Cu(In 1-x ,Ga x)Se 2 (CIGS) absorber layers were deposited on molybdenum (Mo) coated soda-lime glass substrates with varying Ga content (described as Ga/(In+Ga) ratios) with respect to depth. As the responsible mechanisms for the limitation of the performance of the CIGS solar cells with high Ga contents are not well understood, the goal of this work was to investigate differentproperties of CIGS absorber films with Ga/(In+Ga) ratios varied between 0.29 and 0.41 (as determined by X-ray florescence spectroscopy (XRF))in order to better understand the role that the Ga content has on film quality.The Ga grading in the CIGS layer has the effect causing a higher bandgap toward the surface and Mo contact while the band gap in the middle of the CIGS layer is lower.Also, awider and largerGa/(In+Ga) grading dip located deeper in the CIGS absorber layers tend to produce larger grains in the regions of the films that have lower

A small bulk gap and the presence of Dirac electrons due to conductive surface states make tetradymite topological insulators promising candidates for optoelectronic devices. In this work, we demonstrate a highly responsive Bi 2 Te 3 -Si heterostructure photodiode. The thermally evaporated Bi 2 Te 3 film, exhibiting a nanocrystalline nature, shows p-type doping behavior due to bismuth vacancies. As a result of the work function difference between Bi 2 Te 3 and p-type Si, charge transfer occurs and a Schottky barrier is formed. Using the thermionic emission model, the barrier height (Φ B ) is extracted to be ∼0.405 eV. For minimizing the effect of extrinsic defects, the photodiodes were capped with graphene or Si 3 N 4 . Since graphene acts as an efficient photoexcited carrier collector, the graphene capped device outperforms the Si 3 N 4 capped device. The higher quality Bi 2 Te 3 nanocrystalline film of the Si 3 N 4 capped photodiode contributes to a one-order-of-magnitude improvement in responsivity at 1550 nm wavelength, as compared to the graphene capped photodiode. The Si 3 N 4 capped photodiode shows photoresponse even at zero bias for 1550 nm wavelength. Built-in potential due to charge transfer at the interface of Bi 2 Te 3 and Si capped with a graphene electrode exhibits the highest responsivity (8.9 A W −1 ). Broadband photodetection is observed in both types of photodiodes.

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Thin film Cu(In,Ga)Se 2 (CIGS) layers were deposited by a 1-stage and 3-stage coevaporation process on Mo/Glass substrates at various Ga/(Ga+In) ratios (Ga ratio). The sputter rate and the depth profile of 1-stage CIGS absorber layers at various Ga ratios were measured using secondary ion mass spectrometry (SIMS) using different primary voltages and angles of incidence of a Cs beam in order to study how the Ga ratio of CIGS affected the sputter rate. It was determined that there was up to 50% variation in film sputter rate depending on the Ga ratio range, SIMS primary voltage, and angle of incidence. A point-by-point correction method was then developed to correct for relative sputter rate differences in 3-stage CIGS samples with a graded Ga ratio profile.