Unipolar Barrier Research Articles

Multi-dimensional optical information acquisition based on a misaligned unipolar barrier photodetector

Acquiring multi-dimensional optical information, such as intensity, spectrum, polarization, and phase, can significantly enhance the performance of photodetectors. Incorporating these dimensions allows for improved image contrast, enhanced recognition capabilities, reduced interference, and better adaptation to complex environments. However, the challenge lies in obtaining these dimensions on a single photodetector. Here we propose a misaligned unipolar barrier photodetector based on van der Waals heterojunction to address this issue. This structure enables spectral detection by switching between two absorbing layers with different cut-off wavelengths for dual-band detection. For polarization detection, anisotropic semiconductors like black phosphorus and black arsenic phosphorus inherently possess polarization-detection capabilities without additional complex elements. By manipulating the crystal direction of these materials during heterojunction fabrication, the device becomes sensitive to incident light at different polarization angles. This research showcases the potential of the misaligned unipolar barrier photodetector in capturing multi-dimensional optical information, paving the way for next-generation photodetectors.

Independently Accessible Dual-Band Barrier Infrared Detector Using Type-II Superlattices

We report a novel dual-band barrier infrared detector (DBIRD) design using InAs/GaSb type-II superlattices (T2SLs). The DBIRD structure consists of back-to-back barrier diodes: a “blue channel” (BC) diode which has an nBp architecture, an n-type layer of a larger bandgap for absorbing the blue band infrared/barrier/p-type layer, and a “red channel” (RC) diode which has a pBn architecture, a p-type layer of a smaller bandgap for absorbing the red band infrared/barrier/n-type layer. Each has a unipolar barrier using a T2SL lattice matched to a GaSb substrate to impede the flow of majority carriers from the absorbing layer. Each channel in the DBIRD can be independently accessed with a low bias voltage as is preferable for high-speed thermal imaging. The device modeling of DBIRDs and simulation results of the current–voltage characteristics under dark and illuminated conditions are also presented. They predict that the dual-band operation of the DBIRD will produce low dark currents and 45–56% quantum efficiencies for the in-band photons in the BC with λc = 5.58 μm, and a nearly constant 32% in the RC with λc = 8.05 μm. The spectral quantum efficiency of the BC for 500 K blackbody radiation is approximately 50% over the range of λ = 3–4.7 μm, while that of the RC has a peak of 42% at 5.9 μm. The DBIRD may provide improved high-speed dual-band imaging in comparison with NBn dual-band detectors.

Filter-Free UV Photodetectors Based on Unipolar Barrier Van der Waals α-In2Se3/h-BN Heterostructures.

Visible-blind ultraviolet (UV) light detection has a wide application range in scenes like space environment monitoring and medical imaging. To realize miniaturized UV detectors with high performance and high integration ability, new device structures without bulky light filters need to be developed based on advanced mechanisms. Here the unipolar barrier van der Waals heterostructure (UB-vdWH) photodetector is reported that realizes filter-free visible-blind UV detection with good stability, robustness, selectivity, and high detection performance. The UB-vdWH shows a responsivity of 2452AW-1, a photo on-off ratio of 2.94×105 and a detectivity of 1.26×1015Jones as a UV detector, owing to the intentionally designed barrier height that suppresses dark current and photoresponse to visible light during the transport process. The good performance remains intact during 104 test cycles or even under high temperatures, which proves the stability, and robustness of the UB-vdWH, thus shows the huge potential for a wider application range.

Solar blind avalanche photodetector based on a n-β-Ga2O3/n-Si heterojunction via an introduction of AlN buffer layer for interface lattice and band Engineering

The ultrawide-band gap semiconductor Ga2O3 as a photodetector heteroepitaxially grown on Si is expected to be widely used for weak solar-blind signal detections because the optical filters typically used in Si-based UV detectors can be avoided. Photodetectors fabricated from Ga2O3/Si are promising for multi-color detection (Ga2O3-based for UV and Si-based for visible/IR) and are more compatible with traditional Si-based electronic circuits. This paper proposes an n-type semiconductor-barrier-n-type semiconductor (n/B/n) with a unipolar barrier β-Ga2O3/AlN/n-Si heterostructure as a solar-blind avalanche photodetector. Introducing the AlN buffer layer eliminates the native amorphous SiOx layer, reduces lattice mismatch between β-Ga2O3 and Si, and improves the quality of β-Ga2O3 crystallization. Embedding AlN increases the conduction band shift of β-Ga2O3/Si, limits electron migration, reduces device dark current, and increases the reverse breakdown voltage. The β-Ga2O3/AlN (150 nm)/n-Si heterostructure has a high responsivity of 131.3 A/W with a detectivity of 2.9 × 1015 Jones, and an ultrahigh UV/visible (Rpeak/R400nm) rejection ratio of 5.2 × 105 at −55 V. The avalanche gain can also reach 2.7 × 104 at an 85 V reverse bias. This work provides an effective strategy for constructing a high-performance avalanche solar-blind-UV/visible/IR as a multi-color photodetector on one “chip” of a Si-based integrated circuit.

Black Arsenic Phosphorus Mid-Wave Infrared Barrier Detector with High Detectivity at Room Temperature.

The barrier structure is designed to enhance the operating temperature of the infrared detector, thereby improving the efficiency of collecting photogenerated carriers and reducing dark current generation, without suppressing the photocurrent. However, the development of barrier detectors using conventional materials is limited due to the strict requirements for lattice and band matching. In this study, a high-performance unipolar barrier detector is designed utilizing a black arsenic phosphorus/molybdenum disulfide/black phosphorus van der Waals heterojunction. The device exhibits a broad response bandwidth ranging from visible light to mid-wave infrared (520nm to 4.6 µm), with a blackbody detectivity of 2.7× 1010 cmHz-1/2 W-1 in the mid-wave infrared range at room temperature. Moreover, the optical absorption anisotropy of black arsenic phosphorus enables polarization resolution detection, achieving a polarization extinction ratio of 35.5 at 4.6 µm. Mid-wave infrared imaging of the device is successfully demonstrated at room temperature, highlighting the significant potential of barrier devices based on van der Waals heterojunctions in mid-wave infrared detection.

Unipolar barrier structures based on n-HgCdTe with superlattices as a barrier [Review]

Unipolar barrier structures based on <i>n</i>-HgCdTe with superlattices as a barrier [Review]

Theoretical design of uncooled mid-infrared PbSe P+pBn+ barrier detectors

A novel uncooled mid-wavelength infrared (MWIR) P+pBn+ barrier detector based on epitaxial PbSe absorber layer on Ge substrate is theoretically investigated by finite element analysis in order to achieve optimal detection performance. The simulated results show that the P+pBn+ barrier architecture can further effectively reduce the room-temperature dark current to 4.45 mA cm−2 under −0.1 V bias, which is 12 times lower than a PbSe pBn+ unipolar barrier device in a previous study. Moreover, the P+pBn+ barrier architecture exhibits excellent responsivity and detectivity of 1.83 A W −1 and 3.23 × 1010 cm Hz1/2 W−1 at 3.8 μm, respectively. These results suggest that this P+pBn+ barrier detector based on natural MBE epitaxy technology could have potential in the emerging high-sensitivity and high-detectivity uncooled MWIR applications.

Ultralow dark current and high on–off ratio of perovskite photodetectors enabled by 3D/2D/3D heterostructures unipolar barrier

Lead halide perovskite photodetectors exhibit outstanding photoelectric performance in multiple parameters and have become a widely studied hotspot. The perovskite with single crystal structures significantly reduces the density of grain boundaries and defect states, thereby improving the carrier lifetime and mobility. However, the suppression of dark current is one of the most important concerns for the research of perovskite photodetectors. Here, we constructed a pBp unipolar barrier photodetector by inserting two-dimensional perovskite into three-dimensional perovskite through a pressure bonding process. The dark current of the photodetector decreased by more than two orders of magnitude, while the photocurrent remained unchanged. The perovskite unipolar barrier photodetectors exhibit excellent photoelectric performance, with an on–off ratio of 106, a specific detectivity of 4.11 × 1012 Jones, a −3 dB cutoff frequency of 344 kHz, and a linear dynamic range of 160 dB, providing a prospective path for weak light detection.

Long-wave bilayer graphene/HgCdTe based GBp type-II superlattice unipolar barrier infrared detector

Type-II superlattice (T2SL) material is used to design highly efficient next-generation infrared (IR) detectors. The flexibility of the material allows the integration of unipolar barrier IR detector architecture to suppress generation-recombination currents by blocking the majority charge carriers and improve device performance. This paper presents a self-powered T2SL unipolar barrier detector that operates in the long-wave IR regime. It comprises a contact layer made of p+-bilayer graphene (G) and a barrier layer made of p–-Hg1–xCdx=0.41Te (B) placed over a p+-Hg1–xCdx=0.2217Te absorber layer (p) and is known as the GBp detector. The optoelectronic characterization of the unipolar GBp detector is carried out using the Silvaco Atlas TCAD software. Under self-powered mode operation, the proposed GBp detector exhibits an improvement in photocurrent density of about 108 times. The dark current density of 0.4nA/cm2, the photocurrent responsivity of 7.82 A/W, the quantum efficiency of 91.44%, and the detectivity of 4.48 × 1014 cmHZ1/2/W are found at the liquid nitrogen temperature with a bias of –0.5 V. A dichroic ratio of 249 and a response time of less than 1 ps are likewise exhibited by the GBp detector. The substantial electric field at the contact/barrier heterointerface and the high barrier height in the conduction band, which result in an increased photodetection response, are attributed to this improved performance.

Mixed-dimensional WS2/WSe2/Si unipolar barrier heterostructure for high-performance photodetection

Mixed-dimensional WS2/WSe2/Si unipolar barrier heterostructure for high-performance photodetection

Design and modeling of high-performance mid-wave infrared InAsSb-based nBn photodetector using barrier band engineering approaches

We report a new nBn photodetector (nBn-PD) design based on the InAlSb/AlSb/InAlSb/InAsSb material systems for mid-wavelength infrared (MWIR) applications. In this structure, delta-doped compositionally graded barrier (δ-DCGB) layers are suggested, the advantage of which is creation of a near zero valence band offset in nBn photodetectors. The design of the δ-DCGB nBn-PD device includes a 3 µm absorber layer (n-InAs0.81Sb0.19), a unipolar barrier layer (AlSb), and 0.2 μm contact layer (n-InAs0.81Sb0.19) as well as a 0.116 µm linear grading region (InAlSb) from the contact to the barrier layer and also from the barrier to the absorber layer. The analysis includes various dark current contributions, such as the Shockley–Read–Hall (SRH), trap-assisted tunneling (TAT), Auger, and Radiative recombination mechanisms, to acquire more precise results. Consequently, we show that the method used in the nBn device design leads to diffusion-limited dark current so that the dark current density is 2.596 × 10−8 A/cm2 at 150 K and a bias voltage of − 0.2 V. The proposed nBn detector exhibits a 50% cutoff wavelength of more than 5 µm, the peak current responsivity is 1.6 A/W at a wavelength of 4.5 µm and a − 0.2 V bias with 0.05 W/cm2 backside illumination without anti-reflective coating. The maximum quantum efficiency at 4.5 µm is about 48.6%, and peak specific detectivity (D*) is of 3.37 × 1010 cm⋅Hz1/2/W. Next, to solve the reflection concern in this nBn devices, we use a BaF2 anti-reflection coating layer due to its high transmittance in the MWIR window. It leads to an increase of almost 100% in the optical response metrics, such as the current responsivity, quantum efficiency, and detectivity, compared to the optical response without an anti-reflection coating layer.Graphical

Enhanced gain and detectivity of unipolar barrier solar blind avalanche photodetector via lattice and band engineering

Ga2O3-based solar blind avalanche photodetectors exhibit low voltage operation, optical filter-free and monolithic integration of photodetector arrays, and therefore they are promising to be an alternative to the bulky and fragile photomultiplier tubes for weak signal detection in deep-ultraviolet region. Here, by deliberate lattice and band engineering, we construct an n-Barrier-n unipolar barrier avalanche photodetector consisting of β-Ga2O3/MgO/Nb:SrTiO3 heterostructure, in which the enlarged conduction band offsets fortify the reverse breakdown and suppress the dark current while the negligible valance band offsets faciliate minority carrier flow across the heterojunction. The developed devices exhibit record-high avalanche gain up to 5.9 × 105 and detectivity of 2.33 × 1016 Jones among the reported wafer-scale grown Ga2O3-based photodetectors, which are even comparable to the commercial photomultiplier tubes. These findings provide insights into precise manipulation of band alignment in avalanche photodetectors, and also offer exciting opportunities for further developing high-performance Ga2O3-based electronics and optoelectronics.

Unipolar barriers in near-broken-gap heterostructures for high-performance self-powered photodetectors

The two-dimensional heterostructure is a promising research direction in photodetection. However, developing a good photodetector with high responsivity and fast speed is still challenging. Herein, we fabricate a high-performance self-powered broadband (355–1064 nm) photodetector based on a near-broken-gap GeSe/SnS2/InSe heterostructure, where SnS2 is used as a potential hole barrier layer. The device shows an ultrahigh open-circuit voltage (VOC) of 0.57 V, a high power-dependent responsivity of 1.87 A W−1 at 355 nm, and a fast response time of 8 μs in the self-powered mode. Based on the near-broken band alignment, the InSe layer with high electron mobility can efficiently collect the photogenerated electrons from the GeSe layer to improve conversion efficiency. Furthermore, the unipolar hole barrier at the interface can inhibit the Langevin recombination resulting in VOC enhancement. Notably, the anisotropy ratio of photocurrent in our device is also enhanced to ∼3.5, which is higher than GeSe photodetectors and other anisotropic devices counterparts. This work provides an opportunity for the realization of the high-sensitivity polarization-sensitive broadband photodetector.

Ferroelectric and strain-tuned MoSe2/Bi2O2Se van der Waals heterostructure with band alignment evolution.

The vertically stacked two-dimensional van der Waals heterostructure (2D vdWH) provides a unique platform for integrating distinctive properties of various 2D materials by functionalizing the interfacial interaction and regulating its band alignment. Herein, we theoretically propose a new MoSe2/Bi2O2Se vdWH material, in which a zigzag-zipper structure of the Bi2O2Se monolayer is constructed to model its ferroelectric polarization and maintain a small interlayer mismatch with MoSe2. The results show a typical unipolar barrier structure with a large band offset in the conduction band and nearly zero offset in the valence band of MoSe2/Bi2O2Se when the ferroelectric polarization of Bi2O2Se is back to MoSe2, in which the electron migration is blocked and holes can migrate unimpeded. It is also found that the band alignment lies between the type-I and type-II heterostructures and band offsets can be flexibly modulated under the joint action of ferroelectric polarization of Bi2O2Se and in-plane biaxial tensile and compressive strains. This work would facilitate the development of multifunctional devices based on the MoSe2/Bi2O2Se heterostructure material.

Dry reforming of methane by microsecond pulsed dielectric barrier discharge plasma: Optimizing the reactor structures

Dry reforming of CH4 process can convert greenhouse gases into high-value-added fuels and chemicals with its broad application prospects in environmental protection and renewable energy. Non-thermal plasma is considered an effective alternative method because it can activate CH4 and CO2 under low temperature and atmospheric pressure. This paper is aimed to optimize the plasma-assisted dry reforming of CH4 process in a unipolar microsecond pulsed coaxial dielectric barrier discharge by investigating the effects of reactor structures. The results show that the conversions of reactants and the yields of syngas were significantly affected by the reactor structures. Specifically, a multi-stage or foil external electrode and negative polar discharge could promote CH4 and CO2 conversions, gas product yields, and energy conversion efficiencies. For different electrodes, the maximal conversions of CH4 and CO2 were 20.4% and 14.1%, with an energy conversion efficiency of 4.4% under our experimental conditions. Higher conversions, yields, and energy conversion efficiencies were obtained with lower power input when applying heat insulation measures. CH4 conversion was promoted to 27.9% with a moderate energy conversion efficiency of 3.8%, but the conversion of CO2 was only 12% when packing materials into the reactor. The results can provide specific guidance for designing plasma or plasma-catalytic dry reforming reactor.

Comprehensive quantum transport analysis of M-superlattice structures for barrier infrared detectors

In pursuit of designing superior type-II superlattice barrier infrared detectors, this study encompasses an exhaustive analysis of utilizing M-structured superlattices for both the absorber and barrier layers through proper band engineering and discusses its potential benefits over other candidates. The electronic band properties of ideally infinite M-structures are calculated using the eight band k.p method that takes into account the effects of both strain and microscopic interface asymmetry to primarily estimate the bandgap and density-of-states effective mass and their variation with respect to the thicknesses of the constituent material layers. In contrast, for practical finite-period structures, the local density-of-states and spectral tunneling transmission and current calculated using the Keldysh non-equilibrium Green’s function approach with the inclusion of non-coherent scattering processes offer deep insights into the qualitative aspects of miniband and localization engineering via structural variation. Our key results demonstrate how to achieve a wide infrared spectral range, reduce tunneling dark currents, induce strong interband wavefunction overlaps at the interfaces for adequate absorption, and excellent band-tunability to facilitate unipolar or bipolar current blocking barriers. This study, therefore, perfectly exemplifies the utilization of 6.1 Å material library to its full potential through the demonstration of band engineering in M-structured superlattices and sets up the right platform to possibly replace other complex superlattice systems for targeted applications.

Investigation of the surface leakage current of the nBn InGaAsSb infrared photodetector by using photoreflectance spectroscopy

The surface leakage current of the nBn infrared detector based on InGaAsSb/AlGaSb heterostructure was studied by using photoreflectance spectroscopy (PR). The Franz-Keldysh oscillations (FKOs) in PR spectra showed that the minority carriers (electrons) mainly affect the surface electric field in the nbn structures. The results show that the electric field increases due to the photovoltaic effect as the temperature increases. However, the increased ratio of the electric field at low temperature is lower than that of high temperature. At low temperatures, when the temperature drops, the generation-recombination (G-R) associated with dark current is eliminated, and the surface electric field variation becomes lower. By increasing the temperature and dark current, the electric field changes more. In addition, the unipolar barrier photodiode exhibits no surface leakage current at low temperatures without blocking the bulk currents.

Dark Currents of Unipolar Barrier Structures Based on Mercury Cadmium Telluride for Long-Wave IR Detectors

Dark Currents of Unipolar Barrier Structures Based on Mercury Cadmium Telluride for Long-Wave IR Detectors

Evolution of the uniformity in the repetitive unipolar nanosecond-pulse dielectric barrier discharge

The time evolution of dielectric barrier discharge driven by nanosecond pulse high-voltage power is investigated by high-speed video analysis, electrical measurements and spectral diagnostics. It is found that the discharge mode generally goes through the evolution process of filamentary discharge → diffuse discharge → filamentary discharge with the increase in discharge cycle. The time-dependent changes in the standard deviation of image gray levels indicate that the discharge uniformity first improves and then deteriorates in this evolution process. The different pre-ionization density and modulated distribution of space charges and surface charges are considered to be the main reasons for the time evolution of discharge uniformity. In addition, the experiments under different frequencies and voltages show that the transition of the discharge mode is more likely to occur at higher frequency and higher voltage. Further measurement and calculation reveal that the discharge at high frequency and high voltage has the same characteristics, that is, high pre-ionization degree, thick filament diameter and short time lag. These characteristics usually lead to higher seed electron density, larger critical avalanche size and weaker lateral inhibition effect, which make the discharge mode transition more likely to occur.

Design and calculation of type-II superlattice resonant cavity-enhanced photodetector with high quantum efficiency and low dark current

The type-II superlattice (T2SLs) infrared detector with distributed Bragg reflector (DBR) on the basis of unipolar barrier structure is investigated. The traditional binary material InAs/GaSb is used in the device, and two kinds of unipolar barrier structures, nBn and pBp, are used to reduce the generation-recombination (GR) dark current of the device. 6 periods of AlAs0.09Sb0.91/GaSb is selected as the DBR mirror. The target wavelength of DBR mirror is 3.3 μm, which is used as methane detector. The supercell is 7 ML InAs/4 ML GaSb, which has a 50% cutoff wavelength of 4 μm. The quantum efficiency (QE) of the detector with DBR mirror can reach ~ 90% at the target wavelength of 3.3 μm, and is significantly higher than that of the device without DBR mirror. The peak detectivity of pBp RCE PD is about ~1 × 1013 Jones.