Stress management on underlying GaN-based epitaxial films: A new vision for achieving high-performance LEDs on Si substrates

Abstract

High-performance blue GaN-based light-emitting diodes (LEDs) on Si substrates have been achieved by applying a suitable tensile stress in the underlying n-GaN. It is demonstrated by simulation that tensile stress in the underlying n-GaN alleviates the negative effect from polarization electric fields on multiple quantum wells but an excessively large tensile stress severely bends the band profile of the electron blocking layer, resulting in carrier loss and large electric resistance. A medium level of tensile stress, which ranges from 4 to 5 GPa, can maximally improve the luminous intensity and decrease forward voltage of LEDs on Si substrates. The LED with the optimal tensile stress shows the largest simulated luminous intensity and the smallest simulated voltage at 35 A/cm2. Compared to the LEDs with a compressive stress of −3 GPa and a large tensile stress of 8 GPa, the improvement of luminous intensity can reach 102% and 28.34%, respectively. Subsequent experimental results provide evidence of the superiority of applying tensile stress in n-GaN. The experimental light output power of the LEDs with a tensile stress of 1.03 GPa is 528 mW, achieving a significant improvement of 19.4% at 35 A/cm2 in comparison to the reference LED with a compressive stress of −0.63 GPa. The forward voltage of this LED is 3.08 V, which is smaller than 3.11 V for the reference LED. This methodology of stress management on underlying GaN-based epitaxial films shows a bright feature for achieving high-performance LED devices on Si substrates.

Numerical simulation of UV LEDs with GaN and BGaN single quantum well

“…With a methodology based on stress management on underlying GaN-based epitaxial films, the authors demonstrated numerically and experimentally that the optimal tensile stress can increase by over 100% in comparison to the LEDs with compressive stresses [15] . Involving a simple high-quality AlN/Al-GaN buffer template on sapphire substrate which allows a remarkable improvement in the output power of 340 nm-band quaternary InAlGaN-based UV-LEDs, however a maximum output power of 7.1 mW was reached and the authors found that the crystalline quality of the AlN/AlGaN templates strongly affects the output power of UV-LEDs [14] .…”