npsm 새물리 New Physics : Sae Mulli

pISSN 0374-4914 eISSN 2289-0041


Research Paper

New Phys.: Sae Mulli 2020; 70: 524-530

Published online June 30, 2020

Copyright © New Physics: Sae Mulli.

Spectroscopic Characteristics of Zn$_{1-x}$Mn$_{x}$S Thin Films by Ellipsometry and Absorptance Measurements

타원편광분석법과 흡수측정을 이용한 Zn$_{1-x}$Mn$_{x}$S 박막의 분광학적 특성 연구

Dae Jung KIM1, Bong Jin KIM1, Duk Hyeon KIM1, Jong Won LEE2*

1School of Basic Sciences, Hanbat University, Daejeon 34158, Korea

2Department of Advanced Materials Engineering, Hanbat University, Daejeon 34158, Korea


Received: March 16, 2020; Revised: April 6, 2020; Accepted: May 11, 2020

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Zn$_{1-x}$Mn$_{x}$S thin films were grown on GaAs(100) substrates by using hot-wall epitaxy. X-ray diffraction patterns revealed the crystal structure of the epilayer. The optical properties were investigated using spectroscopic ellipsometry at 300 K from 3.0 -- 8.7 eV. The obtained data were analyzed to determine the critical points of the pseudodielectric function spectra, $\langle\varepsilon(E)\rangle=\langle\varepsilon_{1}(E)\rangle+\langle\varepsilon_{2}(E)\rangle$, such as $E_{0}/E_{0}+\Delta_{0}$, $E_{1}$, and three $E_{2}(\Sigma,\Delta,\Gamma)$structures. These critical points were determined by fitting analytical line-shapes to numerically calculated derivatives of the pseudodielectric functions. In particular, the transmittance/absorptance measurements were carried out to obtain the optical properties of the Zn$_{1-x}$Mn$_{x}$S epilayers, and the exact optical energy bandgap ($E_{g}$) was determined by comparing these results with the results of the ellipsometry measurements. Also, the energy band structures from the ellipsometry and the absorptance measurements were analyzed as a function of Mn concentration. The results obtained demonstrate that ellipsometry can be efficiently and non-destructively used to examine the energy bandgap of Zn$_{1-x}$Mn$_{x}$S epilayers.

Keywords: Zn$_{1-x}$Mn$_{x}$S thin film, Spectroscopic ellipsometry, Hot-wall epitaxy, X-ray diffraction patterns, Pseudo dielectric functions, Critical points, Transmission measurement

본 연구에서 사용된 Zn$_{1-x}$Mn$_{x}$S 박막은 열벽적층성장법 (Hot-Wall Epitaxy, HWE)으로 GaAs(100) 기판 위에 Mn 조성에 변화를 주어 성장시켰다. 성장된 박막의 결정구조는 엑스선 회절(XRD) 패턴을 이용하여 확인하였다. 박막의 광학적 특성인 유사유전함수는 분광학적 타원편광분석법 (spectroscopic ellipsometry, SE)을 사용하여 실온에서 3.0 -- 8.7 eV 광자에너지 범위에서 측정하였다. 유사유전함수 스펙트럼 $\langle\varepsilon(E)\rangle=\langle\varepsilon_{1}(E)\rangle+\langle\varepsilon_{2}(E)\rangle$에 나타난 $E_{0}/E_{0}+\Delta_{0}$, $E_{1}$, 그리고 세 개의 $E_{2}(\Sigma,\Delta,\Gamma)$와 같은 임계점 구조들은 타원편광분석법으로 측정한 데이터들을 이용하여 분석하였고, 각각의 정확한 임계점 봉우리들은 유사유전함수의 데이터를 이차 미분한 이계도함수 $d^{2}\langle\varepsilon(E)\rangle/dE^{2}$를 이용하여 구하였다. 특히, Zn$_{1-x}$Mn$_{x}$S 박막의 정확한 광학적 정보를 획득하기 위하여 투과/흡수 측정을 수행하였고, 이를 타원편광분석법으로 조사된 결과와 비교분석하여 정확한 광학적 에너지 밴드갭($E_{g}$)을 얻을 수 있었다. 또한 Mn 조성이 증가함에 따른 타원분광학적 측정과 흡수 측정으로부터 얻은 에너지밴드 구조의 변화를 분석하였고, 이를 통해 타원편광분석법이 Zn$_{1-x}$Mn$_{x}$S 시료의 광학적 에너지밴드갭을 비파괴적으로 평가하는데 유용한 방법임을 알 수 있었다.

Keywords: Zn$_{1-x}$Mn$_{x}$S 박막, 타원편광분석법, 열벽적층성장법, 엑스선 회절패턴, 유사유전함수, 임계점 구조, 흡수 측정

Fig. 1. Transmittance (%) and absorptance (%) of free-standing Zn$_{1-x}$Mn$_{x}$S thin films.

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