Effect of doping of layers surrounding GaN/InGaN multiple quantum wells on their thermal stability

GaN/InGaN quantum wells (QWs), widely used as the active region in blue and green light emitters, are sus-ceptible to structural degradation at temperatures above 900 degrees C. The degradation process is initiated by the diffusion and clustering of gallium vacancies (VGa). The aim of this work is to determine how the vacancy population in different layers surrounding the QWs affects their thermal stability. Silicon and magnesium doping was used to manipulate the vacancy concentrations. Experimental results showed that the availability of VGa in the high-temperature (HT) GaN layer below the QWs has a clear effect on the degradation process. No effect of the vacancy concentration in the layer above the active region indicates that the VGa diffusion associated with QW degradation mainly occurs in the [0001] direction. Magnesium doping (2 x 1019 cm -3) in the HT underlayer reduces the VGa concentration, which improves the thermal stability of the closest QW, showing that vacancies in the barriers also contribute to the degradation process. By using heavy magnesium doping (1019 cm-3) in the barriers alone, the thermal stability of the QWs is significantly improved even when a typical HT n-type GaN underlayer is used. This shows that Mg atoms not only increase the formation energy of VGa, but also limit its diffusivity, enabling the use of GaN:Mg layers as diffusion barriers for VGa.

Automated summary

This study aims to determine the influence of vacancy concentration in different layers surrounding GaN/InGaN quantum wells (QWs) on their thermal stability. Experimental results showed that the vacancy concentration in the GaN layer below the QWs at high temperature has a clear effect on the degradation process, while the vacancy concentration in the layer above the active region has no effect. Magnesium doping can reduce the vacancy concentration and improve the thermal stability of the QWs.