How tunnel junctions changed our perception of III-N optoelectronic devices. III-N micro-LEDs

Speakers: M.Sc. Julia Sławińska and Prof. Czesław Skierbiszewski.
Organism:  Institute of High Pressure Physics, Polish Academy of Sciences, Warsaw. Poland.
Date: 16th November, 2021
Time: 12.00h.
Place: Salon de Grados, Building A.

ABSTRACT

Poor conductivity of the ptype region and difficulties with processing of low resistance ohmic ptype contacts are the most challenging issues to address in nitride based devices. Recently, there has been increasing attention given to the interband tunnel junctions (TJs) for efficient carrier conversion between ntype and ptype material region in nitride devices. Application of TJs eliminates the need for ptype contact deposition and create more freedom in device design. It was clearly demonstrated that TJs resistance for wide bandgap semiconductors can be effectively reduced by making use of the piezoelectric fields in the region of the junction. However, for metalorganic vapour phase epitaxy (MOVPE) it is difficult to activate the ptype conductivity in the (In)GaN:Mg layers which are buried below ntype layers due to the fact that diffusion of hydrogen is completely blocked through ntype region. On the other hand, for plasma assisted molecular beam epitaxy (PAMBE) ptype doping is achieved without post growth activation process. Therefore, PAMBE seems to be better suited than MOVPE for practical realization of the vertical devices with buried ptype regions especially for devices containing interband TJs. In this work we will show current status of IIIN TJs grown by PAMBE. Application of TJs enabled us to demonstrate novel types of IIIN devices, like: (1) vertically integrated light emitting diodes (LEDs) or laser diodes (LDs), (2) distributed feedback LDs. We will discuss in detail the inverted LED structures, operating at cryogenic temperatures. These LEDs contain the TJs below active region, which allow to reverse electric polarization of the diode. The application of TJs opens a possibility for novel architecture of microLEDs. We show an alternative method of nitride microLEDs fabrication, where emission surface was defined by size of the TJ embedded inside diode. MicroLEDs and arrays of microLEDs will be presented.