Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices

This Special Issue on “Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices” is a collection of 20 original articles dedicated to theoretical and experimental research works providing new insights and practical findings in the field of solid-state technology-related topics [...]

Bandgap engineering of α-Ga2O3 by hydrostatic, uniaxial, and equibiaxial strain

Ga2O3 is a wide bandgap semiconductor and an understanding of its bandgap tunability is required to broaden the potential range of Ga2O3 applications. In this study, the different bandgaps of α-Ga2O3 were calculated by performing first-principles calculations using the pseudopotential self-interaction correction method. The relationships between these bandgaps and the material's hydrostatic, uniaxial, and equibiaxial lattice strains were investigated. The direct and indirect bandgaps of strain-free α-Ga2O3 were 4.89 eV and 4.68 eV, respectively. These bandgap values changed linearly and negatively as a function of the hydrostatic strain. Under the uniaxial and equibiaxial strain conditions, the maximum bandgap appeared under application of a small compressive strain, and the bandgaps decreased symmetrically with increasing compressive and tensile strain around the maximum value.

Challenges of Overcoming Defects in Wide Bandgap Semiconductor Power Electronics

The role of crystal defects in wide bandgap semiconductors and dielectrics under extreme environments (high temperature, high electric and magnetic fields, intense radiation, and mechanical stresses) found in power electronics is reviewed. Understanding defects requires real-time in situ material characterization during material synthesis and when the material is subjected to extreme environmental stress. Wide bandgap semiconductor devices are reviewed from the point of view of the role of defects and their impact on performance. It is shown that the reduction of defects represents a fundamental breakthrough that will enable wide bandgap (WBG) semiconductors to reach full potential. The main emphasis of the present review is to understand defect dynamics in WBG semiconductor bulk and at interfaces during the material synthesis and when subjected to extreme environments. High-brightness X-rays from synchrotron sources and advanced electron microscopy techniques are used for atomic-level material probing to understand and optimize the genesis and movement of crystal defects during material synthesis and extreme environmental stress. Strongly linked multi-scale modeling provides a deeper understanding of defect formation and defect dynamics in extreme environments.

Anisotropic radius of curvature of crystal planes in wide-bandgap semiconductor wafers measured by x-ray diffraction

Conventionally, the radius of curvature of crystal planes in a wafer is measured by position-dependent x-ray diffraction along a particular diagonal direction of the wafer. However, we show herein that this method is not reliable for assessing the wafer’s real three-dimensional curvature. Using commercial 2-inch 4H-SiC, GaN, AlN, and β-Ga2O3 wafers, we demonstrate that the choice of the diagonal direction along which the position-dependent x-ray diffraction was acquired strongly affects not only the apparent radius of curvature but also whether it is convex or concave.

Modifying Precursor Solutions to Obtain Screen-Printable Inks for Tungsten Oxides Electrochromic Film Preparation

Tungsten trioxide (WO3) is used to prepare the important electrochromic layer of the electrochromic device as a wide bandgap semiconductor material. In this study, WO3 electrochromic film was successfully prepared by screen printing. To modify the thixotropy and wettability of the ink, polyvinyl alcohol (PVA) and 2-perfluoroalkyl ethanol (FSO) were added in the ammonium meta-tungstate (AMT) solution. We found that the PVA additive could improve the dynamic viscosity of the solution and modify the uniformity of the film. 2-Perfluoroalkyl ethanol (FSO) could lower the surface tension and increase the wettability of the AMT solution on the substrate. By observing the morphology of the printed films, the ink formulas for screen printing were selected. We found the annealing process could help remove PVA. Through characterization of electrochromic performance, it was found that the best performing device had 42.57% modulation and 93.25 cm2·C−1 coloration efficiency (CE) for 600 nm light. This study showed great potential in the preparation of WO3 electrochromic devices by a low-cost screen-printing method.