Waveguide design of green InGaN laser diodes

Abstract

In this paper we investigate the waveguiding (WG) of direct green InGaN laser diodes grown on c-planeGaNsubstrates. The problem of parasitic modes emerges due to the reduced refractive index difference between the GaN waveguide and AlGaN cladding layers for green compared to blue emitting laser diodes. We discuss several approaches to avoid substrate modes. We investigate different materials and designs for optimized WG of green InGaN laser diodes using a 1D transfer matrix simulation tool

Optical absorption edge broadening in thick InGaN layers: Random alloy atomic disorder and growth mode induced fluctuations

“…40,41 Finally, let us emphasize that the ability to control the surface morphology and hence the homogeneity of thick InGaN epilayers is extremely relevant in the framework of applications where the minimization of unwanted disorder is critical. This is especially the case when attempts are made to realize laser waveguides, 42 metamorphic layers, 43 or solar cells. 44,45 To conclude, the structural and optical properties of pseudomorphic In x Ga 1Àx N (0 < x < 0.18) epilayers grown on low dislocation density c-plane FS GaN substrates have been characterized.…”

Cleaved-facet violet laser diodes with lattice-matched Al0.82In0.18N/GaN multilayers as n-cladding

“…Furthermore the 8% refractive index contrast with GaN at 400 nm remains high even at wavelengths of 520 nm where it is 6.25%. 7 For Al 0.08 Ga 0.92 N the index contrast with GaN at 400 nm and 520 nm is 1.7% and 0.8%, respectively. Thus, for lasers around 400 nm, a thin AlInN cladding thickness can be used while for longer wavelengths an increased optical mode confinement can be obtained which can compensate the reduced optical gain of InGaN quantum wells ͑QWs͒ at those wavelengths.…”

“…7 Conventional visible laser diodes use strained Al y Ga 1−y N ͑with y in the range of 8%͒ materials as the waveguide cladding layers where thicknesses of Ͼ1 m are required to minimize the leakage of the guided optical modes into the high index GaN substrate. This requirement on layer thickness could be reduced by using Al y Ga 1−y N with higher Al composition, but this is not possible due to the excess tensile strain introduced which causes cracking.…”

Growth optimization and characterization of lattice-matched Al0.82In0.18N optical confinement layer for edge emitting nitride laser diodes

“…Indeed, the refractive index contrast between the GaN waveguide and Al 0.1 Ga 0.9 N cladding diminishes as the emission wavelength moves to the green range (Dn $ 0.053 for l¼430 nm and Dn$0.035 at l¼520 nm [7]), resulting in lower optical confinement in LD structures. In order to minimize the leakage of the guided optical modes into the high index GaN substrate, the increase of either the thickness or the Al composition of the Al x Ga 1 À x N cladding can be envisaged [8][9][10].…”