Open AccessMeasurement of charge carrier mobilities in thin films on metal substrates by reflection time resolved terahertz spectroscopy
Author(s) -
Hannes Hempel,
Thomas Unold,
Rainer Eichberger
Publication year - 2017
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.25.017227
Subject(s) - terahertz radiation , materials science , terahertz spectroscopy and technology , reflection (computer programming) , optics , spectroscopy , total internal reflection , substrate (aquarium) , optoelectronics , semiconductor , refractive index , crystallite , diffuse reflection , thin film , reflection coefficient , charge carrier , physics , nanotechnology , oceanography , quantum mechanics , computer science , metallurgy , programming language , geology
We show that charge carrier mobilities can be measured by reflection time resolved THz spectroscopy (R-TRTS) even for thin films on metal contacts, such as polycrystalline Cu 2 SnZnSe 4 grown on molybdenum. In the measurement a reduced THz reflection upon photo-excitation is observed in contrast to increased THz reflection commonly observed on insulating substrates, and which excludes standard analytic R-TRTS analyses. Instead, a numerical transfer matrix method is used to model the THz reflection from which we derive carrier mobilities of 100 cm 2 /Vs consistent with literature. We show that R-TRTS on metal substrates is ~100x less sensitive compared to measurements on insulating substrates. These sensitivity of these R-TRTS measurements can be increased by using lower substrate refractive indices, lower substrate conductivities, thicker sample layers or higher THz probe frequencies.