Multi-junction distributed-feedback laser diodes - synergy of high opticalpower and single-mode operation

Figure 1: Multi-junction DFB lasers

This project is a joined projects between the Institute of High Pressure Physics Polish Academy of Science, CEZAMAT Warsaw University of Technology, and our group at Chemnitz University of Technology.
In this project we plan to develop and characterize a completely new optoelectronic device - a multi-junction DFB LD. This combines a distributed feedback (DFB) laser with the concept of multi-junction devices. In general, DFB lasers offer unprecedented spectral purity in a compact system, which has many different application options. However, the development of a GaN-based DFB laser is accompanied by some challenges, as the standard methods for the production of DFB lasers are not applicable in the GaN area. Therefore, it is important to develop new methods for GaN-based DFB lasers. Multi-junction LDs consist of several active regions that are interconnected by tunnel junctions (TJs). As a result, recombination occurs in each QW with the same current flow. Therefore, a N-fold increase in the output power of the multi-junction LD with N sections can be expected. This results in a differential efficiency (photons per injected electron) of over 100 %. However, this comes at the cost of an additional voltage required for each section. The development of GaN-based TJs also presents its difficulties, which must be overcome.
The shematic of the proposed multi-junction DFB LD is presented in fig. 1, which shows a device consisting of three QWs interconnected by TJs and a DFB grating placed on top of the structure. This position of the grating is chosen to ensure strong coupling to the optical mode and lasing at only one wavelength. The aim of this project are LDs with high optical power in single-mode operation.

The Institute of High Pressure Physics PAS will lead the development of GaN-based DFB lasers, multi-junction LDs, GaN-based TJs and the proposed combination in form of a multi-junction DFB laser, as they have more than 20 years of experience in the development of GaN-based LDs. CEZAMAT Warsaw University of Technology, offers state-of-the-art lithographic technologies, in particular electron beam lithography. This technique is used to fabricate surface diffraction gratings on the mesa structure. Our group at Chemnitz University of Technology specializes in the spectroscopic investigation of the physical properties of semiconductor devices. Therefore, we will focus on the characterization and investigation of the individual parts as well as the complete devices with complex structures.
project start: January 2025