With the development of energy efficiency technologies such as 5G communication and electric vehicles, Si-based GaN microelectronics has entered a stage of rapid industrialization. As a new generation of microwave and millimeter wave devices, High Electron Mobility Transistors (HEMTs) show great advantages in frequency, gain, and noise performance. With the continuous advancement of material growth technology, the epitaxial growth of semiconductor heterojunction can accurately control doping level, material thickness, and alloy composition. Consequently, HEMTs have been greatly improved from material structure to device structure. Device performance has also been significantly improved. In this paper, we briefly describe MOCVD growth technology and research progress of GaN HEMT epitaxial films, examine and compare the “state of the art” of enhanced HEMT devices, analyze the reliability and CMOS compatibility of GaN devices, and look to the future directions of possible development.

Semiconductor lasers have developed rapidly with the steady growth of the global laser market. The use of semiconductor laser diodes is currently considered to be the most advanced option for achieving the optimal combination of efficiency, energy consumption, and cost parameters of high-power solid-state and fiber lasers. In this work, an approach for optical mode engineering in planar waveguides is investigated. The approach referred to as Coupled Large Optical Cavity (CLOC) is based on the resonant optical coupling between waveguides and allows the selection of high-order modes. The state-of-art of the CLOC operation is reviewed and discussed. We apply the CLOC concept in our waveguide design strategy. The results in both numerical simulation and experiment show that the CLOC approach can be considered a simple and cost-efficient solution for improving diode laser performance.

Recent experiments have shown that more than 85% of photo-generated carriers can escape from multiple quantum wells (MQWs) sandwiched between p-type and n-type layers (PIN). In this work, we quantitatively analyze the relationship between the energy of carriers and the height of potential barriers to be crossed, based on the GaAs/InGaAs quantum well structure system, combined with the Heisenberg uncertainty principle. It was found that that the energy obtained by electrons from photons is just enough for them to escape, and it was found that the energy obtained by the hole is just enough for it to escape due to the extra energy calculated, based on the uncertainty principle. This extra energy is considered to come from photo-generated thermal energy. The differential reflection spectrum of the structure is then measured by pump–probe technology to verify the assumption. The experiment shows that the photo-generated carrier has a longer lifetime in its short circuit (SC) state, and thus it possesses a lower structure temperature than that in open circuit (OC). This can only explain a thermal energy reduction caused by the continuous carrier escape in SC state, indicating an extra thermal energy transferred to the escaping carriers. This study is of great significance to the design of new optoelectronic devices and can improve the theory of photo-generated carrier transports.

Photonic crystal has been proved to manipulate light effectively and improve the performance of solar cells. In this paper, high-performance GaAs-based solar cells with photonic crystal were fabricated to decrease the dependence on the angle of incident light. Photoluminescence (PL) intensity of solar cells with photonic crystal reduced only 8% when the incident angle changed from 10° to 30°, while the PL intensity of the ordinary solar cells decreased 39% under the same condition. It manifests the photonic crystal can manipulate the incident light in turn reduce the dependence of incident light angle. Besides, the short circuit current of solar cells was increased by 32% after the photonic crystal was added. When the incident angle of light increased to 30° from 0°, the short circuit current of ordinary solar cell decreased 29.5%, while that of solar cell with photonic crystals reduced 12%. Correspondingly, the photoelectric conversion efficiency (PCE) of ordinary solar cells was reduced 31.2%. In contrast, solar cells with photonic crystal decreased only 11.5%. The enhancement factor of the PCE of solar cells with photonic crystal to that of ordinary solar cells increases from 1.26 to 1.6 as the incident angle rises to 30°from 0°. In summary, solar cells with photonic crystal are less sensitive to the incident angle and could absorb more light without angle limits, then increase the PCE. These solar cells with photonic crystals are promising in low-cost and high power conversion efficiency solar cell fields.

According to the classical theory, multi-quantum wells (MQWs) have quantum confinement effect on photo-generated carriers, which limits its application in light-to-electric devices. However, relevant experiments showed that a large proportion of photo-generated carriers can escape from MQWs sandwiched in the p-type layer and n-type layer (PIN structure), but not in the NIN structure. In order to study this phenomenon carefully, we applied positive and negative bias to an NIN structure respectively to simulate the PIN structure. By analyzing the photoluminescence (PL) spectra, we observed a weak escape behavior of photon-generated carriers among QWs in NIN structure. The experiment results indicate that strong electric field could drive carriers to escape from QWs rather than relaxation and recombination, while in NIN structure the inhomogeneous distribution of the electric field intensity reduces the carrier transport efficiency. The further study will give new ideas to design and produce photoelectric devices.