowire photoanodes were studied for photoelectrochemical water splitting applications that can provide deeper insight to enhance the photon-to-electron conversion efficiency.

Spin decoherence in n-type GaAs: The effectiveness of the third-body rejection method for electron-electron scattering

We study the spin decoherence in n-type bulk GaAs for moderate electronic densities at room temperature using the Ensemble Monte Carlo method. We demonstrate that a technique called “third-body rejection method” devised by B. K. Ridley, J. Phys. C: Solid State Phys. 10, 1589 (1977) can be successfully adapted to Ensemble Monte Carlo method and used to tackle the problem of the electron-electron contribution to spin decoherence in the parameter region under study, where the electron-electron interaction can be reasonably described by a Yukawa potential. This scattering technique is employed in a doping region where one can expect that multiple collisions may play a role in carrier dynamics. By this technique, we are able to calculate spin relaxation times which are in very good agreement with the experimental results found by Oertel et al., Appl. Phys. Lett. 93, 13 (2008). Through this method, we show that the electron-electron scattering is overestimated in Born approximation, in agreement with previous results obtained by C. A. Kukkonen and H. Smith, Phys. Rev. B 8, 4601 (1973).

Trap states and carrier dynamics of TiO2 studied by photoluminescence spectroscopy under weak excitation condition

Anatase and rutile TiO(2) were investigated with photoluminescence techniques under the weak excitation condition, where trap states play a vital role in carrier dynamics. The visible emission of anatase and near-infrared (NIR) emission of rutile both exhibit extremely long lifetimes up to milliseconds. The decay processes can be well described by the power-law decay which corresponds to the trapping-detrapping effect. These results indicate that the luminescence processes in both anatase and rutile TiO(2) have a close relationship with trap states. The visible emission band was assigned to the donor-acceptor recombination. Oxygen vacancies and hydroxyl groups mainly serve as the donor and acceptor sites, respectively. The NIR luminescence is originated from the recombination of trapped electrons with free holes, while the trapped electrons were formed through two paths, direct trapping or trap-to-trap hopping. The trap states in anatase and rutile TiO(2) may largely influence the photocatalysis process of TiO(2) and determine the photocatalytic activity under stationary illumination.

Time‐resolved ultrafast carrier dynamics in as‐grown nanocrystalline silicon films: the effect of film thickness and grain boundaries

AbstractIn this letter, we have studied transient photoinduced absorption in as‐grown nanocrystalline silicon films with thickness varied from 5 to 30 nm. Effects of quantum confinement (QC) in z ‐direction and grain boundary distortions alter the carrier dynamics of these films considerably. Based on the determination of critical points in the first Brillouin zone of the band structure of materials, we have time‐resolved the relaxation times of surface‐related states and indirect valleys. When decreasing the film thickness down to the QC limit (∼10 nm) new ultrafast relaxation mechanisms start to play a dominant role in carrier dynamics due to the topological disordering of these ultrathin films. These relaxation mechanisms seem to be related with the traping/de‐traping of the excited carriers prior to recombination. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Hot phonons in GaAs revisited

The importance of hot phonon effects in laser-excited GaAs is reevaluated in view of recent work that has focused on the role of carrier dynamics in the cooling process. Our calculations show that both lattice heating and the details in the carrier dynamics play an important role in the initial state of the cooling process.