JP2005243955A - Light emitting element, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting element which has a p-type MgZnO semiconductor layer of high carrier concentration, and to provide its manufacturing method. <P>SOLUTION: In the light emitting element 1, a light emitting layer 24 has a double-hetero-structure which is formed by a p-type cladding layer 34 which consists of Mg<SB>x</SB>Zn<SB>1-x</SB>O (where 0≤x<1) layer, an active layer 33 which consists of Mg<SB>y</SB>Zn<SB>1-y</SB>O (where 0≤y<1), and an n-type cladding layer 32 which consists of Mg<SB>z</SB>Zn<SB>1-z</SB>O (where 0≤z<1). In the p-type cladding layer 34, C is doped. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a light-emitting element using a semiconductor, particularly a light-emitting element suitable for blue light or ultraviolet light emission, and a method for manufacturing the light-emitting element.

A high-intensity light-emitting element that emits short-wavelength light in the blue light region has been demanded for a long time. Recently, such a light-emitting element has been realized by using an AlGaInN-based material. In addition, by combining with red or green high-luminance light-emitting elements, application to full-color light-emitting devices and display devices is also rapidly progressing. However, since AlGaInN-based materials are mainly composed of relatively rare metals Ga and In, it is difficult to avoid an increase in cost. Another significant problem is that the growth temperature is as high as 700 to 1000 ° C. and a considerable amount of energy is consumed during production. This is not desirable not only from the viewpoint of cost reduction, but also in the sense of going against the currents in recent years when discussions on energy conservation and global warming suppression are frustrating. Therefore, Patent Documents 1 to 7 propose light emitting elements in which a light emitting layer portion is formed of a cheaper ZnO-based compound semiconductor layer on a sapphire substrate.
JP 2001-044500 A JP 2001-048698 A JP 2002-016088 A Japanese Patent Laid-Open No. 2002-092321 JP 2002-105625 A JP 2002-076026 A JP 2002-289918 A

  By the way, although a crystalline ZnO thin film is obtained by epitaxial growth in a vacuum atmosphere, oxygen vacancies are very easily generated. Therefore, the conductivity type is inevitably n-type, and n-type carriers (electrons) that are conductive carriers are generated. There is a problem that it is difficult to obtain few crystals. On the other hand, when the electronic device disclosed in the above publication is manufactured using ZnO, it is essential to obtain a material whose conductivity type is p-type. However, as described above, the oxide crystal tends to be n-type due to the presence of oxygen vacancies, and it is difficult to even create a semi-insulating crystal close to an intrinsic semiconductor. Regarding the method of forming p-type ZnO, the method of simultaneously doping N and Ga disclosed in Patent Documents 2, 5, and 7, the method of doping As disclosed in Patent Document 3, or Patent Document 3, Although there is a method of doping the radical N disclosed in No. 6, there are many problems such as a dopant not being introduced effectively and reproducibility being poor.

  An object of the present invention is to provide a light emitting device having a p-type MgZnO semiconductor layer having a high carrier concentration and a method for manufacturing the same.

Means for Solving the Problems and Effects of the Invention

In order to solve the above-described problem, the present invention provides a light-emitting element in which a light-emitting layer portion is formed of a semiconductor layer containing ZnO, and the light-emitting layer portion has Mg _x Zn _1-x O (where 0 ≦ x <1). A p-type cladding layer composed of layers, an active layer composed of Mg _y Zn _1-y O (where 0 ≦ y <1), and n composed of Mg _z Zn _1-z O (where 0 ≦ z <1). A double heterostructure laminated with a type cladding layer, and the p-type cladding layer is doped with C;
The n-type carrier derived from oxygen deficiency is compensated by C.

  In other words, the group IV element C (carbon) is positively doped to replace the group VI element O (oxygen), thereby generating holes that are p-type carriers. This is considered to be effective in obtaining good p-type characteristics in the MgZnO semiconductor. In addition, when N (nitrogen), which is technically difficult to dope independently into a semiconductor containing ZnO, is simultaneously doped, it can be considered that N is activated to contribute to p-type conversion. In addition, when the light emitting layer portion is configured to have a double hetero structure, it is effective for realizing a light emitting element with high light emission intensity.

  In order to solve the problem, a method for manufacturing a light-emitting element according to the present invention is a method for manufacturing a light-emitting element in which a light-emitting layer portion is formed of a semiconductor layer containing ZnO, in a metal organic chemical vapor deposition method (MOVPE method) or a molecule. In the step of forming the light emitting layer by the line epitaxy method (MBE method), the main feature is that a carbon source gas other than the organometallic compound is supplied together with the organometallic compound that is a raw material of the semiconductor containing ZnO. According to this method, it is possible to positively dope C into the semiconductor thin film. When C substitutes for an O atom, holes that are p-type carriers are generated, and n-type carriers derived from oxygen vacancies can be compensated.

  A hydrocarbon gas can be preferably used as the carbon source gas. By using hydrocarbon gas, it is possible to prevent doping of elements other than C and H. That is, it is possible to prevent a problem that deep impurity levels are formed between bands due to unnecessary elements. In addition, many hydrocarbon gases have relatively low toxicity and are advantageous in that they are easy to handle industrially. Of the hydrocarbon gases, methane gas is particularly suitable in view of its low cost, easy handling, and relatively high reactivity.

  Moreover, when forming a light emitting layer part by a molecular beam epitaxy method, it is good to supply carbon source gas (especially methane gas) on a board | substrate, cracking. Usually, when a ZnO semiconductor thin film is manufactured by the MOVPE method, the substrate temperature is considerably increased, so that C is efficiently taken into the semiconductor thin film even when the carbon source gas is supplied without being activated. On the other hand, since the substrate temperature is relatively low in the MBE method, it is appropriate to supply the substrate on the substrate while thermally decomposing (cracking) using a cracking cell or the like.

  The step of forming the light emitting layer portion includes an n-type layer forming step of forming an n-type MgZnO semiconductor layer and a p-type layer forming step of forming a p-type MgZnO semiconductor layer, and in the n-type layer forming step, a carbon source The gas supply can be stopped, and the carbon source gas can be supplied in the p-type layer formation stage.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 schematically shows a main part of a light-emitting element 1 according to an embodiment of the present invention in a laminated structure, from an Mg _x Zn _1-x O (where 0 ≦ x <1) layer. A p-type cladding layer 34 as a p-type oxide layer, an active layer 33 made of Mg _y Zn _1-y O (where 0 ≦ y <1), and Mg _z Zn _1-z O (where 0 ≦ An n-type cladding layer 32 made of z <1) has a light emitting layer portion 24 having a double heterostructure laminated in this order. In the present embodiment, the light emitting layer portion 24 is heteroepitaxially grown from the p-type cladding layer 34 side via the ZnO buffer layer 11 on the sapphire substrate 10 as a growth substrate. However, the stacking order may be reversed as in the light-emitting element 1 ′ illustrated in FIG.

As shown in FIG. 1, the main surface of the n-type cladding layer 32 is covered with a transparent electrode layer 35 made of a conductive oxide. In the present embodiment, the transparent electrode layer 35 is an ITO (Indium Tin Oxide) electrode 35, but a ZnO-based transparent electrode (for example, an amorphous ZnO transparent electrode doped with about 1 × 10 ²⁰ / cm ^{3 of} Al) may be used. . A metal electrode 22 made of a metal such as Al / Ti, In, or Au is disposed at the center of the transparent electrode layer 35 so as to cover a part of the transparent electrode layer 35. A current-carrying electrode wire (not shown) is joined to the metal electrode 22. On the other hand, a part of the n-type cladding layer 32 and the active layer 33 is removed, and a transparent electrode layer 25 similar to the transparent electrode layer 35 is formed on the exposed surface of the p-type cladding layer 34 and covers a part thereof. A metal electrode 122 is formed in a shape.

  MgZnO has a wurtzite structure, and oxygen atoms and metal atoms (Zn ions or Mg ions) layers are alternately stacked in the c-axis direction. Each of the layers 34, 33, and 32 is grown in the c-axis direction. If oxygen ions are lost in the MgZnO crystal, oxygen vacancies are generated and n-type carriers (electrons) are generated. Oxygen vacancies in the n-type cladding layer 32 are not harmful if they are in an appropriate amount, but rather can be actively used as an n-type carrier source. On the other hand, if too many oxygen vacancies are formed in the p-type cladding layer 34 and the active layer 33, n-type carriers are increased and no p-type conductivity or intrinsic semiconductor characteristics are exhibited. is important.

The n-type clad layer 32 is adjusted so that the n-type carrier concentration is, for example, in the range of 1 × 10 ¹⁷ / cm ³ or more and 1 × 10 ¹⁹ / cm ³ or less so that the light emission recombination in the active layer 33 is optimized. As an n-type dopant, one or more selected from the element group of B, Al, Ga, and In can be added, but oxygen dopant is actively formed as an n-type carrier (electron) source, and no dopant is added. It can also be.

The p-type cladding layer 34 is doped with C. When C substitutes for an O atom, holes that are p-type carriers are generated. Thereby, n-type carriers derived from oxygen vacancies are compensated. The C concentration in the p-type cladding layer 34 may be adjusted, for example, in the range of 1.0 × 10 ¹⁶ atoms / cm ^{3 to} 1.0 × 10 ²⁰ atoms / cm ³ . When the C concentration is less than 1.0 × 10 ¹⁶ atoms / cm ^3, the effect of compensating for n-type carriers derived from oxygen deficiency cannot be sufficiently obtained. On the other hand, it is extremely difficult and uneconomical to achieve a concentration exceeding 1.0 × 10 ²⁰ atoms / cm ³ .

Further, N may be mixed in the p-type cladding layer 34 as a p-type dopant other than C. When N is mixed together with C, N is activated and stabilized as an acceptor, and it can be expected that p-type carriers are generated efficiently and stably. Particularly in this case, it is effective to contain C in the p-type cladding layer 34 at a concentration equal to or higher than the N concentration. It is possible to adjust the N concentration of the p-type cladding layer 34 within a range of, for example, 1.0 × 10 ¹⁶ atoms / cm ³ or more and 1.0 × 10 ¹⁹ atoms / cm ³ or less. It is desirable to achieve both. Further, even if H is mixed with N, the same activation effect as described above can be expected.

  As the active layer 33, an active layer having an appropriate band gap according to the required emission wavelength is used. For example, what is used for visible light emission selects what has the band gap energy Eg (about 3.10 eV-2.18 eV) which can light-emit in wavelength 400nm -570nm. This is an emission wavelength band covering from purple to green, but particularly when used for blue emission, a band gap energy Eg (about 2.76 eV to 2.48 eV) that can be emitted at a wavelength of 450 nm to 500 nm is obtained. Choose what you have. Moreover, what uses the band gap energy Eg (about 4.43eV-3.10eV) which can be light-emitted in wavelength 280nm -400nm is selected as what is used for ultraviolet light emission.

In the active layer 33, the value of the mixed crystal ratio y is a factor that determines the band gap energy Eg. For example, in the case where ultraviolet light emission with a wavelength of 280 nm to 400 nm is performed, the selection is made in the range of 0 ≦ y ≦ 0.5. The band edge discontinuity value formed between the clad layers 32 and 34 on both sides is set to about 0.1 eV to 0.3 eV for a light emitting diode and about 0.25 eV to 0.5 eV for a semiconductor laser light source. Is good. This value indicates that the p-type cladding layer (composition: Mg _x Zn _1-x O) 34, the active layer (composition: Mg _y Zn _1-y O) 33, and the n-type cladding layer (composition: Mg _z Zn _1-z O). ) It can be determined by selecting numerical values of the mixed crystal ratios x, y and z of the layer 32. The active layer 33 may contain C, N, and H.

  Hereinafter, an example of a manufacturing process of the light emitting element 1 will be described. First, the buffer layer 11 made of ZnO is epitaxially grown on the sapphire substrate 10. Next, the p-type cladding layer 34, the active layer 33, and the n-type cladding layer 32 are epitaxially grown in this order (see FIG. 3). The epitaxial growth of these layers can be performed by the MOVPE method or the MBE method described above. Hereinafter, the case of the MOVPE method will be described.

By the MOVPE method, the buffer layer 11, the p-type cladding layer 34, the active layer 33, and the n-type cladding layer 32 can be continuously grown in the same reaction vessel. The temperature in the reaction vessel is adjusted by a heating source (infrared lamp in this embodiment) in order to promote a chemical reaction for layer formation. The following can be used as the main raw material of each layer.
-Oxygen source gas: Although oxygen gas can be used, it is desirable to supply it in the form of an oxidizing compound gas from the viewpoint of suppressing an excessive reaction with an organic metal described later. Specifically, N ₂ O, NO, NO ₂ , CO and the like. In this embodiment, N ₂ O (nitrous oxide) is used. This gas also functions as an N source gas that is a p-type dopant source.
Zn source gas: dimethyl zinc (DMZn), diethyl zinc (DEZn), etc.
Mg source gas: biscyclopentadienyl magnesium (Cp ₂ Mg), etc.
Carbon source gas: Saturated hydrocarbon gas such as CH ₄ (methane). CH ₄ is a C source gas and also functions as an H source gas.

Each of the above source gases is appropriately diluted with a carrier gas (for example, N ₂ gas) and supplied into the reaction vessel. Note that the flow rate ratio of the organometallic gas MO, which serves as the Mg source and the Zn source, is controlled by a mass flow controller MFC or the like depending on the mixed crystal ratio of each layer. The flow rates of N ₂ O, which is an oxygen source gas, and carbon source gas are also controlled by the mass flow controller MFC.

The buffer layer 11 is grown as follows, for example. First, the substrate 10 on which a layer is grown is a sapphire (that is, alumina single crystal) substrate having an a-axis crystal main axis, and the main surface on the oxygen atom plane side is used as a layer growth surface. The growth is carried out by supplying an organometallic gas MO and an oxygen source gas N ₂ O into the reaction vessel, for example, at 400 ° C. by a normal MOVPE method. When the growth of the buffer layer 11 is completed, the p-type cladding layer 34, the active layer 33, and the n-type cladding layer 32 forming the light emitting layer portion 24 are formed in this order by the MOVPE method. The growth temperature of the light emitting layer portion 24 is, for example, 600 ° C. or higher and 1000 ° C. or lower (800 ° C. in this embodiment).

The step of forming the p-type cladding layer 34 can be performed while supplying methane gas as C source gas into the reaction vessel in addition to the organic metal gas MO and N ₂ O as oxygen source gas. When the active layer 33 is formed, the supply of methane gas is stopped, or the amount of methane supply is made smaller than when the p-type cladding layer 34 is formed. In addition, when forming a semiconductor thin film by MBE method instead of MOCVD method, it is good to introduce | transduce methane gas in a reaction container, thermally decomposing (cracking). As a result, the hydrocarbon gas that is inactive at low temperatures reaches the substrate in an activated state and is efficiently taken into the semiconductor thin film. Pyrolysis of methane gas can be performed using a MBE pyrolysis cell (cracking cell).

When growing the active layer 33 and the p-type cladding layer 34, it is effective to maintain the pressure in the reaction vessel at 10 Torr or more in order to suppress the generation of oxygen vacancies. As a result, the release of oxygen is further suppressed, and an MgZnO layer with few oxygen vacancies can be grown. In particular, when N ₂ O is used as the oxygen component source, it is possible to prevent the dissociation of N ₂ O from proceeding rapidly by the above pressure setting, and to more effectively suppress the generation of oxygen vacancies. The higher the atmospheric pressure is, the higher the oxygen desorption suppression effect is. However, even at a pressure up to about 760 Torr (1.01 × 10 ⁵ Pa or 1 atm), the effect is sufficiently remarkable. For example, if it is 760 Torr or less, there is an advantage that the inside of the reaction vessel is at normal pressure or reduced pressure, so that the vessel seal structure can be relatively simple. On the other hand, when a pressure exceeding 760 Torr is adopted, the inside of the container is pressurized, so a slightly stronger sealing structure is taken into consideration so that the gas inside does not leak out. However, the effect of suppressing oxygen withdrawal becomes more remarkable. In this case, the upper limit of the pressure should be set to an appropriate value in consideration of the balance between the cost of the apparatus and the achievable oxygen desorption suppression effect (for example, about 7600 Torr ((1.01 × 10 ⁶ Pa or 10 atm)).

The n-type cladding layer 32 may obtain n-type conductivity by actively forming oxygen vacancies by lowering the oxygen partial pressure during growth, or group III elements such as B, Al, Ga and In may be used. The n-type conductivity may be obtained by adding it alone as an n-type dopant. As dopant gas, about Al, Ga, and In, what was demonstrated by the term of the p-type dopant can be used similarly. As for B, for example, diborane (B ₂ H ₆ ) can be used.

  When the growth of the light emitting layer portion 24 is completed in this way, a part of the active layer 33 and the n-type MgZnO layer 32 is partially removed by photolithography or the like as shown in FIG. 1, and the transparent electrode layers 35 and 25 are further removed. If the metal electrode layers 22 and 122 are formed and then diced together with the substrate 10, the light emitting device 1 is obtained.

FIG. 3 is a schematic diagram illustrating a specific example of a light-emitting element of the present invention in a stacked structure. The schematic diagram which shows the modification of the light emitting element of FIG. 1 by laminated structure. FIG. 3 is an explanatory diagram of a manufacturing process of the light emitting device of FIG. 1.

Explanation of symbols

1,1 ′ Light-Emitting Element 10 Sapphire Substrate 24 Light-Emitting Layer Portion 32 n-type Cladding Layer 33 Active Layer 34 p-Type Cladding Layer

Claims (6)

In the light emitting device in which the light emitting layer portion is configured by a semiconductor layer containing ZnO,
The light emitting layer portion includes a p-type cladding layer made of Mg _x Zn _1-x O (where 0 ≦ x <1) and an active layer made of Mg _y Zn _1-y O (where 0 ≦ y <1). And a double hetero structure in which an n-type cladding layer made of Mg _z Zn _1-z O (where 0 ≦ z <1) is laminated,
The p-type cladding layer is doped with C,
2. The light emitting device according to claim 1, wherein n-type carriers derived from oxygen vacancies are compensated by C.   In a method for manufacturing a light-emitting element in which a light-emitting layer portion is formed of a semiconductor layer containing ZnO, a material for a semiconductor containing ZnO is formed in the step of forming the light-emitting layer portion by metal organic vapor phase epitaxy or molecular beam epitaxy. A method for manufacturing a light-emitting element, comprising supplying an organic metal compound and a carbon source gas other than the organic metal compound.   The method of manufacturing a light emitting device according to claim 2, wherein the carbon source gas is a hydrocarbon gas.   4. The method for manufacturing a light-emitting element according to claim 3, wherein the hydrocarbon gas is methane gas.   5. The light emitting device according to claim 2, wherein when the light emitting layer portion is formed by molecular beam epitaxy, the carbon source gas is supplied onto the substrate while being cracked. Method. The step of forming the light emitting layer includes an n-type layer forming step of forming an n-type MgZnO semiconductor layer and a p-type layer forming step of forming a p-type MgZnO semiconductor layer,
The supply of the carbon source gas is stopped in the n-type layer formation stage, and the supply of the carbon source gas is performed in the p-type layer formation stage. Of manufacturing the light-emitting device.

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