InGaN-based LEDs on convex lens-shaped GaN arrays toward multiwavelength light emitters

Traditional light-emitting diodes emit light at a certain wavelength determined by the semiconductor material’s composition. This limited the possible uses of light-emitting diodes to those that required that precise color of light. Multiwavelength light-emitting diodes could be used in a variety of applications, including lighting, displays, and medical equipment. They can, for example, be employed in color-changing lighting systems that can be altered to generate various moods and atmospheres. Multiwavelength light-emitting diodes can be utilized in screens to produce more vivid and realistic colors. They can be utilized in medical equipment for phototherapy treatments that require specific wavelengths of light to target specific ailments. Furthermore, these multiwavelength light emitters may have applications in biotechnology, such as fluorescence microscopy and optogenetics. They could potentially be utilized to improve data transmission rates and efficiency in the sector of telecommunications.

In a new study published in the peer-reviewed Journal Applied Physics Express, Dr. Yoshinobu Matsuda, Prof. Mitsuru Funato and Prof. Yoichi Kawakami from Kyoto University explored the potential of creating innovative multiwavelength light emitters using InGaN-based light-emitting diodes on convex lens-shaped GaN arrays. Using a combination of thermal reflow and dry etching techniques, the researchers initially fabricated GaN microlens structures on an n-GaN template. The thermal reflow method involved heating the disk-shaped photoresists until they became viscous and flowable under the influence of surface tension, resulting in smooth, curved surfaces. The intended microlens shape of the photoresists was then transferred to the GaN surface using the dry etching technique. The researchers regrew InGaN light-emitting diode structures on top of the GaN microlens array using metalorganic chemical vapor deposition. On the GaN microlens array, n-type GaN, InGaN with spatially distributed In compositions, and p-type GaN were sequentially deposited to create p-i-n junctions that emitted light when a voltage was applied.

The research team created surface and height mapping images of light-emitting diode structures using confocal laser scanning microscopy. These photos demonstrated that the tops of the microstructures had flat facets after development. After the regrowth of the GaN underlayers and InGaN quantum wells, the convex lens-like morphologies were preserved. These findings could be beneficial for improving device performance and understanding how different manufacturing settings affect device attributes. Photoluminescence measurements were used to assess the macroscopic optical characteristics of the InGaN-based light-emitting diode structures. Photoluminescence measurements revealed that the microlens light-emitting diode structure exhibit a broad emission spectrum with a peak at 414 nm. The broadband spectrum was attributed to the peak wavelength distribution of the InGaN quantum wells in the microlens structure. Despite its 3D microstructure, the authors discovered that the light dispersion from the microlens light-emitting diodes was similar to that of planar light-emitting diodes. This was attributed to the microlens light-emitting diodes’ huge planar surface formed after the p-type GaN growth, which allowed for consistent light distribution. Furthermore, regardless of the detecting angle, the spectral geometries of both light emitting diode architectures were consistent, demonstrating consistent emission behavior. Microlens light-emitting diode devices were created using conventional manufacturing techniques for planar light-emitting diode devices and tested for performance. In the current-voltage characteristic, the devices demonstrated a clear rectifying property. The EL spectra ranged from 380 to 500 nm with peak wavelengths at 406 nm when the injection current was around 20 mA. These findings indicated that microlens light-emitting diode devices could be manufactured using typical device techniques for planar light-emitting diodes and that they performed well under DC injection at room temperature.

In a nutshell, Dr. Matsuda and colleagues demonstrated the feasibility of fabricating InGaN-based light-emitting diodes with multiwavelength emission properties using convex lens-shaped GaN microstructures. The results showed the potential for monolithic integration of multiwavelength light emitters on a single chip, which could have applications in solid-state lighting, Li-Fi, and micro light-emitting diodes displays.