Photonic device and method of making

A photonic device comprising:

• a silicon layer, wherein the silicon layer includes a waveguide portion;
• a cladding layer over the waveguide portion, wherein the cladding layer partially exposes a surface of the waveguide portion;
• a low refractive index layer in direct contact with the cladding layer, wherein the low refractive index layer comprises silicon oxide, silicon carbide, silicon oxynitride, silicon carbon oxynitride, aluminum oxide or hafnium oxide;
• and
• a contact etch stop layer (CESL) directly contacting the cladding layer.

A method of making a photonic device, the method comprising:

• depositing a cladding layer over a silicon layer;
• patterning the cladding layer to expose a first portion of the silicon layer, wherein a second portion of the silicon layer is covered by the patterned cladding layer, and a waveguide portion is in the second portion of the silicon layer;
• depositing a low refractive index layer over the patterned cladding layer, wherein a refractive index of the low refractive index layer is less than 2.0;
• and
• depositing a contact etch stop layer (CESL) over the cladding layer, wherein the CESL directly contacts the cladding layer.