Rectifying Current Voltage Characteristics Research Articles

Tunable Quantum Tunneling through a Graphene/Bi2Se3 Heterointerface for the Hybrid Photodetection Mechanism.

Graphene-based van der Waals heterostructures are promising building blocks for broadband photodetection because of the gapless nature of graphene. However, their performance is mostly limited by the inevitable trade-off between low dark current and photocurrent generation. Here, we demonstrate a hybrid photodetection mode based on the photogating effect coupled with the photovoltaic effect via tunable quantum tunneling through the unique graphene/Bi2Se3 heterointerface. The tunneling junction formed between the semimetallic graphene and the topologically insulating Bi2Se3 exhibits asymmetric rectifying and hysteretic current–voltage characteristics, which significantly suppresses the dark current and enhances the photocurrent. The photocurrent-to-dark current ratio increases by about a factor of 10 with the electrical tuning of tunneling resistance for efficient light detection covering the major photonic spectral band from the visible to the mid-infrared ranges. Our findings provide a novel concept of using tunable quantum tunneling for highly sensitive broadband photodetection in mixed-dimensional van der Waals heterostructures.

Work function modulation of electrodes contacted to molybdenum disulfide using an attached metal pad

The transport properties of electronic devices fabricated using two-dimensional materials are severely affected by the Schottky barrier at the contact of an electrode. The Schottky barrier height exhibits a strong correlation with the work function of the electrode. We observed rectifying current–voltage characteristics for a back-gated field effect transistor with a channel of molybdenum disulfide and Al electrodes, where one of the electrodes is attached to a Au pad. This result is explained in terms of the increase in the effective work function of the Al electrode attached to the Au pad. The dependence of a photocurrent on the bias voltage exhibited an opposite tendency to the current–voltage characteristics; this is also attributed to the work function modulation of the electrode, thus resulting in the variation in the Schottky barrier height.

Effect of Bias on the Response of GaN Axial p-n Junction Single-Nanowire Photodetectors.

We present a comprehensive study of the performance of GaN single-nanowire photodetectors containing an axial p-n junction. The electrical contact to the p region of the diode is made by including a p+/n+ tunnel junction as cap structure, which allows the use of the same metal scheme to contact both ends of the nanowire. Single-nanowire devices present the rectifying current-voltage characteristic of a p-n diode but their photovoltaic response to ultraviolet radiation scales sublinearly with the incident optical power. This behavior is attributed to the dominant role of surface states. Nevertheless, when the junction is reverse biased, the role of the surface becomes negligible in comparison to the drift of photogenerated carriers in the depletion region. Therefore, the responsivity increases by about 3 orders of magnitude and the photocurrent scales linearly with the excitation. These reverse-biased nanowires display decay times in the range of ∼10 μs, limited by the resistor-capacitor time constant of the setup. Their ultraviolet/visible contrast of several orders of magnitude is suitable for applications requiring high spectral selectivity. When the junction is forward biased, the device behaves as a GaN photoconductor with an increase of the responsivity at the price of a degradation of the time response. The presence of leakage current in some of the wires can be modeled as a shunt resistance which reacts to the radiation as a photoconductor and can dominate the response of the wire even under reverse bias.

Temperature dependent electrical characteristics of rectifying graphitic contacts to p-type silicon

Graphitic contacts to semiconductors have been shown to provide highly rectifying current–voltage characteristics coupled with high thermal/chemical stability. Energetically deposited graphitic contacts to p-type Si have exhibited rectification ratios (at ±1.0 V) up to 106:1 and ideality factors approaching unity. Here, we report temperature dependent current–voltage (I–V–T) measurements performed on such devices. The measurements and subsequent analysis show that during energetic carbon deposition, deleterious oxide/contaminants are removed from the Si substrate surface. The Richardson constant of the p-type Si extracted from the I–V–T measurements agrees with the theoretical value, indicating that the surface contaminants are removed without significant damage to the underlying Si. Therefore, by energetic deposition of C on Si, C–Si junctions can be formed with low lateral inhomogeneity and low interface defect density. These attributes of the junctions enable the observed near-ideal Schottky diode characteristics.

Deep-ultraviolet photodetector based on exfoliated n-type β-Ga2O3 nanobelt/p-Si substrate heterojunction

Low-dimensional semiconductor p-n junctions as components for optoelectronic devices are considered to be more promising than thin film equivalents. We fabricated heterojunction p-n solar blind photodiodes with the configuration of n-type β-Ga2O3 nanobelts contacted onto p-Si substrates. The junction between β-Ga2O3 and Si was formed by van der Waals interactions. The fabricated heterojunction p-n diodes exhibited typical rectifying current–voltage characteristics, with a rectification ratio as high as 1.56×104 at ±20 V and an ideality factor of approximately eight. Photoresponsive measurements showed that the heterojunction p-n diodes had a high sensitivity and selectivity for light at a wavelength of 254 nm, with fast response and decay characteristics. For the fast-response components, the response time constant was 4.06 s and the decay time constant was 0.16 s. The exfoliated β-Ga2O3 nanobelt/Si p-n heterojunction presented here constitutes a functional unit for low-dimensional ultra-wide bandgap electronic and optoelectronic devices.

Ohmic contacts on n-type β-Ga2O3 using AZO/Ti/Au

AZO interlayers between n-Ga2O3 and Ti/Au metallization significantly enhance Ohmic contact formation after annealing at ≥ 300°C. Without the presence of the AZO, similar anneals produce only rectifying current-voltage characteristics. Transmission Line Measurements of the Au/Ti/AZO/Ga2O3 stacks showed the specific contact resistance and transfer resistance decreased sharply from as-deposited values with annealing. The minimum contact resistance and specific contact resistance of 0.42 Ω-mm and 2.82 × 10-5 Ω-cm2 were achieved after a relatively low temperature 400°C annealing. The conduction band offset between AZO and Ga2O3 is 0.79 eV and provides a favorable pathway for improved electron transport across this interface.

Near infrared electroluminescence from p-NiO/n-InN/n-GaN light-emitting diode fabricated by PAMBE

Near infrared light-emitting diode (LED) based on p-NiO/n-InN/n-GaN was realized by plasma-assisted molecular beam epitaxy (PAMBE) combined with radio frequency (rf) magnetron sputtering. The device exhibited diode-like rectifying current–voltage characteristics with a turn-on voltage of 1.0V. Under forward bias, prominent near infrared (NIR) emissions were observed at peak around 1570nm at room temperature. The NIR emission was ascribed to the band-edge emission of InN epilayer based on the photoluminescence spectrum and band diagram of the heterojunction. Moreover, the study of the LED in terms of the stability was also discussed.

Incorporation of black phosphorus into P3HT:PCBM/n-type Si devices resulting in improvement in electrical and optoelectronic performances

The effect of the incorporation of black phosphorus (BP) into poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) on the electrical conduction mechanisms in the rectifying current–voltage characteristics of P3HT:PCBM/n-type Si devices was investigated. It is found that the forward-voltage currents are limited by thermionic emission mechanism. The incorporation of BP into P3HT:PCBM leads to a combined effect of a reduction in resistivity and an increase in the surface roughness, resulting in improvement in the electrical and optoelectronic performances of P3HT:PCBM/n-type Si devices. The findings show that high responsivity originates from the external light injection efficiency, internal power conversion efficiency, and carrier collection.

All-oxide p–n heterojunction diodes comprising p-type NiO and n-type β-Ga2O3

NiO/β-Ga2O3 all-oxide p–n heterojunction diodes were fabricated for the first time using p-type NiO epitaxial layers grown on n-type β-Ga2O3 substrates. The fabricated diodes exhibited good rectifying current–voltage characteristics, with a rectifying ratio greater than 108 at ±3 V. The capacitance–voltage measurements showed that the built-in voltage was 1.4 V. These results were discussed in terms of the energy band diagram of a type-II heterojunction, where the conduction band and valence band discontinuities were estimated to be 2.2 and 3.4 eV, respectively.

Incorporation of black phosphorus into poly(3-hexylthiophene)/n-type Si devices resulting improvement in rectifying and optoelectronic performances

The effect of the incorporation of black phosphorus (BP) into poly(3-hexylthiophene) (P3HT) on the electrical conduction mechanisms in the rectifying current-voltage characteristics of P3HT/n-type Si devices was investigated. It is shown that the rectifying behavior is affected by the bulk effects of the P3HT layer and the forward-voltage current is limited by thermionic emission and space charge limited current mechanisms. The incorporation of BP into P3HT leads to a combined effect of a significant increase in the hole mobility and the interfacial modification of P3HT/n-type Si, resulting improvement in the rectifying and optoelectronic performances of P3HT/n-type Si devices.

Realization of nitride–oxide based p–n heterojunctions with the n-VO2/p-GaN/sapphire structure

The nitride–oxide based p–n heterojunctions with the n-VO2/p-GaN/sapphire structure was realized by sputtering deposition of VO2 films on p-GaN/sapphire substrates. The structure and electrical properties of the as-grown VO2/p-GaN/sapphire heterostructure were investigated systematically. The distinct reversible semiconductor-to-metal transition (SMT) with resistance change up to nearly two orders of magnitude was observed for the sample deposited at the optimized conditions. Moreover, the clear rectifying current–voltage characteristics originated from the n-VO2/p-GaN interface were demonstrated both before and after SMT of VO2 over layer, which were attributed to the p–n junction behavior and Schottky contact character, respectively. Our present finding demonstrated the feasibility of integrating correlated oxide and wide bandgap nitride semiconductors, and will further motivate research in novel devices with combined functional properties of both kinds of materials.

Near infrared light-emitting diodes based on n-InN/p-NiO/p-Si heterojunction

We fabricated the light-emitting diodes (LEDs) consisting of n-InN/p-NiO/p-Si heterostructure by using plasma-assisted molecular beam epitaxy (PAMBE) combined with radio frequency (RF) magnetron sputtering. The device exhibited diode-like rectifying current–voltage characteristics and had a turn-on voltage of 2.0V. Under forward bias, a prominent narrow near infrared (NIR) emission peaked around 1565nm was observed at room temperature. The NIR emission was demonstrated to come from the band-edge emission of InN layer. Moreover, the study of the LED in terms of the stability and efficiency were also discussed in detail.

Ultraviolet emission from low resistance Cu2SnS3/SnO2 and CuInS2/Sn:In2O3 nanowires

SnO2 and Sn:In2O3 nanowires were grown on Si(001), and p-n junctions were fabricated in contact with p-type Cu2S which exhibited rectifying current–voltage characteristics. Core-shell Cu2SnS3/SnO2 and CuInS2/Sn:In2O3 nanowires were obtained by depositing copper and post-growth processing under H2S between 100 and 500 °C. These consist mainly of tetragonal rutile SnO2 and cubic bixbyite In2O3. We observe photoluminescence at 3.65 eV corresponding to band edge emission from SnO2 quantum dots in the Cu2SnS3/SnO2 nanowires due to electrostatic confinement. The Cu2SnS3/SnO2 nanowires assemblies had resistances of 100 Ω similar to CuInS2/In2O3 nanowires which exhibited photoluminescence at 3.0 eV.

Study on the electroluminescence properties of diodes based on n-ZnO/p-NiO/p-Si heterojunction

We fabricated the light-emitting diodes (LEDs) consisting of n-ZnO/p-NiO/p-Si heterostructure by using metal-organic chemical vapor deposition (MOCVD) combined with radio frequency (RF) magnetron sputtering. The devices exhibited diode-like rectifying current–voltage characteristics and had a turn-on voltage of 6.8V. Under forward bias, a prominent broad emission peaked around 400–650nm was observed at room temperature. The asymmetric electroluminescence (EL) spectra were consisted of two apparent bands, which located at 420 and 495nm corresponding to the violet and green luminescence, respectively. Furthermore, the mechanism of the light emission was tentatively discussed in terms of the band diagrams of the heterojunction.

Ultraviolet electroluminescence from n-ZnO/NiO/p-GaN light-emitting diode fabricated by MOCVD

Ultraviolet light-emitting diodes (LED) based on n-ZnO/NiO/p-GaN were realized by metal-organic chemical vapor deposition (MOCVD). The devices exhibited diode-like rectifying current–voltage characteristics and had a turn-on voltage of 7.5V. High quality NiO film as an electron blocking layer inserted between the ZnO and GaN films showed high resistance state with preferred [111] orientation, which produced a larger ZnO/NiO conduction band offset of 2.93eV than that of ZnO/GaN (0.15eV). The electroluminescence spectra of the n-ZnO/i-NiO/p-GaN heterostructure demonstrated that electrons were effectively confined in the ZnO active region, and thus leading to the enhancement of the excitonic emission from the ZnO side.

Resistive switching artificially induced in a dielectric/ferroelectric composite diode

Ferroelectric resistive switching was artificially induced in a conductive ferroelectric capacitor by inserting a thin dielectric layer at an electrode/ferroelectric interface. Ferroelectric capacitors consisting of semiconducting Bi-deficient Bi1−δFeO3 layers with SrRuO3 electrodes showed no resistive switching, but resistive switching emerged in these ferroelectric capacitors when a thin LaFeO3 dielectric layer was inserted at one of the SrRuO3/Bi1−δFeO3 interfaces. In addition to resistive switching, SrRuO3/LaFeO3/Bi1−δFeO3/SrRuO3 devices showed rectifying current–voltage characteristics, suggesting an asymmetric potential distribution along the stacking direction in the device. The results shed light upon the mechanism of resistive switching in ferroelectric diodes and demonstrate that interface engineering provides a simple but effective approach toward controlling the ferroelectric resistive switching characteristics.

Fermi level shift in La2−xSrxCuO4 probed by heteroepitaxial junctions with Nb-doped SrTiO3

We investigated Fermi-level shifts with carrier doping in La2−xSrxCuO4 (LSCO) (x = 0–0.35) by using heteroepitaxial junctions with Nb–doped SrTiO3. The junctions showed highly rectifying current–voltage characteristics, in accord with the conventional theory of a Schottky or p-n diode. For x = 0–0.20, the built-in potential increased with increase of x, indicating the downward shift of the Fermi-level in La2−xSrxCuO4. The Fermi-level shift however reversed to upward at x ∼ 0.20. This behavior is related to the electronic-structure change, which is characterized by the reversal of dominant carrier type from hole to electron in overdoped La2−xSrxCuO4 confirmed by Hall measurements.

Transparent conductive p-type lithium-doped nickel oxide thin films deposited by pulsed plasma deposition

Transparent p-type Li0.25Ni0.75O conductive thin films were prepared on conventional glass substrates by pulsed plasma deposition. The effects of substrate temperature and oxygen pressure on structural, electrical and optical properties of the films were investigated. The electrical resistivity decreases initially and increases subsequently as the substrate temperature increases. As the oxygen pressure increases, the electrical resistivity decreases monotonically. The possible physical mechanism was discussed. And a hetero p–n junction of p-Li0.25Ni0.75O/n-SnO2:W was fabricated by depositing n-SnO2:W on top of the p-Li0.25Ni0.75O, which exhibits typical rectifying current–voltage characteristics.

Green electroluminescence from an n-ZnO: Er/p-Si heterostructured light-emitting diode

Erbium-doped ZnO (ZnO:Er) thin films with various doping concentrations were deposited on p-Si substrates by ultrasonic spray pyrolysis (USP). The n-ZnO:Er/p-Si heterojunctions were further employed to fabricate light-emitting diodes (LEDs). The devices showed diode-like rectifying current–voltage characteristics with a low reverse breakdown voltage, attributed to the avalanche breakdown. A distinct green electroluminescence peaking at 537nm and 558nm were observed at room temperature under reverse bias. The green electroluminescence originated from the electron impact excitation of Er3+ ions doped in ZnO films.

Chemical bath deposition of ZnO and Ni doped ZnO nanorod

The investigation explores the structural, electric and magnetic characteristics of ZnO and Ni:ZnO nanorods fabricatied via a chemical bath deposition. Vertically aligned ZnO and Ni:ZnO nanorods arrays were grown on sapphire substrate. Interestingly, SEM results reveal a variation of aspect ratio between ZnO and Ni:ZnO nanorods. XRD, XPS and XAS analyses demostrate a good incorporation of Ni dopants in ZnO nanorods. Furthermore, the ZnO nanorod/p-type Si heterojunction displayed rectifying current–voltage characteristic of a pristine p–n junction diode and light emission under forward bias.