Thermal properties of GaN-based semiconductor-metal subwavelength grating VCSELs and novel current injection scheme

摘要

This paper provides a thermal and electrical analysis of semiconductor-metal subwavelength-grating (SMSG) vertical-cavity surface-emitting lasers (VCSELs). In the proposed design, the top distributed Bragg reflector (DBR) of a GaN-based VCSEL is replaced with a GaN-Ag SMSG, which serves as both an optical reflector and an electrical contact. Using a numerical 3D self-consistent thermo-electric model combined with a 3D optical model, we show that GaN-based SMSG VCSELs with aperture sizes of over 50 mu m are capable of laser operation. We also propose spatial tuning of the injected current density to eliminate the current crowding effect in large area VCSELs. The use of GaN-Ag SMSGs in GaN-based VCSELs eliminates the need for a top dielectric DBR and intracavity injection scheme, making the fabrication of monolithic VCSELs possible. It also eliminates the need to use a tunnel junction with optical confinement built into the cavity. Although the GaN-Ag SMSG introduces higher optical losses than a DBR, its advantage is that it permits vertical current injection into the active region, enabling laser emission from broader-area active regions in comparison to conventional VCSELs.