This review article presents a comprehensive update on the recent research trends, advancement and future outlook of selected layered selenide based binary compounds featuring elements from group III, IV, and V of the periodic table.

Optical band gap properties of high-quality few-layer topological insulator Bi2Se3 thin films grown with magnetron sputtering are investigated using broadband absorption spectroscopy.We provide direct optical evidence of a rigid blue-shift to up to 0.5 eV in the band gap of Bi2Se3 as it approaches the two-dimensional limit. The onset of this behavior is most significant below six quintuple layers. The blue shift is very robust and is observed in both protected (capped) and exposed (uncapped) thin films. Our results are consistent with observations that finite-size effects have profound impact on the electronic character of topological insulators, particularly when the top and bottom surface states are coupled. Our result provides new insights, and the need for deeper investigations, into the scaling behavior of topological materials before they can have significant impact on electronic applications.2

We have investigated the transport properties of topological insulator Bi2Se3 thin films grown using magnetron sputtering with an emphasis on understanding the behavior as a function of thickness. We show that thickness has a strong influence on all aspects of transport as the two-dimensional limit is approached. Bulk resistivity and Hall mobility show disproportionately large changes below 6 quintuple layer which we directly correlate to an increase in the bulk band gap of few-layer Bi2Se3, an effect that is concomitant with surface gap opening. A tendency to crossover from a metallic to an insulating behavior in temperature-dependent resistivity measurements in ultra-thin Bi2Se3 is also consistent with an increase in the bulk band gap along with enhanced disorder at the film-substrate interface. Our work highlights that the properties of few-layer Bi2Se3 are tunable that may be attractive for a variety of device applications in areas such as optoelectronics, nanoelectronics and spintronics.

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