Phonons and excitons in ZrSe2–ZrS2 alloys,Journal of Materials Chemistry C

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Phonons and excitons in ZrSe2–ZrS2 alloys
Journal of Materials Chemistry C ( IF 5.7 ) Pub Date : 2020-03-19 , DOI: 10.1039/d0tc00731e
Sean M. Oliver _{1,

2,

3,

4,

5} , Joshua J. Fox _{4,

6,

7,

8,

9} , Arsalan Hashemi _{10,

11,

12,

13} , Akshay Singh _{4,

14,

15,

16,

17} , Randal L. Cavalero _{4,

6,

7,

8,

9} , Sam Yee _{1,

2,

3,

4,

5} , David W. Snyder _{4,

6,

7,

8,

9} , R. Jaramillo _{4,

14,

15,

16} , Hannu-Pekka Komsa _{10,

11,

12,

13,

18} , Patrick M. Vora _{1,

2,

3,

4,

5}

Affiliation

Department of Physics and Astronomy
George Mason University
Fairfax
USA
Quantum Materials Center
Electronic Materials and Devices Department
Applied Research Laboratory
Pennsylvania State University
University Park
Department of Applied Physics
Aalto University
Aalto
Finland
Department of Materials Science and Engineering
Massachusetts Institute of Technology
Cambridge
Department of Physics
Microelectronics Research Unit

Zirconium disulfide (ZrS₂) and zirconium diselenide (ZrSe₂) are promising materials for future optoelectronics due to indirect band gaps in the visible and near-infrared (NIR) spectral regions. Alloying these materials to produce ZrS_xSe_2−x (x = 0…2) would provide continuous control over key optical and electronic parameters required for device engineering. Here, we present a comprehensive analysis of the phonons and excitons in ZrS_xSe_2−x using low-temperature Raman spectroscopy and room-temperature spectroscopic ellipsometry (SE) measurements. We extract the Raman-active vibrational mode frequencies and find that they compare favorably with density functional theory (DFT) calculations. Our simulations and polarization-resolved measurements demonstrate that substitutional doping renders infrared (IR) modes to be Raman-active. This leads to a Raman spectrum dominated by nominally IR phonons, a phenomenon that originates from the large ionicity of the ZrS_xSe_2−x bonds. SE measurements of the complex refractive index quantify the blue-shift of direct, allowed exciton transitions with increasing S content, and we find strong light–matter interactions with low optical loss in the NIR. Correlating these data with DFT allows for an estimation of the Γ-point exciton binding energy at room temperature. This study illustrates the large effects of alloying on ZrS_xSe_2−x and lays the foundation for future applications of this material.

中文翻译：

ZrSe2-ZrS2合金中的声子和激子

由于二硫化锆（ZrS ₂）和二硒化锆（ZrSe ₂）在可见光和近红外（NIR）光谱区域中存在间接带隙，因此是未来光电子学的有前途的材料。将这些材料合金化以产生ZrS _x Se _{2- x}（x = 0…2）将提供对器件工程所需的关键光学和电子参数的连续控制。在这里，我们对ZrS _x Se ₂₋_x中的声子和激子进行全面分析使用低温拉曼光谱和室温光谱椭偏（SE）测量。我们提取了拉曼主动振动模式频率，发现它们与密度泛函理论（DFT）计算具有可比性。我们的仿真和偏振分辨测量结果表明，替代掺杂使红外（IR）模式具有拉曼活性。这会导致名义上的IR声子占主导的拉曼光谱，这种现象源自ZrS _x Se _2-_x的大电离性债券。SE对复数折射率的测量量化了随着S含量的增加，直接的，允许的激子跃迁的蓝移，并且在NIR中我们发现强的光-物质相互作用和低的光损耗。将这些数据与DFT进行关联可以估算室温下的Γ点激子结合能。这项研究说明了合金化对ZrS _x Se _{2- x}的巨大影响，并为该材料的未来应用奠定了基础。

更新日期：2020-03-19

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