Triple perovskite, Nd _1.5 Ba _1.5 CoFeMnO _9−δ , enriched with oxygen defects shows high activity and durability as a bifunctional oxygen electrocatalyst.

We develop inverted n-p junction arrayed vertical-cavity surface-emitting lasers (VCSELs) with 875 devices operating at ~940 nm, optimized for high optical output power in sensing applications. Employment of an n-type GaAs substrate prevents performance degradation caused by defects in p-type GaAs substrates. A tunnel junction enables polarity inversion. The inverted n-p VCSEL arrays, which are preferred for circuit design and packaging, are compared with conventional p-n junction VCSEL arrays on an n-type substrate using three-dimensional device modeling and experimental measurements. The optical output power of large-area 25×35 VCSEL arrays shows ~5.5 W at I ≈ 6 A. The threshold current density and slopes of the L - I curve of the inverted n-p VCSEL arrays are ~1.2 kA/cm ² and 0.98 W/A, respectively, which are similar to those of reference p-n VCSELs. The inverted n-p arrays demonstrate slightly better electrical performance, higher output power, and power conversion efficiency than p-n, enhancing their potential in voltage-controlled sensing systems. This is the first demonstration of the large-area inverted n-p VCSEL arrays, achieving the highest light output power critical for emerging 3D sensing and LiDAR applications.

Growing crack-free, epitaxial ultrawide-bandgap semiconductor films on cost-effective, large-area substrates, such as AlN on Si, poses a significant challenge due to substantial lattice and thermal expansion mismatches. We introduce an approach to mitigate tensile strain or reverse strain signs between the substrate and the AlN layer, thereby suppressing crack formation during the heteroepitaxial growth of thick III-N films. This approach introduces ductile metallic interlayers, specifically Au, to change the strain state of AlN from in-plane tensile to compressive, without initiating cracks. Furthermore, the Au interlayer is grown epitaxially as a single crystal, which prevents the transfer of tensile strain into the AlN film, as confirmed by x-ray diffraction and transmission electron microscopy. We demonstrate crack-free AlN films exceeding 1 μm in thickness. These findings hold significant promise for advancing the field of ultrawide-bandgap semiconductor materials, with potential applications in electronic, optoelectronic, sensing, and energy device applications.