The influence of the Mg doping profile on the electroluminescence efficiency of GaInN light emitting diodes (LED) has been investigated. The Mg doping profile is influenced by segregation as well as by diffusion during the growth. The diffusion of the Mg dopants into the active region can be controlled by the growth temperature of the Mg doped layers. An increase in Mg concentration close to the active region results in an improved hole injection and thus in a higher electroluminescence efficiency of the GaInN quantum wells. However an excessive spread of the Mg doping atoms towards the GaInN quantum well active region leads to nonradiative recombination and thus a lower output power of the LEDs. An LED test structure containing multiple quantum wells which differ in In content and emission wavelength was used to probe the spatial distribution of the radiative recombination of electrons and holes in the active region and to clarify the influence of Mg dopants in the active region on nonradiative recombination.
We report on the development of (AlGaIn)N quantum well LEDs covering the 380 to 430 nm wavelength range, which serve as the primary light source for tri-phosphor luminescence conversion white LEDs. Epitaxial layer growth was performed by low-pressure metal-organic chemical vapor deposition on sapphire substrates. Mesa LEDs were fabricated and either mounted in standard epoxy-based 5 mm radial LED packages or flip-chip bonded on ceramic submounts. Then, LED-chips with peak wavelengths matching the absorption spectrum of an appropriately chosen inorganic tri-phosphor blend, were used for the fabrication of single-chip tri-color luminescence conversion white LEDs. These de-vices allowed us to demonstrate the feasibility of the above concept for improved color rendering and tunability.