Low Reverse Saturation Current Research Articles

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.

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.

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.

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.

Performance analysis of undoped and Mg-doped ZnO/p-Si heterojunction diodes grown by sol–gel technique

This paper reports the comprehensive analysis on the effect of Mg doping on structural, optical and electrical characteristics of MgxZn1−xO/p-Si heterojunction diodes. In this work, undoped and Mg-doped ZnO thin films were directly synthesized on p-Si (silicon) substrate using sol–gel spin coating method. The structural and optical properties of as-fabricated thin films are analyzed by means of XRD, AFM, SEM, ellipsometer and Photoluminescence spectroscopy. The as-grown films are having polycrystalline nature with preferred growth orientation along (002) direction. Although, no peaks due to Mg doping is exhibited in 5% Mg-doped ZnO thin films, however, due to phase segregation, the additional peaks of MgO phase at (200) and (220) direction has started visible for higher Mg-doped ZnO films. The Grain size of the films is diminished from 42.51 to 28.35 nm for Mg-doping increment from 0 to 15%, where as bandgap of the films is increased from 3.27 to 3.83 eV for same doping variation. Electrical parameters of MgxZn1−xO/p-Si heterojunction diodes are studied after forming large area ohmic contacts of Al/Ti and Al on top of ZnO thin film and bottom of Si layer respectively. The significant electrical parameters of the diodes are calculated from current–voltage characteristics measured by semiconductor parameter analyzer and capacitance–voltage characteristics measured by LCR meter. With very high rectification ratio of 41741 and low reverse saturation current of 1.52 nA, Mg0.1Zn0.9O/Si heterojunction diode has potential to be used in future nanoelectronic devices with wider bandgap.

Growth of a lattice-matched GaAsPN p–i–n junction on a Si substrate for monolithic III–V/Si tandem solar cells

A p–i–n GaAs0.75P0.19N0.06 structure lattice-matched to Si was realized on a 2-in. Si (001) substrate for monolithic tandem solar cells. The sample structure had mirror-like surfaces without any indication of pinholes or microcracks. X-ray diffraction results showed that all the layers were coherently grown on the Si substrate. Transmission electron microscopy results evidently showed that a dislocation-free device structure was grown on the Si substrate. Finally, current–voltage characteristics showed rectifying properties with low reverse saturation current, which was indicative of the high crystallinity of the device layer.

Carbon nanotube intramolecular p-i-n junction diodes with symmetric and asymmetric contacts

A p-i-n junction diode based on the selectively doped single-walled carbon nanotube (SWCNT) had been investigated, in which two opposite ends of individual SWCNT channel were doped into the p- and n-type SWCNT respectively while the middle segment of SWCNT was kept as the intrinsic. The symmetric and asymmetric contacts were used to fabricate the p-i-n junction diodes respectively and studied the effect of the contact on the device characteristics. It was shown that a low reverse saturation current of ~20 pA could be achieved by these both diodes. We found that the use of the asymmetric contact can effectively improve the performance of the p-i-n diode, with the rectification ratio enhanced from ~102 for the device with the Au/Au symmetric contact to >103 for the one with the Pd/Al asymmetric contact. The improvement of the device performance by the asymmetric-contact structure was attributed to the decrease of the effective Schottky-barrier height at the contacts under forward bias, increasing the forward current of the diode. The p-i-n diode with asymmetric contact also had a higher rectification ratio than its counterpart before doping the SWCNT channel, which is because that the p-i-n junction in the device decreased the reverse saturated current.

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.

ITO 나노와이어 기반의 투명 산화물 반도체 광전소자

Photoelectric and Energy Device Application Lab (PEDAL), Department of Electrical Engineering, Incheon National University, Incheon 22012, Korea(Received October 18, 2015; Accepted November 4, 2015)Abstract: Highly optical transparent photoelectric devices were realized by using a transparent metal-oxide semiconductor heterojunction of p-type NiO and n-type ZnO. A functional template of ITO nanowires (NWs) was applied to this transparent heterojunction device to enlarge the light-reactive surface. The ITO NWs/n-ZnO/p-NiO heterojunction device provided a significant high rectification ratio of 275 with a considerably low reverse saturation current of 0.2 nA. The optical transparency was about 80% for visible wavelengths, however showed an excellent blocking UV light. The nanostructured transparent heterojunction devices were applied for UV photodetectors to show ultra fast photoresponses with a rise time of 8.3 mS and a fall time of 20 ms, respectively. We suggest this transparent and super-performing UV responser can practically applied in transparent electronics and smart window applications. Keywords: Transparent photoelectric devices, ITO nanowires, NiO, ZnO, Heterojunction*+,- 금속과 산소의 이온결합으로 이루어지는 금속 산화물 반도체 (metal-oxide semiconductor)는 전기전도성이 우수하고 가시광영역의 투과성이 높기 때문에, 다양한 분야에서 활발한 연구가 진행 중이다. 대부분의 산화물 반도체는 높은 전자 이동도 (>10 ㎠/Vs)를 나타내기 때문에 전자 이동도를 높이기 위한 별도의 도

Fabrication of an efficient GLAD-assisted p-NiO nanorod/n-ZnO thin film heterojunction UV photodiode

The glancing angle deposition (GLAD) configuration in RF magnetron sputtering has been utilized to deposit p-type NiO nanorods, which are integrated with n-type ZnO thin film to realize a high performance p–n heterojunction diode for the efficient detection of UV photoradiation. The fabricated nano p-NiO/n-ZnO heterojunction shows excellent rectifying characteristics (rectification ratio ∼ 4 × 103) with a very low reverse saturation current (∼10−10 A). The heterojunction photodiode exhibits a high current gain (3.71 × 103), high photoresponsivity (3.24 × 105 A W−1), with a relatively fast response (∼200 ms) and recovery speed (∼25 ms) towards a very low UV intensity of 0.62 μW cm−2 (λ = 300 nm). Recombination tunneling and space-charge limited current are the probable conduction mechanisms at low and high applied voltages respectively for the fabricated heterojunction diode. The observed high response speed and excellent responsivity of the diode towards deep-UV (λ = 300 nm) radiation might lead to potential military applications such as missile tracking, in addition to optical communications.

Heterojunction photodiode fabricated from hydrogen treated ZnO nanowires grown on p-silicon substrate

A heterojunction photodiode was fabricated from ZnO nanowires (NWs) grown on a p-type Si (100) substrate using a hydrothermal method. Post growth hydrogen treatment was used to improve the conductivity of the ZnO NWs. The heterojunction photodiode showed diode characteristics with low reverse saturation current (5.58 × 10(-7) A), relatively fast transient response, and high responsivity (22 A/W at 363 nm). Experiments show that the photoresponsivity of the photodiode is dependent on the polarity of the voltages. The photoresponsivity of the device was discussed in terms of the band diagrams of the heterojunction and the carrier diffusion process.

Tuning electrical properties of transparent p-NiO/n-MgZnO heterojunctions with band gap engineering of MgZnO

Transparent p-n heterojunctions composed of p-type NiO and n-type MgZnO thin films were fabricated on indium-tin-oxide-coated glass substrates by sol-gel spin coating technique. The p-n junctions exhibit typical current-voltage behaviors with good rectifying characteristics, and their electrical properties can be effectively tuned by band gap engineering of n-MgZnO. With increment of Mg content in n-MgZnO layer, enlarging band gap can lead to the higher forward threshold voltage, higher breakdown voltage, and lower reverse saturation current. The electrical behaviors of the p-n junctions can be further improved by using compositionally graded n-MgZnO layer instead of single n-MgZnO layer. These results suggest that the transparent all-oxide p-NiO/n-MgZnO heterojunctions can find applications in transparent electronic devices.

Pulsed-laser diffusion of n + contacts and n +-p junctions in high purity germanium for nuclear radiation detectors

We report fabrication of thin (< 1 μm) n + contacts, and of n +−p junctions with very low reverse saturation current, on high purity germanium, using a pulsed laser process that requires no heating of the bulk germanium. The junctions appear to be suitable for use in commercial nuclear radiation detectors.

Effect of thermal etching on silicon epitaxial growth by vacuum sublimation

Silicon epitaxial growth by vacuum sublimation was studied with emphasis on the effect of thermal etch of the substrate on the surface concentration of carbon. A calculation of surface concentration of carbon on a Si substrate during thermal etch in the vacuum system shows that prolonged thermal etch at a higher temperature progressively enhances a pile-up of involatile impurity on the substrate surface and formation of precipitates above solid solubility limits, which would cause generation of interfacial defects. This effect was experimentally confirmed with various temperatures and periods of thermal etch and with the use of LOPEX material. Experimentally optimized temperature and period of thermal etch with the use of LOPEX Si yielded a good quality epitaxial P/ N junction; low defect density 0–100 over the area of 10 −4 cm −2, low reverse saturation current of less than 1 × 10 −4 A/ cm 2 at half of breakdown voltage of 90 V. Uniformity of multiplication factor M over the reverse biased P/ N junction was measured with a laser probe. The variation around the average value over the area of a mesa junction structure 600 μm diam. was less than 10 per cent. Static I– V characteristics of PN junction, Schottky barrier NN + diodes and P + NN + diodes fabricated from grown layers by vacuum sublimation were also demonstrated.