Abstract-Optimizing biased semiconductor superlattices for terahertz amplification

Lei, Xiaoli  ; Wang, Dawei ; Wu, Zhaoxin ; Dignam, M.M.

http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6879108

Over the past 15 yr or more, researchers have been trying to achieve gain for electromagnetic fields in the terahertz frequency region using biased semiconductor superlattices, but with little success. In this work, we employ our model of the excitonic states in biased GaAs/Al0.3Ga0.7As semiconductor superlattices to find the optimal structures for amplification of terahertz radiation. In particular, we determine the optimum well width, barrier width, and bias field for terahertz fields with frequencies ranging from 1 to 4 terahertz. We find that gain coefficients on the order of 40 cm−1 should be achievable over most of this frequency range.

Abstract-TERAHERTZ DIELECTRIC RESPONSE AND COUPLED DYNAMICS OF FERROELECTRICS AND MULTIFERROICS FROM EFFECTIVE HAMILTONIAN SIMULATIONS

DAWEI WANG

Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi'an Jiaotong University, Xi'an 710049, P. R. China

JEEVAKA WEERASINGHE

Physics Department, University of North Texas, Denton, Texas 76205, USA

ABDULLAH ALBARAKATI

Physics Department, The University College at Al-Gammom, Umm Al-Qura University Makkah, Saudi Arabia

L. BELLAICHE

Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA

http://www.worldscientific.com/doi/abs/10.1142/S0217979213300168

Ferroelectric and multiferroic materials form an important class of functional materials. Over the last 20 years, first-principles-based effective Hamiltonian approaches have been successfully developed to simulate these materials. In recent years, effective Hamiltonian approaches were combined with molecular dynamics (MD) methods to investigate terahertz dynamical properties of various perovskites. With this combination, a variety of ferroelectric and multiferroic materials, including BaTiO₃, Ba(Sr, Ti)O₃, Pb(Zr, Ti)O₃, BiFeO₃ and SrTiO₃ bulks and films have been simulated, which led to the understanding of complex phenomena and discovery of novel effects. In this paper we first provide technical details about effective Hamiltonians and MD simulation method. Then, we present applications of the combination of these two techniques to different perovskites. Finally, we briefly discuss possible future directions of this approach.

Read More: http://www.worldscientific.com/doi/abs/10.1142/S0217979213300168