Violet GaN based light emitting diodes fabricated by metal organics vapour phase epitaxy

Abstract

For almost 2 decades, p-doping of GaN was not feasible. Since the ionisation energy of any acceptor species is >200 meV, the hole concentration obtained by p-doping is only one hundredth of the acceptor impurity concentration. Mg has been so far the most typical dopant used for p-type GaN. In metal organics vapour phase epitaxy (MOVPE), the precursor was the bismethylcyclopentadienyl Mg, (MeCp) 2Mg. However, two severe drawbacks must be overcome. The Mg precursor and ammonia react in the vapour phase to give solid particles. In addition, H is incorporated during the growth process, therefore, a post growth annealing is required. The Mg doped GaN samples studied were grown by MOVPE on (0001) oriented sapphire substrates. With proper design of the growth chamber and thermal annealing, doping densities up to 2×10 18 cm −3 have been reached. Photoluminescence (PL) and photocapacitance data reveal that in addition to the shallow acceptors, deep states are most likely related to Mg complexes. n-Doping is straightforward. Si is easily introduced via silane and allows a free carrier concentration up to 10 19 cm −3 to be reached. Henceforth p–n junctions and light emitting diodes were achievable.