Photonic crystal structures and methods of making and using photonic crystal structures
View Patent ↗A light emitting device having a buried photonic bandgap (PBG) structure is created using a relatively simple fabrication method known as epitaxial layer overgrowth (ELOG). By burying the PBG structure, the difficulties and disadvantages associated with the known technique of etching holes into a LED emission surface to form the PBG structure are avoided.
1. A light emitting device having improved quantum efficiency, the light emitting device comprising:
a substrate having a top surface;
a buffer layer of Gallium Nitride (GaN) disposed on the top surface of the substrate;
a dielectric mask layer having a pattern of openings formed therein;
a layer of n-type or p-type GaN disposed on the buffer layer and extending vertically through each of the openings formed in the dielectric mask layer and extending laterally away from a periphery of each opening both immediately above and immediately below each opening, the GaN extending vertically and laterally through the openings formed in the dielectric mask layer to create a periodically varying refractive index profile in the light emitting device;
a quantum well (QW) layer disposed above the patterned dielectric mask layer and above the layer of GaN that extends vertically through the openings formed in the dielectric mask layer, said QW layer providing an active region of the light emitting device in which electrons are converted into photons, said periodically varying refractive index profile promoting confinement of light in the active region; and
a layer of n-type or p-type GaN disposed above the active region, wherein if the GaN extending vertically and laterally through the openings formed in the dielectric mask layer is n-type GaN, then the layer of GaN disposed above the active region is p-type GaN, and wherein if the GaN extending vertically and laterally through the openings formed in the dielectric mask layer is p-type GaN, then the GaN disposed above the active region is n-type GaN.
2. The light emitting device of claim 1 , wherein said one or more QW structures comprises one or more layers of Indium Gallium Nitride (InGaN), the light emitting device further comprising:
a layer of Aluminum Gallium Nitride (AlGaN) covering said QW layer.
3. The light emitting device of claim 2 , wherein the n-type or p-type GaN disposed on the buffer layer is n-type GaN, said QW layer being disposed on top of at least portions of the n-type GaN.
4. The light emitting device of claim 3 , wherein the layer of n-type or p-type GaN disposed above said QW layer is a layer of p-type GaN, the layer of p-type GaN being disposed on top of the layer of AlGaN.
5. The light emitting device of claim 4 , wherein the n-type GaN extending vertically and laterally through each of the openings formed in the dielectric mask layer merges laterally above the dielectric mask layer with n-type GaN extending vertically and laterally through others of the openings formed in the dielectric mask layer to form a layer of n-type GaN having a generally merged, planarized top surface on which said one or more layers comprising said QW layer are disposed.
6. The light emitting device of claim 4 , wherein the dielectric mask layer is disposed above said one or more QW structures, and wherein the p-type GaN disposed above said one or more QW structures extends vertically and laterally through each of the openings formed in the dielectric mask layer and forms a layer of p-type GaN having a generally merged, planarized top surface.
7. The light emitting device of claim 1 , wherein the light emitting device is a light emitting diode (LED) device.
8. The light emitting device of claim 1 , wherein the light emitting device is incorporated into a laser device.