Backward Diodes Research Articles

Wet etch methods to achieve submicron active area self-aligned vertical Sb-heterostructure backward diodes

Sb-heterostructure backward diodes are attractive for passive millimeter-wave sensing techniques in Earth Observation applications, facilitating superior sensitivity (non-linearity) and low noise as compared to traditional zero-bias Schottky diodes. Reducing diode active area is imperative to achieve both increased sensitivity and operation at higher frequencies. In this work, we report a wet etch method utilizing citric acid, phosphoric acid, and hydrogen peroxide for simplified fabrication of vertical (250 nm height) Sb-heterostructure (InAs/AlSb/AlGaSb/GaSb) devices down to active area of 0.04 μm2 (critical dimensions 0.2 × 0.2 μm2). While conventional citric/peroxide etch chemistries are ineffective for removal of Sb-based etch products, including Sb2O5, the addition of phosphoric acid has shown to promote dissolution of etch stop layers, maintaining a linear etch rate throughout the device heterostructure. Furthermore, we found that citric acid plays a crucial role in the underlying etch mechanism which can be attributed to the formation of soluble Sb(V)-citrate complexes. Conducting the etching at reduced temperatures has also shown to promote slow-etching facets at reduced etch temperature (4 °C) drastically improving anisotropy. Finally, the etch method is evaluated by current-voltage characterization of the fabricated diodes achieving predictible active area scaling of performance-metrics across 190 devices indicating formation of defect free sidewalls.

High-temperature optoelectronic transport behavior of n-MoS2 nanosheets/p-diamond heterojunction

In the past decades, even though the performance of electronic devices based on MoS2 has reached a very high level, the service life, failure rate and stability of the devices often deteriorate with the increase of temperature when they work in high temperature or harsh environment. In this work, n-MoS2 NSs/p-type boron-doped diamond (BDD) film heterojunction was fabricated by sol–gel method to investigate the temperature dependence of the optoelectronic transport behavior of the device, and the electrical properties of the heterojunction device at high temperature (RT-180 °C) were tested. The heterojunction presented all rectification characteristics from room temperature to 180 °C and exhibited good thermal stability. With the increase in temperature, the rectification ratio reached the maximum at 120 °C and turned into backward diodes at 160 °C and 180 °C. The mechanism of the current and rectification ratio of n-MoS2 NSs/p-BDD heterojunction changing with temperature was mainly attributed to the decrease of tunneling current caused by the shift of Fermi level of the two semiconductors at high temperature. The heterojunction undergoes a transition from tunneling current to thermal excitation current, and the shift of Fermi level to the valence band of n-MoS2 provides support for the transition to reverse diode. In accordance with the carrier transport behavior following ohmic laws, the current conduction of composite tunneling and the space charge limitation under different bias voltages and temperatures were also discussed, which provides theoretical and experimental basis for optimizing the design of new photoelectric devices in the field of high temperature optoelectronics.

Van der Waals heterostructure of Bi2O2Se/MoTe2 for high-performance multifunctional devices

Two-dimensional van der Waals heterostructures exhibit distinctive electronic and optoelectronic properties, making them promising structures for constructing advanced multifunctional devices. However, devices based on conventional charge-carrier transport mechanisms often perform only a single function, which limits its integration and performance. Here, we present a vertical van der Waals heterostructure made of Bi2O2Se and MoTe2, allowing it to act as high-performance backward diode, forward diode, photodetector and photovoltaic device at various working conditions. The applications are enabled by band-alignment switching between p–n heterostructure controlled by minority carrier diffusion and n–n heterostructure governed by the thermionic emission and tunneling-mediated processes. As a backward diode, the device displays a high reverse rectification ratio of 5.0 × 104. As a photodetector, the device demonstrates a broad spectral photoresponse ranging from ultraviolet (365 nm) to near-infrared (1050 nm). When irradiated by 532 nm laser, the photodetector shows a responsivity of up to 11.6 A/W and achieves quick response/recovery speed of 19.6/8.8 μs. As a photovoltaics device, an external quantum efficiency of 78% and a responsivity of 0.33 A/W are observed. This study showcases the potential for high-performance multifunctional devices utilizing Bi2O2Se/MoTe2 heterostructures and provides comprehensive insights into the designed band alignment and its applications.

Polarization-Resolved THz Imaging With Orthogonal Heterostructure Backward Diode Detectors

A fully integrated lens-coupled dual-polarization detector for imaging was designed, fabricated, and characterized in the terahertz (THz) region. Two zero-bias heterostructure backward diodes (HBDs) were monolithically integrated into a planar dual-polarization annular-slot antenna. An impedance matching network consisting of an interdigitated DC block and shorted stubs was implemented for maximum power transfer. The fabricated chip was then mounted on an extended hemispherical silicon lens for high antenna efficiency. The performance of the integrated detector has been characterized at 200 GHz. The detector module can simultaneously measure the two orthogonal linear polarized components of the incident THz waves, and hence obtain the polarization direction. On the basis of this polarimetric detection, polarization-resolved imaging of a Gaussian beam, as well as birefringent samples, was performed using the integrated detectors. The angular resolution of the polarization detection has been demonstrated to be as small as 3°. The single-pixel detector demonstrated here is amenable to array applications for THz focal-plane arrays that will have a significant impact on a wide range of remote sensing, though-barrier imaging, and detection/identification applications.

Temperature dependent transport characteristics of La0.9Sr0.1MnO3 / SrNb0.002Ti0.998O3 device

We report detailed investigations on device functioning capabilities of La0.9Sr0.1MnO3 (LSMO) manganite thin film fabricated on SrNb0.002Ti0.998O3 (SNTO) substrate. The LSMO / SNTO structure has been verified using XRD ϕ–scan measurement. We interpret the device capabilities by investigating the temperature dependent current–voltage (I–V) characteristics. To understand the linearity – nonlinearity nature and temperature effect, current ratio for specific voltages has been identified. Logarithmic scale variation in forward bias current with applied voltages has been studied at different temperatures. For the identification of backward diode behaviour possibility, I–V characteristics at typical temperatures have been studied for forward and reverse currents, simultaneously. The theoretical model fits supporting conduction mechanism in the device understudy has also been investigated for the typical I–V characteristics. The field effect configuration based variation in junction resistance of LSMO / SNTO structure with temperature under applied different junction electric fields and temperature dependent variation in electroresistance (ER) have been recorded to interpret the conduction processes undergoing in the device understudy.

Design and Optimization of a Self-Protected Thin Film c-Si Solar Cell against Reverse Bias

Current mismatch due to solar cell failure or partial shading of solar panels may cause a reverse biasing of solar cells inside a photovoltaic (PV) module. The reverse-biased cells consume power instead of generating it, resulting in hot spots. To protect the solar cell against the reverse current, we introduce a novel design of a self-protected thin-film crystalline silicon (c-Si) solar cell using TCAD simulation. The proposed device achieves two distinct functions where it acts as a regular solar cell at forward bias while it performs as a backward diode upon reverse biasing. The ON-state voltage (VON) of the backward equivalent diode is found to be 0.062 V, which is lower than the value for the Schottky diode usually used as a protective element in a string of solar cells. Furthermore, enhancement techniques to improve the electrical and optical characteristics of the self-protected device are investigated. The proposed solar cell is enhanced by optimizing different design parameters, such as the doping concentration and the layers' thicknesses. The enhanced cell structure shows an improvement in the short-circuit current density (JSC) and the open-circuit voltage (VOC), and thus an increased power conversion efficiency (PCE) while the VON is increased due to an increase of the JSC. Moreover, the simulation results depict that, by the introduction of an antireflection coating (ARC) layer, the external quantum efficiency (EQE) is enhanced and the PCE is boosted to 22.43%. Although the inclusion of ARC results in increasing VON, it is still lower than the value of VON for the Schottky diode encountered in current protection technology.

Back interface passivation for ultrathin Cu(In,Ga)Se2 solar cells with Schottky back contact: A trade-off of electrical effects

Back interface passivation reduces the back recombination of photogenerated electrons, whereas aggravates the blocking of hole transport towards back contact, which complicate the back interface engineering for ultrathin CIGSe solar cells with a Schottky back contact. In this work, theoretical explorations were conducted to study how the two contradictory electrical effects impact cell performance. For ultrathin CIGSe solar cells with a pronounced Schottky potential barrier (E h > 0.2 eV), back interface passivation produces diverse performance evolution trends, which are highly dependent on cell structures and properties. Since a back Ga grading can screen the effect of reduced recombination of photogenerated electrons from back interface passivation, the hole blocking effect predominates and back interface passivation is not desirable. However, when the back Schottky diode merges with the main pn junction due to a reduced absorber thickness, the back potential barrier and the hole blocking effect is much reduced on this occasion. Consequently, cells exhibit the same efficiency evolution trend as ones with an Ohmic contact, where back interface passivation is always advantageous. The discoveries imply the complexity of back interface passivation and provide guidance to manipulate back interface for ultrathin CIGSe solar on TCOs with a pronounced Schottky back contact.

Tunable reverse rectification of layed Janus MSeS (M = Hf, Zr) and SnS2 heterojunctions

Two-dimensional (2D) Janus transition metal dichalcogenides (JTMDs) exhibit suitable band gaps and strong visible light absorption, which are extensively applied to the field of optoelectronic devices. Here, we investigate the electronic properties of 2D JTMDs MSeS (M = Hf, Zr) and SnS2 van der Waals heterojunction through density functional theory. The calculated electronic properties reveal that ZrSeS/SnS2 heterojunction has a type-I band alignment, while HfSeS/SnS2 heterojunction has a type-II band alignment. We build the diodes based on the MSeS (M = Hf, Zr)/SnS2 heterojunctions and study the electronic transport. The currents of the devices exhibit asymmetry, and the negative turn-on voltages suggest that constructed devices are backward diodes. Moreover, it is found that the gate voltage can modulate the rectifying ratio, and the rectifying performance of ZrSeS/SnS2 is better than that of HfSeS/SnS2..

Ohmic co-doped GaN/InGaN tunneling diode grown by MOCVD

Tunnel junctions (TJs) have recently been proposed as a solution for several III-nitride current problems and to enhance new structures. Reported III-nitride TJs grown by metalorganic chemical vapor deposition (MOCVD) resulted in backward diodes with rectifying behavior in forward bias, even with Mg and Si doping in 1020 cm−3. This behavior limits applications in several device structures. We report a TJ structure based on p+In0.15Ga0.85N/n+In0.05Ga0.95N, where the n-side of the junction is co-doped with Si and Mg and with electron and hole concentrations in the mid-1019 cm−3 for both the n and p dopants. Co-doping creates deep levels within the bandgap that enhances tunneling under forward biased conditions. The TJ structure was investigated on both GaN substrates and InGaN templates to study the impact of strain on the TJ I–V characteristics. The resulting TJ I–V and resistivities reported indicate the potential for this TJ approach in several device structures based on III-nitrides. We are not aware of any previous MOCVD grown TJs that show Ohmic performance in both forward and reverse biases.

A 200 GHz Fully Integrated, Polarization-Resolved Quasi-Optical Detector Using Zero-Bias Heterostructure Backward Diodes

We report the design, fabrication, and prototype demonstration of a 200-GHz polarization-resolved quasi-optical detector employing monolithically integrated zero-bias heterostructure backward diodes (HBDs). In this design, polarization resolution is achieved by orthogonally integrating the detectors with a planar dual-polarization annular-slot antenna. The detector chip was fabricated and mounted on an extended hemispherical Si lens to enhance antenna efficiency in the millimeter-wave to terahertz region. The responsivity and radiation patterns of the detector were characterized experimentally; good agreement with theoretical calculations was obtained. By measuring the outputs of two orthogonal HBDs as a function of the polarization angle of the incident wave, the planar detector detects intensity and resolves polarization. On the basis of the polarimetric measurement, we further demonstrate the polarization imaging capability of the proposed detector by using it as an imaging system. The detector is promising for developing terahertz polarimetric sensors and imaging arrays in chemical sensing, biomedical imaging, and radio astronomy applications.

Probing electromagnetic wave energy with an in-series assembly of thermoelectric devices

We study the interaction of radio waves, microwaves, and infrared laser light of power P and period τ with a macroscopic thermoelectric (TEC) device-based detector and probe the energy Pτ as being the energy of these electromagnetic (EM) waves. Our detectors are in-series assemblies of TEC devices. We treat these detectors as equivalent to capacitors and/or inductors. The energy Pτ enables characterizing detector’s parameters, such as equivalent capacitance, inductance, resistance, responsivities, effective power, and efficiency. Through various scaling procedures, Pτ also aids in determining the power P of the EM waves. We compare the performance of our detectors with that of other TEC devices and with radio- and microwave-sensitive devices reported in the current literature, such as spin–orbit torque and spin–torque oscillator devices, heterojunction backward tunnel diodes, and Schottky diodes. We observe that the performance of our detectors is inferior. However, the order of magnitude of our detector’s parameters is in reasonable agreement with those of other TEC and non-TEC devices. We conclude that TEC devices can be used to detect radio waves and that Pτ effectively captures the energy of the EM waves. Considering Pτ as the EM wave’s energy offers a classical approach to the interaction of EM waves with matter in which photons are not involved. With the EM wave’s energy depending upon two variables (P and τ), a similar response could be produced by, e.g., radio waves and visible light, leading to interesting consequences that we briefly outline.

Electrical Properties of GaAs Implanted with High Energy (100meV) 28Si and 120Sn Ions

Single crystal n-GaAs substrates have been implanted at 300 K with 100 MeV 28Si and 120Sn ions to a dose of 1x1018ions/m2 independently. The electrical properties of these samples has been investigated and compared after implantation and annealing up to 850 °C by current voltage (I-V) measurements. It has been observed that the I-V curves for the samples implanted with 28Si ions show p-n junction like characteristics which then show a linear I-V characteristics for the annealing treatment between 150-550 °C. Annealing the samples at 650 °C results in a typical diode like I-V characteristics which become less non-linear after further annealing at 750 °C. Further annealing at 850 °C results in to a back ward diode like behavior. However the I-V curves for the samples implanted with 120Sn ions and annealed up to 450C were linear which then show a weak non linearity for the annealing treatments between 550C-750C. After 850C annealing the samples show a strong nonlinearity typical of a p-n junction. The temperature dependence of resistance of both 28Si and 120Sn implanted GaAs samples after implantation and different annealing steps are investigated and the possible conduction mechanisms are discussed.

Is a passivated back contact always beneficial for Cu (In,Ga)Se2solar cells?

AbstractUltrathin CIGSe solar cells on TCOs (transparent conductive oxides) have many promising potential applications due to their transparency. However, their performance is strongly constrained due to the back contact, often referred to acting as a Schottky junction. In this work, we show that the current limitation due to a back Schottky junction can be responsible for the apparent photocurrent loss and suppression of the forward current, which deteriorates cell performance and leads to the S‐shapedJ‐Vcharacteristics, respectively. However, due to the non‐negligible photocurrent in the back Schottky diode and the current amplification effect of a transistor, cells with a reduced absorber thickness overall exhibit a relieved current suppression, resulting in a lightJ‐Vcurve closer to the one with an Ohmic back contact. Notably, a higher back interface recombination velocity is capable of increasing the forward current of the Schottky diode by recombination, which mitigates the limitation of current flow through the back Schottky junction and thus improves the cell performance. The results show strong implications that introducing high density defects at the back interface is favorable for CIGSe solar cells on TCOs, rather than employing point‐contact structures for interface passivation. This suggests a different path to improve ultrathin CIGSe solar cells on TCOs compared to the devices on Mo with an Ohmic back contact.

III–V nanowire backward diodes with high sensitivity above 1 MV W−1 for low-power microwave energy harvesting

Improved sensitivity of over 1 MV W−1, which exceeds that of conventional well-designed Schottky barrier diodes, was achieved in p-GaAs0.4Sb0.6/n-InAs nanowire backward diodes (NW BWDs) for low-power microwave energy harvesting at 2.4 GHz under zero-bias. The antimony composition in the GaAsSb NWs was increased to 0.6 to form proper interband tunneling of the BWDs. A linear detected characteristic of detection was obtained even when microwave input power was less than 1 μW. Furthermore, the reduction of parasitic capacitance due to the adoption of a reduced pad area helped in the improvement of the sensitivity of the NW BWDs. A large dynamic range in detection of low-power microwaves was obtained through the employment of an extended anode structure. Device simulations clarified that carrier depletion in GaAsSb NWs was the main cause of increased forward breakdown voltage, which resulted in the large dynamic range exhibited by the NW BWDs.

Carrier transport through near-ideal interface for WSe2 van der Waals homojunction diode

Transition-metal dichalcogenides are promising alternatives to conventional materials for next-generation devices owing to their unique characteristics. Because efficient doping is difficult, in designing devices, more than two materials are typically heterogeneously junctioned via van der Waals (vdW) bonds. However, unintended effects at the vdW heterojunction due to lattice mismatch or trap-assisted transport limit the device performance. In this study, we fabricated a vdW homojunction p–n diode with elementally doped WSe2. The device made of pristine WSe2 exhibited forward diode characteristics with an ideal transport characteristic. When WSe2 was doped with the p-dopant bis(trifluoromethane) sulfonimide, the carrier transport mechanism changed from diffusion to tunneling. The device rectified the forward current with a high rectification ratio of 2 × 105 at 300 K. This study provides a comprehensive understanding of the carrier transport mechanism in a high-performance backward vdW homojunction diode.

Improved microwave sensitivity to 706 kV/W by using p-GaAsSb/n-InAs nanowire backward diodes for low-power energy harvesting at zero bias

In this study, a p-GaAs0.4Sb0.6/n-InAs nanowire backward diode (NW BWD) with a large sensitivity of 706 kV/W, exceeding that of Schottky barrier diodes (SBDs), was developed for low-power microwave rectification at zero bias. The interband tunneling of the NW BWDs under zero-bias condition displayed a large nonlinear characteristic of typical BWDs, which is effective for realizing power detection with high sensitivity. The fabricated NW BWDs indicated linear detected voltages (Vdet) when a microwave input power (Pin) of ∼1 µW was applied at 2.4 GHz. From the Vdet, Pin, and return loss obtained from the S-parameter measurements, an impedance-matched voltage sensitivity of 706 kV/W was calculated for the NW BWD at zero bias. The obtained sensitivity value was higher than that of a well-designed SBD, which was ∼62 kV/W at 2.4 GHz. According to the extracted device parameters, it was found that to improve the sensitivity of the NW-BWD, not only the junction capacitance of the diode but also the parasitic pad capacitance needs to be reduced. The high sensitivity is attributed to the high curvature coefficient of −26.7 V−1 and the small junction capacitance of the NW structure of the BWD.

Backward Diode Rectifying Behavior in AgCrO2/In2O3

A backward diode consisting of all nondegenerate and transparent semiconducting oxides (TSOs) offers promising opportunities for designing multifunctional electronic devices. In this letter, we report the backward diode rectifying behavior in the nondegenerate AgCrO2/In2O3 p-n heterojunction. Both AgCrO2 and In2O3 films are transparent. The decrease of grain boundary in the In2O3 film can improve the backward diode rectifying performance. The optimized AgCrO2/In2O3 heterojunction exhibits a very high reverse rectification ratio that exceeds 103 along with a small tunneling current onset voltage. The backward diode rectifying behavior originates from the electron band-to-band tunneling (BTBT) current in the reverse voltage region, which is induced by type-III band alignment. This study will pave the way for achieving transparent backward diodes by using all nondegenerate TSOs p-n heterojunctions.

Effect of Incident Light on Transport Properties of Pulsed Laser Deposited Manganite Thin Films

In this communication, we report the results of different light illumination on electrical transport properties of La0.67Ca0.33Mn0.9Ga0.1O3 (LCMGO) thin films grown on Si (100) ( n-type phosphorus-doped) wafer using Pulsed Laser Deposition (PLD) System. The variation in deposition time changes the thickness of the films. X-ray Diffraction (XRD) reveals the polycrystalline structure of LCMGO thin films. The cross-sectional SEM were taken to determine the thickness of the films with changing deposition time. Atomic Forced Micrographs (AFM) show that island type grains diffuse into one another to form a more uniform distribution of grains as the thickness of the film increases. The charge transport properties have been studied using the I-V measurement at LCMGO/Si interfaces. I-V measurement shows the backwards-diode like the behaviour of the LCMGO/Si p-n junction. The reverse bias current changes under the influence of different incident light illumination. The built-in electric field is generated at the interface when the film was illuminated with UV light. The tunnelling process for backward diode like p-n junction is explained using a modified Simmons model.

Temperature dependence of backward tunnel diode oscillator circuit

In the present paper, a package of BD-4 germanium backward tunnel diodes, which widely used in modern electronic systems were chosen for studying its operation as an oscillator circuit under the influence of a wide range of temperatures ranging from 100 ​K up to 343 ​K. The electrical parameters of the devices based on their I–V characteristics were investigated, where it is clear that peak-to-valley current ratio, valley voltage, forward voltage, voltage span, voltage swing, and current span were decreased from 12.9, 0.35 ​V, 0.65 ​V, 0.31 ​V, 0.65 ​V, and 50.70 ​μA down to 3.2, 0.22 ​V, 0.35 ​V, 0.17 ​V, 0.30 ​V, and 31.30 ​μA, respectively. On the other hand, both peak voltage and negative differential resistance were shown to be almost temperature independent. Besides, a simple sinusoidal LC oscillator circuit that operates at 2.30 ​MHz was designed, implemented and tested, where its output signal voltage waveforms were plotted at different temperature levels within the investigated range. On the other hand, it was shown that the oscillation frequency, peak-to-peak voltage, output power spectrum, and phase-noise were temperatureindependent provided that the diode is adequately biased in its negative resistance region. Finally, the obtained results were shown to be in good agreement in the trend with that previously published.

Modulation of Junction Modes in SnSe2/MoTe2 Broken-Gap van der Waals Heterostructure for Multifunctional Devices.

We study the electronic and optoelectronic properties of a broken-gap heterojunction composed of SnSe2 and MoTe2 with gate-controlled junction modes. Owing to the interband tunneling current, our device can act as an Esaki diode and a backward diode with a peak-to-valley current ratio approaching 5.7 at room temperature. Furthermore, under an 811 nm laser irradiation the heterostructure exhibits a photodetectivity of up to 7.5 × 1012 Jones. In addition, to harness the electrostatic gate bias, Voc can be tuned from negative to positive by switching from the accumulation mode to the depletion mode of the heterojunction. Additionally, a photovoltaic effect with a fill factor exceeding 41% was observed, which highlights the significant potential for optoelectronic applications. This study not only demonstrates high-performance multifunctional optoelectronics based on the SnSe2/MoTe2 heterostructure but also provides a comprehensive understanding of broken-band alignment and its applications.