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The band offsets in InN/p-Si heterojunctions are determined by high resolution x-ray photoemission spectroscopy. The valence band of InN is found to be 1.39 eV below that of Si. Given the bandgap of 0.7 eV for InN, a type-III heterojunction with a conduction band offset of 1.81 eV was found. Agreement between the simulated and experimental data obtained from the heterojunction spectra was found to be excellent, establishing that the method of determination was accurate. The charge neutrality level (CNL) model provided a reasonable description of the band alignment of the InN/p-Si interface and a change in the interface dipole by 0.06 eV was observed for InN/p-Si interface. [ABSTRACT FROM AUTHOR]

Abstract: The temperature dependent electrical transport behavior of n–n InGaN/Si heterostructures grown by plasma-assisted MBE was studied. Structural characteristics of the as-grown InGaN epilayers were evaluated high resolution X-ray diffraction and composition of InGaN was estimated from photoluminescence spectra using standard Vegard''s law. Current density–voltage plots (J–V–T) revealed that the ideality factor (η) and Schottky barrier height (SBH) (Φ b) are temperature dependent and the incorrect values of the Richardson''s constant (A ∗∗) produced, suggests an inhomogeneous barrier at the heterostructure interface. The higher value of the ideality factor compared to the ideal value and its temperature dependence suggest that the current transport is mainly dominated by thermionic field emission. [Copyright &y& Elsevier]

Abstract: Ultra thin films of pure β-Si3N4 (0001) were grown on Si (111) surface by exposing the surface to radio- frequency nitrogen plasma with a high content of nitrogen atoms. Using β-Si3N4 layer as a buffer layer, GaN epilayers were grown on Si (111) substrate by plasma-assisted molecular beam epitaxy. The valence band offset (VBO) of GaN/β-Si3N4/Si heterojunctions is determined by X-ray photoemission spectroscopy. The VBO at the β-Si3N4 / Si interface was determined by valence-band photoelectron spectra to be 1.84eV. The valence band of GaN is found to be 0.41±0.05eV below that of β-Si3N4 and a type-II heterojunction. The conduction band offset was deduced to be ~2.36eV, and a change of the interface dipole of 1.29eV was observed for GaN/β-Si3N4 interface formation. [Copyright &y& Elsevier]

Abstract: Negative differential capacitance (NDC) has been observed in n-GaN/p-Si heterojunctions grown by plasma assisted molecular beam epitaxy (PAMBE). The NDC is observed at low frequencies 1 and 10 kilohertz (kHz) and disappeared at a higher testing frequency of 100 kHz. The NDC is also studied with temperature and found that it has disappeared above 323 ∘C. Current–Voltage characteristics of n-GaN /p-Si heterojunction were measured at different temperatures and are attributed to the space-charge-limited current (SCLC). A simple model involving two quantum states is proposed to explain the observed NDC behavior. [Copyright &y& Elsevier]

The visualization of band alignment for designing heterostructures between transition metal dichalcogenides and germanium plays a vital role in a deeper understanding of carrier dynamics at the heterointerface. Here, to study the band alignment across the MoS2/Ge heterojunction, we have deposited a wafer-scale highly crystalline few atomic layers MoS2 film via a highly controllable and scalable sputtering technique coupled with a post sulfurization process in a sulfur-rich environment. The Raman and XRD spectra of as-fabricated MoS2/Ge heterojunction expose the presence of highly crystalline few atomic layer MoS2 on top of Ge substrate. Interestingly, we found a type-II band alignment at the MoS2/Ge heterointerface having valence band, and conduction band offset values of 0.88 and 0.21 eV, which can provide very efficient recombination through spatially confining charge carriers. The calculation of band offset parameters offers a promising way for device engineering across the MoS2/Ge heterojunction interface. Moreover, to demonstrate the practicability of the fabricated heterostructure, we explored the suitability of our device for broadband photodetection applications. [ABSTRACT FROM AUTHOR]

Abstract: InN layers were directly grown on Ge substrate by plasma-assisted molecular beam epitaxy (PAMBE). The valence band offset (VBO) of wurtzite InN/Ge heterojunction is determined by X-ray photoemission spectroscopy (XPS). The valence band of Ge is found to be 0.18±0.04eV above that of InN and a type-II heterojunction with a conduction band offset (CBO) of ~0.16eV is found. The accurate determination of the VBO and CBO is important for the design of InN/Ge based electronic devices. [Copyright &y& Elsevier]

To achieve good living standards, it is critical to make high-performance toxic gas sensing devices for public safety, environmental pollutant control, industrial operations, and other applications. For this purpose, we demonstrate CuO anchored SnO 2 nanostructures for H 2 S gas sensors. The selectivity was improved by anchoring with CuO for a total 60 s duration at four equal consecutive cycles to achieve good selectivity towards H 2 S molecules. The pristine CuO shows instability and metallic behaviour when it is exposed to H 2 S for a longer time. Furthermore, the proposed gas sensor shows good selectivity toward H 2 S as compared to other gases H 2 , NO 2 , CO 2 , and NH 3. The sensing response was measured at around 69 % at the optimal operating temperature of 150 °C. It is observed that CuS formation has better selectivity as compared to pristine SnO 2 and a slight improvement in sensitivity is observed. As a result, a promising strategy for designing and producing good-performance H 2 S gas sensors would be to CuO anchor on SnO 2 nanostructures. The proposed sensors may be integrated with IoT platforms and used for the detection of H 2 S in the sewer line and leak detection in the petroleum industry. [Display omitted] • SnO 2 thin film was anchored with CuO at different time duration using RF sputtering for H 2 S gas sensing. • The sensor exhibits higher sensing response of 69 % at 150 ºC for 100 ppm of H 2 S with a LoD of 1 ppm. • Comparative analysis was performed for H 2 S gas detection for both SnO 2 and CuO/SnO 2 based sensors. • Excellent selectivity and slight improved sensitivity was observed with CuO/SnO 2 based gas sensor. [ABSTRACT FROM AUTHOR]

To understand the different mechanism occurring at the MoS2-silicon interface, we have fabricated a MoS2/Si heterojunction by exfoliating MoS2 on top of the silicon substrate. Raman spectroscopy and atomic force microscopy (AFM) measurement expose the signature of few-layers in the deposited MoS2 flake. Herein, the temperature dependence of the energy barrier and carrier density at the MoS2/Si heterojunction has been extensively investigated. Furthermore, to study band alignment at the MoS2/Si interface, we have calculated a valence band offset of 0.66 ± 0.17 eV and a conduction band offset of 0.42 ± 0.17 eV using X-ray and Ultraviolet photoelectron spectroscopy. We determined a type-II band alignment at the interface which is very conducive for the transport of photoexcited carriers. As a proof-of-concept application, we extend our analysis of the photovoltaic behavior of the MoS2/Si heterojunction. This work provides not only a comparative study between MoS2/p-Si and MoS2/n-Si heterojunctions but also paves the way to engineer the properties of the interface for the future integration of MoS2 with silicon. [ABSTRACT FROM AUTHOR]

Phase pure wurtzite GaN films were grown on Si (100) substrates by introducing a silicon nitride layer followed by low temperature GaN growth as buffer layers. GaN films grown directly on Si (100) were found to be phase mixtured, containing both cubic (β) and hexagonal (α) modifications. The x-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy studies reveal that the significant enhancement in the structural as well as in the optical properties of GaN films grown with silicon nitride buffer layer grown at 800 °C when compared to the samples grown in the absence of silicon nitride buffer layer and with silicon nitride buffer layer grown at 600 °C. Core-level photoelectron spectroscopy of SixNy layers reveals the sources for superior qualities of GaN epilayers grown with the high temperature substrate nitridation process. The discussion has been carried out on the typical inverted rectification behavior exhibited by n-GaN/p-Si heterojunctions. Considerable modulation in the transport mechanism was observed with the nitridation conditions. The heterojunction fabricated with the sample of substrate nitridation at high temperature exhibited superior rectifying nature with reduced trap concentrations. Lowest ideality factors (∼1.5) were observed in the heterojunctions grown with high temperature substrate nitridation which is attributed to the recombination tunneling at the space charge region transport mechanism at lower voltages and at higher voltages space charge limited current conduction is the dominating transport mechanism. Whereas, thermally generated carrier tunneling and recombination tunneling are the dominating transport mechanisms in the heterojunctions grown without substrate nitridation and low temperature substrate nitridation, respectively. [ABSTRACT FROM AUTHOR]

When exploring the charge transport in the MoS2/Si heterojunction, it is imperative to understand the contribution of different carrier interactions and scattering mechanisms in the conduction process. Here, we have demonstrated an ultrasensitive photodetector based on MoS2/Si (for both p-type and n-type Si) van der Walls (vdW) heterojunction, which provides a high photoresponsivity of greater than 103 A/W along with a large detectivity of ≈ 1012 Jones (Jones = $\text{cm} \cdot \text{Hz}^{ {1/2}} \cdot \text{W}^{-1}$). This high photoresponsivity is attributed to the high absorption rate of incident photons and large current carrying capacity of a few layer MoS2. The tuning of barrier height at the MoS2/n-Si interface with photoexcitation of different wavelengths was interpreted by using Bardeen’s model. The increase in carrier density due to the photon energy results in a reduction of barrier height at the heterojunction. Because of increase in carrier density with wavelength, it was observed that the inverse Auger process prevails at higher wavelength for the relaxation of photoinduced charge carriers at the MoS2/Si interface over other scattering mechanisms. Our obtained results unveil the great potential of the MoS2/Si vdW heterojunction that may pave the way for new generation photodetectors. [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]

We report high photovoltaic efficiency of over 9% in solution-processed, small-molecule (SPSM) 7,7′-(4,4- bis (2-ethylhexyl)-4 H -silolo[3,2- b :4,5- b ′]dithiophene-2,6-diyl) bis (6-fluoro-4(5′-hexyl-[2,2′-bithiophen]-5-yl)benzo[ c ]1,2,5]thiadiazole) p -DTS(FBTTh 2 ) 2 :[6-6]-phenyl C70 butyric acid methyl ester (PC 70 BM) blend based inverted BHJ solar cell by incorporating luminescent zinc oxide doped with sodium (ZnO:Na) quantum dots (QD) ( l -ZnO) as a cathode buffer layer (CBL) in inverted bulk-heterojunction (BHJ) solar cells for the first time. The l -ZnO absorbs ultraviolet (UV) light and down-converts it to visible light. The l -ZnO layer's emission overlaps significantly with the absorption of p -DTS(FBTTh 2 ) 2 , leading to an enhanced absorption by p -DTS(FBTTh 2 ) 2 . This resulted in a significant enhancement of photo-current from 15.4 to 17.27 mA/cm 2 and efficiency from 8% to 9.2% for ZnO and l -ZnO based devices, respectively. This is among one of the highest efficiency values reported so far in the case of SPSM based single junction BHJ solar cells. The luminescent ZnO layer also protects the active layer from UV-induced degradation as solar cells show high stability under constant solar light illumination retaining more than 90% (∼28 h) of its initial efficiency, whereas BHJ solar cells without the luminescent ZnO layer degraded to ∼50% of its initial value under same conditions. Since ZnO is an essential part of inverted organic solar cells, the luminescent l -ZnO CBL has great potential in inverted organic solar cells. [ABSTRACT FROM AUTHOR]

In this work, we report enhanced power conversion efficiency (PCE) of bulk heterojunction polymer solar cells by Förster resonance energy transfer (FRET) from samarium-doped luminescent gadolinium orthovanadate (GdVO4:Sm3+) quantum dots (QDs) to polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) polymer. The photoluminescence emission spectrum of GdVO4:Sm3+ QDs overlaps with the absorption spectrum of PTB7, leading to FRET from GdVO4:Sm3+ to PTB7, and significant enhancements in the charge-carrier density of excited and polaronic states of PTB7 are observed. This was confirmed by means of femtosecond transient absorption spectroscopy. The FRET from GdVO4:Sm3+ QDs to PTB7 led to a remarkable increase in the power conversion efficiency (PCE) of PTB7:GdVO4:Sm3+:PC71BM ([6,6]-phenyl-C71-butyric acid methyl ester) polymer solar cells. The PCE in optimized ternary blend PTB7:GdVO4:Sm3+:PC71BM (1:0.1:1.5) is increased to 8.8% from 7.2% in PTB7:PC71BM. This work demonstrates the potential of rare-earth based luminescent QDs in enhancing the PCE of polymer solar cells. [ABSTRACT FROM AUTHOR]

The present work explores the temperature dependent transport behavior of n-InN nanodot/p-Si(100) heterojunction diodes. InN nanodot (ND) structures were grown on a 20 nm InN buffer layer on p-Si(100) substrates. These dots were found to be single crystalline and grown along [001] direction. The junction between these two materials exhibits a strong rectifying behavior at low temperatures. The average barrier height (BH) was determined to be 0.7 eV from current-voltage-temperature, capacitance-voltage, and flat band considerations. The band offsets derived from built-in potential were found to be ΔEC=1.8 eV and ΔEV=1.3 eV and are in close agreement with Anderson's model. [ABSTRACT FROM AUTHOR]

• Different concentration of carbon nanofibers were loaded on Au pattern interdigitated electrodes over ZnO nanostructures. • Pure CNF, pure ZnO nanostructures, and CNF/ZnO samples were utilized to measure the sensing response for hydrogen gas. • Highest relative response towards hydrogen gas was found in 0.2 wt% CNF/ZnO nanostructures. • Enhanced sensing response can be seen due to formation of p-n heterojunctions between CNF and ZnO. The present report investigates hydrogen gas sensing properties on PAN/(PAN-b-PMMA) derived electrospun nanoporous carbon nanofibers loaded on ZnO nanostructures. Polymer blend of PAN and PAN-b-PMMA is used to obtain the high surface area porous CNF which improve further sensing performance. Moreover, a facile technique such as drop cast method is used to load the CNF (0.1–0.5 wt%) on Au pattern interdigitated electrodes over ZnO nanostructures. Loading of CNF was optimized to ensure proper connection between the electrodes over ZnO surface, which was measured using I–V characteristics. Initially, current decreased for less amount of CNF (0.1–0.2 wt%), which later increased for high concentration of CNF (0.3–0.5 wt%). It was further observed that 0.2 wt% CNF/ZnO nanostructures based sensor exhibited maximum sensing response (73.54%) as compared to CNF (3.29%) and ZnO (44.51%) for 100 ppm hydrogen at 150 °C. This enhanced sensing response may be attributed to diffusion of hydrogen molecules through the nanoporous CNF, thus enabling the formation of p - n heterojunction at the interface of CNF and ZnO. The presence of oxygen functional groups on CNF surface also contributes to the enhancement of the sensing performance. [ABSTRACT FROM AUTHOR]