Institute of Semiconductors

Accurate absolute pressure measurement is of great importance in industrial control, environmental monitoring, and aerospace. Traditional fiber-optic Fabry–Perot (F-P) pressure sensors usually involve complex microfabrication and high-cost demodulation systems, while conventional diaphragm capsule sensors are limited in sensitivity and resolution. This work presents a low-cost, high-resolution fiber-optic F-P absolute pressure sensor. The sensor uses a vacuum capsule as one reflective surface and a partially reflective fiber collimator as the other, forming a low-finesse F-P interferometer. The cavity length is linearly modulated by the elastic deformation of the capsule under pressure, and high-precision demodulation is realized using frequency modulated continuous wave (FMCW) interferometry instead of conventional spectral methods. Static experiments from 10 to 110 kPa show that the sensor exhibits a high sensitivity of 15,105 nm/kPa and a resolution of 3.3 Pa. Furthermore, the sensor operates normally within the range of −20 °C to 70 °C, exhibiting a pressure–temperature cross-sensitivity of 0.081 kPa/°C and a cavity length drift of 496 nm/h. With the advantages of high performance, simple structure, low cost, and good scalability by selecting different capsules, the proposed sensor has promising potential for practical applications in pressure measurement fields.

Na-flux is a promising growth method for producing large-diameter GaN substrates with ultralow dislocation density, required for high-power-density vertical GaN power devices. However, the lateral growth behavior of GaN under near-thermodynamic-equilibrium conditions remains insufficiently understood. In this work, circular apertures were introduced into the GaN substrate by laser processing to deliberately induce lateral growth during Na-flux growth. GaN originating from the aperture edges coalesced toward the center, with coalescence preferentially along the ⟨112̅0⟩ in-plane direction, with {112̅2} semipolar facets exposed at the advancing growth front. Notably, GaN grown above the apertures exhibited an enhanced lateral growth rate independent of the underlying seed, termed freestanding epitaxy. Furthermore, the stress distribution and crystallographic orientation within the lateral growth regions were systematically investigated by Raman spectra and Lang X-ray topography, respectively. Defect-selective etching with molten NaOH-KOH revealed a drastic reduction in the threading dislocation density from ∼106 cm–2 to below 104 cm–2 in the freestanding epitaxial regions. These results demonstrate that GaN lateral growth can be effectively enhanced in the Na-flux method, providing a physical basis for the fabrication of ultralow-dislocation-density GaN substrates.

High-quality nitrogen (N)-polar gallium nitride (GaN) has great potential for fabricating high-power or high-frequency GaN-based high electron mobility transistors (HEMTs). In this article, the successful growth of the N-polar GaN films with high crystalline quality, smooth surface morphology, and low defect density on N-polar free-standing GaN substrates with metal–organic chemical vapor deposition (MOCVD) technology is reported. In particular, it was first observed that dislocations appeared in pairs on the surface of N-polar GaN films through CL images. Moreover, it was found that the size of the dislocation-dots gradually and monotonously decreased with the increase in the growth temperature but increased with the increase in the film thickness of the N-polar GaN films. These phenomena could be explained in terms of the bending, merging, and annihilation of the dislocations during the MOCVD growth process. By optimizing the growth temperature, high-crystalline-quality N-polar GaN films with a dislocation density as low as 4.30 × 105 cm–2 and a surface roughness root-mean-square value as small as 0.28 nm were achieved in this study. These results should pave a solid foundation for the subsequent research and development of high-frequency or high-power N-polar GaN-based electronic devices.

Frequency modulated continuous wave (FMCW) LiDAR -based 3D imaging has significantly advanced in resolution and frame rate. External modulation provides superior frequency-swept slopes but relies on high-quality RF signals. While Arbitrary Waveform Generators (AWGs) meet performance requirements, their high cost and bulkiness limit practical application. This paper proposes a hybrid optoelectronic system using coherent optical injection into a semiconductor laser. Exploiting the period-one oscillation state enables frequency-tunable microwave generation. To counteract nonlinearities, an adaptive predistortion algorithm was evaluated via numerical simulations. Results show linearity improved by four orders of magnitude, reducing nonlinearity from 10^-3 to 10^-7. This system provides a compact, competitive alternative to expensive digital equipment for LiDAR applications.