Photonic crystal light emitting device
A photonic crystal structure is formed in an n-type region of a III-nitride semiconductor structure including an active region sandwiched between an n-type region and a p-type region. A reflector is formed on a surface of the p-type region opposite the active region. In some embodiments, the growth substrate on which the n-type region, active region, and p-type region are grown is removed, in order to facilitate forming the photonic crystal in an an-type region of the device, and to facilitate forming the reflector on a surface of the p-type region underlying the photonic crystal. The photonic crystal and reflector form a resonant cavity, which may allow control of light emitted by the active region.
1 . A light emitting device comprising:
a III-nitride semiconductor structure including an active region disposed between an n-type and a p-type region; and
a photonic crystal structure formed in at least a portion of the n-type region; and
a reflector disposed on at least a portion of a surface of the p-type region opposite the active region.
2 . The device of claim 1 wherein the photonic crystal structure comprises a periodic variation in a thickness of the n-type region.
3 . The device of claim 2 wherein a ratio of the period of the periodic structure and the wavelength of light emitted by the active region in air is about 0.1 to about 5.
4 . The device of claim 1 wherein the photonic crystal structure comprises a planar lattice of holes.
5 . The device of claim 4 wherein the holes have a depth between about 0.05λ and about 5λ, where λ is a wavelength in the III-nitride semiconductor structure of light emitted by the active region.
6 . The device of claim 4 wherein a lattice type, lattice constant, hole diameter, and hole depth are selected to create a predetermined radiation pattern.
7 . The device of claim 6 wherein greater than 50% of radiation exiting the device is emitted in an exit cone defined by an angle of 45 degrees to an axis normal to a surface of the device.
8 . The device of claim 4 wherein the planar lattice is selected from the group consisting of a triangular lattice, a square lattice, a hexagonal lattice, and a honeycomb lattice.
9 . The device of claim 4 wherein the planar lattice includes more than one lattice type.
10 . The device of claim 4 wherein the lattice has a lattice constant a between about 0.1λ and about 10λ, where λ is a wavelength in the III-nitride semiconductor structure of light emitted by the active region.
11 . The device of claim 4 wherein the lattice has a lattice constant a between about 0.1λ and about 4λ, where λ is a wavelength in the III-nitride semiconductor structure of light emitted by the active region.
12 . The device of claim 4 wherein the lattice has a lattice constant a and the holes have a diameter between about 0.1 a and about 0.5 a.
13 . The device of claim 4 wherein the holes are filled with a dielectric.
14 . The device of claim 13 wherein the dielectric has a dielectric constant between about 1 and about 16.
15 . The device of claim 1 wherein a distance between the reflector and the photonic crystal structure is between about λ and about 5λ, where λ is a wavelength in the III-nitride semiconductor structure of light emitted by the active region.
16 . The device of claim 1 wherein a distance between a center of the active region and the photonic crystal structure is less than about 4λ, where λ is a wavelength in the III-nitride semiconductor structure of light emitted by the active region.
17 . The device of claim 1 wherein a total thickness of III-nitride semiconductor layers in the device is less than about 1 μm.
18 . The device of claim 1 wherein a total thickness of III-nitride semiconductor layers in the device is less than about 0.5 μm.
19 . The device of claim 1 wherein a thickness of the n-type region, the active region, and the p-type region is less than about 1 μm.
20 . The device of claim 1 wherein a thickness of the n-type region, the active region, and the p-type region is less than about 0.5 μm.
21 . The device of claim 1 wherein at least a portion of the reflector underlies the photonic crystal structure.
22 . The device of claim 1 further comprising a host substrate bonded to the reflector.
23 . The device of claim 22 further comprising a metal bonding layer disposed between the host substrate and the reflector.
24 . The device of claim 23 wherein the metal bonding layer comprises gold.
25 . The device of claim 22 wherein the host substrate comprises one of Si, GaAs, Cu, Mo, W, and alloys thereof.
26 . The device of claim 1 wherein the reflector comprises silver.
27 . The device of claim 1 wherein the photonic crystal structure is formed in a first portion of the n-type region, the device further comprising a contact formed on a second portion of the n-type region, the second portion being substantially free of the photonic crystal structure.
28 . The device of claim 27 wherein the contact surrounds the photonic crystal structure.
29 . The device of claim 1 further comprising:
a trench extending through the p-type region and the active region to the n-type region; and
a contact disposed on the n-type region within the trench.
30 . The device of claim 29 wherein the contact and the photonic crystal structure are formed on opposite surfaces of the n-type region.
31 . The device of claim 1 wherein the n-type region comprises a first n-type region, the device further comprising:
a second n-type region disposed between the photonic crystal structure and the active region.
32 . The device of claim 1 wherein the photonic crystal structure extends into the active region.
33 . The device of claim 32 wherein the photonic crystal structure extends into the p-type region.
34 . A method of forming a semiconductor light emitting device, the method comprising:
growing a III-nitride semiconductor structure on a growth substrate, the III-nitride semiconductor structure including an active region disposed between an n-type and a p-type region;
bonding the III-nitride semiconductor structure to a host substrate;
removing the growth substrate; and
forming a photonic crystal structure in the n-type region of the III-nitride semiconductor structure.
35 . The method of claim 34 wherein forming a photonic crystal structure comprises etching the photonic crystal structure in a surface of the n-type region exposed by removal of the growth substrate.
36 . The method of claim 34 wherein the n-type region is a first n-type region and where forming a photonic crystal structure comprises:
etching the photonic crystal structure in the first n-type region after growth of the first n-type region;
growing a second n-type region over the photonic crystal structure; and
growing the active region and the p-type region over the second n-type region.
37 . The method of claim 34 wherein:
growing a III-nitride semiconductor structure on a growth substrate comprises growing the p-type region overlying the growth substrate, growing the active region overlying the p-type region, and growing the n-type region overlying the active region;
the host substrate is a first host substrate; and
the first host substrate is bonded to the n-type region; the method further comprising:
after removing the growth substrate, bonding a second host substrate to the p-type region; and
removing the first host substrate.