GaN/InAlN chirped short period superlattice as strain free top cladding for blue laser diode

Abstract

This work presents the theoretical study on strain-free chirped short-period superlattices (C-SPSLs) as the top waveguide core and cladding layers for InGaN laser diodes (LDs) emitting at 450 nm. The total 530 nm thick layers of reference LD containing 100 nm p-GaN waveguide, 30 nm Al0.15Ga0.85N electron blocking layer (EBL) and Al0.065Ga0.935N cladding layers are replaced by 300 nm thick C-SPSL which contains the 33-periods of 10 monolayers (ML) GaN/ 2 ML In0.18Al0.82N, 48-periods of 6 ML GaN/2 ML In0.18Al0.82N, and 97-periods of 2 ML GaN/ 2 ML In0.18Al0.82N. The optical confinement factor of reference LD is 3.28% whereas for C-SPSL LD it is 3.42%. The better optical confinement at reduced thickness using C-SPSL is due to the high refractive index contrast. The strain in the C-SPSL is negligible. The electron leakage has reduced from 2.54 kA cm−2 to 0.166 kA cm−2 at ∼10 kA cm−2 injected current density, whereas the hole transportation has improved by 2.31 kA cm−2. The C-SPSL configuration also favors the electron blocking effect, thus EBL is not required in C-SPSL design. The light output power at a current injection of 500 mA (10 kA cm−2) is 248 mW for the new structure and ∼143 mW for reference LD. The slope efficiency is improved from ∼0.55 to ∼0.89 W A−1. Also, the dynamic resistance from I–V characteristic is ∼1.12 Ω which is lowered to ∼0.94 Ω.