Light extraction from a semiconductor light emitting device via chip shaping
View Patent ↗A method for designing semiconductor light emitting devices is disclosed wherein the side surfaces (surfaces not parallel to the epitaxial layers) are formed at preferred angles relative to vertical (normal to the plane of the light-emitting active layer) to improve light extraction efficiency and increase total light output efficiency. Device designs are chosen to improve efficiency without resorting to excessive active area-yield loss due to shaping. As such, these designs are suitable for low-cost, high-volume manufacturing of semiconductor light-emitting devices with improved characteristics.
1. A light-emitting diode structure comprising:
a multi-layer heterostructure, including a window portion and an active layer for generating light, said multi-layer heterostructure having a flat surface for emitting light, said window portion being transparent and having at least portions of one or more sides of said window portion at an oblique angle with respect to said flat surface, wherein said oblique angle is selected to increase the amount of light escaping from said sides of said window portion,
wherein an inner angle of each angled side of the window portion with respect to the active layer is between 40-70 degrees,
wherein a thickness of the window portion is greater than 50 microns,
wherein the active layer is supported on a first surface of the window portion, the active layer emitting light from one surface into the window portion and emitting light from another surface away from the window portion, at least some light emitted away from the window portion being reflected back in an opposite direction,
wherein said at least portions of one or more sides of said window portion extend outward as said window portion approaches said active layer,
wherein at least some light emitted by the active layer in a direction perpendicular to the active layer impinges on the angled sides of the window portion, and
wherein an ohmic contact electrically connects to the active layer, and wherein the ohmic contact comprises a reflector for reflecting light emitted from the active layer out of the light-emitting diode structure.
2. The diode of claim 1 wherein said window portion is at least a portion of a substrate.
3. The diode of claim 1 wherein said window portion is an insulator.
4. The diode of claim 1 wherein said window portion is a semiconductor.
5. The diode of claim 1 wherein said window portion is a substrate that has replaced a growth substrate on which said active layer was grown.
6. The diode of claim 1 wherein said window portion is frustum shaped wherein one or more entire sides of said window portion are at said oblique angle.
7. The diode of claim 1 further comprising a first ohmic contact formed on said window portion and a second ohmic contact formed on an opposite side of said heterostructure for providing electrical contact through said diode.
8. The diode of claim 1 wherein said oblique angle is not constant.
9. The diode of claim 1 further comprising a reflective electrical contact formed on a surface of said heterostructure opposite a primary light output surface of said diode.
10. The diode of claim 1 further comprising two ohmic contacts formed on a surface of said heterostructure opposite a primary light output surface of said diode for providing current through said diode.
11. The diode of claim 1 wherein said window portion comprises GaP.
12. The diode of claim 1 wherein said active layer is formed by a combination of materials selected from the group consisting of Al, In, Ga, and P.
13. The diode of claim 1 wherein the entire multi-layer heterostructure forms a truncated pyramid.
14. The diode of claim 1 wherein said window portion is a first window portion, said diode further comprising a second window portion on a side of said active layer opposite the side facing said first window portion.
15. The diode of claim 1 further comprising an epoxy encapsulating said multi-layer heterostructure.
16. The diode of claim 1 wherein a surface of said active layer has an area greater than an area of a surface of said window portion facing away from said active layer.
17. The diode of claim 1 wherein a primary light output surface of said diode is other than a surface of said window portion.