JP2006040998A - Semiconductor light emitting device and epitaxial wafer therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high luminance semiconductor light emitting device by constructing a light reflection layer from first and second light reflection layers in the semiconductor light emitting device containing the light reflection layer to widen a light reflection band compared with the conventional one. <P>SOLUTION: The semiconductor light emitting device comprises at least a conductive semiconductor substrate 1, the light reflection layer (3 and 10) formed on the principal plane of the semiconductor substrate 1, and a light emittier (4, 5, and 6) including an active layer 5 containing a pn junction grown on the light reflection layer. The light reflection layer consists of a first light reflection layer 3 whose central wavelength of reflection spectrum is set to the central wavelength of the emission spectrum emitted from the light emitting portion or shorter; and a second light reflection layer 10 having a different central wavelength of reflection spectrum in a visible wavelength band other than the central wavelength of reflection spectrum of the first light reflection layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high-luminance semiconductor light-emitting device including a high-efficiency light reflecting layer having a high reflectance and an epitaxial wafer for the semiconductor light-emitting device.

  In recent years, the demand for high-intensity semiconductor light-emitting devices manufactured using an epitaxial wafer for AlGaInP-based light-emitting devices, in particular, light-emitting diodes (LEDs) has been greatly increased. Conventional applications were electric bulletin boards, display lamps for consumer electronics, etc., but recent major applications are traffic signals, automotive lamps, etc., which are extremely bright LEDs in recent years. The application range has expanded rapidly with the development. In particular, an AlGaInP-based semiconductor is a direct transition semiconductor having the largest band gap among III-V group compound semiconductors excluding nitrides. When a light emitting element is manufactured using the semiconductor, an AlGaInP-based semiconductor has a light emission band of 560 nm to 660 nm. Since very high brightness can be obtained, research and development are still underway.

  At present, the internal quantum efficiency of high-brightness LEDs that are generally manufactured and sold is already extremely high for all manufacturers, and in order to achieve higher brightness than ever, external quantum efficiency is improved over internal quantum efficiency. Is extremely effective.

  FIG. 4 shows a typical structure of a red band AlGaInP-based LED. All epitaxial layers are grown by metal organic chemical vapor deposition (MOVPE).

In the LED in FIG. 4, a buffer layer 2 made of n-type GaAs is grown on a semiconductor substrate 1 made of n-type GaAs, and an n-type light reflection layer 3 is laminated thereon. The n-type light reflecting layer 3 plays a role of reflecting light from the active layer 5 toward the semiconductor substrate 1 made of n-type GaAs in the opposite direction, so that the light is reflected on the semiconductor substrate 1 made of n-type GaAs. The external quantum efficiency of the LED can be increased without being absorbed. For example, the n-type light reflecting layer 3 has a configuration in which an n-type Al _0.4 Ga _0.6 As layer and an n-type Al _0.5 In _0.5 P layer are stacked as a pair. Here, the film thicknesses of the n-type Al _0.4 Ga _0.6 As layer and the n-type Al _0.5 In _0.5 P layer are λ / (4 × n1) with respect to the emission wavelength λ, where the refractive indexes are n1 and n2, respectively. ), Λ / (4 × n2).

Here, Patent Document 1 discloses a method for solving an infrared light emission problem in an LED using a GaAs layer as a part of a light reflection layer in a semiconductor light emitting device. At the same time, by making one of the pair of materials constituting the light reflecting layer the same composition as the light emitting layer side of the active layer, the light reflecting layer is excited by the light emitted from the active layer and emits light. A method is disclosed in which the wavelength of the emitted light is the same as the wavelength emitted by the active layer, and the light emission output is generally increased.
Japanese Patent Laid-Open No. 10-290026

  However, even if the structure in Patent Document 1 is used, it does not efficiently reflect all the light emitted from the active layer, and it is difficult to bring about an epoch-making effect.

  Accordingly, an object of the present invention is to provide a semiconductor light emitting device having a light reflection layer, the light reflection layer being composed of a first light reflection layer and a second light reflection layer, and having a wider light reflection band than before. Accordingly, it is an object to provide a semiconductor light emitting device with high brightness.

  In order to achieve the above object, the present invention is configured as follows.

  The semiconductor light-emitting device according to the first aspect of the present invention includes a conductive semiconductor substrate, a light reflecting layer provided on the main surface of the semiconductor substrate, and an active structure having a pn junction grown on the light reflecting layer. In the semiconductor light emitting device including at least a light emitting portion including a layer, the light reflecting layer has a wavelength equal to or shorter than a center wavelength of an emission spectrum of light emitted from the light emitting portion. A first light reflecting layer having a center wavelength set, and a second light reflecting layer having a center wavelength of a different reflection spectrum in a visible wavelength region other than the center wavelength of the reflection spectrum of the first light reflecting layer. It is characterized by that.

  As a method for forming an electrode in the semiconductor light emitting device, a mode in which an electrode is partially formed on a light emitting portion and an electrode is formed on the entire surface or partially on the back surface of a semiconductor substrate is common.

  The semiconductor light-emitting element includes not only one in which each of the first reflective layer and the second reflective layer is formed, but also one in which a plurality of first reflective layers and second reflective layers are formed.

  According to a second aspect of the present invention, in the semiconductor light emitting device according to the first aspect, the light reflection layer has a wavelength that is equal to or shorter than a center wavelength of an emission spectrum of light emitted from the light emitting portion. Second light having a first light reflecting layer in which the center wavelength of the reflection spectrum is set, and having the center wavelength of the reflection spectrum set longer than the center wavelength of the emission spectrum of the light emitted from the light emitting unit A reflection layer is provided.

  According to a third aspect of the present invention, in the semiconductor light-emitting device according to the first or second aspect, the number of pairs of semiconductor layers constituting the first light reflecting layer is 5 pairs or more and 30 pairs or less.

  According to a fourth aspect of the present invention, in the semiconductor light emitting device according to the third aspect, the number of pairs of semiconductor layers constituting the second light reflecting layer is 1 pair or more and 20 pairs or less.

  According to a fifth aspect of the present invention, in the semiconductor light emitting device according to any one of the first to fourth aspects, the material of the semiconductor layer constituting the first light reflecting layer and the second light reflecting layer is GaAs, AlGaAs, AlAs. , AlGaInP, GaInP, or AlInP.

According to a sixth aspect of the present invention, in the semiconductor light emitting device according to any one of the first to fifth aspects, the first light reflecting layer and the second light reflecting layer are each composed of a combination of a low refractive index portion and a high refractive index portion. The material of the low refractive index portion is Al _x Ga _1-x As (where 0.6 ≦ X ≦ 1.0), (Al _Y Ga _1-Y ) _0.5 In _0.5 P (where 0. 6 ≦ Y ≦ 1.0), and the material of the high refractive index portion is Al _x Ga _1-x As (where 0 ≦ X ≦ 0.6), (Al _Y Ga _1-Y ) _0.5 In _0.5 P (where 0 ≦ Y ≦ 0.6).

  According to a seventh aspect of the invention, in the semiconductor light emitting device according to any one of the first to sixth aspects, the semiconductor substrate is made of GaAs or Ge.

  According to an eighth aspect of the present invention, in the semiconductor light emitting device according to any one of the first to seventh aspects, the active layer includes a light emitting layer and a barrier layer having a wider band gap than the light emitting layer. It is characterized by laminating a plurality of layers.

  According to a ninth aspect of the present invention, in the semiconductor light emitting device according to any one of the first to eighth aspects, a current spreading layer made of a metal oxide is formed on the light emitting portion via at least one semiconductor layer. It is characterized by.

  An epitaxial wafer for a semiconductor light-emitting device according to the invention of claim 10 is a conductive semiconductor substrate, a light reflecting layer provided on the main surface of the semiconductor substrate, and a pn junction grown on the light reflecting layer. In the epitaxial wafer for a semiconductor light-emitting device comprising at least a light-emitting portion including an active layer having the light-emitting portion, the light reflecting layer substantially coincides with a center wavelength of an emission spectrum of light emitted from the light-emitting portion, or more Also includes a first light reflection layer in which the center wavelength of the reflection spectrum is set to a short wavelength, and the center wavelength of the reflection spectrum is set to a longer wavelength side than the center wavelength of the emission spectrum of the light emitted from the light emitting unit. The second light reflecting layer is provided.

  According to an eleventh aspect of the present invention, in the epitaxial wafer for a semiconductor light emitting device according to the tenth aspect, the number of pairs of the first light reflecting layers is 5 pairs or more and 30 pairs or less.

  According to a twelfth aspect of the present invention, in the epitaxial wafer for a semiconductor light emitting device according to the eleventh aspect, the number of pairs of the second light reflecting layers is 1 pair or more and 20 pairs or less.

  The invention of claim 13 is the epitaxial wafer for a semiconductor light emitting device according to any one of claims 10 to 12, wherein the semiconductor material constituting the first light reflecting layer and the second light reflecting layer is GaAs, AlGaAs, It is selected from AlAs, AlGaInP, GaInP, and AlInP.

According to a fourteenth aspect of the present invention, in the epitaxial wafer for a semiconductor light emitting device according to any one of the tenth to thirteenth aspects, the first light reflection layer and the second light reflection layer are a low refractive index portion and a high refractive index portion, respectively. And the material of the low refractive index portion is Al _x Ga _1-x As (provided that 0.6 ≦ X ≦ 1.0), (Al _Y Ga _1-Y ) _0.5 In _0.5 P (provided that 0.6 ≦ Y ≦ 1.0), and the material of the high refractive index portion is Al _x Ga _1-x As (where 0 ≦ X ≦ 0.6), (Al _Y Ga _{1 -Y} ) _0.5 In _0.5 P (where 0 ≦ Y ≦ 0.6).

  According to a fifteenth aspect of the present invention, in the epitaxial wafer for a semiconductor light emitting device according to any one of the tenth to fourteenth aspects, a current spreading layer made of a metal oxide is provided on the light emitting portion via at least one semiconductor layer. An epitaxial wafer for a semiconductor light emitting device, characterized by being formed.

<Key points of the invention>
In order to achieve the above object, a semiconductor light emitting device or an epitaxial wafer for a semiconductor light emitting device of the present invention has a structure including at least one first light reflecting layer having a short wavelength design and one or more second light reflecting layers having a long wavelength design. It has become. Here, the first light reflection layer with a short wavelength design is a light reflection whose center wavelength of the reflection spectrum is equal to or shorter than the center wavelength of the emission spectrum of the light emitted from the light emitting unit. Composed of layers. Further, the second light reflecting layer having a long wavelength design is a light reflecting layer having a central wavelength of a different reflection spectrum in a visible wavelength region other than the central wavelength of the reflection spectrum of the first light reflecting layer, preferably from the light emitting unit. The light reflection layer is configured such that the center wavelength of the reflection spectrum is set longer than the center wavelength of the emission spectrum of the emitted light.

  When the first light reflecting layer having the short wavelength design and the second light reflecting layer having the long wavelength design are paired and disposed on the substrate side of the light emitting unit including the active layer having a pn junction, so-called By stagger tuning, light reflection in a wider band than before is practiced, and a semiconductor light emitting device with extremely high luminance can be obtained.

  Here, it is free to select which of the first light reflecting layer with the short wavelength design and the second light reflecting layer with the long wavelength design is the substrate side (lower side). Efficiency is improved when the light reflection layer is on the upper side.

  First of all, as a premise, the material of the low refractive index portion (A layer) and the material of the high refractive index portion (B layer) used for the light reflecting layer (DBR) is the active layer, if only speaking of the band gap. It is composed of a material that is much larger than the energy of the emitted light and a material that has almost the same energy (band gap) as that of the light (for this reason, even if light absorption occurs in the light reflection layer) Infrared is not generated).

  Next, the design of the light reflection layer (DBR) is performed by changing the film thickness of the A layer and the B layer when the material is the same in both the long wavelength design and the short wavelength design. In terms of band gap, the long wavelength design DBR and the short wavelength design DBR are equal. The light energy of the active layer is long wavelength = low energy, short wavelength = high energy. Therefore, if the light reflection layer (DBR) is designed to have a long wavelength on the upper side, a long wave is first introduced. However, since the reflection on the short wave side is hardly performed, it passes through this upper DBR (second light reflection layer of long wavelength design) and is reflected by the lower short wavelength design DBR. It will be absorbed by the upper long wavelength design DBR.

  On the other hand, if the first light reflection layer of the short wavelength design is on the upper side, the light having a high energy (short wave light) is reflected first, and the light having a low energy transmitted (long wave light) is first reflected in the lower long wave design. It can be reflected by the two-light reflecting layer. When the light having a small energy and the light having large energy pass through the first light reflecting layer with the short wavelength design on the upper side and go to the second light reflecting layer with the long wave design on the lower side, the constituent materials of the light reflecting layer In relation, light with lower energy has less absorption and naturally has a higher transmittance.

  Therefore, from the above, the reflection efficiency is higher when the first light reflection layer of the short wavelength design is on the upper side in that the absorption loss is suppressed as much as possible. That is, the light emission output is increased. However, although the efficiency is deteriorated, the second light reflecting layer of the long wave design can be positioned on the upper side.

  According to the present invention, the following excellent effects can be obtained.

  The semiconductor light emitting device or the epitaxial wafer for a semiconductor light emitting device of the present invention has a structure including at least one pair of a first light reflecting layer with a short wavelength design and a second light reflecting layer with a long wavelength design. A semiconductor light-emitting element having a wider reflection band than the reflection band of the light reflection layer provided in the semiconductor light-emitting element can be obtained, and higher luminance can be achieved.

  In addition, by applying the metal oxide to the current spreading layer, a semiconductor light emitting device having a luminance equal to or higher than that of the conventional one and drastically reducing manufacturing costs can be obtained.

  Hereinafter, the present invention will be described based on the illustrated embodiments.

  FIG. 1 shows a first embodiment of an epitaxial wafer for a semiconductor light-emitting device according to the present invention. A conductive semiconductor substrate 1 and light reflection provided on the main surface of the substrate via a buffer layer 2 are shown. It comprises at least a light emitting part (4, 5, 6) including a layer (3, 10) and an active layer 5 having a pn junction grown on the light reflecting layer.

  The light reflection layer includes the first light reflection layer 3 that substantially matches the center wavelength of the emission spectrum of the light emitted from the light emitting unit or has a shorter center wavelength of the reflection spectrum than that of the emission spectrum. And at least 1 pair or more of the 2nd light reflection layers 10 in which the center wavelength of the reflection spectrum was set to the long wavelength side rather than the center wavelength of the emission spectrum of the light radiated | emitted from a light emission part are provided. In the case of this embodiment, the first light reflecting layer 3 with a short wavelength design is provided on the upper side (light emitting part side), and the second light reflecting layer 10 with a long wavelength design is provided on the lower side (substrate side).

The first light reflection layer 3 and the second light reflection layer 10 are each configured as a DBR (distributed Bragg reflection layer) in which a low refractive index portion and a high refractive index portion are combined, and the material of the low refractive index portion is Al. _x Ga _1-x As (where 0.6 ≦ X ≦ 1.0), (Al _Y Ga _1-Y ) _0.5 In _0.5 P (where 0.6 ≦ Y ≦ 1.0) The material of the high refractive index portion is Al _x Ga _1-x As (where 0 ≦ X ≦ 0.6), (Al _Y Ga _1-Y ) _0.5 In _0.5 P (where 0 ≦ Y ≦ 0. 6) Either. The number of pairs of semiconductor layers constituting the first light reflecting layer 3 is 5 pairs or more and 30 or less, and the number of pairs of semiconductor layers constituting the second light reflecting layer 10 is 1 pair or more and 20 pairs or less. Note that these light reflecting layers do not use GaAs as a constituent material, and therefore do not emit infrared light.

  FIG. 5 shows a second embodiment of the epitaxial wafer for a semiconductor light emitting device of the present invention. FIG. 5 includes a contact layer 11 and a current spreading layer 12 made of ITO on a p-type cladding layer 6. Is different.

  In order to confirm the effect of the present invention, the semiconductor light emitting devices of the conventional example and Examples 1, 2, and 3 were manufactured as prototypes.

[Conventional example]
A red band LED having the structure shown in FIG. 4 and an emission wavelength of around 640 nm was manufactured.

In the manufacturing process, an n-type GaAs buffer layer 2, an n-type first light reflecting layer 3, an n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P are formed on a semiconductor substrate 1 made of n-type GaAs. An n-type cladding layer 4 made of, an undoped active layer 5, a p-type cladding layer 6 made of p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, and a current spreading layer 7 made of p-type GaP were sequentially grown.

  The growth temperature in the growth by the MOVPE method was 650 ° C. from the buffer layer 2 made of n-type GaAs to the p-type cladding layer 6, and the current spreading layer 8 made of p-type GaP was grown at 660 ° C. Other growth conditions were a growth pressure of 50 Torr, a growth rate of each layer of 0.3 to 1.0 nm / sec, and a V / III ratio of about 200. However, only the V / III ratio of the current spreading layer 7 made of p-type GaP was set to 9.

Incidentally, the V / III ratio mentioned here is the ratio (quotient) when the denominator is the number of moles of a group III material such as TMGa or TMAl and the molecule is the number of moles of a group V material such as AsH ₃ or PH _3. Point to.

Examples of raw materials used in the MOVPE growth include organic metals such as trimethylgallium (TMGa), triethylgallium (TEGa), trimethylaluminum (TMAl), and trimethylindium (TMIn), arsine (AsH ₃ ), and phosphine (PH ₃ A hydride gas such as) was used.

For example, hydrogen selenide (H ₂ Se) was used as an additive material for an n-type layer such as the n-type buffer layer 2. Diethyl zinc (DEZn) was used as the additive material for the conductivity determining impurities of the p-type layer such as the p-type cladding layer 6. In addition, silane (SiH ₄ ), diethyl tellurium (DETe), and dimethyl tellurium (DMTe) can also be used as an additive material for the conductivity determining impurity of the n-type layer. In addition, dimethyl zinc (DMZn) can also be used as a p-type layer additive raw material.

Incidentally, the first light reflecting layer 3 has a structure in which n-type AlAs (about 51 nm) and n-type Al _0.4 GaAs (about 45 nm) are sequentially laminated, and the number of pairs is 15 pairs.

  Then, a circular p-type (surface) electrode 8 having a diameter of 125 μm was formed on the upper surface of the epitaxial wafer in a matrix by a vacuum deposition method. For this p-type electrode, gold / zinc (AuZn) alloy, nickel (Ni), and gold (Au) were deposited in the order of 60 nm, 10 nm, and 1000 nm, respectively. Further, an n-side electrode 9 was formed on the entire bottom surface of the epitaxial wafer. The n-type electrode 8 is formed by depositing gold / germanium (AuGe) alloy, nickel (Ni), and gold (Au) in the order of 60 nm, 10 nm, and 500 nm, respectively, and then alloying the electrodes into an nitrogen gas atmosphere. Medium at 400 ° C. for 5 minutes.

  Then, this epitaxial wafer was processed into a chip shape having a chip size of 300 μm square by a dicing apparatus or the like, and then die bonding and wire bonding were performed to manufacture an LED element.

  In addition, a light reflecting layer applied to the LED shown in the conventional example was epitaxially grown on a semiconductor substrate made of GaAs as a single piece and separately manufactured as a sample for measuring light reflectance. The result of measuring the light reflectance of this sample is shown in FIG.

  As a result of evaluating various characteristics of the LED fabricated as described above, the light emission output was 1.51 mW and the forward operation voltage was 1.93 V (all the evaluation results when energizing 20 mA).

[Example 1]
A red band LED having the structure shown in FIG. 1 and an emission wavelength of around 640 nm was manufactured.

In the manufacturing process, an n-type GaAs buffer layer 2, an n-type second light reflecting layer 10, an n-type first light reflecting layer 3, an n-type are formed on a semiconductor substrate 1 made of n-type GaAs by the MOVPE method. An n-type cladding layer 4 made of (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, an undoped active layer 5, a p-type cladding layer 6 made of p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, and a current made of p-type GaP. Dispersion layer 7 (film thickness 12 μm) was grown sequentially. The growth temperature in the growth by the MOVPE method was 650 ° C. from the buffer layer 2 made of n-type GaAs to the p-type cladding layer 6, and the current spreading layer 8 made of p-type GaP was grown at 660 ° C. Other growth conditions were a growth pressure of 50 Torr, a growth rate of each layer of 0.3 to 1.0 nm / sec, and a V / III ratio of about 200. However, only the V / III ratio of the p-type GaP current dispersion layer 7 was set to 9. Incidentally, the V / III ratio mentioned here is a ratio (quotient) when the denominator is the number of moles of a group III material such as TMGa or TMAl and the molecule is the number of moles of a group V material such as AsH ₃ or PH _3. Point to.

Examples of raw materials used in the MOVPE growth include organic metals such as trimethylgallium (TMGa), triethylgallium (TEGa), trimethylaluminum (TMAl), and trimethylindium (TMIn), arsine (AsH ₃ ), and phosphine (PH ₃ A hydride gas such as) was used.

For example, hydrogen selenide (H ₂ Se) was used as an additive material for the conductivity determining impurities of the n-type layer such as the buffer layer 2 made of n-type GaAs. Diethyl zinc (DEZn) was used as an additive material for the conductivity determining impurities of the p-type layer such as the p-type cladding layer 6. In addition, silane (SiH ₄ ), diethyl tellurium (DETe), and dimethyl tellurium (DMTe) can also be used as an additive material for the conductivity determining impurity of the n-type layer. In addition, dimethyl zinc (DMZn) can be used as an additive material for the conductivity determining impurity of the p-type layer.

Incidentally, the first light reflecting layer 3 has a structure in which a semiconductor layer (about 51 nm) made of n-type AlAs and a semiconductor layer (about 45 nm) made of n-type Al _0.4 Ga _0.6 As are sequentially laminated (DBR: distributed Bragg reflective layer). The number of pairs was 15 pairs.

Further, the second light reflecting layer 10 provided under the first light reflecting layer is formed by sequentially forming a semiconductor layer (about 55 nm) made of n-type AlAs and a semiconductor layer (about 48 nm) made of n-type Al _0.4 Ga _0.6 As. A laminated structure (DBR: distributed Bragg reflection layer) was used, and the number of pairs was 10 pairs.

  Then, a circular p-type (surface) electrode 8 having a diameter of 125 μm was formed on the upper surface of the epitaxial wafer in a matrix by a vacuum deposition method. For this p-type electrode, gold / zinc (AuZn) alloy, nickel (Ni), and gold (Au) were deposited in the order of 60 nm, 10 nm, and 1000 nm, respectively. Further, an n-side electrode 9 was formed on the entire bottom surface of the epitaxial wafer. The n-type electrode 8 is formed by depositing gold / germanium (AuGe) alloy, nickel (Ni), and gold (Au) in the order of 60 nm, 10 nm, and 500 nm, respectively, and then alloying the electrode as an alloy in a nitrogen gas atmosphere. Medium at 400 ° C. for 5 minutes.

  Then, this epitaxial wafer was processed into a chip shape having a chip size of 300 μm square by a dicing apparatus or the like, and further, die bonding and wire bonding were performed to manufacture an LED element.

  In addition, the light reflecting layers (first light reflecting layer and second light reflecting layer) applied to the LED shown in this example are epitaxially grown on a semiconductor substrate made of GaAs as a single sample for light reflectivity measurement. did.

  The light reflectance measurement result of this sample is shown in FIG. According to this measurement result, it can be seen that a light reflection layer having a wider reflection band than the reflectance spectrum of the conventional example (white dots) shown in FIG.

  As a result of evaluating various characteristics of the LED fabricated as described above, the light emission output was 1.65 mW, and the forward operation voltage was 1.94 V (all evaluation results when energized with 20 mA).

  From this result, by using the light reflecting layer shown in this embodiment, it is possible to have a wider reflection band than the conventional light reflecting layer, thereby increasing the light emission output.

[Example 2]
A red band LED having the structure shown in FIG. 1 and an emission wavelength of around 640 nm was manufactured.

In the manufacturing process, an n-type GaAs substrate 1, a buffer layer 2 made of n-type GaAs, an n-type second light reflecting layer 10, an n-type first light reflecting layer 3, an n-type (Al _0.7 An n-type cladding layer 4 made of Ga _0.3 ) _0.5 In _0.5 P, an undoped active layer 5, a p-type cladding layer 6 made of p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, and a current spreading layer 7 made of p-type GaP Were grown sequentially.

  The growth temperature in the growth by the MOVPE method was 650 ° C. from the buffer layer 2 made of n-type GaAs to the p-type cladding layer 6, and the current spreading layer 8 made of p-type GaP was grown at 660 ° C. Other growth conditions were a growth pressure of 50 Torr, a growth rate of each layer of 0.3 to 1.0 nm / sec, and a V / III ratio of about 200.

However, only the V / III ratio of the current spreading layer 7 made of p-type GaP was set to 9. Incidentally, the V / III ratio mentioned here is the ratio (quotient) when the denominator is the number of moles of a group III material such as TMGa or TMAl and the molecule is the number of moles of a group V material such as AsH ₃ or PH _3. Point to.

As a raw material used in the growth by the MOVPE method, for example, trimethylgallium (TMGa), organic metal such as triethylgallium (TEGa), trimethylaluminum (TMAl), trimethylindium (TMIn), arsine (AsH ₃ ), phosphine ( A hydride gas such as PH ₃ ) was used.

For example, hydrogen selenide (H ₂ Se) was used as an additive material for the conductivity determining impurity of the n-type layer such as the n-type buffer layer 2. Diethyl zinc (DEZn) was used as an additive material for the conductivity determining impurities of the p-type layer such as the p-type cladding layer 6. In addition, silane (SiH ₄ ), diethyl tellurium (DETe), and dimethyl tellurium (DMTe) can also be used as an additive material for the conductivity determining impurity of the n-type layer. In addition, dimethyl zinc (DMZn) can be used as an additive material for the conductivity determining impurity of the p-type layer.

Incidentally, the first light reflection layer 3 has a structure (DBR: distributed Bragg reflection layer) in which a semiconductor layer made of n-type AlAs (about 51 nm) and a semiconductor layer made of n-type Al _0.4 GaAs (about 45 nm) are sequentially laminated, The number of pairs was 15 pairs.

Further, at this time, the second light reflecting layer 10 provided under the first light reflecting layer includes a semiconductor layer (about 47 nm) made of n-type AlAs and a semiconductor layer (about 41 nm) made of n-type Al _0.4 Ga _0.6 As. The structure was sequentially laminated (DBR: distributed Bragg reflection layer), and the number of pairs was 10 pairs.

  Then, a circular surface electrode 8 having a diameter of 125 μm was formed in a matrix on the upper surface of the epitaxial wafer by a vacuum deposition method. For this surface electrode, gold / zinc (AuZn) alloy, nickel (Ni), and gold (Au) were deposited in the order of 60 nm, 10 nm, and 1000 nm, respectively. Further, a back electrode 9 was formed on the entire bottom surface of the epitaxial wafer. The back electrode 8 is formed by depositing gold / germanium (AuGe) alloy, nickel (Ni), and gold (Au) in the order of 60 nm, 10 nm, and 500 nm, respectively, and then alloying the electrode into an alloy in a nitrogen gas atmosphere. Performed at 400 ° C. for 5 minutes.

  Thereafter, the epitaxial wafer was processed into a chip shape having a chip size of 300 μm square by a dicing apparatus or the like, and further, die bonding and wire bonding were performed to manufacture an LED element.

  As a result of evaluating various characteristics of the LED fabricated as described above, the light emission output was 1.70 mW, and the forward operation voltage was 1.95 V (all evaluation results when energized with 20 mA).

  From this result, by using the light reflecting layer shown in this embodiment, it is possible to have a wider reflection band than the conventional light reflecting layer, thereby increasing the light emission output.

[Example 3]
A red-band LED having a structure shown in FIG.

In the manufacturing process, an n-type GaAs buffer layer 2, an n-type second light reflecting layer 10, an n-type first light reflecting layer 3, an n-type are formed on a semiconductor substrate 1 made of n-type GaAs by the MOVPE method. N-type cladding layer 4 made of (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, undoped active layer 5, p-type cladding layer 6 made of p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, p-type Al _0.1 A contact layer 11 made of Ga _0.9 As was sequentially grown. The growth temperature in the growth by the MOVPE method is 650 ° C. from the buffer layer 2 made of n-type GaAs to the p-type cladding layer 6, and other growth conditions are a growth pressure of 50 Torr, and the growth rate of each layer is 0.3 to 1.0 nm / sec and the V / III ratio were about 200.

As a raw material used in the growth by the MOVPE method, for example, trimethylgallium (TMGa), organic metal such as triethylgallium (TEGa), trimethylaluminum (TMAl), trimethylindium (TMIn), arsine (AsH ₃ ), phosphine ( A hydride gas such as PH ₃ ) was used.

For example, hydrogen selenide (H ₂ Se) was used as an additive material for the conductivity determining impurities of the n-type layer such as the buffer layer 2 made of n-type GaAs. Diethyl zinc (DEZn) was used as an additive material for the conductivity determining impurities of the p-type layer such as the p-type cladding layer 6. In addition, silane (SiH ₄ ), diethyl tellurium (DETe), and dimethyl tellurium (DMTe) can also be used as an additive material for the conductivity determining impurity of the n-type layer. In addition, dimethyl zinc (DMZn) can be used as an additive material for the conductivity determining impurity of the p-type layer.

Incidentally, the first light reflecting layer 3 has a structure in which a semiconductor layer (about 51 nm) made of n-type AlAs and a semiconductor layer (about 45 nm) made of n-type Al _0.4 Ga _0.6 As are sequentially laminated (DBR: distributed Bragg reflective layer). The number of pairs was 15 pairs.

Further, the second light reflecting layer 10 provided under the first light reflecting layer is formed by sequentially forming a semiconductor layer (about 55 nm) made of n-type AlAs and a semiconductor layer (about 48 nm) made of n-type Al _0.4 Ga _0.6 As. A laminated structure (DBR: distributed Bragg reflection layer) was used, and the number of pairs was 10 pairs.

Next, after this epitaxial wafer was unloaded from the MOVPE apparatus, a current spreading layer 12 made of ITO having a film thickness of 250 nm was formed on the surface of the wafer, that is, on the surface side of the p-type contact layer 11 by vacuum deposition. At this time, the glass substrate for evaluation set in the same batch on which ITO was deposited was taken out, cut into a size capable of Hall measurement, and the electrical characteristics of the ITO simple substance were evaluated. The carrier concentration was 1.19 × 10 ²¹ / cm ³ , mobility 19.6 cm ² / Vs, resistivity 2.39 × 10 ⁻⁴ Ω · cm.

  Then, a circular surface electrode 8 having a diameter of 125 μm was formed in a matrix on the upper surface of the epitaxial wafer by a vacuum deposition method. For this surface electrode, gold (Au) and nickel (Ni) were deposited in the order of 600 nm and 20 nm, respectively. Further, a back electrode 9 was formed on the entire bottom surface of the epitaxial wafer. The back electrode 8 is formed by depositing gold / germanium (AuGe) alloy, nickel (Ni), and gold (Au) in the order of 60 nm, 10 nm, and 500 nm, respectively, and then alloying the electrode into an alloy in a nitrogen gas atmosphere. Performed at 400 ° C. for 5 minutes.

  Then, this epitaxial wafer was processed into a chip shape having a chip size of 300 μm square by a dicing apparatus or the like, and further, die bonding and wire bonding were performed to manufacture an LED element.

  As a result of evaluating various characteristics of the LED fabricated as described above, the light emission output was 1.52 mW and the forward operation voltage was 1.94 V (all evaluation results when energizing 20 mA).

  From this result, by using the light reflecting layer shown in the present embodiment, it can have a wider reflection band than the conventional light reflecting layer, and even in a thin film LED using ITO as a current spreading layer, An LED equivalent to the conventional one could be obtained.

  Since an LED using a metal oxide for the current spreading layer does not form the current spreading layer with a semiconductor material such as GaP, it is possible to improve both the throughput of the device and reduce the raw material cost for forming the current spreading layer. it can. However, when this thin film structure is produced in the conventional method, there is a problem that the light emission output is reduced due to the reduction of the light extraction area due to the phenomenon of the film thickness of the current dispersion layer. However, by adopting the structure of the light reflecting layer shown in this embodiment, a high-intensity LED element having a light emission output equivalent to or higher than that of the conventional one can be manufactured at a lower cost than the conventional one. It was.

<Reason for optimum conditions>
The first light reflection layer in the present invention has a structure in which the reflection center wavelength of the reflection spectrum is designed to be substantially the same as or shorter than the center wavelength in the emission spectrum of the light emitted from the active layer. take. That is, it is a light reflecting layer that mainly reflects the emission peak wavelength.

  Naturally, it is difficult to obtain a semiconductor light emitting device with high luminance if the reflectance of the first light reflecting layer, which is the main component with respect to the emission wavelength, is low. Therefore, a certain number of pairs is required to obtain a high-luminance semiconductor light emitting device. However, the reflectivity does not increase infinitely in proportion to the number of pairs, and when it exceeds a certain number of pairs, it gradually becomes saturated and there is no large difference. Therefore, if it is too thick, the effect of improving the reflectivity is diminished, and the demerit due to the increase in cost becomes larger.

  Therefore, it can be said that there is an optimum value for the number of pairs of the first light reflecting layer, and the range thereof is at least 5 pairs or more and at most 30 pairs or less.

  Next, the 2nd light reflection layer in this invention is a light reflection layer which has the center wavelength of a different reflection spectrum in visible regions other than the center wavelength of the reflection spectrum which said 1st light reflection layer has. In other words, the first light reflecting layer reflects the main part of the light emitted from the active layer, and the second light reflecting layer reflects light in the reflection band that cannot be covered by the first light reflecting layer. It is designed to effectively increase light extraction efficiency and light output.

  And it can be said that the said 2nd light reflection layer also has the optimal value in the number of pairs for the same reason as said 1st light reflection layer. The range is at least one pair and at most 20 pairs.

  The reason why the range of the number of pairs is narrower than that of the first light reflecting layer is that the first light reflecting layer is responsible for the main part of the light emitted from the active layer. is there. Therefore, the necessary second light reflecting layer is sufficient in a narrower range or a smaller number of pairs than the first light reflecting layer.

  Next, the material used for the light reflecting layer preferably has as large a difference in refractive index between the paired layers as possible, and preferably has a wide band gap.

  The reason for the former is the basic part of the light reflection layer (distributed Bragg reflection film), and a pair made of a material having a large refractive index difference can widen the reflection band, and its reflection intensity (reflection rate). ) Can be increased. The reason for the latter is that it is desired to suppress the absorption of light emitted from the active layer in the light reflection layer as much as possible.

  The significance of the existence of the light reflection layer is to prevent the light extraction efficiency and thus the light emission output from being lowered by reflecting the light upward so that the light emitted from the active layer is not absorbed by the substrate material GaAs or Ge. Is for the purpose. The same can be said for absorption by the light reflecting layer. Therefore, it is preferable that the band gap of the light reflection layer is as wide as possible.

However, it is difficult to make the above-described refractive index difference and band gap compatible. In general, AlGaAs-based materials, AlGaInP-based materials, and the like used for the light reflection layer have a trade-off relationship. Therefore, there is an optimum value for the material and composition of the light reflecting layer to be set in a preferable range, and the material of the low refractive index part constituting the first light reflecting layer and the second light reflecting layer is Al. _x Ga _1-x As (where 0.6 ≦ X ≦ 1.0), (Al _Y Ga _1-Y ) _0.5 In _0.5 P (where 0.6 ≦ Y ≦ 1.0) The material of the high refractive index portion is Al _x Ga _1-x As (where 0 ≦ X ≦ 0.6), (Al _Y Ga _1-Y ) _0.5 In _0.5 P (where 0 ≦ Y ≦ 0. 6) is preferable.

[Modification 1]
In the embodiments of the present invention, no structure is interposed between the active layer and the p-type cladding layer in any structure. However, for example, even if an intrinsic undoped layer is provided here or a structure in which a pseudo undoped layer is provided which becomes a pseudo undoped layer even if it contains some conductivity type impurities, the output of the LED element is simply used. Only the effect of improving the reliability of the image is produced, and the effect intended by the present invention can be obtained.

[Modification 2]
In the embodiment of the present invention, only a red LED element having a light emission wavelength of 640 nm is used as an example of manufacture. However, in other LED elements manufactured using the same AlGaInP-based material, for example, LED elements having a light emission wavelength of 560 nm to 660 nm. However, the material of each layer used at this time, the carrier concentration, etc. have no significant changes other than the active layer. Accordingly, the same effect can be obtained even if the emission wavelength of the LED element is set to a wavelength band different from that of the embodiment of the present invention.

[Modification 3]
In the embodiments of the present invention, an LED structure in which a buffer layer is always provided is used as an example of manufacture, but an LED element structure in which the layer is omitted can also be adopted.

[Example 4]
In the embodiment of the present invention, the conductivity determining impurity added to the p-type layer is zinc (Zn) and the conductivity determining impurity added to the n-type layer is selenium (Se), but this is added to the p-type layer. Magnesium (Mg) can be used as the conductivity determining impurity, or silicon (Si) or tellurium (Te) can be used as the conductivity determining impurity added to the n-type layer.

[Modification 5]
In the embodiments of the present invention, the surface electrode is always circular in shape. However, other shapes such as a square, a rhombus, and a polygon can obtain the intended effect of the present invention. it can.

[Modification 6]
In the embodiment of the present invention, an example in which only ITO is used as the current spreading layer has been described, but in addition to this, indium oxide (In ₂ O ₃ ), zinc oxide (ZnO), gallium-doped zinc oxide (GZO), Even when a metal oxide generally known for low resistance such as aluminum-added zinc oxide (AZO) or boron-added zinc oxide (BZO) is applied to the current spreading layer, the intended effect of the present invention can be obtained. .

[Modification 7]
In the embodiments of the present invention, only examples in which GaAs is used as the semiconductor substrate have been described. On the other hand, an LED epitaxial wafer having Ge as the semiconductor substrate, or the initial semiconductor substrate as GaAs or Ge. The effect intended by the present invention can be obtained also in an epitaxial wafer for LED using a metal substrate having a thermal conductivity equal to or higher than that of Si or Si as an alternative semiconductor substrate.

1 is a cross-sectional structure diagram of an AlGaInP red LED element according to an embodiment of the present invention. It is the figure which showed the reflection spectrum of the light reflection layer in one Example of this invention compared with the prior art example. It is the figure which showed the light emission output of the LED element in one Example of this invention compared with the prior art example. It is sectional drawing of the AlGaInP type | system | group red LED element concerning a prior art example. It is sectional drawing of the AlGaInP type | system | group red LED element concerning the other Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Buffer layer 3 Light reflection layer (1st light reflection layer)
4 n-type cladding layer 5 undoped active layer 6 p-type cladding layer 7 current dispersion layer (comprising p-type GaP) 8 surface electrode 9 back electrode 10 second light reflecting layer 11 contact layer 12 current dispersion layer (comprising ITO)

Claims (15)

Semiconductor light emission comprising at least a conductive semiconductor substrate, a light reflecting layer provided on the main surface of the semiconductor substrate, and a light emitting part including an active layer having a pn junction grown on the light reflecting layer In the element
The light reflection layer includes a first light reflection layer in which the center wavelength of the reflection spectrum is set to a wavelength shorter than or equal to the center wavelength of the emission spectrum of the light emitted from the light emitting section; and A semiconductor light emitting device comprising a second light reflecting layer having a central wavelength of a different reflection spectrum in a visible wavelength region other than the central wavelength of the reflection spectrum of the first light reflecting layer. The semiconductor light emitting device according to claim 1,
The light reflection layer includes a first light reflection layer in which the center wavelength of the reflection spectrum is set to a wavelength shorter than or equal to the center wavelength of the emission spectrum of the light emitted from the light emitting section; and A semiconductor light emitting element comprising a second light reflecting layer in which a center wavelength of a reflection spectrum is set on a longer wavelength side than a center wavelength of an emission spectrum of light emitted from the light emitting section. The semiconductor light emitting device according to claim 1 or 2,
The number of pairs of semiconductor layers constituting the first light reflecting layer is 5 pairs or more and 30 pairs or less. The semiconductor light-emitting device according to claim 3.
The number of pairs of semiconductor layers constituting the second light reflecting layer is 1 pair or more and 20 pairs or less. The semiconductor light-emitting device according to claim 1,
A semiconductor light emitting device, wherein a material of a semiconductor layer constituting the first light reflection layer and the second light reflection layer is selected from GaAs, AlGaAs, AlAs, AlGaInP, GaInP, and AlInP . The semiconductor light-emitting device according to claim 1,
The first light reflection layer and the second light reflection layer are each composed of a combination of a low refractive index portion and a high refractive index portion, and the material of the low refractive index portion is Al _x Ga _1-x As (however, 0 .6 ≦ X ≦ 1.0), (Al _Y Ga _1-Y ) _0.5 In _0.5 P (provided that 0.6 ≦ Y ≦ 1.0), and the material of the high refractive index portion is Al _x Ga _1-x As (where 0 ≦ X ≦ 0.6), (Al _Y Ga _1-Y ) _0.5 In _0.5 P (where 0 ≦ Y ≦ 0.6) A semiconductor light emitting device characterized. The semiconductor light-emitting device according to claim 1,
A semiconductor light emitting element, wherein the semiconductor substrate is made of GaAs or Ge. The semiconductor light-emitting device according to claim 1,
A semiconductor light-emitting device, wherein the active layer has a structure composed of a light-emitting layer and a barrier layer having a wider band gap than the light-emitting layer, and a plurality of these layers are stacked. The semiconductor light-emitting device according to claim 1,
A semiconductor light emitting element, wherein a current spreading layer made of a metal oxide is formed on the light emitting part via at least one semiconductor layer. Semiconductor light emission comprising at least a conductive semiconductor substrate, a light reflecting layer provided on the main surface of the semiconductor substrate, and a light emitting part including an active layer having a pn junction grown on the light reflecting layer In device epitaxial wafers,
The light reflection layer includes a first light reflection layer in which the center wavelength of the reflection spectrum is set to be substantially equal to or shorter than the center wavelength of the emission spectrum of the light emitted from the light emitting unit, An epitaxial wafer for a semiconductor light emitting device, comprising: a second light reflecting layer in which a center wavelength of a reflection spectrum is set longer than a center wavelength of an emission spectrum of light emitted from the light emitting unit. In the epitaxial wafer for semiconductor light emitting devices according to claim 10,
The number of pairs of said 1st light reflection layer is 5 pairs or more and 30 pairs or less, The epitaxial wafer for semiconductor light-emitting devices characterized by the above-mentioned. In the epitaxial wafer for semiconductor light emitting devices according to claim 11,
The number of pairs of said 2nd light reflection layer is 1 pair or more and 20 pairs or less, The epitaxial wafer for semiconductor light-emitting devices characterized by the above-mentioned. In the epitaxial wafer for semiconductor light emitting devices according to any one of claims 10 to 12,
An epitaxial for a semiconductor light emitting device, wherein a semiconductor material constituting the first light reflecting layer and the second light reflecting layer is selected from GaAs, AlGaAs, AlAs, AlGaInP, GaInP, and AlInP Wafer. In the epitaxial wafer for semiconductor light-emitting devices in any one of Claims 10 thru | or 13,
The first light reflection layer and the second light reflection layer are each composed of a combination of a low refractive index portion and a high refractive index portion, and the material of the low refractive index portion is Al _x Ga _1-x As (however, 0 .6 ≦ X ≦ 1.0), (Al _Y Ga _1-Y ) _0.5 In _0.5 P (provided that 0.6 ≦ Y ≦ 1.0), and the material of the high refractive index portion is Al _x Ga _1-x As (where 0 ≦ X ≦ 0.6), (Al _Y Ga _1-Y ) _0.5 In _0.5 P (where 0 ≦ Y ≦ 0.6) An epitaxial wafer for semiconductor light emitting devices. In the epitaxial wafer for semiconductor light-emitting devices in any one of Claims 10 thru | or 14,
An epitaxial wafer for a semiconductor light emitting element, wherein a current spreading layer made of a metal oxide is formed on the light emitting portion via at least one semiconductor layer.

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