Tunnel junctions for two-color nitride light emitting diodes and laser diodes grown by plasma assisted molecular beam epitaxy

One of the most challenging issues to address in nitride based devices like light emitting diodes (LEDs) and laser diodes (LDs) is poor conductivity of p-type region. Additionally, high resistance of the p-type contact, that is very difficult to reduce, determines performance and influences design of InGaN LEDs and LDs. Recently, there has been increasing attention given to the interband tunnel junctions (TJ) for effective carrier conversion between n-type and p-type material region in nitride LEDs and LDs. It was clearly demonstrated that TJ resistance for wide bandgap semiconductors can be effectively suppressed by making use of the piezoelectric fields in the region of the junction [1]. Low resistance TJ were investigated and realized using GaN/InGaN/GaN heterostructures. The MBE technology seems to be more efficient than MOVPE for practical realization of the devices with TJ. For MOVPE it is difficult to activate the p-type conductivity in the (In)GaN:Mg layers which are deeply buried below n-type layers due to the fact that diffusion of hydrogen is completely blocked through n-type layers. Therefore several attempts for hybrid MOVPE/MBE growth was performed and TJ LEDs [2], TJ LDs [3] and TJ VCSELs [4] were shown where active p-i-n region was grown by MOVPE and p-n TJ by MBE. However, the presence of the impurities in the MOVPE p-type surface used for MBE regrowth can deteriorate/limit performance of devices grown by hybrid method.