Photodiode Behavior Research Articles

Photosensitive properties of Schottky type photodiodes prepared by spin coating of isoniazid Schiff base thin film on p-Si

In this study, a layer of isonicotinohydrazide and pyrene-based Schiff base (PyMIs) was formed on the front side of a p-Si semiconductor using the spin coating method, and an Al/PyMIs/p-Si/Al diode was fabricated. The I-V characteristics of the fabricated diode were measured under dark and from 20 to 100 mW/cm2 illumination intensities for both forward and reverse bias. Diode parameters, including saturation current (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${I}_{0}$$\\end{document}), ideality factor (n), and barrier height (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\varphi }_{b}$$\\end{document}) were investigated for all measurements based on thermionic emission theory. The values n changed from 2.51 to 2.05, and the \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\varphi }_{b}$$\\end{document} changed from 0.77 eV to 0.86 eV as light intensity increased from dark to 100 mW/cm2. The series resistance (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${R}_{s}$$\\end{document}) values of the diode were investigated using the modified Norde’s function and Cheung’s functions. An analysis of the forward \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$log\\left( I \\right) - log\\left( V \\right)$$\\end{document} plot of Al/PyMIs/p-Si (MOmS)-type diode specified the carrier transport domination by ohmic conduction in the lower bias regions, by the space-charge-limited current (SCLC) at medium bias regions and the trap-charge limit current (TCLC) transport mechanism at higher bias regions. The fabricated diode exhibited typical photodiode behavior with reverse current values increasing from 9.13 × 10− 6 A to 1.05 × 10− 4 A, respectively. Furthermore, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$I-V$$\\end{document} characteristics illuminated from 20 to 100 mW/cm2 were also studied, and they indicated that the Al/PyMIs/p-Si diode could operate in a photovoltaic regime.

Effect of Cr doping and photoresponse properties of photodiode based on CdO thin films

AbstractCadmium oxide (CdO) and chromium (Cr) doped CdO thin films with various Cr wt% contents (0.1, 0.5, 1, 2 at.%) are synthesised on soda lime glass (SLG) substrates. Results from X-ray analysis indicate that all thin films are in cubic nature with (111) preferential orientation. Cr doping does not appear to result in a transition from one crystal phase to another. CdO with the 2.0 wt% Cr doping absorbs much more light than undoped CdO in low wavelength region (< ≈450 nm), giving a maximum absorption peak in the ultraviolet region. Cr doped CdO/p-Si heterojunction shows the Cr wt% content-sensitive rectification property, achieving a high ratio of 105. In addition, Cr doped CdO/p-Si heterojunction exhibits photodiode behavior and possesses an improved photo-to-dark current ratio of ≈153. This work introduces an occasion to develop the optoelectronic devices based on Cr doped CdO thin films.

Using wafer scale ferroelectric domains of LiNbO3 to form permanent planar p–n junction in narrow band gap nanocrystals

p–n junctions based on nanocrystals now serve as fundamental components in optoelectronics. However, the process of designing these p–n junctions has largely relied on empirical choices, either for ligand exchange or for the selection of charge transport layers. Therefore, a systematic strategy is still lacking. In this study, we explore the utilization of ferroelectric domains as a general method for remotely inducing the formation of a p–n junction. To ensure compatibility with devices of various designs, we employ a commercially available periodically poled LiNbO3 (PPLN) substrate commonly used in nonlinear optics. We engineer a PPLN/graphene/HgTe heterostructure and demonstrate its planar photodiode behavior. Through x-ray photoemission microscopy, we confirm that the rectifying behavior stems from the influence of the ferroelectric domains, by ruling out the possibility of the formation of non-ohmic contacts at the electrode/semiconductor interfaces. This approach proves to be quite general and holds promise for the future design of high-speed nanocrystal-based photodiodes.

Investigation of Ag/ZnO/p-Si heterostructure for diode and photodiode applications in visible spectrum

Photodiodes have gained great attention for lightning control and optical communication over the last two decades. To obtain faster and more sensitive photodiodes are important for industrial applications. In this study, atomic layer deposition (ALD) technique was used to fabricate ZnO interlayer on p-Si, and thermal evaporation technique was employed to deposit Ag rectifying and Al ohmic contacts on ZnO and back surface of p-Si, respectively. The UV–Vis spectrometer was used to characterize optical behaviors of the ZnO interlayer. I-V measurements were conducted to characterize of Ag/ZnO/p-Si heterostructure for various solar light power intensities of dark, 20, 40, 60, 80 and 100 mW cm−2 and at various wavelengths from 351 nm to 800 nm by 50 nm intervals. According to I-V characteristics, the device exhibited increasing current at reverse biases depending on increasing light power intensity, and this confirmed photodiode behavior. Various diode parameters such as rectifying ratio, threshold voltage, series resistance, barrier height, etc. were determined and discussed in details from forward bias characteristics to investigate diode characteristics of the Ag/ZnO/p-Si heterostructure. The photodetection parameters such as responsivity, specific detectivity and external quantum efficiency (EQE) also were investigated. The Ag/ZnO/p-Si heterostructure exhibits good photodetection performance at all visible range of electromagnetic spectrum and can be good candidate for optoelectronic applications.

Photodiode behavior and capacitive performance of ZnO nanoflakes synthesized by electrochemical deposition

ZnO flake interlayers were fabricated by the electrochemical deposition technique on p-Si to obtain Au/ZnO/p-Si heterostructures for Schottky-type photodiode applications and to test the capacitive performance of the structures. ZnO flake structures were investigated by x-ray diffractometry and scanning electron microscopy measurements, and their crystalline and flake-like structures were confirmed. The Au/ZnO/p-Si heterostructures were characterized by current–voltage (I–V) measurements for various illumination densities of light from dark to 150 mW cm−2. Various heterostructure parameters such as the ideality factor, barrier height, series resistance and rectifying ratio (RR) values were determined by I–V characteristics. The heterostructure exhibited a high RR of 6.85 × 103. The detection parameters revealed 0.49 mA W−1 responsivity and 2.69 × 109 Jones specific detectivity values. Furthermore, capacitance–voltage (C–V) measurements were employed to obtain the capacitive behavior of the Au/ZnO/p-Si heterostructure at various frequencies. Based on these results, Au/ZnO/p-Si heterostructures have potential for photodiode applications.

Investigation of electrical, photodiode and photovoltaic properties of Au/SiO2/n-Si structures with GO and P3C4MT interface

This study mainly focused on investigating the electrical and photodiode properties of Au/SiO2/n-Si heterostructures with graphene oxide (GO) and poly(3-cyclohexyl-4-methyl-2,5-thiophene) (P3C4MT) interface. For this, GO and P3C4MT thin layer was grown as an interfacial layer between Au and SiO2/n-Si to create this Au/(GO:P3C4MT)/SiO2/n-Si hetero structure. From the current–voltage (I–V) measurements, the values of electrical and photodiode parameters such as ideality factors (n), rectification ratios (RR), saturation currents (I0), barrier heights (Φbo), photocurrent (Iph), photosensivity (RR), photoresponse (R), and detectivity (D*) were examined under dark and variable illuminations (from 20 to 100 mW/cm2 by 20 mW/cm2 steps) at room temperature, respectively. Au/(GO:P3C4MT)/SiO2/n-Si heterostructure exhibited a photoconducting behavior under variable illuminations. Furthermore, the photovoltaic properties such as short circuit current (Isc) and open circuit voltage (Voc) were examined under variable illuminations intensities. The experimental results shows that Au/(GO:P3C4MT)/SiO2/n-Si hetero structure under light illumination exhibits a perfect photodiode behavior, and thus this structure can be used as photodiode in optoelectronic devices.

Synthesis of Alq3 by a facile co-precipitation approach and study the impact of CNTs support on its microstructure and electronic characteristics for photodiode development

The global demand for renewable energy as an alternative to traditional fossil fuels has motivated the scientific community to develop highly efficient nanocomposite materials that can be used for enhancement to optoelectronic technology. In the present work, organometallics Alq3 and Alq3/CNTs were prepared by cost-effective chemical route. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed to identify the structural and morphological features. The hybrid Alq3/CNTs exhibited polycrystalline structure with a large surface area. The optical band gap of Alq3 film was evaluated within the visible spectrum in the range of 3.047 eV which reduced to 2.979 eV by CNTs integration. Ag/Alq3/p-Si/Al and Ag/Alq3/CNTs/p-Si/Al photodiodes were fabricated using thermal evaporating technique. Current-voltage and capacitance/conductance-voltage were measured to analyze the photodiode behavior. The main electronic parameters like were determined using different models indicating that the composite photodiode of high performance in which was decreased whereas was increased with doping. Besides, the photocurrent sensitivity was increased from to due to increase of free charge carriers.

Optoelectronic Properties of Triphenylamine Organic Thin Film Layered Al/p-Si /TPA/Al Heterojunction for Photodiode Application

Organic semiconductors provide many advantages in diode fabrication due to their variable electrical properties, flexibility and easy and cheap production processes. In this study, triphenylamine (TPA) organic compound was used for the Al/p-Si/TPA/Al Schottky structure. The effect of the triphenylamine on the electrical properties of the produced diode was studied by current-voltage measurements in dark and under various illumination intensities. The main electrical parameters such as barrier height (ΦB), ideality factor (n), series resistance (R s), and interface state density (N ss) were obtained from the I-V characteristics. The n, and R s values of the diode were found as 1.88, 0.80 eV and 2195 Ω for dark, and 3.96, 0.71 eV and 17 Ω for 100 mW cm−2 illumination intensity. Besides, the fabricated device exhibited photodiode behavior as obtained from the photocurrent measurement for the diode, depending on the illumination intensity. Additionally, it was found that the Al/p-Si/TPA/Al diode had a higher photocurrent (I ph ) in illuminated conditions than in dark conditions. The main photovoltaic parameters such as open circuit voltage (V oc ) and short circuit current (I sc ) were also investigated. Photo-responsivity and response time (τ r, τ d) of the diode was obtained as 0,015 A W−1 and 800 ms respectively. All these results show that the Al/p-Si/TPA/Al diode has potential in optoelectronic device applications.

The photovoltaic and photodiode properties of Au/Carmine/n-Si/Ag diode

In this study, carmine films were deposited on glass slides and n-Si substrates using a spin coater. The scanning electron microscope (SEM) and absorbance analyses of the deposited carmine film on glass were performed. Twenty-four (24) Au/Carmine/n-Si/Ag dots were identically fabricated, and their current–voltage (I–V) characteristics were taken at room temperature, both in the dark and under daylight. It was seen that all diodes exhibited a rectifying behavior. The ideality factor (n, IF), barrier height (Φb, BH), rectification ratio (RR), and series resistance (Rs) of each dot were determined using the thermionic emission (TE) theory and modified Norde’s functions, respectively. Although the dots were prepared on the same substrate, there was a difference from one dot to the next. The n and Φb values of the 24 dots were found in the range of 1.52–2.72 and 0.76–0.85 eV in the dark, respectively. Furthermore, a high current rectification ratio of 104 was achieved for the 11 dots in the dark. The photovoltaic and photodiode properties of one (labeled as D18) of the Au/Carmine/n-Si/Ag dots under the different light intensities varied from 30 to 100 mW/cm2 at room temperature, and its capacitance–voltage (C–V) characteristics were investigated only in the dark. The D18 dot exhibited typical photodiode behavior with a fill factor (FF) value of 36.2 % and an experimental efficiency (ŋ) of 2.45 % under 30 mW/cm2 light intensity, respectively. It also has a high ON/OFF current (Ion/Ioff) ratio of 7.45x103. Because the maximum current value of the Au/Carmine/n-Si/Ag photodiode has not changed, it exhibits good stability for 12 on/off cycles.According to these experimental findings, the high-performing Au/Carmine/n-Si/Ag diode displays good photodiode behavior, and photodiodes based on the carmine thin film can be used to develop future optoelectronic devices.

MoTe2-Based Schottky Barrier Photodiode Enabled by Contact Engineering

Two-dimensional (2D) atomic crystalline materials have attracted the scientific community owing to their remarkable electrical and optical applications, such as solar cells, light-emitting diodes, and photodiodes. This study demonstrates a Schottky barrier photodiode (SPD) using different metal architectures in lateral and vertical contacts on n-type 2H phase semiconducting molybdenum ditelluride (MoTe2) synthesized by the self-flux crystal growth method. High-work-function palladium and low-work-function indium metals have been deposited on MoTe2 to fabricate a field-effect transistor confirming diode characteristics. The device shows an ideality factor of 1.09 and a rectification ratio of 102, indicating ideal diode characteristics based on a single MoTe2 channel. In addition, we measured the device in the dark and used the green laser to analyze the photodiode behavior of SPD in a wide range of light intensity. A single channel using contact architecture-based study is helpful to apply in other 2D materials to achieve the simplest fundamental diodes for future nanoelectrical and optoelectronic devices.

Tetra-4-(4’-Меthоxyphenoxy)Phthalocyanine Copper Complex: Synthesis, Mesomorphism, Spectral and Photophysical Properties of Thin Films

A copper complex of tetra-4-(4'-methoxyphenoxy)phthalocyanine was obtained by template synthesis. Its spectral properties in solutions of chloroform, DMF, and sulfuric acid were studied. It has been established that the studied copper phthalocyanine in chloroform solution exists mainly in the monomeric form. The mesomorphism study by the method of polarization optical microscopy showed that the compound is mesogenic, exhibiting a columnar mesophase within a wide temperature range. On cooling, the compound vitrifies with preservation of the mesophase texture. Thin films of individual phthalocyaninate and its mixture with a fullerene derivative (PCBM) were obtained by spin-coating. The film thickness and surface relief were evaluated by atomic force microscopy. The spectral (absorption and fluorescence) and photophysical properties of the films have been studied. It is shown that the presence of photovoltage in individual phthalocyaninate is two times higher than in its composition with PCBM. Over time (after one year), the photovoltaic response of the film based on the individual phthalocyaninate significantly decreased, while in the film with the addition of PCBM it increased three times compared to the initial values ​​for freshly prepared samples. This behavior of photodiodes based on phthalocyanine – fullerene compositions is not typical and was observed for the first time.

Poboljšanje apsorpcionih svojstava TiO2 nanocevi pomoću CH3NH3PbBr3 perovskita kao fotosenzitivizatora

Organic-inorganic perovskites have attracted much attention from researchers due to their high absorption in the visible part of the spectrum and low-cost fabrication. After absorption of the light, electron-hole pairs are formed. To separate electron-hole pairs and reduce recombination, perovskite is combined with TiO2 which has as a consequence, a spontaneous transition of electrons from perovskite to TiO2. This research aims to increase the contact surface of perovskite and TiO2 nanotubes by filling the nanotubes with perovskite material. The solution of methylammonium lead bromide perovskite (CH3NH3PbBr3) in dimethylformamide (DMF) was deposited on anodically synthesized TiO2 nanotubes by the high vacuum system and inert gas. The procedure involved degassation of the sample under high vacuum for 3 h at 200 °C, cooling of the sample, and putting the solution of CH3NH3PbBr3 in DMF, after which it was treated with inert gas (N2), as an overpressure which enabled the filling of the nanotubes with perovskite material. The diffuse reflectance spectroscopy measurement of the sample proved that deposition of CH3NH3PbBr3 improves the absorption properties of TiO2 nanotubes. The I-V characteristics of the sample showed photodiode behavior and characteristic hysteresis curve for perovskite material. The value of current under visible light for the sample without preconditioning was 46 mA, while after preconditioning value of current was 76 mA. The results indicate that a perovskite photodiode with increased contact between TiO2 and perovskite was made, which is the basis for future solar cell construction.

High gain GaN ultraviolet Schottky photodetector with Al-doped ZnO interlayer

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.

Photodiode behaviors of the AgSbS2 nanocrystals in a Schottky structure

Cubic phase AgSbS2 nanocrystals (NCs) were synthesized by the hot-injection method, and they were inserted between the Al and p-Si to fabricate Al/AgSbS2/p-Si photodiode by the thermal evaporation method. AgSbS2 NCs were characterized by XRD, SEM and TEM instruments to confirm the crystal phase, surface morphology as well as crystalline size. The XRD pattern revealed that the cubic crystalline structure of the AgSbS2. The spherical shapes and well surface morphology were affirmed by SEM and TEM analysis. Al/AgSbS2/p-Si photodiode was characterized by I–V measurements depending on the light power intensity and by C–V measurement for various frequencies. I–V characteristics revealed that the Al/AgSbS2/p-Si exhibited good photodiode behavior and a high rectifying ratio. Various diode and detector parameters were extracted from I–V measurements, and they were discussed in detail. The C–V characteristics highlighted that the Al/AgSbS2/p-Si photodiode showed voltage and frequency dependent profile at the accumulation region. The fabricated Al/AgSbS2/p-Si photodiode can be thought for optoelectronic applications.

On the investigation of the electro-optical sensor potential of Boswellia serrata resin

In a first step, Boswellia serrata (Bs) resin was purchased in its natural state and dissolved in deionized water and coated on the n-Si wafer by spin coating method as a thin film with about 1 μm. SEM images and EDX analyses of Bs resin film on the n-Si wafer were obtained. It has been seen that the fabricated Bs/n-Si device has an unsymmetrical current-voltage (I–V) graph and a good rectifier feature. Then, we analyzed some electrical characteristics of Bs/n-Silicon heterojunction. Using light intensity-dependent (in the range of 100–250 mW/cm2) current-voltage (I–V) and in dark, capacitance-conductance-voltage (C-G-V) and capacitance-frequency (C-f) measurements of Bs/n-Si heterojunction were investigated. The heterojunction shows a photodiode behavior such that the reverse-bias photocurrent exceeds the dark reverse current and the reverse bias current increased linearly with increasing light intensity. Hence, we determined the sensitivity, responsivity, detectivity and main rectifying junction parameters such as rectifying ratio, ideality factor, barrier height, and series resistance. Furthermore, the barrier heights from the reverse bias C–V measurements were determined and it was found to depend on the frequency. In forward biases, the C decreased with increasing frequency while G increased. In summary, it was concluded that Bs forming a p-n heterostructure with n-Si is a potential material for optoelectronic applications.

CuPc/C60 heterojunction for high responsivity zero bias organic red light photodetector

Organic photodetector (OPD), having copper phthalocyanine (CuPc) and fullerene (C60) bilayer heterojunction as an active layer, has been fabricated by employing thermal evaporation method for the red light detection applications. The spectral response has been observed to cover from 300 to 800 nm for the OPD. Experimental results of the OPD reflect good photodiode behavior. Noteworthy, our fabricated OPD has exhibited responsivity of 0.052 A/W and external quantum efficiency (EQE) of 9.28% at wavelength 700 nm and 0 V. Maximum photocurrent density to dark current density ratio has been found to be 4.5 × 104 under the illumination of red light. Detectivity at wavelength 700 nm and 0 V has been found to be on the order of 1011 Jones for the same OPD. Response time and recovery time are found to be 16 and 36 ms, respectively. Our fabricated OPD exhibits excellent stability. Thus, the CuPc/C60 based OPD has been found to be quite promising for the low cost molecular photodetector applications due to its zero bias high responsivity and detectivity.

Investigation of electrical properties of organophosphazene layer based photodiode

New cyclotriphosphazene compound bearing dioxyphenylcoumarin group (DCP-1) was synthesized from the reactions of 7,8-dihydroxy-3-(4-chlorophenyl)coumarin (3) containing chlorine as a side group at para position with cyclotriphosphazene (DCP). The structures of the compounds were determined using 1H, 13C APT, 31P NMR, FT-IR and elemental analysis spectroscopy methods. The organic layer was deposited onto the p-Si substrate to obtain an Al/p-si/phosphazene (DCP-1)/Al diode. The photoresponse and photocapacitance properties of the diode were analyzed under various solar light intensities. The photocurrent and photocapacitance results suggest that the studied device exhibits both photodiode and photocapacitor behavior. The diode indicates a linear photoresponse behavior. The photoswitching behavior of the diode is controlled by solar light intensity. The interface states density of the diode was found to be order of 1012 eV-1cm2. The value of interface states density indicates that the photocapacitor behavior of the diode is significant for photocapacitor applications.

Illumination Dependent Electrical Data Identification of the CdZnO Interlayered Metal-Semiconductor Structures

Electrical data of the Schottky structure with CdZnO interlayer have been evaluated for different illumination intensities. Considering such parameters as, the ideality factor (n), reverse saturation current (Io), zero bias barrier height (ΦBo), series and shunt resistances (Rs and Rsh) and surface states (Nss), we concluded that these parameters extremely depend on the illumination power and applied bias voltage. In consequence of the Ohm’s law and Norde’s method used for Rs determination, the Rs values decreased with increasing illumination intensity. The energy distribution of the Nss and voltage dependent profile of resistance (Ri) of the structure were extracted from the forward bias current-voltage (I-V) data. The fabricated CdZnO interlayered metal-semiconductor structure appears to have photodiode behavior. Accordingly, the alteration in the basic electrical parameters by the increment in illumination levels indicates that, the carrier generation takes place in the depletion layer and the conductivity of the CdZnO interlayered structure is improved.

Fabrication of a New Hybrid Coronene/n-Si Structure by Using Spin Coating Technique and its Photoresponse and Admittance Spectroscopy Studies

Coronene/n-Si Schottky structure has been fabricated by Coronene thin film deposited on n-Si substrate using the spin coating technique. The current-voltage (I-V) characteristics of the diode have been evaluated under various illumination intensities to determine photodiode behavior. Photovoltaic parameters of the fabricated diode have been calculated at different illumination intensities. The Coronene/n-Si diode presents a photovoltaic status with a maximum short-circuit current (Isc) of 13.1 μA and open circuit voltage (Voc) of 0.16 V under 100 mW/cm2 illumination intensity. The recombination process of the Coronene/n-Si diode shows the existence of bimolecular recombination mechanism associated with the trap levels in the band gap. Also, the series resistance and interface state density distribution of the photodiode have been estimated by capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics at various frequencies. The experimental results indicated that the Al/Coronene/n-Si diode can be used as a photodiode in optoelectronic and photovoltaic applications.

Controlled Island Formation of Large-Area Graphene Sheets by Atmospheric Chemical Vapor Deposition: Role of Natural Camphor.

Camphor-based mono-/bilayer graphene (MLG) sheets have been synthesized by very facile atmospheric chemical vapor deposition processes on Si/SiO2, soda lime glass, and flexible polyethylene terephthalate films. The effect of camphor concentration with respect to distance between camphor and the Cu foil (D) has been varied to investigate the controlled formation of a homogeneous graphene sheet over a large area on Cu foil. Raman studies show a remarkable effect of camphor at a typical distance (D) to form a monolayer to multilayer graphene (MULG) sheet. The signature of MLG to MULG sheets appears due to increase in the number of nucleation sites, even over the subsequent domains that contribute stacks of graphene over each other as observed by high-resolution transmission electron microscopy images. Moreover, the increase in camphor concentration at a particular distance generates more defect states in graphene as denoted by D band at 1360 cm–1. Uniform distribution of large-area MLG demonstrates an intense 2D/G ratio of ∼2.3. Electrical and optical measurements show a sheet resistance of ∼1 kΩ/sq with a maximum transmittance of ∼88% at 550 nm for low camphor concentration. An improvement in the rectification and photodiode behavior is observed from the diodes fabricated on n-Si/MULG as compared to n-Si/MLG in dark and light conditions.