Abstract
The electronic band structure of highly mismatched alloys (HMAs) was very successfully explored using electromodulation (EM) spectroscopy, i.e., photoreflectance (PR), electroreflectance, and contactless electroreflectance (CER). With these techniques, the optical transitions between the valence band and the E− and E+ bands, which are formed in the conduction band of dilute nitrides and dilute oxides, were observed and used to formulate the band anticrossing model, which well describes the electronic band structure of HMAs. In this tutorial, principles of EM spectroscopy are presented and shortly discussed. Special attention is focused on PR and CER techniques, which are nondestructive and have recently been widely applied to study the electronic band structure of HMAs and low dimensional heterostructures containing HMAs. For these methods, experimental setups are described, and theoretical approaches to analyze the experimental data are introduced. Finally, to show the utility of EM spectroscopy, selected examples of the application of this method to study various issues in HMAs are presented and briefly discussed.
Highlights
Alloying semiconductor compounds is a well recognized method to tailor properties of the materials
The idea of study the band alignment in quantum wells (QWs) with EM spectroscopy is based on the comparison of energies of optical transitions derived from EM measurements with those calculated for various band alignments
We described principles of EM spectroscopy together with many details of experimental setups for measurements of PR, ER, and contactless electroreflectance (CER) spectra and the analysis of EM spectra
Summary
Alloying semiconductor compounds is a well recognized method to tailor properties of the materials. It allows for an independent control of the valence and conduction band (CB) offsets greatly expanding potential range of applications of these alloys It emphasizes the need for a reliable experimental method to determine details of the electronic structure of HMAs. Electromodulation (EM) spectroscopy played a key role in the original discovery of the BAC interaction induced splitting of the conduction band of GaInNAs8 but it was used to reveal complex details of the electronic band structure of a large variety of HMAs.[8,11,12,14,15,17,18,19,22,23,28,29,38–73]. This tutorial should be of interest for students and researchers interested in EM spectroscopy itself
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