JP2012204362A - Method of manufacturing nitride semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a high-performance nitride semiconductor light-emitting element.SOLUTION: A method of manufacturing a nitride semiconductor light-emitting element comprises the steps of: forming an n-type nitride semiconductor layer on a substrate; forming a light-emitting layer on the n-type nitride semiconductor layer; forming a p-type nitride semiconductor layer on the light-emitting layer; heat-treating the p-type nitride semiconductor layer at a first temperature in an atmosphere containing oxygen; and heat-treating the p-type nitride semiconductor layer, which is heat-treated at the first temperature, at a second temperature lower than the first temperature in a vacuum atmosphere.

Description

  The present invention relates to a method for manufacturing a nitride semiconductor light emitting device.

  In order to use the compound semiconductor light emitting device for various lighting applications, a light emitting device capable of emitting three primary colors of red, green, and blue light is indispensable. Regarding light-emitting diodes (LEDs), until recently, blue LEDs of the three primary colors were lacking without being completed, and thus LEDs could not be used for various lighting applications.

  However, since the development of blue LEDs using nitride semiconductors in the 1990s, lighting products that use LEDs are not limited to traffic lights, but also backlights for LCD monitors, backlights for LCD TVs, and even for home use. It is used for various lighting applications.

  Recently, liquid crystal televisions equipped with LED backlights have begun to spread rapidly as their prices fall. Moreover, the lighting fixture using LED has the merit that it enables low power consumption, space saving and mercury-free compared with the conventional lighting fixture, and is desirable for the environment. Then, after the summer of 2009, lighting fixtures using LEDs have been released at a much lower price than before, and their spread is rapidly progressing.

  White light is used for the backlights of the above-described lighting fixtures and liquid crystal televisions. Generally, white light is a combination of a blue LED and a YAG (yttrium, aluminum, garnet) yellow phosphor, or a blue LED, a green fluorescent light. This is realized by a combination of body and red phosphor. That is, in order to realize white light, a blue LED is always required.

  In a light emitting layer of a semiconductor light emitting device such as a so-called short wavelength LED such as a blue LED or a blue green LED or an LD (laser diode), gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), or their A nitride semiconductor such as a mixed crystal is used. An example of a blue LED using a nitride semiconductor will be described below with reference to FIG.

  FIG. 7 is a schematic cross-sectional view showing an example of a conventional double heterojunction blue LED. Referring to FIG. 7, a blue LED 100 includes a lower clad layer 102 made of an n-type GaN layer doped with Si, a light emitting layer 103 made of an InGaN layer, and a p-type AlGaN doped with Mg on a substrate 101 made of sapphire. An upper cladding layer 104 made of p-type GaN and a contact layer 105 made of p-type GaN are stacked in this order. A conductive thin film 106 is formed on the contact layer 105, and a p-side electrode 107 is provided on a part of the conductive thin film 106. On the other hand, an n-side electrode 108 is provided on a part of the lower cladding layer 102.

  In the blue LED 100, when current is injected from the p-side electrode 107, the current is diffused in the surface direction of the conductive thin film 106. Then, the diffused current flows into the upper clad layer 104 and the light emitting layer 103 over a wide area, whereby light emission in a wide region of the light emitting layer 103 is possible.

  Developments for improving the performance of nitride semiconductor light emitting devices such as the blue LEDs described above have been promoted from various viewpoints. For example, Patent Document 1 proposes a technique for improving the performance of a nitride semiconductor light-emitting device by devising a process for forming a p-side electrode. Specifically, when alloying the translucent electrode formation layer and the p seat electrode formation layer, after heat treatment at a relatively low temperature in an atmosphere containing oxygen, heat treatment at a relatively high temperature in an atmosphere not containing oxygen As a result, while maintaining the ohmic contact between the p-type layer made of a group III nitride semiconductor and the translucent electrode, the bonding force between the p seat electrode and the conductive wire is reduced due to the oxidation of the surface of the p seat electrode. Suppression techniques have been proposed.

In general, a nitride semiconductor light emitting device is formed by MOCVD (Metal Organic Chemical Vapor Deposition) method. A p-type nitride semiconductor layer, for example, a GaN layer doped with Mg is formed by MOCVD method. In this case, this layer is known to have high resistance without exhibiting p-type conductivity. This is because a gas containing hydrogen such as ammonia (NH ₃ ) is used as a reaction gas, so that H is taken into the GaN crystal and this H is combined with Mg doped in the GaN layer to form a Mg—H composite. It is considered that Mg is inactivated by forming. For this reason, the resistance of the nitride semiconductor light emitting device is reduced by annealing the GaN layer to remove H in the layer.

For example, in Patent Document 2, by annealing a Mg-doped GaN layer at a high temperature in an atmosphere that does not substantially contain hydrogen, the joint of the Mg—H composite is cut to form H into GaN. A technique has been proposed in which the resistance of the GaN layer is reduced by expelling out of the crystal to promote the release of holes from Mg. Patent Document 3 proposes a technique for annealing a GaN layer doped with Mg at a relatively low temperature in an O ₂ mixed atmosphere.

JP 2002-368270 A JP-A-10-178206 Japanese Patent Laid-Open No. 10-209493

  However, if annealing is performed on the GaN layer at a high temperature, N loss from the GaN layer is likely to occur, and donor-type defects are generated in the GaN layer due to N loss, resulting in a hole concentration in the GaN layer. There is a problem that it falls. Further, there is a concern that the annealing process at a high temperature for a long time may damage an MQW (Multiple Quantum Well) layer as a light emitting layer. Furthermore, the hole concentration of the GaN layer can be further increased according to the impurity doping amount, and the performance of the nitride semiconductor light emitting device is still not sufficient.

  In view of the above circumstances, an object of the present invention is to provide a method for manufacturing a nitride semiconductor light emitting device having high performance.

  The present invention includes a step of forming an n-type nitride semiconductor layer on a substrate, a step of forming a light-emitting layer on the n-type nitride semiconductor layer, and a step of forming a p-type nitride semiconductor layer on the light-emitting layer. The step of heat-treating the p-type nitride semiconductor layer at a first temperature in an oxygen-containing atmosphere and the second step of lowering the p-type nitride semiconductor layer heat-treated at the first temperature lower than the first temperature in a vacuum atmosphere And a step of heat-treating at a temperature.

  In the method for manufacturing a nitride semiconductor light emitting device, the first temperature is preferably 400 ° C. or higher and 700 ° C. or lower, and the second temperature is preferably 200 ° C. or higher.

  In the method for manufacturing a nitride semiconductor light emitting device, the pressure of the atmosphere containing oxygen is preferably 1 atm or more and the vacuum atmosphere is preferably 10 Pa or less.

  In the method for manufacturing a nitride semiconductor light emitting device, the oxygen content in an oxygen-containing atmosphere is preferably 1% by volume or more and 30% by volume or less.

In the method for manufacturing the nitride semiconductor light emitting element, p-type nitride semiconductor layer is, Al _x In _y Ga _z N of (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ z ≦ 1, x + y + z = 1) The nitride semiconductor represented by the formula is preferably doped with a p-type impurity.

  In the method for manufacturing a nitride semiconductor light emitting device, the p-type nitride semiconductor layer is preferably doped with Mg.

  The method for manufacturing a nitride semiconductor light emitting device preferably further includes a step of forming a conductive thin film on the p-type nitride semiconductor layer after the step of heat treatment at the second temperature.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the nitride semiconductor light-emitting device which has high performance can be provided.

It is a perspective view which shows typically an example of the nitride semiconductor light-emitting device which can be produced with the manufacturing method of the nitride semiconductor light-emitting device of this Embodiment. It is typical sectional drawing along line II-II of FIG. FIG. 3 is a schematic cross-sectional view illustrating each step of the example of the method for manufacturing the nitride semiconductor light emitting element shown in FIG. 1. It is typical sectional drawing of the laminated body produced for examination of the effect of various annealing treatments. It is a figure which shows the relationship between various annealing treatments and the hole density | concentration of a p-type nitride semiconductor layer. It is sectional drawing which shows typically an example of the structure of the nitride semiconductor light-emitting device produced in the Example. It is sectional drawing which shows typically an example of the structure of the conventional nitride semiconductor light-emitting device.

  Hereinafter, embodiments of a nitride semiconductor light emitting device according to the present invention will be described with reference to the drawings. The following embodiments are merely examples, and various embodiments can be implemented within the scope of the present invention. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts.

<Nitride semiconductor light emitting device>
FIG. 1 is a perspective view schematically showing an example of a nitride semiconductor light-emitting device that can be manufactured by the method for manufacturing a nitride semiconductor light-emitting device of the present embodiment. FIG. 2 is a line II-II in FIG. It is typical sectional drawing along.

  Referring to FIGS. 1 and 2, the nitride semiconductor light emitting device 10 has a stacked body in which a lower cladding layer 12, a light emitting layer 13, and an upper cladding layer 14 are stacked in this order on a substrate 11. A conductive thin film 15 is formed on the upper clad layer 14, and a first electrode 16 is provided on the conductive thin film 15. A second electrode 17 is provided on the lower cladding layer 12.

  In the nitride semiconductor light emitting device 10, a double heterojunction is formed by the lower cladding layer 12, the light emitting layer 13, and the upper cladding layer 14. In addition, as the light emitting layer 13, various semiconductor layers containing undoped, n-type, p-type, and both n-type and p-type impurities are selected as necessary, and an arbitrary interface of these semiconductor layers is pn It becomes the joint surface.

(substrate)
As the substrate 11, Al _x1 In _y1 Ga _z1 N (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1, 0 ≦ z1 ≦ 1, x1 + y1 + z1 = 1), GaP, GaAs, NdGaO ₃ , LiGaO ₂ , Al ₂ O ₃ (Sapphire), MgAl ₂ O ₄ , ZnO, Si, SiC, SiGe, or a substrate having at least a material represented by the formula of ZrB _{2 on} the surface is preferably used.

(N-type nitride semiconductor layer)
The lower cladding layer 12 as an n-type nitride semiconductor layer has a band gap larger than the band gap of the light emitting layer 13 and functions to block electrons and holes in the light emitting layer 13 by a potential barrier based on the gap difference. Have Further, the lower cladding layer 12 may include a buffer layer between the substrate 11 and the light emitting layer 13 and a contact layer for good ohmic contact with the second electrode 17. That is, the lower cladding layer 12 may be a single layer or a plurality of layers.

When the lower clad layer 12 is a single layer, the material is expressed by the formula of Al _x2 In _y2 Ga _z2 N (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1, 0 ≦ z2 ≦ 1, x2 + y2 + z2 = 1). It is preferable to use a nitride semiconductor doped with an n-type impurity such as Si. When the lower cladding layer 12 has a plurality of layers, a nitride represented by the formula Al _x2 In _y2 Ga _z2 N (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1, 0 ≦ z2 ≦ 1, x2 + y2 + z2 = 1) The semiconductor may include an n-type nitride semiconductor layer in which an n-type impurity such as Si is doped, and an undoped nitride semiconductor layer.

  As the laminated structure of the lower clad layer 12 composed of a plurality of layers, for example, a buffer layer, an undoped layer, an n-type doped layer, an n-type contact layer, and the like can be appropriately selected and laminated. More specifically, it may be a laminated structure such as InGaN / GaN, InGaN / AlGaN, AlGaN / GaN, InGaN / InGaN, or a periodic laminated structure in which a plurality of layers are repeatedly laminated. Note that these laminated structures may form a superlattice structure.

(Light emitting layer)
The light emitting layer 13 may have a laminated structure such as an MQW structure or an SQW structure (Sigle Quantum Well). In particular, the light emitting layer 13 preferably has an MQW structure in which barrier layers and well layers are alternately stacked. The optimum thickness of each of the barrier layer and the well layer varies depending on the wavelength at which the well layer emits light, and the thickness of the well layer is preferably 2 nm or more and 20 nm or less.

The materials of the barrier layer and the well layer include Al _x3 In _y3 Ga _z3 N (0 ≦ x3 ≦ 1, 0 ≦ y3 ≦ 1, 0 ≦ z3 ≦ 1, x3 + y3 + z3 = 1) and Al _x4 In _y4 Ga _z4 N A nitride semiconductor represented by the formula (0 ≦ x4 ≦ 1, 0 ≦ y4 ≦ 1, 0 ≦ z4 ≦ 1, x4 + y4 + z4 = 1) can be used. Further, at least one of the barrier layer and the well layer may be doped with a p-type impurity or an n-type impurity. In the case where the light emitting layer 13 includes a plurality of well layers, at least one well layer may perform the light emitting action.

(P-type nitride semiconductor layer)
The upper clad layer 14 as the p-type nitride semiconductor layer has a band gap larger than the band gap of the light emitting layer 13, similarly to the lower clad layer 12. Has the function of blocking electrons and holes. Further, the upper clad layer 14 may include a layer that functions as an evaporation preventing layer, a carrier block layer, or a current spreading layer. That is, the upper cladding layer 14 may be a single layer or a plurality of layers.

If the upper cladding layer 14 is a single layer, as the material is represented by the formula _{Al x In y Ga z N (} 0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ z ≦ 1, x + y + z = 1) It is preferable to use a nitride semiconductor doped with a p-type impurity such as Mg. If the upper cladding layer 14 is a plurality of _{layers, Al x In y Ga z N} (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ z ≦ 1, x + y + z = 1) nitride represented by the formula The semiconductor may include a p-type nitride semiconductor layer obtained by doping a p-type impurity such as Mg and an undoped nitride semiconductor layer.

  Such a laminated structure of the upper clad layer 14 composed of a plurality of layers may be a laminated structure such as InGaN / GaN, InGaN / AlGaN, AlGaN / GaN, InGaN / InGaN, and a plurality of layers are repeatedly laminated. A periodic laminated structure may be used. Note that these laminated structures may form a superlattice structure.

In addition, the thickness of the upper cladding layer 14 is preferably 500 nm or less. Since the thickness of the upper cladding layer 14 is 500 nm or less, the light emitting layer 13 can be prevented from being exposed to heat at a high temperature for a long time when the upper cladding layer 14 is formed. An increase in the non-light emitting region due to thermal degradation can be suppressed. In the present embodiment, the upper clad layer 14 can have a hole concentration of 3 × 10 ¹⁷ holes / cm ³ or more.

(Contact layer)
Here, in the present embodiment, it is preferable to provide a contact layer between the upper clad layer 14 and the conductive thin film 15. By providing the contact layer, the contact resistance between the upper cladding layer 14 and the conductive thin film 15 can be reduced. As such a contact layer, a nitride semiconductor represented by the formula of Al _x5 In _y5 Ga _z5 N (0 ≦ x5 ≦ 1, 0 ≦ y5 ≦ 1, 0 ≦ z5 ≦ 1, x5 + y5 + z5 = 1) It is preferable to use a nitride semiconductor layer doped with p-type impurities at a higher concentration than the cladding layer 14. When the upper cladding layer 14 and the conductive thin film 15 are in direct contact without forming a contact layer, the upper cladding layer 14 has a high concentration of p-type impurities near the surface on the conductive thin film 15 side. It is preferable that

(Conductive thin film)
The conductive thin film 15 transmits light from the light emitting layer 13 and forms a contact with the semiconductor layer to be contacted to diffuse current over the entire surface, thereby expanding the light emitting area of the light emitting layer 13 below the conductive thin film 15. It has the function to do. For this reason, it is preferable to use a material having a lower resistance than that of the contact layer or the upper clad layer 14 as the material of the conductive thin film 15, so that the current injected from the first electrode 16 is supplied to the conductive thin film 15. It can be diffused in the surface direction. For example, ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), AZO (Aluminum Zinc Oxide), and GZO (Gallium Zinc Oxide) can be preferably used as the material constituting the conductive thin film 15. . Among these, it is particularly preferable to use ITO from the viewpoint of translucency and contact resistance.

  The thickness of the conductive thin film 15 is preferably 100 nm or more and 400 nm or less. When the thickness of the conductive thin film 15 is 100 nm or more, the sheet resistance can be kept low, and when the thickness is 400 nm or less, the high light transmittance of the conductive thin film 15 can be maintained.

(First electrode and second electrode)
The first electrode 16 and the second electrode 17 serve as a wire bond base that is electrically connected to an external circuit. The first electrode 16 and the second electrode 17 can be formed in a known manner, and for example, materials such as Ti, Al, and Au can be used. The first electrode 16 and the second electrode 17 are not limited to a single layer structure, and may have a multilayer structure. When the first electrode 16 and the second electrode 17 have a multilayer structure, it is preferable to form an Au layer having a thickness of 500 nm or more as the uppermost layer. Thereby, when mounting the nitride semiconductor light emitting element 10 in a package, wire bond stability with an external circuit can be ensured.

  A part of the light emitted from the light emitting layer 13 is emitted in the direction of the upper cladding layer 14 side. Therefore, the first electrode 16 is an electrode arranged in the light extraction direction from the light emitting layer 13 to the upper cladding layer 14 side. On the other hand, the 2nd electrode 17 shown by FIG. 1 and FIG. 2 has illustrated the arrangement | positioning in case the board | substrate 11 consists of an insulating material. That is, when an insulating material is used as the substrate 11, the second electrode 17 is provided on a partially exposed region of the lower cladding layer 12, and when a conductive material is used as the substrate 11, the second electrode 17 is It can be formed on the bottom surface of the substrate 11.

<Nitride Semiconductor Light-Emitting Device Manufacturing Method>
In the method for manufacturing a nitride semiconductor light emitting device according to the present embodiment, when the nitride semiconductor light emitting device is manufactured, the formed p-type nitride semiconductor layer is heat-treated at a first temperature in an atmosphere containing oxygen (first step). After the first annealing treatment, heat treatment (second annealing treatment) is performed at a second temperature lower than the first temperature in a vacuum atmosphere.

  FIG. 3 is a schematic cross-sectional view illustrating each step of the example of the method for manufacturing the nitride semiconductor light emitting device shown in FIG. Hereinafter, a method for manufacturing the nitride semiconductor light emitting device 10 of the present embodiment will be described with reference to FIG.

(Formation of n-type nitride semiconductor layer)
First, the substrate 11 is placed in an MOCVD apparatus, and a lower cladding layer 12 as an n-type nitride semiconductor layer is grown on the substrate 11 by MOCVD, as shown in FIG.

  For example, in a MOCVD apparatus, the substrate 11 is heated at 1000 ° C. or more, and a group III source gas, a doping gas containing an n-type impurity such as Si, and a nitrogen source material gas are MOCVD together with a carrier gas such as nitrogen and hydrogen. The lower clad layer 12 is grown on the substrate 11 by being introduced into the apparatus.

In this case, as the group III source gas, for example, TMG ((CH ₃ ) ₃ Ga: trimethylgallium) gas, TEG ((C ₂ H ₅ ) ₃ Ga: triethylgallium) gas, TMA ((CH ₃ ) ₃ Al: trimethylaluminum) gas, TEA ((C ₂ H ₅ ) ₃ Al: triethylaluminum) gas, TMI ((CH ₃ ) ₃ In: trimethylindium) gas, or TEI ((C ₂ H ₅ ) ₃ In: triethyl Indium) gas can be used. As the doping gas, for example, it can be used SiH ₄ (silane) gas. As the nitrogen source material gas, for example, ammonia gas can be used.

(Formation of light emitting layer)
Next, in the MOCVD apparatus, a light emitting layer 13 is grown on the lower cladding layer 12 by MOCVD as shown in FIG.

For example, the substrate 11 in the MOCVD apparatus is heated at 1000 ° C. or higher, a Ga source material gas and a nitrogen source material gas are introduced into the MOCVD apparatus, and a barrier layer made of GaN is grown on the lower clad layer 12. Then, an In source gas, a Ga source gas, and a nitrogen source source gas are introduced into the MOCVD apparatus, and a well layer made of In _p Ga _1-p N (0 <p <1) is grown on the barrier layer. By repeating this, the light emitting layer 13 having an MQW structure having a periodic laminated structure can be grown. The group III source gas and the nitrogen source gas that can be used are the same as described above.

(Formation of p-type nitride semiconductor layer)
Next, in the MOCVD apparatus, as shown in FIG. 3C, an upper cladding layer 14 as a p-type nitride semiconductor layer is grown on the light emitting layer 13 by MOCVD.

  For example, in a MOCVD apparatus, the substrate 11 is heated at 1000 ° C. or more, and a group III source gas, a doping gas containing a p-type impurity such as Mg, and a nitrogen source gas are mixed with a carrier gas such as nitrogen and hydrogen. An upper cladding layer 14 is grown on the light emitting layer 13 by introducing into the device.

In this case, for example, Cp ₂ Mg (cyclopentadienyl magnesium) gas or (EtCp) ₂ Mg (bisethylcyclopentadienyl magnesium) gas can be used as the doping gas. Since (EtCp) ₂ Mg gas is liquid under normal temperature and normal pressure conditions, it has better response when changing the amount introduced into the MOCVD apparatus than Cp ₂ Mg gas, which is solid under those conditions And it is easy to keep the vapor pressure constant. The group III source gas and the nitrogen source gas that can be used are the same as described above.

  In the MOCVD apparatus, a contact layer may be formed on the upper clad layer 14 by MOCVD. Since the contact layer is preferably doped with p-type impurities at a higher concentration than the upper clad layer 14, the amount of doping gas introduced is larger in the growth of the contact layer than when the upper clad layer 14 is grown. It is preferable to make it.

(First annealing treatment)
Next, the laminated body in which the substrate 11, the lower clad layer 12, the light emitting layer 13, and the upper clad layer 14 formed in this manner are laminated in this order is heat-treated at a first temperature in an oxygen-containing atmosphere. Thus, the first annealing process is performed. For example, the laminated body is accommodated in an annealing furnace, a gas containing oxygen is introduced into the annealing furnace to make the annealing furnace an atmosphere containing oxygen, and the annealing furnace is heated at a first temperature. When a contact layer is formed on the upper clad layer 14, it is preferable to perform a first annealing process after the contact layer is formed.

(Second annealing treatment)
Subsequently, the laminated body after the first annealing treatment is heat-treated in a vacuum atmosphere at a second temperature lower than the first temperature, thereby performing the second annealing treatment. For example, the inside of the annealing furnace containing the laminated body after the first annealing treatment is depressurized to form a vacuum atmosphere, and the inside of the annealing furnace is heated at a second temperature lower than the first temperature. In addition, a vacuum atmosphere means the case where atmospheric pressure is 10 Pa or less.

  Hydrogen (H) is taken into the upper cladding layer 14 before the first annealing treatment, and part of the doped Mg is inactivated by forming a Mg—H complex with this hydrogen (H). Yes. For this reason, the hole concentration of the upper cladding layer 14 is lower than the concentration assumed from the concentration of doped Mg. The hole concentration of the upper cladding layer 14 can be increased by performing the first annealing process and the second annealing process on the upper cladding layer 14 as described above. The reason is considered as follows.

  In the first annealing treatment, when the upper clad layer 14 is heated in an atmosphere containing oxygen (O), the joint between Mg and hydrogen (H) in the Mg—H composite is cut by thermal energy. Then, oxygen (O) reacts with hydrogen (H) on the surface of the upper clad layer 14, whereby hydrogen (H) is desorbed from the surface of the upper clad layer 14, and the deactivated Mg is activated. In the second annealing process, the annealing furnace is placed in a vacuum atmosphere, and the upper cladding layer 14 is heated at a second temperature lower than the first temperature, thereby efficiently removing hydrogen (H) from the upper cladding layer 14. Can be done automatically.

  By performing the first annealing process in an atmosphere containing oxygen (O), even if the first heating temperature is lower than the temperature of the conventional annealing process, oxygen (O) plays a catalytic role, and the upper cladding The desorption of hydrogen (H) from the surface of the layer 14 can be efficiently performed, and subsequently the second annealing process is performed in a vacuum atmosphere, so that the second heating temperature is lower than the first heating temperature. Also, desorption of hydrogen (H) from the upper cladding layer 14 can be performed efficiently. Accordingly, hydrogen (H) can be desorbed by a heat treatment at a temperature lower than that in the prior art, so that nitrogen (N) escape generated by heating at a high temperature can be suppressed.

  As described above, hydrogen (H) can be efficiently desorbed from the upper cladding layer 14 and nitrogen desorption from the upper cladding layer 14 can be suppressed, so that Mg is activated, Generation of donor-type defects caused by nitrogen desorption can be suppressed, and as a result, the hole concentration of the upper cladding layer 14 can be greatly increased.

Here, the following examination was performed in order to verify the above-mentioned effect. First, as shown in FIG. 4, an undoped GaN layer 22 and a p-type GaN layer 23 doped with Mg are grown in this order on a sapphire substrate 21 by MOCVD, so that four stacked bodies 20 are obtained. Produced. The Mg doping concentration was 4 × 10 ¹⁹ atoms / cm ³ . And after performing each process of following (1)-(4) with respect to each of each produced laminated body 20, the hole density | concentration (piece / cm) of the p-type GaN layer 23 of each laminated body 20 after a process. ³ ) was measured by the Hall measurement method.
(1) No annealing treatment.
(2) Annealing was performed at 800 ° C. for 5 minutes in an N ₂ atmosphere and normal pressure environment.
(3) N ₂ atmosphere, after 5 min annealing at 800 ° C. under normal pressure, the atmosphere containing O ₂ (O ₂ is 2 vol%, N ₂ 98 vol%), at 600 ° C. under normal pressure Annealing treatment was performed for 10 minutes, followed by annealing at 420 ° C. for 5 minutes in a vacuum environment.
(4) Annealing treatment is performed at 600 ° C. for 10 minutes in an atmosphere containing oxygen (O ₂ is 2% by volume, N ₂ is 98% by volume) under normal pressure, and then annealed at 420 ° C. for 5 minutes in a vacuum Processed.
(In the above examination, the atmospheric pressure environment means 1 atm or more, and the vacuum environment means 10 Pa or less.)
FIG. 5 shows the hole concentration in the p-type GaN layer 23 of each stacked body 20 that has been subjected to the processes (1) to (4). Referring to FIG. 5, the hole concentration was higher in the cases (3) and (4) than in the case (1) and the case (2) that is the conventional annealing method. From this result, the p-type nitride semiconductor layer is heat-treated in an oxygen-containing atmosphere at a first temperature lower than the temperature of the conventional annealing treatment, and then in a vacuum atmosphere at a second temperature lower than the first temperature. As a result, it was confirmed that the hole concentration of the p-type nitride semiconductor layer can be increased.

In the first annealing treatment, as the gas containing oxygen, O ₂ , O ₃ , CO, CO ₂ , NO, NO ₂ or the like can be used. Moreover, it is preferable that 1st heating temperature is 400 degreeC or more and 700 degrees C or less. Thereby, since desorption of hydrogen (H) at a temperature lower than a heating temperature (for example, 800 ° C. or higher) necessary for conventional annealing treatment is possible, nitrogen desorption can be efficiently suppressed, Moreover, the influence of the damage to the light emitting layer 13 can be suppressed. The first heating temperature is more preferably 600 ° C. or lower.

Further, it is preferable to introduce nitrogen gas (N ₂ ) into the annealing furnace together with the gas containing oxygen during the first annealing treatment. Thereby, nitrogen (N) escape from the upper cladding layer 14 can be further suppressed. In particular, the oxygen content in the processing chamber is preferably 2% by volume or more and 30% by volume or less, which effectively suppresses nitrogen (N) escape from the upper clad layer 14 and oxygen (O). Reaction with hydrogen (H) can be performed efficiently.

  Moreover, it is preferable that the pressure in the process chamber at the time of the first annealing process is 1 atm or more. Thereby, nitrogen (N) escape can be suppressed and reaction of oxygen (O) and hydrogen (H) can be performed efficiently. Moreover, it is preferable that the first annealing treatment is performed for a time of 0.1 minutes to 60 minutes. In addition, the second annealing treatment is preferably performed for a time of 0.1 minutes to 60 minutes.

(Formation of conductive thin film)
Returning to FIG. 3, next, as shown in FIG. 3D, the conductive thin film 15 is formed on the upper cladding layer 14. For example, the conductive thin film 15 made of ITO or IZO can be deposited on the upper clad layer 14 by using an electron beam evaporation method, a vacuum evaporation method, a sputtering method, an ion plating method, or the like. When a contact layer is formed, the conductive thin film 15 is formed on the contact layer. The conductive thin film 15 is preferably annealed. Thereby, the resistance of the conductive thin film 15 can be reduced.

(Formation of first electrode and second electrode)
Next, as shown in FIG. 3E, a mask 18 having a predetermined shape is formed on the conductive thin film 15 so that a part of the conductive thin film 15 is exposed. As the mask 18, for example, a resist film formed by a photolithography method can be used.

  Then, as shown in FIG. 3 (f), by etching from above the mask 18, the portion not covered with the mask 18 is etched to expose a part of the lower cladding layer 12. Thereafter, the mask 18 is removed, and a p-side electrode as the first electrode 16 and an n-side electrode as the second electrode 17 are formed on the surface of the upper cladding layer 14 and the surface of the lower cladding layer 12, respectively. The nitride semiconductor light emitting device shown in FIGS. 1 and 2 can be manufactured.

  For the above reasons, according to the method for manufacturing a nitride semiconductor light emitting device of the present embodiment, the hole concentration of the upper cladding layer 14 can be increased, and thus the nitride semiconductor light emitting device 10 having high performance is manufactured. can do.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

Example 1
In this example, the nitride semiconductor light emitting device shown in FIG. 6 was produced. Hereinafter, a specific method for manufacturing the nitride semiconductor light emitting device of FIG. 6 will be described.

First, as a substrate, a template substrate 31 was prepared in which an AlN buffer layer, an undoped GaN layer, and an n-type GaN layer were formed on a sapphire substrate having a roughened surface. The concentration of Si doped in the n-type GaN layer was 6 × 10 ¹⁸ / cm ³ .

This template substrate 31 is placed in an MOCVD apparatus, the template substrate 31 is heated at 1000 ° C., and in this state, an Si-doped GaN layer 32 having a thickness of 1.5 μm as an n-type nitride semiconductor layer is formed on the template substrate 31. Was vapor-phase grown by MOCVD. In the MOCVD method, SiH ₄ was used as an n-type impurity doping gas, and the concentration of Si doped in the Si-doped GaN layer 32 was 6 × 10 ¹⁸ / cm ³ .

  Next, the temperature in the MOCVD apparatus is lowered to 850 ° C., and the light emitting layer 33 in which the barrier layer is provided on the periodic laminated structure in which the six barrier layers and the six well layers are alternately laminated. Was vapor-phase grown by MOCVD.

Next, the temperature in the MOCVD apparatus is raised to 1100 ° C., and a p-type nitride semiconductor layer in which the Mg-doped AlGaN layer 34 and the Mg-doped GaN layer 35 are stacked in this order on the light emitting layer 33 is formed by MOCVD. Vapor phase growth. The concentrations of Mg doped in the Mg-doped AlGaN layer 34 and the Mg-doped GaN layer 35 were 2 × 10 ¹⁹ pieces / cm ³ and 5 × 10 ¹⁹ pieces / cm ³ , respectively.

Next, the temperature in the MOCVD apparatus was raised, and a Mg-doped GaN layer 36 having a thickness of 20 nm as a contact layer was vapor-phase grown on the Mg-doped GaN layer 35 by MOCVD. The concentration of Mg doped in the Mg-doped GaN layer 36 was 5 × 10 ¹⁹ pieces / cm ³ .

Next, a laminated body in which the Si-doped GaN layer 32, the light emitting layer 33, the Mg-doped AlGaN layer 34, the Mg-doped GaN layer 35, and the Mg-doped GaN layer 36 are laminated in this order on the template substrate 31 is used in an annealing furnace. installed. Then, a mixed gas composed of ₂ % by volume of O ₂ gas and 98% by volume of N ₂ gas is introduced into the annealing furnace, the temperature in the annealing furnace is raised to 600 ° C., and in this state for 10 minutes. A first annealing treatment was performed by heating. The pressure in the annealing furnace at this time was 1 atmosphere.

  Next, the temperature in the annealing furnace was lowered to 420 ° C. and the inside of the processing chamber was reduced to a vacuum atmosphere at a pressure of 10 Pa. In this state, the second annealing treatment was performed by heating for 5 minutes.

  Next, the laminated body after the heat treatment was taken out from the annealing furnace, and the laminated body and a target made of ITO were placed in a sputtering apparatus. And after heating the template substrate 31 of a laminated body and raising the temperature of a laminated body to 180 degreeC, argon gas is introduce | transduced in a sputtering device, 1.28 kWh sputtering power is supplied, Mg doped GaN A conductive thin film 37 made of ITO having a thickness of 320 nm was formed on the layer 36.

  Next, for the purpose of improving the crystallinity, adhesion, and contact property of each layer, the laminate with the conductive thin film 37 formed is taken out of the sputtering apparatus and installed in an annealing furnace. The heat treatment was performed. The heat treatment was performed by holding the laminated body for 10 minutes in a state where the annealing furnace was heated to 600 ° C. in a vacuum atmosphere.

  Next, the laminated body after the heat treatment was taken out from the annealing furnace and placed in an etching apparatus in which a mask having a predetermined shape was placed on the surface of the conductive thin film 37. In the etching apparatus, each of the conductive thin film 37, the Mg-doped GaN layer 36, the Mg-doped GaN layer 35, the Mg-doped AlGaN layer 34, the light-emitting layer 33, and the Si-doped GaN layer 32 that are exposed from the mask from above. A part of this was etched to expose the surface of the Si-doped GaN layer 32.

  Next, the stacked body after the etching was taken out from the etching apparatus, and a resist mask having openings of predetermined shapes on the surface of the conductive thin film 37 and the exposed surface of the Si-doped GaN layer 32 was formed. Then, the template substrate on which the resist mask is formed is placed in an electron beam evaporation apparatus, and a Ti film, a Pt film, and an Au film are formed on the surfaces of the conductive thin film 37 and the Si-doped GaN layer 32 on which the resist mask is formed. Films were deposited in this order, after which the resist mask was removed by lift-off. Thereby, the p-side electrode 38 and the n-side electrode 39 in which the Ni film, the Pt film, and the Au film were laminated in this order were formed on the surfaces of the conductive thin film 37 and the Si-doped GaN layer 32, respectively. The thicknesses of the Ni film, Pt film, and Au film were 100 nm, 50 nm, and 500 nm, respectively.

  Next, the laminated body on which the p-side electrode 38 and the n-side electrode 39 were formed was taken out from the electron beam evaporation apparatus and placed in a lamp annealing apparatus. And it heat-processed at 500 degreeC, and produced the nitride semiconductor light-emitting device shown in FIG.

(Comparative Example 1)
A nitride semiconductor light emitting device was fabricated by the same method as in Example 1 except that the following annealing treatment was performed instead of the first annealing treatment and the second annealing treatment.

In the annealing process, the laminated body is placed in an annealing furnace, a processing gas composed of N ₂ gas is introduced into the annealing furnace, the temperature in the annealing furnace is raised to 800 ° C., and heated in this state for 5 minutes. As a result, annealing treatment was performed. The pressure in the annealing furnace at this time was 1 atmosphere.

  The nitride semiconductor light emitting device of Example 1 had a lower driving voltage and higher luminous efficiency than the nitride semiconductor light emitting device of Comparative Example 1.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention can be used for electronic devices such as LEDs, LDs, high temperature devices, and power devices.

  DESCRIPTION OF SYMBOLS 10 Nitride semiconductor light emitting element, 11 board | substrate, 12 lower clad layer, 13,33 light emitting layer, 14 upper clad layer, 15,37 conductive thin film, 16 1st electrode, 17 2nd electrode, 18 mask, 21 sapphire substrate, 22 GaN layer, 23 p-type GaN layer, 31 template substrate, 32 Si-doped GaN layer, 34 Mg-doped AlGaN layer, 35 Mg-doped GaN layer, 36 Mg-doped GaN layer, 38 p-side electrode, 39 n-side electrode.

Claims (7)

Forming an n-type nitride semiconductor layer on the substrate;
Forming a light emitting layer on the n-type nitride semiconductor layer;
Forming a p-type nitride semiconductor layer on the light emitting layer;
Heat-treating the p-type nitride semiconductor layer at a first temperature in an oxygen-containing atmosphere;
And a step of heat-treating the p-type nitride semiconductor layer heat-treated at the first temperature at a second temperature lower than the first temperature in a vacuum atmosphere.   2. The method for manufacturing a nitride semiconductor light emitting element according to claim 1, wherein the first temperature is 400 ° C. or more and 700 ° C. or less, and the second temperature is 200 ° C. or more.   3. The method for manufacturing a nitride semiconductor light emitting element according to claim 1, wherein a pressure of the atmosphere containing oxygen is 1 atm or more, and the vacuum atmosphere is 10 Pa or less.   4. The method for manufacturing a nitride semiconductor light-emitting element according to claim 1, wherein the oxygen content in the atmosphere containing oxygen is 1% by volume or more and 30% by volume or less. The p-type nitride semiconductor _{layer, Al x In y Ga z N} (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ z ≦ 1, x + y + z = 1) p in the nitride semiconductor represented by the formula The method for manufacturing a nitride semiconductor light-emitting element according to claim 1, wherein the nitride semiconductor light-emitting element is doped with a type impurity.   The method for manufacturing a nitride semiconductor light-emitting element according to claim 1, wherein the p-type nitride semiconductor layer is doped with Mg.   The method for manufacturing a nitride semiconductor light-emitting element according to claim 1, further comprising a step of forming a conductive thin film on the p-type nitride semiconductor layer after the step of heat-treating at the second temperature. .

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