Nanowires/nanopyramids shaped light emitting diodes and photodetectors

Abstract

A light emitting diode device comprising: a plurality of nanowires or nanopyramids grown on a graphitic substrate, said nanowires or nanopyramids having a p-n or p-i-n junction, a first electrode in electrical contact with said graphitic substrate; a light reflective layer in contact with the top of at least a portion of said nanowires or nanopyramids, said light reflective layer optionally acting as a second electrode; optionally a second electrode in electrical contact with the top of at least a portion of said nanowires or nanopyramids, said second electrode being essential where said light reflective layer does not act as an electrode; wherein said nanowires or nanopyramids comprise at least one group III-V compound semiconductor; and wherein in use light is emitted from said device in a direction substantially opposite to said light reflective layer.

Claims

1. A device comprising: a plurality of nanowires or nanopyramids grown on a graphitic substrate, the plurality of nanowires or nanopyramids having a p-n or p-i-n junction and each of the plurality of nanowires having a top and a bottom, the bottom of each of the plurality of nanowires or nanopyramids being in contact with the graphitic substrate, and the plurality of nanowires or nanopyramids comprising at least one group III-V compound semiconductor; a first electrode in electrical contact with the graphitic substrate; a planar second electrode having a thickness of 20 nm or less in contact with the top of at least a portion of the plurality of nanowires or nanopyramids; and a metallic light reflective layer having a thickness of from 20 nm to 400 nm in contact with the planar second electrode; wherein the device comprises a flip chip light emitting diode that emits light and the light is emitted in a direction substantially opposite to the metallic light reflective layer.

2. The device of claim 1, wherein the device further comprises a hole-patterned mask deposited on the graphitic substrate, the hole-patterned mask comprising a plurality of holes, and wherein the plurality of nanowires or nanopyramids are grown through the holes of the hole-patterned mask on the graphitic substrate.

3. The device of claim 1, wherein the plurality of nanowires or nanopyramids are grown epitaxially on the graphitic substrate.

4. The device of claim 1, wherein the graphitic substrate is graphene.

5. The device of claim 1, wherein the graphitic substrate has a thickness of 20 nm or less.

6. The device of claim 1, wherein the graphitic substrate is graphene having up to 10 atomic layers.

7. The device of claim 1, wherein the device further comprises a support adjacent the graphitic substrate, opposite to the plurality of nanowires or nanopyramids grown on the graphitic substrate.

8. The device of claim 7, wherein the support is fused silica or quartz.

9. The device of claim 1, wherein the device further comprises an intermediate layer adjacent the graphitic substrate, opposite to the plurality of nanowires or nanopyramids grown on the graphitic substrate.

10. The device of claim 9, wherein the intermediate layer is hexagonal boron nitride (hBN), a metal grid, or a Ag nanowire network.

11. The device of claim 1, wherein the plurality of nanowires or nanopyramids comprise GaN, AlGaN, InGaN, or AlInGaN.

12. The device of claim 1, wherein the plurality of nanowires or nanopyramids comprise a multiple quantum well.

13. The device of claim 1, wherein the plurality of nanowires or nanopyramids contain an electron blocking layer.

14. The device of claim 1, wherein the device emits light in the UV spectrum.

15. The device of claim 1, wherein the device comprises a plurality of nanowires and the p-n or p-i-n junction within each of the plurality of nanowires is axial.

16. The device of claim 1, wherein the plurality of nanowires or nanopyramids comprise a tunnel junction.

17. The device of claim 1, wherein the plurality of nanowires or nanopyramids comprise an (Al)GaN/Al(Ga)N superlattice.

18. The device of claim 1, wherein the plurality of nanowires or nanopyramids comprise AlGaN with an increasing or decreasing concentration of Al along a direction in each of the plurality of nanowires or nanopyramids.

19. The device of claim 1, wherein the plurality of nanowires or nanopyramids are doped using Mg or Be.

20. The device of claim 1, wherein each of the plurality of nanowires or nanopyramids is separated by space, and the space between each of the plurality of nanowires or nanopyramids is filled by a supporting and electrically isolating filler material transparent to the light emitted from the device.

21. The device of claim 1, wherein the metallic light reflective layer has a thickness of at least 50 nm.

22. The device of claim 1, wherein the planar second electrode is graphitic.

23. The device of claim 1, wherein the light is not emitted in all directions.

24. The device of claim 1, wherein the light is emitted in a single direction.

25. A device comprising: a plurality of nanowires or nanopyramids grown on a graphitic substrate, the plurality of nanowires or nanopyramids having a p-n or p-i-n junction and each of the plurality of nanowires having a top and a bottom, the bottom of each of the plurality of nanowires or nanopyramids being in contact with the graphitic substrate, and the plurality of nanowires or nanopyramids comprising at least one group III-V compound semiconductor; a first electrode in electrical contact with the graphitic substrate; a planar second electrode having a thickness of 20 nm or less in contact with the top of at least a portion of the plurality of nanowires or nanopyramids; and a metallic light reflective layer having a thickness of 20 to 400 nm in contact with the planar second electrode; wherein the metallic light reflective layer reflects incoming light onto at least a portion of the plurality of nanowires or nanopyramids; and wherein the device comprises a flip chip photodetector device and wherein in use light is absorbed in the device.

26. The device of claim 25, wherein each of the plurality of nanowires or nanopyramids is separated by space and the space between each of the plurality of nanowires or nanopyramids is filled by a supporting and electrically isolating filler material transparent to visible and/or UV light entering into the device.

27. The device of claim 25, wherein the device absorbs light in the UV spectrum.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a possible flip chip design. In use therefore, light is emitted through the top of the device (marked hu). Support 1 is preferably formed from fused silica (best option), quartz, silicon carbide, sapphire or AlN. The use of other transparent supports is also possible. The use of fused silica or quartz is preferred. In use, the support, if still present, is positioned upper most in the device and hence it is important that the support is transparent to the emitted light and thus allows light out of the device.

(2) Layer 2, which is a preferred optional layer, is positioned between the support and the graphene layer 3 in order to reduce the sheet resistance of graphene. Suitable materials for layer 2 include inert nitrides such as hBN or a metallic nanowire network such as Ag nanowire network or metal grid.

(3) Layer 3 is the graphene layer which can be one atomic layer thick or a thicker graphene layer, such as one which is up to 20 nm in thickness.

(4) Nanowires 4 are grown from substrate layer 3 epitaxially. Ideally, the nanowires are formed from Al(In)GaN, AlN or GaN and are doped to create n-i-p or n-p junctions.

(5) A filler 5 can be positioned between grown nanowires. A top electrode/light reflective layer 6 is positioned on top of nanowires 4. The light reflective layer may also be provided with a p-electrode comprising Ni or Au. In use, this layer reflects any light emitted by the device to ensure that the light is emitted through the top of the device opposite the reflective layer. This is the so called flip chip arrangement as the device is upside down compared to a conventional LED.

(6) Electrode 10 is positioned on the graphene layer 3. That electrode might comprise Ti, Al, Ni or/and Au. The graphene layer may be provided with a mask 7 to allow growth of the nanowires in definitive positions on the graphene.

(7) The whole device is soldered to conductive tracks/pads 13 on a submount 8 via solder layer 9.

(8) When a forward current is passed across the device, visible or UV light, dependent on composition of matter, is generated in the nanowires and is emitted, possibly after reflecting off the reflective layer out the top of the device.

(9) When a reverse current is passed across the device and when the device is exposed to visible or UV light, the nanowires absorb the visible or UV light, dependent on composition of matter, and converts it into current, working as a photodetector.

(10) FIG. 2 shows a potential nanowire of the invention. The nanowire is provided with different components in an axial direction by variation of the elements being supplied during the growing phase. Initially, an n-type doped GaN material is deposited, followed by n-AlN or n-(Al)GaN. In the central section of the nanowire as shown are a series of multiple quantum wells formed from (In)(Al)GaN. There follows the p-doped region based on AlGaN or (Al)GaN, and an electron blocking layer based on p-Al(Ga)N and finally a p-GaN layer.

(11) FIG. 3 shows an alternative chip design in which the nanowires are grown radially creating core shell structures. In use therefore, light is emitted through the top of the device (marked hu). Support 1 is preferably formed from fused silica or quartz. In use, the support, if still present, is positioned upper most in the device and hence it is important that the support is transparent to the emitted light and thus allows light out of the device.

(12) Layer 2, which is a preferred intermediate layer, is positioned between the support and the graphene layer 3 in order to reduce the sheet resistance of graphene. Suitable materials for layer 2 include inert nitrides such as hBN or a metallic nanowire network such as silver nanowire network or metal grid.

(13) Layer 3 is the graphene layer which can be one atomic layer thick or a thicker graphene layer, such as one which is up to 20 nm in thickness.

(14) Nanowires 4 are grown from layer 3 epitaxially. Ideally, the nanowires are formed from Al(In)GaN, AlN or GaN and are doped to create n-i-p or n-p junctions. The graphene can be provided with a mask layer 7.

(15) A filler 5 can be positioned between grown nanowires. A top electrode/light reflective layer 6 is positioned on top of nanowires 4. The light reflective layer may also be provided with a p-electrode comprising Ni or/and Au or may itself be an electrode. In use, this layer reflects any light emitted by the device to ensure that the light is emitted through the top of the device opposite the reflective layer. This is the so called flip chip arrangement as the device is upside down compared to a conventional LED.

(16) Electrode 10 is positioned on the graphene layer 3. When a forward current is passed across the device, visible or UV light, dependent on composition of matter, is generated in the nanowires and is emitted, possibly after reflecting off the reflective layer out the top of the device.

(17) The whole device is soldered to conductive tracks/pads 13 on a submount 8 via solder layer 9.

(18) When a reverse current is passed across the device and when the device is exposed to visible or UV light, the nanowires absorb the visible or UV light, dependent on composition of matter, and converts it into current, working as a photodetector.

(19) FIG. 4 shows a nanowire grown radially but having the same components as those of FIG. 2 in a shell arrangement. The nanowire is provided with different components in a radial direction by variation of the elements being supplied during the growing phase. Initially, an n-doped GaN material is deposited, followed by n-AlN or n-(Al)GaN. In the central shell of the nanowire as shown are a series of multiple quantum wells formed from (In)(Al)GaN. There follows the p-doped region based on Al(Ga)N, and an electron blocking shell based on p-Al(Ga)N and finally a p-GaN shell.

(20) FIG. 5 shows a photodetector. In use therefore, light is accepted through the top of the device. Support 1 is preferably formed from fused silica, quartz, silicon carbide or AlN. The use of fused silica or quartz is preferred. In use, the support, if still present, is positioned upper most in the device and hence it is important that the support is transparent to the accepted light and thus allows light in to the device.

(21) Layer 2, which is a preferred optional layer, is positioned between the support and the graphene layer 3 in order to reduce the sheet resistance of graphene. Suitable materials for layer 2 include inert nitrides such as hBN or a metallic nanowire network such as Ag nanowire network or metal grid.

(22) Layer 3 is the graphene layer which can be one atomic layer thick or a thicker graphene layer, such as one which is up to 20 nm in thickness.

(23) Nanowires 4 are grown from substrate layer 3 epitaxially. Ideally, the nanowires are formed from Al(In)GaN, AlN or GaN and are doped to create n-i-p or n-p junctions.

(24) A filler 5 can be positioned between grown nanowires. A top electrode layer 11 is positioned on top of nanowires 4. This electrode is ideally a p-electrode comprising Ni or Au.

(25) Electrode 10 is positioned on the graphene layer 3. The graphene layer may be provided with a mask 7 to allow growth of the nanowires in definitive positions on the graphene.

(26) The whole device is soldered to conductive tracks/pads 13 on a submount 8 via solder layer 9.

(27) When a reverse current is passed across the device and when the device is exposed to visible or UV light, the nanowires absorb the visible or UV light, dependent on composition of matter, and converts it into current, working as a photodetector.

(28) FIG. 6: (a) Schematic diagram showing the growth of nanowires on graphite flake and the top and bottom contacts to the nanowires. Tilted view SEM image (b) and high-resolution SEM image (c) of selectively grown GaN nanowires on multi-layer graphene flakes by MBE.

(29) The graphite flake 3 (or graphene) is transferred on a support substrate such as fused silica substrate 1. A mask material 7 such as Al.sub.2O.sub.3 and SiO.sub.2 is deposited on the graphite flake. A big hole of 10 μm in diameter is etched in the mask material using photolithography such that the graphite surface is exposed in the hole. The sample is transferred into the MBE chamber for the nanowire growth. The substrate is heated to the growth temperature and a nucleation layer consisting of Al and AlN is deposited on the substrate, which is followed by the initiation of the (Al)GaN nanowires/nanopyramids growth.

(30) FIG. 7: Tilted view SEM images of GaN nanowires grown on (a) multi-layer graphene flakes by MBE. (b) GaN nanowires grown on hole patterned multi-layer graphene flakes by MBE.

(31) The graphite flake (or graphene) is transferred on a support substrate such as fused silica substrate. A mask material such as Al.sub.2O.sub.3 and SiO.sub.2 is deposited on the graphite flake. A big hole of 1 μm in diameter and several small holes of ˜80 nm in diameter is etched in the mask material using e-beam lithography such that the graphite surface is exposed in the holes. The sample is transferred into the MBE chamber for nanowire growth. The substrate is heated to the growth temperature and a nucleation layer consisting of Al and AlN is deposited on the substrate, which is followed by the initiation of the (Al)GaN nanowires are grown. FIG. 7 shows the tilted view SEM image of GaN nanowires grown in the big hole region (a) and small hole patterns (b).

(32) FIGS. 8a and b shows the growth of nanopyramids. Support 1 is preferably formed from fused silica (best option), quartz, silicon carbide, sapphire or AlN. The use of other transparent supports is also possible. The use of fused silica or quartz is preferred. In use, the support, if still present, is positioned upper most in the device and hence it is important that the support is transparent to the emitted light and thus allows light out of the device.

(33) Layer 3 is the graphene layer which can be one atomic layer thick or a thicker graphene layer, such as one which is up to 20 nm in thickness.

(34) Nanopyramids 40 are grown from layer 3 epitaxially. Ideally, the nanopyramids are formed from Al(In)GaN, AlN or GaN and are doped to create n-i-p or n-p junctions. A core shell nanopyramid can be grown be changing the nature of the flux supplied during the growth period.

(35) A filler 5 (not shown) can be positioned between grown nanopyramids. A top electrode/light reflective layer (not shown) can be positioned on top of nanopyramids. The light reflective layer may also be provided with a p-electrode comprising conducting materials such as Ni or Au. In use, this layer reflects any light emitted by the device to ensure that the light is emitted through the top of the device opposite the reflective layer. This is the so called flip chip arrangement as the device is upside down compared to a conventional LED.

(36) The graphene layer may be provided with a mask 7 to allow growth of the nanopyramids in definitive positions on the graphene.

(37) FIG. 9: (a) Low magnification and (b) High magnification tilted view SEM images of GaN nanopyramids grown on patterned single or double layer graphene by MOVPE.

(38) A graphene layer is transferred on a support substrate such as fused silica substrate. A mask material such as Al.sub.2O.sub.3 and SiO.sub.2 is deposited on the graphene. Several small holes of ˜100 nm in diameter and pitch in the range between 0.5 and 5 μm are etched in the mask material using e-beam lithography such that the graphene surface is exposed in the holes. The sample is then transferred into the MOVPE reactor for the nanopyramid growth. The substrate is heated to the growth temperature and a nucleation layer consisting of AlGaN is deposited on the substrate, which is followed by the growth of the (Al)GaN nanopyramids. FIG. 9 shows the tilted view SEM image of patterned GaN nanopyramids grown on graphene.

(39) FIG. 10 shows an alternative chip design in which the nanowires are grown radially creating core shell structures. In use therefore, light is emitted through the top of the device (marked hu). Support 1 is preferably formed from fused silica or quartz. In use, the support, if still present, is positioned upper most in the device and hence it is important that the support is transparent to the emitted light and thus allows light out of the device.

(40) Layer 2, which is a preferred intermediate layer, is positioned between the support and the graphene layer 3 in order to reduce the sheet resistance of graphene. Suitable materials for layer 2 include inert nitrides such as hBN or a metallic nanowire network such as silver nanowire network or metal grid.

(41) Layer 3 is the graphene layer which can be one atomic layer thick or a thicker graphene layer, such as one which is up to 20 nm in thickness.

(42) Nanowires 4 are grown from layer 3 epitaxially. Ideally, the nanowires are formed from Al(In)GaN, AlN or GaN and are doped to create n-i-p or n-p junctions. The graphene can be provided with a mask layer 7.

(43) A filler 5 can be positioned between grown nanowires. A second electrode 6 is positioned on top of nanowires 4. A metallic light reflective layer is also provided in contact with the second electrode. In use, this layer reflects any light emitted by the device to ensure that the light is emitted through the top of the device opposite the reflective layer. This is the so called flip chip arrangement as the device is upside down compared to a conventional LED.

(44) Electrode 10 is positioned on the graphene layer 3. When a forward current is passed across the device, visible or UV light, dependent on composition of matter, is generated in the nanowires and is emitted, possibly after reflecting off the reflective layer out the top of the device.

(45) The whole device is soldered to conductive tracks/pads 13 on a submount 8 via solder layer 9.

(46) When a reverse current is passed across the device and when the device is exposed to visible or UV light, the nanowires absorb the visible or UV light, dependent on composition of matter, and converts it into current, working as a photodetector.