Low Ideality Factor Research Articles

Hybrid gallium nitride/organic heterojunction with improved electrical properties for optoelectronic applications

The rectifying behavior and performance parameters of a hybrid organic/inorganic poly(3,4-ethylenedioxythiophene) polystyrene sulfonate/Si-doped GaN layer (PEDOT:PSS/Si:GaN) are studied. The characteristics of both organic and inorganic layers have been individually examined, and a heterojunction between the same has been realized. AFM studies on optimized samples reveal low surface roughness (~ 3.7 nm), and cross-sectional scanning electron microscopy images reveal uniform deposition of PEDOT:PSS layer over Si:GaN. The optimized heterojunction (thickness ~ 600 nm) presents a threshold voltage ~ 0.4 V with a rectifying behavior and a low ideality factor (n ~ 1.6) as compared to most of the related hybrid heterojunctions reported. The low ideality factor also points toward reduced trap-assisted tunneling and current leakage. A detailed comparison of heterojunction parameters including barrier height (ΦB) of the samples and ideality factor is also presented.

DNA assisted regioregular poly (3, 3‴-didodecylquarterthiophene), rr-PQT-12 fiber: Organic bio-electronic devices

Abstract Present work has focused on the development of bio-organic hybrid materials based on hydrophobic DNA-complex incorporated in polymer and the study of charge transport properties across the junction formed by sandwiching it between conducting electrodes (called hetero-structured vertical diode). The inclusion of hydrophilic DNAs, both natural DNA and synthetic DNA (single strand DNA, ss-DNA and double strand DNA, ds-DNA), in organic semiconducting polymer specially regioregular poly (3, 3‴-didodecylquarterthiophene) (rr-PQT-12), have done in chloroform. Prior to DNAs inclusion, hydrophobic DNA-DDAB complexes have formed by reaction of hydrophilic DNA and didodecyldimethylammonium bromide, DDAB in aqueous solvent. Thereafter, as-mixed solution has been aged for 45 min to obtain fibrils' growth and used for the fabrication of devices. Various parameters including rectification ratio, ideality factor, saturation current, barrier height and device stability have been measured to study the nature of charge transport and effect of DNAs on the performance of devices. The device performance has been observed better with the incorporation of G-C rich DNAs. ds-DNA based devices exhibit improved rectification ratio i.e. two times higher than that of ss-DNA and three times higher than that of rr-PQT-12 with least turn-on voltage (0.56 V) or even low ideality factor (3.02), due to hot carrier injection phenomenon by assembled rr-PQT-12 to nearby nucleotide bases.

Electrical characteristics of silicon percolating nanonet-based field effect transistors in the presence of dispersion

We studied the current-voltage characteristics of percolating networks of silicon nanowires (nanonets), operated in back-gated transistor mode, for future use as gas or biosensors. These devices featured P-type field-effect characteristics. It was found that a Lambert W function-based compact model could be used for parameter extraction of electrical parameters such as apparent low field mobility, threshold voltage and subthreshold slope ideality factor. Their variation with channel length and nanowire density was related to the change of conduction regime from direct source/drain connection by parallel nanowires to percolating channels. Experimental results could be related in part to an influence of the threshold voltage dispersion of individual nanowires.

Detailed investigation of defect states in Erbium doped In2O3 thin films

Erbium doped Indium Oxide (In2O3:Er) thin films (TFs) were synthesised by spin-on technique. Secondary Ion Mass Spectrometry confirmed that Er is incorporated into the In2O3 lattice and formed an In-O-Er layer. The current–voltage loop produced a lower loop current window of ∼3.6×10−4A for In2O3:Er TF based devices. The Au/In2O3:Er/Si Schottky devices have lower ideality factor (∼6) and higher barrier height (∼0.63eV) at 300K than Au/In2O3/Si control samples. A blue shift in the main band-gap (∼50nm) was calculated for In2O3:Er TFs from 10K photoresponse. The Au/In2O3:Er/Si samples show higher photosensitivity in the temperature range 10K–300K and maximum (∼15 times) in the UV region at 10K as compared to the Au/In2O3/Si devices. In addition, the Au/In2O3:Er/Si devices have better UV to visible cut-off ratio (∼3 times). Excellent temporal responses were recorded for Au/In2O3:Er/Si in the UV region as compared to Au/In2O3/Si.

Phase Stabilized α‐CsPbI3 Perovskite Nanocrystals for Photodiode Applications

AbstractHigh‐performance and high‐reliability photodiodes are demonstrated by using α‐CsPbI3 perovskite nanocrystals (NCs) phase‐stabilized with a low‐temperature solution‐treated active layer. In addition to the high charge mobility, the high absorption coefficient, and IR‐blind characteristics of the perovskite material, the defect‐tolerant nature of α‐CsPbI3 perovskite NCs are combined to realize hysteresis‐free and high detectivity photodiodes. To further minimize interface defects originating from multi‐layer photodiode construction, a poly(3‐hexylthiophene) layer is strategically introduced as a passivation and electron blocking layer, resulting in a low diode ideality factor of 1.5 and a noise equivalent power of 1.6 × 10−13 W Hz−0.5. As a result, high detectivity of 1.8 × 1012 Jones is demonstrated with near‐zero hysteresis. Furthermore, the optimized photodiode exhibits excellent stability under high humidity conditions owing to the intrinsic nature of the defect‐tolerant α‐CsPbI3 perovskite NCs.

Demonstration of AlN Schottky Barrier Diodes With Blocking Voltage Over 1 kV

This letter reports the first demonstration of 1-kV-class AlN Schottky barrier diodes on sapphire substrates by metal organic chemical vapor deposition. The device structure mimics the silicon-on-insulator (SOI) technology, consisting of thin $n$ -AlN epilayer as the device active region and thick resistive AlN underlayer as the insulator. At room temperature, the devices show outstanding performances with a low turn-ON voltage of 1.2 V, a high ON/OFF ratio of $\sim 10^{5}$ , a low ideality factor of 5.5, and a low reverse leakage current below 1 nA. The devices also exhibit excellent thermal stability over 500 K owing to the ultra-wide bandgap of AlN. The breakdown voltage of the devices can be further improved by employing field plate, edge termination technologies, and optimizing the SOI-like device structure. This letter presents a cost-effective route to high performance AlN-based Schottky barrier diodes for high-power, high-voltage, and high-temperature applications.

Vital Role of Oxygen for the Formation of Highly Rectifying Schottky Barrier Diodes on Amorphous Zinc-Tin-Oxide with Various Cation Compositions.

We present electrical properties of Schottky barrier diodes on room-temperature deposited amorphous zinc-tin-oxide (ZTO) with Zn/(Zn + Sn) contents between 0.12 and 0.72. A combinatorial approach with continuous composition spread pulsed laser deposition is used to achieve the wide range of compositions with four samples each on 50 × 50 mm2 glass substrates. The Schottky barrier contacts were fabricated by the reactive direct-current sputtering of platinum. Best diode properties (rectification ratio SV = 2.7 × 107, ideality factor η = 1.05, and effective barrier height ϕB,eff = 1.25 eV) are obtained for a composition of 0.63 Zn/(Zn + Sn). Aging on the timescale of days and months is observed that leads to improved device properties (higher rectifications and lower ideality factors). In particular, the diodes with the lowest performance in the as-prepared state show the biggest improvements. The best diode properties after the aging process (SV = 3.9 × 107, η = 1.12, and ϕB,eff = 1.31 eV) were also observed for 0.63 Zn/(Zn + Sn).

Investigation of Defects Origin in p-Type Si for Solar Applications

In order to improve the efficiency of a solar cell based on silicon, one must find a compromise between its price and crystalline quality. That is precisely why the knowledge of defects present in the material is of primary importance. This paper studies the defects in commercially available cheap Schottky titanium/gold silicon wafers. The electrical properties of the diodes were defined by using current–voltage and capacitance–voltage measurements. Low series resistance and ideality factor are proofs of the good quality of the sample. The concentration of the acceptors is in accordance with the manufacturer’s specifications. Deep level transient spectroscopy measurements were used to identify the defects. Three hole traps were found with activation energies equal to 0.093 eV, 0.379 eV, and 0.535 eV. Comparing the values with the available literature, the defects were determined as connected to the presence of iron interstitials in the silicon. The quality of the silicon wafer seems good enough to use it as a substrate for the solar cell heterojunctions.

Wettability effects of graphene oxide aqueous solution in photodetectors based on graphene oxide/silicon heterojunctions via ultraviolet ozone treatment

We report the wettability effects of graphene oxide (GO) aqueous solution on the electrical and photoresponse properties of GO-silicon (Si) photodetectors via ultraviolet ozone (UVO) treatment. GO-Si vertical heterojunctions were fabricated using a spray-coating method. In the GO/p-Si heterojunctions without UVO treatment (GO/p-Si), an island-like assembly of GO sheets was formed, indicating that a GO stacking structure may have an island shape on the substrate due to partial surface coverage. In contrast, for those with UVO treatment (GO/UVO-p-Si), a relatively more close-packed GO deposition may occur due to the more hydrophilic property of the substrate surface, leading to the full surface coverage of the p-Si surface. Photodetectors based on GO/p-Si and GO/UVO-p-Si heterojunctions exhibit distinct electrical and photoresponse properties. The GO/UVO-p-Si-based devices showed a higher photo-to-dark current ratio, higher turn-on voltage, and lower ideality factor compared to the GO/p-Si-based devices. The transport mechanism in the photodetectors can be explained in terms of space-charge-limited conduction and the tunneling of charge carriers through the GO layer.

A theoretical scaling for rectifying and surface properties of highly-crystalline N[sbnd]C anthracene Schottky junctions

This article describes an anthracene derivative nitropyridine conjugated (NC) substituent has been efficiently used in Schottky junction applications. The effect of solution aging with a long period from 1h to 1 week on diode parameters such as ideality factor, barrier height, and series resistance were studied in details. The barrier height varied almost linearly with aging and the values increased from 0.623 to 0.860eV, 0.710 to 0.884eV, 0.715 to 0.836eV and 0.678 to 0.683eV determined from I–V method, Cheung’s, Norde’s functions and C-V method, respectively, on the other hand, the ideality factor decreased from 3.08 to 1.55 and 3.24 to 1.52 determined from I–V and Cheung functions respectively, with increase in aging. Low ideality factor suggests an ideal Schottky junction formation. The series resistance values obtained from Norde’s function and Cheung functions exhibited a good agreement and a strong dependence to solution aging.

Influence of sputtering conditions on room-temperature fabricated InGaZnO-based Schottky diodes

Indium gallium zinc oxide (InGaZnO or IGZO) has attracted much attention in recent years for flexible and transparent electronics, because of its superior electric properties, optical transparency and low processing temperature. In this work, Schottky diodes with a structure of Pd/IGZO(100nm)/Ti/Au were fabricated by radio-frequency magnetron sputtering at room temperature without any thermal treatment. The relationship between different IGZO deposition parameters and the forward and reverse current-voltage characteristics of the diodes was systematically studied. We have experimentally revealed that an increase in the oxygen partial pressure during the sputtering process can effectively improve the barrier height of these diodes. However, either high oxygen partial pressure or high sputtering power leads to a deterioration of ideality factor and a decreased rectification ratio. By using relatively low sputtering power (≤70W) and low oxygen content of sputtering atmosphere (~2.5%), high-performance diodes have been achieved with high rectification ratio, low ideality factor, and high barrier height of 1.3×105, 1.14, and 0.73eV, respectively. All diodes with IGZO layer sputtered in oxygen-argon atmosphere show a high reversed breakdown voltage ~−6V.

Low Reverse Saturation Current Density of Amorphous Silicon Solar Cell Due to Reduced Thickness of Active Layer

One of the most important characteristic curves of a solar cell is its current density-voltage (J-V) curve under AM1.5G insolation. Solar cell can be considered as a semiconductor diode, so a diode equivalent model was used to estimate its parameters from the J-V curve by numerical simulation. Active layer plays an important role in operation of a solar cell. We investigated the effect thicknesses and defect densities (N_d) of the active layer on the J-V curve. When the active layer thickness was varied (for N_d = 8×10¹⁷ cm^-3) from 800 nm to 100 nm, the reverse saturation current density (J_o) changed from 3.56×10^-5 A/cm² to 9.62×10^-11 A/cm² and its ideality factor (n) changed from 5.28 to 2.02. For a reduced defect density (N_d = 4×10¹⁵ cm^-3), the n remained within 1.45≤n≤1.92 for the same thickness range. A small increase in shunt resistance and almost no change in series resistance were observed in these cells. The low reverse saturation current density (J_o = 9.62×10^-11 A/cm²) and diode ideality factor (n = 2.02 or 1.45) were observed for amorphous silicon based solar cell with 100 nm thick active layer.

High performance Schottky diodes based on indium-gallium-zinc-oxide

Indium-gallium-zinc-oxide (IGZO) Schottky diodes exhibit excellent performance in comparison with conventional devices used in future flexible high frequency electronics. In this work, a high performance Pt IGZO Schottky diode was presented by using a new fabrication process. An argon/oxygen mixture gas was introduced during the deposition of the Pt layer to reduce the oxygen deficiency at the Schottky interface. The diode showed a high barrier height of 0.92 eV and a low ideality factor of 1.36 from the current–voltage characteristics. Even the radius of the active area was 0.1 mm, and the diode showed a cut-off frequency of 6 MHz in the rectifier circuit. Using the diode as a demodulator, a potential application was also demonstrated in this work.

TiO2 Nanowires/Poly(Methyl Methacrylate) Based Hybrid Photodetector: Improved Light Detection.

Hybrid photodetector with a maximum external quantum efficiency of ~3.08% in the UV region at 370 nm, was fabricated by spin-coated poly(methyl methacrylate) (PMMA) polymer onto glancing angle deposited (GLAD) vertically aligned TiO2 nanowire (NW) arrays. The TiO2 NWs/PMMA detector shows excellent rectification and constant 1.3 times photo-responsivity in the reverse bias condition from -1 V to -10 V. The photodiode possesses a low ideality factor of 5.1 as compared to bared TiO2 NWs device of 7.1. The hybrid device produces sharp turn-on of -0.8 s and turn-off transient of -0.9 s respectively.

Graphene, conducting polymer and their composites as transparent and current spreading electrode in GaN solar cells

Understanding the physics of charge carrier transport at graphene/p-GaN interface is critical for achieving efficient device functionality. Currently, the graphene/p-GaN interface is being explored as light emitting diodes, however this interface can be probed as a potential photovoltaic cell. We report the intimate interfacing of mechanically exfoliated graphene (EG), conducting polymer (PEDOT:PSS) and composite of reduced graphene oxide (rGO) and PEDOT:PSS with a wide band gap p-GaN layer. To explore their potential in energy harvesting, three heterojunction devices such as: (i) EG/p-GaN/sapphire, (ii) PEDOT:PSS/p-GaN/sapphire and (iii) PEDOT:PSS(rGO)/p-GaN/sapphire are designed and their photovoltaic characteristics are examined. It is interesting to observe that the EG/p-GaN/sapphire solar cell exhibits high open-circuit voltage of 0.545 V with low ideality factor and reverse saturation current. However, improved short circuit current density (13.7 mA/cm2) is noticed for PEDOT:PSS/p-GaN/sapphire solar cell because of enhanced conductivity accompanied by high transmittance for PEDOT:PSS. Further, the low series resistance for PEDOT:PSS(rGO)/p-GaN/sapphire is observed suggesting that the PEDOT:PSS and rGO composite is well dispersed and exhibits low interfacial resistances with p-GaN. The present investigation leverages the potential of graphene, conducting polymer and their composites as dual capability of (a) transparent and current spreading electrode and (b) an active top layer to make an intimate contact with wide bandgap p-type GaN for possible prospect towards high performance diodes, switches and solar cells.

1.7-kV and 0.55-$\text{m}\Omega \cdot \text {cm}^{2}$ GaN p-n Diodes on Bulk GaN Substrates With Avalanche Capability

We report vertical GaN-on-GaN p-n diodes with a breakdown voltage (BV) of 1.7 kV and a low differential specific ON-resistance $R_{\mathrm{\scriptscriptstyle ON}}$ of 0.55 $\text{m}\Omega \cdot \text {cm}^{2}$ with current spreading considered (or 0.4 $\text{m}\Omega \cdot \text {cm}^{2}$ using the diode bottom mesa size), resulting in a figure-of-merit ( $V_{B}^{2}/R_{\mathrm{\scriptscriptstyle ON}})$ of 5.3 GW/cm2 (or 7.2 GW/cm $^{2})$ . These devices exhibit a current swing over 14 orders of magnitude and a low ideality factor of 1.3. Temperature dependent $I$ – $V$ measurements show that the BV increases with increasing temperature, a signature of avalanche breakdown.

Tension assisted metal transfer of graphene for Schottky diodes onto wafer scale substrates

We developed an effective graphene transfer method for graphene/silicon Schottky diodes on a wafer as large as 6 inches. Graphene grown on a large scale substrate was passivated and sealed with a gold layer, protecting graphene from any possible contaminant and keeping good electrical contact. The Au/graphene was transferred by the tension-assisted transfer process without polymer residues. The gold film itself was used directly as the electrodes of a Schottky diode. We demonstrated wafer-scale integration of graphene/silicon Schottky diode using the proposed transfer process. The transmission electron microscopy analysis and relatively low ideality factor of the diodes indicated fewer defects on the interface than those obtained using the conventional poly(methyl methacrylate)-assisted transfer method. We further demonstrated gas sensors as an application of graphene Schottky diodes.

Study of the characteristics current-voltage and capacitance-voltage in nitride GaAs Schottky diode

This article reports the study of Au/GaN/GaAs Schottky diodes, where the thin GaN film is prepared by nitridation of GaAs substrates with thicknesses of 0.7 and 0.8 nm. The resulting GaN sample with thickness 0.8 nm is then treated with an annealing operation (heating to 620 °C) to improve the current transport. The current-voltage ( I-V ) and capacitance-voltage ( C-V ) of the Au/GaN/GaAs structures were investigated at room temperature. In fact, the I-V characteristics show that the annealed sample has low series resistance ( R s ) and ideality factor ( n ) (63 Ω, 2.27 respectively) when compared to the values obtained in the untreated sample (1.83 kΩ, 3.31 respectively). The formation of the GaN layer on the gallium arsenide surface is investigated through calculation of the interface state density N SS with and without the presence of series resistance R s . The value of the interface state density N SS ( E ) close to the mid-gap was estimated to be in the order of 4.7×10 12 cm -2 eV -1 and 1.02× 10 13 cm -2 eV -1 with and without the annealing operation, respectively. However, nitridation with the annealing operation at 620 °C improves the electrical properties of the resultant Schottky diode.

N-ZnO/p-4H-SiC diode: Structural, electrical, and photoresponse characteristics

Epitaxial n-type ZnO film has been grown, on a commercial 5 μm thick p-type 4H-SiC(00.1) Al doped epilayer, by atomic layer deposition. A full width at half maximum of the ZnO 00.2 diffraction peak rocking curve of 0.34° ± 0.02° has been measured. Diodes formed on the n-ZnO/p-4H-SiC heterostructure show rectifying behavior with a forward to reverse current ratio at the level of 109 at ±4 V, a leakage current density of ∼6 × 10−8 A/cm2, and a low ideality factor equal to 1.17 ± 0.04. In addition, the diodes exhibit selective photoresponse with a maximum at 367 nm, and with a current increase of ∼103 under illuminations with respect to the dark value, which makes such devices prospective candidates for ultraviolet light sensors.

Improved surface and electrical properties of passivated GaSb with less alkaline sulfide solution

The surface quality of HCl-etched and ammonium sulfide [(NH4)2S]-based treated bulk n-GaSb(100) were compared using x-ray photoelectron spectroscopy (XPS) and TOF-SIMS. It has been found that native oxides present on the GaSb surface are more effectively removed when etched with concentrated HCl solution. With additional [(NH4)2SO4+S] substances or hydrogen ions in the passivation solution, the treated samples displayed significant reduction of native oxides and formation of the sulfides compared with pure (NH4)2S solution. The treated samples also result in a noteworthy improvement in the current–voltage (I–V) characteristics of Au/n-GaSb Schottky contacts, as evidenced by the lower ideality factor (n), higher barrier height (Φb) and higher rectification ratio at ±0.2V. The I–V measurement provided definitive confirmation of XPS and TOF-SIMS results, establishing the need for less alkaline solution for greater passivation stability.