Influence of delta doping on intersubband transition and absorption in AlGaN/GaN step quantum wells for terahertz applications

Effects of delta doping location and density on intersubband transitions in AlGaN/GaN step quantum wells for terahertz (THz) applications have been investigated by solving Schrödinger and Poisson equations self-consistently. It shows that delta doping near the GaN well/AlGaN step well interface causes a blue-shift, while delta doping in the barrier or near barrier/GaN well and barrier/step well interfaces cause a red-shift first and then a blue-shift with increasing doping density. The shifts are attributed to the combination of many body effect and internal field modulation effect, and can be more than 200% or 70% of the e1–e2 transition energy, as for blue-shift or red-shift, respectively. In addition, the influences of delta-doping location and density on the absorption coefficient are also investigated in detail. Delta doping at the middle of a layer is found much more desirable over uniform-doping in order to improve the absorption coefficient, especially in the step well.