TWI792190B - Light emitting element - Google Patents

Abstract

The present invention proposes a light-emitting element, which at least includes: a first conduction type semiconductor including a lower confinement layer; an active layer arranged above the lower confinement layer; a second conduction type semiconductor including an upper confinement layer, and the upper confinement layer is disposed on the active layer. Above the layer; wherein, the active layer has a multi-quantum well structure, and the multi-quantum well structure is composed of a plurality of stacked pairs repeatedly stacked, each stacked pair includes a well layer and an energy barrier layer, and the energy barrier layer has a gradual composition, and a gradual composition The energy gap of the barrier layer is varied linearly between the energy gap of the lower confining layer and the energy gap of the well layer. The invention can improve the quantum efficiency of the active layer to increase the brightness of the whole light-emitting element, and delay electrons passing through the active layer to increase the light generation rate.

Description

Light emitting element

The present invention relates to a multiple quantum well with a barrier layer of graded composition and a semiconductor element using the multiple quantum well, especially a light-emitting element in an optical semiconductor element.

Optical semiconductor elements such as light-emitting elements include light-emitting diodes (Light-emitting diodes, LEDs) and laser diodes (Laser Diodes, LDs). Surface or p-i-n junction, in order to achieve the purpose of light. Please refer to Figure 1. The light-emitting element (such as LED) in the conventional conventional technology is formed by epitaxy, and its structure includes from bottom to top: substrate (Substate) 1, distributed Bragg reflector (distributed Bragg reflector, DBR) layer 2, lower cladding layer (lower cladding layer) 3, lower confinement layer (confinement layer) LC, active layer (active layer) 4, upper confinement layer UC, upper cladding layer (upper cladding layer) 5 and window The window layer 6 is a lower electrode 8 under the substrate 1 , and an upper electrode 7 is formed on the window layer 6 . The lower electrode 8, the substrate 1, the distributed Bragg reflection layer 2, and the lower cladding layer 3 are of the first conductivity type, such as n-type, and the upper electrode 7, the upper cladding layer 5, and the window layer 6 are of the second conductivity type, such as p-type, The lower confinement layer LC, the active layer 4 and the upper confinement layer UC are undoped.

Generally speaking, the active layer 4 is a light-emitting layer with a multiple quantum well structure. The multiple quantum wells are composed of a plurality of stacked pairs 40 that are repeatedly stacked. Each stacked pair 40 includes a well layer. )41 and energy barrier layer (barrier layer)42. For example, the material of the well layer 41 is indium gallium phosphide (InGaP), In _0.5 Ga _0.5 P, with a thickness of 10-15 angstroms (Å), and an energy band gap of 1.805 eV. The energy barrier layer 42 is made of aluminum gallium indium phosphide (AlGaInP), Al _0.7 Ga _0.3 InP, with a thickness of 25 angstroms and an energy gap of 2.249 eV. Please also refer to FIG. 2A , the energy band diagram of the multiple quantum wells in the active layer 4 . It can be clearly seen from FIG. 2A that the width from the head H1 to the bottom H2 of the well layer 41 is consistent, so the number of carriers (electrons/holes) that can be accommodated in the well H of the well layer 41 is also limited. In other words, the carrier recombination rate of H in the well is limited, so the quantum efficiencies of the well layer 41 and the active layer 4 are also limited, and the brightness of the entire light-emitting element is limited and cannot be improved.

Based on the factor that the moving speed of holes is lower than that of electrons, please refer to Figure 2B together, which shows that the electron/hole recombination (recombination) region in the active layer 4 of the traditional light-emitting device is biased to concentrate near the upper confinement layer UC area, and the area of the electron/hole recombination area is small. In other words, only part of the quantum wells biased towards the upper confinement layer UC in the multiple quantum wells are used, so the quantum efficiency of the active layer 4 is also limited.

Traditional light-emitting devices still have problems of reliability and lifetime. Please refer to Figure 3 together. Since the materials of the lower confinement layer LC, upper confinement layer UC and energy barrier layer 42 are all Al _0.7 Ga _0.3 InP, and can Both gaps are 2.249eV, and because the moving speed of electrons is faster than that of holes, some electrons will quickly gather in a large amount in the p-type metal from the lower confinement layer LC on the left through the active layer 4 and the upper confinement layer UC. Electrode Type Top Electrode 7 . Electrons passing through the active layer 4 quickly leads to a decrease in light generation rate, which reduces the reliability of the light-emitting element, and the accumulation of electrons in the p-type metal electrode also causes damage to the p-type metal electrode, which shortens the life of the light-emitting element.

In view of this, the object of the present invention is to provide a light-emitting element, which can increase the quantum efficiency of the active layer to enhance the brightness of the entire light-emitting element, and delay electrons from passing through the active layer to improve the light generation rate, and avoid damage to the p-type metal electrode And improve the life of the light-emitting element.

A light-emitting element of the present invention at least includes: a first conduction type semiconductor including a lower confinement layer; an active layer disposed above the lower confinement layer; and a second conduction type semiconductor including an upper confinement layer, The upper confinement layer is disposed above the active layer; wherein, the active layer has a multiple quantum well structure, and the multiple quantum well structure is composed of a plurality of stacked pairs stacked repeatedly, and each stacked pair includes a well layer and an energy barrier layer, the energy barrier layer has a graded composition that changes the energy gap of the energy barrier layer in a linear manner between the energy gap of the lower confinement layer and the energy gap of the well layer; the graded composition In the barrier layer, the thickness across the barrier layer decreases in a linear fashion towards the upper confinement layer.

In another embodiment, the material of the lower confinement layer is Al _x Ga _1-x InP, where 0<x<1; the material of the barrier layer is Al _z Ga _1-z InP, where 0≤z<1 ; and, 0≤z≤x.

In another embodiment, the energy gap of the upper confinement layer is higher than the energy gap of the lower confinement layer.

In another embodiment, the material of the lower confinement layer is _{AlxGa1 -} xInP, where 0<x<1; the material of the upper confinement layer is _{AlyGa1 -} yInP, where 0<y≤1 , and y>x.

In another embodiment, the material of the lower confinement layer is Al _x Ga _1-x InP, where 0<x<1; the material of the barrier layer is Al _z Ga _1-z InP, where 0≤z<1 ; and, 0≤z≤x.

In another embodiment, the second conductivity type semiconductor further includes an upper cladding layer, and a heavily doped hole conduction layer is disposed between the upper cladding layer and the upper confinement layer.

Please refer to Fig. 4 at first, a kind of light-emitting element (Light-emitting diode, light-emitting element) 100 of the present invention, this light-emitting element 100 can be light-emitting diode (Light-emitting diode, LED) and laser diode (Laser) Diode, LD). In order to facilitate understanding of the spirit of the present invention, the following embodiments take the structure of an LED as an example, but those skilled in the art should understand that the spirit and structure of the present invention are also applicable to LDs. The light-emitting element 100 comprises at least: a first electrode 10; a substrate 11, the substrate 11 is in contact with the first electrode 10, and the substrate 11 can be arranged above or below the first electrode 10; a distributed Bragg reflection Mirror (DBR) layer 12, the DBR layer 12 is arranged on the top of the substrate 11, the DBR layer 12 can be in contact with the upper surface of the substrate 11; a lower cladding layer 13, the lower cladding layer 13 is arranged on the DBR layer 12, the lower cladding layer 13 can be in contact with the upper surface of the DBR layer 12; the lower confinement layer 1_LC, the lower confinement layer 1_LC is arranged above the lower cladding layer 13, and the lower confinement layer 1_LC can be in contact with the The upper surface of the lower cladding layer 13 is in contact; an active layer 14, the active layer 14 is arranged above the lower confinement layer 1_LC, and the active layer 14 can be in contact with the upper surface of the lower confinement layer 1_LC; an upper confinement layer 1_UC , the upper confinement layer 1_UC is disposed above the active layer 14, the upper confinement layer 1_UC can be in contact with the upper surface of the active layer 14; an upper cladding layer 15, the upper cladding layer 15 is disposed on the upper confinement layer 1_UC, the upper cladding layer 15 can be in contact with the upper surface of the upper confinement layer 1_UC; a window layer 16, the window layer 16 is arranged above the upper cladding layer 15, and the window layer 16 can be in contact with the upper confinement layer 1_UC The upper surface of the cladding layer 15 is in contact with a second electrode 17 , the second electrode 17 is disposed above the window layer 16 , and the second electrode 17 can be in contact with the window layer 16 . In other words, the structure of the light-emitting element 100 is sequentially formed by epitaxial technology from bottom to top: the substrate 11, the DBR layer 12, the lower cladding layer 13, the lower confinement layer 1_LC, the active layer 14, The upper confinement layer 1_UC, the upper cladding layer 15 and the window layer 16 are, for example, formed by molecular beam epitaxy (Molecular Beam Epitaxy, MBE), metal organic vapor phase epitaxy (metal organic vapor phase epitaxy, MOPVE), Low pressure vapor phase epitaxial method (LPMOVPE) or Metal Organic Chemical Vapor Deposition (MOCVD) and other related technologies are formed in-situ in a chamber.

The substrate 11 is a substrate of a first conductivity type, such as n-type gallium arsenide (GaAs), with a thickness between 300 μm and 350 μm. The DBR layer 12 is a first conductive type DBR layer, such as an n-type DBR layer, and the DBR layer 12 may be aluminum gallium arsenide (AlGaAs). The lower cladding layer 13 is a first conductive cladding layer, such as an n-type cladding layer, and the lower cladding layer 13 may be aluminum indium phosphide (AlInP). The material of the lower confinement layer 1_LC may be _{AlxGa1 -} xInP, where 0<x<1. The active layer 14 is a light-emitting layer, and the structure and materials of the active layer 14 will be described later. The material of the upper confinement layer 1_UC may be _{AlyGa1 -yInP} , where 0<y≤1. The upper cladding layer 15 is a second conductive cladding layer, such as a p-type cladding layer, and the upper cladding layer 15 may be aluminum indium phosphide (AlInP). The window layer 16 is a second conduction type window layer, such as a p-type window layer, and the window layer 16 has a wider or indirect (indirect) energy gap (energy gap) and higher conductivity. 16 may be gallium phosphide (GaP), gallium arsenide phosphide (GaAsP) or aluminum gallium arsenide (AlGaAs). The first electrode 10 is a first conductivity type electrode, such as an n-type electrode; the second electrode 17 is a second conductivity type electrode, such as a p-type electrode; the n-type electrode can be a gold-germanium-nickel (AuGeNi) alloy , and the p-type electrode can be beryllium gold (BeAu) alloy. In other words, when the first conductivity type is n-type, the second conductivity type is p-type; or, when the first conductivity type is p-type, the second conductivity type is n-type. In other words, the substrate 11 , the DBR layer 12 and the lower cladding layer 13 constitute a semiconductor of the first conduction type, and the upper cladding layer 15 and the window layer 16 constitute a semiconductor of the second conduction type. The lower confinement layer 1_LC, the active layer 14 and the upper confinement layer 1_UC are undoped. In other words, the light emitting device 100 sequentially includes from bottom to top: the first conductive type semiconductor, the active layer 14 and the second conductive type semiconductor.

The active layer 14 is a light-emitting layer with a multiple quantum well structure. The multiple quantum well structure is composed of a plurality of stacked pairs 141 repeatedly stacked. Each stacked pair 141 includes a well layer 1411 and an energy barrier layer 1412 . For example, the material of the well layer 1411 is indium gallium phosphide (InGaP), In _w Ga _1-w P, where 0<w<1; the material of the barrier layer 1412 is aluminum gallium indium phosphide (AlGaInP), Al _z Ga _1-z InP, where 0≤z<1.

The energy barrier layer 1412 has a graded composition (such as Al), and the graded composition (Al) changes the energy barrier layer 1412 linearly between the energy gap of the lower confinement layer 1_LC and the energy gap of the well layer 1411. Energy gap. The graded composition (Al) decreases in the barrier layer 1412 in a linear manner across the thickness of the barrier layer 1412 and towards the upper confinement layer 1_UC. For example, please also refer to Fig. 5, the material of the lower confinement layer 1_LC can be Al _x Ga _1-x InP, where 0<x<1 and x=0.7 (in this case, Al _0.7 Ga _0.3 InP), the lower confinement layer The energy gap of the confinement layer 1_LC is 2.249eV. The well layer 1411 has a thickness of 10-15 angstroms (Å), and w=0.5 (In _0.5 Ga _0.5 P at this time), and the energy gap of the well layer 1411 is 1.805eV. The energy barrier layer 1412 has a thickness of 25 angstroms. When z=0 (Ga _1.0 InP at this time), the energy barrier layer 1412 has an energy gap of 1.805eV (which is the same as the well layer 1411's energy gap of 1.805eV) ; When z=0.7, the energy gap of the energy barrier layer 1412 is 2.249eV (this is the same as the energy gap of the lower confinement layer 1_LC of 2.249eV). The z value of the graded composition (Al) in the energy barrier layer 1412 is from z=0.7 relatively close to the lower confinement layer 1_LC, to cross the thickness of the energy barrier layer 1412 and towards the direction of the upper confinement layer 1_UC , and decreases linearly to z=0. In other words, the z value of the graded composition (Al) in the energy barrier layer 1412 is derived from the lower surface of the energy barrier layer 1412 relatively close to the lower confinement layer 1_LC at z=0.7 (in this case, Al _0.7 Ga _0.3 InP, equivalent to In the lower confinement layer 1_LC x=0.7), to traverse the thickness of the energy barrier layer 1412 and towards the direction of the upper confinement layer 1_UC, and reduce to z= 0 (Ga _1.0 InP at this time), 0≤z≤x. In other words, the graded composition (Al) makes the energy gap of the energy barrier layer 1412 change in a linear manner between the energy gap of the lower confinement layer 1_LC and the energy gap of the well layer 1411 . It can be clearly seen from Fig. 5 that the width of the well head H1' of the well layer 1411 is greater than the width of the bottom H2', so the carrier in the well H' of the well layer 1411 of the light-emitting element 100 of the present invention can accommodate ( The number of electrons/holes) is also more than the well layer of traditional light-emitting elements. In other words, the carrier recombination rate and quantum efficiency of H′ in the well layer 1411 are improved, and thus the brightness of the light-emitting device 100 of the present invention is improved.

The energy gap of the upper confinement layer 1_UC may be higher than that of the lower confinement layer 1_LC. For example, the material of the upper confinement layer 1_UC can be _{AlyGa 1-y} InP, where 0<y≤1 and y>x, and for example y=1 (Al _1.0 InP at this time), the energy of the upper confinement layer 1_UC The gap is 2.275eV, which is higher than the energy gap of 2.249eV of Al _0.7 Ga _0.3 InP of the lower confinement layer 1_LC. At this time, even if the moving speed of the electrons is greater than that of the holes, when part of the electrons go from the lower confinement layer 1_LC on the left side to the upper confinement layer 1_UC through the active layer 14, due to the energy gap of the upper confinement layer 1_UC ( 2.275eV) higher than the energy gap 2.249eV of the Al _0.7 Ga _0.3 InP of the lower cladding layer 13 to form an energy gap G (please also refer to Figure 6), the energy gap G makes some electrons advance in The upper confinement layer 1_UC is hindered from concentrating between the upper confinement layer 1_UC and the active layer 14 and will not largely collect in the second electrode 17 of p-type metal electrode type. Since the electrons are collected between the upper confinement layer 1_UC and the active layer 14, the light generation rate is improved and the usage rate of a part of the multiple quantum well structure of the active layer 14 close to the upper confinement layer 1_UC is also increased. The quantum efficiency, brightness and reliability of the light-emitting element 100 of the invention are also improved; and because the collection of electrons in the p-type metal electrode is reduced, the damage to the p-type metal electrode is also reduced, so that the life (including brightness) of the light-emitting element 100 of the present invention is reduced. life and voltage life) increase.

Another way to increase the carrier recombination rate and improve the internal quantum efficiency of the active layer 14, please refer to FIG. 7, is to set between the upper cladding layer 15 and the upper confinement layer 1_UC in the previous embodiment Also a heavily doped hole conduction layer C of Al _1.0 InP, which is doped with carbon tetrabromide (CBr ₄ , carbon tetrabromide) at a concentration greater than 1.0×10 ²⁰ atoms/cm ³ . Compared with the traditional light-emitting element in FIG. 2B, the light-emitting element 100 in FIG. 7 of the present invention can quickly generate holes from the upper cladding layer 15 due to the setting of the heavily doped hole conducting layer C. Therefore, the holes can move deeper into the active layer 14 and move toward the lower confinement layer 1_LC, which makes the area of the electron/hole recombination region larger. In other words, in the multi-quantum well structure of the active layer 14, some of the quantum wells biased towards the upper confinement layer 1_UC, some of the quantum wells in the central region, and some of the quantum wells biased towards the lower confinement layer 1_UC are used, so the active layer 14 Quantum efficiency can be significantly improved.

Please refer to FIG. 8A and FIG. 8B together. Of course, the light-emitting element 100 of the present invention can also be in the multiple quantum well structure in the active layer 14. Only part of the quantum well structure adopts the aforementioned gradient composition, and the rest of the quantum well structure Then a conventional quantum well structure with non-gradient composition as shown in FIG. 2A can be used.

The light-emitting element of the present invention uses a graded composition in the energy barrier layer in the active layer, so that the graded composition changes the energy gap of the energy barrier layer in a linear manner between the energy gap of the lower confinement layer and the energy gap of the well layer, so that the energy gap of the well layer The carrier recombination rate and quantum efficiency in the well are improved, and thus the brightness of the light-emitting element of the present invention is improved. The energy gap of the upper confinement layer of the light-emitting element of the present invention is higher than that of the lower confinement layer, so electrons are collected between the upper confinement layer and the active layer, which improves the light generation rate and the utilization rate of the multiple quantum well structure of the active layer Therefore, the quantum efficiency, brightness and reliability are also improved; and because the collection of electrons in the p-type metal electrode is reduced, the damage to the p-type metal electrode is also reduced, so that the life of the light-emitting element of the present invention is increased. The light-emitting element of the present invention is also provided with a heavily doped hole conduction layer between the upper cladding layer and the upper confinement layer, and the holes from the upper cladding layer can quickly enter the active layer, so that the holes can go deeper into the active layer The area of the electron/hole recombination region becomes larger, and the quantum efficiency of the active layer is significantly improved.

But what is described above is only a preferred embodiment of the present invention, and should not limit the scope of implementation of the present invention with this, that is, all simple equivalent changes and modifications made according to the patent scope of the present invention and the new description content, All still belong to the scope covered by the patent of the present invention. In addition, any embodiment or scope of claims of the present invention does not necessarily achieve all the objectives or advantages or features disclosed in the present invention. In addition, the abstract and the title are only used to assist the search of patent documents, and are not used to limit the scope of rights of the present invention. In addition, terms such as "first" and "second" mentioned in this specification or the scope of the patent application are only used to name elements (elements) or to distinguish different embodiments or ranges, and are not used to limit the number of elements. upper or lower limit.

[Tradition] 1: base 2: DBR layer 3: Lower cladding layer 4: Active layer 40: stacked pairs 41: well layer 42: Barrier layer 5: Upper cladding layer 6: window layer 7: Upper electrode 8: Bottom electrode H: Well H1: wellhead H2: bottom of the well LC: Lower Confined Layer UC: Upper Confined Layer [this invention] 100: light emitting element 10: The first electrode 11: Base 12: DBR layer 13: Lower cladding layer 14:Active layer 141: stacked pair 1411: well layer 1412: barrier layer 15: Upper cladding layer 16: window layer 17: Second electrode 1_LC: lower limited layer 1_UC: Upper Confinement Layer C: Heavily doped hole conduction layer G: energy gap gap H': inside the well H1': wellhead H2': Bottom of the well

Fig. 1 is a structural cross-sectional view of a conventional light-emitting element. FIG. 2A is a schematic diagram of the energy bands of the multiple quantum well structure of the active layer of a conventional light-emitting device. FIG. 2B is a schematic diagram of the electron/hole recombination region of the active layer of a conventional light-emitting device. Figure 3 is a schematic diagram of the collection of electrons in a metal electrode in a conventional light-emitting device. Fig. 4 is a cross-sectional view of the structure of the light-emitting element of the present invention. Fig. 5 is a schematic diagram of the energy bands of the multiple quantum well structure of the active layer of the light-emitting device of the present invention. Fig. 6 is a schematic diagram showing that part of the electrons are hindered by the upper confinement layer due to the difference in energy gap of the light-emitting device of the present invention. Fig. 7 is a schematic diagram of the electron/hole recombination region provided with the heavily doped hole conducting layer of the light-emitting element of the present invention. Fig. 8A is a schematic diagram (1) of the energy bands of the partial quantum well structure of the active layer of the light-emitting element of the present invention using graded composition. Fig. 8B is a schematic diagram (2) of the energy bands of the partial quantum well structure of the active layer of the light-emitting element of the present invention using graded composition.

14:Active layer

141: stacked pair

1411: well layer

1412: barrier layer

1_LC: lower limited layer

1_UC: Upper Confinement Layer

H': inside the well

H1': wellhead

H2': Bottom of the well

Claims (6)

A light emitting element, at least comprising: A semiconductor of the first conductivity type, including a lower confinement layer (1_LC); an active layer (14) disposed above the lower confinement layer (1_LC); and A second conductivity type semiconductor, comprising an upper confinement layer (1_UC), the upper confinement layer (1_UC) is arranged above the active layer (14); Wherein, the active layer (14) has a multiple quantum well structure, and the multiple quantum well structure is composed of a plurality of stacked pairs (141) repeatedly stacked, and each of the stacked pairs (141) includes a well layer (1411) and an energy barrier layer (1412) having a graded composition linearly between the energy gap of the lower confinement layer (1_LC) and the energy gap of the well layer (1411) changing the energy gap of the energy barrier layer (1412); the graded composition in the energy barrier layer (1412), across the thickness of the energy barrier layer (1412) and towards the direction of the upper confinement layer (1_UC) Decreases in a linear fashion. The light-emitting element as claimed in item 1, wherein the material of the lower confinement layer (1_LC) is Al _x Ga _1-x InP, where 0<x<1; the material of the energy barrier layer (1412) is Al _z Ga _{1 -z} InP, where 0≤z<1; and, 0≤z≤x. The light-emitting device according to claim 1, wherein the energy gap of the upper confinement layer (1_UC) is higher than the energy gap of the lower confinement layer (1_LC). The light-emitting element as claimed in item 3, wherein the material of the lower confinement layer (1_LC) is _{AlxGa1 -} xInP, where 0<x<1; the material of the upper confinement layer ( _{1_UC} ) is _{AlyGa1 -} yInP, where 0<y≤1, and y>x. The light-emitting element as claimed in item 4, wherein the material of the lower confinement layer (1_LC) is Al _x Ga _1-x InP, where 0<x<1; the material of the energy barrier layer (1412) is Al _z Ga _{1 -z} InP, where 0≤z<1; and, 0≤z≤x. The light-emitting device as described in Claim 5, wherein the second conduction type semiconductor further comprises an upper cladding layer (15), and a heavily doped hole conduction layer (C) is arranged on the upper cladding layer (15) and the between the upper confinement layer (1_UC).

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