Strong tribo-piezoelectric effect in bilayer indium nitride (InN)

The high electronegativity between the atoms of two-dimensional (2D) group-III nitrides makes them attractive to demonstrating a strong out-of-plane piezo-electricity effect. Energy harvesting devices can be predicted by cultivating such salient piezoelectric features. This work explores the tribo-piezoelectric properties of 2D-indium nitride (InN) as a promising candidate in nanogenerator applications by means of first-principles calculations. In-plane interlayer sliding between two InN monolayers leads to a noticeable rise of vertical piezoelectricity. The vertical resistance between the InN bilayer renders tribological energy by the sliding effect. During the vertical sliding, a shear strength of 6.6–9.7 GPa is observed between the monolayers. The structure can be used as a tribo-piezoelectric transducer to extract force and stress from the generated out-of-plane tribo-piezoelectric energy. The A–A stacking of the bilayer InN elucidates the highest out-of-plane piezoelectricity. Any decrease in the interlayer distance between the monolayers improves the out-of-plane polarization and thus, increases the inductive voltage generation. Vertical compression of bilayer InN produces an inductive voltage in the range of 0.146–0.196 V. Utilizing such a phenomenon, an InN-based bilayer compression-sliding nanogenerator is proposed, which can tune the generated tribo-piezoelectric energy by compressing the interlayer distance between the InN monolayers. The considered model can render a maximum output power density of ~ 73 mWcm−2 upon vertical sliding.

Group III-Nitrides and Their Hybrid Structures for Next-Generation Photodetectors

In the last few decades, there has been a phenomenal rise and evolution in the field of III–Nitride semiconductors for optoelectronic applications such as lasers, sensors and detectors. However, certain hurdles still remain in the path of designing high-performance photodetectors (PDs) based on III-Nitride semiconductors considering their device performance. Recently, a lot of progress has been achieved in devices based on the high quality epilayers grown by molecular beam epitaxy (MBE). Being an ultra-high vacuum environment based-technique, MBE has enabled the realization of high-quality and highly efficient PDs which have exhibited competitive figures of merit to that of the commercial PDs. Moreover, by combining the novel properties of 2D materials with MBE-grown III-Nitrides, devices with enhanced functionalities have been realized which would pave a way towards the next-generation photonics. In the current chapter, the basic concepts about photodetection have been presented in detail, followed by a discussion on the basic properties of the III-Nitride semiconductors, and the recent advancements in the field of MBE-grown III-Nitrides-based PDs, with an emphasis on their hybrid structures. Finally, an outlook has been provided highlighting the present shortcomings as well as the unresolved issues associated with the present-day devices in this emerging field of research.

Модифицированная теория связанных волн и численный метод для анализа брэгговских зеркал с произвольным профилем показателя преломления

An analytical and effective numerical approach to the analysis of the optical characteristics of Bragg mirrors with an arbitrary refractive index profile is developed. Analytical expressions obtained using the modified theory of coupled waves for the coefficients of reflection / transmission of light from / through the BM with high accuracy predict its main characteristics at both low and high contrast of the refractive index. The hybrid numerical method includes the numerical calculation of the transfer matrix for one period of the knowledge base and its analytical multiplication for an arbitrary number of periods. The developed methods are applied to the analysis of the properties of practically important BMs made on the basis of sprayed pairs of Ta2O5 / SiO2 dielectrics, Group III nitrides and arsenides. The characteristics of the knowledge base with smooth (gradient) interfaces are considered in detail.

Electronic Structure of Rock Salt Alloys of Rare Earth and Group III Nitrides

Lattice parameters and electronic properties of RE1−xAxN alloys, where RE = Sc, Y, Lu and A = Al, Ga, and In, have been derived from first principles. The materials are expected to exhibit a linear decrease in cubic lattice parameters and a tendency to a linear increase in band gaps as a function of composition. These effects are connected with a strong mismatch between ionic radii of the RE and group III elements, which leads to chemical pressure in the mixed RE and group III nitrides. The electronic structures of such systems are complex, i.e., some contributions of the d- and p-type states, coming from RE and A ions, respectively, are present in their valence band regions. The findings discussed in this work may encourage further experimental efforts of band gap engineering in RE-based nitrides via doping with group III elements.