Improving efficiency of GaN-based materials for solar cells and LEDs

Researchers working on renewable energy resources have focused on gallium-nitride (GaN) based-materials, which have big potential for full-color solar cells and LEDs. Among their limitations, however, has been the poor efficiency of long-wavelength devices, known as the green gap problem. One of the restrictions is a result of the low carrier concentration and mobility in the p-type region.

Sang et al. illustrate a method for improving the performance of the p-type region in GaN-based long-wavelength devices by using a unique polarization effect in the GaN-based material, which generated 2D hole gas.

“Our method is to fabricate multiple layers in which the indium composition is the gradient change and to obtain a 2D hole gas at each interface,” said author Liwen Sang. “Then we engineer this 2D hole gas to 3D hole gas, which improves the performance of the p-type region,” said Sang.

The researchers will use this method to fabricate full-color solar cells and LEDs made of GaN-based material.

“This new method to fabricate the p-type region is very helpful for improving the efficiency of long-wavelength LEDs and solar cells,” Sang said.

The conversion efficiency of the InGaN solar cell with the proposed multiple-layer structure was improved by over 1.5 times compared to the single layer p-type InGaN.

The researchers obtained a hole mobility as high as approximately 40 centimeters squared divided by voltage multiplied by seconds, which is more than 10 times higher than the single-layer p-type InGaN with the same average indium mole fraction.

The proposed research can also be utilized to develop GaN-based laser diodes and other optical devices.

Source: “Polarization-induced hole doping for long-wavelength In-rich InGaN solar cells,” by Liwen Sang, Masatomo Sumiya, Meiyong Liao, Yasuo Koide, Xuelin Yang, and Bo Shen, Applied Physics Letters (2021). The article can be accessed at https://doi.org/10.1063/5.0071506 .