1 with an example of Ga-V alloys and commented below. Differences between HMAs and well-matched alloys (i.e., regular alloys) are illustrated in Fig. The range of bandgap engineering (i.e., tuning the bandgap, band alignment, and built-in strain) can be significantly expanded for highly mismatched alloys (HMAs). In addition, the built-in compressive (or tensile) strain strongly affects the electronic band structure and thereby narrows the bandgap tuning. Valavanis, Quantum Wells, Wires and Dots Theoretical and Computational Physics of Semiconductor Nanostructures ( John Wiley & Sons, 2016). ), the different lattice constants of binary compounds strongly limit the content of semiconductor alloys, which can be grown on a given substrate, because of the lattice mismatch and the critical thickness for this alloy. Kroemer, “ The 6.1 Å family (InAs, GaSb, AlSb) and its heterostructures: A selective review,” Physica E 20, 196 (2004). However, with a few exceptions (e.g., AlSb, GaSb, and InAs, which are known as 6.1 Å family compounds 4 4. Because of this, semiconductor alloys are widely used in devices such as light emitters, solar cells, and transistors. and grow low dimensional heterostructures with a desired band alignment and quantum confinement for electrons and holes. Meyer, “ Band parameters for nitrogen-containing semiconductors,” J. Ram-Mohan, “ Band parameters for III–V compound semiconductors and their alloys,” J. Thus, it is possible to tune the bandgap 1,2 1. 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.Īlloying semiconductor compounds is a well recognized method to tailor properties of the materials. For these methods, experimental setups are described, and theoretical approaches to analyze the experimental data are introduced. 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. In this tutorial, principles of EM spectroscopy are presented and shortly discussed. 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. 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).
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