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1. ∼8.5 μ m-emitting InP-based quantum cascade lasers grown on GaAs by metal-organic chemical vapor deposition

   https://doi.org/10.1063/5.0122272  

   Xu, S. ; Zhang, S. ; Kirch, J. D. ; Suri, S. ; Pokharel, N. ; Gao, H. ; Kim, H. ; Dhingra, P. ; Lee, M. L. ; Botez, D. ; et al ( October 2022 , Applied Physics Letters)

   Room-temperature, pulsed-operation lasing of 8.5  μm-emitting InP-based quantum cascade lasers (QCLs), with low threshold-current density and watt-level output power, is demonstrated from structures grown on (001) GaAs substrates by metal-organic chemical vapor deposition. Prior to growing the laser structure, which contains a 35-stage In 0.53 Ga 0.47 As/In 0.52 Al 0.48 As lattice-matched active-core region, a ∼2  μm-thick nearly fully relaxed InP buffer with strained 1.6 nm-thick InAs quantum-dot-like dislocation-filter layers was grown. A smooth terminal buffer-layer surface, with roughness as low as 0.4 nm on a 10 × 10  μm 2 scale, was obtained, while the estimated threading-dislocation density was in the mid-range × 10 8  cm −2 . A series of measurements, on lasers grown on InP metamorphic buffer layers (MBLs) and on native InP substrates, were performed for understanding the impact of the buffer-layer's surface roughness, residual strain, and threading-dislocation density on unipolar devices such as QCLs. As-cleaved devices, grown on InP MBLs, were fabricated as 25  μm × 3 mm deep-etched ridge guides with lateral current injection. The results are pulsed maximum output power of 1.95 W/facet and a low threshold-current density of 1.86 kA/cm 2 at 293 K. These values are comparable to those obtained from devices grown on InP: 2.09 W/facet and 2.42 kA/cm 2 . This demonstrates the relative insensitivity of the device-performance metrics on high residual threading-dislocation density, and high-performance InP-based QCLs emitting near 8  μm can be achieved on lattice-mismatched substrates. 

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2. Disorder‐Induced Broadband‐Distributed Bragg Reflectors in Dielectric and Nanoporous GaN Systems

   https://doi.org/10.1002/pssr.202100598  

   Monavarian, Morteza ; Abaie, Behnam ; Mishkat-Ul-Masabih, Saadat ; Mirkhosravi, Farnood ; Mafi, Arash ; Feezell, Daniel ( March 2022 , physica status solidi (RRL) – Rapid Research Letters)

   Distributed Bragg reflectors (DBRs) are the key building blocks of various optoelectronic and photonics devices. Broadband DBRs in the visible spectral range using the concept of Anderson localization of light in a disordered system are presented. The results demonstrate a ≈2.5X (from ≈80 to ≈200 nm) enhancement of the stopband width for a random DBR compared with a periodic DBR with the same configuration for both dielectric and nanoporous GaN material systems. The described method is beneficial for various applications, including air‐guiding waveguides and light‐emitting diodes with improved light‐extraction efficiency.

    

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3. Oxide-Confined VCSELs for High-Speed Optical Interconnects

   Feng, M ; Holonyak, N. Jr. ; Wu, C.-H. ( July 2018 , IEEE journal of quantum electronics)

   The electrically pumped vertical-cavity surface- emitting laser (VCSEL) was first demonstrated with metal cavities by Iga (1979); however, the device threshold current was too high. Distributed Bragg reflector cavities proposed by Scifres and Burnham (1975) were adopted to improve the optical cavity loss. Yet, it was not a practical use until the discovery of the native oxide of AlGaAs and the insertion of quantum wells to provide simultaneous current and optical confinement in semiconductor laser by Holonyak and Dallesasse (1990). Later, the first “low- threshold” oxide-confined VCSEL was realized by Deppe (1994) and opened the door of commercial application for a gigabit energy-efficient optical links. At present, we demonstrated that the oxide-confined VCSELs have advanced error-free data trans- mission [bit-error rate (BER) ≤ 10−12]to 57 Gb/s at 25 °C and 50 Gb/s at 85 °C, and also demonstrated that the pre-leveled 16-quadrature amplitude modulation orthogonal frequency- division multiplexing data were achieved at 104 Gbit/s under back-to-back transmission with the received error vector mag- nitude, SNR, and BER of 17.3%, 15.2 dB, and 3.8 × 10−3, respectively. 

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4. Efficient and Stable Blue Light Emitting Diodes Based on CsPbBr 3 Nanoplatelets with Surface Passivation by a Multifunctional Organic Sulfate

   https://doi.org/10.1002/aenm.202201605  

   Liu, He ; Worku, Michael ; Mondal, Animesh ; Shonde, Tunde Blessed ; Chaaban, Maya ; Ben‐Akacha, Azza ; Lee, Sujin ; Gonzalez, Fabiola ; Olasupo, Oluwadara ; Lin, Xinsong ; et al ( July 2022 , Advanced Energy Materials)

   Metal halide perovskite nanocrystals (NCs) have emerged as highly promising light emitting materials for various applications, ranging from perovskite light‐emitting diodes (PeLEDs) to lasers and radiation detectors. While remarkable progress has been achieved in highly efficient and stable green, red, and infrared perovskite NCs, obtaining efficient and stable blue‐emitting perovskite NCs remains a great challenge. Here, a facile synthetic approach for the preparation of blue emitting CsPbBr₃nanoplatelets (NPLs) with treatment by an organic sulfate is reported, 2,2‐(ethylenedioxy) bis(ethylammonium) sulfate (EDBESO₄), which exhibit remarkably enhanced photoluminescence quantum efficiency (PLQE) and stability as compared to pristine CsPbBr₃NPLs coated with oleylamines. The PLQE is improved from ≈28% for pristine CsPbBr₃NPLs to 85% for EDBESO₄treated CsPbBr₃NPLs. Detailed structural characterizations reveal that EDBESO₄treatment leads to surface passivation of CsPbBr₃NPLs by both EDBE²⁺and SO₄^2–ions, which helps to prevent the coalescence of NPLs and suppress the degradation of NPLs. A simple proof‐of‐concept device with emission peaked at 462 nm exhibits an external quantum efficiency of 1.77% with a luminance of 691 cd m⁻²and a half‐lifetime of 20 min, which represents one of the brightest pure blue PeLEDs based on NPLs reported to date.

    

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5. Large‐Area Heteroepitaxial Nanostructuring of Molecular Semiconductor Films for Enhanced Optoelectronic Response in Flexible Electronics

   https://doi.org/10.1002/adfm.202113085  

   Park, Kwang‐Won ; Vijayan, Raaghesh ; Andrew, Trisha L. ( February 2022 , Advanced Functional Materials)

   Organized nano‐ and microstructures of molecular semiconductors display interesting optical and photonic properties, and enhanced charge carrier mobilities, as compared to disordered thin films. However, known directed‐growth and self‐organization strategies cannot create structured molecular heterojunctions and cannot be practically incorporated into existing device fabrication routines to create large‐area optoelectronic devices. Here, an ultrathin (<2 nm) seed layer of the compound coronene creates 1D nanostructures of an electron‐transporting molecule (IFD) is shown, which possesses an intrinsic proclivity to form disordered thin films in the absence of the seed layer. It is revealed that nanostructured IFD films exhibit enhanced light absorption and emission, and greater electron mobilities, as compared to amorphous counterparts. This seed layer strategy creates uniform IFD nanowires over large areas of up to 18 mm²at low processing temperatures. Notably, the coronene seed layer creates IFD nanowires when applied over either oxide surfaces or predeposited organic layers, meaning that this structuring approach can be integrated into diode manufacturing routines to realize large‐area flexible optoelectronic devices. Flexible organic light‐emitting diodes and fullerene‐free organic solar cells containing IFD nanowires in the photoactive layer to demonstrate that molecular nanostructures can lead to robust, large‐area device arrays on flexible substrates being fabricated.

    

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