Blue and green laser diodes with gallium nitride or indium gallium nitride cladding laser structure
View Patent ↗A novel indium gallium nitride laser diode is described. The laser uses indium in either the waveguide layers and/or the cladding layers. It has been found that InGaN waveguide or cladding layers enhance optical confinement with very small losses. Furthermore, the use of InGaN waveguide or cladding layers can improve the structural integrity of active region epilayers because of reduced lattice mismatch between waveguide layers and the active region.
1. A semiconductor laser having an asymmetric stack of wavequide layers, comprising:
an active region including at least one quantum well containing indium, gallium, and nitride, the active region having a first side and a second side;
a first waveguide layer immediate adjacent to the first side, said first wavequide layer comprising a nitride of indium (In) and gallium (Ga) in the ratio of In y Ga 1-y N, where y>0, said first waveguide layer being essentially free of aluminum;
a first cladding layer having a refractive index less than a refractive index of the active region, the first cladding layer adjacent the first waveguide layer, the first cladding layer consisting of gallium nitride, the first cladding layer to provide optical confinement such that an output of the semiconductor laser is directed in a direction approximately parallel to a plane of an interface between the first cladding layer and the first waveguide layer;
a second waveguide layer adjacent to the second side, said second waveguide layer comprising a nitride of indium (In) and gallium (Ga) in the ratio of In x Ga 1-x N, where x>0, said second waveguide layer being essentially free of aluminum; and
a second cladding layer adjacent the second waveguide layer, the second cladding layer consisting essentially of a nitride of aluminum (Al) and gallium (Ga), the second cladding layer to provide optical confinement such that an output of the semiconductor laser is directed in a direction approximately parallel to a plane of an interface between the second cladding layer and the second waveguide layer.
2. The semiconductor laser of claim 1 wherein the first cladding layer is at least 20 nm thick.
3. The semiconductor laser of claim 1 further comprising:
a thin current barrier layer between and in physical contact with the active region and the second waveguide layer.
4. The semiconductor laser of claim 3 wherein the current barrier layer is magnesium (Mg) doped.
5. The semiconductor laser of claim 4 wherein the current confinement layer is between 5 nm and 40 nm.