JP2009088230A - Semiconductor light-emitting element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide: a semiconductor light-emitting element which has an InGaN active layer of high In composition having a uniform composition distribution, the semiconductor light-emitting element emitting light of ≥480 nm in light emission wavelength with high luminous efficiency and being superior in mass-productivity; and a manufacturing method thereof. <P>SOLUTION: A semiconductor laser diode 10 has an active layer 16 made of [In<SB>x</SB>Ga<SB>1-x</SB>N (0<x<1)], wherein a ZnO layer 13 lattice-matching the active layer 16 is used to form an epitaxial wafer emitting light in a visible range of a long wavelength, for example, in the green light range; and an (a)-plane sapphire substrate 11A is used for epitaxial growth of the ZnO layer 13. The ZnO layer 13 is obtained which has a superior crystal surface. The lattice constant of the ZnO layer 13 is close to the lattice constant of the active layer 16 whose In composition ratio is so set that the light emission wavelength is ≥480 nm. Consequently, phase separation and an influence of a piezoelectric field caused when the In composition ratio of the active layer 16 is made large are suppressed, and light emission with high light emission efficiency can be achieved in the visible range of the long wavelength, for example, in the green light range. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting device and a method for manufacturing the semiconductor light emitting device, and more particularly to a semiconductor light emitting device capable of outputting light in the visible region having a wavelength longer than that of blue (light having an emission wavelength of 480 nm or more). About.

  Conventionally, a semiconductor light emitting device using InGaN as a semiconductor light emitting device emitting blue light (emission wavelength of 480 nm or less) is known (for example, see Patent Document 1).

By the way, in order to obtain longer-wavelength green light emission (light having an emission wavelength of 480 nm or more) with a semiconductor light emitting device using an active layer of a nitride semiconductor such as InGaN, by increasing the composition ratio of In, It is conceivable to narrow the forbidden band width of the active layer.
Japanese Patent Laid-Open No. 06-061527 JP 2001-44500 A Kato et al, Appl. Phys. Lett, Vol. 84, No 22, 31 May 2004.

  By the way, when an In composition ratio is increased in order to obtain a longer wavelength green light emission (light having a light emission wavelength of 480 nm or more) in a semiconductor light emitting device using InGaN, phase separation occurs and an active layer having a uniform In composition. It becomes difficult to obtain the light emission efficiency.

  Further, when a piezoelectric field is generated due to the crystal structure, there is a problem that the light emission recombination probability is lowered and the light emission efficiency is further lowered. In addition, since the lattice constant differs greatly from that of the substrate, there are a large number of threading dislocations, and there is a problem that the light emission efficiency is lowered and good reliability cannot be obtained.

  In order to suppress these, it is conceivable to use an epi layer lattice-matched (close to the lattice constant) to the InGaN active layer. In order to grow the epi layer, a substrate is required, and a sapphire substrate is a candidate.

  When a ZnO epi layer is directly grown using a c-plane sapphire substrate, a 30 ° rotated domain is formed, and it has been reported that it is effective to insert an MgO buffer layer to suppress this. (For example, refer nonpatent literature 1).

  Further, there is known a technique for realizing a device using a ZnO-based compound such as a semiconductor light-emitting device in which a ZnO-based compound crystal layer having excellent crystallinity is obtained and having improved device characteristics (see, for example, Patent Document 2). ). In this prior art, when an a-plane sapphire substrate is used, a ZnO-based compound layer grows in a direction perpendicular to the c-axis direction of the sapphire substrate, so that the a-axis of ZnO grows side by side along the c-axis of sapphire. As a result, along the c-axis length (12.991 mm), four crystals of ZnO-based compounds with a-axis length (3.25 mm) are arranged, and the crystal matching degree is very good, about 0.07%, and excellent crystals A surface is considered to be obtained.

  The present invention has been made in view of such conventional problems, and an object of the present invention is an element having a high In composition InGaN active layer having a uniform composition distribution, and an emission wavelength of 480 nm or more. It is an object of the present invention to provide a semiconductor light emitting device capable of realizing the above light emission with high luminous efficiency and excellent in mass productivity, and a method for manufacturing the same.

In order to solve the above problem, a semiconductor light emitting device according to the first aspect of the present invention includes a sapphire substrate, a zinc oxide (ZnO) -based epilayer, a sapphire substrate, and the zinc oxide (ZnO) -based epilayer. A buffer layer therebetween, a lower contact layer formed on the buffer layer, an active layer made of gallium indium nitride [In _x Ga _1-x N (0 <x <1)], and the active layer or the oxidation An upper clad layer and a lower clad layer lattice-matched to at least one of the zinc (ZnO) -based epi layers, and an upper contact layer formed on the upper clad layer are provided.

According to this configuration, it has an active layer made of [In _x Ga _1-x N (0 <x <1)], and emits light in a long-wavelength visible region (light having a light emission wavelength of 480 nm or more) such as a green region. An epitaxial wafer for a semiconductor laser diode is provided. In order to form this epitaxial wafer, a zinc oxide (ZnO) based epitaxial layer lattice-matched to the active layer is used. A sapphire substrate is used as a substrate for epitaxial growth of a zinc oxide (ZnO) -based epi layer.

  The lattice constant (= 5.1955 格子) corresponding to the unit cell c of ZnO is equal to the lattice constant (= 5.186Å) corresponding to the unit cell c of gallium nitride GaN and the lattice constant corresponding to the unit cell c of indium nitride InN ( = 5.76 Å), which is very close to the unit cell c of gallium indium nitride InGaN having an In composition of about 20%.

  For this reason, the phase separation that occurs when the In composition ratio of the active layer is increased is suppressed, the distortion of the active layer is reduced, the influence of the piezoelectric field is suppressed, and the lattice constant differs greatly from the substrate. Threading dislocation is suppressed. As a result, the band gap energy of the InGaN-based active layer is about 2.2 eV, and light emission with high emission efficiency is possible in a long-wavelength visible region (light having a light emission wavelength of 480 nm or more) such as a green region.

  In addition, since a buffer layer is formed between the sapphire substrate and the zinc oxide (ZnO) -based epi layer, this also suppresses threading dislocations, improves the crystallinity of the InGaN-based active layer, and improves the luminous efficiency. Will improve.

  Therefore, an element having an InGaN active layer with a high In composition having a uniform composition distribution, and a semiconductor laser diode capable of realizing light emission with a light emission wavelength of 480 nm or more with high light emission efficiency can be obtained. In addition, since a large sapphire substrate is available at low cost, a semiconductor laser diode excellent in mass productivity can be obtained using the sapphire substrate.

  The semiconductor light emitting element according to the invention of claim 2 is characterized in that the buffer layer is formed on the c-plane in the plane orientation of the sapphire substrate.

  According to this configuration, a zinc oxide (ZnO) based epitaxial layer lattice-matched to the active layer is used to form an epitaxial wafer for a semiconductor laser diode that emits light in a long wavelength visible region such as a green region. A sapphire substrate having a c-plane (0001) as a main surface is used as a substrate for epitaxial growth of this zinc oxide (ZnO) -based epilayer. Further, the lattice constant (= 5.1955) corresponding to the unit cell c of ZnO is very close to the unit cell c of gallium indium nitride InGaN having an In composition of about 20%. For this reason, the phase separation that occurs when the In composition ratio of the active layer is increased is suppressed, the distortion of the active layer is reduced, the influence of the piezoelectric field is suppressed, and the lattice constant differs greatly from the substrate. Threading dislocation is suppressed. Thereby, it is possible to emit light with high luminous efficiency in a long wavelength visible region such as a green region.

  According to a third aspect of the present invention, in the semiconductor light emitting device, the buffer layer is formed on the a-plane in the plane orientation of the sapphire substrate.

According to this configuration, a zinc oxide (ZnO) based epitaxial layer lattice-matched to the active layer is used to form an epitaxial wafer for a semiconductor laser diode that emits light in a long wavelength visible region such as a green region. And a sapphire substrate a _- (20 11) as a principal a surface as a substrate for epitaxial growth of zinc oxide (ZnO) based epitaxial layer. A surface of the sapphire substrate (11 _- 20) on, because it is grown a buffer layer and a zinc oxide (ZnO) based epitaxial layer made of ZnO in order, along the a-axis of the ZnO along the c-axis of the sapphire growth To do. As a result, an excellent crystal plane buffer layer and zinc oxide (ZnO) -based epi layer are obtained. Further, the lattice constant (= 5.1955) corresponding to the unit cell c of ZnO is very close to the unit cell c of gallium indium nitride InGaN having an In composition of about 20%. For this reason, the phase separation that occurs when the In composition ratio of the active layer is increased is suppressed, the distortion of the active layer is reduced, the influence of the piezoelectric field is suppressed, and the lattice constant differs greatly from the substrate. Threading dislocation is suppressed. Thereby, it is possible to emit light with high luminous efficiency in a long wavelength visible region such as a green region.

  According to a fourth aspect of the present invention, the buffer layer is made of magnesium oxide (MgO).

  According to this configuration, the buffer layer made of MgO is inserted between the sapphire substrate having the c-plane (0001) as the main surface and the zinc oxide (ZnO) -based epi layer, so that a domain rotated by 30 ° is formed. Is suppressed. That is, the growth of the ZnO a-axis rotated by 30 ° with respect to the sapphire a-axis is suppressed. Thereby, even when a c-plane sapphire substrate is used as a substrate on which a zinc oxide (ZnO) -based epi layer is epitaxially grown, the strain of the active layer is reduced and an active layer with good crystallinity is obtained.

  Therefore, even when a c-plane sapphire substrate is used, it is possible to obtain a semiconductor laser diode capable of realizing light emission with a light emission wavelength of 480 nm or more with high light emission efficiency with an element having a high In composition active layer having a uniform composition distribution. it can.

  The semiconductor light-emitting device according to the invention of claim 5 is characterized in that the buffer layer is zinc oxide (ZnO).

According to this configuration, a surface of the sapphire substrate _- on (11 20), since the grown buffer layer and the zinc oxide (ZnO) based epitaxial layer made of zinc oxide (ZnO) in order, the c-axis of sapphire The ZnO a axis grows along. As a result, an excellent crystal plane ZnO buffer layer and zinc oxide (ZnO) -based epi layer are obtained. Thereby, the distortion of the active layer is reduced, and an active layer with good crystallinity is obtained.

  The semiconductor light-emitting device according to the invention of claim 6 is made of GaN or InN between the zinc oxide (ZnO) -based epi layer and the active layer, and has a film thickness of 1 ML or more and the zinc oxide (ZnO) -based epi. A pseudo-lattice matching layer made of GaN having a critical thickness or less with respect to the layer is provided.

  According to this configuration, since the pseudo-lattice matching layer is formed between the zinc oxide (ZnO) -based epi layer and the active layer, the oxide layer / between the zinc oxide (ZnO) -based epi layer and the active layer / A steep interface is obtained between the nitride layers, and a good crystal of the active layer made of InGaN is obtained. As a result, it is possible to obtain a semiconductor laser diode as a highly reliable semiconductor light emitting element with high luminous efficiency. Also, by forming a pseudo-lattice matching layer between the zinc oxide (ZnO) -based epi layer and the active layer, the half-value width is narrower than when there is no pseudo-lattice matching layer, and the emission characteristics are good (the emission intensity is strong). ) A semiconductor laser diode can be obtained.

  In the semiconductor light emitting device according to claim 7, the pseudo lattice matching layer is formed by stacking GaN and InN having a film thickness of 1ML or more and a critical film thickness or less with respect to the zinc oxide (ZnO) -based epilayer. It consists of a superlattice layer.

  According to this configuration, a pseudo lattice matching layer composed of a superlattice layer is formed between the zinc oxide (ZnO) -based epi layer and the active layer, so that the zinc oxide (ZnO) -based epi layer and the active layer are between A steep interface is obtained between a certain oxide layer / nitride layer, and a good crystal of an active layer made of InGaN is obtained. As a result, it is possible to obtain a semiconductor laser diode as a highly reliable semiconductor light emitting element with high luminous efficiency. Also, by forming a pseudo-lattice matching layer consisting of a superlattice layer between the zinc oxide (ZnO) -based epi layer and the active layer, the half-value width is narrower than when there is no pseudo-lattice matching layer, and the emission characteristics are good A semiconductor laser diode (with high emission intensity) can be obtained.

  The semiconductor light emitting device according to the invention of claim 8 is characterized in that a composition ratio of indium (In) in the active layer is 20% or more.

A method of manufacturing a semiconductor light emitting device according to claim 9 includes a buffer layer forming step of forming a buffer layer on a sapphire substrate, and a ZnO layer of forming a zinc oxide (ZnO) based epi layer on the buffer layer A lower contact layer forming step for forming a lower contact layer on the ZnO layer, and a lower clad layer for forming a clad layer lattice-matched to at least one of the zinc oxide (ZnO) -based epi layer or the active layer Forming step, forming an active layer made of gallium indium nitride [In _x Ga _1-x N (0 <x <1)] on the cladding layer, and the zinc oxide (ZnO) -based epi layer A pseudo lattice matching layer forming step of forming a pseudo lattice matching layer between the active layer and the active layer, and a cladding layer lattice-matched to at least one of the zinc oxide (ZnO) -based epi layer or the active layer on the active layer To form A Department clad layer forming step, characterized in that an upper contact layer formation step of forming a contact layer on the upper cladding layer.

  According to this configuration, the phase separation that occurs when the In composition ratio of the active layer is increased is suppressed, the strain of the active layer is reduced, the influence of the piezoelectric field is suppressed, and the lattice constant of the substrate is greatly different. Therefore, the threading dislocation that occurs is suppressed. As a result, the band gap energy of the InGaN-based active layer is about 2.2 eV, and light emission with high emission efficiency is possible in a long-wavelength visible region (light having a light emission wavelength of 480 nm or more) such as a green region. In addition, since a buffer layer is formed between the sapphire substrate and the zinc oxide (ZnO) -based epi layer, this also suppresses threading dislocations, improves the crystallinity of the InGaN-based active layer, and improves the luminous efficiency. Will improve.

  Therefore, an element having an InGaN active layer with a high In composition having a uniform composition distribution, and a semiconductor laser diode capable of realizing light emission with a light emission wavelength of 480 nm or more with high light emission efficiency can be obtained. In addition, since a large sapphire substrate is available at low cost, a semiconductor laser diode excellent in mass productivity can be obtained using the sapphire substrate.

  Furthermore, since a pseudo lattice matching layer is formed between the zinc oxide (ZnO) -based epi layer and the active layer, the oxide layer / nitride layer between the zinc oxide (ZnO) -based epi layer and the active layer is formed. A steep interface is obtained, and a good crystal of the active layer made of InGaN is obtained. As a result, it is possible to obtain a semiconductor laser diode as a highly reliable semiconductor light emitting element with high luminous efficiency. In addition, a semiconductor laser diode having a narrower half-value width and better light emission characteristics (higher light emission intensity) than in the case where there is no pseudo lattice matching layer can be obtained.

  According to a tenth aspect of the present invention, there is provided a method for manufacturing a semiconductor light emitting device, wherein the sapphire substrate has a c-plane orientation, and the buffer layer is magnesium oxide (MgO).

  According to this configuration, even when a c-plane sapphire substrate is used as a substrate on which a zinc oxide (ZnO) -based epilayer is epitaxially grown, distortion of the active layer is reduced and an active layer with good crystallinity can be obtained.

  The method for manufacturing a semiconductor light emitting device according to an eleventh aspect is characterized in that the surface orientation of the sapphire substrate is a-plane and the buffer layer is zinc oxide (ZnO).

According to this configuration, a surface of the sapphire substrate _- on (11 20), since the grown buffer layer and the zinc oxide (ZnO) based epitaxial layer made of zinc oxide (ZnO) in order, the c-axis of sapphire The ZnO a axis grows along. As a result, an excellent crystal plane ZnO buffer layer and zinc oxide (ZnO) -based epi layer are obtained. Thereby, the distortion of the active layer is reduced, and an active layer with good crystallinity is obtained.

  In the method of manufacturing a semiconductor light emitting device according to the invention of claim 12, in the step of forming the pseudo lattice matching layer, the pseudo lattice matching layer made of GaN or InN has a critical film thickness of 1 ML or more with respect to the ZnO layer. It is characterized by being formed in the following film thickness.

  According to this configuration, a steep interface is obtained between the oxide layer / nitride layer between the zinc oxide (ZnO) -based epi layer and the active layer, and a good crystal of the active layer made of InGaN is obtained. As a result, it is possible to obtain a semiconductor laser diode as a highly reliable semiconductor light emitting element with high luminous efficiency.

  According to the present invention, a device having an InGaN active layer with a high In composition having a uniform composition distribution, and capable of realizing light emission with a light emission wavelength of 480 nm or more with high light emission efficiency and excellent mass productivity. An element can be obtained.

  Hereinafter, embodiments embodying the present invention will be described with reference to the drawings. In the description of each embodiment, the same parts are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
A semiconductor laser diode 10 as a semiconductor light emitting device according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing a schematic configuration of a semiconductor laser diode 10 according to the first embodiment, and FIG. 2 is a unit cell diagram showing a plane orientation of a sapphire substrate. FIG. 3 is an explanatory diagram showing physical characteristics of zinc oxide (ZnO), gallium nitride (GaN), and the like.

The semiconductor laser diode 10, as shown in FIG. 1, and the sapphire substrate 11A, a surface of the sapphire substrate 11A _- a buffer layer 12 made of (11 20) ZnO formed on (see FIG. 2), the buffer layer 12 And a ZnO layer 13 as a zinc oxide (ZnO) -based epi layer formed thereon.

The semiconductor laser diode 10 includes a lower contact layer 14 formed on the ZnO layer 13, an active layer 16 made of gallium indium nitride [In _x Ga _1-x N (0 <x <1)], and an active layer. 16 or a lower clad layer 15 and an upper clad layer 17 lattice-matched to at least one of a ZnO layer 13 as a zinc oxide (ZnO) based epilayer, and an upper contact layer 18 formed on the upper clad layer 17, It has.

  An epitaxial wafer for a semiconductor laser diode that emits light in a long-wavelength visible region (light having a light emission wavelength of 480 nm or more) such as a green region includes a lower contact layer 14, a lower cladding layer 15, an active layer 16, an upper cladding layer 17, and an upper portion. The contact layer 18 is used. This epitaxial wafer is formed on the ZnO layer 13. The upper portion of the semiconductor layer is formed in a ridge structure.

  Further, the semiconductor laser diode 10 is formed on the lower electrode 20 formed on the exposed portion of the lower contact layer 14 that is partially exposed by etching a part of the epitaxial wafer, and on the upper contact layer 18. An upper electrode 21 and a passivation film 19 are provided.

  In this semiconductor laser diode 10, the conductivity type of the lower contact layer 14 and the lower cladding layer 15 is n-type, and the conductivity type of the upper cladding layer 17 and the upper contact layer 18 is p-type.

The buffer layer 12 is a layer provided for lattice matching with the sapphire substrate 11A. The buffer layer 12 is, a surface _- is formed by a ZnO grown at low temperature on the sapphire substrate 11A to (11 20) the main surface.

  The ZnO layer 13 is formed on the buffer layer 12 by growing ZnO at a high temperature in order to improve crystallinity.

The n-type lower contact layer 14 is a layer for realizing ohmic contact with the lower electrode 20 formed on the exposed portion of the lower contact layer 14. The lower contact layer 14 is zinc magnesium beryllium cadmium oxide _{[Zn 1-abc Mg a Be} b Cd c O (0 ≦ a <1,0 ≦ b <1,0 ≦ c <1, a + b + c ≦ 1)] (Oxide-based compound semiconductor layer: oxide) or aluminum gallium indium nitride [Al _1-pq Ga _p In _q N (0 ≦ p <1, 0 ≦ q <1, p + q ≦ 1)] (nitride-based compound semiconductor Layer: nitride). For example, the lower contact layer 14 may be an oxide such as zinc magnesium oxide (ZnMgO) or zinc oxide (ZnO), or a nitride such as gallium indium nitride (InGaN), aluminum gallium indium nitride (AlInGaN), or gallium nitride (GaN). Composed of things.

The n-type lower cladding layer 15 is a lattice-matched cladding layer that is lattice-matched so as to have a lattice constant equal to or smaller than the lattice constant of the InGaN-based active layer 16, and is an InGaN-based cladding layer that functions as a core. The refractive index is smaller than that of the active layer 16 and plays a role of stably confining light in the active layer 16. The lower cladding layer 16 is zinc magnesium beryllium cadmium oxide _{[Zn 1-abc Mg a Be} b Cd c O (0 ≦ a <1,0 ≦ b <1,0 ≦ c <1, a + b + c ≦ 1)] consisting of (oxide) or aluminum gallium indium nitride _{[Al 1-pq Ga p in} q N (0 ≦ p <1,0 ≦ q <1, p + q ≦ 1)] ( nitride). For example, the lower cladding layer 15 is made of an oxide such as zinc magnesium oxide (ZnMgO) or zinc oxide (ZnO), or nitrided such as gallium indium nitride (InGaN), aluminum gallium indium nitride (AlInGaN), or gallium nitride (GaN). Composed of things. The lower cladding layer 15 is not limited to being lattice-matched to the InGaN-based active layer 16, but may be any layer that is lattice-matched to at least one of the active layer 16 or the ZnO layer 13.

  The active layer 16 is an InGaN-based active layer formed in a quantum well structure (single or multiple quantum well) in which an InGaN well layer and an InGaN barrier layer, or an InGaN well layer and an AlInN barrier layer are stacked. In this active layer 16, the composition ratio of indium (In) in the well layer made of InGaN is set so that the emission wavelength is 480 nm or more (emission wavelength in the green region). Specifically, the composition ratio of indium (In) is 20% or more.

The active layer 16 has a double heterojunction structure sandwiched between the lower cladding layer 15 and the upper cladding layer 17. When a voltage is applied in the forward direction by the external electrode, electrons are injected from the lower cladding layer 15. Holes are injected from the upper cladding layer 17. As a result, the active layer 16 is in an inversion distribution state, and stimulated emission occurs. Further, both end surfaces of the active layer 16 constitute reflectors to form a resonator, and light is amplified while being repeatedly guided and emitted as laser light to the outside. Then, the reflection loop reaches an equilibrium state, and the laser light reaches a continuous oscillation state. The active layer 16 is not limited to the quantum well structure, and may be an active layer made of gallium indium nitride [In _x Ga _1-x N (0 <x <1)].

The p-type upper clad layer 17 is a lattice-matched clad layer that is lattice-matched so as to have a lattice constant equal to or smaller than the lattice constant of the InGaN-based active layer 16, and functions as a core. The refractive index is smaller than that of the active layer 16 and plays a role of stably confining light in the active layer 16. The upper cladding layer 17 is made of zinc magnesium beryllium cadmium [Zn _1-abc Mg _a Be _b Cd _C O (0 ≦ a <1, 0 ≦ b <1, 0 ≦ c <1, a + b + c ≦ 1)] consisting of (oxide) or aluminum gallium indium nitride _{[Al 1-pq Ga p in} q N (0 ≦ p <1,0 ≦ q <1, p + q ≦ 1)] ( nitride). For example, the upper cladding layer 17 is made of an oxide such as zinc magnesium oxide (ZnMgO) or zinc oxide (ZnO), or nitrided such as gallium indium nitride (InGaN), aluminum gallium indium nitride (AlInGaN), or gallium nitride (GaN). Composed of things. The upper cladding layer 17 is not limited to being lattice-matched to the InGaN-based active layer 16 but is a layer lattice-matched to at least one of the active layer 16 or the ZnO layer 13 as a zinc oxide (ZnO) -based epilayer. I just need it.

  The p-type upper contact layer 18 is a layer for realizing ohmic contact with the upper electrode layer 21. The passivation film 21 functions as a protective film.

The lower electrode 20 is composed of, for example, an Au / Ti electrode.
The upper electrode layer 21 is made of, for example, a Ni / Au or Pd / Pt / Au electrode.

Next, a method for manufacturing the semiconductor laser diode 10 having the above configuration will be described. (Process 1)
First, a surface _- washing (11 20) to (sapphire wafer) sapphire substrate having a major surface 11A.

This cleaning is performed by, for example, organic cleaning or chemical etching. The organic cleaning is ultrasonic cleaning with dichlorobenzene and acetone, or ultrasonic cleaning with acetone and ethanol. Chemical etching, H ₃ PO ₄ and H ₂ SO ₄ of 1: 110 ° C. with a solution of a rate of 3, 30min or 5% HF solution, or H ₃ PO ₄ and H ₂ SO _4, 1: 3 Perform at 160 ° C for 30 min with the solution of the ratio.

(Process 2)
Next, a thermal cleaning process is performed on the cleaned sapphire substrate 11A.

  In this thermal cleaning process, for example, heating is performed at a temperature of 800 ° C. for 30 minutes in vacuum or in an atomic hydrogen irradiation in a growth chamber to remove organic substances and the like. Alternatively, heating is performed at a temperature of 650 ° C. in a vacuum, at a temperature of 550 ° C. in oxygen, or at a temperature of 750 ° C. in a vacuum for 10 minutes.

(Process 3)
Then, a surface of the sapphire substrate 11A (11 _- 20) a buffer layer 12 made of ZnO on, RFMBE (radio-frequency molecular beam epitaxy) ( buffer layer forming step) of growing at a low temperature under the law. The conditions in this case are, for example, growth temperature Tg = 400 to 500 ° C., plasma power (RF power) P = 300 W, and O ₂ flow rate 3 sccm (standard cc / min). A high-purity Zn metal material is evaporated in a Knudsen cell and supplied to the substrate surface.

  The buffer layer 12 has a thickness of about 10-200 nm and a growth temperature Tg of about 250-650 ° C.

(Process 4)
Next, high-temperature annealing is performed for surface improvement and lattice relaxation.
This high-temperature annealing is performed, for example, at 800-1000 ° C. for 3-5 min in vacuum, or 1000 ° C., 2 h in vacuum, or 750 ° C. for 10 min under Zn irradiation.

(Process 5)
Next, the ZnO layer 13 is grown on the buffer layer 12 at a high temperature by the RFMBE method (ZnO layer forming step). The conditions in this case are, for example, growth temperature Tg = 800 ° C., plasma power P = 300 W, O ₂ flow rate 3 sccm, 250-500 nm / h, or Tg = 650 ° C., plasma power P = 350 W, O ₂ flow rate 1 sccm, 200 nm / h, or Tg = 500 ° C., plasma power P = 300 W, O ₂ flow rate 3 sccm, 400 nm / h. A high-purity Zn metal material is evaporated in a Knudsen cell and supplied to the substrate surface.

(Step 6)
Next, the oxygen supply is stopped and cooling is performed slowly. For example, the temperature is lowered to 350 ° C at 5-10 ° C / min.
Thereafter, an epitaxial wafer for the semiconductor laser diode 10 that emits light in a long-wavelength visible region such as a green region (light having an emission wavelength of 480 nm or more) is formed on the ZnO layer 13 as a zinc oxide (ZnO) -based epilayer. It is formed using the RFMBE method by the following steps.

(Step 7)
A lower contact layer 14 is formed on the ZnO layer 13 (lower contact layer forming step).
The growth temperature when the lower contact layer 14 is formed is less than 750 ° C.

Specifically, the conditions for forming the lower contact layer 14 by depositing nitrides such as AlGaInN and InGaN by the RFMBE method are as follows: growth temperature Tg = 400 to 750 ° C., plasma power P = 300 to 500 W, The flow rate of nitrogen gas (N ₂ ) is 1 to 5 sccm. The conditions for forming the lower contact layer 14 by depositing nitrides such as AlGaInN and InGaN by GSMBE (gas source molecular beam epitaxy) method using ammonia (NH ₃ ) as a group V material are Tg = Set the flow rate of ammonia gas (NH ₃ ) to 10 to 100 sccm at 400 to 750 ° C. Group III material is a high-purity metal material evaporated in a Knudsen cell and supplied to the epitaxial wafer.

The conditions for forming the lower contact layer 14 by depositing an oxide such as ZnMgO or ZnO by the RFMBE method are as follows: growth temperature Tg = 400 to 750 ° C., plasma power P = 300 to 500 W, oxygen gas ( O ₂ ) The flow rate is 1 to 5 sccm. Group II materials are supplied to epitaxial wafers by evaporating high-purity metal materials in a Knudsen cell.

  The lower contact layer 14 has n-type conductivity by doping silicon (Si).

(Process 8)
Next, a lower clad layer 15 lattice-matched to at least one of the active layer 16 or the ZnO layer 13 is formed on the lower contact layer 14 (lower clad layer forming step).

  The lower cladding layer 15 has a lower refractive index than the InGaN active layer 16.

  The growth temperature when forming the lower cladding layer 15 is less than 750 ° C. Further, by depositing a lattice matching material as the lower cladding layer 15, crystal information (plane orientation, lattice constant, etc.) of the ZnO layer 13 is transmitted to the active layer 16, and the InGaN active layer 16 having a uniform In composition. Is realized.

Specifically, when the lower cladding layer 15 is formed by depositing a nitride such as AlGaInN or InGaN by the RFMBE method, the growth temperature Tg = 400 to 750 ° C., the plasma power P = 300 to 500 W, The flow rate of nitrogen gas (N ₂ ) is 1 to 5 sccm. The conditions for forming the lower cladding layer 15 by depositing nitrides such as AlGaInN and InGaN by the GSMBE method are Tg = 400 to 750 ° C. and the ammonia gas (NH ₃ ) flow rate is 10 to 100 sccm. . Group III raw material is a high-purity metal raw material evaporated in a Knudsen cell and supplied to the epitaxial wafer surface.

The lower clad layer 15 is formed by depositing an oxide such as ZnMgO or ZnO by the RFMBE method. The growth temperature is Tg = 400 to 750 ° C., the plasma power is P = 300 to 500 W, oxygen gas ( O ₂ ) The flow rate is 1 to 5 sccm. Group II material is a high-purity metal material evaporated in a Knudsen cell and supplied to the epitaxial wafer surface. The lower cladding layer 15 has n-type conductivity by doping silicon (Si).

(Step 9)
Next, an active layer 16 made of gallium indium nitride [Inx Ga1-x N (0 <x <1)] is formed on the lower cladding layer 15 (active layer forming step).

In this case, the growth temperature of the InGaN-based active layer 16 is less than 750 ° C.
Specifically, for example, an InGaN well layer / InGaN barrier layer or an InGaN well layer / AlInN barrier layer is deposited by RFMBE or GSMBE. The conditions in this case are a growth temperature Tg = 400 to 750 ° C., a plasma power P = 300 to 500 W, and a nitrogen gas (N ₂ ) flow rate of 1 to 5 sccm. In the GSMBE method, Tg = 400 to 750 ° C., and the ammonia gas (NH ₃ ) flow rate is 10 to 100 sccm. Group III material is a high-purity metal material evaporated in a Knudsen cell and supplied to the substrate. Group III raw material is a high-purity metal raw material evaporated in a Knudsen cell and supplied to the epitaxial wafer surface.

(Process 10)
Next, an upper clad layer 17 lattice-matched to at least one of the active layer 16 or the ZnO layer 13 is formed on the active layer 16 (upper clad layer forming step).

The upper cladding layer 17 is set to have a refractive index lower than that of the InGaN active layer 16.
In this case, the growth temperature when the upper clad layer 17 is formed is less than 750 ° C.

Specifically, for example, the conditions for depositing and forming nitrides such as AlGaInN and InGaN by RFMBE are as follows: growth temperature Tg = 400 to 750 ° C., plasma power P = 300 to 500 W, nitrogen gas (N ₂ ) The flow rate is 1 to 5 sccm. The upper cladding layer 17 is formed by depositing nitrides such as AlGaInN and InGaN by the GSMBE method. Tg = 400 to 750 ° C., and the ammonia gas (NH ₃ ) flow rate is 10 to 100 sccm. . Group III raw material is a high-purity metal raw material evaporated in a Knudsen cell and supplied to the epitaxial wafer surface.

The upper clad layer 17 is formed by depositing an oxide such as ZnMgO or ZnO by the RFMBE method. The growth temperature is Tg = 400 to 750 ° C., the plasma power is P = 300 to 500 W, oxygen gas ( O ₂ ) The flow rate is 1 to 5 sccm. Group II material is a high-purity metal material evaporated in a Knudsen cell and supplied to the epitaxial wafer surface.

  The p-type upper clad layer 17 uses magnesium Mg, beryllium Be, magnesium Mg and silicon Si (co-doped), etc. as the p-type dopant.

(Step 11)
Next, the upper contact layer 18 is formed on the upper cladding layer 17 (upper contact layer forming step).
In this case, the growth temperature when the upper contact layer 17 is formed is less than 750 ° C.

Specifically, for example, nitrides such as GaN and InGaN are deposited by RFMBE or GSMBE to form a p-type contact layer. The conditions in this case are a growth temperature Tg = 400 to 750 ° C., a plasma power P = 300 to 500 W, and a nitrogen gas (N ₂ ) flow rate of 1 to 5 sccm. Group III material is a high-purity metal material evaporated in a Knudsen cell and supplied to the substrate.

  As the p-type dopant, magnesium Mg, beryllium Be, magnesium Mg and silicon Si (co-doped), or the like is used.

  In addition, it is preferable to use separate growth apparatuses for depositing nitrides such as AlGaInN and oxides such as ZnMgBeCdO. In this case, each apparatus is connected by vacuum piping, and the epitaxial wafer is brought into the atmosphere during the deposition. There is no touch.

By the above procedure, an epitaxial wafer for a long wavelength visible laser diode such as a green region can be manufactured with a high yield.
Thereafter, the following steps are further performed.

(Step 12)
Next, a part of the epitaxial wafer is etched to expose a part of the lower contact layer 14.

(Step 13)
Next, a ridge structure is formed.
The ridge structure is a kind of semiconductor laser structure, and can realize an actual refractive index waveguide structure that can reduce light loss in the optical waveguide (laser beam path). Although it is a relatively simple structure, precise control of the processing technique is required to keep the oscillation state of the laser light stable.

  Specifically, the ridge structure is formed by photolithography and dry etching techniques.

(Step 14)
Next, a passivation film 19 is formed.
The passivation film 19 functions as a protective layer, and is formed by depositing SiO ₂ and ZrO ₂ by a PCVD (Plasma Chemical Vapor Deposition) method.

(Step 15)
Next, the lower electrode 20 is formed on the exposed portion of the lower contact layer 14 (lower electrode forming step).
Specifically, an electrode pattern is formed by photolithography, the passivation film 19 is removed, electrode metal is deposited by resistance heating, EB (electron beam) or sputtering, and then sintered (sintering). For example, an Au / Ti electrode is formed as the p-type upper electrode layer 19. In this case, the formed n-type lower electrode 20 is in ohmic contact with the n-type lower contact layer 14.

(Step 16)
Next, the p-type upper electrode 21 is formed.
Specifically, an electrode pattern is formed by photolithography, the passivation film 19 is removed, electrode metal is deposited by resistance heating, EB (electron beam) or sputtering, and then sintered (sintering). For example, a Ni / Au or Pd / Pt / Au electrode is formed as the p-type upper electrode 21. In this case, the formed p-type upper electrode layer 21 is in ohmic contact with the p-type upper contact layer 18.

(Step 17)
Next, the laser diode end face is formed.
Specifically, the laser diode end face is formed by a dry etching technique or cleavage. Then, coating is performed on the end face of the formed laser diode, and the manufacture of the semiconductor laser diode 10 that emits light in a long-wavelength visible region such as a green region (light having an emission wavelength of 480 nm or more) is completed.

  Specifically, an AR (reduced reflection) coating film and an HR (high reflection) coating film are deposited by the PCVD method. According to 1st Embodiment comprised as mentioned above, there exist the following effects.

  The main feature of the semiconductor laser diode 10 shown in FIG. 1 is an element having an InGaN active layer with a high In composition having a uniform composition distribution, and realizes light emission having a light emission wavelength of 480 nm or more with high light emission efficiency. Therefore, it has the following configuration.

It has an active layer 16 made of gallium indium nitride [In _x Ga _1-x N (0 <x <1)], and emits light in a long-wavelength visible region (light having a light emission wavelength of 480 nm or more) such as a green region. An epitaxial wafer for the semiconductor laser diode 10 is provided.

  In order to form the epitaxial wafer, the ZnO layer 13 is used as a zinc oxide (ZnO) -based epilayer lattice-matched (close to the lattice constant) to the active layer 16.

An a-plane sapphire substrate 11A is used as a substrate on which the ZnO layer 13 is epitaxially grown. That, a surface of the sapphire substrate 11A _- is the ZnO layer 13 is epitaxially grown on (11 20) (see FIG. 2).

With this configuration, a surface (11 _- 20) to on the sapphire substrate 11A having the principal, because it is grown a buffer layer 12 and the ZnO layer 13 made of ZnO in order, along the c-axis of the sapphire ZnO The a-axis grows side by side. As a result, along the c-axis length of sapphire (13.001 mm), four crystals of ZnO a-axis length (3.2407 mm) are arranged, and the crystal matching is very good at about 0.07%, which is an excellent crystal A surface buffer layer 12 and a ZnO layer 13 are obtained. Thereby, the distortion of the active layer 16 is reduced, and an active layer with good crystallinity is obtained.

Further, as shown in FIG. 3, the lattice constant (= 5.1955 Å) corresponding to the unit lattice c of ZnO is equal to the lattice constant (= 5.186 Å) corresponding to the unit lattice c of gallium nitride GaN and the indium nitride InN. It has a value between the lattice constant (= 5.76 Å) corresponding to the unit cell c, and is very close to the unit cell c of gallium indium nitride InGaN having an In composition of about 20%.
Thus, the lattice constant of the ZnO layer 13 having an excellent crystal plane is such that the indium (In) composition ratio of the well layer made of InGaN has an emission wavelength of 480 nm or more (emission wavelength in the green region). It is close to the lattice constant of the InGaN-based active layer 16 set to 20% or more.

  Therefore, phase separation that occurs when the In composition ratio of the active layer 16 is increased is suppressed, distortion of the active layer 16 is reduced, the influence of the piezoelectric field is suppressed, and the lattice constant of the substrate is greatly different. Is prevented from occurring. As a result, the band gap energy of the InGaN-based active layer 16 is about 2.2 eV, and light emission with high emission efficiency is possible in a long-wavelength visible region such as a green region (light emission wavelength is 480 nm or more). .

  Therefore, an element having an InGaN active layer 16 with a high In composition having a uniform composition distribution, and a semiconductor laser diode capable of realizing light emission with a light emission wavelength of 480 nm or more with high light emission efficiency can be obtained.

  Since the sapphire substrate 11A can be prepared in a large size and at a low cost, the semiconductor laser diode 10 having excellent mass productivity can be obtained using the sapphire substrate.

  ○ Since the buffer layer 12 in which ZnO is grown at a low temperature is formed between the sapphire substrate 11A and the ZnO layer 13, this also suppresses threading dislocations and improves the crystallinity of the InGaN-based active layer 16, Luminous efficiency is improved.

(Second Embodiment)
FIG. 4 shows a semiconductor laser diode 10A as a semiconductor light emitting device according to the second embodiment of the present invention.

The main feature of this semiconductor laser diode 10A is that it has the following configuration.
In the first embodiment, the c-plane sapphire substrate 11C is used, whereas the a-plane sapphire substrate 11A is used as a substrate on which the ZnO layer 13 is epitaxially grown. That is, the ZnO layer 13 is epitaxially grown on the c-plane (0001) (see FIG. 2) of the sapphire substrate 11C.
Between the sapphire substrate 11C and the ZnO layer 13, two buffer layers of a buffer layer 22 made of MgO and a buffer layer 12 made of ZnO are formed.
Other configurations are the same as those in the first embodiment.

Next, a method for manufacturing the semiconductor laser diode 10A will be described.
(Step 1a)
First, the sapphire substrate (sapphire wafer) 11c whose principal surface is the c-plane (0001) is cleaned.
This cleaning is performed by the organic cleaning or chemical etching described in the above (Step 1).

(Step 2a)
Next, a thermal cleaning process is performed on the cleaned sapphire substrate 11C.
This thermal cleaning process is the same as the thermal cleaning process described in (Step 2) above.

(Step 3a)
Next, the buffer layer 22 made of MgO is grown on the c-plane (0001) of the sapphire substrate 11C by the RFMBE method (buffer layer forming step).

The conditions in this case are, for example, that the thickness of the buffer layer 22 is 1-20 nm, the growth temperature Tg = 600 ° C., the plasma power (RF power) P = 300 W, and the O ₂ flow rate 3 sccm (standard cc / min). A high-purity Mg metal material is evaporated in a Knudsen cell and supplied to the substrate surface.

(Step 3b)
Next, the buffer layer 12 made of ZnO is grown on the buffer layer 22 made of MgO at a low temperature by the RFMBE method (buffer layer forming step).

The conditions in this case are, for example, growth temperature Tg = 400 to 500 ° C., plasma power (RF power) P = 300 W, and O ₂ flow rate 3 sccm (standard cc / min). A high-purity Zn metal material is evaporated in a Knudsen cell and supplied to the substrate surface.

The buffer layer 12 has a thickness of about 10-200 nm and a growth temperature Tg of about 250-650 ° C.
Thereafter, the above (Step 4) to (Step 6) are performed.

  On the ZnO layer 13 as the zinc oxide (ZnO) -based epilayer formed in this way, the semiconductor laser diode 10A for emitting light in a long-wavelength visible region (light having an emission wavelength of 480 nm or more) such as a green region. An epitaxial wafer is formed by performing the above (Step 7) to (Step 11). Thereafter, the above (Step 12) to (Step 17) are further performed to complete the manufacture of the semiconductor laser diode 10A.

  According to 2nd Embodiment comprised as mentioned above, in addition to the effect which the said 1st Embodiment show | plays, there exist the following effects.

  ○ Since the buffer layer 22 made of MgO is inserted between the sapphire substrate 11C having the c-plane (0001) as the main surface and the ZnO layer 13, formation of a domain rotated by 30 ° is suppressed. That is, the growth of the ZnO a-axis rotated by 30 ° with respect to the sapphire a-axis is suppressed. Thereby, even when the c-plane sapphire substrate 11C is used as a substrate on which the ZnO layer 13 is epitaxially grown, the distortion of the active layer 16 is reduced, and an active layer with good crystallinity is obtained.

  Therefore, even when a c-plane sapphire substrate is used, a semiconductor laser diode capable of realizing light emission with a light emission wavelength of 480 nm or more with high light emission efficiency by an element having a high In composition InGaN active layer 16 having a uniform composition distribution is obtained. Can do.

  The polarity of the ZnO layer 13 can be controlled by controlling the film thickness of the buffer layer 22 made of MgO. For example, when the thickness of the buffer layer 22 is less than 2 nm, the ZnO layer 13 grows with an oxygen (O) polarity, and when the thickness is less than 3 nm, the ZnO layer 13 grows with a zinc (Zn) polarity.

  When the conductivity type of the lower contact layer 14 is n-type, the polarity of the ZnO layer 13 may be either oxygen (O) polarity or zinc (Zn) polarity. On the other hand, when the conductivity type of the lower contact layer 14 is p-type, the ZnO layer 13 needs to be grown with zinc (Zn) polarity.

(Third embodiment)
FIG. 5 shows a semiconductor laser diode 10B as a semiconductor light emitting device according to the third embodiment of the present invention.

  The semiconductor laser diode 10B is characterized in that a pseudo lattice matching layer 30 is provided between the ZnO layer 13 and the InGaN-based active layer 16 in the semiconductor laser diode 10 according to the first embodiment shown in FIG. is there.

The pseudo lattice matching layer 30 is inserted between an oxide layer such as ZnO and a nitride layer such as InGaN. In the present embodiment, since the lower contact layer 14 is made of a nitride such as InGaN, the pseudo lattice matching layer 30 is provided between the ZnO layer 13 and the lower contact layer 14.
Other configurations are the same as those in the first embodiment.

  The pseudo lattice matching layer 30 is made of GaN having a thickness of 1 ML (molecular layer) or more and a critical thickness with respect to the ZnO layer 13. The “critical film thickness” referred to here is obtained by calculating how much film thickness can be grown on the lower ZnO layer 13. The critical film thickness of the pseudo-matched layer 30 made of GaN is about 20 nm at the maximum. This critical film thickness forms the active layer 16 or the like made of InGaN on the upper surface. Therefore, considering the layer formed on the pseudo lattice matching layer 30, the critical film thickness of the pseudo lattice matching layer 30 made of GaN is The thickness can be increased to about 50 nm. Thus, the critical film thickness of the pseudo-lattice matching layer 30 made of GaN can be set in the range of 1 ML or more and 50 nm or less, and is preferably set in the range of 1 ML or more and about 20 nm or less.

  In the first embodiment, the pseudo lattice matching layer 30 is formed after the ZnO layer 13 is formed on the buffer layer 12 in the above (Step 5). At this time, by simultaneously supplying Ga and nitrogen radicals (N) to the surface of the ZnO layer 13 at a temperature lower than 750 ° C., for example, at a low temperature of about 500 ° C., the oxygen (O) polarity c-plane (0001) of the ZnO layer 13. A pseudo-lattice matching layer 30 is formed by 4ML growth of GaN crystal on the top or zinc (Zn) polarity c-plane (0001).

  The reason why the growth temperature of the GaN crystal is performed at a low temperature is to suppress the interface reaction between the ZnO layer 13 and the pseudo lattice matching layer 30 made of GaN. Here, after growing 4ML of GaN, grow 1ML of InN, grow 1ML of InN and then grow 4ML of GaN, or grow a layer in which GaN layers and InN layers are stacked alternately to grow a pseudo lattice The matching layer 130 may be formed.

  The lattice constant difference between ZnO and GaN is about 1.8% on the a-axis, and the lattice constant difference between ZnO and InN is about 8.8% on the a-axis, respectively, but the GaN layer and InN layer constituting the pseudo lattice matching layer 30 are different. The lattice constant of ZnO can be maintained by setting the total film thickness to be equal to or less than the critical thickness of InGaN obtained by taking the average composition of the GaN layer and the InN layer. Here, the pseudo lattice matching layer 30 having n-type conductivity is formed by doping the pseudo lattice matching layer 30 with silicon (Si).

In addition, after growing a GaN crystal at a low temperature of about 500 ° C., heat treatment is performed at a temperature of about 700-1000 ° C. for 30 minutes to 2 hours to crystallize the pseudo-lattice matching layer 30 made of a GaN thin film deposited at a low temperature. The streak pattern appears gradually. Thereby, the crystallinity of the layer formed on the upper part of the pseudo lattice matching layer 30 made of GaN can be improved. If the temperature at which the GaN crystal is grown is too high, Ga diffuses into ZnO and Ga ₂ ZnO ₄ is formed, so it is necessary to set the temperature optimally (crystallization of the pseudo lattice matching layer 30).

  According to 3rd Embodiment comprised as mentioned above, in addition to the effect which the said 1st Embodiment show | plays, there exist the following effects.

  ○ Since the pseudo lattice matching layer 30 is formed between the ZnO layer 13 and the lower contact layer 14, it is an oxide layer / nitride layer between the ZnO layer 13 and the active layer 16, that is, an oxide layer. A steep interface is obtained between the ZnO layer 13 and the lower contact layer 14 which is a nitride layer, and a good crystal of the active layer 16 made of InGaN is obtained. As a result, it is possible to obtain a semiconductor laser diode as a highly reliable semiconductor light emitting element with high luminous efficiency.

  ○ By forming the pseudo-lattice matching layer 30 between the ZnO layer 13 and the active layer 16, the half-value width is narrower than that without the pseudo-lattice matching layer 30, and the semiconductor has good emission characteristics (high emission intensity) A laser diode can be obtained.

  ○ The pseudo-lattice matching layer 30 is made of GaN having a thickness of 1 ML or more and a critical thickness or less with respect to the ZnO layer 13, so that the ZnO layer is formed on the upper portion while maintaining the lattice constant of the underlying ZnO layer 13 By growing the active layer 16 made of InGaN lattice-matched to 13, an active layer having a good crystal can be obtained.

(Fourth embodiment)
FIG. 6 shows a semiconductor laser diode 10B as a semiconductor light emitting device according to the fourth embodiment of the present invention.

  The semiconductor laser diode 10C is characterized in that a pseudo lattice matching layer 30 is provided between the ZnO layer 13 and the InGaN-based active layer 16 in the semiconductor laser diode 10 according to the first embodiment shown in FIG. is there.

  In this embodiment, since the lower contact layer 14 is made of an oxide such as ZnMgO and the lower clad layer 15 is made of a nitride such as InGaN, the pseudo lattice matching layer 31 is formed of the lower contact layer 14 and the lower clad layer. 15 is provided.

  This pseudo lattice matching layer 31 has the same configuration as the pseudo lattice matching layer 30 shown in FIG. Other configurations are the same as those in the first embodiment.

  According to 4th Embodiment comprised as mentioned above, in addition to the effect which the said 1st Embodiment show | plays, there exist the following effects.

  ○ Since the pseudo lattice matching layer 31 is formed between the lower contact layer 14 and the lower cladding layer 15, the oxide layer / nitride layer between the ZnO layer 13 and the active layer 16, that is, the oxide layer A steep interface is obtained between a certain lower contact layer 14 and the lower cladding layer 15 which is a nitride layer, and a good crystal of the active layer 16 made of InGaN is obtained. As a result, it is possible to obtain a semiconductor laser diode as a highly reliable semiconductor light emitting element with high luminous efficiency.

  ○ By forming the pseudo-lattice matching layer 31 between the ZnO layer 13 and the active layer 16, the half width is narrower than that without the pseudo-lattice matching layer 31, and the semiconductor has good emission characteristics (high emission intensity). A laser diode can be obtained.

  ○ The pseudo-lattice matching layer 31 is made of GaN having a film thickness of 1 ML or more and a critical film thickness or less with respect to the ZnO layer 13, so that the ZnO layer is formed on the upper part while maintaining the lattice constant of the underlying ZnO layer 13 By growing the active layer 16 made of InGaN lattice-matched to 13, an active layer having a good crystal can be obtained.

(Fifth embodiment)
FIG. 7 shows a semiconductor laser diode 10D as a semiconductor light emitting device according to the fifth embodiment of the present invention.

  The semiconductor laser diode 10D is characterized in that, in the semiconductor laser diode 10 according to the first embodiment shown in FIG. 1, a pseudo lattice matching layer 32 made of a superlattice layer is provided between the ZnO layer 13 and the InGaN-based active layer 16. It is in the point provided.

  In the present embodiment, since the lower cladding layer 15 is made of an oxide such as ZnMgO, the pseudo lattice matching layer 32 from the superlattice is provided between the lower cladding layer 15 and the active layer 16 made of InGaN.

  The pseudo lattice matching layer 32 made of the superlattice layer is a layer in which GaN and InN having a thickness of 1 ML or more and a critical thickness of the ZnO layer 13 are stacked. Other configurations are the same as those in the first embodiment.

  According to 5th Embodiment comprised as mentioned above, in addition to the effect which the said 1st Embodiment show | plays, there exist the following effects.

  Since a pseudo lattice matching layer 32 made of a superlattice layer is formed between the lower cladding layer 15 and the active layer 16 made of InGaN, an oxide layer / nitride layer between the ZnO layer 13 and the active layer 16 That is, a steep interface is obtained between the lower cladding layer 15 which is an oxide layer and the active layer 16 which is a nitride layer, and a good crystal of the active layer 16 made of InGaN is obtained. As a result, it is possible to obtain a semiconductor laser diode as a highly reliable semiconductor light emitting element with high luminous efficiency.

  ○ By forming a pseudo lattice matching layer 32 made of a superlattice layer between the ZnO layer 13 and the active layer 16, the half width is narrower than that without the pseudo lattice matching layer 32, and the light emission characteristics are good (light emission) A semiconductor laser diode having a high intensity can be obtained.

  ○ The lattice constant of the underlying ZnO layer 13 is formed by stacking the pseudo-lattice matching layer 32 made of a superlattice layer by laminating GaN and InN having a thickness of 1 ML or more and a critical thickness or less with respect to the ZnO layer 13. While maintaining the above, an active layer 16 made of InGaN lattice-matched with the ZnO layer 13 is grown on the upper portion, thereby obtaining an active layer having a good crystal.

In addition, this invention can also be changed and embodied as follows.
In each of the above embodiments, the present invention is also applicable to a semiconductor laser diode having a structure in which a light guide layer is provided between the lower cladding layer and the active layer and between the active layer and the upper cladding layer. Accordingly, the semiconductor laser diode has a configuration having a separate confinement heterostructure (SCH), and a semiconductor laser diode with high emission efficiency can be obtained.

  In each of the above embodiments, the lower side from the active layer 16 is n-type and the upper side is p-type. However, the present invention also applies to a semiconductor laser diode having a configuration in which the lower side from the active layer 16 is p-type and the upper side is n-type. Is applicable.

  In the third and fourth embodiments shown in FIGS. 5 and 6, the pseudo lattice matching layers 30 and 31 grow a binary material of GaN at the initial growth stage, and the In composition gradually increases on the GaN layer. It may be a pseudo-lattice matching layer in which an increased layer (InGaN gradient composition layer) is formed. In this configuration, a sharp interface between the oxide layer and the nitride layer can be obtained by growing a binary material of GaN at the initial stage of growth of the pseudo lattice matching layers 30 and 31.

In the third and fourth embodiments, the pseudo-lattice matching layers 30 and 31 are formed of GaN having a thickness of 1 ML (molecular layer) or more and a critical thickness with respect to the ZnO layer 13, for example, 4 ML. Instead of GaN, 4ML InN may be grown.
In the fifth embodiment, the pseudo-lattice matching layer 32 made of a superlattice layer may be formed of a layer in which GaN and InN having a thickness of 1 ML or more and a critical thickness with respect to the ZnO layer 13 are stacked. . For example, the pseudo-lattice matching layer 32 may be configured by a layer in which 4ML GaN and 1ML InN are alternately stacked, or a layer in which 1ML GaN and 4ML InN are alternately stacked. In the case of the pseudo-lattice matching layer 32 composed of a superlattice layer having such a laminated structure, the critical film thickness of the pseudo-lattice matching layer 32A is defined as the critical film thickness corresponding to InGaN when the average composition of GaN and InN is taken. Is done.

  And in any case of such a configuration, the pseudo-lattice matching layer 32 made of a superlattice layer has a film thickness of 1 ML or more and a critical film thickness or less with respect to the substrate. By growing the active layer 16 made of InGaN lattice-matched with the ZnO layer 13 while maintaining the lattice constant of 13, the active layer 16 having a good crystal can be obtained. As a result, a semiconductor light emitting device such as a semiconductor laser diode having high emission efficiency and high reliability can be obtained.

The present invention is also applicable to a configuration in which the pseudo-lattice matching layers 30, 31, and 32 described in the third to fifth embodiments are provided in the semiconductor laser diode according to the second embodiment shown in FIG.
In the first embodiment, a surface of the sapphire substrate 11A (11 _- 20) forming a buffer layer 12 made of ZnO on (see FIG. 2), a ZnO layer 13 as a zinc oxide (ZnO) based epitaxial layer configuration _- (20 11) and on the equivalent plane, forming a buffer layer 12 and the ZnO layer 13 _- but then are, a surface not limited to (11 20), a plane perpendicular to the c-plane (0001) In addition, the present invention is applicable.

  In each of the above embodiments, the semiconductor light emitting element configured as a semiconductor laser diode has been described. However, the present invention can also be applied to a semiconductor light emitting element such as a light emitting diode (LED) having a pn junction.

  In each of the above embodiments, the active layer 16 is made of InGaN. However, the present invention can also be applied to a semiconductor light emitting device in which the active layer 16 is made of another group III-V nitride compound semiconductor such as AlGaInN. It is.

Sectional drawing which shows schematic structure of the semiconductor laser diode which concerns on 1st Embodiment. The unit cell figure showing the surface orientation of a sapphire substrate. Explanatory drawing which shows the physical characteristics of zinc oxide, gallium nitride, indium nitride, aluminum nitride, sapphire, and magnesium oxide. Sectional drawing which shows schematic structure of the semiconductor laser diode which concerns on 2nd Embodiment. Sectional drawing which shows schematic structure of the semiconductor laser diode which concerns on 3rd Embodiment. Sectional drawing which shows schematic structure of the semiconductor laser diode which concerns on 4th Embodiment. Sectional drawing which shows schematic structure of the semiconductor laser diode which concerns on 5th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 10A, 10B, 10C, 10D ... Semiconductor laser diode as semiconductor light emitting element, 12 ... ZnO buffer layer, 13 ... ZnO layer, 14 ... Lower contact layer, 15 ... Lower clad layer, 16 ... Active layer, 17 ... Upper Cladding layer, 18 ... upper contact layer, 19 ... passivation film, 20 ... lower electrode, 21 ... upper electrode, 30, 31, 32 ... pseudo lattice matching layer.

Claims (12)

A sapphire substrate, a zinc oxide (ZnO) -based epi layer, a buffer layer between the sapphire substrate and the zinc oxide (ZnO) -based epi layer, a lower contact layer formed on the buffer layer, and gallium indium nitride An active layer made of [In _x Ga _1-x N (0 <x <1)], and an upper cladding layer and a lower cladding layer lattice-matched to at least one of the active layer or the zinc oxide (ZnO) -based epilayer And an upper contact layer formed on the upper clad layer.   The semiconductor light emitting element according to claim 1, wherein the buffer layer is formed on a c-plane in a plane orientation of the sapphire substrate.   The semiconductor light emitting element according to claim 1, wherein the buffer layer is formed on an a-plane in a plane orientation of the sapphire substrate.   3. The semiconductor light emitting device according to claim 1, wherein the buffer layer is magnesium oxide (MgO).   4. The semiconductor light emitting device according to claim 1, wherein the buffer layer is zinc oxide (ZnO).   A pseudo-lattice made of GaN or InN between the zinc oxide (ZnO) -based epilayer and the active layer, and having a film thickness of 1 ML or more and less than the critical film thickness with respect to the zinc oxide (ZnO) -based epilayer The semiconductor light emitting device according to claim 1, further comprising a matching layer.   The pseudo-lattice matching layer comprises a superlattice layer in which GaN and InN having a thickness of 1 ML or more and a critical thickness or less with respect to the zinc oxide (ZnO) -based epilayer are stacked. The semiconductor light emitting device described.   8. The semiconductor light emitting device according to claim 1, wherein a composition ratio of indium (In) in the active layer is 20% or more. 9. A buffer layer forming step for forming a buffer layer on the sapphire substrate, a ZnO layer forming step for forming a zinc oxide (ZnO) -based epi layer on the buffer layer, and a lower contact for forming a lower contact layer on the ZnO layer A layer forming step, a lower clad layer forming step of forming a clad layer lattice-matched to at least one of the zinc oxide (ZnO) -based epi layer and the active layer, and gallium indium nitride [In _x Ga ₁ an active layer forming step of forming an active layer made of _-x N (0 <x <1)], a pseudo lattice matching layer forming step of forming a pseudo lattice matching layer between the substrate and the active layer, An upper clad layer forming step of forming a clad layer lattice-matched to at least one of a zinc oxide (ZnO) -based epi layer and an active layer on the active layer; and forming a contact layer on the upper clad layer The method of manufacturing a semiconductor light emitting element characterized by comprising a contact layer formation step.   10. The method of manufacturing a semiconductor light emitting device according to claim 9, wherein the surface orientation of the sapphire substrate is a c-plane, and the buffer layer is magnesium oxide (MgO).   10. The method of manufacturing a semiconductor light emitting device according to claim 9, wherein the surface orientation of the sapphire substrate is a-plane, and the buffer layer is zinc oxide (ZnO). The step of forming the pseudo lattice matching layer is characterized in that the pseudo lattice matching layer made of GaN or InN is formed to a thickness not less than 1 ML and not more than a critical thickness with respect to a ZnO layer. The manufacturing method of the semiconductor light-emitting device of description.

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