A method of combining the AlGaN/GaN superlattices and Mg delta doping was proposed to achieve a high conductivity p-type GaN layer. The experimental results provided the evidence that the novel doping technique achieves superior p-conductivity. The Hall-effect measurement indicated that the hole concentration was increased by 2.06 times while the sheet resistivity was reduced by 48%. The fabricated green-yellow light-emitting diodes using the achieved high conductivity p-type GaN layer showed an 8- and 10-times enhancement of light output power and external quantum efficiency, respectively. The subsequent numerical calculation was conducted by using an Advanced Physical Model of Semiconductor Device to reveal the mechanism of enhanced device performance. This new doping technique offers an attractive solution to the p-type doping problems in wide-bandgap GaN or AlGaN materials.

N-polar GaN films were grown on c -plane sapphire substrates by metal organic chemical vapor deposition and implanted with C or O ion were studied. High-resolution X-ray diffraction results show that, after implantation, there were clear increases in the full widths at half maximum of rocking curves. However, the increases disappeared after annealing at 1050 °C for 30 min. Photoluminescence (PL) spectra obtained from the N-polar GaN films before and after implantation indicated a significant increase in the yellow luminescence (YL) band after C-implantation while O-implantation sample showed only a slight increase. It can be concluded that gallium vacancies and related complex defects were not the major factor for YL. The present result confirmed that the implanted C impurity and its complexes are responsible for the increased YL intensities.

The lateral light emitting diodes (LEDs) fabricated on insulated sapphire substrate usually suffer current crowding effect, which would lead to a serious degeneration of luminescence properties and reliability issues. To relieve the current crowding effect and improve the device performance, n-AlGaN interlayers with gradual changing Al fractions were introduced into the n-GaN layer of the green LEDs. The gradually decreased Al composition in the introduced n-AlGaN interlayer resulted in a barrier in the conduction band, which could promote a more uniform distribution of electrons along the horizontal direction and then reduce the current crowding effect. In addition, the AlGaN/GaN heterojunction produced large amounts of two-dimensional electron gas at the interface, which could balance the electron distribution at the AlGaN/GaN interface and reduce the current crowding effect as well. The introduced current spreading process improved the luminescence intensity of LED. Ultimately, electroluminescence spectra were measured and confirmed the improved luminescence intensity via gradually decreased Al composition in the introduced n-AlGaN interlayer.

A method to improve the performance of ultraviolet light-emitting diodes (UV-LEDs) with stair-like Si-doping GaN layer is investigated. The high-resolution X-ray diffraction shows that the UV-LED with stair-like Si-doping GaN layer possesses better quality and a lower dislocation density. In addition, the experimental results demonstrate that light output power and wall plug efficiency of UV-LED with stair-like Si-doping GaN are significantly improved. Through the analysis of the experimental and simulation results, we can infer that there are two reasons for the improvement of photoelectric characteristics: reduction of dislocation density and alleviating of current crowding of UV-LEDs by introduced stair-like Si-doping GaN.