摘要
Although there are numerous optical spectroscopy techniques and methods that have been used to extract the fundamental bandgap of a semiconductor,most of them belong to one of these three approaches:(1)the excitonic absorption,(2)modulation spectroscopy,and(3)the most widely used Tauc-plot.The excitonic absorption is based on a many-particle theory,which is physically the most correct approach,but requires more stringent crystalline quality and appropriate sample preparation and experimental implementation.The Tauc-plot is based on a single-particle theo⁃ry that neglects the many-electron effects.Modulation spectroscopy analyzes the spectroscopy features in the derivative spectrum,typically,of the reflectance and transmission under an external perturbation.Empirically,the bandgap ener⁃gy derived from the three approaches follow the order of E_(ex)>E_(MS)>E_(TP),where three transition energies are from exci⁃tonic absorption,modulation spectroscopy,and Tauc-plot,respectively.In principle,defining E_(g) as the single-elec⁃tron bandgap,we expect E_(g)>E_(ex),thus,E_(g)>E_(TP).In the literature,E_(TP) is often interpreted as E_(g),which is conceptual⁃ly problematic.However,in many cases,because the excitonic peaks are not readily identifiable,the inconsistency be⁃tween E_(g) and E_(TP) becomes invisible.In this brief review,real world examples are used(1)to illustrate how excitonic absorption features depend sensitively on the sample and measurement conditions;(2)to demonstrate the differences between E_(ex),E_(MS),and E_(TP) when they can be extracted simultaneously for one sample;and(3)to show how the popular⁃ly adopted Tauc-plot could lead to misleading results.Finally,it is pointed out that if the excitonic absorption is not ob⁃servable,the modulation spectroscopy can often yield a more useful and reasonable bandgap than Tauc-plot.
尽管有多种光谱技术可用来提取半导体的禁带宽度或带隙,但它们大多属于以下三种方法之一:(1)激子吸收,(2)调制光谱,(3)最广泛使用的Tauc图。激子吸收基于多粒子理论,在物理意义上是最明确的,但对晶体质量、样品制备和实验实施有更高的要求。Tauc图基于单粒子理论,忽略了多电子效应。调制光谱分析反射和透射在外部微扰下的微分光谱特征。经验上,从这三种方法得到的带隙能量按顺序为E_(ex)>E_(MS)>E_(TP),其中3个跃迁能量分别来自激子吸收、调制光谱和Tauc图。原则上,如果定义E_(g)为单电子带隙,我们期望E_(g)>E_(ex),因此,E_(g)>E_(TP)。在文献中,E_(TP)通常被解释为E_(g),这在概念上是有问题的。然而,在许多情况下,由于激子吸收峰不容易被观测到,人们意识不到E_(g)和E_(TP)之间的不一致问题。这篇简短的综述使用真实样品的例子,(1)说明激子吸收特征如何依赖于样品和测量条件;(2)展示当它们可以同时提取时,E_(ex)、E_(MS)和E_(TP)之间的差异;(3)演示广泛采用的Tauc图如何可能导致误导性的结果。最后指出,如果不能观察到激子吸收峰,调制光谱通常可以比Tauc图得到更有用和合理的带隙。
作者
ZHANG Yong
张勇(Department of Electrical and Computer Engineering,University of North Carolina at Charlotte,Charlotte,NC 28223,USA)
出处
《发光学报》
北大核心
2025年第7期1271-1282,共12页
Chinese Journal of Luminescence
基金
Supported by Bissell Distinguished Professor Endowment Fund at UNC-Charlotte。
作者简介
Corresponding Author:张勇(1960-),男,福建福州人,博士,讲席教授,1994年于Dartmouth Col⁃lege获得博士学位,主要从事半导体光电材料物理与器件物理的研究。E-mail:yong.zhang@charlotte.edu。
