Semiconductor-air gap grating fabrication using a sacrificial layer process

A method of making an optical diffracting device, said method comprising the steps of:

• growing a first semiconductor layer on a semiconductor substrate;
• depositing a dielectric layer on the first semiconductor layer;
• patterning and etching the dielectric layer to form openings in the dielectric layer to expose selective areas on the first semiconductor layer where the openings define substantially parallel strips;
• etching holes in the first semiconductor layer through the strip openings in the dielectric layer so that the dielectric layer acts as a mask;
• growing sacrificial regions in the etched holes in the first semiconductor layer with a semiconductor material that is compatible for epitaxial growth with the material of the first semiconductor layer, said sacrificial region semiconductor material having an index of refraction that is different than the index of refraction of the first semiconductor layer;
• removing the dielectric layer;
• growing a second semiconductor layer on the first semiconductor layer in contact with the sacrificial regions by an epitaxial growth process;
• etching access vias through the second semiconductor layer to expose the sacrificial regions;
• and
• etching away the sacrificial region material through the etching access vias to define a diffraction grating made out of channels of air.