Efficiency Studies of Semipolar GaInN-GaN Quantum Well Structures

In order to clarify the reasons for the fairly poor electroluminescence (EL) performance of semipolar LED structures grown on patterned sapphire wafers, we have analyzed both, pure photoluminescence (PL) test structures without doping only containing 5 GaInN quantum wells and full EL test structures, all emitting at a wavelength of about 510 nm. Evaluating the PL intensity over a wide range of temperatures and excitation powers, we conclude that such quantum wells possess a fairly large internal quantum efficiency of about 20%. However, on EL test structures containing nominally the same quantum wells, we obtained an optical output power of only about 150μW at an applied current of 20mA. This may be due partly to some thermal destruction of the quantum wells by the overgrowth with p-GaN. Even more important seems to be the not yet finally optimized p-doping of such structures.