To constantly improve performance requirements for InGaN lasers, we investigate the effect of the In mole fractionin the upper waveguide layer on the performance of InGaN-based blue laser diodes. The research results can be employed to improve the performance of InGaN-based blue laser diodes which have many potential applications in areas such as solid-state lighting, laser displays, and optical storage. Our study is motivated by electron leakage limiting the output power of laser diodes. Due to mobility differences, the injection rate of holes will be slower than that of electrons to bring about varying amounts of hole injection in several quantum wells, which makes electrons leak into the waveguide layer and reduces the carrier density in the active layer. Additionally, the polarization effect of InGaN materials will lead to energy band offset and quantum confinement Stark effect. To this end, many optimization ideas have been proposed, but most of them focus on multiple quantum wells and barriers, lower waveguide layers, and electron barrier layers. Our study shows that the upper waveguide layer also plays a crucial role in the performance of InGaN-based blue laser diodes. By adjusting the In mole fraction of the upper waveguide layer, the corresponding band structure can be changed to alleviate the electron current overflowing from the quantum well, thereby improving the radiation recombination rate and optical output.

Based on the experimental sample structure, an InGaN-based blue laser with the same structure is constructed by PICS3D simulation software. Its photoelectric performance, such as the optical power curve, voltammetry curve, and spectral peak curve, achieves strict comparison. The internal parameters are measured in a manner consistent with the experimental sample. In the reference, the reflectivity of the front cavity surface is modified to 10%, 45%, and 82% in turn, and different slope efficiencies are obtained. The internal loss and carrier injection rate of the laser are indirectly measured by linear fitting. We also adopt the same setting parameters, measure internal parameters in the same way, and compare them with references. It is found that the relative errors of internal loss and carrier injection efficiency are 3.5% and 5.3%, which proves the reliability of subsequent data in our paper. Subsequently, a series of InGaN-based blue lasers are constructed, and the In mole fraction in the upper waveguide layer is optimized by comparing the optical output power, carrier distribution, optical field distribution, radiation recombination coefficient, and energy band curve parameters under different In contents. During employing a constant In component, we find that as the In mole fraction increases, the effective potential barrier to electrons gradually rises, with improved electron leakage. However, when the In mole fraction exceeds 8%, the high component difference will lead to bending energy bands and accumulated excessive charges at the interface, which will cause space separation of electrons and holes, and the wave function overlap will be reduced. In addition, with the rising In mole fraction, the light field also moves away from the active region, thereby resulting in a decrease in the light field limiting factor and a decrease in light output efficiency. Therefore, a series of InGaN-based blue light lasers with gradient components are constructed, and the optimal gradient component is obtained through comprehensive comparison.

Firstly, the original sample with strictly consistent parameters and structure is set according to the references, and its optical power curve and wavelength are also consistent with the experimental sample (Fig. 2). The internal loss is measured by adopting the same variable cavity surface method as the experimental process (Fig. 3), which is compared with the references and shows credibility. Secondly, the optical power, electron leakage rate, and wave function coincidence rate of the upper waveguide layer with different constant In contents are compared (Fig. 5). Subsequently, a series of gradient component upper waveguide structures are constructed with fixed final values of the gradient, the initial value of the gradient is changed, and their optical power is compared (Fig. 6). Finally, two different optimized structures with better optical power have been proposed, and both of them reduce electronic leakage and improve slope efficiency, thereby enhancing photoelectric conversion efficiency (Fig. 7). The sample with gradient components has the most suitable height of electron and hole barriers, thus leading to a higher hole injection amount. In terms of optics, our proposed sample changes the refractive index of the material through a gradient upper waveguide layer, which makes the center of the light field move towards the active region (Fig. 11) and is conducive to limiting more carriers to the stimulated radiation recombination in the quantum well.

We investigate the effect of the In mole fraction in the upper waveguide layer on the performance of InGaN-based blue laser diodes. The results show that appropriately increasing the In mole fraction of the upper waveguide layer can reduce the carrier leakage of the original structure, which exerts a significant influence on the output optical power. The In mole fraction in the upper waveguide layer of the original experimental structure is increased to about 8%, and then the slope efficiency rises by 53.54% of the original value and reaches 2.09 W/A at 1.5 A injection current. When the In mole fraction of the upper waveguide layer is changed to 5%-8%, the high hole barrier can be alleviated, with improved electron injection. Meanwhile, the optical field is more concentrated and the optical loss is reduced. The slope efficiency is increased by 69.70% compared with the original structure and reaches 2.31 W/A at 1.5 A injection current. The research results provide valuable references for the design and fabrication of high-performance InGaN-based blue laser diodes.