More Like this

1. Photonic Integrated Circuit for Rapidly Tunable Orbital Angular Momentum Generation Using Sb 2 Se 3 Ultra‐Low‐Loss Phase Change Material

   https://doi.org/10.1002/adom.202200098  

   Alam, Md Shah ; Gnawali, Rudra ; Hendrickson, Joshua R. ; Beamer, Diane ; Payne, Tamara E. ; Volk, Andrew ; Agha, Imad ( July 2022 , Advanced Optical Materials)

   The generation of rapidly tunable optical vortex (OV) beams is one of the most demanding research areas of the present era as they possess orbital angular momentum (OAM) with additional degrees of freedom that can be exploited to enhance signal‐carrying capacity by using mode division multiplexing and information encoding in optical communication. Particularly, rapidly tunable OAM devices at a fixed wavelength in the telecom band stir extensive interest among researchers for both classical and quantum applications. This article demonstrates the realistic design of a Si‐integrated photonic device for rapidly tunable OAM wave generation at a 1550‐nm wavelength by using an ultra‐low‐loss phase change material (PCM) embedded with a Si‐ring resonator with angular gratings. Different OAM modes are achieved by tuning the effective refractive index using rapid electrical switching of Sb₂Se₃ film from amorphous to crystalline states and vice versa. The generation of OAM waves relies on a traveling wave modulation of the refractive index of the micro‐ring, which breaks the degeneracy of oppositely oriented whispering gallery modes. The proposed device is capable of producing rapidly tunable OV beams, carrying different OAM modes by using electrically controllable switching of ultra‐low‐loss PCM Sb₂Se₃.

    

   more » « less
2. The Thermoelectric Properties of Bismuth Telluride

   https://doi.org/10.1002/aelm.201800904  

   Witting, Ian T. ; Chasapis, Thomas C. ; Ricci, Francesco ; Peters, Matthew ; Heinz, Nicholas A. ; Hautier, Geoffroy ; Snyder, G. Jeffrey ( April 2019 , Advanced Electronic Materials)

   Bismuth telluride is the working material for most Peltier cooling devices and thermoelectric generators. This is because Bi₂Te₃(or more precisely its alloys with Sb₂Te₃for p‐type and Bi₂Se₃for n‐type material) has the highest thermoelectric figure of merit,zT, of any material around room temperature. Since thermoelectric technology will be greatly enhanced by improving Bi₂Te₃or finding a superior material, this review aims to identify and quantify the key material properties that make Bi₂Te₃such a good thermoelectric. The largezTcan be traced to the high band degeneracy, low effective mass, high carrier mobility, and relatively low lattice thermal conductivity, which all contribute to its remarkably high thermoelectric quality factor. Using literature data augmented with newer results, these material parameters are quantified, giving clear insight into the tailoring of the electronic band structure of Bi₂Te₃by alloying, or reducing thermal conductivity by nanostructuring. For example, this analysis clearly shows that the minority carrier excitation across the small bandgap significantly limits the thermoelectric performance of Bi₂Te₃, even at room temperature, showing that larger bandgap alloys are needed for higher temperature operation. Such effective material parameters can also be used for benchmarking future improvements in Bi₂Te₃or new replacement materials.

    

   more » « less
3. Sr(Ag 1−x Li x ) 2 Se 2 and [Sr 3 Se 2 ][(Ag 1−x Li x ) 2 Se 2 ] Tunable Direct Band Gap Semiconductors

   https://doi.org/10.1002/ange.202301191  

   Zhou, Xiuquan ; Wilfong, Brandon ; Chen, Xinglong ; Laing, Craig ; Pandey, Indra R. ; Chen, Ying‐Pin ; Chen, Yu‐Sheng ; Chung, Duck‐Young ; Kanatzidis, Mercouri G. ( February 2023 , Angewandte Chemie)

   Synthesizing solids in molten fluxes enables the rapid diffusion of soluble species at temperatures lower than in solid‐state reactions, leading to crystal formation of kinetically stable compounds. In this study, we demonstrate the effectiveness of mixed hydroxide and halide fluxes in synthesizing complex Sr/Ag/Se in mixed LiOH/LiCl. We have accessed a series of two‐dimensional Sr(Ag_1−xLi_x)₂Se₂layered phases. With increased LiOH/LiCl ratio or reaction temperature, Li partially substituted Ag to form solid solutions of Sr(Ag_1−xLi_x)₂Se₂withxup to 0.45. In addition, a new type of intergrowth compound [Sr₃Se₂][(Ag_1−xLi_x)₂Se₂] was synthesized upon further reaction of Sr(Ag_1−xLi_x)₂Se₂with SrSe. Both Sr(Ag_1−xLi_x)₂Se₂and [Sr₃Se₂][(Ag_1−xLi_x)₂Se₂] exhibit a direct band gap, which increases with increasing Li substitution (x). Therefore, the band gap of Sr(Ag_1−xLi_x)₂Se₂can be precisely tuned via fine‐tuningxthat is controlled by only the flux ratio and temperature.

    

   more » « less
4. Sr(Ag 1−x Li x ) 2 Se 2 and [Sr 3 Se 2 ][(Ag 1−x Li x ) 2 Se 2 ] Tunable Direct Band Gap Semiconductors

   https://doi.org/10.1002/anie.202301191  

   Zhou, Xiuquan ; Wilfong, Brandon ; Chen, Xinglong ; Laing, Craig ; Pandey, Indra R. ; Chen, Ying‐Pin ; Chen, Yu‐Sheng ; Chung, Duck‐Young ; Kanatzidis, Mercouri G. ( February 2023 , Angewandte Chemie International Edition)

   Synthesizing solids in molten fluxes enables the rapid diffusion of soluble species at temperatures lower than in solid‐state reactions, leading to crystal formation of kinetically stable compounds. In this study, we demonstrate the effectiveness of mixed hydroxide and halide fluxes in synthesizing complex Sr/Ag/Se in mixed LiOH/LiCl. We have accessed a series of two‐dimensional Sr(Ag_1−xLi_x)₂Se₂layered phases. With increased LiOH/LiCl ratio or reaction temperature, Li partially substituted Ag to form solid solutions of Sr(Ag_1−xLi_x)₂Se₂withxup to 0.45. In addition, a new type of intergrowth compound [Sr₃Se₂][(Ag_1−xLi_x)₂Se₂] was synthesized upon further reaction of Sr(Ag_1−xLi_x)₂Se₂with SrSe. Both Sr(Ag_1−xLi_x)₂Se₂and [Sr₃Se₂][(Ag_1−xLi_x)₂Se₂] exhibit a direct band gap, which increases with increasing Li substitution (x). Therefore, the band gap of Sr(Ag_1−xLi_x)₂Se₂can be precisely tuned via fine‐tuningxthat is controlled by only the flux ratio and temperature.

    

   more » « less
5. Deep Level and Near‐Band‐Edge Recombination in Semiconducting Antiperovskite Hg 3 Se 2 I 2 Single Crystals

   https://doi.org/10.1002/adom.201800328  

   Das, Sanjib ; McCall, Kyle M. ; Peters, John A. ; He, Yihui ; Kim, Joon‐Il ; Liu, Zhifu ; Kanatzidis, Mercouri G. ; Wessels, Bruce W. ( September 2018 , Advanced Optical Materials)

   The wide‐bandgap, semiconducting ternary compound Hg₃Se₂I₂has shown promise as room‐temperature hard‐radiation detector. Since this compound was first reported, there has been significant improvement in crystal growth using a chemical vapor transport method with a polyethylene growth agent. To study the effects of this additional precursor on crystal quality, the nature of radiative and nonradiative defects using photoluminescence (PL) and photocurrent (PC) studies of Hg₃Se₂I₂single crystals are investigated. In contrast to earlier studies, excitation intensity‐dependence of PL emission shows that the near‐band‐edge (NBE) emission bands are all excitonic in nature. The PL intensity decreases with increasing temperature, with the higher energy peaks quenching by 40 K and the deeper levels quenched after 110 K. The PC spectra show a complex structure at room temperature related to NBE transitions in the band structure, while at low temperature only the direct gap transition is observed due to phonons freezing out. The PC spectra at low temperature also indicate several midgap levels that are attributed to native defects within the bulk crystal. These results indicate that the high quality of Hg₃Se₂I₂single crystals is maintained when the transport agent is used during growth, although there are still a variety of defects present.

    

   more » « less