Search

We report the synthesis method of ultralong one-dimensional (1D) inorganic perovskite nanorods with single-crystal-like molecular orientation for photodetector applications.

This paper demonstrates the electrical and current transport properties of prepared Ti/α-amylase/p-InP metal/polymer/semiconductor (MPS) junction by current–voltage (I–V) approach. The microstructure of the fabricated MPS junction is confirmed by transmission electron microcopy (TEM) measurement. The MPS junction exhibited a good rectification nature over the Ti/p-InP metal/semiconductor (MS) junction. The derived barrier height (BH) of MPS junction (0.78 eV) is higher than the MS junction (0.70 eV), that indicates the BH is influenced by the polymer layer. The BH is extracted by the I–V, Z(V)–Vd plot, Cheung’s function, α(V)–V plot, Norde method and Ψs–V plot and found the values are comparable with one another, which indicates their steadiness and validity. The estimated interface state density (NSS) of the MPS junction is less than the MS junction, suggesting that the α-amylase layer decreased the NSS value. The forward log (I)–log (V) plot of the MS and MPS junctions reveals the ohmic nature at lower-bias region and space-charge-limited conduction at higher-bias region. Results reveal that the reverse leakage current conduction mechanism of the MS and MPS junctions is governed by Poole–Frenkel emission in lower-bias region, whereas, at higher bias region, Schottky emission is dominant current conduction mechanism. These exploration results establish that the α-amylase polymer layer is potential for use in organic–inorganic devices.

Recently, research on the use of additives in photoactive layers to improve the efficiency of solar cells has continued to be conducted. Among them, carbon-based additives serve to increase a device's efficiency by simply and effectively improving the carrier movement. In this work, inverted polymer solar cells (iPSCs) are fabricated based on a blend of PTB7-Th:PC71BM and PTB7:PC71BM bulk heterojunction as photoactive materials using mixed additives of 4Cl-carbon-based contorted hexabenzocoronene (4Cl-cHBC). The 4Cl-cHBC additives, a kind of contorted polycyclic aromatic hydrocarbon, added to bulk heterojunction in the iPSC devices, provide a cocrystal modifier and effective charge separation to enhance device performance. The reason for this efficiency improvement is that cocrystal is formed due to a combination between 4Cl-cHBC and the PTB7-Th:PC71BM bulk heterojunction, which reduces bimolecular recombination in the device and significantly increases short-circuit current and fill factor. The RS and RSh values of iPSCs based on PTB7-Th:PC71BM with and without the 4Cl-cHBC additives decreased from 7.0 Ω cm2 to 4.0 Ω cm2, and increased from 813 Ω cm2 to 1226 Ω cm2, respectively. The calculated average carrier lifetimes at 500 nm for PTB7-Th:PC71BM and PTB7-Th:PC71BM with 4Cl-cHBC additives are 4.46 ps and 3.06 ps, respectively. The carrier lifetimes show that the charge separation of PTB7-Th:PC71BM with 4Cl-cHBC additives is more than 45% faster. As a result, the iPSCs based on the blend of PTB7-Th:PC71BM and PTB7:PC71BM with 4Cl-cHBC additives showed maximum power conversion efficiencies of 9.46 and 8.62%, which were 20.6 and 19.95% higher than those of the reference, respectively.

A novel and facile hydrothermal route was designed to produce h-BN-C quantum dots (h-BN-C QDTs) using h-BN powder as a precursor and Potassium Sodium Tartare as an intercalant. The resulting yellow solution possessed mono or few-layers of quantum dots with an average size of ~2.5 nm. Due to the incorporation of functional groups (carbon, oxygen) on the surface of h-BN, an enhancement of photo luminescent magnitude and a blue shift were observed in photoluminescence spectra from h-BN-C QDTs solution. Further, h-BN-C QDTs exhibits a bright blue fluorescence under the irradiation by a 365 nm UV light. Next, h-BN QDTs was utilized as the dielectric active layer by using simple drop casting method between the electrodes and fabricated the nonvolatile resistive switching devices. The fabricated devices exhibited the nonvolatile bipolar resistive switching characteristics with 103 ON/OFF ratio and turned ON and OFF threshold voltages of −1.9 V and +1.4 V, respectively. Further, the switching mechanisms of h-BN-C QDTs were found to be space charged trapping. It provides a route toward tailoring the optical and electrical properties of the h-BN materials and can be utilized in the future potential applications.

Herein, the performance of AlGaN/GaN high-electron-mobility transistor (HEMT) devices fabricated on Si and sapphire substrates is investigated. The drain current of the AlGaN/GaN HEMT fabricated on sapphire and Si substrates improved from 155 and 150 mA/mm to 290 and 232 mA/mm, respectively, at VGS = 0 V after SiO2 passivation. This could be owing to the improvement in the two-dimensional electron gas charge and reduction in electron injection into the surface traps. The SiO2 passivation resulted in the augmentation of breakdown voltage from 245 and 415 V to 400 and 425 V for the AlGaN/GaN HEMTs fabricated on Si and sapphire substrates, respectively, implying the effectiveness of SiO2 passivation. The lower transconductance of the AlGaN/GaN HEMT fabricated on the Si substrate can be ascribed to the higher self-heating effect in Si. The X-ray rocking curve measurements demonstrated that the AlGaN/GaN heterostructures grown on sapphire exhibited a full-width half maximum of 368 arcsec against 703 arcsec for the one grown on Si substrate, implying a better crystalline quality of the AlGaN/GaN heterostructure grown on sapphire. The AlGaN/GaN HEMT fabricated on the sapphire substrate exhibited better performance characteristics than that on the Si substrate, owing to the high crystalline quality and improved surface.

This study presents the optimization of the lateral device geometry and thickness of the channel and barrier layers of AlGaN/GaN high electron mobility transistors (HEMTs) for the enhancement of breakdown voltage (VBR) characteristics using a TCAD simulation. The effect of device geometry on the device performance was explored by varying the device design parameters, such as the field plate length (LFP), gate-to-drain length (LGD), gate-to-source length (LGS), gate length (LG), thickness of the Si3N4 passivation layer (Tox), thickness of the GaN channel (Tch), and AlGaN barrier (Tbarrier). The VBR was estimated from the off-state drain current versus the drain voltage (IDS–VDS) curve, and it exhibited a strong dependence on the length and thickness of the parameters. The optimum values of VBR for all the device’s geometrical parameters were evaluated, based on which, an optimized device geometry of the field-plated AlGaN/GaN HEMT structure was proposed. The optimized AlGaN/GaN HEMT structure exhibited VBR = 970 V at IGS = 0.14 A/mm, which was considerably higher than the results obtained in previous studies. The results obtained in this study could provide vital information for the selection of the device geometry for the implementation of HEMT structures.

The effects of rapid thermal annealing temperature on structural, morphological, and optical properties of copper phthalocyanine (CuPc) films on n-Si are investigated. The deposited CuPc films on n-Si substrate form nanoparticles and are slightly elongated with an increase in surface roughness with increase in annealing temperature due to the aggregation of the native grains. The electrical and current transport properties of a fabricated Au/CuPc/n-Si metal-polymer-semiconductor (MPS)-type Schottky barrier diodes (SBDs) are explored at various annealing temperatures (range 100–300 °C) by current–voltage (I–V) and capacitance–voltage (C–V) measurements. Results reveal that the estimated barrier height decreases with increasing annealing temperature and could be ascribed to the diffusion of Au atoms into CuPc films transferring negative charges to the molecule inducing an n-type doping of the organic film. An analysis of the forward log (I)–log (V) plot of Au/CuPc/n-Si (MPS)-type SBDs indicated the carrier transport domination by ohmic conduction in the lower bias and by the space-charge-limited current (SCLC) transport mechanism at higher bias regions irrespective of annealing temperatures that might be related to additional traps initiating from the CuPc. Poole–Frenkel emission governs the current transport in the reverse bias regardless of annealing temperature.

An Au/Pr6O11/n-GaN metal/insulator/semiconductor (MIS) junction was prepared with a high-k praseodymium oxide insulator layer and probed its structural, chemical and electrical characteristics by XRD, TEM, XPS, I–V and C–V approaches. XRD, TEM and XPS examinations confirm the Pr6O11 film growth on n-type GaN surface. Electrical results demonstrate the fabricated junctions show a good rectifying nature with a low leakage current. The series resistance (RS) and shunt resistance (RSh) were derived for the Au/n-GaN Schottky electrode (SE) and MIS junction. MIS junction possesses a higher barrier height (BH) compared to the Au/n-GaN SE, implying the insulator layer altered the BH. By employing Cheung’s, Norde and surface potential plots, the BH, ideality factor and RS were evaluated and the results were comparable. Lower interface state density (NSS) was obtained for the MIS junction than the SE, which confirmed that the Pr6O11 insulator layer plays a vital role in lowering the NSS. Results demonstrated the Poole–Frenkel emission controls the current conduction mechanism in reverse-bias of both SE and MIS junction. Observations stated that the Pr6O11 thin film is a suitable high-k insulating material for the fabrication of GaN-based MIS devices.

Magnetite (Fe3O4) layers were prepared on n-type GaN surface by the e-beam method and its microstructural and compositional characteristics were evaluated by XRD, XPS and TEM techniques. The XRD, XPS and TEM evaluations confirmed the formation of the Fe3O4 layer on the n-GaN surface. Then, the Au/Fe3O4/n-GaN metal/interlayer/semiconductor (MIS) junction was fabricated and its electrical properties investigated with the I-V and C-V approaches. The MIS junction showed a good rectification nature with a high barrier height (0.83 eV) compared to the SE (0.71 eV). This implies that the barrier height was markedly affected by the Fe3O4 layer. Further, the barrier height was extracted by means of Cheung's, Norde and ψS-V plot and it was found that the values are nearly matched with one another, indicating that the methods used were consistent and valid. The frequency-dependent properties of the MIS and SE junctions have also been discussed. The interface state density (NSS) of the MIS junction was found to be lower than the SE, indicating that the Fe3O4 layer plays a vital role in the decreased NSS. Based on the analysis, it can be concluded that the Fe3O4 layer is an apt material for the fabrication of new electronic device applications.

Metal-semiconductor-metal (MSM) photodetectors (PDs) with interdigitated Pt finger electrodes were fabricated on Ge films grown epitaxially on a (100) Si substrate (Ge-on-Si) by rapid thermal chemical vapor deposition (RTCVD), and the effects of the finger dimensions on their optoelectrical properties were investigated. The two-step Ge heteroepitaxial growth technique through RTCVD, where a Ge seed layer was used in first-step growth at 350° C followed by second-step growth of a Ge film at high temperatures (500° C), led to the formation of a high-quality Ge epitaxial layer with excellent surface and interface morphologies. The dark current of Ge-on-Si MSM PD increased with decreasing finger width/spacing, which could be associated with electric field crowding near the contact electrode. As a result of the significant creation of electronhole pairs followed by their subsequent drift through the Ge epilayer toward the finger electrode, the Ge-on-Si MSM PDs exhibited a considerable spectral response to wavelengths in the range, 1530–1550 nm, regardless of the finger dimensions. A higher electric field was observed in the finger electrodes closer to each other, which enhanced the collection efficiency of the photo-generated carriers, which could be responsible for higher responsivity of Ge-on-Si MSM PDs with a smaller finger width/spacing.

Radio frequency magnetron sputtered Al-doped zinc oxide (AZO) thin films were formed on n-type gallium nitride (GaN). X-ray diffraction reflections and Raman modes confirmed the formation of the AZO films. The optical band gap of the deposited AZO film was found to be 3.31 eV and exhibited a fairly smooth surface and continuous growth across the surface with a grainy structure. The Au/AZO/n-GaN heterojunction Schottky diode was fabricated and investigated the influence of the presence of AZO layer in Au/n-GaN Schottky diode, characterizing its electrical and breakdown voltage properties. The AZO layer led to an excellent improvement in the rectifying behavior with an increase in barrier height of the Au/n-GaN Schottky diode from 0.69 to 0.90 eV. Reverse breakdown voltage of the Au/n-GaN Schottky diode and Au/AZO/n-GaN heterojunction diode were obtained to be 86 and 232 V, respectively, without any edge termination methods. The AZO layer effectively reduced the interface states in the Au/n-GaN Schottky diodes. Schottky and Poole-Frenkel emission mechanisms dominated the reverse current in Au/n-GaN Schottky diode and Au/AZO/n-GaN heterojunciton diode, respectively. The results signify the importance of the metal-insulator-semiconductor structure and in particular the AZO layer in reducing the leakage current and improving the device performance. A further improvement in breakdown voltage can be achieved by employing field plate and guard-ring structures for edge termination.

Oxygen (O2) plasma treatment on germanium (Ge) surface was employed to depin Fermi-level in Al/n-type Ge interface. The Al contact to n-type Ge without and with O2 plasma treatments for 1 and 2 min showed rectifying characteristics despite the low work function of Al, which could be associated with the Fermi-level pinning. An increase in O2 plasma treatment time resulted in a decrease in Schottky barrier height along with the improvement of the homogeneity of Schottky interface. On the other hand, Al contact to O2 plasma-treated n-type Ge for 3 min exhibited Ohmic behavior, implying the depinning of Fermi-level in Al/n-type Ge interface. A transition from rectifying to Ohmic behavior observed in Al/n-type Ge contact with O2 plasma treatment for 3 min could be attributed to the more homogenous and stoichiometric formation of Ge-oxide layer. Such a high quality Ge-oxide layer effectively passivated unsatisfied surface states in Ge, which could be responsible for Fermi-level depinning of Ge.

There is a recent interest in semiconducting superlattice films because their low dimensionality can increase the thermal power and phonon scattering at the interface in superlattice films. However, experimental studies in all cross-plane thermoelectric (TE) properties, including thermal conductivity, Seebeck coefficient, and electrical conductivity, have not been performed from these semiconducting superlattice films because of substantial difficulties in the direct measurement of the Seebeck coefficient and electrical conductivity. Unlike the conventional measurement method, we present a technique using a structure of sandwiched superlattice films between two embedded heaters as the heating source, and electrodes with two Cu plates, which directly enables the investigation of the Seebeck coefficient and electrical conductivity across the Al2O3/ZnO superlattice films, prepared by the atomic layer deposition method. Used in combination with the promising cross-plane four-point probe 3-ω method, our measur...

The current transport mechanism in permalloy/n-type Ge Schottky diodes was studied over the temperature range from 200 to 400 K. At temperatures above 250 K, the forward current-voltage (I-V) characteristics of the diode were ideal and obeyed the thermionic emission theory. Below 250 K, however, the recombination process was found to contribute to current transport. Similarly, in reverse bias, the thermionic emission mechanism appeared to dominate current transport at temperatures above 250 K, and the carrier generation mechanism dominated the reverse current below 250 K. A temperature-driven change in the current conduction mechanism from conduction dominated by low-barrier-height patches to conduction dominated by high-barrier-height regions suggests inhomogeneity in the Schottky barrier height. The barrier height inhomogeneity led to deviations in the Richardson constant from its theoretical value at lower temperatures. The room-temperature low-frequency noise measurements taken at different forward biases for the permalloy/n-type Ge Schottky diodes showed a 1/fγ dependence with a tight variation of γ between 1.20 and 1.31. The current dependence of the noise power spectral density exhibited a 1/f noise behavior, indicating the operation of the permalloy/n-type Ge Schottky diodes in the thermionic emission mode.

Significant effort has been devoted to constructing two-dimensional transition metal dichalcogenides-based hybrid heterojunctions with enhanced performance or unique functionalities for versatile device applications in emerging electronics and optoelectronics. In this study, we report the temperature-dependent electronic charge transport characteristics in MoS2/p-type Ge heterojunction diodes. From the current-voltage (I-V) characteristics of the heterojunction device, it is observed that different transport phenomena can occur depending upon the temperature and bias voltage. The charge transport is dominated by thermionic emission in the high-temperature regime above 300 K, whereas in low-temperature regime below 300 K, the charge transport mechanism transitions from the thermionic emission to the tunneling mechanism associated with trap sites. In particular, the I-V characteristics in the low-temperature regime show a transition from the direct tunneling at a low bias to the Fowler-Nordheim tunneling mechanism at a high bias. This could be well described by the electrical analyses on temperature-dependent I-V behavior and corresponding energy band diagrams.

The temperature-dependent current-voltage (I-V) characteristics of permalloy (Ni0.8Fe0.2) Schottky contacts to n-type GaN have been investigated. Magnetization measurements revealed the ferromagnetic behavior of Ni0.8Fe0.2 film on n-type GaN. The Schottky barrier parameters, such as the barrier height and ideality factor, determined by thermionic emission depended on the measurement temperature, suggesting the presence of lateral inhomogeneity in the Schottky barrier. The experimental data modified by the thermionic emission model along with a Gaussian distribution of the barrier heights indicated the presence of a double Gaussian barrier distribution in the Ni0.8Fe0.2/n-type GaN Schottky contact. The mean barrier heights and standard deviations for each Gaussian distribution were 0.84 & 1.32 eV and 0.10 & 0.17 eV over temperature range of 125–200 K and 225–400 K, respectively. The noise spectral density of the current fluctuations measured as a function of frequency (f) at room temperature followed a 1/fγ dependence with a γ value close to unity, irrespective of the applied forward bias. The 1/f-type noise was attributed to the barrier inhomogeneity existing at the Ni0.8Fe0.2/n-type GaN Schottky interface as revealed from the temperature-dependent I–V characteristics.

Cupric oxide (CuO) is synthesized by simple chemical bath deposition method and deposited on n-type InP substrate using e-beam evaporation technique. First, the structural and chemical compositional analysis of CuO/n-InP are analysed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). XRD and XPS results confirmed that the formation of CuO on n-type InP substrate. Then, Au/CuO/n-InP heterojunction is fabricated with a CuO interlayer and correlated its results with the Au/n-InP Schottky junction (SJ). The barrier height (Φb) and ideality factor (n) are extracted through I-V and C-V methods and the respective values are 0.66 eV (I-V)/0.80 eV (C-V) and 1.24, and 0.78 eV (I-V)/0.94 eV (C-V) and 1.62 for the SJ and HJ diodes, respectively. By applying Cheung's and Norde functions, the Φb, ideality factor and series resistance (RS) are derived for the SJ and HJ diodes. The derived interface state density (NSS) of HJ is lower than the SJ; results demonstrated that the CuO interlayer plays an important role in the decreased NSS. The Poole-Frenkel emission is the dominant current conduction mechanism in reverse bias of both SJ and HJ diodes.

We have investigated the low temperature (LT) growth of GeSn–Ge–Si structures using rapid thermal chemical vapor deposition system utilizing Ge2H6 and SnCl4 as the reactive precursors. Due to inappropriate phenomena, such as, Ge etch and Sn segregation, it was hard to achieve high quality GeSn epitaxy at the temperature > 350 °C. On the contrary, we found that the SnCl4 promoted the reaction of Ge2H6 precursors in a certain process condition of LT, 240–360 °C. In return, we could perform the growth of GeSn epi layer with 7.7% of Sn and its remaining compressive strain of 71.7%. The surface propagated defects were increased with increasing the Sn content in the GeSn layer confirmed by TEM analysis. And we could calculate the activation energies at lower GeSn growth temperature regime using by Ge2H6 and SnCl4 precursors about 0.43 eV.

Ge p-i-n photodetectors with and without graphene on active area fabricated and investigated the graphene effects on opto-electrical properties of photodetectors. The photodetectors were characterized with respect to their dark, photocurrents and responsivities in the wavelength range between 1530-1630 nm. For a 250 um-diameter device at room temperature, it was found that dark current of p-i-n photodetector with graphene were reduced significantly compared with photodetector without graphene. This improvement is attributed to the passivation of the graphene layers that leads to the efficient light detection. Therefore, it is noted that the uniform coverage of graphene onto the Ge surface plays a significant role in advancing their opto-electrical performance of photodetector.

We fabricated an GaN Schottky photodiode (PD) with Al-doped ZnO (AZO) interlayer for ultraviolet (UV) photodetection, and its optoelectrical properties with a comparison to the GaN Schottky PD without AZO interlayer. The AZO-interlayered GaN Schottky PD was highly sensitive to 350 nm laser irradiation, having a photoresponsivity of 11.1 AW–1 and detectivity of 1.04 × 1012 cm·Hz1/2·W–1 at -2 V as against 0.28 AW−1 and 2.23 × 1010 cm·Hz1/2·W–1 for the GaN Schottky PD without AZO interlayer. The transient photoresponse revealed a rise and decay time of 203 and 293 ms, respectively for the AZO-interlayered GaN Schottky PD. The introduction of AZO interlayer resulted in a reduction in the noise spectral density, leading to an increase in the detectivity by more than an order, as compared to GaN Schottky PD without AZO interlayer. An improved photodetection behavior of the AZO-interlayered GaN Schottky PD could be ascribed to effective GaN surface passivation and reduction of the surface states by the AZO interlayer. The utilization of the AZO in GaN-based UV photodetectors can provide a potential and simplistic approach towards the fabrication of high performance GaN-based UV photodetectors.

We fabricated MoS2/n-type GaN 2D/3D heterojunction diode, investigated its structural properties and temperature-dependent current–voltage (I–V) characteristics. The MoS2 2D film on GaN is 5.2-nm-thick with ~ 0.64 nm interlayer distance. The Barrier height and ideality factor of the MoS2/n-type GaN heterojunction increase and decrease, respectively with rising temperature, associated with the barrier height inhomogeneities. The barrier height inhomogeneity evaluation considering the Gaussian distribution of barrier heights indicate the presence of double Gaussian barrier distribution with mean barrier heights of 0.95 and 1.44 eV and standard deviations of 0.11 and 0.18 eV in the temperature range of 125–225 and 225–400 K, respectively. Reverse current showed an electric field dependence with the carrier transport dominated by Poole-Frenkel emission irrespective of the temperature.

In2S3 is one of the fascinating materials for a range of optoelectronic applications due to its suitable bandgap and stability. Nonetheless, its photoluminescence (PL) originating from defect states within its bandgap were hardly reported. In this work, high quality In2S3 thin films on SiO2 substrates were synthesized by using physical vapor deposition of In2S3 powder in a hot-wall Quartz tube-furnace. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy studies of the grown In2S3 films showed that extremely high crystalline quality tetragonal β-In2S3 films were synthesized with preferred growth direction of [1 0 3]. Absorption spectroscopy revealed the In2S3 films have a direct band of ~2.66 eV. Interestingly, our In2S3 films showed an extremely strong PL peak at room temperature at ~1.6 eV. The observed strong PL from our In2S3 films can be attributed to originating from the oxygen isoelectronic substitution at the sulfur site, and its efficiency was affected by oxygen concentrations in In2S3 films. Our In2S3 thin films exhibited remarkably high PL quantum yields (QY) of up to 14% which is comparable to that of GaAs quantum wells (QWs) and CdSe quantum dots (QDs).

Au-CuPc nanocomposite films were prepared by simultaneous evaporation of Au and CuPc with various Au and CuPc concentrations. Microstructural analysis of Au-CuPc films revealed elongated Au cluster formation from isolated Au nanoclusters with increasing Au concentration associated with coalescence of Au clusters. Au-CuPc films with different compositions were employed as interlayer in Al/n-Si Schottky diode. Barrier height and series resistance of the Al/n-Si Schottky diode with Au-CuPc interlayer decreased with increasing Au concentration. This could be associated with the enhancement of electron tunneling between neighboring clusters due to decrease in spacing of Au clusters and formation of conducting paths through the composite material. Interface state density of the Al/n-Si Schottky diode with Au-CuPc interlayer increased with increasing Au concentration. This might be because the inclusion of metal decreases the crystallinity and crystal size of the polymer matrix accompanied by the formation of local defect sites at the places of metal nucleation.

The effects of Al and Ti seed layers were studied for undoped and Fe-doped ZnO thin films deposited on n-type Si substrates by electron beam (e-beam) evaporation. The films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The films grown on seed layers showed wurtzite hexagonal crystal nanorod and nanowire structures. A higher angle phase shift was observed in the doped thin films compared to the pristine ZnO films. Microstructural studies confirmed the growth of nanorods and nanowires with average widths of ~32 nm and ~8–29 nm, respectively. The nanostructures were denser and more crystalline on the Al seed layer than on the Ti seed layer for the doped thin films. However, in the undoped thin films, a more crystalline nature was observed on the Ti seeded layer than the Al seeded layer.

An Au/Cu2ZnSnS4 (CZTS)/n-GaN heterojunction (HJ) is fabricated with a CZTS interlayer and probed its chemical states, structural, electrical and frequency-dependent characteristics by XPS, TEM, I-V and C-V measurements. XPS and TEM results confirmed that the CZTS films are formed on the n-GaN surface. The band gap of deposited CZTS film is found to be 1.55eV. The electrical properties of HJ correlated with the Au/n-GaN Schottky junction (SJ). The Au/CZTS/n-GaN HJ reveals a good rectification nature with high barrier height (0.82eV) compared to the Au/n-GaN SJ (0.69eV), which suggests the barrier height is influenced by the CZTS interlayer. The barrier height values assessed by I-V, Cheung's and Norde functions are closely matched with one other, thus the methods used here are reliable and valid. The extracted interface state density (NSS) of Au/CZTS/n-GaN HJ is lower compared to the Au/n-GaN SJ that suggests the CZTS interlayer plays an important role in the reduction of NSS. Moreover, the capacitance-frequency (C-f) and conductance-frequency (G-f) characteristics of SJ and HJ are measured in the range of 1kHz-1MHz, and found that the capacitance and conductance strappingly dependent on frequency. It is found that the NSS estimated from C-f and G-f characteristics is lower compared to those estimated from I-V characteristics. Analysis confirmed that Poole-Frenkel emission dominates the reverse leakage current in both SJ and HJ, probably related to the structural defects and trap levels in the CZTS interlayer.

A combination of graphene quantum dots and chemically reduced graphene oxide films was obtained by spray-coating their dispersions onto an indium tin oxide coated polyethylene terephthalate substrate. Herein, the graphene quantum dots played a major role in the absorption of ultraviolet light and generation of carriers, whereas the reduced graphene films acted as the transparent electron pathway network. Consequently, the fabricated structure showed good transparency and flexibility, and achieved noticeable ultraviolet sensing. The facile, inexpensive, and extremely low temperature techniques used can be easily upgraded to a larger scale and are compatible with other substrates. In addition, a combination of reduced graphene oxide and graphene quantum dots offers a potential graphene-based platform for foldable optoelectronic device applications.

High-k rare-earth samarium oxide (Sm 2 O 3 ) films are formed on n-GaN surface and analyzed its compositional properties by XPS measurements. XPS results specify that the Sm 2 O 3 films are formed at the interface. Then, the Au/Sm 2 O 3 /n-GaN MIS junction is prepared with a Sm 2 O 3 as insulating layer and correlated its electrical properties with the Au/n-GaN MS junction. The MIS junction shows highest barrier height ((0.81 eV (I-V)/1.0 eV (C-V)) for MIS junction than the MS junction (0.68 eV (I-V)/0.90 eV (C-V)). Excellent rectifying property is observed with lowest reverse leakage current and higher barrier height for the MIS junction than the MS junction, implying that the Sm 2 O 3 insulating layer effectively modified the barrier height. The barrier heights determined from I-V, Cheung's, Norde and Ψ S –V plot closely matched with each other, suggesting that these techniques are reliable and valid. The estimated interface state density of the MIS junction (1.990 × 10 11 cm −2 eV −1 (E C -0.82 eV)) is lower than the MS junction (9.204 × 10 12 cm −2 eV −1 (E C -0.70 eV)), which demonstrates that the Sm 2 O 3 insulating layer performs an important role in lowering the interface state density. The frequency-dependent characteristics of the MS and MIS junctions are discussed in the frequency range of 10 kHz to 1 MHz and found that the determined capacitance values decrease with increasing frequency. The forward I-V characteristic of the MS and MIS junctions reveals the ohmic behavior at low voltage regions and space-charge-limited conduction at higher voltage regions. Results reveal that the reverse leakage current in the studied MS and MIS junctions is controlled by a Poole-Frenkel emission.