Fabrication of 4-Inch Nano Patterned Wafer with High Uniformity by Laser Interference Lithography

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.

Visualizing light-to-electricity conversion process in InGaN/GaN multi-quantum wells with a p-n junction

Absorption and carrier transport behavior plays an important role in the light-to-electricity conversion process, which is difficult to characterize. Here we develop a method to visualize such a conversion process in the InGaN/GaN multiquantum wells embedded in a p-n junction. Under non-resonant absorption conditions, a photocurrent was generated and the photoluminescence intensity decayed by more than 70% when the p-n junction out-circuit was switched from open to short. However, when the excitation photon energy decreased to the resonant absorption edge, the photocurrent dropped drastically and the photoluminescence under open and short circuit conditions showed similar intensity. These results indicate that the escaping of the photo-generated carriers from the quantum wells is closely related to the excitation photon energy.

Improvement of green InGaN-based LEDs efficiency using a novel quantum well structure

The green light emitting diodes （LEDs） have lower quantum efficiency than LEDs with other emission wavelengths in the visible spectrum. In this research, a novel quantum well structure was designed to improve the electroluminescence （EL） of green InGaN-based LEDs. Compared with the conventional quantum well structure, the novel structure LED gained 2.14 times light out power （LOP） at 20-mA current injection, narrower FWHM and lower blue-shift at different current injection conditions.

Surface Morphology Improvement of Non-Polar a-Plane Ga N Using a Low-Temperature GaN Insertion Layer

We demonstrate that a low-temperature Ga N insertion layer could significantly improve the surface morphology of non-polar a-plane Ga N.The two key factors in improving the surface morphology of non-polar a-plane Ga N are growth temperature and growth time of the Ga N insertion layer.The root-mean-square roughness of a-plane Ga N is reduced by 75%compared to the sample without the Ga N insertion layer.Meanwhile,the Ga N 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 Ga N.