Permanent Bandgap Engineering in Quasi-2D Tellurium Synthesized via Hot-Pressing

When and Where

Dec 2, 2022
3:45pm - 4:00pm

Hynes, Level 3, Room 310

Presenter

Naveed Hussain

Ahmed Shehzad

Maxim Shcherbakov

Co-Author(s)

Naveed Hussain¹,Ahmed Shehzad²,Maxim Shcherbakov¹

University of California, Irvine¹,Shenzhen University²

Abstract

Naveed Hussain¹,Ahmed Shehzad²,Maxim Shcherbakov¹

University of California, Irvine¹,Shenzhen University²

Two-dimensional (2D) tellurium (Te) is an emerging 2D semiconductor [1] with attractive characteristics, such as high carrier mobility, large electro-optic activity, superior air-stability, and strong spin–orbit coupling, etc. [2-3] The application of quasi-2D Te in optics and optoelectronics has been restricted due to its narrow indirect band gap of ~ 0.35 eV. Quasi-2D Te has been theoretically predicted to undergo dramatic indirect-direct bandgap transition [4] (0.35 eV to 1.92 eV) through strategies such as confinement effect [5] and external strain, [6] making it promising for nano-optoelectronics. [7] Another study predicts enabling of a colossal bandgap opening, resulting in strong absorption of UV to UV-blue visible lights upon induction of a biaxial compressive strain in quasi-2D tellurium.[8] However, experimentally achieving such massive yet irreversible bandgap modulation has remained a daunting task. Bandgap modulation through mechanical straining in ultrathin 2D materials has long remained an exciting avenue to achieve desired functionalities at nanoscale.[3] However, most of these demonstrations have reported volatile or short-lived strains, causing a reversible narrow bandgap modulation and temporary tailoring of their properties. By maintaining a high-pressure enforced non-slipping condition and exploiting the coefficient of thermal expansion (CTE) mismatch between tellurium and the growth substrates at elevated temperatures, we report a strategy that yields non-volatile strain induction in ultrathin 2D nanoflakes of tellurium, achieving an optimal irreversible biaxial compressive strain as high as -4.7 % on a sapphire substrate. Consequently, UV-Vis absorption and photoluminescence (PL) spectroscopy studies reveal a permanent indirect-direct bandgap modulation from 0.35 eV (bulk) to 3.18±0.1 eV (2D) at a modulation rate of 691 meV/%, which is ~400% larger than that of highest ever reported value is achieved in strained tellurium nanoflakes.[9] Our micro-Raman, micro-PL and high-resolution transmission electron microscopy studies further confirm the long-lived retention of modulated bandgap, resulting in superior absorbance and ultrabright photoemission in UV spectral region. Strained 2D tellurium exhibits robust band-to-band radiative excitonic recombination and high intrinsic quantum efficiency of c.a. 79.5±0.5%, calculated by using the following formula: [10] PL Quantum Yield (%)=τ/τr=79.5±0.5% Where τr and τnr are radiative and non-radiative recombination lifetimes. Our findings indicate the superior performance of strained 2D tellurium for optoelectronic applications and its possible utilization for UV sources in the classical and quantum optical regimes. The strategy suggests that controlled and non-volatile bandgap engineering can be generalized to other 2D semiconductors for on-demand applications in nano(opto)-electronics. Bibliography [1] Y. Wang, G. Qiu, R. Wang, S. Huang, Q. Wang, Y. Du, W. A. Goddard, M. J. Kim, X. Xu, Nature Electronics 2018, 1, 228-236. [2] G. Qiu, C. Niu, Y. Wang, M. Si, Z. Zhang, W. Wu, P. D. Ye, Nature Nanotechnology 2020, 15, 585-591. [3] Y. Wang, S. Yao, P. Liao, S. Jin, M. J. Kim, G. J. Cheng, W. Wu, Advanced Materials 2020, 32, 2002342. [4] B. Wu, X. Liu, J. Yin, H. Lee, Materials Research Express 2017, 4, 095902. [5] X. Huang, J. Guan, Z. Lin, B. Liu, S. Xing, W. Wang, J. Guo, Nano Lett 2017, 17, 4619-4623. [6] Zhili Zhu, Xiaolin Cai, Chunyao Niu, ChongzeWang, Qiang Sun, Xiaoyu, Z. G. Han, and Yu Jia, cond-mat. 2016. [7] M. Amani, C. Tan, G. Zhang, C. Zhao, J. Bullock, X. Song, V. R. Shrestha, Y. Gao, K. B. Crozier, M. Scott, A. Javey, ACS Nano 2018. [8] H. Ma, W. Hu, J. J. N. Yang, 2019. [9] Y. L. Huang, Y. Chen, W. Zhang, S. Y. Quek, C.-H. Chen, L.-J. Li, W.-T. Hsu, W.-H. Chang, Y. J. Zheng, W. Chen, Nature communications 2015, 6, 1-8. [10] H. Zhang, L. V. Besteiro, J. Liu, C. Wang, G. S. Selopal, Z. Chen, D. Barba, Z. M. Wang, H. Zhao, G. P. Lopinski, Nano Energy 2021, 79, 105416.