Heterojunction Photodiodes Research Articles

Single‐Crystalline Ge1−xSnx/Si p–n Heterojunction Photodiodes with Sn Compositions up to 10%

AbstractGeSn/Si heterojunction photodiodes are attractive because they can extend light detection wavelength range. However, the development of such photodiodes via epitaxial growth faces great challenges due to unavoidable issues such as lattice and thermal mismatches between Si and GeSn. Here, print Si nanomembranes are transferred on GeSn/Ge/Si substrates to form the GeSn/Si heterojunction photodiodes. The p‐Ge0.977Sn0.023/n‐Si heterojunction photodiodes exhibit a good rectifying behavior with a low dark current density of 40 mA cm−2and responsivity of 0.41 A W−1at 1550 nm under a reverse bias of −2 V. In addition, the detection wavelength range of p‐Ge0.9Sn0.1/n‐Si is extended to 2100 nm because of the increased Sn composition. The bandgap calculation of as‐grown GeSn with various Sn compositions is carried out. It confirms that the enhanced responsivity and extended detection wavelength ranges are attributed to the reduced bandgap from 750 to 601 meV when the Sn composition is increased from 2.3% to 10%. The result shows that the transfer printing of a freestanding single‐crystalline Si nanomembrane to a bulk GeSn/Ge/Si substrate can provide an excellent alternative route for realizing GeSn/Si heterojunction photodiodes.

Heterointerface-engineered type Ⅱ SnO2/boron-doped diamond heterojunction photodiodes with diverse diode characteristics and binary photoresponse

As an inevitable existence in semiconductor heterostructures, interfacial states have a non-negligible impact on the performance of heterojunction-based optoelectronic devices. Here, we develop high-performance photodiodes based on heterointerface-engineered type II SnO2/boron-doped diamond (BDD) heterojunctions. We modulate the type of the interfacial states of SnO2/BDD heterojunctions by changing the partial pressure of oxygen during the process of SnO2 deposition by RF magnetron sputtering. As a result, backward rectifying, Zener, and forward rectifying diodes are obtained. The diversity of the diode characteristics is related to the carrier tunneling and avalanche multiplication effects. In addition, the I–V curve of the Zener diode has a negative differential resistance precursor under UV light irradiation. The photogenerated holes in the forward rectifier diode are easily trapped at the heterointerface during transmission. Zener and forward rectifier diodes can output positive and negative photocurrents (i.e., binary photoresponse) under on/off periodic light illumination owing to photovoltaic and pyro-phototronic effects. These results reveal the potential of SnO2/BDD heterojunctions in the field of optical logic computing devices.

Optical and Electrical Characterization of a ZnO/Coronene-Based Hybrid Heterojunction Photodiode

Optical and Electrical Characterization of a ZnO/Coronene-Based Hybrid Heterojunction Photodiode

The fabrication and characterization of thermal evaporated n-ZnS/p-Si heterojunction and ZnS-Au Schottky photodiodes

The wide bandgap of zinc sulfide (ZnS) is optimum for the detection of UV wavelengths. In the research work presented here, thermal evaporated ZnS layer is paired with Si and Au to form heterojunction and Schottky photodiodes. The devices showed UV detection capabilities. The barrier height of the n-ZnS/p-Si heterojunction varied from 0.06 to 0.1 eV when the ambient temperature was increased up to 420 K. The series resistance and ideality factors varied from 20 to 130 kΩ and 2–3 respectively. The built-in potential was about 0.76 V. The heterojunction showed a responsivity of 0.08 A/W and quantum efficiency of 0.3. The Au/ZnS Schottky junction was found to have an ideality factor of 2.53 with a barrier height of 0.46 eV. The response times of both the devices were found to be almost similar but it was much faster than that of the isolated ZnS film. This is due to the faster movement of photogenerated charges in the electric field of the junction.

Ultraviolet photodiode fabricated from TiO2 nanorods/p-silicon heterojunction

In this paper, an ultraviolet (UV) photodiode in p-n heterojunction configuration is fabricated from TiO2 nanorods hydrothermally deposited on p-type silicon substrate. Under UV illumination condition, the heterojunction photodiode shows superior UV detection capability achieving a photoresponsivity of 1.41 A/W, a photosensitivity of 80 and a detectivity of 8.32 × 1011 Jones with a quick response speed of 25 ms. More significantly, the presented fabrication approach can be applicable to other metal–oxide semiconductor based optoelectronic devices.

Vertically Stacked vdW Double Heterojunction Photodiode with Ultrawide Bandgap Gallium Oxide Electron Reservoir

AbstractCo‐integration of visible and infrared (IR) photodetection into a simple configuration is of essential importance for broadband multispectral imaging, and various heterostructures based on group IV, III–V, and recent 2D semiconductors have been studied in efforts to circumvent limits on photoresponsivity and response speed in IR ranges. In this work, a vertically stacked double heterojunction (DHJ) photodiode (PD) with ultrawide‐bandgap gallium oxide (Ga2O3) is reported on, and the performance is compared with p‐WSe2/n‐Ge PD. The fabricated n‐Ga2O3/p‐WSe2/n‐Ge PD responds to a broad spectral range from vis to shortwave IR (SWIR) (1550 nm) with a response time of ≈2.6 µs and responsivity of 17.2 A W−1. The superior performance is attributed to amplified photocurrent gains, and the additional n‐Ga2O3 has a high electron carrier density with negligible hole density at room temperature and thus, can play a role as an electron reservoir while being transparent to the spectral ranges. vScanning photocurrent microscopy analysis is performed to provide the mechanism. The demonstrated SWIR imaging shows that the proposed DHJ provides a potential pathway for high‐speed multispectral vision applications.

Vibronic Exciton-Phonon States in Stack-Engineered van der Waals Heterojunction Photodiodes.

Stack engineering, an atomic-scale metamaterial strategy, enables the design of optical and electronic properties in van der Waals heterostructure devices. Here we reveal the optoelectronic effects of stacking-induced strong coupling between atomic motion and interlayer excitons in WSe2/MoSe2 heterojunction photodiodes. To do so, we introduce the photocurrent spectroscopy of a stack-engineered photodiode as a sensitive technique for probing interlayer excitons, enabling access to vibronic states typically found only in molecule-like systems. The vibronic states in our stack are manifest as a palisade of pronounced periodic sidebands in the photocurrent spectrum in frequency windows close to the interlayer exciton resonances and can be shifted “on demand” through the application of a perpendicular electric field via a source-drain bias voltage. The observation of multiple well-resolved sidebands as well as their ability to be shifted by applied voltages vividly demonstrates the emergence of interlayer exciton vibronic structure in a stack-engineered optoelectronic device.

Flexible Perovskite and Organic Semiconductor Heterojunction Devices for Tunable Band-Selective Photodetection

Filter-free band-selective photodetectors with tunable band edges possess extensive applications in smart sensors, artificial intelligence, the internet of everything, and so forth. However, such photodetectors operated with the charge collection narrowing effect require a thick active layer over millimeters, leading to rather a large device size, high material cost, and limited mechanical flexibility. In this work, we report a flexible thin-film perovskite and organic semiconductor (OSC) heterojunction device, which can achieve adjustable band-selective photodetection by utilizing the easy tunability of the perovskite band gap. First, heterojunction photodiodes with only two active layers of perovskites and OSCs are fabricated, in which the perovskite contributes to light absorption and rectification characteristics simultaneously. The fundamental device operation mechanism is investigated by combining the band alignments of the heterojunctions and their potential distributions observed with Kelvin probe force microscopy. It uncovers that the presence of built-in electric fields in the heterojunctions caused by moderate band alignments and appropriate difference in hole and electron concentrations between the perovskites and the OSCs is significant for the properties of the photodiodes. The resultant photodiodes exhibit a high rectification ratio of up to 103, decent photodetection performance, and mechanical flexibility. Furthermore, photodetectors based on perovskite/OSC/perovskite stack heterojunctions can realize the functions of filterless band-selective photodetection in a single device, and the band edges in the photodetection can be modulated by tuning the perovskite band gap. Therefore, this work provides flexible thin-film photodiodes with the potential of miniaturization and low-cost fabrication and demonstrates tunable band-selective photodetection for advanced applications.

Unraveling the Origin of Dark Current in Organic Bulk Heterojunction Photodiodes for Achieving High Near-Infrared Detectivity

Organic infrared materials are attractive due to their high absorption coefficients and facile tuning of the absorption spectrum beyond that of silicon. Although bulk heterojunctions (BHJs) are widely used in organic photodetectors (OPDs), achieving a high signal-to-noise ratio in the near-infrared spectrum is often challenging due to the inherently large dark currents in low-bandgap polymers and their blending morphology effect. Herein, we investigate the origin of dark currents in near-infrared OPDs and reveal a strategy to improve the detectivity in terms of two aspects: (1) donor–acceptor blending morphology and (2) effects of carrier injection from outer electrodes. To do so, a series of random terpolymers were synthesized in a similar band structure and their blending morphology with the PC71BM acceptor was gradually controlled. As the phase separation was smaller, the dark current gradually reduced while the responsivity increased, leading to a higher detectivity. Complex charge-transporting paths formed under the fine percolating network account for the dark current reduction, while the increased heterojunction area facilitates the dissociation of the photogenerated excitons. From our thermal admittance spectroscopy, deeper sub-bandgap states were found under the smaller phase separation, further contributing to the dark current reduction. Second, the carrier injection effect was revealed by inserting a charge-blocking layer at the active layer/electrode interface. While manipulating both parameters could yield a high near-infrared detectivity up to 1012 Jones at −0.5 V, the blending morphology effect turns out to be more dominant over the carrier injection effect in suppressing the dark current and achieving higher detectivity in BHJ OPDs.

HgCdTe/black phosphorus van der Waals heterojunction for high-performance polarization-sensitive midwave infrared photodetector.

New-generation infrared detectors call for higher operation temperature and polarization sensitivity. For traditional HgCdTe infrared detectors, the additional polarization optics and cryogenic cooling are necessary to achieve high-performance infrared polarization detection, while they can complicate this system and limit the integration. Here, a mixed-dimensional HgCdTe/black phosphorous van der Waals heterojunction photodiode is proposed for polarization-sensitive midwave infrared photodetection. Benefiting from van der Waals integration, type III broken-gap band alignment heterojunctions are achieved. Anisotropy optical properties of black phosphorous bring polarization sensitivity from visible light to midwave infrared without external optics. Our devices show an outstanding performance at room temperature without applied bias, with peak blackbody detectivity as high as 7.93 × 1010 cm Hz1/2 W−1 and average blackbody detectivity over 2.1 × 1010 cm Hz1/2 W−1 in midwave infrared region. This strategy offers a possible practical solution for next-generation infrared detector with high operation temperature, high performance, and multi-information acquisition.

High-performance dual-mode ultra-thin broadband CdS/CIGS heterojunction photodetector on steel.

An ultra-thin CdS/CIGS heterojunction photodiode fabricated on steel firstly exhibits dual-mode broadband photodetection from ultraviolet to near infrared spectrum. In the photovoltaic mode, the CIGS photodiode, working as a self-driven photodetector, shows an outstanding photodetection capability (under a light power density of 20 µW cm-2 at 680 nm), reaching a record detectivity of ∼4.4×1012 Jones, a low noise equivalent power (NEP) of 0.16 pW Hz-1/2 and a high Ilight/Idark ratio of ∼103, but a relatively low responsivity of ∼0.39 A W-1 and an external quantum efficiency (EQE) of ∼71%. Working under the same illumination but in the photoconductive mode (1 V reverse bias), the responsivity and EQE are significantly enhanced to 1.24 A W-1 and 226%, respectively, but with a relatively low detectivity of 7×1010 Jones and a higher NEP of 10.1 pW Hz-1/2. To explain these results, a corrected photoconductive gain (G) model indicates that minority electrons could be localized in the defects, surface states and depletion region of the CIGS photodiode, causing excess hole accumulation in the ultra-thin CIGS photodiode and thus high EQE over 100% (G over 1).

Laser ablation fabrication of a p-NiO/n-Si heterojunction for broadband and self-powered UV–Visible–NIR photodetection

We report on the optoelectronic characteristics of p-NiO/n-Si heterojunction photodiode for broadband photodetection, fabricated by depositing a p-type NiO thin film onto a commercial n-type silicon substrate using pulsed laser deposition (PLD) technique. The structural properties of the PLD-grown p-NiO material were analysed by means of x-ray diffraction and x-ray photoelectron spectroscopy, confirming its crystalline nature and revealing the presence of Ni vacancies, respectively. Hall measurements confirmed the p-type semiconducting nature of the NiO thin film having a carrier concentration of 8.4 × 1016 cm−3. The current–voltage (I–V) characteristics of the p-NiO/n-Si heterojunction photodevice were investigated under different wavelengths ranging from UV to NIR. The self-bias properties under different illuminations of light were also explored systematically. Under self-bias condition, the photodiode exhibits excellent responsivities of 12.5 mA W−1, 24.6 mA W−1 and 30.8 mA W−1 with illumination under 365 nm, 485 nm, and 850 nm light, respectively. In addition, the time dependency of the photoresponse of the fabricated photodevice has also been investigated and discussed thoroughly.

Controllable carrier polarity in 2D HfS2(1−x)Te2x for short-wave infrared photodiodes

Infrared photodetectors and cameras have been demonstrated important applications in intelligent society. The current infrared detectors based on III-V/II-VI semiconductors, however, always suffer from complex preparation processes, high cost, and cryogenic operations. Two-dimensional (2D) layered materials with tunable bandgaps and good optoelectronic properties, therefore, show great potential for high-performance infrared photodetection. Furthermore, the tunable carrier polarities in 2D layered materials are the essential requirements for fabrication of functional elements (p-n junctions or inverters). Here, we reported synthesized 2D HfS2(1−x)Te2x single-crystalline materials with highly-tunable carrier polarity (n-type, intrinsic, p-type, or semimetal) for short-wave infrared (SWIR) photodetection. Electrical measurements and density-functional theory calculations show their carrier polarity and bandgaps can be modulated simultaneously by varying chemical compositions. We then demonstrated HfS0.68Te1.32/HfS1.8Te0.2 van der Waals heterojunction photodiodes which exhibited a desired room-temperature specific detectivity of 3.5 × 109 cm Hz1/2 W−1 and fast response time of 78.9/ 95 μs in SWIR regime. Our work provides an alternative strategy for broadband detection using bandgap engineering and tunable carrier polarities in 2D layered materials.

Synthesis and characterization of 4-[2(3-acetylphenyl) diazenyl]-3,5-dimethylphenol for heterojunction photodiode applications

Synthesis of azo dye, 4-[2(3-acetylphenyl) diazenyl]-3,5-dimethylphenol (ADD), is presented. The structural, linear optical and non-linear optical properties of ADD are studied together with the Ag/ADD/p-Si/Al heterojunction photodiode characteristics. The synthetic ADD is examined by using both Fourier transform infrared spectroscopy and nuclear magnetic resonance techniques. Its structure is also investigated using both X-ray diffraction and scanning electron microscopy techniques. Based on the spectrophotometric measurements of ADD thin film, several linear-optical parameters are calculated from the absorption spectra. The single-oscillator model is used to explain the dispersion parameters of ADD thin films. Semi-empirical relations are used to calculate the non-linear optical parameters from the linear optical parameters. The good optical properties of ADD thin films qualify ADD to be used in optoelectronic applications. So, Ag/ADD/p-Si/Al heterojunction photodiode is fabricated and its electrical properties are studied. Moreover, the Ag/ADD/p-Si/Al photodiode parameters (sensitivity, resistivity and detectivity) show good response to different illumination intensities.

High-performance multicolor p-Ag:NiOx/n-Si heterojunction photodiode enhanced by Ag-doped NiOx

Silver (Ag)-doped NiOx (Ag:NiOx) is employed to enhance the broad-band spectrum from ultraviolet (UV) and visible to infrared response of multicolor p-NiOx/n-Si heterojunction photodiodes (HPDs). The Ag:NiOx is spin coated on n-Si substrate with a molar ratio (AgNO3:Ni(CH3COO)2) of 1.6:1. In comparison with conventional p-NiOx/n-Si HPDs, p-Ag:NiOx/n-Si HPDs significantly increase the rectification ratio from 5.7 × 102 to 3.4 × 104 (60 times). The Ag-doped NiOx largely enhance the photoresponse of the prepared HPDs in the wavelength range of 300–1000 nm. The enhancement factor exceeds 100 times for the wavelength longer than 500 nm, and reaches a maximum (213 times) at 900 nm. The Ag-doped NiOx increases photo-to-dark current ratio in the prepared HPDs, the ratio is enhanced by about 180 times in the visible and infrared light. The mechanism is caused by that the conductivity of Ag-doped NiOx is increased owing to the inducing crystallization of NiOx by Ag atoms. The Ag atoms accumulate at the grain boundaries of Ag:NiOx nanoclusters and passivate the point defects of Ag:NiOx. The Ag atoms in Ag:NiOx diffuse into the n-Si and convert the top surface of n-Si into p-Si. The graded potential in p-Si and built-in field at p-Si/n-Si interface accelerate the photo-generated carriers to be extracted, leading to a higher broad-band phtotoresponse.

A self-powered β-Ga2O3/CsCu2I3 heterojunction photodiode responding to deep ultraviolet irradiation

In this paper, a lead-free halide perovskite CsCu2I3 film with high stability was prepared by the anti-solvent assisted crystallization method. Then, we coupled it with Ga2O3 to prepare a corresponding heterojunction deep ultraviolet (UV) photodetector. After testing, we concluded that the photodetector is sensitive to 254 nm UV light. The photodetector has good reproducibility, and has an ultra-high photo-to-dark current ratio (PDCR) of more than 105. In addition, under a bias of 10 V and an illuminated intensity of 200 μW/cm2, the responsivity (R) and specific detectivity (D*) reached 20 mA/W and 107 cm Hz1/2 W−1 (Jones), and the external quantum efficiency (EQE) is 10%. Meanwhile, the prepared photodetector could operate at zero bias, i.e., self-powered operation, along with a photocurrent of about 1 nA under illumination with UV light intensity of 200 μW/cm2.

X-ray Sensitive hybrid organic photodetectors with embedded CsPbBr3 perovskite quantum dots

X-ray detection is an important technology for medical diagnosis as well as industrial and security inspections. While today's commercial X-ray detectors are bulky, photodetectors based on organic semiconductors have attracted increasing attention owing to their low temperature processing capabilities, flexibility and low cost. Nonetheless, the low X-ray attenuation coefficient of organic semiconductors still hinders their practical application. Herein, a new organic-inorganic hybrid strategy is proposed to improve the X-ray sensitivity of organic photodetectors (OPDs). A solution-processed X-ray sensitive hybrid OPD is fabricated by embedding CsPbBr 3 quantum dots (QDs) into a P3HT:PC 61 BM bulk heterojunction photodiode. The QDs, acting as embedded scintillators in the organic active layer, maintain a high radioluminescence. The proposed hybrid structure enables indirect X-ray detection in a comprehensive manner. These hybrid photodetectors exhibit suppressed dark current densities in the range of tens of picoamperes per square centimeters for different weight ratios of blended QDs. The best OPD achieves a sensitivity of 229.6 e nGy −1 mm −2 (3.67 μC Gy −1 cm −2 ) and a dark current of 23.3 pA cm −2 at a low operating voltage (−3 V) for 20–80 kV “soft” X-rays, thus representing great potential for the development of next generation low cost, portable, and highly sensitive X-ray detectors. • An all-in-one X-ray photodetector is realized by embedding CsPbBr 3 QDs into the P3HT:PC 61 BM photodiode. • The hybrid photodetectors exhibit suppressed dark current densities and high photosensitivity. • Great enhancement in X-ray sensitivity is achieved with CsPbBr 3 QDs.

Near-Infrared Self-Powered Linearly Polarized Photodetection and Digital Incoherent Holography Using WSe2/ReSe2 van der Waals Heterostructure.

Polarization-sensitive photodetection has attracted considerable attention as an emerging technology for future optoelectronic applications such as three-dimensional (3D) imaging, quantum optics, and encryption. However, traditional photodetectors based on Si or III-V InGaAs semiconductors cannot directly detect polarized light without additional optical components. Herein, we demonstrate a self-powered linear-polarization-sensitive near-infrared (NIR) photodetector using a two-dimensional WSe2/ReSe2 van der Waals heterostructure. The WSe2/ReSe2 heterojunction photodiode with semivertical geometry exhibits excellent performance: an ideality factor of 1.67, a broad spectral photoresponse of 405-980 nm with a significant photovoltaic effect, outstanding linearity with a linear dynamic range wider than 100 dB, and rapid photoswitching behavior with a cutoff frequency up to 100 kHz. Strongly polarized excitonic transitions around the band edge in ReSe2 lead to significant 980 nm NIR linear-polarization-dependent photocurrent. This linear polarization sensitivity remains stable even after exposure to air for longer than five months. Furthermore, by leveraging the NIR (980 nm)-selective linear polarization detection of this photodiode under photovoltaic operation, we demonstrate digital incoherent holographic 3D imaging.

High performance MoTe2/Si heterojunction photodiodes

We report the fabrication of high performance MoTe2/Si heterojunction photodiodes by direct growth of MoTe2 patterns on a commercial Si substrate by a feasible chemical vapor deposition method. The devices exhibit an ultrafast response speed with a rise/fall time of 5/8 μs, a broadband (400–1550 nm) photoresponse, a high on/off ratio of ∼104, and self-powered photo-detection with a zero bias responsivity of 0.26 A W−1 and a detectivity of 2 × 1013 Jones at 700 nm wavelength. The devices further show high stability in air for one month. This investigation offers the feasibility to fabricate high performance MoTe2/Si photodiodes for future vital optoelectronic applications.

Photon-trapping array for enhanced midwave infrared photoresponse

Photonic structures have been attracting great attention as they have the ability to manipulate the photoresponse. Here, we report a hole array for effective photon trapping, therefore facilitating optoelectrical conversion of a midwave infrared photodetector. The integrated device consists of an InAsSb-based heterojunction photodiode and an embedded symmetric hole array penetrating through the top wide bandgap layers into the absorption region, which enables lower dark current, better broadband absorption, and improved polarization-independent photoresponse. The photoresponse enhancements of 26%–170% are achieved in the 2–5 µm range under zero power supply at temperatures from 293 K to 78 K. Combined with the effect of slightly decreasing in bulk dark current density, the zero-bias detectivity is increased by 29% at room temperature without sacrificing the response speed, where the enhanced detectivity increases to 2.09 × 109 Jones. This proposed approach provides a new strategy to boost optoelectrical conversion of photodetectors, thereby facilitating robust photodetection for widespread applications.