JP5682938B2 - Semiconductor light emitting device - Google Patents

Description

  The present invention relates to a semiconductor light emitting device suitable for emitting ultraviolet light or blue light.

Currently, semiconductor light emitting devices are attracting attention as products that will be the next generation in the lighting field, and are expected to become a large market in the near future.
Zinc oxide (ZnO) is a direct transition type semiconductor having a band gap energy of about 3.2 to 3.4 eV, and is excited compared to gallium nitride (GaN), which is currently widely used as a material for semiconductor light emitting devices. The child bond energy is as extremely high as 60 meV, the raw materials are inexpensive and abundant, and are harmless to the environment and the human body. Therefore, it is a material that can realize a light-emitting device from ultraviolet light to blue light that is highly efficient and has low power consumption and excellent environmental performance.

  However, since ZnO tends to cause defects such as oxygen vacancies or zinc atoms at interstitial positions, it tends to be n-type with many electrons, making it difficult to form a p-type conductive layer. However, in recent years, many studies have been made to realize p-type by using a group I or group V element as an acceptor impurity and to produce a highly efficient light-emitting element using a ZnO-based semiconductor.

Examples of a semiconductor light emitting device manufactured by forming a thin film doped with an acceptor on a ZnO single crystal substrate are described in Patent Document 1 and Patent Document 2. Further, for example, Patent Document 3 describes a method for manufacturing a ZnO thin film in which nitrogen (N) is introduced on a sapphire substrate. Further, Patent Document 4 and Non-Patent Document 1 describe a method of manufacturing a ZnO thin film in which N is introduced using a substrate (for example, ScAlMgO ₄ ) made of a material having high lattice constant matching with zinc oxide.

JP 2004-247411 A JP 2004-247681 A JP 2004-221352 A JP 2005-223219 A A. Tsukazaki, A. Ohtomo, T. Onuma, M. Ohtani, T. Makino, M. Sumiya, K. Ohtani, SFChichibu, S. Fuke, Y. Segawa, H. Ohno, H. Koinuma, and M. Kawasaki, Nature Materials, 2005, 4, pp.42-46.

  However, a ZnO thin film grown on a crystal substrate other than ZnO has defects and lattice distortion due to a difference in crystal lattice constant, and a thin film with good crystallinity cannot be obtained. Therefore, the residual electron concentration is high. In addition, since a self-compensation effect is strongly generated, it is necessary to perform a lot of doping in order to obtain a p-type layer. However, when the concentration of the p-type dopant is increased, the crystallinity is deteriorated and the residual electron concentration is increased. Therefore, the effective acceptor concentration is not increased so much and the resistance is not lowered.

In addition, in the manufacturing methods described in Patent Document 3 and Patent Document 4, it has been attempted to form a ZnO buffer layer on an Al ₂ O ₃ or ScAlMgO ₄ substrate and form a ZnO thin film thereon. However, since ZnO grown on these substrates usually has an oxygen surface as the main growth surface, the solubility of the p-type dopant is low, and the acceptor concentration cannot be increased, so it is difficult to reduce the resistance.

  When a ZnO single crystal substrate is used as in the semiconductor light emitting devices described in Patent Document 1 and Patent Document 2, when a surface whose zinc surface is the main growth surface is used, the solubility of the p-type dopant is high, and the acceptor concentration is reduced. Even if N atoms, which are close to O atoms and have an atomic radius and are most likely to achieve p-type, are highly doped, the acceptor level in ZnO is very deep, and the resistance reduction is low. Have difficulty.

  Patent Documents 5 and 6 describe examples of semiconductor light-emitting elements in which a group I or group V element is used as a p-type dopant and two or more elements are doped. Both of these use group I or group V elements as p-type dopants, further suppress the electrostatic energy rise due to coulomb repulsion between the p-type dopants, and increase the solubility of the p-type dopants simultaneously with the n-type dopants. It is a method of doping.

However, since p-type and n-type doping is performed simultaneously, the total doping amount increases, crystallinity is likely to deteriorate, and defects increase. Therefore, the p-type and n-type dopant amounts are controlled to control p. Forming a shape layer is difficult.
JP 2001-48698 A JP 2004-221132 A

As described above, it is very difficult to reliably form a high-quality p-type ZnO thin film with low resistance, and there have been few reports of successful high-efficiency light emission. In addition, there has been no report of a successful example of forming a low resistance p-type thin film on an n- type ZnO single crystal substrate.
Accordingly, an object of the present invention is to provide a semiconductor light-emitting device that reliably forms a low-resistance p-type semiconductor layer on an n-type ZnO-based single crystal substrate with high quality, is excellent in mass productivity, and has high emission intensity. To do.

In order to achieve the above object, a semiconductor light emitting device according to the present invention comprises a Mg _a Zn _1-a O (comprising a ZnO compound doped simultaneously with nitrogen and copper during film formation on an n-type ZnO single crystal substrate. However, 0 <a <1) is characterized in that a p-type semiconductor layer made of a single crystal thin film is formed and a pn junction is formed.
The p-type semiconductor layer preferably has a doped nitrogen concentration of 2 × 10 ¹⁷ / cm ³ to 10 ²¹ / cm ³ in terms of the number of atoms and a doped copper concentration of 1 × 10 ^{17 in} terms of the number of atoms. / ^cm 3 is preferably a ^{to 10} 21 / cm ^3.

In this semiconductor light emitting device, the n-type ZnO-based single crystal substrate is made of ZnO-based single crystal with any one of Al, Fe, Ga, In as a donor impurity or a combination thereof, and the concentration is 1.0 in terms of the number of atoms. It is desirable that the n-type ZnO-based single crystal substrate be doped to have a resistance of × 10 ¹⁷ / cm ³ or more to reduce the resistance.
The n-type ZnO-based single crystal substrate preferably has a resistivity of 0.5 Ω · cm or less.

In these semiconductor light emitting devices, the n-type ZnO-based single crystal substrate is any one of Al, Fe, Ga, In, or a combination thereof as a donor impurity on the ZnO-based single crystal, and the concentration is 1 in terms of the number of atoms. It may be a ZnO-based single crystal substrate on which an n-type ZnO-based thin film whose conductivity is controlled by doping so as to be 0.0 × 10 ¹⁷ / cm ³ or more and whose resistance is reduced is formed. The n-type ZnO-based thin film may have a resistivity of 0.5 Ω · cm or less.

The surface on which the p-type semiconductor layer is formed on the n-type ZnO-based single crystal substrate is a surface containing zinc atoms, that is, a c (0001) plane, an m (10-10) plane, or a (11− 20) The surface is desirable.
It is desirable that the plane orientation of the n-type ZnO single crystal substrate is within ± 1 degree with respect to the c (0001) plane, the m (10-10) plane, or the a (11-20) plane. .

The n-type ZnO-based single crystal substrate may be a Mg _b Zn _1-b O (where 0 ≦ b <1) single crystal substrate. Alternatively, it is an n-type ZnO-based single crystal substrate on which an n _- type ZnO-based thin film Mg _d Zn _1-d O (where 0 ≦ d <1 and d ≦ b) reduced in resistance by doping with donor impurities is formed. May be.

Alternatively, the n-type ZnO-based single crystal substrate is an n-type low-resistance n-type cladding layer made of a Mg _b Zn _1-b O (where 0 ≦ b <1) single crystal substrate is doped by doping with a donor impurity. An n-type semiconductor layer of type ZnO-based thin film Mg _d Zn _1-d O (where 0 ≦ d <1 and d ≦ b) is formed, and the p-type semiconductor layer is formed on the n-type semiconductor layer In addition, a pn junction may be formed at the junction surface with the n-type semiconductor layer.
Further, in these semiconductor light emitting devices, a p-type cladding layer made of a single crystal thin film of Mg _c Zn _1-c O (where 0 <c ≦ 1 and a <c) is laminated on the p-type semiconductor layer. Also good.

According to the present invention, a high-quality, low-resistance p-type semiconductor layer can be reliably formed on an n-type ZnO-based single crystal substrate, and a semiconductor light-emitting device that is excellent in mass productivity and strong in emission intensity (brightly emits light). Can be provided.

The best mode for carrying out the present invention will be described below with reference to the drawings.
[Embodiment of Semiconductor Light Emitting Element]
FIG. 1 is a schematic sectional view showing an embodiment of a semiconductor light emitting device according to the present invention.
The semiconductor light-n-type ZnO-based single crystal substrate and an n-type semiconductor layer 14, a p-type semiconductor layer 13 thereon, made of ZnO based compound nitrogen N and copper Cu were simultaneously doped during deposition p A p-type semiconductor layer is formed, and a pn junction is formed at a pn junction surface (interface) 18. The p-type semiconductor layer 13 is directly formed on the n-type ZnO single crystal substrate, which is the n-type semiconductor layer 14, by epitaxial growth in which crystal growth is performed in accordance with the lattice information.

  Then, a p-type ohmic electrode is formed as the first electrode 12 on the p-type semiconductor layer 13, and an n-type ohmic electrode is formed as the second electrode 15 on the back surface of the n-type ZnO single crystal substrate that is the n-type semiconductor layer 14. ing. The formation method will be described later.

The n-type semiconductor layer 14 has an n-type ZnO single crystal substrate whose resistance has been reduced by doping with a donor impurity, for example, Al, Fe, Ga, In as donor impurities alone or in combination, and the concentration is atomic. It is desirable to use an n-type ZnO-based single crystal substrate in which the conductivity is controlled by doping so that the number thereof is 1.0 × 10 ¹⁷ / cm ³ or more and the resistance is reduced. Alternatively, an n-type ZnO single crystal substrate on which a low-resistance n-type ZnO thin film is formed may be used.

The p-type semiconductor layer 13 is a ZnO-based semiconductor thin film prepared by doping _a Mg _a Zn _1-a O (where 0 ≦ a ≦ 1 ) single crystal thin film with nitrogen and copper.
In general, Mg _x Zn _1-x O (where 0 ≦ x ≦ 1 ) (including ZnO) is a semiconductor whose band gap energy can be controlled to about 3.3 to 7.8 eV by the ratio of Zn and Mg. . That is, each light emission corresponding to the band gap can be obtained, and Mg _x Zn _1-x O (where 0 ≦ x ≦ 1 ) is replaced with Mg _y Zn _1-y O (wherein the band gap is larger). By using a carrier confinement structure in which 0 ≦ y ≦ 1 and x <y) are sandwiched as cladding layers, an improvement in light emission efficiency can be expected.

It has the characteristics that the exciton binding energy is extremely high as 60 to 115 meV, the raw material is inexpensive, harmless to the environment and the human body, and it emits blue light from ultraviolet rays with high efficiency, low power consumption and excellent environmental properties. It is a material that can be applied to devices.
Since Mg _x Zn _1-X O has almost the same lattice constant as that of ZnO, it is possible to form a high-quality thin film, and since the coefficient of thermal expansion is close, it is possible to suppress strain caused by temperature changes. Is possible.

  In order to solve the above-mentioned problems, the present inventors have used a ZnO-based single crystal substrate, and have fully evaluated and understood the characteristics of the ZnO-based single crystal substrate. ZnO-based single crystal substrates have recently been excellent in crystallinity, but still have a high resistivity of 100 Ω · cm or higher, and after forming a layer for the purpose of controlling conductivity, a p-type semiconductor layer is formed. There was a need.

Therefore, when ZnO-based single crystal is grown on a ZnO-based single crystal substrate, Al, Fe, Ga, and In are used alone or in combination as donor impurities, and the concentration is 1.0 × in terms of the number of atoms. An n-type ZnO system in which a layer having excellent crystallinity, high mobility, and n-type layer resistivity of 0.5 Ω · cm or less is formed in advance by doping so as to be 10 ¹⁷ / cm ³ or more. A single crystal plate substrate was prepared.

As a result, an increase in the series resistance can be suppressed, and the characteristics of the pn junction and the light emission can be greatly improved.
Further, the surface defect level density of the c (0001) plane (Zn plane), m (10-10) plane, and a (11-20) plane, which are planes containing zinc atoms, of the ZnO single crystal substrate is c (0001). The ZnO-based semiconductor thin film was prepared by simultaneously doping nitrogen and copper into any one of the above surfaces, focusing on the fact that it is smaller than the oxygen surface) and thermodynamically stable.

FIG. 2 schematically shows a surface containing these zinc atoms of a ZnO-based single crystal. (A) shows the c (0001) plane (Zn plane), (b) shows the m (10-10) plane, and (c) shows the a (11-20) plane by hatching.
If the plane orientation of the n-type ZnO-based single crystal substrate is within ± 1 degree with respect to the c (0001) plane, m (10-10) plane, and a (11-20) plane, it is called a terrace. In addition to the case where the flat portion is wide and almost free of unevenness, even if a surface including a step appears, a film having good crystallinity can be formed up to such an angle.

  Nitrogen to be doped as an acceptor works as an acceptor when single doping is performed. However, even if doping is performed at a high concentration in order to obtain a low-resistance p-type layer, a deep level is formed, so that the activation rate is increased. However, since it is difficult to reduce the resistance, it was necessary to improve the activation rate of nitrogen.

Therefore, the activation rate was improved by doping copper simultaneously with nitrogen during the formation of the thin film, and it effectively worked as an acceptor. The concentration of nitrogen to be doped was in the range of 2 × 10 ¹⁷ / cm ³ to 10 ²¹ / cm ³ in terms of the number of atoms. This is because at 10 ¹⁷ / cm ³ or less, the resistance of the p-type layer increases and the luminous efficiency deteriorates, and when it exceeds 10 ²¹ / cm ³ , the crystallinity deteriorates.

The concentration of copper nitrogen simultaneously with doping ranged from ^{1 × 10 17 / cm 3 ~10} 21 / cm 3. If it is 10 ¹⁷ / cm ³ or less, the effect of simultaneously doping copper is insufficient, the resistance of the p-type layer becomes high and the light emission intensity becomes weak, and if it exceeds 10 ²¹ / cm ³ , the crystallinity deteriorates. is there.

FIG. 3 is a schematic cross-sectional view showing another embodiment of the semiconductor light emitting device according to the present invention.
In the semiconductor light emitting device shown in FIG. 3A, an n-type ZnO single crystal substrate made of Mg _b Zn _1-b O (where 0 ≦ b ≦ 1 ) is used as an n-type semiconductor layer 14, During the film formation, _a p-type semiconductor layer 13 made of a ZnO-based compound made of Mg _a Zn _1-a O (where 0 ≦ a ≦ 1 ) is doped simultaneously with nitrogen N and copper Cu, and an n-type semiconductor layer 14 is formed. And a pn junction at a junction surface (interface) 18 with the. Furthermore, a p-type cladding layer 16 made of a single crystal thin film of Mg _c Zn _1-c O (where 0 <c ≦ 1 and a <c) is laminated on the p-type semiconductor layer 13.
Then, a p-type ohmic electrode is formed as the first electrode 12 on the p-type cladding layer 16, and an n-type ohmic electrode is formed as the second electrode 15 on the back surface of the n-type ZnO-based single crystal substrate that is the n-type semiconductor layer 14. ing.

In the semiconductor light emitting device shown in FIG. 3B, an n-type ZnO-based single crystal substrate made of Mg _b Zn _1-b O (where 0 ≦ b ≦ 1 ) is used as an n-type cladding layer 17, and Mg is formed on the upper surface thereof. _An n-type semiconductor layer 14 made of _d Zn _1-d O (where 0 ≦ d ≦ 1 and d ≦ b) is formed, and on top of that , Mg simultaneously doped with nitrogen N and copper Cu during film formation _A p-type semiconductor layer 13 made of a ZnO-based compound made of _a Zn _1-a O (where 0 ≦ a ≦ 1 ) is formed, and a pn junction is formed at a junction surface (interface) 18 with the n-type semiconductor layer 14. .
Then, a p-type ohmic electrode is formed as the first electrode 12 on the p-type semiconductor layer 13, and an n-type ohmic electrode is formed as the second electrode 15 on the back surface of the n-type ZnO-based single crystal substrate which is the n-type cladding layer 17. ing.

In the semiconductor light emitting device shown in FIG. 3C, an n-type ZnO-based single crystal substrate made of Mg _b Zn _1-b O (where 0 ≦ b ≦ 1 ) is used as an n-type cladding layer 17, and Mg is formed on the upper surface thereof. _An n-type semiconductor layer 14 made of _d Zn _1-d O (where 0 ≦ d ≦ 1 and d ≦ b) is formed, and on top of that , Mg simultaneously doped with nitrogen N and copper Cu during film formation _A p-type semiconductor layer 13 made of a ZnO-based compound made of _a Zn _1-a O (where 0 ≦ a ≦ 1 ) is formed, and a pn junction is formed at a junction surface (interface) 18 with the n-type semiconductor layer 14. . The structure up to this point is the same as that of the semiconductor light emitting device of (b), but Mg _c Zn _1-c O (where 0 <c ≦ 1 and a <c) is simply formed on the p-type semiconductor layer 13. A p-type cladding layer 16 made of a crystal thin film is laminated.
Then, a p-type ohmic electrode is formed as the first electrode 12 on the p-type cladding layer 16, and an n-type ohmic electrode is formed as the second electrode 15 on the back surface of the n-type ZnO single crystal substrate which is the n-type cladding layer 17. ing.

These semiconductor light emitting element is applied structure to the basic structure shown in FIG. 1, to form a clad layer. The clad layer has a p-type layer and an n-type layer, and is disposed outside the p-type semiconductor layer and the n-type semiconductor layer, respectively, with the pn junction as the center. This clad layer is also expressed by Mg _c Zn _1-c O (p-type clad layer) and Mg _d Zn _1-d O (n-type clad layer), respectively. However, if the p-type semiconductor layer is Mg _a Zn _1-a O (where 0 ≦ a ≦ 1 ) and the n-type semiconductor layer is Mg _b Zn _1-b O (where 0 ≦ b ≦ 1 ), a <c B <d.

By providing this clad layer, carriers are confined, the probability of recombination is increased, and light emission efficiency is improved. When producing the clad layer, not only Zn but also Mg metal is mixed in the Zn crucible 6 in FIG. 4 to be described later, or an alloy of ZnMg is put in place of Zn single metal, The amount of Mg in the thin film can be controlled.
However, when the n-type ZnO single crystal substrate serves as a cladding layer, d <b is necessary. However, when an n-type thin film is provided for the purpose of controlling conductivity, d = b may be used.

[Example of Manufacturing Method of Semiconductor Light Emitting Element]
The method for manufacturing a semiconductor light emitting device of the present invention will be described in detail below.
FIG. 4 shows a crystal growth apparatus (hereinafter referred to as “reactive vapor deposition apparatus”) using a reactive vapor deposition method with plasma assist as an example of a ZnO thin film growth apparatus.

This reactive vapor deposition apparatus includes a chamber 20 that is a decompression vessel having a gas supply port 7 and an exhaust port 9 that are ports for introducing oxygen and nitrogen, and a vacuum pump that keeps the inside of the chamber 20 in a vacuum state (see FIG. Not shown).
The source gas introduced into the chamber 20 is a G3 grade or higher cylinder gas (purity 99.99% or higher) as the oxygen gas, and a G3 grade or higher cylinder gas (purity 99.995% or higher) as the nitrogen gas. Grades lower than this cannot be used because the impurity concentration increases and electrical characteristics and crystallinity deteriorate.

  In the chamber 20, there are a dedicated substrate mask 3 for holding an n-type ZnO-based single crystal substrate (hereinafter also simply referred to as “substrate”) 2 as a base for thin film growth, and a heater 1 for heating the substrate 2. A temperature sensor 21 is provided for checking the heating temperature.

Further, a crucible 6 as a solid metal element source for supplying zinc Zn and a crucible heater 8 for heating the crucible 6 to evaporate zinc are mounted in the chamber 20, and a temperature for confirming the heating temperature. A sensor 22 is provided.
As the raw material Zn, metallic zinc particles having a purity of 99.99% or more are used. If the purity is lower than this, the impurity concentration becomes large, and electrical characteristics and crystallinity are deteriorated, so that it cannot be used.

Further, when a clad layer made of a Mg _x Zn _1-x O (where 0 <x ≦ 1) thin film is prepared, not only metal zinc particles but also metal magnesium particles are mixed in an appropriate ratio in the crucible 6 for Zn. The amount of magnesium is controlled by adding particles of ZnMg alloy instead of metallic zinc particles.

  Also, a crucible 10 as a solid metal element source for supplying copper and a crucible heater 11 for heating the crucible 10 to evaporate copper are attached in the chamber 20, and a temperature sensor for confirming the heating temperature. 23 is also provided. As the raw material Cu, metallic copper particles having a purity of 99.99% or more are used.

  The inside of the chamber 20 is exhausted from the exhaust port 9 by a vacuum pump (not shown), and is kept in a vacuum state when the thin film is manufactured. The thin film growth and the degree of vacuum in the chamber 20 are appropriately controlled by a control panel (not shown). In addition, a plasma generating coil 4 is provided above the crucible 6 and the crucible 10 in the chamber 20, and similarly, the output of plasma generated by the control panel is appropriately controlled. A shutter 5 is provided between the plasma generating coil 4 and the substrate mask 3 so as to be interposed and retractable.

Below, the process of growing the ZnO-type semiconductor thin film used as a p-type semiconductor layer on an n-type ZnO-type single crystal substrate is demonstrated in detail.
In an annealing electric furnace (not shown), the n-type ZnO-based single crystal substrate is heated at 800 ° C. to 1000 ° C. for 2 hours (H), and the surface is planarized. If the heating temperature at this time is lower than 800 ° C., the planarization is not sufficient, and if it exceeds 1000 ° C., Zn and O atoms are lost and defects are generated.

  Next, at a predetermined position on the substrate mask 3 in the chamber 20 of the reactive vapor deposition apparatus shown in FIG. 4, the zinc surface of the n-type ZnO-based single crystal substrate 2 subjected to the annealing treatment is shown (the lower surface in FIG. 4). Attach so that Also, metallic zinc (size 2-5 mm, purity 99.9999% or more) is quantitatively packed in the crucible 6, and metallic copper (size 2-5 mm, purity 99.9999% or more) is also quantitatively packed in the crucible 10.

Then, the inside of the chamber 20 of the reactive vapor deposition apparatus is evacuated to about (1.0 to 2.0) × 10 ⁻⁵ Pa by a vacuum pump. When the degree of vacuum is low, the content of impurities in the deposited film is high and the crystallinity is deteriorated. After confirming the vacuum state, the heater power for heating the substrate (not shown) is turned on, and heated by the heater 1 at 500 to 700 ° C. for 0.5 to 1 hour (H), and the surface of the n-type ZnO-based single crystal substrate 2 Perform cleaning. If the heating temperature at this time is lower than this or the heating time is shorter than this, the cleaning becomes insufficient, and if the heating temperature is higher or the heating time is longer than this, defects of Zn and O increase.

Next, nitrogen (cylinder gas) is introduced, an RF power source (not shown) is turned on under an internal pressure of the chamber 20 of 8.0 × 10 ⁻¹ Pa, and the plasma generating coil 4 is activated to generate plasma. Let The internal pressure 8.0 × 10 ⁻¹ Pa of the chamber 20 is a pressure necessary for generating plasma in the present embodiment.
At this time, the surface of the n-type ZnO single crystal substrate 2 is planarized and cleaned at a plasma output of 30 to 300 W for 5 to 10 minutes. If the plasma output is less than 30 W or the treatment time is shorter than 5 minutes, the effect of the treatment is reduced. Further, if the plasma output is larger than 300 W or the processing time is longer than 10 minutes, the substrate is damaged.

  After completion of this cleaning, the substrate heating temperature is adjusted to the film formation temperature. The ZnO-based semiconductor thin film is formed at a film formation temperature of 300 to 900 ° C. When the film formation temperature is lower than 300 ° C., the crystallinity is remarkably deteriorated, and when it exceeds 900 ° C., film formation cannot be performed. After the temperature adjustment, the crucible heating heater power source (not shown) is turned on, and the crucible 6 is heated by the crucible heater 8. The heating temperature of the crucible 6 is 300-600 degreeC. When the temperature is lower than 300 ° C., Zn does not evaporate, and when the temperature is higher than 600 ° C., the film formation rate becomes too high, and the crystallinity is remarkably deteriorated.

  Next, oxygen (cylinder gas) which is another raw material is introduced, the RF power is turned on again, and the plasma generating coil 4 is activated to generate plasma. The plasma output at this time is performed between 20 and 250 W. This is because when the plasma output is lower than 20 W, film formation cannot be performed, and when it is higher than 250 W, the film formation rate becomes too high, and the crystallinity is significantly deteriorated.

In order to produce a ZnO-based semiconductor thin film that becomes a p-type semiconductor thin film by doping, doping is performed by mixing nitrogen (cylinder gas) as a doping material into oxygen gas. The flow rate of oxygen and nitrogen is controlled by mass flow, and the chamber internal pressure is adjusted to be 1.0 × 10 ⁻¹ to 1.0 Pa. This pressure is a condition that the film formation rate is high, the crystallinity is good, and doping is performed smoothly. When the chamber internal pressure is lower than 1.0 × 10 ⁻¹ Pa, oxygen and nitrogen are reduced. Therefore, ZnO cannot be synthesized efficiently and the film cannot be formed well, or the doping amount is too small and p-type characteristics do not appear. On the other hand, when the pressure is higher than 1.0 Pa, the raw material Zn is oxidized and the reaction does not proceed.

  Oxygen and nitrogen are set to have a partial pressure of nitrogen: oxygen = 1: 0.5 to 10, and then the crucible shutter 5 is opened to start the formation of a ZnO-based semiconductor thin film (p-type semiconductor layer). The reason for setting the partial pressure ratio is that if the nitrogen ratio is larger than this, the crystallinity is deteriorated, and if it is smaller, the carrier concentration is lowered and the resistance of the p-type semiconductor layer is increased.

  Further, the doping of copper simultaneously with nitrogen is performed by turning on the crucible heater 11 of the crucible 10 provided for copper evaporation at the same time as heating the crucible 6 for zinc. The heating temperature of the crucible 10 by the crucible heater 11 is between 1000 ° C and 1500 ° C. The film formation time is 30 to 500 minutes, and the film thickness of the ZnO-based semiconductor thin film is 0.2 to 2.0 μm. The film formation time is the time necessary to obtain this film thickness.

In the course of copper evaporated from the crucible 10 is a solid metal source to zinc evaporated from the n-type ZnO-based single crystal substrate 2 or on the crucible 6 reaches its substrate 2, by incorporating into the ZnO thin film, deposited A ZnO-based semiconductor thin film in which nitrogen and copper are simultaneously doped is directly formed on the n-type ZnO-based single crystal substrate 2 as a p-type semiconductor layer by epitaxial growth.

  After completion of the film formation time, the shutter 5 is closed, the heating of the crucible 6 by the heater 8 and the heating of the crucible 10 by the heater 11 and the heating of the substrate 2 by the heater 1 are stopped, the plasma power supply is turned off, and oxygen gas and nitrogen gas are turned off. Installation will also stop. When the temperature of the substrate 2 and the crucibles 6 and 10 is lowered, the sample (the ZnO-based semiconductor thin film formed on the n-type ZnO-based single crystal substrate 2) and the crucibles 6 and 10 are taken out.

  The electrode is manufactured by attaching a sample on which a film is formed to a mask dedicated to electrode preparation and using a vacuum evaporation apparatus. An aluminum Al film having a thickness of 0.03 to 0.5 μm is formed on the back surface of the n-type ZnO single crystal substrate which is the n-type semiconductor layer 14 or the n-type cladding layer 17 shown in FIGS. N-type ohmic electrodes are formed. The reason for this thickness is that the thickness is sufficient to obtain ohmic contact and the strength of the electrode can be sufficiently obtained.

On the p-type semiconductor layer 13 or the p-type cladding layer 16 made of a ZnO-based semiconductor thin film in FIGS. 1 and 3, nickel Ni is formed to a thickness of 0.008 to 0.02 μm, and gold Au is further added to 0.03 to 0.03 μm. A 0.3 μm film is formed to form a p-type ohmic electrode as the first electrode 12. In order to provide adhesion, Ni is first formed into a film, and then Au is formed in order to obtain sufficient ohmic and strength as an electrode. Each electrode size is 1 × 1 mm ² .

  In the above-described embodiment, an example in which the formation of a ZnO-based semiconductor thin film (p-type semiconductor layer) on an n-type ZnO-based single crystal substrate is performed by a reactive deposition method with plasma assist has been described in detail. However, the present invention is not limited to this, and the formation of the ZnO-based semiconductor thin film on the n-type ZnO-based single crystal substrate is performed by a pretreatment and a film forming method from the same viewpoint as the reactive deposition method with plasma assist described above. It is also possible to carry out by metal organic vapor phase epitaxy (MOCVD) method with various parameters adjusted and improved, molecular beam epitaxy growth (MBE) method using metal zinc element source, laser deposition method, sputtering method or the like. .

[Evaluation of Semiconductor Light-Emitting Device According to the Invention]
The semiconductor light emitting device shown in FIG. 1 according to the present invention manufactured under the above conditions was evaluated.
The semiconductor light emitting device used for this evaluation has Al, Fe, Ga, In as donor impurities alone, or a combination thereof, and the conductivity is improved by doping 1.0 × 10 ¹⁷ / cm ³ or more in terms of the number of atoms. The n-type ZnO single crystal substrate controlled and reduced in resistance was used as an n-type semiconductor layer 14 and a p-type semiconductor layer 13 was pn-junctioned with a ZnO-based semiconductor layer doped with nitrogen and copper. The ZnO-based semiconductor layer as the p-type semiconductor layer 13 was prepared by doping nitrogen and copper during the formation of the Mg _a Zn _1-a O (where 0 ≦ a ≦ 1 ) single crystal thin film .

FIG. 5 is a diagram showing an EL spectrum of the evaluation result.
The vertical axis indicates the intensity (au) of light emitted by current injection (arbitrary unit), and the horizontal axis indicates the wavelength (nm) of light. The solid line data in this graph is the emission spectrum of a conventional semiconductor light emitting device fabricated using a p-type semiconductor layer doped only with nitrogen, and the broken line data is a p-type semiconductor layer doped with nitrogen and copper simultaneously. 1 is an emission spectrum of a semiconductor light emitting device according to the present invention fabricated using au represents, for example, the count number of the measuring device, but varies greatly depending on the measurement conditions. In this experiment, the measurement conditions are fixed, but comparison with other measurement data is not possible.

FIG. 5 shows that the semiconductor light emitting device according to the present invention using the p-type semiconductor layer simultaneously doped with nitrogen and copper emits much lighter than the conventional semiconductor light emitting device using the p-type semiconductor layer doped only with nitrogen. It can be seen that it is strong (peak wavelength around 380 nm). This is presumably because the copper worked effectively as an acceptor by doping copper simultaneously with nitrogen during film formation .

The present invention provides a semiconductor light emitting device capable of reliably forming a high-quality, low-resistance p-type semiconductor layer on an n-type ZnO-based single crystal substrate , excellent in mass productivity, and having high emission intensity (bright emission). be able to. Therefore, the semiconductor light-emitting device according to the present invention can be used as a light-emitting diode, and can be used in a wide variety of applications such as various display devices, printers, and lighting fixtures. It can also be used as a semiconductor laser element and can be used for a wide variety of applications such as writing to a large-capacity storage medium.

It is typical sectional drawing which shows one Embodiment of the semiconductor light-emitting device by this invention. It is explanatory drawing of the surface containing the zinc atom of an n-type ZnO type | system | group single crystal. It is typical sectional drawing which shows embodiment of the other different structure of the semiconductor light-emitting device by this invention. It is typical sectional drawing which shows the structural example of the ZnO thin film growth apparatus (reactive vapor deposition apparatus) used for manufacture of the semiconductor light-emitting device by this invention. It is a diagram which shows the EL spectrum of the evaluation result of the semiconductor light-emitting device by this invention.

1: Heater for substrate heating 2: n-type ZnO-based single crystal substrate (substrate)
3: Substrate mask 4: Coil for plasma generation 5: Shutter 6: Crucible (for zinc, magnesium and ZnMg) 7: Gas supply port
8: Crucible heater (for zinc, magnesium and ZnMg)
9: Exhaust port 10: Crucible (for copper) 11: Crucible heater (for copper)
12: First electrode (p-type ohmic electrode)
13: p-type semiconductor layer 14: n-type semiconductor layer 15: second electrode (n-type ohmic electrode)
16: p-type cladding layer 17: n-type cladding layer 18: pn junction surface (interface)
20: Chamber (vacuum vessel) 21, 22, 23: Temperature sensor

Claims (13)

p-type by a thin film of Mg _a Zn _1-a O (where 0 <a <1) single crystal composed of a ZnO-based compound doped simultaneously with nitrogen and copper during film formation on an n-type ZnO single crystal substrate A semiconductor light emitting element, wherein a semiconductor layer is formed and a pn junction is formed. The semiconductor light emitting device according to claim 1,
The p-type semiconductor layer has a doped nitrogen concentration of 2 × 10 ¹⁷ / cm ³ to 10 ²¹ / cm ³ in terms of the number of atoms, and a doped copper concentration of 1 × 10 ¹⁷ / cm ^{3 in} terms of the number of atoms. A semiconductor light-emitting element characterized by having a density of -10 ²¹ / cm ³ . The semiconductor light emitting device according to claim 1 or 2,
The n-type ZnO-based single crystal substrate is made of ZnO-based single crystal with any one of Al, Fe, Ga and In as a donor impurity or a combination thereof, and the concentration is 1.0 × 10 ¹⁷ / cm ³ in terms of the number of atoms. A semiconductor light-emitting device, which is an n-type ZnO single crystal substrate doped so as to have a low resistance as described above. The semiconductor light-emitting device according to claim 3.
The n-type ZnO-based single crystal substrate has a resistivity of 0.5 Ω · cm or less, a semiconductor light emitting device. The semiconductor light emitting device according to claim 1 or 2,
The n-type ZnO-based single crystal substrate is a ZnO-based single crystal, and any one or combination of Al, Fe, Ga, and In as a donor impurity, and the concentration is 1.0 × 10 ¹⁷ / cm in terms of the number of atoms. ^3. A semiconductor light emitting device comprising: an n-type ZnO single crystal substrate on which an n-type ZnO-based thin film whose conductivity is controlled by doping to be ³ or more and whose resistance is reduced is formed. The semiconductor light emitting device according to claim 5, wherein
The n-type ZnO-based thin film formed on the n-type ZnO-based single crystal substrate has a resistivity of 0.5 Ω · cm or less, a semiconductor light emitting device. The semiconductor light-emitting device according to claim 1,
A surface of the n-type ZnO-based single crystal substrate on which the p-type semiconductor layer is formed is a surface containing zinc atoms. The semiconductor light emitting device according to claim 7,
The surface containing zinc atoms is a c (0001) plane, an m (10-10) plane, or an a (11-20) plane. The semiconductor light emitting device according to claim 8,
The n-type ZnO single crystal substrate has a plane orientation within ± 1 degree with respect to the c (0001) plane, m (10-10) plane, or a (11-20) plane. A semiconductor light emitting device. The semiconductor light-emitting device according to claim 1,
The n-type ZnO-based single crystal _{substrate, Mg b Zn 1-b O} ( provided that, 0 ≦ b <1) semiconductor light-emitting element which is a single crystal substrate. The semiconductor light-emitting device according to claim 1,
The n-type ZnO-based single crystal substrate has an n-type ZnO-based thin film Mg _d Zn _1-d O (where 0 ≦ d <1 and d ≦ b) formed with low resistance by doping with donor impurities. A semiconductor light-emitting element, which is a ZnO-based single crystal substrate. The semiconductor light emitting device according to claim 1 or 2,
The n-type ZnO-based single crystal _{substrate, Mg b Zn 1-b O} ( provided that, 0 ≦ b <1) on the n-type cladding layer composed of a single crystal substrate, an n-type ZnO whose resistance is reduced by doping donor impurity An n-type semiconductor layer of the system thin film Mg _d Zn _1-d O (where 0 ≦ d <1 and d ≦ b) is formed, and the p-type semiconductor layer is formed on the n-type semiconductor layer, A semiconductor light emitting element, wherein a pn junction is formed at a junction surface with the n-type semiconductor layer. The semiconductor light-emitting device according to claim 1,
A semiconductor light emitting device comprising a p-type cladding layer made of a single crystal thin film of Mg _c Zn _1-c O (where 0 <c ≦ 1 and a <c) on the p-type semiconductor layer. .

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