Search

Ga 2 O 3 -based Ultraviolet-C photodetector (UVCPD) is considered the most promising UVCPD at present and is divided into Metal-Semiconductor-Metal (MSM) and PN junction types. Compared with MSM-PDs, PN-PDs exhibit superior transient performance due to the built-in electric field. However, current Ga 2 O 3 -based PN-PDs lack consideration for carrier collection and electric field distribution. In this study, PN-PDs with an interdigital n-Ga 2 O 3 layer and finger electrodes are fabricated on p-GaN/n-Ga 2 O 3 epilayers. Ultrafast response times of 31 µs (1/e decay) and 2.76 µs (fast component) are realized, which outperforms all Ga 2 O 3 UVC-PDs up to now. Under 0 V self-powered, the responsivity (0.25 A W -1 ) of interdigital PD is enhanced by the interdigital electrode structure due to increasing carriers' collection length. Under bias, the performances of interdigital PD with 41.7 A W -1 responsivity and 8243 selection ratios are significantly elevated by enhancing the built-in electric field in the Ga 2 O 3 region, which is 34.76 and 39.4 times those of traditional PDs, respectively. The intrinsic enhancing mechanism of interdigital structure is also investigated by interdigital PDs with various electrode spacings and perimeters. In summary, this paper not only reports a highly performed interdigitated structure p-GaN/n-Ga 2 O 3 UVCPDs, but also provides guidelines for structure design in Ga 2 O 3 -based PN-PDs., (© 2023 Wiley‐VCH GmbH.)

Flexible optoelectronic platforms, which integrate optoelectronic devices on a flexible substrate, are promising in more complex working environments benefiting from the mechanical flexibility. Herein, for the first time to the best of our knowledge, a flexible GaN-based vertical cavity surface-emitting laser (VCSEL) in the ultraviolet A (UVA) range was demonstrated by using a thin-film transfer process based on laser lift-off (LLO) and spin-coating of a flexible substrate. The lasing wavelength is 376.5 nm with a linewidth of 0.6 nm and threshold energy of 98.4 nJ/pulse, corresponding to a threshold energy density of 13.9 mJ/cm 2 . The flexible substrate in this study is directly formed by spin-coating of photosensitive epoxy resin, which is much simplified and cost-effective, and a 2-in. wafer scale GaN-based membrane can be successfully transferred to a flexible substrate through this method. Such flexible UVA VCSELs are promising for the development of next-generation flexible and wearable technologies.

Indium tin oxide (ITO) is often used as a current spreading layer in the GaN-based vertical-cavity surface-emitting lasers (VCSELs). However, the absorption coefficient of ITO is significant, which reduces the laser output power, raises the threshold, and makes VCSELs hardly lase in the ultraviolet range. To find a transparent conductive structure that can replace ITO, we propose a periodic p-AlGaN/u-GaN/p-GaN structure. In the simulation of light-emitting diodes, the optimized parameter is obtained with multi-period 10 nm p-Al 0.1 Ga 0.9 N/2 nm u-GaN/8 nm p-GaN combined with n-GaN/n-Al 0.2 Ga 0.8 N in the n region. Applying the structure to 435 nm VCSELs and comparing it to a common VCSEL with the ITO current spreading layer, it can be found that the new structure reduces the threshold from 9.17 to 3.06 kA/cm 2 . The laser power increases from 1.33 to 15.4 mW. The optimized structure has a high laser power and a lower threshold, which can be used in future investigations.

Flexible optoelectronics is a technique for fabricating optoelectronic devices on a flexible substrate. Compared with conventional devices, flexible optoelectronic devices can be used in more complex working environments benefiting from the mechanical flexibility. Herein, for the first time to the best of our knowledge, a flexible GaN-based microdisk laser on a polyethylene terephthalate (PET) substrate in the ultraviolet A (UVA) range was demonstrated by using thin film transfer process based on laser lift-off (LLO). The lasing wavelength is 370.5 nm with a linewidth of 0.15 nm and a threshold power density of 200 kW/cm 2 . Additionally, a distributed Bragg reflector (DBR) was deposited on the backside of the microdisk as the bottom mirror between GaN microdisk and PET substrate, which can provide better mode confinement inside the microdisk and increases the oscillation intensity. The lasing wavelength of the flexible laser shows a 2-nm redshift under different bending curvature of the substrate, which is promising for applications such as mechanical sensing.

Recently, inorganic halide perovskites, especially CsPbBr 3 , have been attracting attention because of their high efficiency, wide color gamut, and narrow luminescent spectrum. To elevate the perovskite devices' performance, optimizations of crystalline quality, device structures, and fabrication process are essential. Currently, the state-of-the-art fabrication approach of CsPbBr 3 is spin-coating in an inert environment (nitrogen, argon, etc.), which requires temperature and humidity control. In this work, a CsPbBr 3 -based visible photodetector (PD) is realized in a humid atmosphere, whose performances were comparable to those reported in an inert glovebox. The dependencies of responsivity and transient time on CsBr coating layer numbers and electrode period were also investigated. The best device performance was obtained with 4 layers of CsBr coating with a responsivity of 107.2 mA/W, detectivity of 4.29 × 10 10  Jones, and quantum efficiency of 25.4%. The rise time of the 3-4-layer CsBr-coated PD was reduced by the higher crystalline quality and carrier mobility, while the decay time of the 1-layer CsBr-coated PD was faster since the dense defect induced non-radiative recombination centers. With the period T increasing, the responsivity decreased, while the transient times increased. We believe that our results could benefit the future optimization of perovskite materials and PDs.

Based on the molecular energy transfer mechanism, relative gains at 1067 and 637 nm wavelengths are achieved in thermally activated delayed fluorescence molecule AQ(PhDPA) 2 and Nd complex with chelating phosphine oxide as ligands codoped polymer waveguides, with the excitation of low-power UV light-emitting diodes (LEDs) instead of traditional semiconductor lasers as pump sources. For AQ(PhDPA) 2 -Nd(DBTTA) 3 (DBFDPO) (DBTTA = dibenzotetrathienoacene, DBFDPO = 4,6-bis (diphenylphosphoryl) dibenzofuran) -codoped polymethylmethacrylate (PMMA), and AQ(PhDPA) 2 -Nd(DBTTA) 3 (FDPO) (FDPO = 9,9-bis (diphenylphosphorylphenyl) fluorene)-codoped PMMA polymers with a mass ratio of 1:4 respectively, when they are spin-coated as upper claddings, the relative gains of 2.2 and 1.8 dB cm -1 at 1067 nm are obtained in evanescent-field waveguides with cross-section of 4 × 8 µm 2 under excitation of 300 mW 405 nm LED, and the gains of 3.9 and 4.9 dB cm -1 at 637 nm are achieved with pumping of 530 mW 450 nm LED respectively. By growing a 100 nm-thick aluminum reflector with the waveguides, the optical gain at 1067 and 637 nm can be enhanced to 3.5 and 6.1 dB cm -1 , corresponding to AQ(PhDPA) 2 -Nd(DBTTA) 3 (DBFDPO) and AQ(PhDPA) 2 -Nd(DBTTA) 3 (FDPO)-codoped PMMA polymers, respectively., (© 2023 Wiley-VCH GmbH.)

Chelate phosphine oxide ligand (9,9-dimethyl-9H-xanthene-4,5-diyl) bis (diphenylphosphineoxide) (XPO) is prepared as a neutral ligand to synthesize complex Nd (TTA) 3 (XPO) (TTA = 2-thenoyltrifluoroacetone). An appropriate energy gap between the XPO and TTA ligands, which can support two additional energy transfer routines from the first excited triplet state (T 1 ) energy level of the XPO to that of the TTA, improves energy transfer in the Nd complex. Based on intramolecular energy transfer mechanism, optical gains at 1.06 and 1.31 µm are demonstrated in Nd (TTA) 3 (XPO)-doped polymer waveguides with the excitation of low-power light-emitting diodes (LEDs) instead of semiconductor lasers as pump sources. Using the vertical top-pumping mode of a 365 nm LED, relative gains of 22.5 and 8.4 dB cm -1 are obtained at 1.06 and 1.31 µm, respectively, in a 0.2 cm long embedded waveguide with a cross-section of 8 × 5 µm 2 . The active core layer is Nd (TTA) 3 (XPO)-doped SU-8 polymer. Moreover, relative gains are achieved in evanescent-field waveguide with a cross-section of 6 × 4 µm 2 . The 21.0 and 5.6 dB cm -1 relative gains are achieved at 1.06 and 1.31 µm, respectively, with a net gain of 13.8 ± 0.3 dB cm -1 obtained at 1.06 µm in a 0.9 cm long SU-8 waveguide with Nd (TTA) 3 (XPO)-doped polymethylmethacrylate as upper cladding., (© 2023 Wiley-VCH GmbH.)

Based on the intramolecular energy transfer mechanism between organic ligand TMHD (2, 2, 6, 6-tetramethyl-3, 5-heptanedione) and central Er 3+ ions, optical gains at 1.55 µm were demonstrated in three structures of polymer waveguides using complex Er(TMHD) 3 -doped polymethylmethacrylate (PMMA) as the active material. With the excitation of two low-power UV light-emitting diodes (LEDs) instead of 980 or 1480 nm lasers, relative gains of 3.5 and 4.1 dB cm -1 were achieved in a 1-cm-long rectangular waveguide with an active core of Er(TMHD) 3 -doped PMMA polymer. Meanwhile, relative gain of 3.0 dB cm -1 was obtained in an evanescent-field waveguide with cross-section of 4 × 4 µm 2 using passive SU-8 polymer as core and a ∼1-µm-thick Er(TMHD) 3 -doped PMMA as upper cladding. By growing a 100 nm thick aluminum mirror and active lower cladding, the optical gain was doubled to 6.7 dB cm -1 in evanescent-field waveguides because of the stimulated excitation of Er 3+ ions in the upper and lower cladding and the improved absorption efficiency.

In this Letter, GaN-based green resonant-cavity light-emitting diodes (RCLEDs) with a low-cost aluminum (Al) metal bottom mirror, a dielectric top mirror, and a copper (Cu) supporting plate were fabricated. The green-emitting epitaxial wafer was grown on a patterned sapphire substrate (PSS) to ensure high crystal quality (CQ). Laser lift-off (LLO) of the PSS and electrical plating of a Cu supporting plate were then carried out to realize the vertical device structure. The emission wavelength and full width at half maximum (FWHM) of the main emission peak of the device are ∼518 nm and 14 nm, respectively. Under the current density of 50 A/cm 2 , a relatively high light output power (LOP) of 11.1 mW can be obtained from the green RCLED. Moreover, when the current injection is 20 mA (8 A/cm 2 ), the corresponding forward bias voltage is as low as ∼2.46 V. The reasons for the low operating voltage and high LOP can be attributed to the improvement of CQ, the release of residual compressive stress of the GaN-based epilayer due to the removal of PSS, and better heat dissipation properties of the Cu supporting plate.

Since the emerging development of CsPbBr 3 perovskite, chemical vapor deposition (CVD) has become one of the most promising fabrication techniques by which to precisely deposit uniform perovskite thin films. However, there have been few reports on the growth dynamics and chemical reaction parameters ( e.g. , activation energy) for perovskite CVD. In this work, different deposition rates of CVD-grown CsPbBr 3 thin films were obtained at different substrate temperatures. Dynamics equations were developed to relate the inflow rates, desorption coefficients and concentrations of reactants on the substrates. Only a small amount of reactant became activated at low temperature and a small amount of PbBr 2 resided on the substrate at high temperature, and accordingly the maximal deposition rate was achieved at 250 °C. The Arrhenius activation energy of CVD-grown CsPbBr 3 was also calculated, and found to be 31.64 kJ mol -1 . We believe that our work provides a detailed picture of perovskite CVD growth.

A 980 nm semiconductor laser is always selected as the pump source for erbium-ytterbium co-doped optical waveguide amplifiers. In this work, two low-cost blue-violet LEDs, rather than an expensive 980 nm laser, were used to pump an Er 3+ -Yb 3+ co-doped phosphate planar waveguide. When the signal power was 0.4 mW at a 1550 nm wavelength, internal optical gains of about 4.1 and 4.5 dB/cm were respectively obtained under the excitations of a 32 mW/cm 2 , 275 nm LED and a 914 mW/cm 2 , 405 nm LED. It was found that 51.17% of the total Er 3+ ions in the 2 H 9/2 state contributed to the luminescence at 1550 nm, and a theoretical model of gain simulation was established under the excitation of a 405 nm LED. The calculated gain of about 4.1 dB/cm was found to be in accordance with the experimental optical gain results.

III-nitrides based microdisks with the mushroom-type shape are key components for integrated nanophotonic circuits. The air gap undercut in the mushroom-type microdisk is essential for maintaining vertical optical confinement, but this structure is still facing the difficulty of electrical injection. In this work, we demonstrate an electrically injected GaN-based microdisk of such structure. The device is featured with a copper substrate and copper supporting pedestal, through which current can be efficiently injected into the microdisk with low leakage current (less than 10 nA). Bright emission at ∼420 nm was demonstrated from the microdisk under current injection. The copper substrate and supporting pedestal can also extract thermal energy out of the microdisk effectively, and the structure in this work shows a low thermal resistance of ∼788.86 K/W. Low threshold lasing action at ∼405 nm was realized under the optically pumped condition and the threshold energy is ∼35 nJ/pulse. Clear whispering gallery modes were observed and the Q factor is as high as 4504, indicating the high quality of the microdisk cavity. This work is the first step towards low threshold efficient electrically injected microdisk laser with a mushroom-type shape.

Two-dimensional (2D) Ruddlesden-Popper perovskites with bulky organic cations have attracted extensive attention in light-emitting devices and photovoltaics due to their robust environment stability, tunable luminescent color, strong exciton binding and promising efficiency. A quantum well (QW) structure is spontaneously formed by sandwiching PbBr4 layers into bulky organic cations. However, some intrinsic excitonic mechanisms in these materials still need to be elucidated. In this study, the exciton-phonon interaction of quasi-2D (PEA)2(CsPbBr3)n-1PbBr4 with different PbBr4 layer numbers (n) was analyzed by temperature-varied photoluminescence (PL), scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD). The mechanism of bandgap shifting with temperature was found to be dominated by the thermal expansion effect in the large-n 2D and bulk perovskite, and gradually switched to exciton-phonon interaction in the n = 1 (PEA)2PbBr4 phase, indicating enhanced exciton-phonon interaction in the thinner quantum well structure. Further analysis showed that the enhanced exciton-phonon interaction originated from the longitudinal optical phonon-exciton Fröhlich interaction rather than acoustic phonon-exciton coupling. We believe that our results will benefit the further optimization of light-emitting devices based on 2D perovskites.

Low threshold continuous-wave (CW) lasing of current injected InGaN quantum dot (QD) vertical-cavity surface-emitting lasers (VCSELs) was achieved at room temperature. The VCSEL was fabricated by metal bonding technique on a copper substrate to improve the heat dissipation ability of the device. For the first time, lasing was obtained at yellow-green wavelength of 560.4 nm with a low threshold of 0.61 mA, corresponding to a current density of 0.78 kA/cm2. A high degree of polarization of 94% were measured. Despite the operation in the range of "green gap" of GaN-based devices, single longitudinal mode laser emission was clearly achieved due to the high quality of active region based on InGaN QDs and the excellent thermal design of the VCSELs.