Back surface field (BSF) materials are key functional layers that suppress rear-surface recombination and regulate carrier transport in III–V solar cells. This work investigates the performance degradation behavior of GaInP solar cells with AlInP and AlGaInP BSF layers under 1 MeV electron irradiation. Through a combination of optoelectronic measurements and TCAD simulations, the carrier transport and recombination mechanisms before and after irradiation are comprehensively analyzed. Although both devices deliver comparable initial photovoltaic performance, distinct degradation trends emerge under high-fluence electron irradiation. After a cumulative fluence of 1 × 10¹⁵ e/cm², the cell with an AlInP BSF suffers more severe degradation owing to inferior radiation hardness. Irradiation-induced defects reduce the minority-carrier lifetime and enhance Shockley–Read–Hall (SRH) nonradiative recombination, resulting in a 14% drop in short-circuit current density. In contrast, the AlGaInP BSF exhibits favorable radiation tolerance, and the corresponding device undergoes only a 2% loss in short-circuit current density. The influence of the BSF structure on carrier transport and recombination is systematically analyzed, providing experimental and theoretical support for the design of space-grade GaInP top cells.

We report a wet-etched InP half-ridge polarization rotator on a thick generic stack by treating the wet-window overlay as an optical length, not a process allowance. The hybrid-mode angle follows the sum of ridge width and overlay clearance; the conversion length must match the corresponding half-beat. Three devices on one mask measure 14.8–18.0 dB polarization extinction and 1.34–1.47 dB insertion loss at 1550 nm, above the 10–14 dB range of production building blocks. Simulation of the drawn geometry gives 18.5 dB extinction and 1.28 dB insertion loss; the 18.0 dB device agrees within its uncertainty.

Ultraviolet (UV) photodetectors are essential for flame monitoring, environmental sensing, UV photography, optical communication, and biochemical analysis, and III-nitride quantum-well structures are promising platforms for such devices. Two-dimensional Ti₃C₂T_x MXene, which combines metallic conductivity with a termination-dependent work function, offers an attractive route to modifying the surface and interface transport of GaN-based photodetectors. The purpose of this work is to determine whether integrating a Ti₃C₂T_x MXene surface region onto a grating-electrode GaN/AlGaN asymmetric coupled-quantum-well UV photodetector selectively enhances the photoresponse or predominantly modifies the overall device conductance. The device was fabricated and assessed under 254 nm illumination. Optical and scanning electron microscopy verified the patterned device and the continuous grating region, and the fabrication sequence explained the integration procedure. Static current–voltage (I–V) characteristics of the same device were measured both before and after Ti₃C₂T_x MXene coverage. Nonlinear transport and a discernible light–dark current gap were present in both states. Before MXene coverage, the device produced a dark current of 1.98 μA, a net photocurrent of 1.90 μA, and a light-to-dark current ratio of 1.96 at +3 V; after coverage, the corresponding values were 0.837 mA, 0.835 mA, and 2.00. The increase in the dark current was reproduced on three grating-electrode devices, for which MXene coverage raised the dark current by a factor of between about 4 × 10² and 1.3 × 10³ depending on the device and the sweep direction, whereas a control structure without the grating electrode remained nearly three orders of magnitude below the MXene-covered devices. Switching the 254 nm source at a fixed bias of +1 V produced reproducible switching between two current levels with a light-to-dark ratio of 2.10–2.15; the transitions were completed within the 0.1 s sampling interval. Ti₃C₂T_x MXene coverage raised the total current level in both electrical states while maintaining a detectable relative light–dark contrast from +1 to +5 V, indicating that the dominant measured change was an increase in device conductance rather than a selective enhancement of the relative photoresponse. Within the scope of this transport study centered on static I–V measurements and supplemented by a single-device time-resolved measurement, the results demonstrate static separation between the dark and 254 nm-illuminated states and modification of the overall electrical transport by MXene coverage on the same device; they do not claim an improvement in photodetector figures of merit, and absolute figures of merit are not reported because the optical power incident on the device was not calibrated.

Thermal degradation of InGaN quantum dots (QDs) during the temperature ramp for GaN quantum-barrier growth can compromise micro-light-emitting-diode active regions. Five-period InGaN/GaN QD structures with low-temperature-grown GaN (LT-GaN) caps of 0 nm (C0), 2 nm (C2), and 4 nm (C4) were studied. The nominal total GaN quantum barrier was fixed at 10 nm by adjusting the higher-temperature-grown GaN portion to 10, 8, and 6 nm, respectively. The active regions were characterized by high-resolution X-ray diffraction, aberration-corrected transmission electron microscopy, and temperature-dependent photoluminescence; post-ramp surface-reference specimens were examined by atomic force microscopy; and 10 μm × 10 μm micro-LEDs were evaluated by electroluminescence spectroscopy and integrating-sphere external quantum efficiency measurements. Compared with C0 and C2, C4 displayed clearer satellite reflections, more laterally continuous InGaN-rich contrast, and weaker thermal photoluminescence quenching; its surface reference also showed a more continuous terrace-like morphology with fewer fine depressions. The C4 micro-LED reached a peak external quantum efficiency of 4.45% at 20 A cm⁻², compared with 2.58% at 150 A cm⁻² for C0 and 1.80% at 140 A cm⁻² for C2. Together, these results associate more effective thermal protection with a reduced relative contribution from defect-assisted nonradiative recombination and enhanced device efficiency.

Size-dependent efficiency degradation remains a major challenge for deeply scaled GaN-based micro-light-emitting diodes (micro-LEDs) because etched sidewalls increasingly influence carrier recombination. Here, square micro-LEDs with lateral dimensions of 5–50 μm were fabricated from the same plasma-assisted molecular-beam-epitaxy-grown wafer containing a five-period InGaN quantum-well/1 nm Al_0.1Ga_0.9N interlayer/InGaN quantum-dot-like (QW–QD) composite active region. Contrary to the conventional size effect, the light output power density and external quantum efficiency (EQE) increased as the mesa size decreased. The peak EQEs were 3.66%, 4.53%, 5.63%, 7.04%, and 7.27% for the 50, 40, 30, 10, and 5 μm devices, respectively, corresponding to an approximately 98.6% increase from 50 to 5 μm. The favorable scaling is consistent with localization-mediated suppression of lateral carrier loss combined with size-dependent light extraction. The present measurements do not quantitatively separate injection, internal efficiency, and extraction contributions. These results demonstrate the potential of ultrathin-interlayer QW–QD active-region engineering for scaled GaN micro-LEDs.