WO2010059132A1 - Structure de diode électroluminescente et procédé de formation d'une structure de diode électroluminescente - Google Patents

Structure de diode électroluminescente et procédé de formation d'une structure de diode électroluminescente Download PDF

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Publication number
WO2010059132A1
WO2010059132A1 PCT/SG2009/000438 SG2009000438W WO2010059132A1 WO 2010059132 A1 WO2010059132 A1 WO 2010059132A1 SG 2009000438 W SG2009000438 W SG 2009000438W WO 2010059132 A1 WO2010059132 A1 WO 2010059132A1
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layer
quantum well
well layer
forming
metal
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PCT/SG2009/000438
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English (en)
Inventor
Wei Liu
Chew Beng Soh
Soo Jin Chua
Jing Hua Teng
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Agency For Science, Technology And Research
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Priority to US13/130,649 priority Critical patent/US8421058B2/en
Publication of WO2010059132A1 publication Critical patent/WO2010059132A1/fr

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/04—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a quantum effect structure or superlattice, e.g. tunnel junction
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/08—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a plurality of light emitting regions, e.g. laterally discontinuous light emitting layer or photoluminescent region integrated within the semiconductor body
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/26—Materials of the light emitting region
    • H01L33/30—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table
    • H01L33/32—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table containing nitrogen

Definitions

  • the present invention relates broadly to a light emitting diode structure and a method of forming a light emitting diode structure.
  • LEDs red, green and blue light emitting diodes
  • “White” LEDs in production currently are typically modified blue LEDs i.e. Gallium Nitride (GaN)-based with Indium Gallium Nitride (InGaN)-active-layer LEDs that emit blue light having wavelengths between about 450 nm and 470nm.
  • the InGaN-GaN structure is covered with a yellowish phosphor coating comprising cerium- doped yttrium aluminum garnet (Ce3+:YAG) crystals which have been powdered and bound in a type of viscous adhesive.
  • Such a LED chip emits blue light, part of which is efficiently converted to a broad-spectrum centered at about 580 nm (yellow light emission) by the Ce3+:YAG material. Since yellow light stimulates the red and green receptors of the eye, the resulting mix of blue and yellow light gives the appearance of white light, the resulting shade typically referred to as "lunar white”.
  • the pale yellow emission of the Ce3+::YAG material can be tuned by substituting the cerium with other rare earth elements such as terbium and gadolinium, and can be further adjusted by substituting some, or all, of the aluminum in the YAG with gallium.
  • LEDs Due to the spectral characteristics of such LEDs, one problem that can arise is that the red and green colours of objects illuminated in the blue yellow light are not as vivid as in broad-spectrum light. Further, manufacturing variations and varying thickness in the phosphor coating typically cause LEDs to produce light with different colour temperatures, e.g. ranging from yellow to cold blue. As such, disadvantageously, the resulting LEDs are required to be sorted by their actual characteristics during manufacture.
  • white LEDs can be made by coating near ultraviolet emitting LEDs with a mixture of high efficiency europium-based red and blue emitting phosphors with green emitting copper and aluminum doped zinc sulfide.
  • This method is analogous to how typical fluorescent lamps work.
  • the ultraviolet light typically causes photo-degradation to the epoxy resin of the LEDs and other materials used in LED packaging.
  • the photo-degradation typically leads to shorter lifetimes.
  • this method is typically less energy efficient than the blue LED with YAG:Ce phosphor coating type discussed above, since the Stokes shift of this method is larger, and thus, more energy is required to be converted to heat, even if light is produced under this method with better spectral characteristics and colour rendering.
  • a light emitting diode structure comprising, a superlattice comprising: a first barrier layer; a first quantum well layer comprising a first metal-nitride based material formed on the first barrier layer; a second barrier layer formed on the first quantum well layer; and a second quantum well layer comprising the first metal- nitride based material formed on the second barrier layer; and wherein a difference between conduction band energy of the first quantum well layer and conduction band energy of the second quantum well layer is matched to a single or multiple optical phonon energy for reducing electron kinetic energy in the superlattice.
  • the superlattice may be repeatedly formed n times in the structure whereby 2 ⁇ n ⁇ 10.
  • a difference between conduction band energy of the first barrier layer and the conduction band energy of the first quantum well layer may be matched to a single or multiple optical phonon energy for reducing electron kinetic energy in the superlattice.
  • the second quantum well layer may be arranged to have a mole fraction of the metal element more than that of the first quantum well layer to facilitate the match of the conduction band energy difference.
  • the structure may further comprise an active region quantum well layer comprising a third barrier layer; an electron capture region layer comprising the first metal-nitride based material formed on the third barrier layer; a third quantum well layer comprising the first metal-nitride based material formed on the electron capture region layer, the third quantum well layer having quantum dot nanostructures embedded therein; and wherein material composition and thickness of the electron capture region layer is configured to facilitate electron capture.
  • the active region quantum well layer may be repeatedly formed m times in the structure whereby 1 ⁇ m ⁇ 5.
  • the structure may further comprise a p-type contact structure formed on an outermost one of the quantum well layers, the p-type contact structure comprising a p-type metal-nitride layer.
  • the p-type contact structure may comprise a multiple-stage doping profile.
  • the p-type contact structure may be doped with magnesium (Mg).
  • Mg magnesium
  • Each barrier layer may comprise a second metal-nitride based material having a different metal element compared to the first metal-nitride based material.
  • the first metal-nitride based material may comprise Indium-Gallium-Nitride (InGaN).
  • the mole fraction of Indium in the first quantum well layer may be in a range of about 0.05 to about 0.35.
  • the mole fraction of Indium in the second quantum well layer may be in a range of about 0.0810 to about 0.38.
  • the mole fraction of Indium in the third quantum well layer may be in a range of about 0.15 to about 0.45.
  • the mole fraction of Indium in the fourth quantum well layer may be in a range of about 0.20 to about 0.50.
  • the structure may be capable of emitting amber light.
  • the structure may further comprise one or more blue/green light emitting multiple quantum well layers whereby the structure is capable of emitting white light.
  • the optical phonon energy may be a longitudinal optical phonon energy.
  • a method of forming a light emitting diode structure comprising the steps of: forming a superlattice, by forming a first barrier layer; forming a first quantum well layer on the first barrier layer, the first quantum well layer comprising a first metal-nitride based material; forming a second barrier layer on the first quantum well layer; forming a second quantum well layer on the second barrier layer, the second quantum well layer comprising the first metal-nitride based material; and wherein a difference between conduction band energy of the first quantum well layer and conduction band energy of the second quantum well layer is matched to a single or multiple optical phonon energy for reducing electron kinetic energy in the superlattice.
  • the method may further comprise forming the superlattice repeatedly for n times whereby 2 ⁇ n ⁇ 10.
  • a difference between conduction band energy of the first barrier layer and the conduction band energy of the first quantum well layer may be matched to a single or multiple optical phonon energy for reducing electron kinetic energy in the superlattice.
  • the method may further comprise forming the second quantum well layer to have a mole fraction of the metal element more than that of the first quantum well layer to facilitate the match of the conduction band energy difference.
  • the method may further comprise forming an active region quantum well layer, by forming a third barrier layer; forming an electron capture region layer comprising the first metal-nitride based material on the third barrier layer; forming a third quantum well layer comprising the first metal-nitride based material on the electron capture region layer, the third quantum well layer having quantum dot nanostructures embedded therein; and wherein material composition and thickness of the electron capture region layer is configured for facilitating electron capture.
  • the method may further comprise forming the active region quantum well layer repeatedly for m times whereby 1 ⁇ m ⁇ 5.
  • the method may further comprise forming a p-type contact structure on an outermost one of the quantum well layers, the p-type contact structure comprising a p-type metal-nitride layer.
  • the p-type contact structure may comprise a multiple-stage doping profile.
  • the structure may be capable of emitting amber light.
  • the method may further comprise forming one or more blue/green light emitting multiple quantum well layers whereby the structure is capable of emitting white light.
  • the optical phonon energy may be a longitudinal optical phonon energy.
  • Figure 1 (a) is a schematic diagram illustrating a light emitting diode (LED) structure in an example embodiment.
  • Figure 1 (b) is a schematic diagram illustrating the LED structure in more detail.
  • Figure 2(a) shows a secondary ion mass spectrometry (SIMS) depth profile of a LED sample of an example embodiment comprising a p-GaN epilayer with multiple- stage doping of about 7x10 17 cm "3 at a first stage, about 2x10 18 cm '3 at a second stage and about 7x10 18 cm “3 at a third stage.
  • SIMS secondary ion mass spectrometry
  • Figure 2(b) shows a SIMS depth profile of a conventional LED with a uniformly type doped GaN epilayer having a constant doping of concentration of about 2x10 18 cm "
  • Figure 3 is a schematic diagram illustrating a LED structure in an example embodiment.
  • Figure 4 shows an electroluminescence spectra under varying injection currents of an amber-orange LED sample formed according to the example embodiment.
  • FIG 5 is a schematic diagram illustrating an InGaN/GaN multiple quantum wells (MQWs) layer of Figure 3 in more detail.
  • MQWs multiple quantum wells
  • Figure 6 is a schematic diagram illustrating a p-GaN layer of Figure 3 in more detail.
  • Figure 7 shows an electroluminescence spectrum for a white LED sample formed according to the example embodiment.
  • Figure 8 is a flowchart illustrating a method of forming a light emitting diode structure in an example embodiment.
  • Figure 9 is a schematic energy diagram illustrating band-gap engineering in an example embodiment.
  • Example embodiments described below can provide a structure and a method for forming a high power white LED comprising band-gap engineered InGaN/GaN quantum dots (QDs)/quantum wells (QWs) and a p-GaN layer with a multi-stage doping profile.
  • QDs InGaN/GaN quantum dots
  • QWs quantum wells
  • Figure 1 (a) is a schematic diagram illustrating a light emitting diode (LED) structure in an example embodiment.
  • Figure 1(b) is a schematic diagram illustrating the light emitting diode (LED) structure in more detail.
  • a light emitting diode structure 100 is formed using a GaN template 102.
  • the GaN template 102 comprises a sapphire substrate 130, a low-temperature GaN buffer 132 formed on the substrate 130, a undoped U-GaN layer 134 formed on the buffer 132 and a n-doped n-GaN layer 136 formed on the u- GaN layer 134.
  • the LED structure 100 comprises layer 104 having one or more In 3 Ga 1- 3 N/GaN/In b Ga 1-b N/GaN superlattices; layer 106 having a single or multiple stacks of QDs/QWs structures; and a p-GaN epilayer 108 with a multi-stage Magnesium (Mg) doping profile.
  • layer 104 having one or more In 3 Ga 1- 3 N/GaN/In b Ga 1-b N/GaN superlattices
  • layer 106 having a single or multiple stacks of QDs/QWs structures
  • a p-GaN epilayer 108 with a multi-stage Magnesium (Mg) doping profile Mg
  • a GaN spacer layer 110 is formed on the GaN template 102.
  • the ln a Ga 1-a N/GaN/ln b Gai -b N/GaN superlattices structure layer 104 is added after the growth of the GaN spacer layer 110.
  • the superlattices structure layer 104 comprises a first quantum well layer In 3 Ga 1-2 N and a second quantum well layer ln b Ga 1-b N.
  • the superlattices structure layer 104 can be repeated n times where 2 ⁇ n ⁇ 10.
  • the purpose of the superlattices structure layer 104 is to slow down fast moving electrons through thermalisation and increase dwell time of electrons in the active region layer, e.g. the layer 106, by band-gap engineering.
  • the !n a Ga 1-a N/GaN/ln b Ga 1-b N/GaN superlattices structure layer 104 is designed such that conduction band energy difference (i.e. conduction band offset), or the first quantized energy level of the superlattice comprising GaN 112 and In 3 Ga 1-3 N 114, and GaN 116 and ln b Ga 1-b N 118, is matched to a single or multiple optical phonon energy, preferably longitudinal optical phonon energy.
  • conduction band energy difference i.e. conduction band offset
  • Figure 9 is a schematic energy diagram illustrating band-gap engineering in the example embodiment.
  • Numeral 902 shows the conduction band energy of GaN 112 ( Figure 1)
  • numeral 904 shows the conduction band energy of In 3 Ga 1-9 N 114 ( Figure 1)
  • numeral 906 shows the conduction band energy of GaN 116 ( Figure 1)
  • numeral 908 shows the conduction band energy of ln b Ga 1-b N 118 ( Figure 1).
  • by matching a difference between the conduction band energy 904 of In 3 Ga 1-3 N 114 ( Figure 1) and the conduction band energy 908 of ln b Ga 1-b N 118 ( Figure 1) ie.
  • a difference between the conduction band energy 902 of GaN 112 ( Figure 1) and the conduction band energy 904 of In 3 Ga 1-3 N 114 ( Figure 1), ie. see numeral 910, is also matched to a single or multiple optical phonon energy such that electron kinetic energy is reduced through emission of for example longitudinal optical phonons.
  • the GaN 116 is kept thin, ie. about 3 to 20 nm, to facilitate electron tunnelling, and promoted due to the band-gap engineering described above. Therefore, the above design is effective in reducing the electron kinetic energy through emission of e.g. longitudinal optical phonons.
  • the superlattices structure layer 104 when electrons pass through the superlattices structure layer 104, they begin to move at a slower speed before they enter into the active region e.g. the layer 106, thus, providing a higher probability of recombination. In this way, recombination efficiency or carrier injection efficiency and internal quantum efficiency of the LED structure 100 is increased.
  • a GaN cap layer 119 is formed.
  • the InGaN QDs/QWs structure layer 106 can be repeated m times where 1 ⁇ m ⁇ 5.
  • a U-GaN barrier layer 120 is formed. After growth of the U-GaN barrier layer 120, a ln w Ga-i -w N layer 122 with a low indium mole fraction is grown.
  • the ln x Gai -x N QDs/QWs 124 are grown on the ln w Ga 1-w N layer 122.
  • the ln w Ga 1-w N layer 122 serves as an electron capture region before electrons transit to the ln x Ga 1-x N QDs/QWs 124 for radiative recombination to give yellow, amber or red emission.
  • the ln w Gai -w N layer 122 also functions as a wetting layer to enhance the incorporation of Indium nitride quantum dots during an In burst process.
  • the ln x Gai -x N QDs/QWs 124 is a ln x Ga 1-x N quantum well layer 125 having quantum dot nanostructures or quantum dots 127 embedded therein.
  • carrier capture efficiency is increased. That is, energy potential can be lowered and the electrons can be further slowed down in the ln w Ga 1-w N layer 122 before entering ln x Gai -x N QDs/QWs 124.
  • the ln w Ga 1-w N layer 122 is preferably maintained at a thickness range from about 3 to 20nm, and preferably a thickness of about 7nm for optimum carrier capture efficiency. It has been recognised by the inventors that if the ln w Gai_ w N layer 122 is too thick (e.g. more than 20 nm), the material quality and formation of the quantum dot nanostructures may be adversely affected.
  • a AIN layer 126 and a GaN cap layer 128 are formed.
  • the p-contact layer or p-GaN epilayer 108 having a multiple-stage Mg doping profile is formed on the GaN cap layer 128.
  • a Biscyclopentadienilmagnesium (Cp 2 Mg) precursor is used as the p-dopant for the p GaN epilayer 108.
  • the doping concentration is varied in steps from the bottom of the epilayer 108 to the top by changing the Cp 2 Mg flow rate or a Trimethylgallium (TMGa) flow rate.
  • SIMS Secondary ion mass spectrometry
  • depth profiling is carried out on one sample of the example embodiment comprising an epilayer with a multiple stage Mg doping profile to determine composition distribution of the different elements, namely Gallium (Ga), Magnesium (Mg), Nitrogen (N) and Indium (In) with depth, based on their atomic weight.
  • the Mg dopant in a conventional uniformly-doped p- GaN layer used in a conventional LED is also measured using SIMS.
  • Figure 2(a) shows a SIMS depth profile of the LED sample of the example embodiment comprising a p-GaN epilayer with multiple-stage doping of about 7x10 17 cm ' 3 at a first stage, about 2x10 18 cm “3 at a second stage and about 7x10 18 cm '3 at a third stage.
  • Figure 2(b) shows a SIMS depth profile of the conventional LED with a uniformly type doped GaN epilayer having a constant doping of concentration of about 2x10 18 cm " 3 .
  • there is a step like profile see numerals 202, 204) in the Mg distribution of the sample of the example embodiment.
  • the Mg composition is estimated to be about 7 *10 17 cm “3 at the interface with the GaN cap layer (compare cap layer 128 in Figure 1 (a)) after the growth of the stacked QDs/QWs.
  • the p-doping is then increased in steps to about 2 *10 18 cm “3 and subsequently to about 7 *10 18 cm “3 at the top of the epilayer (compare epilayer 108 in Figure 1(a)), which is intended to contact a transparent Ni/Au electrode.
  • Mg concentration is shown to be substantially constant (see numeral 206) across the whole p-contact layer in the conventional uniformly-doped p-GaN as shown in Figure 2(b).
  • a highly doped p-contact layer is likely to cause diffusion of the dopant into the active regions of a LED structure. Further, a highly doped p-contact layer is likely to cause hole mobility to be lowered.
  • a p-GaN epilayer with multiple-stage doping of the sample of the example embodiment can address the above problems.
  • the concentration of the dopant of the epilayer at the metal contact interface is controlled to be higher relative to other areas of the epilayer while the concentration of the dopant of the epilayer nearer to the active regions (compare layer 106 of Figure 1 (a)) is controlled to be lower. Therefore, a good ohmic contact can be formed with the metal contact while diffusion of the dopant into the active regions can be lowered.
  • hole mobility is likely to be high. This can encourage holes to travel deeper into the active regions and thus, result in a higher electron-hole recombination volume.
  • thickness of the multi-step p-type doping contact layer or epilayer of the sample of the example embodiment can be grown thicker than the conventional one- step p-contact layer to facilitate surface patterning such that light extraction is advantageously enhanced.
  • growth of a white light emitting diode is performed using a metalorganic chemical vapour deposition system.
  • Trimethylgallium (TMGa), Trimethyllndium (TMIn), Trimethylaluminium (TMA), Biscyclopentadienilmagnesium (Cp 2 Mg) and silane (SiH 4 ) are used as the precursors. Hydrogen and nitrogen are used as the carrier gas for effective incorporation of the relevant elements on the LED surfaces.
  • FIG. 3 is a schematic diagram illustrating a light emitting diode (LED) structure 300 in an example embodiment.
  • LED light emitting diode
  • a sapphire substrate 302 is provided.
  • a low temperature GaN buffer 304 is grown in the range of about 520 0 C to about 55O 0 C for a thickness of about 25 nm to facilitate nucleation of GaN on the sapphire substrate 302.
  • a high temperature undoped GaN layer 306 is grown to a thickness of about 2 ⁇ m at about 1020 0 C to about 1030°C on the GaN buffer 304.
  • a highly silicon- doped GaN layer 308 with a thickness of about 2-2.5 ⁇ m and having a concentration in the range of about 1 *10 18 to about 9*10 18 cm "3 is then formed on the undoped GaN layer 306.
  • N-type doping is achieved using SiH 4 .
  • the spacer layer 310 is grown at a temperature of between about 800 0 C to about 900 0 C with a thickness in the range of about 50 to about 200 nm.
  • the sapphire substrate 302 and the various layers 304, 306 and 308 are collectively termed as a GaN template 312.
  • a n-GaN barrier 316 (with Si doping of n of about 2 *10 17 to about 1 x10 18 cm '3 ) having a thickness between about 3 to about 20 nm is grown at a temperature of about 75O 0 C to about 900 0 C.
  • the thickness of the barrier 316 is preferably below about 5nm to enable carrier tunnelling.
  • the temperature is then lowered to a temperature of about 760°C to about 800 0 C to grow a ln a Gai -a N layer 318 (where 0.05 ⁇ a ⁇ 0.35) with a thickness of about 2 to about 10 nm.
  • a GaN barrier 320 of between about 3 to about 20 nm thick is then added at a temperature of about 75O 0 C to about 900 0 C.
  • a ln b Ga 1-b N layer 322 (having 0.0810 ⁇ b ⁇ 0.38, where b>a) having a thickness of about 2 to about 10 nm is formed in the temperature range of about 73O 0 C to about 79O 0 C on the GaN barrier 320.
  • the relationship b>a is chosen such that the conduction band energy difference (i.e. conduction band offset) of the superlattices carrier thermalisation layer 314 is matched to a single or multiple longitudinal optical phonon energy, as described above with reference to Figure 9.
  • the TMIn flow rate for growth of the ln b Ga 1-b N layer 322 is higher than that used for the ln a Ga 1-a N layer 318.
  • these four layers 316, 318, 320, 322, GaN/ln a Ga 1-a N/GaN/ln b Ga 1-b N, are repeated for a period n (where 2 ⁇ n ⁇ 10). Only one set is shown in Figure 3 for illustration. Compare with superlattices structure layer 104 of Figure 1(b).
  • an undoped GaN cap layer 324 is then grown on top of the superlattice layer 314 at a temperature of about 75O 0 C to about 900°C.
  • the GaN cap layer 324 has a thickness of between about 3 to about 20.
  • the thickness of the barrier 324 is preferably below about 5nm to enable carrier tunnelling.
  • a u-GaN barrier 326 is grown on the GaN cap layer 324 at a temperature of about 75O 0 C to about 900 0 C to a thickness of between about 3 to about 20 nm. The temperature is then lowered to a temperature range of about 750°C-810°C for the growth of an ln w Ga 1-w N layer 328 (where 0.15 ⁇ w ⁇ 0.45) for a thickness of about 3 to about 20 nm. After the growth of the ln w Ga 1-w N layer 328, TMGa flow is set to zero for TMIn treatment to grow InGaN QDs e.g. 330 for a time duration from about 6s to about 30s.
  • the TMIn flow is set in the range of about 5.0 to about 100 ⁇ mol/ min and the growth temperature is in the range of about 700-760 0 C.
  • the growth conditions can determine the size and composition of Indium in the InGaN QDs e.g. 330.
  • a ln x Ga 1-x N QW layer 332 (where 0.20 ⁇ x ⁇ 0.50) is grown at the same temperature above.
  • the amount of indium incorporation determines the colour of emission.
  • the u-GaN barrier 326, the ln w Ga 1-w N layer 328, the InGaN QDs e.g. 330 and the ln x Ga 1-x N QW layer 332 are repeated for a period m (where 1 ⁇ m ⁇ 5). Only one set is shown in Figure 3 for illustration. Compare with layer 106 of Figure 1(b).
  • the individual quantum wells of layer 332 are capped with a AIN layer 334 which prevents diffusion of the In rich InGaN QDs e.g. 330 to the quantum wells of layer 332, or, into the GaN barrier layer 326.
  • the AIN layer 334 is kept thin compared to the well layer 332 (preferably below about 3 nm). It is noted that after the growth of the InGaN well layer 332, sufficient time of e.g. about 30 seconds is provided for Indium and Gallium adatoms migration before the growth of the AIN layer 334.
  • the growth temperature of the AIN layer 334 is set at about 10 to about 1000 0 C higher than the growth of the InGaN well layer 332 to obtain better crystal quality.
  • the structure 300 up to AIN layer 334 can be used as an amber- orange LED, provided that top contact structures are formed.
  • Figure 4 shows an electroluminescence spectra under varying injection currents of an amber-orange LED sample formed according to the example embodiment. It can be observed that the intensity or light power output increases substantially linearly with an increase in injection current. Further, it can be observed that the peak wavelengths (see e.g. 402, 404) remain substantially constant which implies that the colour emitted remains substantially constant with increasing injection current.
  • growth of a green or blue InGaN/GaN multiple quantum wells (MQWs) layer 336 for color tuning, e.g. to obtain a white LED, can be performed.
  • MQWs multiple quantum wells
  • a green or blue or a stack of both green and blue color MQWs can be grown on the AIN layer 334.
  • FIG. 5 is a schematic diagram illustrating the InGaN/GaN MQWs layer 336 of Figure -3 in more detail.
  • a GaN layer 502 of about 7 to about 20 nm thick is first grown at a temperature of about 75O 0 C to about 900 0 C. The temperature is then lowered to between about 76O 0 C to about 800 0 C for growth of a ln y Ga 1-y N well 504 (where 0.15 ⁇ y ⁇ 0.25) and having a thickness of about 2 to about 5 nm.
  • the quantum wells 502-504 are repeated for a period of m (where 1 ⁇ m ⁇ 5). Only one set is shown in Figure 5 for illustration.
  • a GaN layer 506 of about 7 to about 20 nm thick is first grown at a temperature of about 75O 0 C to about 900 0 C.
  • a ln y Ga 1-y N well 508 (where 0.30 ⁇ y ⁇ 0.40) is then grown at a temperature range of between about 74O 0 C to about 78O 0 C and having a thickness of about 2 to about 5 nm.
  • the quantum wells 506- 508 are repeated for a period of m (where 1 ⁇ m ⁇ 5). Only one set is shown in Figure 5 for illustration.
  • a thin GaN cap layer 335 is grown to a thickness of about 15 to about 30 nm at about 78O 0 C to about 900 0 C. Compare layer 128 of Figure 1(b).
  • an electron blocking layer 337 of P-AI 2 Ga 1- Z N (where 0.1 ⁇ z ⁇ 0.3) is then grown to a thickness of about 20 to about 50 nm.
  • the TMA flow rate for the growth of the P-AI 2 Ga- I-2 N layer 337 is kept at between about 40 to about 100 ⁇ mol/ min with a growth temperature of about 78O 0 C to about 900 0 C.
  • the Cp 2 Mg source is kept at a rate of about 0.3 to about 1.8 ⁇ mol/ min during growth.
  • This layer 337 serves to block electrons from directly traversing to a subsequent p-GaN region (see numeral 338 of Figure 3) hence enabling effective recombination at the MQWs e.g. 502- 508.
  • a p-GaN layer 338 with a multiple-stage doping profile is formed to contact with an electrode (not shown).
  • the dopant used is Mg.
  • FIG. 6 is a schematic diagram illustrating the p-GaN layer 338 of Figure 3 in more detail.
  • the temperature is maintained at about 780 0 C to about 95O 0 C.
  • Three or more growth steps for the p-GaN 338 can be adopted.
  • a lower Mg doping in the range of about 10 17 to about 10 18 cm "3 is used.
  • a Mg doping of about 10 18 to about 5x10 18 cm "3 is used.
  • the doping concentration is increased to between about 5x10 18 to about 10 19 cm '3 , by increasing the Cp 2 Mg flow.
  • a sample white LED is fabricated using the example embodiment. It is found that strong white emission is obtained with Indium contact placed on the p-GaN epilayer and n+-GaN layer.
  • Figure 7 shows an electroluminescence spectrum for the white LED. Using an injection current of about 6OmA, it can be observed that there are the three emission peaks at about 437.4 nm (blue light) at numeral 702, about 500.9 nm (green light) at numeral 704 and about 566.6 nm (yellow light) at numeral 706 based on fitting. Different shades of white emission can be obtained with a combination of stacked QDs/QWs (compare 106 of Figure 1 (a)) and blue and/or green emission QWs.
  • FIG. 8 is a flowchart 800 illustrating a method of forming a light emitting diode structure in an example embodiment.
  • a first barrier layer of a superlattice is formed.
  • a first quantum well layer is formed on the first barrier layer, the first quantum well layer comprising a first metal-nitride based material.
  • a second barrier layer is formed on the first quantum well layer.
  • a second quantum well layer is formed on the second barrier layer, the second quantum well layer comprising the first metal-nitride based material.
  • a difference between conduction band energy of the first quantum well layer and conduction band energy of the second quantum well layer is matched to a single or multiple optical phonon energy for reducing electron kinetic energy in the superlattice.
  • the above described example embodiments can increase carrier injection efficiency.
  • the above described example embodiments can increase carrier capture efficiency.
  • the above described example embodiments can increase electron-hole recombination volume and thus increase internal quantum efficiency.
  • the above described example embodiments can increase power output of InGaN quantum dots- based LEDs.
  • the material used include GaN and InGaN.
  • the material are not limited to the above and can include any different metal-nitride based material.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Led Devices (AREA)

Abstract

L'invention porte sur une structure de diode électroluminescente et sur un procédé de formation d'une structure de diode électroluminescente. La structure comprend un super-réseau comprenant : une première couche barrière ; une première couche de puits quantique comprenant un premier matériau à base de nitrure métallique formée sur la première couche barrière ; une seconde couche barrière formée sur la première couche de puits quantique ; et une seconde couche de puits quantique comprenant le premier matériau à base de nitrure métallique formée sur la seconde couche barrière. Une différence entre une énergie de bande de conduction de la première couche de puits quantique et une énergie de bande de conduction de la seconde couche de puits quantique correspond à l'énergie d'un seul ou de plusieurs phonons optiques longitudinaux pour réduire l'énergie cinétique électronique dans le super-réseau.
PCT/SG2009/000438 2008-11-21 2009-11-20 Structure de diode électroluminescente et procédé de formation d'une structure de diode électroluminescente WO2010059132A1 (fr)

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US61/116,690 2008-11-21

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