WO2004036659A1

WO2004036659A1 - Optical semiconductor device

Info

Publication number: WO2004036659A1
Application number: PCT/JP2003/011755
Authority: WO
Inventors: Yoshihiro Ito; Michio Kadota
Original assignee: Murata Manufacturing Co., Ltd.
Priority date: 2002-10-01
Filing date: 2003-09-16
Publication date: 2004-04-29
Also published as: AU2003264432A1; JP2004128106A

Abstract

An optical semiconductor device comprising a desired compound semiconductor layer having a band gap energy (Eg) smaller than that of ZnO. An n-type contact layer (6), an n-type cladding layer (7), an active layer (8), a p-type cladding layer (9) and a p-type contact layer (10) are formed in this order on a ZnO monocrystal substrate (1). The active layer (8) is expressed by a composition formula of BaxZn1-xO (wherein 0 < x < 0.55), and made of a mixed crystal compound wherein ZnO is dissolved in the Ba component so that the band gap energy (Eg) becomes smaller than that of ZnO. The n-type cladding layer (7) and the p-type cladding layer (9) are made of a compound semiconductor which has a larger band gap energy (Eg) than the active layer (8) and is expressed by a composition formula of MgzZn1-zO (wherein 0 ≤z <1).

Description

Description Optical semiconductor device technology

The present invention relates to an optical semiconductor device, and more particularly, to an optical semiconductor device such as a light emitting device that emits light in a blue / ultraviolet region and a multilayer reflector. Background art

ΖπΟ (zinc oxide), a type of Π-VI compound semiconductor, has a very large exciton binding energy, and the electrons and holes recombine directly to efficiently emit light. Research on light-emitting elements has been actively conducted.

By the way, a light emitting element has a so-called double hetero structure in which an active layer that emits light by current injection is sandwiched between a pair of cladding layers having a larger band gap energy Eg than the active layer, thereby improving luminous efficiency. Are known.

In the light emitting device, in order to improve the luminous efficiency, the band gap difference △ Eg between the active layer and the cladding layer must be increased.

(i) Decrease the band gap energy E g of the active layer, or

(ii) increase the band gap energy Eg of the cladding layer, or

(iii) It is necessary to reduce the band gap energy E of the active layer and increase the band gap energy E g of the cladding layer.

Further, since the wavelength of the emitted light depends on the band gap energy of the active layer, light of a desired wavelength can be emitted by changing the band gap energy of the active layer.

Technologies for increasing the band gap difference AEg have already been proposed for light emitting devices based on ZnO.

For example, a technique in which Cd is dissolved in ZnO to form an active layer of a CdZnO-based mixed crystal compound, and the band gap energy Eg of the active layer is set to be smaller than that of ZnO. / 1 641 1 pan fret), a ZnO-based mixed crystal compound in which part of O is replaced with a group VI element other than O, for example, S or Se, is used as the active layer, and the band gap energy E g of the active layer is set to Z A technology that attempts to reduce the size of nO is known (Japanese Patent Application Laid-Open No. 2002-16285).

As a technique for increasing the bandgap energy Eg of the cladding layer to be larger than that of ZnO, for example, a technique of dissolving Mg in ZhO or a technique disclosed in Japanese Patent Application Laid-Open No. 10-270749. Japanese Patent Application Laid-Open No. 2001-77420), and a technique in which a group VI element, particularly C is dissolved in ZnO is proposed.

In addition, as a technique in which other components are contained in ZnO, a transparent oxide having a band gap energy Eg of 3.5 eV or more, for example, containing 1 to 10 wt% of BaO or S 「0 in a ヱ 110 film is included. technically and allowed (JP 2000-1 59547 JP), sigma 00 8 ₃ Ya 3 r was allowed to 0.5 containing 5% to 20% against Shi atomic concentration Zn ²⁺ technology has also been proposed (Japanese Patent Kaihei 8–1 99343).

However, in the international publication 00/1 641 1 broth, the band gap energy Eg of the active layer is being reduced by using a CdZnO-based mixed crystal compound for the active layer. However, Cd is toxic, so there is a problem when considering environmental aspects.

In Japanese Patent Application Laid-Open No. 2002-16628, a group VI element other than O, for example, S or Se is used to partially replace O, thereby obtaining a mixed crystal compound having a small bandgap energy E g. Although the electronegativity of O is 3.5, the electronegativities of S and Se are 2.5 and 2.4, respectively, and the difference in electronegativity is 1.0 or more. Very large.

Since the difference in electronegativity is very large, the poling characteristics are remarkable, but the solid solubility is small. Therefore, the eutectic (eutectic mixture) of ZnO and ZnS (or ZnSe) is obtained. Is easily generated, and it is difficult to generate ZnOS or ZnOS e (hereinafter, referred to as “ZnO-based mixed crystal compound”).

That is, JP-A-2002-16285 is considered to be able to produce a {η} -based mixed crystal compound in terms of bowing characteristics. However, since the solid solubility is very small, a ZnO-based mixed crystal compound is actually used. There is a problem that it is difficult to generate the compound semiconductor, and thus it is difficult to obtain a compound semiconductor having a smaller band gap energy Eg than that of ZnO.

Also, JP-A-10-270749 and JP-A-2001-77420 attempt to increase the band gap energy Eg of the Z ηθ-based thin film, and reduce the band gap energy E g of the active layer. It's not a trivial one.

Also, Japanese Patent Application Laid-Open No. 2000-155954 relates to a low-reflection heat ray shielding glass in which a zinc oxide thin film and a silver film are laminated on a glass substrate, and not to an optical semiconductor element such as a light emitting element. Different uses.

Further, Japanese Patent Application Laid-Open No. 8-199343 relates to a transparent conductive film used for a transparent electrode of a liquid crystal display device, and performs etching with low resistance by adding Ba or Sr to ZnO. It is intended to obtain a transparent conductive film having excellent characteristics, and is not intended to modulate the bandgap energy as in an optical semiconductor device such as a light-emitting device. Disclosure of the invention

The present inventors have made intensive studies to achieve the above object, when a solid solution of B _a or S _r in Z _n O, band gap depending on the content and the deposition temperature of the B a or S r We have learned that the energy E g can be modulated (hereinafter, such modulation is called “band modulation”).

The present invention has been made based on such findings, and the optical semiconductor device according to the present invention has at least one of Ba and Sr dissolved in ZnO, and these Ba and Sr It is characterized by having at least one or more compound semiconductor layers whose band gap energy is modulated according to the content of Sr.

Further, the optical semiconductor device according to the present invention has at least one layer in which at least one of Ba and Sr is dissolved in ZnO and the band gap energy is modulated according to the film formation temperature. It is characterized by having the above compound semiconductor layer.

According to the optical semiconductor element, a compound semiconductor layer having a desired band gap energy Eg can be easily obtained by the band modulation action.

Further, according to the optical semiconductor element, it is possible to obtain an optical semiconductor element such as a light emitting element having a desired compound semiconductor layer having a band gap energy smaller than that of ZnO or a multilayer reflector.

The optical semiconductor device of the present invention is characterized in that at least one of the compound semiconductor layers is an active layer that emits light by current injection.

According to the above configuration, since the active layer is formed of the band-modulated compound semiconductor layer, the band gap energy of the active layer can be reduced.

Further, the optical semiconductor device of the present invention is characterized in that it comprises a multilayer film in which a plurality of the compound semiconductor layers having different band gap energies are alternately stacked.

Further, even when the content of Ba and Sr is constant, a light-emitting element or a multilayer film having a compound semiconductor layer having a desired band gap energy smaller than ZnO depending on the film formation temperature. An optical semiconductor device such as a reflecting mirror can be obtained.

According to the above configuration, by increasing the band gap energy of the multilayer film to be larger than the band gap energy of the active layer, light emitted from the active layer can be reflected by the multilayer film.

Further, the optical semiconductor device of the present invention is characterized in that the multilayer film forms an active layer that emits light by current injection.

In addition, the band gap energy of the multilayer film is compared with the band gap energy of the active layer. By increasing the size, it is possible to obtain a multilayer mirror capable of reflecting light emitted from the active layer, and it is possible to obtain an optical semiconductor device having improved luminous efficiency by preventing energy loss.

According to the above configuration, since the active layer is formed of a multilayer film including a plurality of band-modulated compound semiconductor layers, it is possible to obtain an active layer having a multiple quantum well structure with good luminous efficiency.

Further, the optical semiconductor device of the present invention is characterized in that the active layer is sandwiched between cladding layers having a bandgap energy larger than that of the active layer.

According to the above configuration, an active layer having a small band gap energy can be sandwiched by a clad layer having a large band gap energy, and a semiconductor device having a double hetero structure having excellent luminous efficiency can be obtained. .

Further, the cladding layer is formed of a semiconductor material containing ZnO as a main component, or is formed of a semiconductor material in which Mg is dissolved in Zηθ, or It is characterized by being formed of a semiconductor material containing G a N as a main component.

According to the above configuration, a cladding layer having a larger band gap energy Eg than the active layer can be easily obtained.

In the optical semiconductor device of the present invention, the compound semiconductor layer may have a composition formula of B axZn 1 -χθ (0 <x <1) and a composition formula of SryZn 1−y O (0 <y <1) Thus, a compound semiconductor layer composed of a ternary mixed crystal compound can be obtained.

In addition, the inventors of the present invention have conducted intensive research. As a result, by setting the mole fraction of the Ba component or the Sr component to the Zn component to be less than 0.55, the pouring characteristics are remarkably exhibited, and the eutectic is formed. It has been found that a desired mixed crystal compound can be obtained without being generated.c.Therefore, in the optical semiconductor device of the present invention, X and y are 0 <x <0.55 and 0 <y, respectively. <0.55. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic sectional view of one embodiment (first embodiment) of an optical semiconductor device according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between the composition molar ratio X of the elements to be dissolved and the band gap energy Eg.

FIG. 3 is a schematic cross-sectional view showing a second embodiment of the optical semiconductor device according to the present invention. FIG. 4 is an enlarged sectional view of a main part of FIG. FIG. 5 is a schematic sectional view showing an optical semiconductor device according to a third embodiment of the present invention. FIG. 6 is an enlarged sectional view of a main part of FIG.

FIG. 7 is a measurement diagram showing a relationship between the molar composition ratio X of the Ba component and the c-axis length of the Ba x Zn—X O thin film.

FIG. 8 is an X-ray spectrum when the molar composition ratio X of the Ba component is 0.41.

FIG. 9 is a characteristic diagram showing the relationship between the molar composition ratio X of the Ba component and the band gap energy Eg.

FIG. 10 is a characteristic diagram showing the relationship between the substrate temperature T and the bandgap energy Eg. BEST MODE FOR CARRYING OUT THE INVENTION

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of a light emitting diode (hereinafter, referred to as “LEDJ”) as one embodiment (first embodiment) of an optical semiconductor device according to the present invention.

In the figure, reference numeral 1 denotes a single crystal substrate containing ZnO as a main component (hereinafter referred to as η Ο Ο substrate), wherein the Ζ Ο substrate 1 is conductive and has a zinc polar surface 1 a And an oxygen polar surface 1b.

In the LED, a light emitting layer 2 is formed on a zinc polar surface 1 a of a ZnO substrate 1, and the surface of the light emitting layer 2 is made of indium tin oxide (hereinafter referred to as “IT OJ”). A transparent electrode 3 having a thickness of about 150 nm is formed, and a Ni film, an AI film, and an Au film are sequentially laminated at approximately the center of the surface of the transparent electrode 3 to form a total thickness of about 30 nm. A 0 nm p-side electrode 4 is formed.

On the oxygen polarity surface 1b of the ZnO substrate 1, an n-side electrode 5 having a total thickness of about 300 nm in which a Ti film and an Au film are sequentially laminated is formed.

The light emitting layer 2 is specifically composed of a multilayer film in which an n-type contact layer 6, an n-type cladding layer 7, an active layer 8, a p-type cladding layer 9, and a p-type contact layer 10 are sequentially laminated. ing.

That is, the active layer 8 is sandwiched between the _Π -type cladding layer 7 and the ρ-type cladding layer 9, and the η-type cladding layer 7 is connected to the η-side electrode 5 via the η-type contact layer 6 and the Ζηθ substrate 1. The ρ-type cladding layer 9 is connected to the transparent electrode 3 via the ρ-type contact layer 10.

Each layer forming the light emitting layer 2 is formed of a material having ZnO as a base material.

The active layer 8 emits light by recombination of electrons as n-type carriers and holes as p-type carriers, and the wavelength of emitted light is determined by the bandgap energy E g of the active layer 8. .

The bandgap energy Eg of the active layer 8 and the bandgear of the cladding layers 7 and 9 Since the luminous efficiency can be improved as the band gap difference ΔΕ g from the gap energy E g increases, the band gap energy E g of the active layer 8 needs to be reduced.

Therefore, in the present embodiment, in order to obtain a band gap energy Eg smaller than the band gap energy Eg (= 3.3 eV) of ZnO, the active layer 8 is made of a mixed crystal compound of ZnO and BaO, that is, a composition formula Ba xZn l- It is formed of BaZn O-based mixed crystal compound represented by χθ. ;

By mixing ZnO with BaO, a large bowing characteristic can be obtained, whereby an active layer 8 having a bandgap energy Eg smaller than ZnO can be obtained.

Hereinafter, the reason will be described in detail.

A mixed crystal compound is generally represented by the composition formula A X B 1 -X C (or A B 1 -X Cx), and its band gap energy Eg is represented by the following equation (1).

Eg (X) = a + bx + cx2 (1) where a and b are constants.

C is a constant called a poing parameter, and is expressed by Equation (2). c = ci + ce-(2) where the first term ci on the right-hand side indicates the band gap energy Eg obtained by approximating the virtual crystal, and the molar composition ratio X of element A (or element C), which is a solid solution element, This is a term that is proportionally distributed.

The second term ce on the right side is a term caused by the non-uniformity of the lattice, and is expressed by equation (3).

ce = Ac2ZT ■■■ (3) where, c is the difference in electronegativity between element A and element B (or element B and element C), and T is the bandwidth parameter.

Figure 2 shows the relationship between the molar composition ratio X of the solid solution element (element A or element C) and the band gap energy Eg. The horizontal axis is the molar composition ratio of the solid solution element x, and the vertical axis is the band. The gap energy E g is shown.

That is, when the pouring parameter c is Γο, the molar composition ratio X and the band gap energy E g are directly proportional to the dashed line, and the gang gap energy E g increases linearly as the molar composition ratio X increases. I do.

However, when the bowing parameter c is other than Γ0 ”, the relationship between the molar composition ratio X and the band gap energy E g is not linear but non-linear.

That is, in this case, the Boeing parameter. Depends on the difference Δc in electronegativity between element A and element B (or element B and element C), as is clear from equations (2) and (3).

In other words, if the difference Δc is large, the value of _c e is large, and accordingly the bowing parameter c is large, and the bowing characteristic is conspicuous.

For example, Z n O and G a N type G a N and O and AIN to be mixed ¹ J a semiconductor compound having the same crystal structure, a mixed crystal compound represented by the composition formula AI XGA 1 one xN Generate However, since the electronegativity of Ga is 1.6 and the electronegativity of AI is 1.5, the difference △ c is as small as 0.1. Cannot be obtained, and the band gap energy E g cannot be reduced as shown by the dashed line.

On the other hand, for example, when attempting to mix S in ZnO as in Patent Document 2, the electronegativity of S is 2.5, whereas the electronegativity of O is 3.5. Since the difference Ac is as large as 1.0, a large parabolic bowing characteristic can be obtained as shown by the two-dot chain line.

However, in this case, since the difference in electronegativity Ac is too large, a eutectic of ∑00 and 2 ^ 5 is easily formed, and a mixed crystal compound (Z π O 1—XSX) as an intermediate product is obtained. Becomes difficult.

Similarly, when trying to mix Se with Z ηθ, the electronegativity of Se is 2.4,

Difference △ _c of electronegativity of O is 1.1 and greater, it becomes difficult to obtain the desired mixed crystal compound (ZnO I- xS ex).

On the other hand, when BaO and ZnO are mixed crystals, the electronegativity of Ba is 0.9, the electronegativity of Zn is 1.6, and the difference Ac is 0.7, which is moderately large. However, as shown by the solid line, the bowing characteristic appears remarkably in a parabolic shape.

In addition, the difference in electronegativity Ac is not excessively large, so that a eutectic of ZnO and BaO is not generated, and a BaZnO-based mixed crystal compound can be generated with high efficiency.

Further, in the present embodiment, the molar composition ratio x is set such that the mathematical formula (4) is satisfied by the above composition formula B a x Zn l−χθ.

0 <x <0.55− (4) That is, in order to obtain a BaZnO-based mixed crystal compound, the molar composition ratio X must be larger than 0, but when X becomes 0.55, the point S As shown in the figure, when the mixed crystal compound has the same value as the band gap energy E g 1 of ZnO and the molar composition ratio X of the Ba component is increased to 0.55 or more, the band gap energy E of the active layer 8 is increased. g becomes larger than the band gap energy Eg 1 of ZnO.

Therefore, in the present embodiment, a BaZηθ-based mixed crystal compound is generated such that the molar composition ratio X is 0 <x and 0.55, for example, 0.3.

The n-type cladding layer 7 and the p-type cladding layer 9 need to have a band gap energy Eg larger than that of the active layer 8 to effectively confine carriers in the active layer 8. 1-ZO ( _z is 0≤z <1, for example, 0.2) mixed with ZnO and n-type cladding layer 7 is about 2000 nm thick, p-type cladding layer 9 Is formed to a thickness of about 600 nm.

The n-type contact layer 6 and the p-type contact layer 10 are both formed with a thickness of about 200 nm with a thickness of about ηθ. Next, a method for manufacturing the LED will be described.

First, a ZnO single crystal is prepared by the SCVT (Seeded Chemical Vapor Transport) method, etc., and the ZnO single crystal is cut out into a plane perpendicular to the c-axis direction of the crystal axis and mirror-polished. It is prepared and its polarity is confirmed by SNDM (Scanning Nonlinear Dielectric Microscopy).

After determining the polarity of the ZnO substrate 1, the electron cyclotron resonance (Electron cyclotron)

Cyclotron Resonance;

Hereinafter, a ZnO thin film is laminated on the zinc polar surface 1a of the ZnO substrate 1 using a sputtering device (hereinafter referred to as “ECRJ”).

That is, an ECR sputtering apparatus divided into a plasma generation chamber and a film formation chamber is prepared, and the ZnO substrate 1 is set at a predetermined position in the film formation chamber so that the zinc polar surface 1a is the upper surface. The substrate 1 is heated to a temperature of 300 to 800 ° C.

Next, a reactive gas such as oxygen and a gas for plasma generation such as argon are supplied to the plasma generation chamber, and microwave discharge is performed at a frequency (2.45 GHz) at which the cyclotron resonates. A plasma is generated in the generation chamber.

After that, high-frequency power (for example, 150 W) is applied to the sputter target, and the target (ZnO) is sputtered using plasma generated in the plasma generation chamber. An n-type contact layer 6 made of ZnO is formed on the surface of the substrate 1.

Next, reactive sputtering was performed using a target obtained by sintering MgO and ZnO at a desired mixed crystal ratio, and an n-type cladding layer composed of Mg z Zn l-zO (0≤z <1) Form 7.

Thereafter, reactive sputtering is performed in the same manner, and an active layer 8 composed of Ba x Zn l- χθ (0 <x <0.55) and a p-type clad composed of gz Zn 1 -zO (0≤z <1) are sequentially formed. A layer 9 and a p-type contact layer 10 made of ZnO are formed.

The thickness of each thin film is set to a desired thickness by controlling the reaction time.

Next, a Ti film and an Au film are sequentially formed on the surface of the oxygen polar surface 1b of the ZnO substrate 1 by a vacuum evaporation method to form an n-side electrode 5, and then a p-type contact is formed by a vacuum evaporation method. A transparent electrode 3 is formed by forming an ITO film on the surface of the layer 10, and then a NA is formed by a lift-off method, and Au is sequentially laminated to form a P-side electrode 4.

As described above, in the first embodiment, the band gap energy E g of the active layer 8 is made smaller than the band gap energy E g of the cladding layers 7 and 9 by mixing BaO and Zηθ. Therefore, a light-emitting element having good luminous efficiency can be obtained.

In the first embodiment, an ECR sputtering apparatus is used, and a sputtering process is performed. Since a ZnO-based thin film is formed according to the theory, it is not necessary to separately provide an expensive apparatus, and the thin film can be formed at a low cost.

In addition, since the plasma generation chamber and the film formation chamber are separated from each other, it is possible to obtain a high quality thin film while minimizing the plasma damage of the {η} thin film.

Figure 3 is a schematic cross-sectional view of an LED according to a second embodiment of the optical semiconductor device according to the present invention, in this second embodiment, the We ₀ 0 substrate 1 and η shape contactor Bok layer 6 A multilayer reflector 11 is interposed between them.

That is, as described above, the active layer 8 emits light according to its band-cap energy E g due to recombination of electrons, which are π-type carriers, and holes, which are ρ-type carriers. Light is emitted not only to the transparent electrode 3 side but also to the ZnO substrate 1 side.

Then, the light emitted to the ZnO substrate 1 side is absorbed by the ZnO substrate 1 and the like and disappears, thereby causing energy loss.

Accordingly, in the second embodiment, the multilayer reflector 1 1 having a thickness of 20-30 ₀ interposed between the ZnO substrate 1 and the n-type contact layer 6, emitted in ZnO substrate 1 side Light is reflected by the multilayer film reflecting mirror 11 and radiated to the transparent electrode 3 side to prevent energy loss and avoid a decrease in light emission efficiency.

As shown in FIG. 4, the multilayer mirror "I1" has a band gap energy Eg larger than that of the active layer 8, and alternately includes two types of compound semiconductor layers having different band gap energies Eg. It is formed of a multi-layered multilayer film.

That is, for example, when the active layer 8 is formed of BaXZn1-XO (x is, for example, 0.4), the first compound semiconductor layer 1 la Ba x Zn l— χθ (x is, for example, 0.2), and the second compound semiconductor layer 11 b is formed of Ba x Zn 1 -χθ (χ is, for example, 0.1). A large number of thin films 11 1, 1 12, 11 m-1, and 11 m each having a compound semiconductor layer 11 a and a second compound semiconductor layer 11 b are stacked.

The thicknesses t 1 and t 2 of the first and second compound semiconductor layers 11 a and 11 b are determined by Expressions (5) and (6). Thus, the number of stacked layers of each of the laminated films 11 1, 11 2, 11 1 m -1 and 11 m is 20 to 30.

t 1 = λ / (4 x η 1) ... (5) t 2 = λ / (4 X η 2) ... (6) where λ is the emission wavelength, and η 1 is the first compound semiconductor layer 11 a And n 2 is the refractive index of the first compound semiconductor layer 11 b.

In the second embodiment, the multilayer mirror 11 is formed of a multilayer film in which a large number of two types of compound semiconductor layers are alternately stacked, but a large number of three or more types of compound semiconductor layers are sequentially formed. It may be formed by a laminated multilayer film. Also, the second embodiment can be easily manufactured by the ECR sputtering method similarly to the first embodiment.

FIG. 5 shows a laser diode as an optical semiconductor device according to a third embodiment of the present invention.

Hereafter, this is a schematic cross-sectional view of “LDJ”. In the third embodiment, the active layer 20 has a multiple quantum well structure.

That is, in the LD, a light emitting layer 14 is formed on a zinc polar surface 13 a of a conductive ZnO substrate 13, and a Ni film, an AI film, and an A film are formed on the surface of the light emitting layer 14. A p-side electrode 15 having a total film thickness of about 300 nm in which u films are sequentially stacked is formed.

Further, an n-side electrode 16 having a total thickness of about 300 nm in which a Ti film and an Au film are sequentially laminated is formed on the oxygen polar surface 13 b of the ZnO substrate 13.

The light emitting layer 14 is, specifically, a π-type contact layer 17, an n-type cladding layer 18, an r> -type light guiding layer 19, an active layer 20, a p-type light guiding layer 21, and a p-type cladding layer. 22, a current limiting layer 23 and a p-type contact layer 24 are formed of a multilayer film sequentially laminated.

That is, the active layer 20 is sandwiched between the n-type cladding layer 18 and the p-type cladding layer 22 via the n-type guide layer 19 and the p-type guide layer 21, respectively.

The n-type cladding layer 18 is connected to the π-side electrode 16 via the η-type contact layer 17 and the ΖηΟ substrate 13, and the ρ-type cladding layer 22 is connected to the current limiting layer 23 and the ρ-type contact layer 24. Connected to the 電極 side electrode 15 via

Thus, the active layer 20 is formed of Ba χ Ζη 1— χθ, and as shown in FIG. 6, the barrier layers 20 a (X is, for example, 0.1) and the ゥ layer 20 b ( X has a multi-quantum well structure in which 2 to 5 layers, for example, 0.3) are alternately laminated with a thickness of 3 nm each.

When the refractive index of the active layer 20 is larger than that of the n-type cladding layer 18 and the p-type cladding layer 22, light can be confined in the active layer 20, but since the active layer 20 is a thin film, it can be sufficiently filled. When light cannot be confined, it is necessary to prevent light from leaking from the active layer 20. Therefore, the active layer 20 and the r> -type cladding layer 18 and p An n-type light guide layer 19 and a p-type light guide layer 21 having an intermediate refractive index between the cladding layers 18 and 22 and the active layer 20 are interposed between the cladding layers 22 and 22.

Then, an n-type contact layer 17 having a thickness of about 1,500 nm made of Zηθ is formed on the zinc polar surface 13 a of the Zηθ substrate 13, and the surface of the n-type contact layer 17 is formed on the surface of the n-type contact layer 17. Is formed as an n-type cladding layer 18 having a thickness of about 2000 nm made of Mg z Z n 1 -ZO (z is 0≤z <1, for example, 0.2). On the surface of 8, a film consisting of Z ηθ An n-type light guide layer 19 having a thickness of about 40 nm is formed.

On the surface of the n-type light guide layer 19, an active layer 20 having the above-mentioned multiple quantum well structure is laminated, and on the surface of the active layer 20, MgzZn1-zO (z is O ^ z For example, a p-type light guide layer 21 having a thickness of about 40 nm made of, for example, 0.2) is formed, and the surface of the p-type light guide layer 21 further includes Mg z Zn 1 —z O (z 0 ≦ z <1, and a p-type cladding layer 22 of, for example, 0.2) and having a thickness of about 2,000 nm is formed.

Furthermore, on the surface of the P-type cladding layer 22, a current of 400 nm in thickness consisting of Mg z Z n 1 -ζθ (z is 0≤z <1, for example, 0.2) is applied so that current flows only in the oscillation region. A limiting layer 23 is formed in a predetermined shape so as to have a groove 23a, and then a p-type contact layer 24 is formed on the surface of the p-type cladding layer 22 so as to cover the current limiting layer 23 in a cross-sectional shape of a letter. I have.

Then, the LD is also manufactured by a method and a procedure substantially similar to those of the first embodiment.

That is, first, a ∑00 single crystal is prepared by a thirty method or the like, a ZnO single crystal is cut into a plane perpendicular to the c-axis direction of the crystal axis, and mirror-polished to prepare a ZnO substrate. Confirm by SN DM method.

Next, similarly to the first embodiment, an ECR sputtering apparatus is prepared, and the ZnO substrate 13 is set at a predetermined position in the film forming chamber so that the zinc polar surface 13 a is the upper surface. The substrate 1 is heated to a temperature of 300 to 800 ° C.

Next, a reactive gas such as oxygen and a plasma generation gas such as argon are supplied to the plasma generation chamber, and microwave discharge is performed to generate plasma in the plasma generation chamber, and the target (ZnO) is sputtered. Then, an n-type contact layer 17 made of ZnO is formed on the surface of the ZnO substrate 13 by reactive sputtering.

In the same manner as above, reactive sputtering is sequentially performed while appropriately changing the target to a desired substance, and the n-type contact layer 17, the π-type cladding layer 18, the n-type light guide layer 19, the active layer 20, A p-type light guide layer 21, a p-type cladding layer 22, and a current limiting layer 23 are sequentially formed.

Then, after forming the current limiting layer 23, the formed ZnO substrate 13 is once taken out of the ECR sputtering apparatus, a photoresist is applied to the surface of the current limiting layer 23, and a known photolithography technique is used. The resist film is patterned and subjected to etching with an alkaline solution such as NaOH to form the current limiting layer 23 in a predetermined shape.

Next, the ZnO substrate 13 is returned to a predetermined position in the ECF sputtering apparatus again, and reactive sputtering is performed to form a p-type contact layer 24 having a T-shaped cross section and Zηθ.

Then, similarly to the first embodiment, a Ti film and an Au film are sequentially formed on the surface of the oxygen-polar surface 13 b of the ZnO substrate 13 by a vacuum evaporation method, and n A side electrode 16 is formed, and then Ni, AI, and Au are sequentially laminated on the surface of the P-type contact layer 24 by vacuum evaporation to form a p-side electrode. Form 1 5

Thus, similarly to the first and second embodiments, the third embodiment also includes two types of compound semiconductor layers having different band gap energies E g in which 830 and ∑ ₀ O are mixed and crystallized. That is, the active layer 20 having a multiple quantum well structure formed by the barrier layer 20 a and the p-type layer 20 b is provided, and the band gap energy E g of the active layer 20 is changed to the band gap energy E g of the cladding layers 19 and 21. Since it is smaller than that, a light-emitting element having good luminous efficiency can be obtained.

Note that the present invention is not limited to the above embodiment.

In the above embodiment, Ba O and ZnO are mixed crystals. However, S r (electronegativity: 1 · 0) having an electronegativity approximately equal to that of Ba is substantially the same, By using a mixed crystal compound having the composition formula S ry O η 1-y O (0 <y <0.55) for the active layer, a compound semiconductor having a desired band gap energy E g smaller than ZnO can be obtained. A layer can be obtained, and a light emitting element and a multilayer reflector having excellent luminous efficiency can be obtained.

Further, in the above embodiment, the film formation is performed by heating the substrate temperature to an arbitrary constant temperature selected from 300 to 800 ° C., but by changing the substrate temperature for each layer, An optical semiconductor device such as a light-emitting device having a band-modulated compound semiconductor layer can be obtained.

Further, in the above embodiment, the bandgap energy Eg is modulated by the ternary mixed crystal compound composed of the composition formula BaXZn1-X0 or SryZn1-yO. It is not limited to crystals.

Further, other elements, for example, Ga, AI, or N may be contained as a dopant.

Further, in the above embodiment, the cladding layer is formed of a mixed crystal compound consisting of M gz Z n 1— _Z O (0≤z <1), but the band gap energy E g is 3.46 to 33. Even when is used, an optical semiconductor device with improved luminous efficiency can be obtained by using the above-described active layers 8 and 20 of the present invention.

Further, in the above embodiment, the compound semiconductor layer is formed on the ZnO substrate, but instead of the ZnO substrate, a sapphire substrate, a Sί substrate, a SiC substrate, a GaN substrate, or the like may be used. May be used.

In addition to the ECR sputtering method, MBE (molecular beam epitaxy) method,

MOCVD (metal organic chemical vapor phase), laser ablation, or the like may be used.

Next, examples of the present invention will be specifically described.

(First embodiment) The present inventors performed sputtering using a mixture of ∑00 and 830 as a sputter target using a capacitively coupled RF sputtering apparatus to form a BaZnO-based thin film on a C-plane sapphire substrate. The crystal state and band gap energy E g were measured.

That is, first, sintered bodies of five types of mixtures having different mixing ratios of ZnO and BaO were prepared.

Next, using a substrate temperature T of 650 ° C., argon (Ar) as a plasma generation gas, and oxygen as a reaction gas, 5 Osccm of argon and oxygen were supplied to the sputtering apparatus, and a high frequency of 1 OOW was supplied. Electric power was applied, and sputtering was performed using the mixture as a target to form a BaZnO-based thin film having a thickness of 5 OO nm on a C-plane sapphire substrate.

When the molar composition ratio x of the Ba component in the BaZnO-based thin film was measured by wavelength-dispersive X-ray analysis (WDX), the molar composition ratio X was 0, 0.10, 0.1. 29, 0.41, and 0.55.

Next, the relationship between the c-axis length of the Ba XZn 1-χθ thin film and the molar composition ratio X of Ba was examined by the X-ray diffraction (XRD) method.

The c-axis length was determined by the peak of ZnO (002) in XRD.

FIG. 7 shows the measurement results. The abscissa indicates the molar composition ratio X of the Ba component, and the ordinate indicates the c-axis length (nm) of the BaXZn1-xO thin film.

As is clear from FIG. 7, when the Ba component is not contained in the thin film, the c-axis length is 0.52065 nm, but as the molar composition ratio x of the Ba component increases, the c-axis The length has become shorter, which indicates that the Ba component is incorporated in the ZnO crystal lattice.

Next, the relationship between the diffraction angle and the X-ray intensity when the molar composition ratio X of the Ba component was 0.41 was examined.

FIG. 8 is an X-ray spectrum showing the measurement results, with the horizontal axis representing the diffraction angle 20 / ω and the vertical axis representing the X-ray intensity (cps).

As is evident from Fig. 8, the peak of X-ray intensity is only the peak derived from ZnO and the C-plane sapphire substrate, and the peak derived from BaO does not exist. Therefore, it can be seen that Ba is incorporated into the ZnO crystal lattice without the formation of a eutectic, and a mixed crystal compound represented by the composition formula Ba x Zn 1 x O is generated .

Next, the present inventors measured the band gap energy of each thin film at room temperature (25 ° C.) by a photoluminescence method.

Fig. 9 shows the measurement results. The horizontal axis shows the molar composition ratio X of the Ba component, and the vertical axis shows the band gap energy Eg (eV).

As is evident from Fig. 9, the pouring characteristics increase as the molar composition ratio X of the Ba component increases. The band gap energy E g changes parabolically, and the band gap energy E g can be made smaller than that of ZnO.

However, when the molar composition ratio X of the Ba component exceeds 0.55, the bandgap energy Eg increases as compared with ZnO alone.

That is, it is understood that by setting the molar composition ratio X of the Ba component to 0 <x <0.55, a compound semiconductor layer having a smaller band gap energy Eg than ZnO can be obtained.

(Second embodiment)

The present inventors changed the substrate temperature (film formation temperature) and examined the relationship between the substrate temperature T and the bandgap energy Eg.

That is, the mixing ratio of ZnO and BaO is 90:

Using the target prepared in 10 and setting the substrate temperature to 400 ° C, 500 ° C, 600 ° C, and 650 ° C, respectively, as in the first embodiment, the capacitively coupled RF sputtering device BaZnO-based thin films with a thickness of 500 nm were fabricated on a C-plane sapphire substrate using, and the band gap energy E g of each thin film was measured by photoluminescence method.

FIG. 10 shows the measurement results. The horizontal axis represents the substrate temperature T (° C.), and the vertical axis represents the band gap energy Eg (eV).

As is clear from FIG. 10, even when the content of Ba is kept constant, a thin film having a desired band gap energy E g can be obtained by changing the substrate temperature T low. I knew I could do it. Industrial applicability

As described above, the optical semiconductor device according to the present invention is useful as a pickup unit used when writing information to a storage device or reading information stored in the storage device. It is suitable for a pickup unit that writes to and reads data from a storage device.

Claims

The scope of the claims

1. At least one of Ba and Sr is formed as a solid solution in ZnO, and at least one compound semiconductor layer in which band gap energy is modulated according to the content of Ba and Sr is provided. An optical semiconductor device, comprising:

2. At least one of Ba and Sr is formed as a solid solution in ZnO and has at least one compound semiconductor layer whose band gap energy is modulated according to the film formation temperature. Optical semiconductor device.

3. The optical semiconductor device according to claim 1, wherein at least one of the compound semiconductor layers constitutes an active layer that emits light by current injection.

4. The optical semiconductor device according to claim 1, wherein a plurality of the compound semiconductor layers having different band gap energies are provided with a multilayer film in which a large number of layers are alternately stacked.

5. The optical semiconductor device according to claim 4, wherein the multilayer film forms an active layer that emits light by current injection.

6. The optical semiconductor device according to claim 3, wherein the active layer is sandwiched between cladding layers having a band gap energy larger than that of the active layer.

7. The optical semiconductor device according to claim 6, wherein the cladding layer is formed of a semiconductor material containing ZnO as a main component.

8. The optical semiconductor device according to claim 6, wherein the cladding layer is formed of a semiconductor material in which Mg is dissolved in ZnO.

9. The optical semiconductor device according to claim 6, wherein the cladding layer is formed of a semiconductor material containing GaN as a main component.

10. The compound semiconductor layer is represented by either a composition formula Ba χ Ζη 1 -χΟ (0 <χ <1) or a composition formula S ry Z n 1 -y O (0 <y <1). 10. The optical semiconductor device according to claim 1, wherein:

11. The optical semiconductor device according to claim 10, wherein X and y satisfy 0 <x <0.55 and 0 <y <0.55, respectively.