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Abstract: Indium nitride (InN) epilayers have been successfully grown by nitrogen-plasma-assisted molecular beam epitaxy (NPA-MBE) on Si (111) substrates using different buffer layers. Growth of a (0001)-oriented single crystalline wurtzite–InN layer was confirmed by high resolution X-ray diffraction (HRXRD). The Raman studies show the high crystalline quality and the wurtzite lattice structure of InN films on the Si substrate using different buffer layers and the InN/β–Si3N4 double buffer layer achieves minimum FWHM of E 2 (high) mode. The energy gap of InN films was determined by optical absorption measurement and found to be in the range of ~0.73–0.78eV with a direct band nature. It is found that a double-buffer technique (InN/β–Si3N4) insures improved crystallinity, smooth surface and good optical properties. [Copyright &y& Elsevier]

We report the study of ultrafast carrier dynamics of low temperature grown GaAs over wide spectral range (2.75 eV–0.88 eV) with above and below bandgap (E g) optical excitations using ultrafast transient absorption spectroscopy. The presence of defects and their subsequent effect on the pathway and lifetime of carrier relaxation with probing at different energy levels is presented. The carrier relaxation pathways and their corresponding models are predicted. It is observed that for pumping (2.58 eV) and probing above E g , the transient behavior is dominated by band filling while renormalization is in prominence when probed near to E g. For below E g pumping (0.88 eV) the optical behavior is mostly governed by defects. The calculated trap time is in the range of ~128 fs to ~807 fs while overall recombination time shows a wide variation from ~1.38 ps to ~1.25 ns depending on the position of traps/defects in the forbidden band. • Comprehensive analysis of transient behaviour of LT-GaAs is presented and models are proposed for the possible carrier dynamics as per rate equation model. • Below bandgap pumping gives a behaviour of trap/defect states. • For above band gap pumping, band filling effect dominates but near to band edge bandgap renormalisation overpowers bandfilling. • In LT-GaAs there are basically two trap bands. • Decay time is governed by position of trap state in forbidden gap. [ABSTRACT FROM AUTHOR]

The broken time reversal symmetry states may result in the opening of a band gap in TlBiSe2 leading to several interesting phenomena which are potentially relevant for spintronic applications. In this work, the quantum interference and magnetic proximity effects have been studied in Ni80Fe20/p-TlBiSe2/p-Si (Magnetic/TI) heterostructure using physical vapor deposition technique. Raman analysis shows the symmetry breaking with the appearance of A21u mode. The electrical characteristics are investigated under dark and illumination conditions in the absence as well as in the presence of a magnetic field. The outcomes of the examined device reveal excellent photo response in both forward and reverse bias regions. Interestingly, under a magnetic field, the device shows a reduction in electrical conductivity at ambient conditions due to the crossover of weak localization and separation of weak antilocalization, which are experimentally confirmed by magnetoresistance measurement. Further, the photo response has also been assessed by the transient absorption spectroscopy through analysis of charge transfer and carrier relaxation mechanisms. Our results can be beneficial for quantum computation and further study of topological insulator/ferromagnet heterostructure and topological material based spintronic devices due to high spin orbit coupling along with dissipationless conduction channels at the surface states. [ABSTRACT FROM AUTHOR]

We report the band gap tuning and facilitated charge transport at perylenediimide (PDI)/GaN interface in organic–inorganic hybrid nanostructure system over flexible titanium (Ti) foil. Energy levels of the materials perfectly align and facilitate high efficiency charge transfer from electron rich n-GaN to electron deficient PDI molecules. Proper interface formation resulted in band gap tuning as well as facilitated electron transport as evident in I–V characteristics. Growth of PDI/GaN hybrid system with band gap tuning from ultra-violet to visible region and excellent electrical properties open up new paradigm for fabrication of efficient optoelectronics devices on flexible substrates. [ABSTRACT FROM AUTHOR]

Here, we studied two different 2D monolayer systems (i.e., h‐BN and SiC), which exhibit unique electronic and magnetic properties. We analyzed the effects of Transition Methods (TM) doped atoms (i.e., Mn, Ni, and Sc) on the single vacancy (SV) h‐BN and SiC systems using first principles calculations. Through comparison we found that Mn substitution in SV h‐BN and SiC can modify their electronic and magnetic properties having larger magnetic moment as compared to other dopants (i.e., Ni and Sc.). Band structure and PDOS plots confirmed that TM doping in SV h‐BN can convert the pure h‐BN (insulator) to semiconductor, metal, or semi‐metal, it is also observed from the results that Mn‐doped h‐BN has higher band gap approximately equal to Eg ~ 2.7 eV during the negative spin and has smaller band gap, that is, (Eg ~ 1.1 eV) during the positive spin. Similarly doping with the TM atoms on the SV SiC monolayer system can convert pure SiC to metal or half metal. In addition, Mn‐doped SiC showed semimetal property having 0 eV band gap. These finding will help us to vary the electronic and magnetic properties of the pure h‐BN and SiC sheets which can be used for the opto‐electronic and spintronic applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • The p-TlBiSe 2 is an exotic topological insulator with less defect and disordered state, has considerable band gap and potential in spintronics and photo electric devices. • The p-TlBiSe 2 / n -Si heterojunction will synergize the transport property and will open a new dimension for the Si based optical industries. • Our manuscript contains very significant work in the area of heterojunction device fabrications with topological insulators and Si. We realized the heterostructure of quasi-2D-topological insulators films and n -Si for the formation of the p-n diode. • The good rectification ratio (RR ∼ 718 at ± 3 V) and figure of merit (FOM) in p-TlBiSe 2 / n -Si heterojunction for switching and other electronics applications. • The ultrafast measurements of p-TlBiSe 2 / n -Si heterojunction showed optical excitation in TlBiSe 2 with a strong modification of exciton transitions in Si. • Evidence of efficient charge separation in photoexcited p-TlBiSe 2 / n -Si heterojunction due to the presence of the charge state (CT). • The p-TlBiSe 2 / n -Si heterojunction has shown good responsivity and broadband photo detectivity from visible to near-infrared region in dual quadrants. • The 2-diode simulation is used to study the devices for various detrimental mechanisms such as recombination by studying the Current density- Voltage (J - V) and ideality factor-Voltage (n - V) curve. The study gives important insight into the optimization of devices for solar cells. The work presents a study of quasi-2D thin topological insulator film of TlBiSe 2 and its heterojunction TlBiSe 2 /Glass and TlBiSe 2 /Si by thermal coating. The vibrational modes were identified in both the heterojunctions using Raman spectroscopy with the identification of the surface phonon mode (SPM) in the TlBiSe 2 /Si heterojunction. Ultrafast dynamics were studied for the relaxation dynamics of the charge carriers in these heterojunctions. The study identified the interface phenomenon in the form of charge states (CT) in TlBiSe 2 /Si p-n heterojunction. The p-TlBiSe 2 / n -Si heterojunction showed good p-n diode characteristics with a rectification ratio under the dark. Its optical response was studied by varying optical power (2.37–3.78 µW) and wavelength (500–1900 nm). It showed excellent photoresponse in the visible to near-infrared (NIR) range which peaks at 900 nm wavelength in both forward as well reverse bias. The explanation of its optical and electrical performance was modeled in terms of band structure, surface states, and interface phenomenon. The study is important in terms of the implementation of next-generation topological insulator-based photodetectors. [ABSTRACT FROM AUTHOR]

Indene-C 60 bisadduct (ICBA) is one of the rare acceptors which can supersede commonly used phenyl-C71-butyric acid methyl ester (PCBM70) in enhancing the performance of bulk heterojunction (BHJ) solar cells owing to its shallower lowest unoccupied molecular orbital (LUMO) level. However, ICBA tends to decrease the photocurrent for most of the low band-gap polymers synthesized to date. Here we examine the interaction of ICBA with the one of the popular low band-gap polymers poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4- b ]thiophenediyl]] (PTB7), at femtosecond level, to explore key dynamics governing the operation of BHJ cells involving ICBA. The photo-physics of binary and ternary systems based on PTB7 coupled with PCBM70 and/or ICBA are studied by means of transient absorption spectroscopy (TAS) and electrochemical impedance spectroscopy (EIS) and supported by morphology analysis. Our study suggests that both inefficient charge-separation and poor charge transport of ICBA is responsible for relatively low photocurrent generation. [ABSTRACT FROM AUTHOR]

Two dimensional chalcogenides and metal sulfide materials with their sensitive surfaces are promising and potential postulant for the purpose of chemical gas sensing as a consequence of extraordinary vast surface area to volume ratio and significant band gap. We demonstrate a highly selective and sensitive NO 2 gas sensor using vertically aligned 2D SnS 2 flakes, grown by a chemical vapor deposition method in controlled gas flow. The vertically aligned SnS 2 flakes were confirmed by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. The sensing behaviour of the vertical aligned structures was analyzed for various concentrations of NO 2 at different temperatures. The sensor exhibits high gas sensing response (ΔR/R%) of ~164 at 120 °C with 50 ppm of NO 2 gas, which is the highest response among the SnS 2 based reports. The device shows excellent sensing response at room temperature but poor recovery. The selectivity of the sensor was performed under different gas environments and found highly selective towards NO 2 gas, and the results are supported by electronic structure calculations. Based on experimental results and electronic structure calculations, a gas sensing mechanism is proposed. The result indicates that fabricated sensor can be used in air purification industries and in air monitoring. • Vertically aligned 2D SnS 2 flakes were grown by CVD in controlled gas flow. • Highly selective and sensitive NO 2 gas sensor was fabricated using vertically aligned 2D SnS 2 flakes. • The sensor exhibits high gas sensing response (ΔR/R%) of ~164 at 120 °C with 50 ppm of NO 2 gas. • The selectivity of the sensor is supported by electronic structure calculations. • The sensing mechanism responsible for the dramatically increased sensitivity was also discovered. [ABSTRACT FROM AUTHOR]

Two dimensional chalcogenides and metal sulfide materials with their sensitive surfaces are promising and potential postulant for the purpose of chemical gas sensing as a consequence of extraordinary vast surface area to volume ratio and significant band gap. We demonstrate a highly selective and sensitive NO 2 gas sensor using vertically aligned 2D SnS 2 flakes, grown by a chemical vapor deposition method in controlled gas flow. The vertically aligned SnS 2 flakes were confirmed by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. The sensing behaviour of the vertical aligned structures was analyzed for various concentrations of NO 2 at different temperatures. The sensor exhibits high gas sensing response (ΔR/R%) of ~164 at 120 °C with 50 ppm of NO 2 gas, which is the highest response among the SnS 2 based reports. The device shows excellent sensing response at room temperature but poor recovery. The selectivity of the sensor was performed under different gas environments and found highly selective towards NO 2 gas, and the results are supported by electronic structure calculations. Based on experimental results and electronic structure calculations, a gas sensing mechanism is proposed. The result indicates that fabricated sensor can be used in air purification industries and in air monitoring. • Vertically aligned 2D SnS 2 flakes were grown by CVD in controlled gas flow. • Highly selective and sensitive NO 2 gas sensor was fabricated using vertically aligned 2D SnS 2 flakes. • The sensor exhibits high gas sensing response (ΔR/R%) of ~164 at 120 °C with 50 ppm of NO 2 gas. • The selectivity of the sensor is supported by electronic structure calculations. • The sensing mechanism responsible for the dramatically increased sensitivity was also discovered. [ABSTRACT FROM AUTHOR]