WO2007024122A1 - Semiconductor light emitting device - Google Patents

Semiconductor light emitting device Download PDF

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Publication number
WO2007024122A1
WO2007024122A1 PCT/KR2006/003363 KR2006003363W WO2007024122A1 WO 2007024122 A1 WO2007024122 A1 WO 2007024122A1 KR 2006003363 W KR2006003363 W KR 2006003363W WO 2007024122 A1 WO2007024122 A1 WO 2007024122A1
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Prior art keywords
layer
light emitting
emitting device
semiconductor light
nitride semiconductor
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PCT/KR2006/003363
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French (fr)
Inventor
Eun-Hyun Park
Do-Yeol Ahn
Tae-Kyung Yoo
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Epivalley Co., Ltd.
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Publication of WO2007024122A1 publication Critical patent/WO2007024122A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier 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 with at least one potential-jump barrier or surface barrier 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
    • 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
    • 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
    • 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
    • H01S5/34346—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 characterised by the materials of the barrier layers
    • H01S5/34393—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 characterised by the materials of the barrier layers not only based on AIIIBV compounds
    • 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
    • H01S5/347—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 AIIBVI compounds, e.g. ZnCdSe- laser

Definitions

  • the present invention relates to a semiconductor light emitting device, and more particularly, to a semiconductor light emitting device which can overcome lattice mismatch between a well layer and a barrier layer of an active layer and improve internal quantum efficiency by relaxing a piezo effect in the well layer, by using a compound semiconductor layer containing Al Ga In N (O ⁇ x ⁇ l, O ⁇ y ⁇ l, 0 ⁇ x+y ⁇ l) x y 1-x-y as the well layer and a compound semiconductor layer containing Mg Zn O (O ⁇ a ⁇ l) a 1-a as the barrier layer.
  • Exemplary semiconductor light emitting devices include a light emitting diode (LED) and a laser diode (LD).
  • FIG. 1 is a view illustrating one example of a conventional semiconductor light emitting device, especially, a Ill-nitride semiconductor light emitting device.
  • the conventional semiconductor light emitting device includes a substrate 100, a buffer layer 200 epitaxially grown on the substrate 100, an n-type nitride semiconductor layer 300 epitaxially grown on the buffer layer 200, an active layer 400 epitaxially grown on the n-type nitride semiconductor layer 300, a p-type nitride semiconductor layer 500 epitaxially grown on the active layer 400, a p-side electrode 600 formed on the p-type nitride semiconductor layer 500, a p-side bonding pad 700 formed on the p-side electrode 600, and an n-side electrode 800 formed on the n-type nitride semiconductor layer 301 exposed by mesa-etching the p-type nitride semiconductor layer 500 and the active layer 400.
  • a GaN substrate can be used as a homo-substrate, and an Al 2 O 3 substrate, an SiC substrate or an Si substrate can be used as a hetero- substrate.
  • any kinds of substrates on which the nitride semiconductor layers can be grown can be used.
  • the nitride semiconductor layers epitaxially grown on the substrate 100 are generally grown by the metal organic chemical vapor deposition (MOCVD).
  • MOCVD metal organic chemical vapor deposition
  • the buffer layer 200 serves to overcome differences in lattice constant and thermal expansion coefficient between the hetero-substrate 100 and the nitride semiconductor.
  • USP 5,122,845 discloses a method for growing an AlN buffer layer having a thickness of IOOA to 500A on a sapphire substrate at 38O 0 C to 800 0 C.
  • USP 5,290,393 discloses a method for growing an Al Ga N (0 ⁇ x ⁇ l) buffer layer having a thickness of 1OA to x 1-x
  • the international laid-open gazette WO/20173042 discloses a method for growing an SiC buffer layer (seed layer) at 600 0 C to 990 0 C, and growing an In Ga N (0 ⁇ x ⁇ l) layer thereon.
  • the n-type nitride semiconductor layer 300 is doped with at least one selected from the group consisting of Si, Ge and Sn as an n-type dopant.
  • the n-type nitride semiconductor layer 300 is made of GaN and doped with Si.
  • USP 5,733,796 discloses a method for doping an n-type semiconductor layer at a target doping concentration by controlling a mixture ratio of Si and another source material.
  • the active layer 400 generates light quanta (light) by recombination of an electron and a hole.
  • the active layer 400 is made of In Ga N (0 ⁇ x ⁇ l) and comprised x 1-x of one well layer or plural well layers.
  • the international laid-open gazette WO/ 02/021121 discloses a method for partially doping a plurality of quantum well layers and barrier layers.
  • the p-type nitride semiconductor layer 500 is doped with at least one selected from the group consisting of Zn, Mg, Ca and Be as a p-type dopant.
  • P-type conductivity is attained by activation.
  • USP 5,247,533 discloses a method for activating a p-type nitride semiconductor layer by electron beam irradiation.
  • USP 5,306,662 discloses a method for activating a p-type nitride semiconductor layer by annealing at temperature over 400 0 C.
  • the international laid-open gazette WO/2017022655 discloses a method for endowing a p-type nitride semiconductor layer with p-type conductivity without activation, by using ammonia and a hydrogen group source material as a nitrogen precursor for the growth of the p-type nitride semiconductor layer.
  • the p-side electrode 600 facilitates current supply to the entire p-type nitride semiconductor layer 500 and emission of light generated in the active layer 400.
  • USP 5,563,422 discloses a light transmittable electrode formed almost over the entire surface of a p-type nitride semiconductor layer, ohmic-contacting with the p-type nitride semiconductor layer, and made of Ni and Au.
  • USP 6,515,306 discloses a method for forming an transmittable electrode made of ITO over an n-type superlattice layer formed on a p-type nitride semiconductor layer.
  • the p-side electrode 600 can be formed thick not to transmit light, namely, to reflect light to the substrate side.
  • a light emitting device using the p- side electrode 600 is called a flip chip.
  • USP 6,194,743 discloses an electrode structure including an Ag layer having a thickness over 20nm, a diffusion barrier layer covering the Ag layer, and a bonding layer made of Au and Al covering the diffusion barrier layer.
  • the p-side bonding pad 700 and the n-side electrode 800 are formed for current supply and external wire bonding.
  • USP 5,563,422 discloses a method for forming an n- side electrode with Ti and Al
  • USP 5,652,434 discloses a a p-side bonding pad directly contacting with a p-type nitride semiconductor layer by removing a part of a light transmittable electrode.
  • the light emitting device emits light by converting electric energy into photon energy by recombination of an electron and a hole in the well layer(s) composing the active layer.
  • efficiency of the recombination of the electron and the hole determines internal quantum efficiency of the light emitting device.
  • the active layer includes an In Ga N (O ⁇ x ⁇ l) well x 1-x layer and an Al In Ga N (O ⁇ x ⁇ l, O ⁇ y ⁇ l, O ⁇ x+y ⁇ l) barrier layer.
  • x y 1-x-y according to the material property of the nitride, a strong piezoelectric field is generated in the active layer due to a difference in lattice constant between the well layer and the barrier layer. Accordingly, energy band bending occurs in the well layer, so that cause spatial separation of distributions of the electrons and holes. As a result, the recombination rate of the electrons and holes decrease. Disclosure of Invention Technical Problem
  • the present invention is achieved to solve the above problems.
  • An object of the present invention is to improve internal quantum efficiency of a semiconductor light emitting device by minimizing electric field generation by a piezo effect of a well layer through reducing lattice mismatch between the well layer and a barrier layer.
  • a semiconductor light emitting device comprising a plurality of semiconductor layers having an active layer generating light by recombination of an electron and a holes, wherein the active layer includes an Al x Ga y In 1-x-y N (O ⁇ x ⁇ l, O ⁇ y ⁇ l, O ⁇ x+y ⁇ l) well layer and a Mg a Zn 1-a O (O ⁇ a ⁇ 1) barrier layer.
  • an energy band gap of the Mg a Zn 1-a O (O ⁇ a ⁇ l) barrier layer is larger than that of the Al Ga In N (O ⁇ x ⁇ 1 , O ⁇ y ⁇ 1 , O ⁇ x+y ⁇ 1 ) well layer.
  • a lattice constant of the Al x Ga y In 1-x-y N (O ⁇ x ⁇ l, O ⁇ y ⁇ l, O ⁇ x+y ⁇ l) well layer matches with a lattice constant of the Mg a Zn 1-a O (O ⁇ a ⁇ l) barrier layer.
  • the active layer is formed by alternately stacking the Al x Ga y In 1-x-y N
  • the plurality of semiconductor layers include a nitride semiconductor layer containing Al Ga In N (O ⁇ m ⁇ l, O ⁇ n ⁇ l, O ⁇ m+n ⁇ l). It means that the semi- m n 1 -m-n conductor light emitting device is a kind of Ill-nitride semiconductor light emitting device.
  • the plurality of semiconductor layers include an oxide semiconductor layer containing Mg Zn O (O ⁇ r ⁇ l). It means that the MgZnO oxide semiconductor r 1-r layer can be used as a layer other than the barrier layer of the light emitting device.
  • the Al Ga In N (0 ⁇ x ⁇ 1 , O ⁇ y ⁇ 1 , O ⁇ x+y ⁇ 1 ) well layer has a thickness x y 1 -x-y of 5 A to 5000A, more preferably, 5v to 100OA. Accordingly, the present invention can be applied to both a light emitting device with a quantum well structure and a light emitting device with a double heterojunction structure.
  • the Mg Zn O (0 ⁇ a ⁇ 1) barrier layer has a thickness of 5 A to lOOOOA, o a 1 ⁇ o more preferably 1OA to 5000A.
  • the energy barrier is lower and confinement of the electron and the hole diminishes.
  • a semiconductor light emitting device comprising a substrate, a buffer layer epitaxially grown on the substrate, an n-type nitride semiconductor layer epitaxially grown on the buffer layer, an active layer being epitaxially grown on the n-type nitride semiconductor layer and the active layer including an Al x Ga y In 1 -x-y N (O ⁇ x ⁇ l, O ⁇ y ⁇ l, 0 ⁇ x+y ⁇ l) well layer and a Mg a Zn 1-a O (0 ⁇ a ⁇ 1) barrier layer, a p-type nitride semiconductor layer epitaxially grown on the active layer, a p-side electrode formed on the p-type nitride semiconductor layer, and an n-side electrode formed on the n-type nitride semiconductor layer exposed by me
  • a semiconductor light emitting device comprising a plurality of semiconductor layers having an active layer for generating light by recombination of an electron and a hole, the device includes the active layer including an Al Ga In N (O ⁇ x ⁇ l, O ⁇ y ⁇ l, 0 ⁇ x+y ⁇ l) x y 1 -x-y well layer, and a Mg Zn O (O ⁇ a ⁇ l) layer adjacent to the active layer.
  • the active layer including an Al Ga In N (O ⁇ x ⁇ l, O ⁇ y ⁇ l, 0 ⁇ x+y ⁇ l) x y 1 -x-y well layer, and a Mg Zn O (O ⁇ a ⁇ l) layer adjacent to the active layer.
  • the internal quantum efficiency of the semiconductor light emitting device can be improved through the Mg Zn O (O ⁇ a ⁇ l) a 1-a barrier layer overcoming mismatch in lattice constant between the Al Ga In N x y 1-x-y
  • FIG. 1 is a cross-sectional view illustrating one example of a conventional semiconductor light emitting device
  • FIG. 2 is a schematic view illustrating energy band bending by a piezo field
  • Fig. 3 is a graph showing lattice constants of InGaN and MgZnO by In and Mg mole fractions;
  • Fig. 4 is a graph showing optical gains of an active layer containing an In Ga N well layer and a Mg Zn O barrier layer, an active layer containing an In Ga N
  • Fig. 5 is a graph showing photoluminescence of the active layer consisting of the In
  • the active layer consisting of the
  • FIG. 6 is a cross-sectional view illustrating a semiconductor light emitting device in accordance with an embodiment of the present invention. Mode for the Invention
  • Fig. 2 is a schematic view illustrating energy band bending by a piezo field. Since an electron and a hole tend to move a low energy state, wave functions of the electron and the hole are distributed as shown in Fig. 2. When an interval between the maximum values of the wave functions of the electron and that of the hole increases, an overlapping probability of the wave functions decreases, and thus a recombination probability of the electron and the hole also decreases.
  • the direct influence of the piezo field results in reduction of luminescence and blue shift of light emitting wavelengths by external voltage application.
  • the present inventors have done researches on various materials to solve the foregoing problems, and found that the predescribed problems could be solved and light emitting efficiency could be improved by forming an active layer includong a nitride semiconductor containing Al x Ga y In 1-x-y N (O ⁇ x ⁇ l, O ⁇ y ⁇ l, 0 ⁇ x+y ⁇ l) as a well layer and an oxide semiconductor containing Mg a Zn 1-a O (O ⁇ a ⁇ l) as a barrier layer.
  • Fig. 3 is a graph showing lattice constants of InGaN and MgZnO according to In and Mg mole fractions.
  • the lattice constant of Mg Zn O (O ⁇ a ⁇ l) exists within the latt a 1-a ice constant range of In Ga N (O ⁇ x ⁇ l), and thus the lattice constant matching region x 1-x is formed between Mg Zn O (O ⁇ a ⁇ l) and In Ga N (O ⁇ x ⁇ l).
  • a difference 'Ec' in conduction band energy band gap between Mg a Zn 1-a O (O ⁇ a ⁇ l) and In x Ga 1-x N (O ⁇ x ⁇ l) is represented by 1.6x + a -
  • Fig. 4 is a graph showing theoretically-calculated optical gains of an active layer containing an In Ga N well layer and a Mg Zn O barrier layer, an active layer to 0 15 0 85 J to 0 2 0 8 J J containing an In Ga N well layer and an Al Ga N barrier layer, and an active
  • Fig. 5 is a graph showing theoretically-calculated photo luminescence of the active layer containing the In Ga N well layer and the Mg Zn O barrier layer, the active
  • the active layer containing the ZnO well layer and the Mg Zn O barrier layer 0 15 0 85 0 2 0 8 active layer containing the ZnO well layer and the Mg Zn O barrier layer.
  • the theoretical photoluminescence of the active layer containing the In Ga N well layer and the Mg Zn O barrier layer is considerably improved. Because the ZnO system has higher exiton binding energy than that of the InGaN system by at least three times, the active layer containing the ZnO well layer and the Mg Zn O barrier layer has larger optical gain and photoluminescence than that of the active layer containing the In Ga N well layer and the Al Ga N barrier layer.
  • the well layer had a thickness of 4nm and the barrier layer had a thickness of 7nm.
  • the In Ga N (O ⁇ x ⁇ l) well layer is used.
  • the x 1-x well layer is made of Al Ga In N (O ⁇ x ⁇ l, O ⁇ y ⁇ l, 0 ⁇ x+y ⁇ l)
  • energy band bending x y 1 -x- y of the well layer can be overcome, thereby improving recombination efficiency of the electron and the hole and internal quantum efficiency.
  • Fig. 6 is a cross-sectional view illustrating an example of a light emitting device in accordance with the present invention, especially, a Ill-nitride semiconductor light emitting device.
  • the semiconductor light emitting device comprises a substrate 10, a buffer layer 20 epitaxially grown on the substrate 10, an n-type nitride semiconductor layer 30 epitaxially grown on the buffer layer 20, an active layer 40 epitaxially grown on the n-type nitride semiconductor layer 30, a p-type nitride semiconductor layer 50 epitaxially grown on the active layer 40, a p-side electrode 60 formed on the p-type nitride semiconductor layer 50, a p-side bonding pad 70 formed on the p-side electrode 60, and an n-side electrode 80 formed on the n-type nitride semiconductor layer 31 exposed by mesa-etching the p-type nitride semiconductor layer 50 and the active layer 40.
  • the active layer 40 is formed by alternately stacking an Al Ga In N (O ⁇ x ⁇ l, x y 1 -x-y
  • This a 1-a structure serves to overcome band bending of the well layer.
  • the outermost layer of the active layer 40 can be the well layer
  • the n-type nitride semiconductor layer 30, the p-type nitride semiconductor layer 50, or part of the n-type nitride semiconductor layer 30 and the p-type nitride semiconductor layer 50 can be made of the Mg Zn O (O ⁇ a ⁇ l) layer.
  • the semiconductor light emitting device including the Al x Ga y In 1-x-y N (O ⁇ x ⁇ 1 , O ⁇ y ⁇ 1 , O ⁇ x+y ⁇ 1 ) well layer can be expanded to the semiconductor light emitting device in which the n-type nitride semiconductor layer and the p-type nitride semiconductor layer which contacts the active layer or a n-type nitride semiconductor layer and a p-type nitride semiconductor layer that is a part of them is made of the Mg a Zn 1-a O (O ⁇ a ⁇ 1) layer.

Abstract

The present invention discloses a semiconductor light emitting device comprising a plurality of semiconductor layers including an active layer for generating light by recombination of an electron and a hole. Here, the active layer includes an Alx Gay In1-x-y N (0≤x≤l, 0≤y≤l, 0≤x+y≤l) well layer and a Mga Zn1-a O (0<a< 1) barrier layer.

Description

Description
SEMICONDUCTOR LIGHT EMITTING DEVICE
Technical Field
[1] The present invention relates to a semiconductor light emitting device, and more particularly, to a semiconductor light emitting device which can overcome lattice mismatch between a well layer and a barrier layer of an active layer and improve internal quantum efficiency by relaxing a piezo effect in the well layer, by using a compound semiconductor layer containing Al Ga In N (O≤x≤l, O≤y≤l, 0<x+y≤l) x y 1-x-y as the well layer and a compound semiconductor layer containing Mg Zn O (O≤a≤l) a 1-a as the barrier layer. Exemplary semiconductor light emitting devices include a light emitting diode (LED) and a laser diode (LD). Background Art
[2] Fig. 1 is a view illustrating one example of a conventional semiconductor light emitting device, especially, a Ill-nitride semiconductor light emitting device. The conventional semiconductor light emitting device includes a substrate 100, a buffer layer 200 epitaxially grown on the substrate 100, an n-type nitride semiconductor layer 300 epitaxially grown on the buffer layer 200, an active layer 400 epitaxially grown on the n-type nitride semiconductor layer 300, a p-type nitride semiconductor layer 500 epitaxially grown on the active layer 400, a p-side electrode 600 formed on the p-type nitride semiconductor layer 500, a p-side bonding pad 700 formed on the p-side electrode 600, and an n-side electrode 800 formed on the n-type nitride semiconductor layer 301 exposed by mesa-etching the p-type nitride semiconductor layer 500 and the active layer 400.
[3] In the case of the substrate 100, a GaN substrate can be used as a homo-substrate, and an Al 2 O 3 substrate, an SiC substrate or an Si substrate can be used as a hetero- substrate. However, any kinds of substrates on which the nitride semiconductor layers can be grown can be used. [4] The nitride semiconductor layers epitaxially grown on the substrate 100 are generally grown by the metal organic chemical vapor deposition (MOCVD). [5] The buffer layer 200 serves to overcome differences in lattice constant and thermal expansion coefficient between the hetero-substrate 100 and the nitride semiconductor.
USP 5,122,845 discloses a method for growing an AlN buffer layer having a thickness of IOOA to 500A on a sapphire substrate at 38O0C to 8000C. USP 5,290,393 discloses a method for growing an Al Ga N (0<x<l) buffer layer having a thickness of 1OA to x 1-x
5000A on a sapphire substrate at 2000C to 9000C. The international laid-open gazette WO/05/053042 discloses a method for growing an SiC buffer layer (seed layer) at 6000C to 9900C, and growing an In Ga N (0<x≤l) layer thereon. x 1-x
[6] The n-type nitride semiconductor layer 300 is doped with at least one selected from the group consisting of Si, Ge and Sn as an n-type dopant. In general, the n-type nitride semiconductor layer 300 is made of GaN and doped with Si. USP 5,733,796 discloses a method for doping an n-type semiconductor layer at a target doping concentration by controlling a mixture ratio of Si and another source material.
[7] The active layer 400 generates light quanta (light) by recombination of an electron and a hole. Normally, the active layer 400 is made of In Ga N (0<x≤l) and comprised x 1-x of one well layer or plural well layers. The international laid-open gazette WO/ 02/021121 discloses a method for partially doping a plurality of quantum well layers and barrier layers.
[8] The p-type nitride semiconductor layer 500 is doped with at least one selected from the group consisting of Zn, Mg, Ca and Be as a p-type dopant. P-type conductivity is attained by activation. USP 5,247,533 discloses a method for activating a p-type nitride semiconductor layer by electron beam irradiation. USP 5,306,662 discloses a method for activating a p-type nitride semiconductor layer by annealing at temperature over 4000C. In addition, the international laid-open gazette WO/05/022655 discloses a method for endowing a p-type nitride semiconductor layer with p-type conductivity without activation, by using ammonia and a hydrogen group source material as a nitrogen precursor for the growth of the p-type nitride semiconductor layer.
[9] The p-side electrode 600 facilitates current supply to the entire p-type nitride semiconductor layer 500 and emission of light generated in the active layer 400. USP 5,563,422 discloses a light transmittable electrode formed almost over the entire surface of a p-type nitride semiconductor layer, ohmic-contacting with the p-type nitride semiconductor layer, and made of Ni and Au. USP 6,515,306 discloses a method for forming an transmittable electrode made of ITO over an n-type superlattice layer formed on a p-type nitride semiconductor layer.
[10] On the other hand, the p-side electrode 600 can be formed thick not to transmit light, namely, to reflect light to the substrate side. A light emitting device using the p- side electrode 600 is called a flip chip. USP 6,194,743 discloses an electrode structure including an Ag layer having a thickness over 20nm, a diffusion barrier layer covering the Ag layer, and a bonding layer made of Au and Al covering the diffusion barrier layer.
[11] The p-side bonding pad 700 and the n-side electrode 800 are formed for current supply and external wire bonding. USP 5,563,422 discloses a method for forming an n- side electrode with Ti and Al, and USP 5,652,434 discloses a a p-side bonding pad directly contacting with a p-type nitride semiconductor layer by removing a part of a light transmittable electrode. [12] Generally, the light emitting device emits light by converting electric energy into photon energy by recombination of an electron and a hole in the well layer(s) composing the active layer. Here, efficiency of the recombination of the electron and the hole determines internal quantum efficiency of the light emitting device.
[13] Generally, in the nitride semiconductor light emitting device, although there are slight differences by wavelength, the active layer includes an In Ga N (O≤x≤l) well x 1-x layer and an Al In Ga N (O≤x≤l, O≤y≤l, O≤x+y≤l) barrier layer. However, x y 1-x-y according to the material property of the nitride, a strong piezoelectric field is generated in the active layer due to a difference in lattice constant between the well layer and the barrier layer. Accordingly, energy band bending occurs in the well layer, so that cause spatial separation of distributions of the electrons and holes. As a result, the recombination rate of the electrons and holes decrease. Disclosure of Invention Technical Problem
[14] The present invention is achieved to solve the above problems. An object of the present invention is to improve internal quantum efficiency of a semiconductor light emitting device by minimizing electric field generation by a piezo effect of a well layer through reducing lattice mismatch between the well layer and a barrier layer. Technical Solution
[15] In order to achieve the above-described object of the invention, there is provided a semiconductor light emitting device comprising a plurality of semiconductor layers having an active layer generating light by recombination of an electron and a holes, wherein the active layer includes an Al x Ga y In 1-x-y N (O≤x≤l, O≤y≤l, O≤x+y≤l) well layer and a Mg a Zn 1-a O (O≤a≤ 1) barrier layer.
[16] Preferably, an energy band gap of the Mg a Zn 1-a O (O≤a≤l) barrier layer is larger than that of the Al Ga In N (O≤x≤ 1 , O≤y ≤ 1 , O≤x+y ≤ 1 ) well layer. x y 1-x-y
[17] Preferably, a lattice constant of the Al x Ga y In 1-x-y N (O≤x≤l, O≤y≤l, O≤x+y≤l) well layer matches with a lattice constant of the Mg a Zn 1-a O (O≤a≤l) barrier layer.
[18] Preferably, the active layer is formed by alternately stacking the Al x Ga y In 1-x-y N
(O≤x≤l, O≤y ≤ 1 , O≤x+y ≤ 1 ) well layer and the Mg Zn O (O≤a≤ 1 ) barrier layer. a 1-a
[19] Preferably, the plurality of semiconductor layers include a nitride semiconductor layer containing Al Ga In N (O≤m≤l, O≤n≤l, O≤m+n≤l). It means that the semi- m n 1 -m-n conductor light emitting device is a kind of Ill-nitride semiconductor light emitting device.
[20] Preferably, the plurality of semiconductor layers include an oxide semiconductor layer containing Mg Zn O (O≤r≤l). It means that the MgZnO oxide semiconductor r 1-r layer can be used as a layer other than the barrier layer of the light emitting device. [21 ] Preferably, the Al Ga In N (0<x< 1 , O≤y≤ 1 , O≤x+y≤ 1 ) well layer has a thickness x y 1 -x-y of 5 A to 5000A, more preferably, 5v to 100OA. Accordingly, the present invention can be applied to both a light emitting device with a quantum well structure and a light emitting device with a double heterojunction structure. When the well layer is thinner than 5 A, confinement of the electron and the hole in the well layer diminishes to rapidly reduce light emitting efficiency. In addition, it is difficult to form a uniform thickness on the entire substrate. Therefore, a property can be seriously unstable. When the well layer is thicker than 5000A, since the well layer is grown at a low temperature, quality of a thin film and efficiency of the light emitting device are reduced. [22] Preferably, the Mg Zn O (0<a< 1) barrier layer has a thickness of 5 A to lOOOOA, o a 1^ o more preferably 1OA to 5000A. When the barrier layer is thinner than 5 A, the energy barrier is lower and confinement of the electron and the hole diminishes. When the barrier layer is thicker than 5000A, since the barrier layer is grown at a low temperature, quality of the thin film and light emitting efficiency are reduced. [23] According to another aspect of the present invention, there is provided a semiconductor light emitting device comprising a substrate, a buffer layer epitaxially grown on the substrate, an n-type nitride semiconductor layer epitaxially grown on the buffer layer, an active layer being epitaxially grown on the n-type nitride semiconductor layer and the active layer including an Al x Ga y In 1 -x-y N (O≤x≤l, O≤y≤l, 0<x+y≤l) well layer and a Mg a Zn 1-a O (0<a< 1) barrier layer, a p-type nitride semiconductor layer epitaxially grown on the active layer, a p-side electrode formed on the p-type nitride semiconductor layer, and an n-side electrode formed on the n-type nitride semiconductor layer exposed by mesa-etching the p-type nitride semiconductor layer and the active layer.
[24] According to yet another aspect of the present invention, there is provided a semiconductor light emitting device comprising a plurality of semiconductor layers having an active layer for generating light by recombination of an electron and a hole, the device includes the active layer including an Al Ga In N (O≤x≤l, O≤y≤l, 0≤x+y≤l) x y 1 -x-y well layer, and a Mg Zn O (O≤a≤l) layer adjacent to the active layer. When the a 1-a outermost layer of the active layer is the well layer, this structure can be efficiently used.
Advantageous Effects
[25] In accordance with the present invention, the internal quantum efficiency of the semiconductor light emitting device can be improved through the Mg Zn O (O≤a≤l) a 1-a barrier layer overcoming mismatch in lattice constant between the Al Ga In N x y 1-x-y
(O≤x≤l, O≤y≤l, 0≤x+y≤l) well layer and the barrier layer with maintaining higher band gap energy than that of the well layer. Brief Description of the Drawings
[26] The present invention will become better understood with reference to the accompanying drawings which are given only by way of illustration and thus are not limitative of the present invention, wherein:
[27] Fig. 1 is a cross-sectional view illustrating one example of a conventional semiconductor light emitting device;
[28] Fig. 2 is a schematic view illustrating energy band bending by a piezo field;
[29] Fig. 3 is a graph showing lattice constants of InGaN and MgZnO by In and Mg mole fractions;
[30] Fig. 4 is a graph showing optical gains of an active layer containing an In Ga N well layer and a Mg Zn O barrier layer, an active layer containing an In Ga N
J to0 2 0 8 J J to 0 15 0 85 well layer and an Al Ga N barrier layer, and an active layer containing a ZnO well
0 2 0 8 layer and a Mg Zn O barrier layer;
J to0 2 0 8 J
[31] Fig. 5 is a graph showing photoluminescence of the active layer consisting of the In
Ga N well layer and the Mg Zn O barrier layer, the active layer consisting of the
0 15 0 85 J to0 2 0 8 J J b
In Ga N well layer and the Al Ga N barrier layer, and the active layer consisting
0 15 0 85 02 0 8 of the ZnO well layer and the Mg Zn O barrier layer; and
J to0 2 0 8 J
[32] Fig. 6 is a cross-sectional view illustrating a semiconductor light emitting device in accordance with an embodiment of the present invention. Mode for the Invention
[33] A semiconductor light emitting device in accordance with preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
[34] Fig. 2 is a schematic view illustrating energy band bending by a piezo field. Since an electron and a hole tend to move a low energy state, wave functions of the electron and the hole are distributed as shown in Fig. 2. When an interval between the maximum values of the wave functions of the electron and that of the hole increases, an overlapping probability of the wave functions decreases, and thus a recombination probability of the electron and the hole also decreases. The direct influence of the piezo field results in reduction of luminescence and blue shift of light emitting wavelengths by external voltage application.
[35] The present inventors have done researches on various materials to solve the foregoing problems, and found that the predescribed problems could be solved and light emitting efficiency could be improved by forming an active layer includong a nitride semiconductor containing Al x Ga y In 1-x-y N (O≤x≤l, O≤y≤l, 0<x+y≤l) as a well layer and an oxide semiconductor containing Mg a Zn 1-a O (O≤a≤l) as a barrier layer.
[36] In an active layer including an In x Ga 1-x N (O≤x≤l) well layer and a Mg a Zn 1-a O (O≤a≤l) barrier layer, optical gains and photoluminescence are theoretically calculated by using a non-Markovian model considering a many-body effect. [37] In the case of In Ga N (O≤x≤l) which is a wurtzite crystal structure, by a quantity x 1-x of 'x' of In, a lattice constant 'a' is represented as 3.1892 + 0.3408x A, and an energy band gap 'Eg' is represented as 3.44 - 1.55x eV. [38] In the case of Mg Zn O (O≤a≤l) which is a wurtzite crystal structure, by a quantity a 1-a of 'a' of Mg, a lattice constant 'a' is represented as 3.2505 - 0.0515a A, and an energy band gap 'Eg' is represented as 3.35 + (0.64a / 0.33) eV. [39] Fig. 3 is a graph showing lattice constants of InGaN and MgZnO according to In and Mg mole fractions. The lattice constant of Mg Zn O (O≤a≤l) exists within the latt a 1-a ice constant range of In Ga N (O≤x≤l), and thus the lattice constant matching region x 1-x is formed between Mg Zn O (O≤a≤l) and In Ga N (O≤x≤l). In addition, in con- a 1-a x 1-x sideration of a Fermi energy level, a difference 'Ec' in conduction band energy band gap between Mg a Zn 1-a O (O≤a≤l) and In x Ga 1-x N (O≤x≤l) is represented by 1.6x + a -
0.15 eV. A region of this value to be positive is preferably applied to the present invention. It is because the energy band gap of the well layer must be smaller than that of the barrier layer. [40] In the lattice constant matching region (x = 0.15, a = 0.2) of the In x Ga 1-x N (O≤x≤ 1) well layer and the Mg a Zn 1-a O (O≤a≤l) barrier layer, optical gains and photo Iu- minescence are calculated by using the non-Markovian model.
[41] Fig. 4 is a graph showing theoretically-calculated optical gains of an active layer containing an In Ga N well layer and a Mg Zn O barrier layer, an active layer to 0 15 0 85 J to0 2 0 8 J J containing an In Ga N well layer and an Al Ga N barrier layer, and an active
0 15 0 85 0 2 0 8 layer containing a ZnO well layer and a Mg Zn O barrier layer. The active layer containing the In Ga N well layer and the Mg Zn O barrier layer attains large
0 15 0 85 0 2 0 8 optical gain. [42] That is because, recombination efficiency of the electron and the hole is improved by overcoming energy band bending of the well layer by removing the piezo field through lattice constant matching between the well layer and the barrier layer. [43] Fig. 5 is a graph showing theoretically-calculated photo luminescence of the active layer containing the In Ga N well layer and the Mg Zn O barrier layer, the active
0 15 0 85 0 2 0 8 layer containing the In Ga N well layer and the Al Ga N barrier layer, and the
0 15 0 85 0 2 0 8 active layer containing the ZnO well layer and the Mg Zn O barrier layer. The theoretical photoluminescence of the active layer containing the In Ga N well layer and the Mg Zn O barrier layer is considerably improved. Because the ZnO system has higher exiton binding energy than that of the InGaN system by at least three times, the active layer containing the ZnO well layer and the Mg Zn O barrier layer has larger optical gain and photoluminescence than that of the active layer containing the In Ga N well layer and the Al Ga N barrier layer.
0 15 0 85 02 0 8
[44] In the simulation for obtaining the theoretical calculation values, the well layer had a thickness of 4nm and the barrier layer had a thickness of 7nm. An electric field by simultaneous polarization of the In Ga N well layer and the Mg Zn O barrier layer
0 15 0 85 0 2 0 8 was not considered. However, even in consideration of the electric field by simultaneous r polarization,' it is ex rpected that the active lay Jer containing & the In 0 15 Ga 0 85 N well layer and the Mg Zn O barrier layer will be remarkably improved from the conventional active layer. [45] In this embodiment, the In Ga N (O≤x≤l) well layer is used. However, even if the x 1-x well layer is made of Al Ga In N (O≤x≤l, O≤y≤l, 0≤x+y≤l), energy band bending x y 1 -x- y of the well layer can be overcome, thereby improving recombination efficiency of the electron and the hole and internal quantum efficiency.
[46] Fig. 6 is a cross-sectional view illustrating an example of a light emitting device in accordance with the present invention, especially, a Ill-nitride semiconductor light emitting device. The semiconductor light emitting device comprises a substrate 10, a buffer layer 20 epitaxially grown on the substrate 10, an n-type nitride semiconductor layer 30 epitaxially grown on the buffer layer 20, an active layer 40 epitaxially grown on the n-type nitride semiconductor layer 30, a p-type nitride semiconductor layer 50 epitaxially grown on the active layer 40, a p-side electrode 60 formed on the p-type nitride semiconductor layer 50, a p-side bonding pad 70 formed on the p-side electrode 60, and an n-side electrode 80 formed on the n-type nitride semiconductor layer 31 exposed by mesa-etching the p-type nitride semiconductor layer 50 and the active layer 40.
[47] The active layer 40 is formed by alternately stacking an Al Ga In N (O≤x≤l, x y 1 -x-y
O≤y≤ 1 , 0≤x+y≤ 1 ) well layer 41 and a Mg Zn O (O≤a≤ 1 ) barrier layer 42. This a 1-a structure serves to overcome band bending of the well layer.
[48] On the other hand, the outermost layer of the active layer 40 can be the well layer
41. In order to prevent generation of the piezo field by a difference in lattice constant between the well layer 41 and the n-type nitride semiconductor layer 30 or the p-type nitride semiconductor layer 50, the n-type nitride semiconductor layer 30, the p-type nitride semiconductor layer 50, or part of the n-type nitride semiconductor layer 30 and the p-type nitride semiconductor layer 50 can be made of the Mg Zn O (O≤a≤l) layer. a 1-a
[49] As discussed earlier, in accordance with the present invention, the semiconductor light emitting device including the Al x Ga y In 1-x-y N (O≤x≤ 1 , O≤y ≤ 1 , O≤x+y ≤ 1 ) well layer can be expanded to the semiconductor light emitting device in which the n-type nitride semiconductor layer and the p-type nitride semiconductor layer which contacts the active layer or a n-type nitride semiconductor layer and a p-type nitride semiconductor layer that is a part of them is made of the Mg a Zn 1-a O (O≤a≤ 1) layer. [50] Although the preferred embodiments of the present invention have been described, it is understood that the present invention should not be limited to these preferred embodiments but various changes and modifications can be made by one skilled in the art within the spirit and scope of the present invention as hereinafter claimed.

Claims

Claims
[1] A semiconductor light emitting device comprising a plurality of semiconductor layers having an active layer generating light by recombination of an electron and a hole, wherein the active layer includes an Al x Ga y In 1-x-y N (O≤x≤l, O≤y≤l, 0<x+y≤l) well layer and a Mg a Zn 1-a O (O≤a≤l) barrier layer.
[2] The semiconductor light emitting device of claim 1, wherein an energy band gap of the Mg a Zn 1-a O (0<a< 1) barrier layer is larger than that of the Al x Ga y In 1-x-y N
(O≤x≤l, O≤y≤l, O≤x+y≤l) well layer.
[3] The semiconductor light emitting device of claim 1, wherein a lattice constant of the Al Ga In N (O≤x≤ 1 , O≤y ≤ 1 , O≤x+y ≤ 1 ) well layer matches with a lattice x y 1-x-y constant of the Mg Zn O (O≤a≤ 1) barrier layer. a 1-a
[4] The semiconductor light emitting device of claim 1, wherein the active layer is formed by alternately stacking the Al Ga In N (O≤x≤ 1 , O≤y ≤ 1 , O≤x+y ≤ 1 ) x y 1-x-y well layer and the Mg Zn O (O≤a≤ 1) barrier layer. a 1-a
[5] The semiconductor light emitting device of claim 1, wherein the device includes a substrate is selected from the group consisting of Al O , Si, SiC, ZnO, GaN, GaAs, InP, SiGe, Glass and LNBO substrates.
[6] The semiconductor light emitting device of claim 1, wherein the Al Ga In N x y 1-x-y
(O≤x≤l, O≤y≤l, O≤x+y≤l) well layer is doped with a dopant, and the dopant is at least one selected from the group consisting of Si, Zn, C, Mg, Be, Ca, Ge, Sn, O, S, Se and Te.
[7] The semiconductor light emitting device of claim 1, wherein the Mg a Zn 1-a O
(O≤a≤l) barrier layer is doped with a dopant, and the dopant is at least one selected from the group consisting of Si, Zn, C, Mg, Be, Ca, Ge, Sn, O, S, Se and Te.
[8] The semiconductor light emitting device of claim 1, wherein the plurality of semiconductor layers comprise a nitride semiconductor layer containing Al m Ga n
In N (0≤m≤ l, 0≤n≤l, 0≤m+n≤ l). l-m-n
[9] The semiconductor light emitting device of claim 1, wherein the plurality of semiconductor layers comprise an oxide semiconductor layer containing Mg Zn O (O≤r≤l).
[10] A semiconductor light emitting device comprising; a substrate, a buffer layer epitaxially grown on the substrate, an n-type nitride semiconductor layer epitaxially grown on the buffer layer, an active layer being epitaxially grown on the n-type nitride semiconductor layer, and including an Al Ga In N (O≤x≤l, O≤y≤l, O≤x+y≤l) well layer and a Mg x y 1-x-y a
Zn O (O≤a≤ 1 ) barrier layer, l-a a p-type nitride semiconductor layer epitaxially grown on the active layer, a p-side electrode formed on the p-type nitride semiconductor layer and an n-side electrode formed on the n-type nitride semiconductor layer exposed by mesa-etching the p-type nitride semiconductor layer and the active layer.
[11] The semiconductor light emitting device of claim 10, wherein the Al Ga In N x y 1-χ-y (O≤x≤l, O≤y≤l, O≤x+y≤l) well layer has a thickness of 5 A to 5000A.
[12] The semiconductor light emitting device of claim 10, wherein the Mg Zn O
(O≤a≤l) barrier layer has a thickness of 5A to 10000A.
[13] A semiconductor light emitting device comprising a plurality of semiconductor layers including an active layer generating light by recombination of an electron and a hole, wherein the device includes the active layer including an Al x Ga y In 1-x-y
N (O≤x≤l, O≤y≤l, O≤x+y≤l) well layer, and a Mg Zn l-a O (O≤a≤l) layer adjacent to the active layer.
[14] The semiconductor light emitting device of claim 13, wherein the Al x Ga y In 1-x-y N
(O≤x≤l, O≤y≤l, O≤x+y≤l) well layer of the active layer is adjacent to the Mg a
Zn l-a O (O≤a≤l) layer.
[15] The semiconductor light emitting device of claim 13, wherein the Mg a Zn l-a O
(O≤a≤l) layer is doped with an n-type dopant. [16] The semiconductor light emitting device of claim 13, wherein the Mg Zn O a l-a
(O≤a≤l) layer is doped with a p-type dopant.
PCT/KR2006/003363 2005-08-25 2006-08-25 Semiconductor light emitting device WO2007024122A1 (en)

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JP2002329887A (en) * 2001-04-27 2002-11-15 Shin Etsu Handotai Co Ltd Method for manufacturing light-emitting element
JP2004153062A (en) * 2002-10-31 2004-05-27 Shin Etsu Handotai Co Ltd Zn-based semiconductor light emitting element and its manufacturing method
JP2004193270A (en) * 2002-12-10 2004-07-08 Sharp Corp Oxide semiconductor light emitting element
KR20050055916A (en) * 2003-12-09 2005-06-14 삼성전기주식회사 Nitride semiconductor light emitting device and method of manufacturing the same

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2002170993A (en) * 2000-11-30 2002-06-14 Shin Etsu Handotai Co Ltd Light emitting element and its fabricating method, visible light emitting device
JP2002329887A (en) * 2001-04-27 2002-11-15 Shin Etsu Handotai Co Ltd Method for manufacturing light-emitting element
JP2004153062A (en) * 2002-10-31 2004-05-27 Shin Etsu Handotai Co Ltd Zn-based semiconductor light emitting element and its manufacturing method
JP2004193270A (en) * 2002-12-10 2004-07-08 Sharp Corp Oxide semiconductor light emitting element
KR20050055916A (en) * 2003-12-09 2005-06-14 삼성전기주식회사 Nitride semiconductor light emitting device and method of manufacturing the same

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