Seminarium Fizyki Ciała Stałego

Deep UV-emitter based on group-III nitrides:Challenges and new approachesAfter a short introduction into the present status of UV emitters, their application potential especially in view of water purification and medical disinfection as well as plant growth, different solutions will be compared. Dominating at present low-pressure mercury lamps have to be replaced for environmental reasons. Only group-III nitrides containing high concentrations o f Al can reach the desired spectral range. In case of such pure AlGaN/AlGaN quantum well structures one looses the advantage of In-containing QW-structures being highly inert to threading dislocation densities. AlGaN has dislocation densities by 1-2 orders of magnitude higher compared to best GaN. An additional huge problem is the dopability of AlGaN. This holds not only for p-doping due to a much deeper Mg-acceptor level but also for n-doping with Si due to the formation of DX-like centers with increasing band gap and following compensation issues. A third big issue hampering at present the applicability of deep nitride-based UV emitters are heat generation and its dissipation as well as the high contact resistivity respectively the high optical absorption of p-GaN contact layers limiting the external quantum efficiency of such devices.Whereas GaAs diluted with a small amount of nitrogen has been widely studied over years for application of telecommunication laser diodes much less is know for GaN diluted with arsenic. We will show first experimental evidences for the theoretical prediction of W. Walukiewicz, that the introduced changes in the band gap are predominantly a shift of the valence band of GaN(As). This implies that the acceptor level will become shallower and p-doping more efficient. Results based on the growth of GaN(As) with up to 5% As and characterized by in-situ XPS-photoemission spectroscopy and optical studies will be presented. Results are obtained with the Team Tech project DUETT of FNP (Deep UV-emitter Team Tech, 2017-2020) and will be presented for the first time.