Zhibiao Hao

An analytical model for AlGaN-based distributed polarization doping (DPD) p–n diodes is developed, integrating temperature-dependent lifetimes and thermionic-field emission effects. Validated against experimental data from Kumabe et al., IEEE Trans. Electron Devices 71, 3396 (2024), the model captures the conduction transition from Shockley–Read–Hall-recombination-dominated to drift-dominated transport at the moderate temperature. We quantitatively define the depletion approximation's validity and demonstrate the DPD structure's capability to decouple carrier mobility from injection efficiency. This framework provides a rigorous foundation for optimizing polarization-engineered wide-bandgap power electronics across a wide temperature range.

InGaN red light-emitting diode (LED) has attracted increasing interest in recent years due to its important role in full-color micro-LED displays. Covering an AlGaN capping layer on top of a high-indium-composition InGaN quantum well can improve the performance of an InGaN red LED, which is considered to compensate for stress and suppress the decomposition of InN. However, the AlGaN capping layer can also cause changes in the polarization electric field, which have been almost overlooked in previous studies. In this work, theoretical simulations reveal that the polarization effect of the AlGaN capping layer necessitates a trade-off between the long wavelength and high luminous intensity of InGaN red LEDs, thereby yielding an optimal Al composition of 0.4. Meanwhile, experimental results demonstrate that the micro-LED with an Al composition of 0.4 in the capping layer exhibits the most uniform luminescence. The underlying reason for this optimal luminous uniformity is elucidated by stress engineering via time-of-flight secondary ion mass spectrometry characterization, which verifies the in-plane uniformity of the indium composition within the quantum wells—a feature not addressed in previous research. The 30 × 30 μm2 micro-scale light-emitting diode achieves the longest emission wavelength of ∼650 nm and the highest on-wafer external quantum efficiency of 1.8%, which further corroborates the theoretical simulation results.

Thin‐film lithium niobate (TFLN) has a proven record of building high‐performance electro‐optic (EO) modulators. However, it has consistently posed challenges in securing low driving voltage, wide electro‐optic bandwidth, low insertion loss, and high modulation efficiency simultaneously. Here, we demonstrate a telecom‐wavelength EO modulator on the TFLN platform incorporating multifunctional benzocyclobutene (BCB) material. The low dielectric constant (low‐k) BCB effectively reduces RF loss of the modulator and enables perfect velocity matching with a narrow electrode gap, thereby overcoming the conventional voltage–bandwidth trade‐off. Meanwhile, in combination with a bilayer inversely tapered waveguide, it also facilitates the realization of high‐efficiency edge couplers, significantly reducing the coupling loss of the modulator. In addition, the underlying TFLN slab is selectively removed to eliminate dielectric relaxation, ensuring a stable low‐frequency EO response and bias‐drift‐free operation. The fabricated 13‐mm‐long modulator exhibits low half‐wave voltages V _π of 1.5 V in the C‐band and 1.19 V in the O‐band, corresponding to half‐wave voltage‐length products of 1.95 V·cm and 1.55 V·cm, respectively. Thanks to the BCB‐clad edge coupler, an ultra‐low coupling loss of 0.54 dB per facet is obtained. Ultra‐wide EO bandwidths exceeding 110 GHz across the C + O‐bands are demonstrated, and high‐speed PAM8 data transmission with data rates up to 390 Gbit/s is successfully recorded in both C‐ and O‐bands. The proposed modulator architecture not only delivers excellent overall performance, but also simplifies the fabrication process and expands the application potential.

Avalanche photodiodes (APDs) are essential semiconductor optoelectronic devices that could effectively improve the optical receiver sensitivity due to the internal gain. Based on Si/Ge photodiodes (PDs) from standard foundry process design kits, this work demonstrates a simple tuning method to transform PDs into APDs and further improve optical receiver sensitivity by carefully increasing the bias voltage before breakdown. The tuning principle is demonstrated theoretically and experimentally. A useful method distinguishing whether a foundry-fabricated PD can be tuned to the APD is proposed via confirming if the tunneling breakdown happens before avalanche. Subsequently, based on the foundry-fabricated Si/Ge PD, the receiver sensitivity is improved by 5 dB via increasing bias voltage from 2 to 12 V under the non-return-to-zero bit rate of 10 Gbps, at the incident power of −16 dBm and gain of 3 the bit error rate is suppressed by eight orders of magnitude.

This chapter mainly discusses the fundamental principles of photovoltaic detection, namely, the energy conversion procedure of light into electrical signals in photodetectors (PD) and avalanche photodetectors (APD). After briefly introducing the basic principles of PIN PD and APD, the chapter mainly focuses on analyzing dark current’s noise sources and origin, bridging the relationship between the device’s sensitivity performance and its material and device characteristics. From these analyses, the readers could understand that the sensitivity of PIN PD, especially under high data rates, can be significantly enhanced by merely increasing the bias voltage to turn it into APD mode. A step further, this chapter provides deeper insights into modifying the APD structure from the perspective of carrier transportation and impact ionization engineering. Besides, Geiger mode APD, which is capable of sensing weak light signals at a single photon level, is also described. In the final part of the chapter, the challenges of these detectors are discussed, and many recent technical approaches, including linear high-gain APD, digital alloys APD, and SPAD with dynamic memristor quenching, have been presented to tackle these challenges. By demonstrating the basic principles of photovoltaic detectors, particularly APD, to the analysis of receiver sensitivity, this chapter could provide comprehensive and valuable insights for designing and optimizing high-sensitivity detection systems. These systems find applications in various fields, including optical interconnection, optical communication, and LiDAR.

Laser diodes with narrow linewidth are essential for optical communication, spectral analysis, and precision measurement. This study reinterprets the linewidth narrowing mechanism in external-cavity diode lasers (ECDLs) from a perspective that the noise-induced frequency fluctuations are suppressed by the rapidly varying phase in frequency domain introduced by the external cavity. We highlight the importance of the localized high slope in the rising edge of the feedback spectrum in forming stable narrow linewidth laser modes. Based upon this understanding, we introduce an alternative to traditional Lorentzian optical feedback. We demonstrated that asymmetric lineshapes, such as Fano, can serve as the optical feedback of ECDLs with enhanced performance. Theoretical analysis and numerical simulations reveal that Fano-based external cavity lasers, benefiting from a feedback spectrum with a steeper local slope than Lorentz-based cavities, can achieve superior linewidth narrowing under the same fabrication conditions. This study offers a novel approach for the design and application of narrow linewidth laser diodes.

We demonstrate hermetically packaged W-band photodiode (PD) modules for photonic-based low-noise microwave generation. The residual phase noise and fractional frequency instability at 100 GHz for the modules are evaluated for the first time.

We designed a 4H-SiC spiral-ring resonator with a Free Spectral Range (FSR) of 145 GHz and normal dispersion. This resonator is based on the Euler adiabatic bending structure, which exhibits an intrinsic Q factor exceeding 10⁶ and the Kerr comb generation within this resonator was observed.

Micro-scale light-emitting diodes (micro-LEDs) have received widespread attention in recent years for applications in display and optical communication. Compared with conventional quantum well active regions, quantum dots (QDs) can increase the carrier concentration at the same current density, which is beneficial for improving the efficiency and bandwidth of LEDs at low current densities. This is exactly what micro-LEDs need for display and communication applications. In this Perspective, we give a general introduction to InGaN QDs and provide an overview of the growth of InGaN QDs by metal-organic chemical vapor deposition. We then discuss the advances in green and red micro-LEDs based on InGaN QDs for display applications. This is followed by recent progress on high-speed blue micro-LEDs, which have great potential for use in chip-to-chip optical interconnections. Finally, we address the remaining challenges for a further improvement in InGaN QD-based micro-LEDs.

We present a two-segment compound-cavity directly-modulated 1577 nm distributed feedback (DFB) laser based on identical epitaxial layer (IEL) scheme and uniform gratings. The laser exhibits a small-signal 3-dB bandwidth exceeding 50 GHz, and a modulation rate of 144 Gbps is implemented via four-level pulse-amplitude modulation (PAM-4) format. The eye diagrams remain open after transmission through 2.5 km single-mode fiber (SMF), demonstrating a great potential for 800 GbE applications or even higher data rates.