Sara Bakhshi

Controllable red and blue shifting of InGaAsP quantum well bandgap energy for photonic device integration

We demonstrate bandgap tuning of InGaAsP multiple quantum well structures by utilizing an impurity-free vacancy diffusion technique. Substantial modification of the bandgap energy toward the red and blue parts of the spectrum has been observed using SiO2/SiOyNx/SiNx capping layers and by controlling the associated oxygen and nitrogen content. The resulting degree of tuning, up to 120 nm red shift and 140 nm blue shift of the band-to-band wavelength emission, has been studied using room-temperature photoluminescence, in agreement with the emission spectra obtained from semiconductor optical amplifier waveguide strips.

Stoichiometric effects in polycrystalline CdTe

The effect of the vapor phase Cadmium (Cd) to Tellurium (Te) ratio on the electronic properties of CdTe films is being studied. The stoichiometry of CdTe films is being altered by varying the gas phase Cd/Te ratio during the Elemental Vapor Transport (EVT) deposition process. Resistivity-temperature measurements and solar cells made with polycrystalline EVT-CdTe suggest changes in the native cadmium vacancy (VCd) concentration and carrier lifetime. The findings are in good agreement with the recently updated defect levels using the HSE approximation. Photoluminescence (PL) analysis has also demonstrated variation in the formation of defect complexes with the Cd/Te ratio. 2-Photon TRPL lifetime measurements showed improved minority-carrier lifetime for CdCl2 treated samples deposited at low Cd/Te ratios.

Study the effect of TiO 2 annealing and TiCl 4 treatment on the performance of dye-sensitized solar cells

The structure and quality of the TiO2 is crucial for achieving high efficiency in dye-sensitized solar cells (DSCs). In this work we have studied the effect of annealing temperature, TiCl4 concentration/ treatment time and the number of the TiO2 layers on the performance of a DSC device. It is found that increasing the annealing temperature and treatment time with application of diluted TiCl4 increased the efficiency. These items along with including a bi-layer semiconductor led to a 30% performance increase in comparison to the original solar cell just by considering the best concentration and time product for TiCl4 treatment step. The enhancement in the performance is likely due to high porosity of the semiconductor layer. Also, the lessened TiCl4 concentration decreases the harmful effects of the harsh solution but still allows for band edge improvement. Lastly, the bi-layer consisted of transparent and opaque TiO2 paste. The first consist of 15-20nm particles and the latter comprises of ~100 nm particles. Each contributes to enhancement, as the dye and sunlight have greater absorption and scattering capabilities. Currently in progress is the synthesis and fabrication of new dyes, for compatibility efforts with the semiconductor.