JP4431933B2 - LIGHT EMITTING DEVICE MANUFACTURING METHOD AND LIGHT EMITTING DEVICE - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a light-emitting element using a semiconductor, particularly a light-emitting element suitable for blue light or ultraviolet light emission.
[0002]
[Prior art]
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. In view of this, Japanese Patent Application Laid-Open No. 2001-44500 proposes a light emitting element in which a cheaper ZnO-based compound semiconductor layer is heteroepitaxially grown on a sapphire substrate.
[0003]
By the way, ZnO-based oxides can be obtained by vapor phase growth in a vacuum atmosphere. However, since bulk single crystal growth is difficult, heteroepitaxial growth using a different material substrate such as sapphire is employed. In order to form the light-emitting layer part with good crystallinity described above, it is necessary to insert an appropriate buffer layer between the substrate and the light-emitting layer part. Japanese Patent Laid-Open No. 2001-44500 discloses that the buffer layer (contact layer) is formed together with the subsequent light emitting layer by MBE (Molecular Beam Epitaxy) method or MOVPE (Metalorganic Vapor Phase Epitaxy) method.
[0004]
[Problems to be solved by the invention]
However, since the MBE method has a low pressure in the growth atmosphere, it is not easy to suppress the generation of oxygen vacancies, and it is very difficult to form a ZnO-based oxide layer that is indispensable for constituting a light-emitting element. On the other hand, in the vapor phase growth method using the MOVPE method, the oxygen partial pressure during the growth can be freely changed. Therefore, by raising the atmospheric pressure to some extent, it is possible to suppress the occurrence of oxygen desorption and hence oxygen deficiency. However, in the normal continuous growth type MOVPE method, when a disorder such as an atomic defect or displacement occurs, the layer growth from the next layer is continued without the disorder being repaired. As a buffer layer for determining the thickness, a high-quality buffer layer is not necessarily obtained, and as a result, there is a problem that it is difficult to obtain an element with high luminous efficiency.
[0005]
The subject of the present invention is Mg_aZn_1-aAn object of the present invention is to provide a method for manufacturing a light-emitting element capable of realizing a high-quality light-emitting layer portion made of an O-type oxide, and a light-emitting element that can be manufactured thereby.
[0006]
[Means for solving the problems and actions / effects]
  In order to solve the above problems, a method for manufacturing a light-emitting element of the present invention includes:
  The light emitting layer is Mg_aZn_1-aIn the method for manufacturing a light-emitting element made of an O (where 0 ≦ a ≦ 1) type oxide, the contact side with the light-emitting layer portion is at least Mg_aZn_1-aA buffer layer formed as an O-type oxide layer is grown on the substrate, and a light emitting layer is grown on the buffer layer;
  Mg_aZn_1-aThe O-type oxide has a wurtzite crystal structure composed of metal atomic layers and oxygen atomic layers that are alternately stacked in the c-axis direction, and the buffer layer is the c-axis of the wurtzite crystal structure. When the buffer layer is grown, the metal atomic layer is formed as a metal monoatomic layer on the substrate using the atomic layer epitaxy method, and then the remaining oxygen atomic layer is grown. Grow a metal atomic layerAnd
  The substrate is an oxide single crystal substrate made of an oxide having a corundum type structure in which oxygen atoms form a hexagonal atomic arrangement and have a C-plane of the hexagonal atomic arrangement as a main surface,
The entire buffer layer is formed on the main surface serving as the oxygen surface of the oxide single crystal substrate in such a manner that the c-axis of the wurtzite crystal structure is oriented in the layer thickness direction.It is characterized by that.
[0007]
  Further, the light-emitting element of the present invention has Mg on the substrate._aZn_1-aA light emitting element in which a light emitting layer portion made of an O (where 0 ≦ a ≦ 1) type oxide is formed, and a contact side with the light emitting layer portion is at least Mg between the substrate and the light emitting layer portion_aZn_1-aWhile arranging the buffer layer made into an O-type oxide layer,
  The substrate is an oxide single crystal substrate made of an oxide having a corundum type structure in which oxygen atoms form a hexagonal atomic arrangement and have a C-plane of the hexagonal atomic arrangement as a main surface,
  Mg_aZn_1-aThe O-type oxide has a wurtzite crystal structure composed of metal atomic layers and oxygen atomic layers alternately stacked in the c-axis direction,
  The buffer layer is formed by orienting the c-axis of the wurtzite crystal structure in the layer thickness direction,On the main surface to be the oxygen surface of the oxide single crystal substrate,One atomic layer portion in contact with the substrate is formed as a metal monoatomic layer, and the remaining oxygen atomic layers and metal atomic layers are alternately grown in a form following the monoatomic layer.
[0008]
According to the present invention, the entire buffer layer formed on the substrate or at least the contact side with the light-emitting layer portion has the same component system as the light-emitting layer portion._aZn_1-aIt is composed of an O-type oxide (however, the mixed crystal ratio a is not necessarily the same as that of the light emitting layer portion: hereinafter, the mixed crystal ratio a may be omitted and simply described as MgZnO-type oxide or MgZnO). . The part of the buffer layer on the bonding interface side and the light emitting layer part have basically the same crystal structure (wurtzite type) and the same component system, so the interaction between the components across the bonding interface Local disorder of the crystal structure due to is less likely to occur, which is advantageous in realizing a light emitting layer portion with good crystallinity. The entire buffer layer can be made of, for example, an MgZnO type oxide. In this way, it is possible to carry out vapor phase growth of the buffer layer and the light emitting layer portion very simply in the same facility.
[0009]
In the manufacturing method of the present invention, when the buffer layer is grown, in particular, after the metal atomic layer is formed as a metal monoatomic layer on the substrate by the atomic layer epitaxy (ALE) method, An oxygen atomic layer and a metal atomic layer are grown. By adopting the ALE method, once the first metal monolayer is completed, the formation of the metal atomic layer can be saturated by one atomic layer (so-called self-stop function), and the atoms arranged in the layer can be deficient or Disturbances such as displacement are unlikely to occur. After completing one atomic layer of such a disordered metal atomic layer, a subsequent metal atomic layer and oxygen atomic layer are grown to obtain a buffer layer with extremely good crystallinity. Since the light emitting layer portion grown thereon also has good crystallinity, it is convenient for realizing a high performance light emitting element. Further, in the light emitting device of the present invention, the buffer layer is formed by adopting the above manufacturing method, and the c-axis of the wurtzite crystal structure is oriented in the layer thickness direction, and the one atomic layer portion in contact with the substrate is a metal monoatomic layer Further, the remaining oxygen atom layers and metal atom layers are alternately grown in a form subsequent to the monoatomic layer. The buffer layer having such a structure has very good crystallinity, and as a result, the light emitting layer portion grown on the buffer layer is low in defects and less disturbed, and as a result, a light emitting efficiency is realized.
[0010]
The ALE method can be carried out in the form of a metal organic vapor phase epitaxy (MOVPE) method in which an organic metal gas and an oxygen component source gas are supplied into a reaction vessel in which a substrate is arranged. . Specifically, only the organometallic gas used as the raw material for the metal atomic layer is circulated in the reaction vessel, and the first metal atomic layer constituting the buffer layer is formed so as to be saturated by one atomic layer. Atomic layer. As shown in FIG. 8A, the organic metal (MO) molecule chemically adsorbs metal atoms on the substrate while decomposing and leaving the bonded organic group. At this time, when the ALE method is adopted, the metal atoms are adsorbed in a form in which some of the bonded organic groups remain, and the residual organic groups are oriented to the surface side as shown in FIG. 8B. A metal atomic layer is formed in the form. Since this oriented residual organic group inhibits the adsorption of new metal atoms, when one atomic layer is completed, this oriented residual organic group inhibits the adsorption of new metal atoms, so that the self-stop function is exhibited. It becomes prominent, and disturbance such as defects and displacement is extremely difficult to occur in the atoms arranged in the layer.
[0011]
In addition, in the MOVPE method, the oxygen partial pressure during growth can be freely changed, so that the oxygen detachment and hence the generation of oxygen vacancies can be effectively suppressed by increasing the atmospheric pressure to some extent. As a result, p-type Mg is indispensable for light-emitting elements._aZn_1-aO layer, especially oxygen deficiency concentration of 10 / cm³P-type Mg_aZn_1-aO layer can be realized. The lower the oxygen deficiency concentration, the better (that is, 0 / cm).³Will not prevent you from becoming).
[0012]
When the MOVPE method is used, if the entire buffer layer is made of an MgZnO type oxide, the growth of the buffer layer and the light emitting layer portion can be carried out in the same reaction vessel. It is possible to carry out consistently only by adjusting the ratio with gas. Further, purging in the container when switching from the growth of the buffer layer to the growth of the light emitting layer portion can be shortened or omitted compared to the case where the buffer layer is made of another material such as GaN.
[0013]
In order to obtain a light-emitting element with high luminance, it is effective to grow the light-emitting layer portion as having a double heterostructure as described below. That is, as the light emitting layer portion on the buffer layer, Mg_aZn_1-aA first conductivity type cladding layer (p-type or n-type) made of an O-type oxide, an active layer, and a second conductivity-type cladding layer (n-type or p-type) having a conductivity type different from that of the first conductivity-type cladding layer. Type) is grown with a double heterostructure stacked in this order.
[0014]
In this case, the growth of the p-type MgZnO layer or the MgZnO active layer by the MOVPE method is 10 torr (9.8 × 10 6⁴By performing in an atmosphere having a pressure equal to or higher than Pa), oxygen deficiency generation during film formation can be more effectively suppressed, and a p-type MgZnO layer or MgZnO active layer having good characteristics can be obtained. In this case, the oxygen partial pressure (O₂Oxygen-containing molecules other than oxygen also contain oxygen₂10 torr (9.8 × 10)⁴Pa) or better. Further, when an n-type MgZnO layer is formed on the buffer layer and an MgZnO active layer and a p-type MgZnO layer are grown on the buffer layer, if an oxygen deficiency occurs in the n-type MgZnO layer, the MgZnO active that grows later The n-type MgZnO layer is preferably grown so as not to cause oxygen vacancies as much as possible because the layer and the p-type MgZnO layer are also affected by disturbance. In this case, the conductivity type of the n-type MgZnO layer is changed to n-type by adding an n-type dopant. On the other hand, when the p-type MgZnO layer is formed on the buffer layer and the MgZnO active layer and the n-type MgZnO layer are formed thereon, the layer contributing to light emission is not formed on the n-type MgZnO layer. For the n-type MgZnO layer, a method of making the conductivity type n-type by positive formation of oxygen vacancies can be employed.
[0015]
Mg_aZn_1-aIn order for O to be p-type, it is necessary to add an appropriate p-type dopant as described above. As such a p-type dopant, one or more of N, Ga, Al, In, Li, Si, C, and Se can be used. Of these, the use of N is particularly effective in obtaining good p-type characteristics. Further, it is effective to use one or more of Ga, Al, In and Li, particularly Ga, as the metal element dopant. By co-adding these with N, good p-type characteristics can be obtained more reliably.
[0016]
In order to secure sufficient light emission characteristics, p-type Mg_aZn_1-aThe p-type carrier concentration in the O layer is 1 × 10¹⁶Piece / cm³8 × 10 or more¹⁸Piece / cm³It should be the following. p-type carrier concentration is 1 × 10¹⁶Piece / cm³If it is less than this, it may be difficult to obtain sufficient light emission luminance. On the other hand, the p-type carrier concentration is 8 × 10¹⁸Piece / cm³Exceeds the amount, the amount of p-type carriers injected into the active layer becomes excessive, and p-type Mg_aZn_1-aIn some cases, the number of p-type carriers that do not contribute to light emission due to back diffusion into the O layer, or overcoming the barrier and flowing into the n-type cladding layer increases, leading to a decrease in light emission efficiency. N-type Mg_aZn_1-aFor the O layer, the n-type carrier concentration is 1 × 10 6 for the same reason.¹⁶Piece / cm³8 × 10 or more¹⁸Piece / cm³It should be the following.
[0017]
Next, as a material of the substrate, for example, aluminum oxide, gallium oxide, magnesium oxide, gallium nitride, aluminum nitride, silicon, silicon carbide, gallium arsenide, indium-tin composite oxide, glass, or the like can be used. In addition, the following embodiments are particularly suitable for the present invention. That is, Mg_aZn_1-aAs shown in FIG. 2, the O-type oxide has a wurtzite crystal structure composed of metal atom layers and oxygen atom layers alternately stacked in the c-axis direction, and the oxygen atoms are arranged in a hexagonal atomic arrangement. Make. Accordingly, the substrate may be an oxide single crystal substrate in which oxygen atoms form a hexagonal atomic arrangement and the C plane ((0001) plane) of the hexagonal atomic arrangement is a main surface. This is effective in improving the crystal matching of the light emitting layer and thus obtaining a light emitting layer portion having good crystallinity. In this case, the entire buffer layer is Mg_aZn_1-aThe O-type oxide layer is formed on the main surface of the oxide single crystal substrate so that the c-axis of the wurtzite crystal structure is oriented in the layer thickness direction. Examples of such an oxide single crystal substrate include an oxide having a corundum type structure, and a sapphire substrate can be exemplified as a more specific example.
[0018]
As shown in FIG. 7, an oxide having a corundum structure has a hexagonal atomic arrangement of oxygen (O) atoms, and an O atom (ion) layer and metal atoms (ions) in the c-axis direction. : In the figure, Al) layers are alternately stacked. In this crystal structure, one of the atomic layers appearing at both ends in the c-axis direction is necessarily an O atomic layer surface and the other is a metal atomic layer surface. Of these, the O atom layer surface has the same O atom arrangement as the O atom layer of the wurtzite crystal structure, except for the difference in lattice constant. Therefore, Mg having a wurtzite crystal structure is formed on the main surface of the oxide single crystal substrate having such a crystal structure._aZn_1-aWhen growing an O-type oxide buffer layer, a metal atomic layer on the buffer layer side is stacked on the main surface forming the O atomic layer surface on the substrate side, thereby obtaining a more consistent bonding structure. Will be able to.
[0019]
As disclosed in Japanese Patent Application Laid-Open No. 2001-44500, it is possible to grow a buffer layer and a light emitting layer on the A surface of the sapphire substrate, which has a certain effect on flattening the crystal growth surface. . In this case, since metal atoms and oxygen atoms are mixed on the A plane of the sapphire substrate, the A plane can be obtained by using a normal continuous growth type MOVPE method as disclosed in JP-A-2001-44500. The probability that oxygen atom adsorption and zinc atom adsorption occur simultaneously on the ((11-20) plane) is increased. As a result, the stacking of the buffer layers grown in the c-axis orientation is likely to be disturbed, and a high-quality buffer layer and thus a light emitting layer portion may not always be obtained. However, if the ALE method is used as in the present invention, a metal monoatomic layer is forcibly formed even on such an A-plane, so that a buffer layer of good quality and thus a light emitting layer can be obtained with good reproducibility. Is possible.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 schematically shows a laminated structure of a main part of a light emitting device according to the present invention, in which a light emitting layer in which an n-type cladding layer 34, an active layer 33, and a p-type cladding layer 32 are laminated in this order. Has a part. And each layer 32-34 is all Mg_aZn_1-aO layer (0 ≦ a ≦ 1: or less, also referred to as MgZnO: However, as is clear from the range of the mixed crystal ratio a, even if it is described as MgZnO, this represents the concept of each single oxide of MgO and ZnO. Is included). The p-type MgZnO layer 32 contains a trace amount of, for example, one or more of N, Ga, Al, In, and Li as a p-type dopant. The p-type carrier concentration is 1 × 10 as described above.¹⁶Piece / cm³8 × 10 or more¹⁸Piece / cm³For example, 10¹⁷Piece / cm³-10¹⁸/ Cm³It is adjusted within a range.
[0021]
FIG. 2 shows the crystal structure of MgZnO, which has a so-called wurtzite structure. In this structure, oxygen atom layers and metal atom (Zn ions or Mg ions) layers are alternately stacked in the c-axis direction, and as shown in FIG. 3, the c-axis is along the layer thickness direction. Formed as follows. When oxygen ions are lost and vacancies are generated, oxygen vacancies are generated and electrons that are n-type carriers are generated. If too many oxygen vacancies are formed, n-type carriers increase and p-type conductivity is not exhibited. Therefore, when the p-type MgZnO layer 32 and the MgZnO active layer 33 are formed, it is important to suppress the generation of this oxygen deficiency.
[0022]
As the active layer 33, one 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.
[0023]
For example, the active layer 33 is made of p-type Mg._xZn_1-xIt can be formed of a semiconductor that forms a type I band lineup with the O layer. Such an active layer 33 is, for example, Mg_yZn_1-yIt can be formed as an O layer (however, 0 ≦ y <1, x> y: hereinafter also referred to as an MgZnO active layer). “Type I band lineup is formed between the active layer and the p-type MgZnO layer” means that the conduction band bottom and valence electrons of the p-type cladding layer (p-type MgZnO layer 32) are formed as shown in FIG. A junction structure in which the following magnitude relationship is established between the energy levels Ecp and Evp at the band top and the energy levels Eci and Evi at the conduction band bottom and the valence band top of the active layer:
Eci <Ecp (1)
Evi> Evp (2)
[0024]
In this structure, a potential barrier is generated for both forward diffusion of holes from the active layer 33 to the n-type cladding layer 34 and forward diffusion of electrons (n-type carriers) to the p-type cladding layer 32. Then, if the material of the n-type cladding layer 34 is selected so that the same type I band lineup as in FIG. 4 is formed between the active layer 33 and the n-type cladding layer 34, the conductive layer is located at the position of the active layer. A well-like potential barrier is formed at both the bottom and the top of the valence band, and the confinement effect is enhanced for both electrons and holes. As a result, the promotion of carrier recombination and thus the improvement of luminous efficiency become more remarkable.
[0025]
In the MgZnO 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 range is selected in the range of 0 ≦ y ≦ 0.5. The height of the potential barrier formed is preferably 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. This value is p-type Mg_xZn_1-xO layer 2, Mg_yZn_1-yO active layer 33 and n-type Mg_zZn_1-zIt can be determined by selecting numerical values of the mixed crystal ratios x, y, z of the O layer 34.
[0026]
Hereinafter, an example of the manufacturing process of the light-emitting element will be described. First, as shown in FIG. 5, the buffer layer 11 made of MgZnO is epitaxially grown on the sapphire substrate 10. Next, the n-type MgZnO layer 34 (layer thickness, eg, 50 nm), the MgZnO active layer 33 (layer thickness, eg, 30 nm) and the p-type MgZnO layer 32 (layer thickness, eg, 50 nm) are epitaxially grown in this order (32 to 35 are growth orders). May be reversed). The epitaxial growth of each of these layers can be performed by the MOVPE method as described above.
[0027]
As shown in FIGS. 6A to 6C, the buffer layer 11, the n-type MgZnO layer 34, the MgZnO active layer 33, and the p-type MgZnO layer 32 are all formed in the same reaction vessel by the MOVPE method using the same raw material. Can grow continuously. 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 component 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, N₂O, NO, NO₂, CO etc. In this embodiment, N₂O (nitrous oxide) is used.
Zn source (metal component source) gas: dimethyl zinc (DMZn), diethyl zinc (DEZn), etc.
Mg source (metal component source) gas: biscyclopentadienyl magnesium (Cp₂Mg).
[0028]
Moreover, the following can also be used as a p-type dopant gas;
Li source gas: normal butyl lithium, etc.
-Si source gas: silicon hydride such as monosilane;
C source gas: hydrocarbon (eg, alkyl containing one or more C);
Se source gas: hydrogen selenide and the like.
[0029]
Further, one or more group III elements such as Al, Ga and In can function as a good p-type dopant by co-addition with N which is a group V element. The following can be used as the dopant gas:
Al source gas; trimethylaluminum (TMAl), triethylaluminum (TEAl), etc .;
Ga source gas; trimethylgallium (TMGa), triethylgallium (TEGa), etc .;
In source gas; trimethylindium (TMIn), triethylindium (TEIn), etc.
When N is used as a p-type dopant together with a metal element (Ga), a gas serving as an N source is supplied together with an organometallic gas serving as a Ga source when performing vapor phase growth of the p-type MgZnO layer. . For example, in this embodiment, N used as an oxygen component source₂O becomes a form that also functions as an N source.
[0030]
On the other hand, group III elements such as B, Al, Ga, and In can function as n-type dopants when used alone. 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 (B₂H₆) Can be used.
[0031]
Each of the above source gases is appropriately diluted with a carrier gas (for example, nitrogen gas) and supplied into the reaction vessel. Note that the flow rate ratio of the organometallic gas MO, which becomes the Mg source and the Zn source, is controlled by the mass flow controller MFC or the like depending on the mixed crystal ratio of each layer. Also, oxygen component source gas N₂The flow rates of the O and p-type dopant source gases are also controlled by the mass flow controller MFC.
[0032]
The growth of the buffer layer 11 is performed as follows. FIG. 9 shows a sequence of temperature control in the reaction vessel and introduction of each gas in the present embodiment. First, the substrate 10 on which a layer is grown is a sapphire (that is, alumina single crystal) substrate having a c-axis crystal principal axis, and the main surface on the oxygen atom plane side shown in FIG. 7 is used as a layer growth surface. Prior to the layer growth, the substrate 10 is sufficiently annealed in an oxidizing gas atmosphere. Oxidizing gases are O, CO, N₂Although it can be selected from any of O, since it is shared with an oxygen component source gas during layer growth described later, in this embodiment, N₂O is used. The annealing temperature is preferably 750 ° C. or higher (lower temperature than the melting point of the substrate) and a holding time of 30 minutes or longer in the MOVPE reaction vessel. However, if the substrate surface can be sufficiently cleaned by wet cleaning or the like, the annealing time may be shortened.
[0033]
When the annealing process is completed, as shown in FIG. 9, the substrate temperature is kept in an oxidizing gas atmosphere, and 250 to 350 ° C. (350 ° C. in this embodiment) in order to suppress the occurrence of defects and the like. Reduce to the first temperature set. When the temperature stabilizes at the set value, the supply of the oxidizing gas is stopped, the inside of the reaction vessel is replaced with nitrogen gas, and the oxidizing gas is sufficiently purged out. Although the purge time varies depending on the shape and volume of the reaction vessel, it is effective to secure 5 seconds or more.
[0034]
Next, as shown in FIGS. 6 (a) and 8 (a), an organic metal gas MO is supplied into the reaction vessel, and the first metal atomic layer forming a part of the buffer layer 11 is formed by a single atomic metal by the ALE method. Form as a layer. As already described, in the ALE method, the growth of the metal atomic layer is saturated by one atomic layer due to the self-stop function, and no further growth of the metal atomic layer occurs even if the supply of the organometallic gas MO is continued.
[0035]
Thereafter, the supply of the organometallic gas MO is stopped, the inside of the reaction vessel is replaced with nitrogen gas, and the organometallic gas MO is sufficiently purged out. Then, as shown in FIG. N is also a gas atmosphere₂O is introduced, and one atomic layer is formed by an ALE method. As a result, an MgZnO layer corresponding to one molecular layer is formed on the substrate 10.
[0036]
Thereafter, as shown in FIG. 9, while maintaining the oxidizing gas atmosphere, the temperature in the reaction vessel is raised to a second temperature (750 ° C. in this embodiment) set to 400 to 800 ° C., and further organic By continuously flowing the metal gas, as shown in FIGS. 6B and 8D, the remaining portion of the buffer layer is grown by a normal MOVPE method. At this time, it is possible to obtain a buffer layer 11 having good flatness by growing at a rate of about 0.1 nm / sec until the layer thickness is about 10 nm, and thereafter growing at a rate of 1 nm / sec or more. it can. From the viewpoint of obtaining a buffer layer with higher crystallinity and flatness, the first plurality of molecular layers may be grown by the ALE method.
[0037]
In this embodiment, the buffer layer 11 is formed as a ZnO single oxide layer. However, the MgZnO composite oxide has an appropriate mixed crystal ratio in accordance with the mixed crystal ratio of the layer on the light emitting layer side in contact with the buffer layer 11. It can also be a physical layer. In addition, the Al atomic layer located immediately below the O atomic layer on the outermost surface of the sapphire substrate has two Al atomic sites Al− having different distances from the O atomic layer due to the circumstances peculiar to the corundum crystal structure shown in FIG. 1 and Al-2. In this case, when the metal monoatomic layer laminated on the O atomic layer is a Zn atomic layer, the Coulomb repulsive force between the Zn atom and the Al atom via the O atomic layer is expressed by both sites Al-1 and Al-2. And the difference. Therefore, due to this, in the Zn atomic layer, there is a difference in displacement in the direction perpendicular to the plane with respect to the O atomic layer between the Zn atoms corresponding to both sites, which may lead to subsequent layer stacking disorder or the like. . In order to reduce this influence, as shown in FIG. 10B or FIG. 10C, the first monomolecular layer (or a plurality of molecular layers) is converted into a group II atom (for example, Mg) having an ionic radius smaller than that of Zn. Alternatively, forming a complex oxide layer in which Group II atoms having a large ionic radius (for example, Ca, Sr, Ba, etc.) are mixed at an appropriate ratio can improve the crystallinity of the finally formed light emitting layer. It is effective in raising. In this case, as shown in FIG. 11A, such a composite oxide layer (metal cation composition is A) and a cladding layer (metal cation composition is B) formed immediately above the buffer layer 11: In the figure, in order to connect both cation compositions A and B to the n-type MgZnO layer 54), it is also possible to form a composition gradient layer in which the metal cation composition is inclined in the layer thickness direction in order to enhance the above effect. It is valid. For example, when both the composite oxide layer and the cladding layer are composed of MgZnO, the Mg cation mol content is NMg, the Zn ion mol content is NZn, and the metal cation composition is a composition parameter ν≡NMg. / (NMg + NZn), ν of the composite oxide layer is represented by A, and ν of the clad layer is represented by B. For example, as shown in FIG. And B can be formed as a layer that continuously changes in the layer thickness direction.
[0038]
When the formation of the buffer layer 11 is completed, as shown in FIG. 6C, an n-type MgZnO layer 34, an MgZnO active layer 33, and a p-type MgZnO layer 32 are formed in this order by the MOVPE method. When the n-type MgZnO layer 32 is formed below the p-type MgZnO layer 32 (on the side of the substrate 10) as in this embodiment, an n-type dopant is introduced, and oxygen is introduced in the same manner as the p-type MgZnO layer 32 described later. It is desirable to perform layer growth under conditions where defects and the like do not occur as much as possible. On the other hand, when the n-type MgZnO layer 34 is formed above the p-type MgZnO layer 32, a method of positively generating oxygen vacancies to make the n-type can also be adopted. For example, the MgZnO active layer 53 and the p-type MgZnO layer It is more effective to lower the atmospheric pressure (for example, less than 10 torr) compared to the case of growing 52. Further, the ratio of the feed group II to VI group (feed II / VI ratio) may be increased.
[0039]
Further, when growing the MgZnO active layer 33 and the p-type MgZnO layer 32, it is effective to maintain the pressure in the reaction vessel at 10 torr or higher 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. Especially N as a source of oxygen component₂When O is used, N is set according to the above pressure setting.₂O dissociation is prevented from proceeding rapidly, and the generation of oxygen vacancies can be more effectively suppressed. The higher the atmospheric pressure, the higher the oxygen desorption suppression effect, but 760 torr (1.01 × 10⁵Even at a pressure up to about Pa or 1 atm), the effect is sufficiently remarkable. For example, if it is 760 torr or less, there is an advantage that the container seal structure can be relatively simple because the inside of the reaction vessel is at normal pressure or reduced pressure. 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 apparatus cost and the oxygen desorption suppression effect that can be achieved (for example, 7600 torr ((1.01 × 10⁶Pa or 10 atm)).
[0040]
When the growth of the light emitting layer portion is completed in this way, a part of the active layer 33 and the p-type MgZnO layer 32 is removed by photolithography or the like as shown in FIG. ) And the like, while the metal electrode 122 is formed on the remaining p-type MgZnO layer 32 and then diced together with the substrate 10, the light emitting device 1 is obtained. It is obvious that the light-emitting element 1 has a buffer layer 11 made of MgZnO formed on a substrate 10 and a light-emitting layer portion made of MgZnO. The light extraction is performed mainly from the transparent sapphire substrate 10 side.
[0041]
FIG. 12 shows a modification of the method for manufacturing a light emitting device according to the present invention. Here, as shown in FIG. 12A, layers are formed on the buffer layer 11 in the reverse order of FIG. 5, that is, in the order of the p-type MgZnO layer 32, the MgZnO active layer 33, and the n-type MgZnO layer 34. As shown in FIG. 5, the metal reflective layer 22 that also serves as an electrode is formed on the n-type MgZnO layer 34. Thereafter, the sapphire substrate 10 is peeled off, the transparent electrode 25 made of ITO or the like is formed on the p-type MgZnO layer 32 side, and then diced as shown in FIG. The light extraction of the light emitting element 104 is performed from the transparent electrode 25 side. According to this configuration, since the MgZnO metal layer forming the light emitting layer portion is exposed on the side where the substrate 10 is peeled off, an element with more excellent weather resistance can be obtained.
[0042]
【The invention's effect】
In the production method of the present invention, when growing the buffer layer, in particular, after the metal atomic layer is formed as a metal monoatomic layer on the substrate by the atomic layer epitaxy (ALE) method, the remaining oxygen is formed. An atomic layer and a metal atomic layer are grown. By adopting the ALE method, once the first metal monoatomic layer is completed, the formation of the metal atomic layer can be saturated by one atomic layer (self-stop function), and the atoms arranged in the layer can also be deficient or displaced. It is difficult to cause disturbance. After completing one atomic layer of such a disordered metal atomic layer, a subsequent metal atomic layer and oxygen atomic layer are grown to obtain a buffer layer with extremely good crystallinity. Since the light emitting layer portion to be grown thereon also has good crystallinity, it is convenient for realizing a high performance light emitting element with good reproducibility. Further, in the light emitting device of the present invention, the buffer layer is formed by adopting the above manufacturing method, and the c-axis of the wurtzite crystal structure is oriented in the layer thickness direction, and the one atomic layer portion in contact with the substrate is a metal monoatomic layer. Then, the remaining oxygen atom layers and metal atom layers are alternately grown in a form following the layer. The buffer layer having such a structure has very good crystallinity, and as a result, the light emitting layer portion grown on the buffer layer is low in defects and less disturbed, and as a result, a light emitting efficiency is realized.
[Brief description of the drawings]
FIG. 1 is a diagram conceptually showing a light emitting layer portion having a double hetero structure composed of MgZnO.
FIG. 2 is a schematic diagram showing a crystal structure of MgZnO.
FIG. 3 is a schematic diagram showing an arrangement form of metal ions and oxygen ions in an MgZnO layer.
FIG. 4 is a schematic view of a band of a light-emitting element using a junction structure of a type I band lineup.
FIG. 5 is a schematic diagram illustrating a specific example of a light-emitting element of the present invention.
6 is an explanatory diagram showing an example of a manufacturing process of the light-emitting element shown in FIG.
FIG. 7 is a schematic diagram of a corundum crystal structure.
FIG. 8 is an operation explanatory view of the method for manufacturing a light-emitting element according to the present invention.
FIG. 9 is a diagram illustrating a temperature control sequence and a gas supply sequence in the process of FIG. 6;
FIG. 10 is an explanatory diagram of effects obtained by using a mixed metal atomic layer as a metal monoatomic layer for ALE growth.
FIG. 11 is a schematic view showing an example in which the buffer layer is a metal composition gradient layer.
FIG. 12 is an explanatory view showing an example of a manufacturing process of another light emitting element of the present invention.
[Explanation of symbols]
1,104 light emitting device
10 Sapphire substrate
11 N buffer layer
32 p-type MgZnO cladding layer
33 MgZnO active layer
34 n-type MgZnO cladding layer

Claims (4)

In the method for manufacturing a light emitting device in which the light emitting layer portion is made of Mg _a Zn _1-a O (where 0 ≦ a ≦ 1) type oxide, the contact side with the light emitting layer portion is at least Mg _a Zn _1-a O type oxidized A buffer layer formed as a physical layer is grown on a substrate, and the light emitting layer portion is grown on the buffer layer;
The Mg _a Zn _1-a O-type oxide has a wurtzite crystal structure composed of metal atomic layers and oxygen atomic layers that are alternately stacked in the c-axis direction. The c-axis of the ore-type crystal structure is grown as oriented in the layer thickness direction, and the metal atomic layer is formed on the substrate by atomic layer epitaxy when growing the buffer layer. after formation as, Rutotomoni grown and residual oxygen atom layers and metal atom layers,
The substrate is an oxide single crystal substrate made of an oxide having a corundum type structure in which oxygen atoms form a hexagonal atomic arrangement and a C surface of the hexagonal atomic arrangement is a main surface;
The entire buffer layer is formed on the main surface serving as an oxygen surface of the oxide single crystal substrate so that the c-axis of the wurtzite crystal structure is oriented in the layer thickness direction. Manufacturing method.   The light emitting device manufacturing method according to claim 1, wherein the atomic layer epitaxy method is performed in the form of a metal organic vapor phase epitaxy method in which an organic metal gas and an oxygen component source gas are supplied into a reaction vessel in which the substrate is disposed. The method for manufacturing a light-emitting element according to claim 1, wherein the oxide single crystal substrate is a sapphire substrate . A light-emitting element in which a light-emitting layer portion made of Mg _a Zn _1-a O (where 0 ≦ a ≦ 1) type oxide is formed on a substrate, between the substrate and the light-emitting layer portion, While arranging a buffer layer whose contact side with the light emitting layer portion is at least a Mg _a Zn _1-a O type oxide layer,
The substrate is an oxide single crystal substrate made of an oxide having a corundum type structure in which oxygen atoms form a hexagonal atomic arrangement and a C surface of the hexagonal atomic arrangement is a main surface;
The Mg _a Zn _1-a O-type oxide has a wurtzite crystal structure composed of metal atomic layers and oxygen atomic layers alternately stacked in the c-axis direction,
In the buffer layer, the c-axis of the wurtzite crystal structure is oriented in the layer thickness direction, and a monoatomic layer portion in contact with the substrate is formed on the main surface serving as an oxygen surface of the oxide single crystal substrate. A light-emitting element, wherein the light-emitting element is formed as a metal monoatomic layer, and the remaining oxygen atomic layers and metal atomic layers are alternately grown in a form following the monoatomic layer.

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