Photonic-based thermometers have been attracting intense research interest as a potential alternative to traditional electrical thermometers due to their physical and chemical stability and immunity to electromagnetic interference. However, due to the high requirements for the stability of the laser source, the existing studies on resolution are only theoretical predictions and do not include real-measured results. In this paper, we report on the fabrication and characterization of an on-chip silicon whispering-gallery-mode (WGM) ring resonator thermometer. The strip grating and the ring structure were fabricated on the silicon-on-insulator (SOI) substrate by two-step etching. The quality-factor (Q-factor), temperature sensitivity, and measurement range of the packaged device were 21,400, 42 pm/K, and 150 K, respectively. The real-measured temperature resolution of 2.9 mK was achieved by virtue of the power and polarization stabilization of the laser source.

The degradation characteristics of InGaN-based laser diodes (LDs) grown on Si substrate have been studied under an electrical stress with a pulsed current of 180 mA. After the electrical stress, the light output power, leakage current and capacitance of the LD decreased, while the operation voltage and threshold current increased, and the slope efficiency remained nearly unchanged after the pulsed electrical stress for 620 h. Further analysis shows that the degradation was probably due to the newly generated group-III vacancies and/or related defects, which can not only act as acceptor-like defects to compensate the n-type donors, leading to the reduction of conductance and capacitance, but also work as non-radiative recombination centers affecting the internal quantum efficiency and emission intensity of the active region.

In this letter, we present a high-resolution temperature measurement method utilizing Pound-Drever-Hall (PDH) frequency locking with a silicon nitride (Si ₃ N ₄ ) microring resonator as a photonic thermometer. The temperature response at various intervals demonstrates a measurement resolution less than 1 mK. Through the calculations of the thermal noise floor and frequency linewidth of the Si ₃ N ₄ microring resonator, we establish the theoretical resolution limit of the frequency locking method to be 41 μK at 1 Hz measurement frequency. This precise and stable temperature measurement technique holds immense potential as an in-situ thermometers for diverse quantum chips, thus accelerating the research progress of chip-level quantum metrology.

AlGaN nanostructures have many applications because of their interesting and unique properties. Here we report a simple fabrication method of AlGaN nanostructures by nanolithography on ultraviolet (UV) LEDs grown on Si substrates. We also studied the effects of various AlGaN nanostructure arrays on the performance of the UV (370 nm) thin-film LEDs with an embedded n-type contact. The output power of the UV LEDs with nanostructures was enhanced by 3.9 times compared to the flat UV LEDs, while no penalty was induced for the electrical characteristics of the UV LEDs. Additionally, the far-field radiation pattern of the UV LEDs with nanostructures showed much better directionality and a much stronger intensity than the flat UV LEDs, which would be of great benefit to directional UV curing applications.

An abnormal aging phenomenon is reported for GaN-based near-ultraviolet laser diodes (LDs). Under an electrical stress for several minutes, the threshold current of the LDs decreased, while the light output power and the operation voltage increased. The amplitude of the abnormal aging phenomena was found to be mainly related to the excess Mg concentration in the p-AlGaN electron blocking layer (EBL). It almost disappeared when the Mg concentration in the AlGaN EBL was reduced to 2 × 10 ¹⁹ cm ⁻³ . We propose that this phenomenon was related to the Mg–V _N –H complex defects formed in highly doped AlGaN EBL ([Mg] > 3 × 10 ¹⁹ cm ⁻³ ).