MICRO-LED WITH REFLECTANCE REDISTRIBUTION
A structure and method of micro-LEDs are described. The micro-LEDs have a GaN semiconductor structure containing a multi-quantum well active region configured to emit light of a visible wavelength range and a structure to increase specular reflection of ambient light by proving scattering at one or more interfaces of the micro-LEDs. The interfaces include the air-encapsulant interface, semiconductor-encapsulant interface, or semiconductor-contact interface.
1 . A micro-light-emitting diode (micro-LED) structure comprising:
a micro-LED comprising doped epitaxial semiconductor layers and an active region disposed between the doped epitaxial semiconductor layers, the active region configured to emit light at a predetermined wavelength; and
an optically-transparent medium covering the micro-LED, at least one of the micro-LED and the optically-transparent medium having a structure configured to adjust a direction of ambient light of visible wavelengths that has entered the optically-transparent medium.
2 . The micro-LED structure of claim 1 , wherein the structure comprises nanospheres disposed in etched recesses of one of the doped epitaxial semiconductor layers.
3 . The micro-LED structure of claim 2 , wherein the nanospheres are silica nanospheres that are disposed in etched recesses of an n-doped GaN surface.
4 . The micro-LED structure of claim 1 , wherein the structure comprises hollow nanospheres disposed on a layer between the optically-transparent medium and one of the doped epitaxial semiconductor layers opposing the optically-transparent medium.
5 . The micro-LED structure of claim 4 , wherein the hollow nanospheres are Si hollow nanospheres disposed in a monolayer.
6 . The micro-LED structure of claim 1 , wherein the structure comprises a roughened layer of the optically-transparent medium, the roughened layer having at least one structure selected from structure including periodic structures, corrugated structures, and random structures.
7 . The micro-LED structure of claim 1 , wherein the structure comprises self-assembled periodic nanospheres disposed in a layer on one of the doped epitaxial semiconductor layers.
8 . The micro-LED structure of claim 1 , wherein the structure comprises etched recesses of one of the doped epitaxial semiconductor layers opposing the optically-transparent medium.
9 . The micro-LED structure of claim 8 , wherein the one of the doped epitaxial semiconductor layers is n-doped GaN, and the micro-LED is a thin-film flip chip structure.
10 . The micro-LED structure of claim 1 , wherein the structure comprises plated AlN on a patterned sapphire substrate of the micro-LED.
11 . The micro-LED structure of claim 1 , wherein the structure comprises a distributed Bragg reflector (DBR) adjacent to a top or bottom surface of the micro-LED, the DBR comprising a plurality of nanoporous layers.
12 . The micro-LED structure of claim 1 , wherein the structure comprises a photolithographic structured surface.
13 . The micro-LED structure of claim 1 , wherein:
the structure comprises an engineered surface that creates a controlled alteration of direction of the ambient light from a specular direction, and
the engineered surface is configured to deflect the ambient light into a range of angles at least one of:
to trap the ambient light inside the micro-LED structure to be absorbed by an absorbing backplane under the micro-LED, or
that is outside a typical viewing angle of a user viewing the micro-LED structure.
14 . A micro-light-emitting diode (micro-LED) system comprising:
a plurality of micro-LEDs configured to emit light of different wavelength ranges, each micro-LED comprising:
a micro-LED comprising doped epitaxial semiconductor layers and an active region disposed between the doped epitaxial semiconductor layers, the active region configured to emit light at a predetermined wavelength; and
an optically-transparent medium covering the micro-LED, at least one of the micro-LED or the optically-transparent medium having a structure configured to alter a direction of ambient light of visible wavelengths that has entered the optically-transparent medium; and
control circuitry configured to individually drive each of the micro-LEDs.
15 . The micro-LED system of claim 14 , wherein the structure comprises at least one of:
first nanospheres disposed in etched recesses of one of the doped epitaxial semiconductor layers, and
second nanospheres disposed on a layer between the optically-transparent medium and the one of the doped epitaxial semiconductor layers opposing the optically-transparent medium.
16 . The micro-LED system of claim 14 , wherein the structure comprises at least one of:
etched recesses of one of the doped epitaxial semiconductor layers opposing the optically-transparent medium, or
a distributed Bragg reflector (DBR) adjacent to a top or bottom surface of the micro-LED, the DBR comprising a plurality of nanoporous layers.
17 . A method of fabricating a micro-light-emitting diode (LED) array including a plurality of micro-LEDs, the method comprising, for each micro-LED:
fabricating a micro-LED comprising doped epitaxial semiconductor layers and an active region disposed between the doped epitaxial semiconductor layers, the active region configured to emit light at a predetermined wavelength; and
encapsulating the micro-LED in optically-transparent medium covering the micro-LED, the micro-LED having a structure configured to alter a direction of ambient light of visible wavelengths that has entered the optically-transparent medium.
18 . The method of claim 17 , wherein fabricating the micro-LED comprises forming the structure by at least one of:
etching one of the doped epitaxial semiconductor layers and depositing first nanospheres in recesses formed by the etching, and
depositing second nanospheres on a layer between the optically-transparent medium and the one of the doped epitaxial semiconductor layers opposing the optically-transparent medium.
19 . The method of claim 17 , wherein fabricating the micro-LED comprises forming the structure by at least one of:
etching recesses of one of the doped epitaxial semiconductor layers opposing the optically-transparent medium, and
nanopatterning a sapphire substrate, growing the micro-LED on the sapphire substrate, and removing the sapphire substrate.
20 . The method of claim 17 , wherein fabricating the micro-LED comprises forming the structure by at least one of:
growing a distributed Bragg reflector (DBR) adjacent to at least one of a top surface and a bottom surface of the micro-LED, the DBR comprising a plurality of nanoporous layers, or
forming an engineered surface that creates a controlled alteration of direction of the ambient light from a specular direction.