Band Engineering Improves Efficiency Of Green LEDs
WHU team shows improved carrier injection efficiency and optoelectronic properties of green LEDs by introducing a stacked last quantum barrier structure.
A research team led by Shengjun Zhou at Wuhan University has reported a stacked last quantum barrier (SLQB) GaN/AlN layer to realise highly efficient InGaN-based green (~550 nm) light-emitting diodes (LEDs). The team says that the stacked last quantum barrier structure boosts the hole injection efficiency and alleviates the electron leakage effect, thus improving the device performance
III-nitride LEDs have attracted much attention due to their advantages of low energy consumption, wide colour gamut, long operation lifetime and compact device size. With the emission spectrum covering the visible region, full-colour micro-LED displays can be realised by the colour mixing of red, green and blue LEDs. Generally, high indium content in the InxGa1-xN quantum well is prerequisite to obtain long emission wavelength of LEDs. However, there exists high in-plane compressive stress with the increased indium composition, which brings about a strong polarisation field. As a result, InGaN-based LEDs emitting in green region are still suffering from inferior quantum efficiency, much lower than that of their blue counterparts.
The researchers expand the application of band engineering technique in long wavelength region and investigate the effects of SLQB on optoelectronic properties of green LEDs experimentally and numerically. The light output power of green LED with SLQB is 35 percent higher than that of LED with conventional GaN quantum barrier. Simulation results demonstrate that the polarisation induced negative sheet charges at the SLQB/p-GaN interface can accelerate holes and the AlN layer in SLQB favours an intraband tunnelling process for holes to inject into the active region.
The effective barrier height for electrons is also increased with the introduction of AlN layer in SLQB. Owing to the increased hole injection efficiency and suppressed electron leakage, the emission efficiency of green LED with SLQB is significantly improved.
'Stacked GaN/AlN last quantum barrier for high-efficiency InGaN-based green light-emitting diodes' by Guoyi Tao et al; Optics Letters, 46(18) 4593-4596, 2021.