Enhanced planarity in GaN edge emitting lasers
View Patent ↗A GaN edge emitting laser is provided comprising a semi-polar GaN substrate, an active region, N-side and P-side waveguiding layers, and N-type and P-type cladding layers. The GaN substrate defines a 20 2 1 crystal growth plane and a glide plane. The N-side and P-side waveguiding layers comprise a GaInN/GaN or GaInN/GaInN superlattice (SL) waveguiding layers. The SL layers of the N-side and P-side SL waveguiding layers have layer thicknesses between approximately 1 nm and 5 nm that are optimized for waveguide planarity. In another embodiments, planarization is enhanced by ensuring that the N-side and P-side GaN-based waveguiding layers are grown at a growth rate that exceeds approximately 0.09 nm/s, regardless of whether the N-side and P-side GaN-based waveguiding layers are provided as a GaInN/GaN SL, GaInN/GaInN SL or as bulk layers. In further embodiments, planarization is enhanced by selecting optimal SL layer thicknesses and growth rates.
1. A method of fabricating a GaN edge emitting laser comprising a semi-polar GaN substrate, an active region, an N-side waveguiding layer, a P-side waveguiding layer, an N-type cladding layer, and a P-type cladding layer, wherein:
the GaN substrate defines a 20 2 1 crystal growth plane and a glide plane;
the N-side waveguiding layer comprises a GaN-based superlattice or bulk waveguiding layer;
the P-side waveguiding layer comprises a GaN-based superlattice or bulk waveguiding layer;
the active region is interposed between and extends substantially parallel to the N-side SL waveguiding layer and the P-side SL waveguiding layer;
the N-type cladding layer is interposed between the N-side waveguiding layer and the GaN substrate;
the P-type cladding layer is formed over the P-side waveguiding layer;
a strain-thickness product of the N-side SL waveguiding layer exceeds its strain relaxation critical value and a strain-thickness product of the N-type cladding layer exceeds its strain relaxation critical value such that resulting strain relaxation is mono-directional along the glide plane of the GaN substrate; and
the N-side and P-side GaN-based waveguiding layers are grown at a growth rate that exceeds approximately 0.09 nm/s to optimize waveguide planarity.
2. A method of fabricating a GaN edge emitting laser as claimed in claim 1 wherein the growth rate at which the N-side and P-side GaN-based waveguiding layers are grown is approximately 0.095 nm/s.
3. A method of fabricating a GaN edge emitting laser as claimed in claim 1 wherein the growth rate at which the N-side and P-side GaN-based waveguiding layers are grown is between approximately 0.09 nm/s and approximately 0.10 nm/s.
4. A method of fabricating a GaN edge emitting laser as claimed in claim 1 wherein:
the N-side waveguiding layer comprises a GaInN/GaN or GaInN/GaInN superlattice (SL) waveguiding layer;
the P-side waveguiding layer comprises a GaInN/GaN or GaInN/GaInN superlattice (SL) waveguiding layer; and
the superlattice layers of the N-side and P-side SL waveguiding layers are grown to define respective layer thicknesses that are optimized for waveguide planarity, the layer thicknesses being between approximately 1 nm and approximately 5 nm.