Controlling the Mg doping profile in MOVPE-grown GaN/Al(0.2)Ga(0.8)N light-emitting diodes

The Mg back-diffusion in GaN and Al(0.2)Ga(0.8)N is investigated by secondary ion mass spectrometry (SIMS) on simple test samples as well as complete GaN/AlGaN light-emitting diode (LED) structures for emission wavelengths around 350 nm. The diffusion coefficient in Al(0.2)Ga(0.8)N is shown to be increased by 75 % compared to GaN. In the LED structures, the GaN quantum well acts as a diffusion barrier, which cannot be explained solely by the observed increased Mg diffusion in AlGaN. However, this self-limiting behavior can be exploited to control the Mg doping profile in close proximity to the quantum well active region and hence to optimize the optical output of the LEDs.