AlGaN-based vertical injection laser diodes using inverse tapered p-waveguide for efficient hole transport

An AlGaN deep ultraviolet laser diode design exploiting AlN substrates is presented, featuring an inverse-tapered p-waveguide layer. The 2-D optoelectronic simulation predicts lasing at 290 nm. Spatial balancing of the lasing mode to minimize optical loss in the p-Ohmic metallization is achieved through the use of a narrow bandgap yet transparent n-waveguide layer. Several electron blocking layer (EBL) designs are investigated and compared with a conventionally tapered EBL design. Through judicious volumetric redistribution of fixed negative polarization charge, inverse tapering may be exploited to achieve nearly flat valence band profiles free from barriers to hole injection into the active region, in contrast to conventional designs. Furthermore, proper selection of quantum well barrier and spacer compositions are demonstrated to reduce electron leakage from the active region. Numerical simulations demonstrate that the inverse tapered strategy is a viable solution for efficient hole injection in deep ultraviolet laser diodes operating at shorter wavelengths (<290 nm).