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

Abstract

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 µm 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.