Broadband Optoelectronic Devices Research Articles

A DFB-SOA Based Optical Vector Network Analyzer for Characterization of Bandpass Optical Devices

In this paper a novel optical vector network analyzer (OVNA) utilizing a distributed feedback semiconductor optical amplifier (DFB-SOA) is introduced. The proposed OVNA is implemented by converting the transmission response of the optical device under test (ODUT) into the electrical domain. The main principle of the OVNA is predicated on the optical carrier restoration facilitated by the wavelength-selective amplification attribute of the DFB-SOA. The implemented OVNA effectively determined the transmission spectrum of an optical filter possessing a passband of 9-GHz bandwidth, achieving a commendable resolution of 25 MHz in the measurement process. The dynamic range of the OVNA can be broadened by adjust the driven current under the DFB-SOA. Additionally, the detection range of our system can be expanded through the utilization of broadband optoelectronic devices. Furthermore, the OVNA possesses considerable potential for integration onto a single chip.

Visible nonreciprocal light propagation based on titanium nitride and gold in tandem

The disappearance of the permittivity of epsilon-near-zero (ENZ) materials can significantly enhance the optical nonlinear absorption, which provides a feasible way to realize broadband optoelectronic devices. Here, we used titanium nitride (TiN) film with ENZ wavelength at 540 nm as the saturable absorber (SA), and hexagonal gold nanolayer as the reverse saturable absorber (RSA), which are arranged in tandem to fabricate a broadband nonreciprocal passive photonic diode, and the maximum nonreciprocity factor of 4.8 dB was obtained experimentally in the ENZ region. Our results show the potential applications of TiN in nonlinear optical devices, and may make inroads towards the ENZ-based high-performance broadband optoelectronic devices.

Tuning of the Berreman mode of GaN/AlxGa1-xN heterostructures on sapphire: The role of the 2D-electron gas in the mid-infrared

We investigated the mid-infrared optical properties of GaN/Al(x)Ga(1-x)N-type heterostructures on sapphire substrate grown by the Metal-Organic Chemical Vapor Deposition. We show how the polarization-dependent reflection spectrum is affected by the presence of the strain-induced 2D electron gas at the interfaces between Al(x)Ga(1-x)N and GaN layers. In particular, we show that the 2D electron gas contribution, modeled from its density and transport properties, can play a relevant role at the Berreman mode excitation condition. In this framework, our results offer an advanced approach for the optimization and design of GaN-based broadband optoelectronic and energy management devices.

High-damage-threshold mid-infrared saturable absorber enabled by tantalum carbide nanoparticles.

A stable mid-infrared saturable absorber with a high damage threshold is urgently required for high-performance optical modulation in the mid-infrared regime. Here, we demonstrate stable mid-infrared erbium-doped fiber laser generation modulated by tantalum carbide nanoparticles (TaC NPs) experimentally. The TaC NPs show high physicochemical stability, obvious nonlinear optical absorption, and a high damage threshold. By introducing the TaC-based saturable absorber into an erbium-doped fiber laser, stable nanosecond pulses can be successfully delivered with a minimum pulse duration of 575 ns and signal-to-noise ratio of over 40 dB. The experimental results show that TaC NPs can act as a stable mid-infrared pulse modulator, and may make inroads for developing highly stable broadband optoelectronic devices.

Improved 2 µm broadband luminescence in Tm3+/Ho3+ doping tellurite glass.

Tm3+/Ho3+ doping tellurite glasses (TeO2-ZnO-La2O3) were prepared by applying melt-quenching technique, and the ∼2.0 µm band luminescence characteristics were examined. A broadband and relatively flat luminescence at 1600 to 2200 nm was observed in the tellurite glass co-doped by 1.0 mol% Tm2O3 and 0.085 mol% Ho2O3 under the excitation of 808 nm laser diode (LD), which is the result of spectral overlapping of 1.83 µm band of Tm3+ ions and 2.0 µm band of Ho3+ ions. Further, about 103% enhancement was acquired after the introduction of 0.1 mol% CeO2 and 7.5 mol% WO3 at the same time, which is primarily caused by the cross-relaxation between Tm3+ and Ce3+ ions together with the enhanced energy transfer from the Tm3+:3F4 level to Ho3+:5I7 level due to the increase in phonon energy. Spectral characteristics associated with the radiative transition of Ho3+ and Tm3+ ions on the basis of Judd-Ofelt theory, and the fluorescence decay behaviors after the addition of Ce3+ ions and WO3 component were analyzed to understand the broadband and luminescence enhancement. The findings in this work indicate that tellurite glass with optimal Tm3+-Ho3+-Ce3+ tri-doping combination and appropriate amount of WO3 is a prospective candidate for broadband optoelectronic devices operated in the infrared bands.

Broadband nanosecond pulse generation modulated by zirconium triselenide nanoflakes

Broadband nonlinear optical modulators are necessary for versatile applications in optical communication, laser radar, laser manufacturing, etc. Here, we report that the zirconium triselenide (ZrSe3) nanoflakes exhibit robust broadband nonlinear optical absorption and can modulate the Nd:YVO4 solid-state laser and erbium-doped ZBLAN fiber laser to deliver stable nanosecond pulse experimentally. The ZrSe3 nanoflakes have been prepared by the liquid phase exfoliation method successfully and exhibit broadband nonlinear optical absorption in the near-infrared and the mid-infrared regime. With the nonlinear absorption performance of the ZrSe3 nanoflakes, stable pulsed operation has been achieved with the output pulse width as short as 344.68 ns around 1 µm from the Q-switched Nd:YVO4 solid-state laser and 599 ns around 2.8 µm from the erbium-doped ZBLAN fiber laser successfully. The experimental results suggest that ZrSe3 nanoflakes can act as an excellent nonlinear optical modulator towards the mid-infrared regime and may make inroads toward developing high-performance broadband optoelectronic devices.

High-performance flexible broadband photodetectors enabled by 2D Ta2NiSe5 nanosheets

Flexible broadband optoelectronic devices play a prominent role in the areas of daily life including wearable optoelectronic systems, health care, and bio-imaging systems. Two-dimensional (2D) narrow-bandgap materials with atomic thickness, adjustable bandgap, mechanical flexibility, as well as excellent optical and electrical properties exhibit great potential for applications in flexible optoelectronic devices. Here, we demonstrate a high-performance photodetector based on high-quality ternary Ta2NiSe5 nanosheets with a narrow bandgap of 0.25 eV. The photodetectors exhibit broadband photodetection capability in the visible-infrared (IR) spectrum (405–2200 nm) at room temperature. The maximum values of responsivity can reach up to 280 A W−1 at the wavelength of 405 nm. Meanwhile, the high responsivity of 63.9 A W−1 and detectivity of 3.8 × 109 Jones are achieved at the wavelength of 2200 nm, respectively. In addition, the obtained Ta2NiSe5-based photodetector shows excellent flexibility and the photodetection performance is almost insignificantly degraded after 1000 bending cycles. These results indicate that the 2D Ta2NiSe5 semiconductor has great potential in future wearable IR optoelectronic devices.

2D Nb<sub>2</sub>CT<sub><i>x</i></sub> MXene/MoS<sub>2</sub> heterostructure construction for nonlinear optical absorption modulation

Two-dimensional (2D) nonlinear optical mediums with high and tunable light modulation capability can significantly stimulate the development of ultrathin, compact, and integrated optoelectronics devices and photonic elements. 2D carbides and nitrides of transition metals (MXenes) are a new class of 2D materials with excellent intrinsic and strong light-matter interaction characteristics. However, the current understanding of their photo-physical properties and strategies for improving optical performance is insufficient. To address this issue, we rationally designed and <italic>in situ</italic> synthesized a 2D Nb₂C/MoS₂ heterostructure that outperforms pristine Nb₂C in both linear and nonlinear optical performance. Excellent agreement between experimental and theoretical results demonstrated that the Nb₂C/MoS₂ inherited the preponderance of Nb₂C and MoS₂ in absorption at different wavelengths, resulting in the broadband enhanced optical absorption characteristics. In addition to linear optical modulation, we also achieved stronger near infrared nonlinear optical modulation, with a nonlinear absorption coefficient of Nb₂C/MoS₂ being more than two times that of the pristine Nb₂C. These results were supported by the band alinement model which was determined by the X-ray photoelectron spectroscopy (XPS) experiment and first-principal theory calculation. The presented facile synthesis approach and robust light modulation strategy pave the way for broadband optoelectronic devices and optical modulators.

High-Gain MoS2/Ta2NiSe5 Heterojunction Photodetectors with Charge Transfer and Suppressing Dark Current

Emerging two-dimensional narrow band gap materials with tunable band gaps and unique electrical and optical properties have shown tremendous potential in broadband photodetection. Nevertheless, large dark currents severely hinder the performance of photodetectors. Here, a MoS2/Ta2NiSe5 van der Waals heterostructure device was successfully fabricated with a high rectification ratio of ∼104 and an ultralow reverse bias current of the pA level. Excitingly, the charge transfer and the generation of the built-in electric field of heterostructures have been proved by theory and experiment, which effectively suppress dark currents. The dark current of the heterostructure reduces by nearly 104 compared with the pure Ta2NiSe5 photodetector at Vds = 1 V. The MoS2/Ta2NiSe5 device exhibits excellent photoelectric performance with the maximum responsivity of 515.6 A W-1 and 0.7 A W-1 at the wavelengths of 532 and 1064 nm under forward bias, respectively. In addition, the specific detectivity is up to 3.1 × 1013 Jones (532 nm) and 2.4 × 109 Jones (1064 nm). Significantly, the device presents an ultra-high gain of 6 × 107 and an exceptional external quantum efficiency of 1.2 × 105% under 532 nm laser irradiation. The results reveal that the MoS2/Ta2NiSe5 heterostructure provides an essential platform for the development and application of high-performance broadband optoelectronic devices.

Native defect-related broadband ultrafast photocarrier dynamics in n-type β-Ga2O3

We report two-photon excited ultrafast carrier trapping and recombination in n-type β-Ga2O3 crystals by using femtosecond transient absorption spectroscopy. The broadband absorption spectra arising from the defect are polarization dependent, especially, two absorption peaks can be observed by subtracting the absorption transients under two probe polarizations. We attribute these observed defect-related absorption features to optical transitions from the valence band to different charge states of a native defect (such as gallium vacancies). A model for carrier capture by multilevel of a single defect is proposed to interpret the data, wherein holes are captured more efficiently than electrons by the defects, and the absorption cross sections for the defects are at least ten times larger than that for free carriers. Our results reveal the potential applications of β-Ga2O3 in ultrafast and broadband optoelectronic devices.

Broadband 1T-polytype tantalum disulfide saturable absorber for solid-state bulk lasers

1T-polytype tantalum disulfide ( 1 T-TaS 2 ), an emerging strongly correlated material, features a narrow bandgap of 0.2 eV, bridging the gap between zero-bandgap graphene and large-bandgap 2D nonlinear optical (NLO) materials. Combined with its intense light absorption, high carrier concentration, and high mobility, 1 T-TaS 2 shows considerable potential for applications in broadband optoelectronic devices. However, its NLO characteristics and related applications have rarely been explored. Here, 1 T-TaS 2 nanosheets are prepared by chemical vapor deposition. The ultrafast carrier dynamics in the 400–1100 nm range and broadband NLO performance in the 515–2500 nm range are systematically studied using femtosecond lasers. An obvious saturable absorption phenomenon is observed in the visible to IR range. The nonlinear absorption coefficient is measured to be − 22.60 ± 0.52 cm MW − 1 under 1030 nm, which is larger than that of other typical 2D saturable absorber (SA) materials (graphene, black phosphorus, and MoS 2 ) under similar experimental conditions. Based on these findings, using 1 T-TaS 2 as a new SA, passively Q-switched laser operations are successfully performed at 1.06, 1.34, and 1.94 μm. The results highlight the promise of 1 T-TaS 2 for broadband optical modulators and provide a potential candidate material system for mid-IR nonlinear optical applications.

Correlated Dynamics of Free and Self‐Trapped Excitons and Broadband Photodetection in BEA2PbBr4 Layered Crystals

AbstractSelf‐trapped excitons (STEs) exert a profound impact on the optical properties and device applications of 2D halide perovskites. Particularly distinct exciton self‐trapping and detrapping processes can facilitate the intelligent design of perovskite optoelectronic devices with emerging functionalities. Thus, a comprehensive understanding and regulation of exciton trapping and detrapping dynamics are highly desired. Herein, the authors report a 2D lead halide perovskite (BEA2PbBr4 where BEA is 2‐bromine ethylamine) with exceptional broadband photoluminescence (PL), which originates from multiple STE states. In particular, the unique energy‐level configuration of STEs with respect to free excitons is revealed by exploiting optical spectroscopy. Consequently, these distinct phenomena empower the broadband photodetection capability of BEA2PbBr4 photodetectors over a wide range from ultraviolet to near‐infrared wavelengths. These results provide an essential understanding of the intriguing photophysics of STEs and shed new light on the future development of single‐component perovskite broadband optoelectronic devices.

Tailoring Femtosecond‐Laser Processed Black Silicon for Reduced Carrier Recombination Combined with &gt;95% Above‐Bandgap Absorption

The femtosecond‐pulsed laser processed black silicon (fs‐bSi) features high absorptance in a wide spectral range but suffers from high amount of laser induced damage as compared with bSi fabricated by other methods. Here, the aim is to minimize the charge carrier recombination in the fs‐bSi caused by laser damage as indicated by the sub‐bandgap absorption and as quantified by the carrier lifetime, while maintaining high absorption in the above bandgap. The effect of the laser parameters, including the focal position, the average power, and the scan speed are systematically studied by characterizing the surface morphology, the absorptance spectra, and the minority‐carrier recombination lifetime. For the surface passivation of fs‐bSi, the well‐established atomic layer deposited (ALD) Al2O3 is used. The results show that with the tailored laser parameters, high average absorptance of about 96% in the visible range and minority carrier lifetime of 54 μs at the injection level of Δn = 1 · 1015 cm−3 can be obtained simultaneously. This work paves the way toward high‐performance broadband optoelectronic devices based on surface passivated fs‐bSi.

Robust nanosecond laser passively Q-switched by tin selenide nanoflowers

We report the generation of the robust nanosecond Nd:YVO4 solid-state laser and Er3+:ZBLAN fiber laser passively Q-switched by the tin selenide (SnSe) nanoflowers saturable absorbers. The SnSe nanoflowers prepared via chemical precipitation method exhibit broadband nonlinear optical absorption performance, and can modulate the separate lasers to deliver stable nanosecond pulse ∼1 µm and ∼2.8 µm successfully. The experimental results show that the low-dimensional transition-metal monochalcogenides hold great potential for the broadband robust saturable absorbers, and may pave an avenue toward developing high-performance broadband optoelectronic devices.

Broadband Nonlinear Photoresponse and Ultrafast Carrier Dynamics of 2D PdSe2

AbstractPalladium diselenide (PdSe2) exhibits considerable potential for application in broadband optoelectronic devices. In this work, the broadband nonlinear optical performance and ultrafast carrier dynamics from ultraviolet to near‐infrared of a trilayer PdSe2 are systematically studied. PdSe2 is found to achieve a giant saturable absorption performance. The modulation depth is 22.47% at 520 nm, whereas the nonsaturable loss and saturation intensity are only 3.83% and 15.47 GW cm−2, respectively, which are better than those of many 2D semiconductors. Based on these findings, a PdSe2‐based visible light thresholder is proposed, its function is to extract an undetectable pulse signal drowned in strong stochastic noise and thereby improve the signal‐to‐noise ratio. Pump–probe technique, along with first‐principles calculation and transient absorption spectra, reveals the intrinsic recombination mechanism, including Auger scattering and trap saturation. This work is expected to establish the foundation for the development of next‐generation PdSe2‐based devices in optoelectronics and visible light communication.

Weyl Semiconductor Te/Sb2Se3 Heterostructure for Broadband Photodetection and Its Binary Photoresponse by C60 as Charge‐Regulation Medium

AbstractRecently, elemental semiconductor Tellurium (Te) has been proven as a novel Weyl semiconductor with nontrivial Weyl fermion nature, indicating wonderful application prospect in future topological optoelectronic devices. Herein, large‐area photodetectors (PDs) of Te/Sb2Se3 and Te/C60/Sb2Se3 heterostructure are fabricated based on a molecular beam epitaxy (MBE)‐grown Te film, which is theoretically equivalent to parallel‐connection circuit due to special device architecture. The constructed Te/Sb2Se3 PD exhibits high‐sensitivity and broad spectral detection region from visible (405 nm) to mid‐infrared (4500 nm) wavelengths benefited from efficient synergistic multi‐mechanism including photoconductive and photo‐thermoelectric effects, achieving outstanding performance parameters such as high peak of responsivity (Ri) of 110.8 A W−1, detectivity (D*) of 2.09 × 1013 Jones, and fast rise time about 31 ms at 808 nm, respectively. Furthermore, by depositing C60 between Te and Sb2Se3 as charge‐regulation medium, the novel binary photocurrent signal output phenomenon depending on wavelengths and optical power densities is observed in Te/C60/Sb2Se3 ternary system, for which related mechanism is also investigated combined with spectral absorption characteristics, energy‐band arrangement, and light regulation experiment. This work provides a new pathway to fabricate superior multifunctional Te‐based PD, indicating promising prospects applied to next‐generation broadband optoelectronic devices with light‐controlled logic signal recognition function.

Low-temperature deposition of 2D SnS nanoflakes on PET substrates for flexible photodetectors with broadband response

Flexible photodetectors based on two-dimensional (2D) materials hold the promise to open up an unprecedented era for wearable optoelectronic systems. However, there is a major challenge of the inability to directly deposit 2D materials on polymeric substrates due to their high growth temperature. Here, we demonstrate a novel low-cost method to directly fabricate SnS nanoflakes on the poly-ethylene terephthalate substrates. Moreover, the flexible photodetectors based on SnS nanoflakes feature broadband spectral responses from 355 nm to 1550 nm. The responsivity and detectivity can approach up to 1.28 × 103 A W−1 and 3.02 × 1011 Jones, respectively, under the ultraviolet laser of 355 nm. The devices also exhibit excellent NIR photodetection with a specific responsivity of 69 A W−1 towards the 1550 nm regime. Our research represents an important step toward scalable fabrication of the SnS nanoflakes and this method may pave a path for the future commercialization of flexible broadband optoelectronic devices.

Solution-processed, flexible and broadband photodetector based on CsPbBr3/PbSe quantum dot heterostructures

Due to their promising applications in foldable displays, optical communication equipment and environmental monitoring systems, flexible and broadband optoelectronic devices have gained extensive attention in recent years. Here, a flexible and broadband photodetector based on CsPbBr3/PbSe quantum dot (QD) heterostructures is firstly presented. The integrated QD heterostructures possess consecutive detection range from ultraviolet (UV) to long-wavelength infrared (LW-IR) regions with efficient light absorption and chemical stability, in comparison with the pristine PbSe QDs. Systematic material characterizations reveal the improved exciton dissociation, carrier transport and carrier lifetime of the QD heterostructures. Flexible photodetector Ag/CsPbBr3/PbSe/Ag demonstrate a high responsivity of 7.17 A/W with a specific detectivity of 8.97 × 1012 Jones under 25 μW/cm2 365 nm illumination at 5 V. Furthermore, it could maintain 91.2 % (or 94.9 %) of its initial performance even after bending for thousands of times (or exposing in ambient air for 4 weeks). More importantly, its response time is shortened more than three orders of magnitude as that of pristine PbSe QDs-based photodetectors. Therefore, it provides a feasible and promising method for the next-generation high-performance broadband photodetectors via constructing heterostructures of various QDs.

High‐Performance Broadband Tungsten Disulfide Photodetector Decorated with Indium Arsenide Nanoislands

The 2D tungsten disulfide (WS2), as a typical transition metal dichalcogenide (TMD), has aroused intense research interests in photodetection. However, the limited detection wavelength ranges and low photoresponsivity hinder its further application. To promote the application of WS2 in optoelectronics fields, indium arsenide (InAs) nanoislands decorated WS2 are utilized to fabricate photodetectors in this work. Owing to the photogating effect and localized surface plasmon resonance (LSPR), a significant enhancement of photocurrent response (≈1 mA W−1) is obtained by coupling WS2 with InAs nanoislands. Furthermore, the extended detection wavelength up to 1060 nm is realized due to the efficient light absorption in IR range of InAs nanoislands. The high performance, stability, and reliability in ambient temperature strongly indicate that the InAs nanoislands/WS2 heterostructure can be considered as a promising material for TMDs‐based broadband optoelectronic devices in the future.

Nonlinear Optical Response in Natural van der Waals Heterostructures

AbstractVan der Waals heterostructures (vdWH) composed from individual 2D crystals offer a platform to obtain unprecedented functionalities that are not accessible in other heterostructures. The research to date has been largely limited to exfoliated and restacked flakes, and the controlled growth of such heterostructures remains a significant challenge. Here, an experimental study of the broadband nonlinear optical performance of a naturally occurring vdWH franckeite is presented, which is composed of alternating SnS2‐like and PbS‐like layers stacked on top of each other. Few‐layer franckeite is prepared via liquid‐phase exfoliation method and its broadband ultrafast third‐order nonlinear optical behavior is characterized experimentally. It is found that the layered franckeite exhibits broadband nonlinear optical response and the ultrafast carrier dynamics with the intraband carrier recovery time of ≈16 ps and the interband carrier recovery time of ≈300 ps. With the large optical nonlinearity of layered franckeite, the all‐optical modulator and switcher have been demonstrated based on the spatial phase modulation effect. The experimental results provide a fundamental understanding of the ultrafast nonlinear optical response in a complex naturally occurring vdWH, and may pave an avenue toward developing novel broadband optoelectronic devices.