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We demonstrate that a low-temperature GaN insertion layer could significantly improve the surface morphology of non-polar a-plane GaN.The two key factors in improving the surface morphology of non-polar a-plane GaN are growth temperature and growth time of the GaN insertion layer. The root-mean-square roughness of a-plane GaN is reduced by 75% compared to the sample without the GaN insertion layer. Meanwhile, the GaN insertion layer is also beneficial for improving crystal quality. This work provides a simple and effective method to improve the surface morphology of non-polar a-plane GaN. [ABSTRACT FROM AUTHOR]

Heterojunction phototransistors (HPTs) with scaling emitters have a higher optical gain compared to HPTs with normal emitters. However, to quantitatively describe the relationship between the emitter-absorber area ratio (Ae/Aa) and the performance of HPTs, and to find the optimum value of Ae/Aafor the geometric structure design, we develop an analytical model for the optical gain of HPTs. Moreover, five devices with different Ae/Aaare fabricated to verify the numerical analysis result. As is expected, the measurement result is in good agreement with the analysis model, both of them confirmed that devices with a smaller Ae/Aaexhibit higher optical gain. The device with area ratio of 0.0625 has the highest optical gain, which is two orders of magnitude larger than that of the device with area ratio of 1 at 3 V. However, the dark current of the device with the area ratio of 0.0625 is forty times higher than that of the device with the area ratio of 1. By calculating the signal-to-noise ratios (SNRs) of the devices, the optimal value of Ae/Aacan be obtained to be 0.16. The device with the area ratio of 0.16 has the maximum SNR. This result can be used for future design principles for high performance HPTs. [ABSTRACT FROM AUTHOR]

We report the fabrication of 4-inch nano patterned wafer by two-beam laser interference lithography and analyze the uniformity in detail. The profile of the dots array with a period of 800 nm divided into five regions is characterized by a scanning electron microscope. The average size in each region ranges from 270 nm to 320 nm, and the deviation is almost 4%, which is approaching the applicable value of 3% in the industrial process. We simulate the two-beam laser interference lithography system with MATLAB software and then calculate the distribution of light intensity around the 4 inch area. The experimental data fit very well with the calculated results. Analysis of the experimental data and calculated data indicates that laser beam quality and space filter play important roles in achieving a periodical nanoscale pattern with high uniformity and large area. There is the potential to obtain more practical applications. [ABSTRACT FROM AUTHOR]

The resonant excitation is used to generate photo-excited carriers in quantum wells to observe the process of the carriers transportation by comparing the photoluminescence results between quantum wells with and without a p—n junction. It is observed directly in experiment that most of the photo-excited carriers in quantum wells with a p—n junction escape from quantum wells and form photocurrent rather than relax to the ground state of the quantum wells. The photo absorption coefficient of multiple quantum wells is also enhanced by a p—n junction. The results pave a novel way for solar cells and photodetectors making use of low-dimensional structure. [ABSTRACT FROM AUTHOR]