In this paper, we have analyzed the performance of laser diodes (LDs) with an undoped In x Ga 1−x N waveguide in association with variable In mole fractions varying from 0% to 6%. The InGaN waveguide significantly affected optical confinement and carrier dynamics in the LD. Laser output power, internal quantum efficiency (IQE), quantum well (QW) gain and optical confinement factor (OCF) are analyzed in correlation with In content in the waveguide. The OCF for TE1 mode at x = 0 is 0.0079, and it increases with x. The OCF for x = 0.06 is 0.0109. Quantum states in the QW reduced with In content, which reduced QW gain. However, improved OCF consequently improved the overall gain of the device. Peak IQE for x = 0 is ~0.28, which increased to ~0.683 for x = 0.06. Laser output power, slope efficiency and IQE improved with increasing In content. The threshold current density for x = 0 is 3.911 kA cm −2 , which drops to 1.806 kA cm −2 for x = 0.06. Auger recombination, Shockley-Read-Hall recombination and electron leakage are reduced for high In content in the waveguide. Auger carrier loss remains nearly constant above the threshold, hence efficiency droop above the threshold current density is attributed primarily to leakage current density. The efficiency droop for x = 0 is 25.59%, which increased to 36.66% for x = 0.06 at 25 kA cm −2 current density. However, the IQE for x = 0 at 25 kA cm −2 is 0.202, which increased to 0.436 for x = 0.06 at 25 kA cm −2 . Slope efficiency increases with In content; slope efficiency for x = 0.06 improves by 0.2126 W A −1 . Laser output power is improved by 1.91 W at 25 kA cm −2 for x = 0.06.
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 Al 0.15 Ga 0.85 N electron blocking layer (EBL) and Al 0.065 Ga 0.935 N cladding layers are replaced by 300 nm thick C-SPSL which contains the 33-periods of 10 monolayers (ML) GaN/ 2 ML In 0.18 Al 0.82 N, 48-periods of 6 ML GaN/2 ML In 0.18 Al 0.82 N, and 97-periods of 2 ML GaN/ 2 ML In 0.18 Al 0.82 N. 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.
In this study, we optimized the lattice-matched GaN/In 0.18 Al 0.82 N chirped short-period superlattice (C-SPSL) electron-blocking layer for a laser diode emitting at 450 nm. The effective bandgap of C-SPSL depends upon the quantum well (QW) and quantum barrier (QB) thickness of C-SPSL. In this study the In 0.18 Al 0.82 N QB thickness is constant at 0.5112 nm (1 unit layer (UL) = 1 lattice constant thickness) and the GaN QW thickness is varied as 1 UL, 3 UL, and 5 UL. The estimated effective bandgap for 15 periods of 1 UL GaN/1 UL In 0.18 Al 0.82 N SPSL is ~4.2 eV, for four periods of 3 UL GaN/1 UL In 0.18 Al 0.82 N SPSL it is ~3.93 eV and for two periods of 5 UL GaN/1 UL In 0.18 Al 0.82 N SPSL it is 3.62 eV. Wavefunction hybridization and the built-in electric field play an important role in the bandgap behavior of C-SPSL. The electron leakage decreased from 2534.6 A cm −2 to ~14 A cm −2 while hole transportation improved from 7.7 kA cm −2 to 10 kA cm −2 at 10 kA cm −2 injection current density. The light output power per facet improved from 146 mW to 255 mW. Slope efficiency increased from 0.548 W A −1 to 0.924 W A −1 with the C-SPSL design.
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