Low Reverse Current Research Articles

Electrical properties of CuO/ZnO heterojunctions prepared by spray pyrolysis

In the present work we investigate the influence of deposition sequences on the two layers forming a CuO/Zinc oxide (ZnO) heterojunction. Both layers are prepared using the simple and cost-effective technique of spray pyrolysis. The advantage of this technique is the ability to deposit both layers successively without interruption. For this purpose, four devices are prepared by successfully changing the deposition order of ZnO and CuO layers, and after a delay for the cooling of the first deposited layer. The I–V characteristics of the realized devices reveal that the deposition order plays a crucial role in the device’s performance. We inferred that the deposition of ZnO as the first layer followed by the immediate CuO leads to a device with superior quality, i.e., low ideality factor, low reverse current, and high rectifying ratio. The SEM image and EDX analysis at the interfaces revealed the diffusion of Zn in the CuO layer, while no diffusion of Cu in the ZnO layer was observed. Estimating the density of the interface states from the conductance vs. frequency measurements (G–f) indicates that the direct deposition of CuO on ZnO leads to a lower interface density of states.

Schottky barrier diode consisting of van der Waals heterojunction of MoS2 film and PtCoO2 contact

We investigated the synthesis of delafossite PtCoO2 crystals, performed electronic transport measurements, and researched the formation of heterojunction with layered films. The crystal was deposited onto a c-plane sapphire substrate using the vapor growth method. The in-plane resistivity (460–475 µΩcm) is comparable to that of layered materials, such as few-layer graphite, applied to electrodes. Schottky contacts were obtained between PtCoO2 and n-type MoS2; therefore, a Schottky barrier diode with a low reverse saturation current was fabricated. The Schottky barrier height (ΦB) was estimated to be 0.896 eV. The atomic scale electric dipole at the interface may contributed to achieving a large ΦB. In addition, Fermi level pinning was suppressed owing to the formation of an interface by the dry transfer method.

Richardson constant and characteristics of pentacene organic planar Schottky diode

Planar organic Schottky diodes were fabricated using undoped pentacene as an active layer with both palladium and aluminum as contacts. Pentacene organic thin films were deposited on n-type silicon substrates with 100 (n-Si<100>) and 111 (n-Si<111>) orientations. X-ray diffraction (XRD) measurements revealed that the pentacene films’ XRD patterns exhibit several peaks with various orientations. The energy-dispersive X-ray technique was used for chemical analysis of the pentacene, and scanning electron microscopy was used to characterize the surface morphology. A structural and morphological study of the deposited pentacene indicates a polycrystalline triclinic (anorthic) nature. A current–voltage curve was experimentally constructed at temperatures (T) ranging from 300 K to 360 K with a step of 15 K. The diode parameters, such as saturation current, ideality factor (n), and barrier height (ΦB), were systematically analyzed using thermionic emission theory. The fabricated devices exhibit decreasing n and increasing ΦB values with increasing T. Richardson's constant for pentacene was calculated, which indicated that the conventionally calculated value from the temperature-dependent characteristic curve is much lower than the calculated theoretical value. It was also observed that the device deposited over the n-Si<111> substrate exhibited larger forward and lower reverse currents than the n-Si<100> substrate device.

Improved performance in MoS2 homogeneous junction field effect transistors by optimizing electrodes contact

Junction field effect transistor (JFET) operates by controlling the thickness of depletion layer in channel with a reverse biased pn junction without dielectric issues, leading to high performance in nanoscale. Two-dimensional MoS2 has shown excellent electronic properties in atomic scale. MoS2 is an n-type semiconductor, therefore JFET based on MoS2 either adopts heterogeneous structure or doping of MoS2 needs to be done. Heterogeneous JFET suffers from lattice mismatching and other interface limitations. Homogeneous JFET with stable doping stands out. Herein, we propose a homogeneous JFET with stable doping by toroidal-magnetic-field controlled nitrogen plasma. The gate-channel pn homojunction in JFET exhibits excellent pn diode rectifying behavior with low reverse current. This JFET shows n-channel characteristics, and by improving contact between electrodes and MoS2, 102 improvement in mobility is demonstrated. The ON/OFF ratio reaches 104 in optimized JFETs.

Type-I Heterostructure Based on WS2/PtS2 for High-Performance Photodetectors.

van der Waals (vdW) heterodiodes composed of two-dimensional (2D) layered materials led to a new prospect in photoelectron diodes and photovoltaic devices. Existing studies have shown that Type-I heterostructures have great potential to be used as photodetectors; however, the tunneling phenomena in Type-I heterostructures have not been fully revealed. Herein, a highly efficient nn+ WS2/PtS2 Type-I vdW heterostructure photodiode is constructed. The device shows an ultrahigh reverse rectification ratio of 105 owing to the transmission barrier-induced low reverse current. A unilateral depletion region is formed on WS2, which inhibits the recombination of carriers at the interface and makes the external quantum efficiency (EQE) of the device reach 67%. Due to the tunneling mechanism of the device, which allows the co-existence of a large photocurrent and a low dark current, this device achieves a light on/off ratio of over 105. In addition, this band design allows the device to maintain a high detectivity of 4.53 × 1010 Jones. Our work provides some new ideas for exploring new high-efficiency photodiodes.

Effect of surface irregularities on diamond Schottky barrier diode with threading dislocations

Pyramidal and flat-type hillocks, both known for having a threading dislocation in the center, are utilized to examine the effect of surface irregularities on the characteristics of Schottky barrier diodes (SBDs). By performing RAMAN mapping on both hillocks, crystalline imperfections in three dimensions with clear strain are observed. Surface scanning images obtained via atomic force microscopy show an extremely large surface protrusion with a maximum height of approximately 15 nm in the pyramidal hillock. Owing to crystalline imperfections in the threading dislocation region, the SBDs fabricated on the dislocations exhibit inferior forward characteristics. However, high reverse leakage currents are only observed in dislocations on pyramidal hillocks with surface protrusions, whereas low reverse currents are observed in the flat hillock region without surface irregularities. The phenomenon above is consistent with the characteristics of wide bandgap semiconductors such as silicon carbide.

Current transport mechanism of AlGaN-channel Schottky barrier diode with extremely low leakage current and high blocking voltage of 2.55 kV

This Letter presents work on lateral AlGaN-channel Schottky barrier diodes (SBDs) with impressive reverse blocking characteristics and low onset voltage (VON). A low reverse current (IR) of 28 nA/mm and low VON of 0.60 V are obtained by utilizing an AlGaN back barrier layer with high Al composition and low work function metal as the anode. The fabricated AlGaN-channel SBD with an anode–cathode distance (LAC) of 30 μm achieves a high blocking voltage of 2.55 kV and a power figure-of-merit of 363 MW/cm2. Meanwhile, the current transport mechanism of AlGaN-channel SBDs goes through thermionic emission, thermionic field emission, and trap-assisted tunneling as the reverse bias is gradually increased. The thermal activation energy (EA) is calculated to be 141.3 meV at high reverse bias. IR at 475 K is only 3 μA/mm, which shows an adequate barrier height for rectifying at high temperature even with low VON. The AlGaN-channel SBDs show great promise for next-generation power electronics with balanced forward and reverse characteristics.

In/CdTe/Au p–n junction-diode X/[formula omitted]-ray detectors formed by frontside laser irradiation doping

The fabricated In/p-CdTe/Au diode structures with Schottky (In/p-CdTe) and quasi-ohmic (Au/p-CdTe) contacts were transformed into p–n junction diodes by applying the developed frontside laser irradiation doping technique. The Schottky diodes with In and Au electrodes (both with thickness of 400 nm), deposited on the chemically pre-treated B- and A-face of the detector-grade CdTe(111) single crystals, respectively, were subjected to multiple (from tens to thousands times) irradiation from the In film side with series of nanosecond pulses of a KrF excimer laser. As a result of such irradiation, a thin heavily doped n-type CdTe:In layer was formed, a shallow abrupt p–n junction was created and thus the In/CdTe/Au Schottky diode was transformed into the In/CdTe/Au p–n junction diode. The temperature distributions in the In/CdTe/Au structure under laser irradiation were calculated and the I–V characteristics of the diodes were measured for different energy densities E and number N of laser pulses, respectively. The processes of frontside laser irradiation doping and carrier charge transport mechanisms in the created In/CdTe/Au p–n junction diodes were discussed. The samples with higher performance were obtained when only a part of the In electrode thickness was melted during a single laser action (E∼110 mJ/cm 2) and repeated (N∼300–500) irradiation was employed. The fabricated In/CdTe/Au p–n junction-diode structures with relative low reverse dark currents (∼20–50 nA/cm2) were quite sensitive to X/γ-rays and demonstrated sufficient ability to detect the emission of 241Am, 57Co, and 137Cs isotopes. It has been shown that applying the frontside laser irradiation doping technique to In/CdTe/Au structures, it is possible to transform Schottky diodes with low characteristics into highly rectifying In/CdTe/Au p–n junction diodes which are X/γ-ray detectors with moderate or even high detection parameters.

Improved device performance of recessed-gate AlGaN/GaN HEMTs by using in-situ N2O radical treatment

The N2O radicals in-situ treatment on gate region has been employed to improve device performance of recessed-gate AlGaN/GaN high-electron-mobility transistors (HEMTs). The samples after gate recess etching were treated by N2O radicals without physical bombardment. After in-situ treatment (IST) processing, the gate leakage currents decreased by more than one order of magnitude compared to the sample without IST. The fabricated HEMTs with the IST process show a low reverse gate current of 10−9 A/mm, high on/off current ratio of 108, and high f T × L g of 13.44 GHz⋅μm. A transmission electron microscope (TEM) imaging illustrates an oxide layer with a thickness of 1.8 nm exists at the AlGaN surface. X-ray photoelectron spectroscopy (XPS) measurement shows that the content of the Al–O and Ga–O bonds elevated after IST, indicating that the Al–N and Ga–N bonds on the AlGaN surface were broken and meanwhile the Al–O and Ga–O bonds formed. The oxide formed by a chemical reaction between radicals and the surface of the AlGaN barrier layer is responsible for improved device characteristics.

Substitutionally Doped MoSe2 for High-Performance Electronics and Optoelectronics.

2D materials, of which the carrier type and concentration are easily tuned, show tremendous superiority in electronic and optoelectronic applications. However, the achievements are still quite far away from practical applications. Much more effort should be made to further improve their performance. Here, p-type MoSe2 is successfully achieved via substitutional doping of Ta atoms, which is confirmed experimentally and theoretically, and outstanding homojunction photodetectors and inverters are fabricated. MoSe2 p-n homojunction device with a low reverse current (300 pA) exhibits a high rectification ratio (104 ). The analysis of dark current reveals the domination of the Shockley-Read-Hall (SRH) and band-to-band tunneling (BTB) current. The homojunction photodetector exhibits a large open-circuit voltage (0.68 V) and short-circuit currents (1 µA), which is suitable for micro-solar cells. Furthermore, it possesses outstanding responsivity (0.28 A W-1 ), large external quantum efficiency (42%), and a high signal-to-noise ratio (≈107 ). Benefiting from the continuous energy band of homojunction, the response speed reaches up to 20 µs. Besides, the Ta-doped MoSe2 inverter exhibits a high voltage gain (34) and low power consumption (127 nW). This work lays a foundation for the practical application of 2D material devices.

G-Doping-Based Metal-Semiconductor Junction

Geometry-induced doping (G-doping) has been realized in semiconductors nanograting layers. G-doping-based p-p(v) junction has been fabricated and demonstrated with extremely low forward voltage and reduced reverse current. The formation mechanism of p-p(v) junction has been proposed. To obtain G-doping, the surfaces of p-type and p+-type silicon substrates were patterned with nanograting indents of depth d = 30 nm. The Ti/Ag contacts were deposited on top of G-doped layers to form metal-semiconductor junctions. The two-probe method has been used to record the I–V characteristics and the four-probe method has been deployed to exclude the contribution of metal-semiconductor interface. The collected data show a considerably lower reverse current in p-type substrates with nanograting pattern. In the case of p+-type substrate, nanograting reduced the reverse current dramatically (by 1–2 orders of magnitude). However, the forward currents are not affected in both substrates. We explained these unusual I–V characteristics with G-doping theory and p-p(v) junction formation mechanism. The decrease of reverse current is explained by the drop of carrier generation rate which resulted from reduced density of quantum states within the G-doped region. Analysis of energy-band diagrams suggested that the magnitude of reverse current reduction depends on the relationship between G-doping depth and depletion width.

Self‐Driven WSe2/Bi2O2Se Van der Waals Heterostructure Photodetectors with High Light On/Off Ratio and Fast Response

AbstractBenefiting from the superior electron mobility and good air‐stability, the emerging layered bismuth oxyselenide (Bi2O2Se) nanosheet has received considerable attention with the promising prospects for electronics and optoelectronics applications. However, the high charge carrier concentration and bolometric effect of Bi2O2Se give rise to the high dark current and relatively slow photoresponse, which severely impede further improvement of the performance of Bi2O2Se based photodetectors. Here, a WSe2/Bi2O2Se Van der Waals p‐n heterostructure is reported with a pronounced rectification ratio of 105 and a low reverse dark current of 10−11 A, as well as an enhanced light on/off ratio up to 618 under 532 nm light illumination. The device also exhibits a fast response speed of 2.6 µs and a broadband detection capability from 365 to 2000 nm due to the efficient charge separation and strong interlayer coupling at the interface of the two flakes. Importantly, the built‐in potential in the WSe2/Bi2O2Se heterostructure offers a competitive self‐powered photodetector with the light on/off ratio above 105 and a photovoltaic responsivity of 284 mA W−1. The WSe2/Bi2O2Se heterostructure shows promising potentials for high‐performance self‐driven photodetector applications.

Enhancing the Diode Characteristics of Pulsed Laser–Deposited n‐MgxZn1−xO/p‐Si Heterojunction: Role of Oxygen Ambient Pressure

Herein, diode characteristics of n‐MgxZn1−xO/p‐Si heterojunctions grown by pulsed laser deposition at different oxygen ambient pressures are investigated. It is found that the heterojunctions grown at lower oxygen growth pressure of 1.0 × 10−2 mbar and below do not show rectifying diode‐like behavior, whereas those grown at higher oxygen pressures at and above 2.5 × 10−2 mbar exhibit perfect diode‐like rectifying characteristics. The diode characteristics are found to improve significantly with increasing oxygen ambient pressure during the growth of MgxZn1−xO film. The current–voltage measurements show that the n‐MgxZn1−xO/p‐Si heterojunction diode grown at a higher oxygen ambient pressure of ≈1.0 × 10−1 mbar has the lowest reverse saturation current of ≈19 nA and highest rectification ratio of ≈1.4 × 104. The capacitance–voltage measurements reveal that the depletion layer width of heterojunction diodes increases manifold with increasing oxygen ambient pressure during the growth of MgxZn1−xO, which is understood in terms of decrease in carrier concentrations in the MgxZn1−xO thin films grown at higher oxygen ambient pressures. The n‐MgxZn1−xO/p‐Si heterojunction diodes, grown at high oxygen ambient pressures, with low reverse saturation current, high rectification ratio, and large depletion width may have potential application in wide‐bandgap nanoelectronic devices and UV enhanced photodetectors.

Electron, Neutron, and Proton Irradiation Effects on SiC Radiation Detectors

Owing to their low dark current, high transparency, high thermal conductivity, and potential radiation hardness, there is a special interest in silicon carbide (SiC) devices for radiation monitoring in radiation harsh environments and with elevated temperatures and, especially, for the plasma diagnostic systems in future nuclear fusion reactors. In this work, four-quadrant p-n junction diodes produced on epitaxial 4H-SiC substrates are studied. The impact of electron, neutron, and proton irradiations (up to fluences of $1 \times 10^{16}$ electrons (e)/cm2, $2 \times 10^{15}$ neutrons (n)/cm2, and $2.5\times 10^{15}$ protons (p)/cm2, respectively) on the electrical characteristics is studied by means of current–voltage ( $I$ – $V$ ) and capacitance–voltage ( $C$ – $V$ ) techniques. Regardless of the particle type and applied fluences, the results show similar low reverse currents for irradiated SiC devices, which are at least about four orders of magnitude lower than comparable Si devices. The effects of irradiation on interquadrant resistance and charge build-up in the interquadrant isolation are assessed. Furthermore, device performance as a radiation detector is investigated upon exposure to a collimated 239Pu–241Am–244Cm tri-alpha source. The performance at room temperature is preserved even for the highest irradiation fluences, despite the fact that the rectification character in electrical characteristics is lost. From the results, advantages of using SiC devices in alpha particle detection in harsh environments can be envisaged.

Crystalline trigonal selenium flakes grown by vapor deposition and its photodetector application

In this study, we discuss the growth of crystalline t-Se flakes by physical vapor deposition and fabrication of micro photodiodes (μPDs). Direct growth of crystalline t-Se flakes on a c-plane sapphire substrate was confirmed by X-ray diffraction, Raman spectroscopy and optical absorption spectroscopy. Schottky and Ohmic contacts between t-Se flakes and the electrode were realized using Ti and Au, respectively. For Ohmic characteristics, anomalous transport on an anisotropic crystal structure was observed. The t-Se based Schottky barrier diode (SBD) consisting of Ti and Au electrodes with low reverse saturation current was fabricated. The ideality factor n and the Schottky barrier height ΦB were estimated to be approximately 1.4 and 0.66 eV, respectively. A high responsivity of 0.717 A/W and quantum efficiency of 137% were observed at Vbias = −3 V under irradiation of various powers of red-LED (650 nm), indicating the good performance of μPD for monitoring the red and visible light color.

Low frequency noise in reverse biased double heterostructure P-InAsSbP/n-InAs infrared photodiodes

Low frequency reverse current noise is studied for the first time in InAsSbP/InAs double heterostructure (DH) photodiodes in the frequency range 1 Hz–104 Hz at 300 K and 100 K. At room temperature, the noise in the DH photodiodes is 1/f and might be significantly lower (by ∼17 dB) than in single heterostructure InAsSbP/InAs photodiodes. In the practically most important regime of low reverse currents, Irb, the current dependence of spectral noise density is proportional to , both at 300 K and 100 K. The reverse current noise might provide the limit for the detectivity of DH photodiodes at Irb > 3 × 10−6 A at 300 K and Irb > 8 × 10−9 A at 100 K.

GaAs diode structures with n+-p junction on Ge/Si templates

GaAs layers were grown by metalorganic epitaxy on Ge/Si(001) substrates, which were formed by chemical vapor deposition with decomposition of GeH4 on a hot wire. High structural quality of thin Ge layers (0.2 - 0.3 μm) on a silicon substrate made it possible to grow high-quality GaAs layers. The resulting n+-GaAs/p-GaAs/p-Ge/p+-Si diode structures demonstrate low reverse currents.

The Influence of Anode Trench Geometries on Electrical Properties of AlGaN/GaN Schottky Barrier Diodes

AlGaN/GaN lateral Schottky barrier diodes (SBDs) with three different anode geometries (stripe, circular, and the conventional plane one) and different rows of anode trenches are fabricated and electrically characterized to study the influence of anode trench geometries. The SBDs with anode trenches exhibit the lower on-state resistance (RON) than that with the conventional plane one. It can be explained that the anode trenches made the Schottky metal directly contact to the 2DEG at the sidewall of the AlGaN/GaN interface, removing the AlGaN barrier layer in the conventional plane anode. In addition, the RON of the SBDs with circular trenches is smaller than that of the SBDs with stripe ones. Furthermore, the RON decreases with the increasing rows of anode trenches, which can be attributed to the increased contact area between the Schottky metal and the 2DEG. For the reverse characteristics, the anode trenches do not lead to performance degradation. The fabricated devices exhibit the low reverse current (IR, IR &lt; 1 μA/mm), and the breakdown voltage (VBK) remains unchanged with different anode geometries.

G-doping based nanostructured p-p(v) junction

Geometry-induced quantum effects were recently introduced and observed in periodic nanostructures. Experiments with nanostructured layers confirm dramatic changes in electronic and optical properties. Silicon nanograting layers demonstrated geometry induced doping or G-doping (n-type). Here, fabrication and characterization of G-doped junctions is reported. A junction is formed in p-Si substrate by introducing G-doping into the thin surface layer. The G-doping level is relatively low, and the obtained junction is formed between a p-type substrate and a partially compensated thin surface layer (p–p−). The obtained I–V curves are diode type with extremely low voltage drop in the forward direction and low reverse current. Experimental I–V curves are fitted to the Shockley equation and the ideality factor is found to be in the range of 0.2–0.14. Such a low value confirms that the junction is fundamentally different from the conventional p-n junction. This difference is ascribed to G-doping, which seems to be external voltage-dependent. The p–p(v) abbreviation is introduced to emphasize this voltage dependence of G-doping level.

TiO2 Nanorod Arrays Based Self-Powered UV Photodetector: Heterojunction with NiO Nanoflakes and Enhanced UV Photoresponse.

The self-powered ultraviolet photodetectors (UV PDs) have attracted increasing attention due to their potential applications without consuming any external power. It is important to obtain the high-performance self-powered UV PDs by a simple method for the practical application. Herein, TiO2 nanorod arrays (NRs) were synthesized by hydrothermal method, which were integrated with p-type NiO nanoflakes to realize a high performance pn heterojunction for the efficient UV photodetection. TiO x thin film can improve the morphological and carrier transport properties of TiO2 NRs and decrease the surface and defect states, resulting in the enhanced photocurrent of the devices. NiO/TiO2 nanostructural heterojunctions show excellent rectifying characteristics (rectification ratio of 2.52 × 104 and 1.45 × 105 for NiO/TiO2 NRs and NiO/TiO2 NRs/TiO x, respectively) with a very low reverse saturation current. The PDs based on the heterojunctions exhibit good spectral selectivity, high photoresponsivity, and fast response and recovery speeds without external applied bias under the weak light radiation. The devices demonstrate good stability and repeatability under UV light radiation. The self-powered performance could be attributed to the proper built-in electric field of the heterojunction. TiO2 NRs and NiO nanoflakes construct the well-aligned energy-band structure. The enhanced responsivity and detectivity for the devices with TiO x thin films is related to the increased interfacial charge separation efficiency, reduced carrier recombination, and relatively good electron transport of TiO2 NRs.