Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/80—Constructional details
  • H10H20/81—Bodies
  • H10H20/822—Materials of the light-emitting regions
  • H10H20/824—Materials of the light-emitting regions comprising only Group III-V materials, e.g. GaP
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/30—Structure or shape of the active region; Materials used for the active region
  • H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
  • H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
  • H01S5/34333—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser with a well layer based on Ga(In)N or Ga(In)P, e.g. blue laser
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/80—Constructional details
  • H10H20/81—Bodies
  • H10H20/817—Bodies characterised by the crystal structures or orientations, e.g. polycrystalline, amorphous or porous
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/80—Constructional details
  • H10H20/81—Bodies
  • H10H20/822—Materials of the light-emitting regions
  • H10H20/824—Materials of the light-emitting regions comprising only Group III-V materials, e.g. GaP
  • H10H20/825—Materials of the light-emitting regions comprising only Group III-V materials, e.g. GaP containing nitrogen, e.g. GaN
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
  • H01S5/2004—Confining in the direction perpendicular to the layer structure
  • H01S5/2009—Confining in the direction perpendicular to the layer structure by using electron barrier layers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/30—Structure or shape of the active region; Materials used for the active region
  • H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
  • H01S5/3201—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures incorporating bulkstrain effects, e.g. strain compensation, strain related to polarisation
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/30—Structure or shape of the active region; Materials used for the active region
  • H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
  • H01S5/3211—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures characterised by special cladding layers, e.g. details on band-discontinuities

Definitions

• This invention relates to nitride -based optoelectronic devices and a method of fabricating the same.
• Nitride -based optoelectronics have been extensively studied for fabrication of visible and ultra-violet (UV) light emitting devices. These devices typically have one or more layers of ternary alloys (InGaN, AlGaN, and AlInN), or quaternary alloy (AlInGaN).
• conventional LEDs and LEDs comprise of multiple AlGaN layers and an AlN buffer layer, which are normally grown on either sapphire or 6H- SiC substrates. Because of this heteroepitaxial growth, AlN or AlGaN buffer layers bear a dislocation density on the order of 10 10 cm "2 , and the dislocations propagate through the subsequent layers, resulting in poor material quality.
• indium containing alloys such as InGaN
• the indium clustering provides highly efficient radiative recombination sites for the carriers, and thus the performance of the device is rather insensitive to the dislocations.
• AlGaN-based devices are sensitive to the dislocation density due to the absence of the indium clustering, and therefore the performance of AlGaN- based devices is directly affected by the number of the dislocations.
• a superlattice structure is grown between a buffer layer and cladding layer, in which the superlattice filters out the dislocations propagating from the buffer layer and is also known to relieve the strain built in from the lattice mismatch.
• This structure improved the device performance of UV LEDs.
• MOCVD metal organic chemical vapor deposition
• a NH3 flow modulated AlN growth have successfully improved the quality of the AlN buffer layer.
• Bulk AlN crystals have been achieved by hydride vapor phase epitaxy (HVPE) and physical vapor transport (PVT). See References [1-4].
• the AlGaN- based device Even with a high quality AlN buffer layer or a bulk AlN substrate, the AlGaN- based device still suffers from the undesirable quantum-confined Stark effect (QCSE) as long as a device is grown along a c-direction in which a strong spontaneous polarization exists. Lattice mismatch between layers will induce piezoelectric polarization, which could enhance the degree of the polarization.
• the strong built-in electric fields from the polarizations cause spatial separation between electrons and holes, that in turn give rise to restricted carrier recombination efficiency, reduced oscillator strength, and red-shifted emission. The built-in electric field becomes stronger with higher Al composition.
• the present invention describes a method for fabricating a high- power and high-efficiency light emitting device with a peak emission wavelength ( ⁇ peak ) ranging from 280 nm to 360 nm.
• the present invention also introduces a new device structure using non-polar or semi-polar AlInN and AlInGaN alloys grown on a non-polar or semi-polar bulk (free standing) GaN substrate.
• the present invention is an optoelectronic device (e.g., LED or LD), comprising one or more light emitting layers containing at least Aluminum (Al), Indium (In), and Nitrogen (N), grown or fabricated on a non-polar or semi-polar GaN substrate, wherein the light emitting layers are non-polar or semi- polar layers.
• LED or LD an optoelectronic device
• the light emitting layers containing at least Aluminum (Al), Indium (In), and Nitrogen (N), grown or fabricated on a non-polar or semi-polar GaN substrate, wherein the light emitting layers are non-polar or semi- polar layers.
• the optoelectronic device may further comprise one or more Al x Ini_ x N or AlyIn z Gai_ y _ z N layers closely lattice-matched to the non-polar or semi-polar GaN substrate.
• the closely lattice matched layers may be one or more Al x Ini_ x N or AlyIn z Gai_ y _ z N layers doped with silicon (Si) for n-type conductivity (e.g., an n-type cladding layer doped with Si).
• the device may further comprise one or more Al x lni_ X N or AIyIn 2 Ga i_ y _ z N layers doped with Mg for p-type conductivity (e.g., p-type cladding layer doped with magnesium), on the light emitting active layers.
• the plurality of Al x Ini_ x N or Al y In z Gai_ y _ z N layers, and the light emitting active layers, may form one or more heterostructures, and the light emitting active layers may form one or more quantum- well heterostructures.
• An indium composition of one or more of the Al x Ini_ x N or Al y In z Gai_ y _ z N layers may range from 10% to 30%.
• a light emitting device may comprise (a) an Al x Ini_ x N or Al y In z Gai_ y _ z N based n-type cladding layer on the non-polar or semi-polar GaN substrate; (b) the one or more light emitting layers comprising an Al x Ini_ x N or AlyIn z Gai_ y _ z N based single quantum well (SQW) or multiple quantum well (MQW) on the n-type cladding layers; (c) one or more Al x Ini_ x N or Al y In z Gai_ y _ z N based electron blocking layers on the quantum well layers; and (d) an Al x Ini_ x N or AlyIn z Gai_ y _ z N based p-type cladding layer on the electron blocking layers, (e) wherein the Al x Ini_ x N or Al y In z Gai_ y _ z N layers, (
• the (Al,In,Ga)N quantum well structure may be epitaxially on an (Al,In,Ga)N layer, wherein the (Al,In,Ga)N layer has a dislocation density of an (Al,In,Ga)N layer that is grown epitaxially on, and closely lattice matched to, GaN.
• the dislocation density may be less than 10 6 cm "2 , which is the dislocation density expected from an underlying GaN substrate, and the (Al,In,Ga)N layer does not comprise a lateral epitaxial overgrowth.
• "closely lattice-matched" is close enough that there is no relaxation of the film at the thicknesses grown. No relaxation means no more than the dislocations from the substrate.
• the light emitting device may further comprise the (Al,In,Ga)N quantum well structure epitaxially on a non-polar or semi-polar plane of an (Al,In,Ga)N layer; and a dislocation density of the (Al,In,Ga)N layer that is sufficiently low, wherein the non- polar or semi-polar plane and the dislocation density achieve an internal quantum efficiency of the light emitting device of greater than 15% and an external quantum efficiency of the Light Emitting Device of greater than 1%.
• the present invention further discloses a method of fabricating a deep ultraviolet light emitting device, comprising fabricating one or more Al x Ini_ x N or Al y In z Gai_ y _ z N layers with O ⁇ y ⁇ 1, 0 ⁇ z ⁇ 1, and O ⁇ y + z ⁇ l on a non-polar or semi-polar GaN substrate, wherein the Al x Ini_ x N or Al y In z Gai_ y _ z N layers are non- polar or semi-polar.
• the method typically further comprises epitaxially growing one or more of the Al x Ini_ x N and Al y In z Gai_ y _ z N layers on the non-polar or semi-polar GaN substrate so that the Al x Ini_ x N and Al 5 Jn 2 Ga i_ y _ z N layers are closely lattice- matched to the non-polar or semi-polar GaN substrate.
• the method may further comprise growing at least one of the Al x Ini_ x N and Al y In z Gai_ y _ z N layers as a light emitting active layer with an indium composition ranging from 10% to 30%.
• the method may comprise epitaxially growing one of the Al x lni_ X N or AIyIn 2 Ga i_ y _ z N layers as a first Al x Ini_ x N or Al y In z Gai_ y _ z N layer having a first conductivity type, on a non-polar or semi-polar plane of the GaN substrate so that the first Al x Ini_ x N or Al y In z Gai_ y _ z N layer is closely lattice matched to the GaN substrate; epitaxially growing one of the Al x Ini_ x N or Al y In z Gai_ y _ z N layers as a first Al x Ini_ x N or Al y In z Gai_ y _ z N quantum well barrier layer, on a non-polar or semi-polar plane of the first Al x Ini_ x N or Al y In z Gai_ y _ z N layer;
• Al y In z Gai_ y _ z N layers as an Al x Ini_ x N or Al y In z Gai_ y _ z N quantum well layer, on a non- polar or semi-polar plane of the first Al x Ini_ x N or Al y In z Gai_ y _ z N quantum well barrier layer, and to a thickness and an (Al,In,Ga)N composition that emits electroluminescence having a peak wavelength less than 360 nm; epitaxially growing one of the Al x Ini_ x N or Al y In z Gai_ y _ z N layers as a second Al x Ini_ x N or Al y In z Gai_ y _ z N quantum well barrier layer, on a non-polar or semi-polar plane of the Al x Ini_ x N or Al y In z Gai_ y _ z N quantum well layer, thereby forming a quantum well structure
• Figure 1 is a flowchart illustrating a method of the present invention.
• Figures 2(a), 2(b) and 2c) are cross-sectional schematics illustrating three possible MQW structures (x 4 periods) for non-polar and semi-polar light emitting devices.
• Figure 3 is a cross-sectional schematic of a final structure of a non-polar or semi-polar UV LED, with emission wavelength ranging from 280 nm to 360 nm, and wherein the cladding layer is closely lattice-matched to the GaN substrate.
• the present invention describes a device structure that can be utilized for a high-power and high-efficiency LED and LD, in the wavelength ranging from 280 nm to 360 nm, using non-polar or semi-polar AlInN and AlInGaN grown on non-polar or semi-polar GaN.
• the salient feature of the structure is that the piezoelectric field is reduced, because AlInN and AlInGaN cladding layers can be closely lattice-matched to GaN.
• the spontaneous polarization is also minimized by growing in non-polar or semi-polar crystal orientations. With the relatively wide bandgap and the reduced spontaneous and piezoelectric polarization effects, an efficient non-polar or semi-polar AlInN and AlInGaN based light emitting device can replace conventional AlGaN-based light emitting devices.
• the present invention can be used to fabricate an optoelectronic device emitting light in the wavelength ranging from 280 nm to 360 nm, for example.
• Deep UV LEDs produced by the present invention may be useful for water- and air- purification, and germicidal and biomedical instrumentation systems. LDs in the UV region can be realized, which will increase the capacity of optical storage devices. With LEDs emitting in the region of 350 nm and below, a high-power and high- efficient white LEDs with the phosphor coating may also be produced.
• (Al,Ga,In)N or Ill-Nitride as used herein is intended to be broadly construed to include respective nitrides of the single species, Al, Ga, and In, as well as binary, ternary and quaternary compositions of such Group III metal species. Accordingly, the term (Al, Ga, In)N comprehends the compounds AlN, GaN, and InN, as well as the ternary compounds AlGaN, GaInN, and AlInN, and the quaternary compound AlGaInN, as species included in such nomenclature.
• compositions including stoichiometric proportions as well as "off-stoichiometric" proportions (with respect to the relative mole fractions present of each of the (Ga, Al, In) component species that are present in the composition), can be employed within the broad scope of the invention. Accordingly, it will be appreciated that the discussion of the invention hereinafter in reference to GaN materials is applicable to the formation of various other (Al, Ga, In)N material species. Further, (Al,Ga,In)N materials within the scope of the invention may further include minor quantities of dopants and/or other impurity or inclusional materials.
• One approach to eliminating the spontaneous and piezoelectric polarization effects in Group-Ill nitride optoelectronic devices is to grow the devices on nonpolar planes of the crystal (e.g., along a non-polar crystal direction, along an a-axis or m- axis of Ill-Nitride).
• nonpolar planes of the crystal e.g., along a non-polar crystal direction, along an a-axis or m- axis of Ill-Nitride.
• such planes contain equal numbers of Ga and N atoms and are charge-neutral.
• subsequent nonpolar layers are equivalent to one another so the bulk crystal will not be polarized along the growth direction.
• ⁇ 11-20 ⁇ family known collectively as ⁇ -planes
• ⁇ 10-10 ⁇ family known collectively as m-planes.
• Another approach to reducing polarization effects and effective hole masses in (Ga,Al,In,B)N devices is to grow the devices on semipolar planes of the crystal.
• the term "semipolar plane" can be used to refer to any plane that cannot be classified as c- plane, a-plane, or m-plane.
• a semipolar plane would be any plane that has at least two nonzero h, i, or k Miller indices and a nonzero 1 Miller index.
• semipolar planes include the ⁇ 11-22 ⁇ , ⁇ 10-11 ⁇ , and ⁇ 10-13 ⁇ planes.
• Other examples of semipolar planes in the wurtzite crystal structure include, but are not limited to, ⁇ 10-12 ⁇ , ⁇ 20-21 ⁇ , and ⁇ 10-14 ⁇ .
• the nitride crystal's polarization vector lies neither within such planes or normal to such planes, but rather lies at some angle inclined relative to the plane's surface normal.
• the ⁇ 10-11 ⁇ and ⁇ 10-13 ⁇ planes are at 62.98° and 32.06° to the c-plane, respectively.
• a device comprising one or more Al x Ini_ x N, Al y In z Gai_ y _ z N, or Al y' In z' Gai_ y' _ Z 'N layers, with O ⁇ y ⁇ l, 0 ⁇ z ⁇ 1, 0 ⁇ y + z ⁇ 1, 0 ⁇ y' ⁇ 1, 0 ⁇ z' ⁇ 1, and 0 ⁇ y' + z' ⁇ 1, is grown on a non-polar or semi-polar GaN substrate via MOCVD.
• Block 100 represents the step of loading a substrate into a reactor.
• a bulk non-polar or semi-polar GaN substrate is loaded into a MOCVD reactor and a reactor pressure is set to a value between 5 torr and 760 torr.
• Block 102 represents the step of growing a GaN layer on the substrate.
• the reactor's heater is turned on and ramped to a set point temperature, under hydrogen and/or nitrogen. Once the temperature reaches the set point, 1 ⁇ m to 3 ⁇ m thick unintentionally doped (UID) GaN or Si-doped GaN (by flowing DiSilane (Si 2 H 4 ) into the reactor) is grown.
• UID unintentionally doped
• Si-doped GaN by flowing DiSilane (Si 2 H 4 ) into the reactor
• the temperature is set to a value between 600 0 C and 1000 0 C and trimethyl-indium (TMIn), trimethyl-aluminum (TMAl), and ammonia (NH3) are introduced into the reactor to grow an n-type AlInN or AlInGaN cladding layer on the GaN layer of block 102.
• Triethyl-gallium (TEGa) or trimethyl- gallium (TMGa) is used if the desired layer is a quaternary alloy.
• DiSilane is also flowed into the reactor for n-type doping. All the source flows are kept at a constant level until the cladding layer thickness reaches a minimum of 200 nm. An important condition is that the lattice parameter of the cladding layer must be closely matched to the lattice parameter of the GaN substrate to minimize the strain.
• block 104 illustrates an example of epitaxially growing one of the Al x Ini_ x N or Al y In z Gai_ y _ z N layers, e.g., as a first Al x Ini_ x N or Al y In z Gai_ y _ z N layer having a first conductivity type, on a non-polar or semi-polar plane of the GaN substrate so that the first Al x Ini_ x N or Al y In z Gai_ y _ z N layer is closely lattice matched to the non-polar or semi-polar GaN substrate.
• Block 106 represents growth of the AlInN or AlInGaN active region on the n- type cladding grown in block 104.
• the reactor's temperature set point is decreased by 10 0 C to 80 0 C to incorporate more indium into the well region.
• the AlInGaN barrier layer is grown.
• group III source flow rates and/or NH3 flow rates can be either increased or decreased to obtain the desired composition of the AlInN or AlInGaN active layer.
• the active layer e.g. well layer
• a barrier is grown on top.
• the AlInN (active well layer)/ AlInGaN (barrier), or AlInGaN (active layer)/ AlInGaN (barrier) may be grown and the structure can be repeated to form a MQW.
• the indium composition may range from 10 % to 30 % to achieve a desired ⁇ peak . Possible MQW structures are shown in Figure 2.
• Figures 2(a), 2(b), and 2(c) illustrate epitaxially growing one of the Al x Ini_ x N or Al y In z Gai_ y _ z N layers as a first Al x Ini_ x N or Al y In z Gai_ y _ z N quantum well barrier layer 200, on a non-polar or semi-polar plane of the first Al x Ini_ x N or Al y In z Gai_ y _ z N layer grown in block 104; epitaxially growing one of the Al x Ini_ x N or Al y In z Gai_ y _ z N layers as an Al y In z Gai_ y _ z N or Al x Ini_ x N quantum well layer 202, on a non-polar or semi-polar plane 204 of the first Al x Ini_ x N or Al 5 Jn 2 Ga i_ y _ z N quantum well barrier layer 200, and to
• both the first quantum well barrier layer 200 and the second quantum well barrier layer 208 are Al y In z Gai_ y _ z N, and the quantum well 202 is Al x Ini_ x N.
• both the first quantum well barrier layer 200 and the second quantum well barrier layer 208 are Al y In z Gai_ y _ z N, and the quantum well 202 is Al y In z Gai_ y _ z N with a different composition (e.g., Al y Jn z 'Gai_ y '_ z 'N) from the barrier layers 200, 208.
• both the first quantum well barrier layer 200 and the second quantum well barrier layer 208 are Al y Gai_ y N
• the quantum well 202 is Al x Ini_ x N
• at least one of the Al x Ini_ x N and Al y In z Gai_ y _ z N layers 202 may be grown as a light emitting active layer with an indium composition ranging from 10% to 30%.
• Block 108 represents growing an electron blocking layer (EBL), on the active region grown in block 106, wherein the compositions of group III species in the EBL are adjusted to obtain desired conduction band off-set between EBL and the barrier.
• EBL electron blocking layer
• Block 110 represents the step of growing a p-type AlInN or AlInGaN cladding layer on the EBL layer grown in block 108. Once a desired EBL thickness is achieved, the reactor's set point temperature is increased by 10 0 C to 80 0 C. Then, Cp 2 Mg is introduced into the reactor to achieve a p-type AlInN or AlInGaN layer. The compositions of the p-type alloys will be the same as that of the n-type alloys.
• block 110 illustrates an example of epitaxially growing one of the Al x Ini_ x N or AlyIn z Gai_ y _ z N layers, on the EBL of block 108 and quantum well structure of block 106, as a second Al x Ini_ x N or Al y In z Gai_ y _ z N layer having a second conductivity type.
• a p-type GaN contact layer is grown on the p-type cladding layer grown in block 110.
• a thin and highly Magnesium (Mg)-doped p-type GaN layer may be grown on top to form a contact layer.
• the epitaxial wafer comprising a nitride device (formed in blocks 100-112) is removed and annealed in a hydrogen deficient ambient for 15 minutes, at a temperature of 700 0 C, in order to activate the p-type GaN contact layer grown in block 112 (Mg doped layers), as represented in Block 114.
• the next step is to fabricate a device.
• the process for a UV LED is described here as an example.
• a photolithography technique is used to pattern the p-type contact (p-contact) on the wafer (patterning a p-type contact pattern on the p-GaN layer activated in block 114), as represented in Block 116.
• p-contact metals (20 A ⁇ 100 A Ni/ Au) are deposited by an electron-beam evaporator and annealed under N 2 or N2/O2 ambient for 1 minute to 10 minutes to form a metal alloy, as represented in Block 118 (depositing and alloying p- contact metals on the patterned p-type GaN layer patterned in block 116). Then, the p- GaN contact layer is at least partially removed by a dry-etching technique, as represented in Block 120 (partially removing the p-type GaN contact layer resulting from blocks 114-118).
• the step in Block 120 is to remove the light absorbing GaN layer resulting from blocks 114-118 and expose the p-type cladding layer grown in block 110, as shown in Figure 3.
• a mesa is formed, in the structure resulting from blocks 100-120, by dry-etching, and the etching exposes the n-type cladding layer of block 104, as represented in Block 122.
• n-type contact metals Ti/Al/Ni/Au
• Block 124 depositing and alloying n-type contact metals on the n-type cladding layer grown in block 104 and exposed in block 122).
• Metals for the contact pads are then deposited using an electron-beam evaporator, as represented by Block 126 (depositing metals for contact pads on the alloyed p-contact metals and alloyed n-contact metals of blocks 118 and 124, respectively).
• the substrate of block 100 is typically removed, as represented by block
• Figure 3 shows an example of a final optoelectronic device 300 (e.g., LED or LD) structure obtained after implementing the steps discussed above, comprising one or more Al x Ini_ x N or Al y In z Gai_ y _ z N layers 302, 304, 306, and 308, with 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 1, and 0 ⁇ y + z ⁇ 1, fabricated (e.g., grown) on a non-polar or semi-polar GaN substrate 310 (as shown in e.g., blocks 104, 106, 108 and 110), wherein the Al x Ini_ x N or Al y In z Gai_ y _ z N layers 302, 304, 306, and 308 are non-polar or semi-polar (i.e., grown in a non-polar or semi-polar direction so that a growth surface of the layers 302, 304, 306, and 308 is a non-polar plane (e
• All the layers 302, 304, 306, and 308 contain at least some Indium.
• the Al x lni_ X N or Al y In z Ga i_ y _ z N layers 302, 304, 306, and 308 may comprise at least Al, In and N, for example.
• one or more of the Al x Ini_ x N or Al y In z Gai_ y _ z N layers are closely lattice-matched to the non-polar or semi-polar GaN substrate 310 (e.g., an Al x Ini_ x N or Al y In z Gai_ y _ z N based n-type cladding layer 302 on the non-polar or semi-polar GaN substrate 310), one or more of the Al x Ini_ x N or Al y In z Gai_ y _ z N layers are doped with Si for n-type conductivity (e.g., the n-type cladding layer doped with silicon 302), one or more of the Al x Ini_ x N or Al 5 Jn 2 Ga i_ y _ z N layers are doped with Mg for p-type conductivity (a p-type cladding layer doped with Mg 308), a plurality of the Al x
• the device 300 of Figure 3 further comprises one or more Al x Ini_ x N or AlyIn z Gai_ y _ z N based electron blocking layers (EBLs) 306 on the quantum well layers 304.
• the Al x Ini_ x N or Al y In z Gai_ y _ z N based p-type cladding layer 308 is on the one or more EBLs 306.
• Layer 302 is typically closely lattice matched to the substrate. "Closely lattice-matched" is close enough that there is no relaxation of the film at the thicknesses grown. No relaxation means no more dislocations than the dislocations from the substrate 310.
• Figures 2(a), 2(b), 2(c), and 3 illustrate an optoelectronic device 300, comprising one or more light emitting layers 202, 304 containing at least Al, In, and N, grown on a non-polar or semi-polar GaN substrate 310, wherein the light emitting layers 202, 304 are non-polar or semi-polar layers.
• Figures 2(a), 2(b), 2(c) and 3 also illustrate a first (Al,In,Ga)N layer having a first conductivity type 302 (e.g., but not limited to, n-type); a second (Al,In,Ga)N layer having a second conductivity type 308 (e.g., but not limited to, p-type); an (Al,In,Ga)N quantum-well structure 304 comprising an (Al,In,Ga)N quantum well layer 202 epitaxially on a non-polar or semi-polar plane 204 of a first (Al,In,Ga)N quantum well barrier layer 200, and a second (Al,In,Ga)N quantum well barrier layer 208 epitaxially on a non-polar or semi-polar plane 210 of the (Al,In,Ga)N quantum well layer 202, wherein (1) the quantum well structure 304 is epitaxially on a non- polar or semi-polar plane 318 of an (
• the (Al,In,Ga)N layer 302 is typically grown on a non-polar or semi-polar plane 320 of the substrate 310. Even after the substrate 310 is subsequently removed (see, e.g., block 128 of Figure 1), layer 302 retains the dislocation density associated with epitaxial growth on GaN.
• the (Al,In,Ga)N quantum well structure 304 is epitaxially on an (Al,In,Ga)N layer 302, wherein the (Al,In,Ga)N layer 302 has a low dislocation density of an (Al,In,Ga)N layer that is grown epitaxially on, and closely lattice matched to, GaN (e.g., substrate 310), even after the substrate 310 is removed.
• the (Al, In, Ga)N layers 302 may have a dislocation density of less than 10 6 cm "2 , wherein the (Al,In,Ga)N layer 302 (and/or layers between layer 302 and the substrate 310, and/or layers 304, 306, and 308) do not comprise a lateral epitaxial overgrowth.
• the active region (light emitting region) 304 could achieve an IQE of the light emitting device 300 of greater than 15 %, which was the value obtained by an Al x In y Gai_ x _ y N alloy with Indium contents (y) less than 10 %. Therefore, it is possible to achieve an external quantum efficiency of the light emitting device 300 of greater than 1 %.
• a Bulk GaN substrate is essentially a thick GaN that is free standing.
• One example would be a thick ( ⁇ 300 ⁇ m) GaN grown on a sapphire, which then is lifted-off from the sapphire substrate.
• the GaN substrate is an absorbing layer for the emission wavelength lower than 360 nm. Therefore, it is necessary to remove the GaN substrate to improve the light extraction, as represented in Block 128.
• the GaN substrate can be removed by lapping, polishing, and dry-etching processes. Then, flip-chip packaging with a mirror reflector (as represented in Block 130) can maximize light extraction from the light emitting device, such as the LEDs described above.
• non-polar and semi-polar AlInN and AlInGaN layers utilized heteroepitaxial growth of non-polar and semi-polar AlInN and AlInGaN layers by MOCVD
• the present invention can use any growth techniques.
• non- polar and semi-polar AlInN and AlInGaN could also be grown by molecular beam epitaxy (MBE) with the proper growth conditions.
• MBE molecular beam epitaxy
• a very thin InGaN layer can be deposited prior to the growth of the n-type cladding layer. After a device is grown, the InGaN layer can be etched away by photoelectrochemical (PEC) etching using a UV light source.
• PEC photoelectrochemical
• the existing practice is to grow AlGaN-based UV emitting devices on a c- plane sapphire or SiC substrate in which the surface is either Ga (Al)-face or N-face.
• the plane normal to the c-direction has spontaneous polarization due to the large electronegativity difference.
• the interface between multi-layers of different polarization inherently builds up the polarization charge and results in an internal electric field.
• This electric field can be significantly large for thin layers such as an active layer and changes the energy band structure.
• Lattice mismatch between substrates and subsequent layers introduces a piezoelectric polarization, which could further change the band structure.
• the present invention describes a device structure that has minimized both the spontaneous and piezoelectric polarizations.
• Spontaneous polarization is decreased by growing a device in a non-polar or semi-polar crystal orientation. More importantly, reduction in piezoelectric polarization is achieved by growing AlInN or AlInGaN cladding layers closely lattice-matched to the GaN substrate. Only the quantum-well layers are slightly under the compressive strain. The lattice-matching condition also means there are no additional dislocations arising from the interface between the cladding layer and the substrate. Therefore, the reduction of both the QCSE effect and dislocation density will result in higher IQE. Improved crystal quality also means that high-power and high-efficiency LDs in the UV region can be realized. Because the non-polar and semi-polar bulk GaN substrates are available with high crystal quality, the new structure described in the present invention is expected to more efficient than the state-of-art UV emitting devices that are currently available.

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