Strain field and chemical composition determination of InGaN/GaN and AlGaN/GaN multiple quantum wells grown on SiC substratesThe composition, elastic strain, and structural defects of an InGaN/GaN multiple quantum well ͑MQW͒ are investigated using a combination of x-ray diffraction, transmission electron microscopy, and Rutherford backscattering/channeling. None of the applied techniques alone can unambiguously resolve the thickness of the individual layers, the In composition in the wells, and the elastic strain. These three parameters directly determine the optical properties of the MQW. It is shown that only a combination of these measurements reveals the full structural characterization of the nitride multilayer. A clear correlation between the defect density of In distribution and strain relaxation is evidenced. The experimental result of the ratio of the average perpendicular elastic strain ͗e Ќ ͘ and the average parallel elastic strain ͗e ʈ ͘, ͗e Ќ ͘/͗e ʈ ͘ϭϪ0.52, is in excellent agreement with the value deduced from the elastic constants.

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Two InGaN/GaN MQWs samples were grown with two different showerhead gap position 13 and 25 mm, using Thoma Swan CCS-MOCVD system, in order to study the effect of showerhead gap position on the growth of InGaN/GaN MQWs. Through the measurement results, we find that the surface morphology, interface quality, thickness of QB and QW, In composition and PL spectrum of samples are all change significantly. This can attributes to the change of temperature field, flow field and concentration field in the reactor due to the different showerhead gap position. Moreover, the showerhead gap position also affect the pre-reaction in the reactor, which result in converting the thickness of QB, QW and In composition. Consequently, it make the PL spectrum different.

Optical current sensor has a wide range of applications. The main factors that affect the practical process of optical current transducer (OCT) are the effects of birefringence, temperature and long-term stability. Optical current transducer (OCT) with thin slice type sensing head is designed in this paper. Due to the small size of the sensing element of sensing head, the influence of the transient birefringence caused by temperature gradient is negligible. The long-term operation stability of the system is improved by using the non bonding package; the measurement sensitivity of the system is improved by using a new type of magneto-optical material BiGd: YIG. The experimental system used LD as light source, PIN as photoelectric detector, and PC to acquire output signal and data process. The experimental results show that the output signal is linear with the magnetic field in the range of 1909.19Oe, and the feasibility of this design is verified.

Abstract-The N face GaN epilayer was prepared on the C face SiC substrate by MOCVD system, and the basic character of the N face GaN was investegated. A large number of Ga vacancies was formed by a hot phosphoric acid solution etching, which brought a yellow luminescence in the room temperature photoluminescence spectra..