JP2009177219A - METHOD FOR MANUFACTURING GaN-BASED SEMICONDUCTOR DEVICE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a GaN-based semiconductor device which is capable of lowering its operation voltage while making productivity improvements and reducing manufacturing costs by manufacturing a p-type GaN-based semiconductor without performing additional heat treatment process after the lamination process a semiconductor layer is completed. <P>SOLUTION: As the uppermost layer of a lamination structure of a GaN-based semiconductor to be formed on a substrate, a p-type contact layer composed of AlGaN is formed by a MOVPE method, and then the falling temperature of the p-type contact layer is carried out while ammonia and an inert gas with respect to the GaN semiconductor are introduced into a growing furnace so that the ratio of ammonia becomes 0 to 0.025. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a GaN-based semiconductor element.

In recent years, nitride semiconductors have been used as light-emitting diodes (hereinafter also referred to as LEDs) in the short wavelength region from blue to ultraviolet and materials for semiconductor lasers. The nitride-based semiconductor is a compound semiconductor represented by a general formula In _x Al _y Ga _z N (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1), For example, those having an arbitrary composition such as GaN, InGaN, AlGaN, AlInGaN, AlN, and InN are exemplified. Hereinafter, the nitride-based semiconductor is also referred to as a GaN-based semiconductor.

  In this type of light emitting device using a GaN-based semiconductor material, a p-type layer and an n-type layer are required as a current injection layer and a contact layer with an electrode. Only low conductivity is obtained compared to n-type. Therefore, in a light emitting device in which p-type and n-type GaN-based semiconductors are laminated on a substrate, the p-type contact layer on which the p-side electrode is formed is usually the uppermost layer of the laminate, and the p-type contact layer A p-side electrode is formed so as to cover the entire upper surface. With such a configuration, the direction of the current flowing in the p-type layer when a voltage is applied to the element can be the thickness direction of the layer, and the series resistance of the element can be kept low. Further, although current carriers are difficult to diffuse in the p-type layer having low conductivity, the amount of carriers injected from the p-type layer into the active layer is made uniform in the plane of the active layer. It is.

  For the p-type contact layer, in order to obtain ohmic contact with the electrode, the p-type impurity is magnesium (Mg), and the composition is binary mixed crystal gallium nitride (GaN) containing no indium (In) or aluminum (Al). ) (Patent Document 1). Patent Document 2 discloses an example in which a good ohmic property with respect to a metal electrode is obtained by using GaN doped with Mg at a high concentration in a p-type contact layer.

As a method for growing a GaN-based semiconductor, a metal organic vapor phase epitaxy (MOVPE) method capable of producing a high-quality crystal at a practical growth rate is generally used. However, when a GaN-based semiconductor is grown by the MOVPE method, there is a problem that it cannot be obtained simply by adding a group 2 element. In the case of GaN, since nitrogen atoms may be desorbed from the crystal at about 600 ° C. or higher, it is preferable to lower the temperature while flowing ammonia (NH ₃ ) until the temperature reaches 600 ° C. or lower after completion of growth at a high temperature. This is the same as in the case of using the MOVPE method. However, when the temperature is lowered to room temperature while flowing ammonia, p-type impurities such as Mg and zinc (Zn) in a GaN-based semiconductor are used. GaN grown by adding the group 2 element does not exhibit p-type conductivity and has high resistance. The reason is said that the activity as an acceptor of Mg and Zn is lost by stabilizing the bond between nitrogen atoms and atomic hydrogen around Mg and Zn. This phenomenon of inhibition of the expression of p-type conductivity due to the action of atomic hydrogen is called hydrogen passivation.

As a method for solving this problem and obtaining a low-resistance p-type GaN-based semiconductor, a GaN-based semiconductor is grown while adding a p-type impurity by the MOVPE method, and after the growth is completed, the temperature is lowered to room temperature while flowing ammonia. A method of performing a heat treatment at about 600 ° C. to 800 ° C. in a nitrogen gas (N ₂ ) atmosphere under atmospheric pressure or under pressure is known (Patent Document 4).
As another method, in Patent Document 5, after growing a GaN-based semiconductor while adding a p-type impurity by the MOVPE method, from a growth temperature to a temperature of about 900 to 700 ° C., in a nitrogen-containing atmosphere such as ammonia. In this method, it is said that detachment of harmful nitrogen atoms and hydrogen passivation can be prevented at the same time. In Patent Document 5, as a case of suppressing the incorporation of hydrogen during cooling, there is an example in which after the growth of GaAlInN, it is cooled in ammonia to a temperature of 800 ° C. to 850 ° C. and then cooled in argon. Are listed. In Patent Document 6, after p-type impurities are added and GaN is grown, cooling is performed while supplying ammonia into the growth furnace at a rate of 1.3 liters / minute and hydrogen at a rate of 2.5 liters / minute. An example is described in which p-type GaN is obtained without stopping the supply of ammonia at a temperature of 600 ° C. or higher without performing a heat treatment or the like after cooling.

JP-A-6-268259 JP-A-8-97471 JP 56-45899 A JP-A-5-183189 JP-A-6-326416 JP-A-8-115880

However, if an attempt is made to obtain a GaN-based semiconductor element including a p-type GaN-based semiconductor by the method described in Patent Document 4, a separate heat treatment process is required in addition to the semiconductor layer stacking process. There is a problem that the number of processes is increased, resulting in a decrease in productivity or an increase in cost, and a decrease in yield due to an increase in processing steps.
In addition, when the inventors made a prototype LED using p-type GaN as a p-type contact layer using the methods described in Patent Documents 5 and 6, it was found that there was a problem that the operating voltage was increased. It was. From a practical point of view, a light-emitting element is not simply a high output, and there is a demand for low power consumption from the side of the device / equipment in which the element is incorporated. In addition, since the operating voltage is directly related to the amount of heat generated by the element, it greatly affects the life of the element. There is also a problem that various design restrictions occur because a mounting structure that prioritizes heat dissipation is required as heat generation increases. In particular, in a GaN-based semiconductor light emitting device, in order to generate short-wavelength light, the driving voltage must be increased in principle, and the thermal conductivity of sapphire, which is currently optimal as a substrate for crystal growth However, there is also a problem that heat dissipation is poor. Under these circumstances, there is an extremely strong demand for reducing the operating voltage of a GaN-based semiconductor light emitting element, for example, the forward voltage (Vf) in an LED and the threshold voltage of oscillation in a laser diode, even if it is 0.1 V However, it is considered desirable to reduce it.

  The present invention solves the above-mentioned problem, that is, by producing a p-type GaN-based semiconductor without performing a separate heat treatment step after the semiconductor layer stacking step, thereby improving productivity and reducing costs. An object of the present invention is to provide a method for manufacturing a GaN-based semiconductor device that can reduce the operating voltage of the GaN-based semiconductor device.

The present invention has the following features.
(1) including a step of forming a laminated structure of a GaN-based semiconductor on a substrate,
(A) A raw material and a carrier gas are introduced into a growth furnace in which the substrate is installed, and a p-type contact layer made of Al _a Ga _1-a N (0 <a ≦ 1) is formed by the MOVPE method. After the step of growing as the uppermost layer and the steps (B) and (A), ammonia and a first gas made of an inert gas with respect to the GaN-based semiconductor are introduced into the growth furnace. A step of lowering the temperature of the p-type contact layer while introducing so that the ratio f of the flow rate of ammonia occupying the total flow rate of the gas introduced into the interior satisfies 0 <f <0.025;
A method for manufacturing a GaN-based semiconductor device, comprising:
(2) The method according to (1), wherein the ratio f is 0.001 ≦ f ≦ 0.01.
(3) The step of forming the laminated structure of the GaN-based semiconductor on the substrate further includes
(C) After the step (B), the temperature of the p-type contact layer is lowered while introducing a second gas that is inert to the GaN-based semiconductor and does not contain ammonia into the growth furnace. Process to perform,
The manufacturing method of said (1) or (2) containing.
(4) The manufacturing method according to (3), wherein the switching from the step (B) to the step (C) is performed when the substrate temperature t is t ≦ 950 ° C.
(5) The manufacturing method according to (4), wherein the switching from the step (B) to the step (C) is performed when the substrate temperature t is t ≦ 800 ° C.
(6) The manufacturing method according to (3) to (5), wherein the switching from the step (B) to the step (C) is performed when the substrate temperature t is t> 650 ° C.
(7) The manufacturing method according to (6), wherein, in the step (C), when the substrate temperature t is 650 ° C. <t ≦ 800 ° C., the temperature decreasing rate of the p-type contact layer is changed slowly.
(8) The manufacturing method according to (7), wherein the method of slowly changing the temperature decrease rate of the p-type contact layer includes operating a susceptor heating unit.
(9) In the step (B) or (C), when the substrate temperature t is t ≦ 650 ° C., the rate of temperature decrease of the p-type contact layer is changed rapidly. Production method.
(10) The production method of the above (1) to (9), wherein 0.01 ≦ a ≦ 0.2.
(11) The method according to any one of (1) to (10), wherein the first gas and the second gas include one or more kinds of gases selected from nitrogen gas and rare gases.
(12) The method according to any one of (1) to (11), wherein the p-type contact layer has a thickness of 1 nm to 50 nm.
(13) The manufacturing method according to (1) to (12), wherein Mg is added to the p-type contact layer at a concentration of 1 × 10 ¹⁹ cm ⁻³ to 1 × 10 ²¹ cm ⁻³ .
(14) The GaN-based semiconductor element includes a layer made of p-type GaN having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁸ cm ⁻³ adjacent to the p-type contact layer. ) To (13).
(15) The step of forming the laminated structure of the GaN-based semiconductor on the substrate includes a step of growing a layer made of undoped GaN on the substrate before the step (A). ) To (14).
(16) The method according to any one of (1) to (15), wherein the substrate is a substrate having a concavo-convex shape processed on the surface.
(17) In the step (A), the carrier gas introduced into the growth furnace includes a first carrier gas made of a chemically stable gas and hydrogen gas, and the first carrier gas The production method of (1) to (16), wherein the flow rate is the same as or larger than the flow rate of hydrogen gas.
(18) The manufacturing method according to (17), wherein the first carrier gas includes one or more kinds of gases selected from nitrogen gas and rare gases.
(19) The method of (1) to (16), wherein in the step (A), the carrier gas introduced into the growth furnace does not contain hydrogen gas.
(20) including a step of forming a laminated structure of a GaN-based semiconductor on a substrate,
(D) A raw material and a carrier gas are supplied into a growth furnace in which the substrate is installed, and a p-type contact layer made of Al _b Ga _1-b N (0 <b ≦ 1) is formed by the MOVPE method. Growing as the top layer,
(E) After the completion of the step (D), while introducing a third gas that is inert to the GaN-based semiconductor and does not contain ammonia into the growth furnace used in the step (D), A third temperature lowering step for lowering the temperature of the p-type contact layer;
A method for manufacturing a GaN-based semiconductor device, comprising:
(21) The manufacturing method according to (20), wherein, in the step (E), when the substrate temperature t is 650 ° C. <t ≦ 800 ° C., the temperature decreasing rate of the p-type contact layer is changed slowly.
(22) The manufacturing method according to (21), wherein the method of slowly changing the temperature decrease rate of the p-type contact layer includes operating a susceptor heating means.
(23) The manufacturing method according to (20) to (22), wherein, in the step (E), when the substrate temperature t is t ≦ 650 ° C., the temperature decrease rate of the p-type contact layer is changed rapidly.
(24) The production method of the above (20) to (23), wherein 0.01 ≦ b ≦ 0.2.
(25) The manufacturing method according to (20) to (24), wherein the third gas includes one or more kinds of gases selected from nitrogen gas and rare gases.
(26) The method according to (20) to (25), wherein the p-type contact layer has a thickness of 1 nm to 50 nm.
(27) The manufacturing method of (20) to (26), wherein Mg is added to the p-type contact layer at a concentration of 1 × 10 ¹⁹ cm ⁻³ to 1 × 10 ²¹ cm ⁻³ .
(28) The GaN-based semiconductor element includes a layer made of p-type GaN having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁸ cm ⁻³ adjacent to the p-type contact layer. ) To (27).
(29) The step of forming the laminated structure of the GaN-based semiconductor on the substrate includes a step of further growing a layer made of undoped GaN on the substrate before the step of (D). Thru (28) manufacturing method.
(30) The method according to any one of (20) to (29), wherein the substrate is a substrate having a concavo-convex shape processed on the surface.
(31) In the step (D), the carrier gas introduced into the growth furnace includes a second carrier gas made of a chemically stable gas and hydrogen gas, and the second carrier gas The method according to (20) to (30), wherein the flow rate is the same as or larger than the flow rate of hydrogen gas.
(32) The method according to (31), wherein the second carrier gas contains one or more kinds of gases selected from nitrogen gas and rare gases.
(33) The production method of (20) to (30), wherein the carrier gas introduced into the growth furnace in the step (D) does not contain hydrogen gas.

  The inventors of the present invention made a prototype of an LED using p-type GaN as a p-type contact layer using the method for producing a p-type GaN-based semiconductor described in Patent Documents 5 and 6, and found that the operating voltage was high. As a result of repeated investigations on the cause of this phenomenon, GaN has a relatively low decomposition temperature. Therefore, during the temperature lowering process after growth by the MOVPE method, significant nitrogen atom desorption occurs on the surface of the p-type contact layer. The contact resistance between the p-type contact layer and the p-side electrode was thought to have increased. That is, it is estimated that the contact resistance is increased due to the influence of the n-type conductivity caused by the nitrogen vacancies caused by the detachment of nitrogen atoms, which inhibits the expression of the p-type conductivity on the surface of the p-type contact layer. .

Therefore, according to the present invention, first, in the manufacturing process of the GaN-based semiconductor element, when forming the laminated structure of the GaN-based semiconductor on the substrate, the layer that grows as the uppermost layer, that is, the layer that grows last is the Al _n Ga _{1 By using} a p-type contact layer made of −nN (where 0 <n ≦ 1) (hereinafter also referred to as AlGaN), desorption suppression of nitrogen atoms on the surface of the p-type contact layer in the temperature lowering process after growth is suppressed. I am trying. Since AlGaN has a bond dissociation energy between Al and nitrogen atoms that is larger than the bond dissociation energy between GaN and nitrogen atoms, desorption of nitrogen atoms at a higher temperature than when the p-type contact layer is formed of GaN. This is because it is considered that is difficult to occur. This suppresses the generation of nitrogen vacancies exhibiting n-type conductivity and promotes the expression of p-type conductivity in the surface region of the p-type contact layer. The contact resistance with the p-side electrode is also reduced by growing the p-type contact layer by the MOVPE method suitable for growing a high-quality crystal.

  Next, in the present invention, after growing the p-type contact layer, the amount of ammonia introduced into the growth furnace in the temperature lowering process is extremely reduced as compared with the prior art. As a result, the synergistic effect of suppressing hydrogen passivation and the above-mentioned AlGaN as the material of the p-type contact layer significantly promotes the development of p-type conductivity on the surface of the p-type contact layer. Reduction of contact resistance with the side electrode is achieved.

  Further, in the present invention, in order to suppress hydrogen passivation more effectively, after the p-type contact layer is grown, ammonia introduced into the growth furnace in the temperature lowering process is stopped at a temperature considerably higher than room temperature. Also in this case, as described above, since the material of the p-type contact layer is made of AlGaN, the elimination of nitrogen atoms on the surface is suppressed, so the effect of suppressing hydrogen passivation becomes more dominant. Thus, the contact resistance between the p-type contact layer and the p-side electrode can be further reduced.

According to the present invention, a p-type GaN-based semiconductor having a low resistance can be obtained simply by performing a step of forming a laminated structure of a GaN-based semiconductor on a substrate, so that a separate heat treatment step is not required and It is possible to improve the property and reduce the cost.
In addition, according to the present invention, the p-type contact layer is made of GaN, although AlGaN is used as the material of the p-type contact layer, which was not considered to be the optimum material for the p-type contact layer in the conventional idea. The operating voltage is lower than that of the conventional GaN-based semiconductor element formed. As a result, the power consumption of the element is reduced and the amount of heat generation is reduced, so that deterioration is suppressed and the operating life and reliability of the element are improved.

  The present invention is not limited to an element formed into a chip including a substrate used for forming a laminated structure of a GaN-based semiconductor, but after a step in which the substrate is polished and removed after the laminated structure is formed on the substrate. Alternatively, it is also effective in the manufacture of an element that is made into a chip through a process of peeling the laminated structure from the substrate. This is because, even in the manufacture of such an element, it is desirable to use the p-type contact layer as the last layer grown in the step of forming the GaN-based semiconductor laminated structure on the substrate and to form the p-side electrode in this layer. It is. In forming a stacked structure of GaN-based semiconductor layers on a substrate, a p-type layer is first grown, and then an n-type layer is grown. After forming the stacked structure, the substrate is polished and removed, or the semiconductor layer is formed on the substrate. A method of peeling off the film and forming a p-side electrode on the exposed p-type layer is considered as a possibility, but it is difficult to actually adopt this method. This is because the polished surface and the peeled surface obtained by polishing and removing the substrate from the substrate and peeling the semiconductor layer from the substrate cannot be used for electrode formation as they are because they are very rough. It is necessary to make it. However, if etching is performed on the surface of the p-type GaN-based semiconductor, the contact resistance increases, which tends to be unsuitable for electrode formation.

It is a schematic diagram of the structure of LED which concerns on the Example of this invention. It is a figure which shows the relationship between the output of LED which concerns on the Example and comparative example of this invention, and the ratio of ammonia. It is a figure which shows the relationship between Vf of the LED which concerns on the Example and comparative example of this invention, and the ratio of ammonia. It is a figure which shows the relationship between Vr of the LED which concerns on the Example and comparative example of this invention, and the ratio of ammonia. It is a figure which shows the relationship between the output of LED which concerns on the Example of this invention, and ammonia stop temperature. It is a figure which shows the relationship between Vf of the LED which concerns on the Example of this invention, and ammonia stop temperature. It is a figure which shows the relationship between Vr of the LED which concerns on the Example of this invention, and ammonia stop temperature.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view schematically showing the structure of an LED according to an embodiment of the present invention. This LED has an undoped GaN underlayer 12, an n-type GaN contact layer 13, an active layer 14 mainly composed of InGaN, a p-type AlGaN cladding layer 15, and a p-type layer on a sapphire substrate 11 via a buffer layer (not shown). The GaN high carrier concentration layer 16 and the p-type AlGaN contact layer 17 have a multilayer structure grown sequentially.

  A part of the multilayer structure is removed by dry etching from the outermost surface of the p-type AlGaN contact layer 17 to a depth reaching the n-type GaN contact layer 13, and the n-type GaN contact layer 13 exposed thereby is removed. The n-side electrode 21 is formed. A p-side electrode 22 is formed on the portion where the p-type AlGaN contact layer 17 is not removed.

In the LED of FIG. 1 according to the embodiment of the present invention, when a laminated structure of a GaN-based semiconductor is formed on the sapphire substrate 11, the uppermost layer is made of Al _n Ga _1-n N (0 <n ≦ 1). A type AlGaN contact layer 17 is grown. The AlN mixed crystal ratio n of AlGaN forming the p-type AlGaN contact layer 17 is preferably 1% or more, and is preferably 3% or more in order to sufficiently suppress the elimination of nitrogen atoms at a high temperature. More preferably. When the AlN mixed crystal ratio n exceeds 20%, the band gap increases, the activation rate of the added p-type impurity decreases, and the contact resistance with the p-side electrode tends to increase. Moreover, cracks are likely to occur when the amount of Mg added is increased. When the AlN mixed crystal ratio n is 10% or less, the activation rate of the p-type impurity is increased and the crystal quality is improved, which is more preferable in reducing the contact resistance.

The preferred thickness of the p-type AlGaN contact layer 17 is 1 nm or more. If it is thinner than 1 nm, the contact resistance with the p-side electrode tends to increase. There is no particular upper limit to the thickness of the p-type AlGaN contact layer 17, but if it is formed thicker than necessary, the series resistance increases, so it is preferably 50 nm or less, more preferably 10 nm or less.
The p-type impurity added to the p-type AlGaN contact layer 17 may be any material that generates holes when added to a GaN-based semiconductor, and may be any of those known in the art, such as Mg, Zn, and Be. Can be used. Among these, Mg is preferable because it has a shallow impurity level, is easily activated, easily controlled, and has no toxicity problem. When adding Mg as a p-type impurity to the p-type AlGaN contact layer 17, in order to reduce the contact resistance with the p-side electrode, it is 1 × 10 ¹⁹ cm ⁻³ or more, more preferably 5 × 10 ¹⁹ cm ⁻³ or more. It is preferable to add at a high concentration. When the Mg concentration is 1 × 10 ²¹ cm ⁻³ or more, the crystallinity of the p-type AlGaN contact layer 17 tends to decrease and the contact resistance tends to increase.

In general, in a p-type GaN-based semiconductor, when the amount of p-type impurity added is increased, the carrier concentration does not increase in proportion to the impurity concentration, but rather tends to decrease after saturation at some point. In addition, the crystallinity tends to decrease as the concentration of the p-type impurity increases. Therefore, in order to obtain a p-type layer having a high carrier concentration, GaN having a higher activation rate of p-type impurities is more suitable than AlGaN. Therefore, in order to reduce the operating voltage of the device by promoting current diffusion on the p-type conductive layer side, the carrier concentration is 1 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁸ cm ⁻ directly below the p-type AlGaN contact layer 17. ³ p-type GaN high carrier concentration layer 16 is preferably provided. The p-type GaN high carrier concentration layer 16 having such a carrier concentration grows GaN while adding Mg so that the concentration becomes 5 × 10 ¹⁸ cm ^{−3 to} 5 × 10 ²⁰ cm ^−3. It can be obtained by lowering the temperature by the method of the invention. Providing such a high carrier concentration layer is preferable in the case of a light emitting device in order to increase the amount of carriers injected into the active layer. Further, when Mg is added to the p-type AlGaN contact layer 17 at a concentration of 5 × 10 ¹⁹ cm ⁻³ or more, the series resistance of the p-type AlGaN contact layer 17 tends to increase. The thickness is preferably 10 nm or less, and a p-type GaN high carrier concentration layer 16 having a thickness of 10 nm to 150 nm is preferably provided immediately below the thickness.

  Although the sapphire substrate 11 is illustrated in FIG. 1 as the substrate used for forming the laminated structure of the GaN-based semiconductor, the substrate is not limited to sapphire, and may be appropriately used as long as the GaN-based semiconductor can be grown. A material made of SiC (6H, 4H, 3C), GaN, AlN, Si, spinel, ZnO, GaAs, NGO (NdGaO3), or the like can be used. As for the sapphire substrate, a substrate having a C-plane, A-plane, R-plane or the like as a surface can be used. A substrate in which crystals made of these materials are formed as a surface layer can also be used.

  An uneven shape may be processed and formed on the surface of the sapphire substrate 11. When a concavo-convex shape is processed and formed on the surface of the substrate by a method such as dry etching, and a GaN-based semiconductor is grown thereon, a dislocation defect propagating to the upper semiconductor layer is reduced, or a region where the density of dislocation defects is low (For example, refer to JP 2000-106455 A, JP 2000-331947 A, JP 2001-210598 A, and JP 2002-164296 A). Therefore, when a concavo-convex shape is processed and formed on the surface of the sapphire substrate 11 and grown on the sapphire substrate 11 via the buffer layer or directly after the undoped GaN underlayer 12, the luminous efficiency in the active layer is improved, and the pn junction It is possible to expect favorable effects such as improvement of the withstand voltage characteristics of the contact portion, improvement of the electrical conductivity of the contact layer, reduction of the contact resistance between the contact layer and the electrode, etc. In this case, the light extraction efficiency of the LED can also be improved by growing the undoped GaN foundation layer 12 so that the recesses are embedded (see, for example, JP-A-2002-280611).

  Providing a buffer layer (not shown) on the sapphire substrate 11 is effective in growing a GaN-based semiconductor having a lattice constant different from that of sapphire on the sapphire substrate 11. The undoped GaN foundation layer 12 also has an effect of improving the crystal quality in the GaN-based semiconductor layer formed thereon. Therefore, by forming these buffer layers and undoped GaN foundation layer 12, the conductivity of the contact layer related to the improvement of the light emission efficiency in the active layer, the improvement of the breakdown voltage characteristics of the pn junction, and the reduction of the operating voltage of the element can be obtained. Desirable effects such as improvement and reduction of contact resistance between the contact layer and the electrode can be expected.

The n-type GaN contact layer 13, the active layer 14, and the p-type AlGaN cladding layer 15 constitute a pn junction structure essential for a high-efficiency light-emitting element.
Next, a method for manufacturing the LED of FIG. 1 will be described using examples.

The GaN-based semiconductor constituting this LED is grown by a well-known MOVPE method. Specifically, for example, trimethylgallium (TMG), trimethylaluminum (TMA), trimethylindium (TMI), biscyclopentadienylmagnesium (Cp ₂ Mg) is used as the organometallic raw material. As the gas raw material, ammonia or silane (SiH ₄ ) is used. Hydrogen gas (H ₂ ) and nitrogen gas (N ₂ ) are used as the carrier gas. As an apparatus, a normal pressure horizontal type MOVPE in which these raw materials and carrier gas are supplied from a lateral direction (a direction parallel to the main surface of a substrate installed substantially horizontally) in a growth furnace maintained at a normal pressure. An apparatus can be used conveniently.

  As the sapphire substrate 11, in this example and the comparative example, a C-plane sapphire substrate 11 having a concavo-convex shape formed on the surface is used. First, a pattern in which striped etching masks having a width of 3 μm are periodically arranged in parallel at intervals of 3 μm is formed on the substrate surface by using a photolithography method. The longitudinal direction of the stripe is parallel to the <1 -1 0 0> direction of sapphire. Next, a groove having a substantially rectangular cross section with a depth of 1 μm is formed by dry etching in a portion where the etching mask is not formed and the substrate surface is exposed. Thereafter, the etching mask is removed, and organic cleaning and acid cleaning are performed.

  After the concavo-convex shape is processed on the surface, the sapphire substrate 11 is placed on a susceptor to be heated by a heater in the growth furnace of the MOVPE apparatus. Next, in an atmosphere in which hydrogen gas is introduced at a flow rate of 25 L / min at normal pressure, the substrate temperature is raised to 1100 ° C., and vapor phase etching is performed for about 10 minutes. As a result, the natural oxide film on the surface of the sapphire substrate 11 is removed. Thereafter, the substrate temperature is lowered to 400 ° C., TMG, TMA, and ammonia are introduced, and a buffer layer made of AlGaN is formed.

  Subsequently, the supply of TMG and TMA is stopped, and the substrate temperature is raised to 1000 ° C. with only ammonia flowing. Thereafter, hydrogen gas and nitrogen gas are supplied as carrier gases, ammonia and TMG are supplied as raw materials, and the undoped GaN underlayer 12 is grown. The thickness of the undoped GaN foundation layer 12 is about 2 μm from the upper surface of the convex portion of the surface of the sapphire substrate 11.

  In the initial growth process of the undoped GaN underlayer 12, a three-dimensional GaN crystal having a facet surface inclined with respect to the substrate surface is formed on the convex portion and the concave bottom formed on the surface of the sapphire substrate 11. Separately formed. When the undoped GaN foundation layer 12 grows through such a process, the recesses formed on the surface of the sapphire substrate 11 are filled with the undoped GaN foundation layer 12 leaving almost no cavity.

  After the undoped GaN underlayer 12 is grown, silane is introduced into the growth furnace to form an n-type GaN contact layer 13 having a thickness of about 4 μm. Thereafter, the supply of TMG and silane is stopped, and the substrate temperature is lowered to 700 ° C. When the substrate temperature reaches 700 ° C., the carrier gas is switched from both hydrogen gas and nitrogen gas to only nitrogen gas, ammonia and TMG are introduced, and a barrier layer (barrier layer) made of GaN is grown. The Next, TMI is introduced and a well layer made of InGaN is grown. The supply amounts of TMG and TMI are adjusted so that the InN mixed crystal ratio of InGaN becomes an appropriate value according to the design emission wavelength of the LED. In this example, the center emission wavelength was set to 405 nm. The growth of the barrier layer and the well layer is repeated according to the design repetition number of the multiple quantum well. Thereby, the active layer 14 having a multiple quantum well structure is formed.

After the formation of the multi-quantum well active layer 14, the substrate temperature is raised again to 1000 ° C., and when it reaches 1000 ° C., the carrier gas is switched again to hydrogen gas and nitrogen gas, and TMG, TMA, Cp ₂ Mg are introduced. Thus, the p-type AlGaN cladding layer 15 having a thickness of 50 nm is grown. Subsequently, the supply of TMA is stopped, the flow rate of Cp ₂ Mg is increased, and the p-type GaN high carrier concentration layer 16 having a thickness of 100 nm is grown.

The p-type contact layer growth process and the temperature lowering process thereafter were changed to fabricate the LED of the example according to the present invention and the comparative example of the prior art, and the characteristics were compared.
[Growth of p-type contact layer]
(Examples 1-11 / Comparative Examples 1-3)
After the formation of the p-type GaN high carrier concentration layer 16, TMA is introduced again, the flow rate of Cp ₂ Mg is further increased, and the p-type AlGaN contact layer 17 is grown by 10 nm. At this time, the flow rates of TMG and TMA are adjusted so that the composition of AlGaN constituting the p-type AlGaN contact layer 17 is Al _0.03 Ga _0.97 N. Further, the flow rate ratio of Cp ₂ Mg and the Group 3 element is adjusted so that the Mg concentration of the p-type AlGaN contact layer 17 is 1 × 10 ²⁰ cm ⁻³ .

(Comparative Examples 4-7)
After the formation of the p-type GaN high carrier concentration layer 16, the flow rate of Cp ₂ Mg is further increased, and a p-type GaN contact layer is grown to 10 nm. At this time, the flow ratio of Cp ² Mg and the Group 3 element is adjusted so that the Mg concentration of the p-type GaN contact layer is 1 × 10 ²⁰ cm ⁻³ . Thus, the p-type contact layers of Comparative Examples 4 to 7 are grown in the same manner as the p-type AlGaN contact layer 17 of the example except that the composition is GaN.

[Cooling temperature]
(Examples 1-6 / Comparative Examples 1-7)
After the growth of the p-type AlGaN contact layer 17 (Examples 1 to 6 and Comparative Examples 1 to 3) or the p-type GaN contact layer (Comparative Examples 4 to 7) is completed, TMG, TMA, Cp ₂ Mg, and hydrogen gas are supplied. At the same time, the heating of the substrate is stopped, and the natural temperature drop of the substrate and the GaN-based semiconductor grown thereon starts. Along with the start of this natural temperature drop, the only gas introduced into the growth furnace is ammonia and nitrogen gas. At this time, the flow rates of ammonia and nitrogen gas introduced into the growth furnace were set as in Examples 1 to 6 and Comparative Examples 1 to 7 shown in Table 1. Table 1 also shows the ratio of the flow rate of ammonia in the total flow rate of the gas introduced into the growth furnace (hereinafter also referred to as ammonia ratio). In Example 6 alone, ammonia was not introduced, and only nitrogen gas was introduced into the growth furnace. In any of the examples and comparative examples, the flow rate of each gas was kept constant and kept flowing in the growth furnace until the substrate temperature dropped to room temperature.

(Examples 7 to 11)
After the growth of the p-type AlGaN contact layer 17, the supply of TMG, TMA, Cp ₂ Mg, and hydrogen gas is stopped, the heating of the substrate is stopped, and the substrate and the natural temperature drop of the GaN-based semiconductor grown thereon are stopped. Begins. Along with the start of this natural temperature drop, the only gas introduced into the growth furnace is ammonia and nitrogen gas. At this time, the flow rate of ammonia is 0.02 L / min, and the flow rate of nitrogen gas is 19.98 L / min. Therefore, the ammonia ratio is 0.1%. Thereafter, when the substrate temperature decreases and reaches a predetermined temperature, the introduction of ammonia is stopped. Hereinafter, the temperature at which the introduction of ammonia is stopped is also referred to as an ammonia stop temperature. After the ammonia is stopped, nitrogen is introduced at a flow rate of 20 L / min until the substrate temperature reaches room temperature. The ammonia stop temperatures used in Examples 7-11 are shown in Table 2.

[Elementization]
When the substrate temperature is lowered to room temperature, the epi-wafer having the GaN-based semiconductor laminated structure formed on the substrate is taken out from the growth furnace, and electrode formation and element separation (dividing the epi-wafer into chips) are performed. In the electrode formation, first, a translucent ohmic electrode 22 formed by laminating nickel (Ni) and gold (Au) as a p-side electrode is formed on the upper surface of the p-type AlGaN contact layer 17. Although not shown in FIG. 1, a power supply pad electrode is formed on the p-side electrode later.

  Next, a part of the p-type AlGaN contact layer 17, the p-type GaN high carrier concentration layer 16, the p-type AlGaN cladding layer 15, and the active layer 14 is removed by dry etching, and an n-type GaN contact is performed. Layer 13 is exposed. An ohmic electrode 21 in which titanium (Ti) and aluminum (Al) are laminated is formed on the exposed n-type GaN contact layer 13 as an n-side electrode. Further, after the power supply pad electrode is partially formed on the p-side electrode, element isolation is performed to obtain a square chip having a side of 350 μm.

[Evaluation]
The LED having the structure shown in FIG. 1 manufactured in this manner is energized from the n-side electrode 21 and the pad electrode formed on the p-side electrode 22 using an auto prober, and the output ( Arbitrary unit), forward voltage Vf (V), and reverse withstand voltage Vr (V) were measured. The output and Vf were measured with a current flowing through the LED of 20 mA, and Vr was measured with a current flowing through the LED of 10 μA.

In FIG. 2, the result of having measured the output of LED which concerns on Examples 1-6 and Comparative Examples 1-3 is shown. The horizontal axis of the figure is the ammonia ratio. As can be seen from this figure, the LED output does not change much when the ammonia ratio is 25% and 2.5%, but the ammonia ratio is reduced from 2.5% to 1%. Shows a significant increase of more than an order of magnitude. When the ammonia ratio is less than 2.5%, the GaN-based semiconductor layer to which the p-type impurity is added exhibits sufficient p-type conductivity by suppressing hydrogen passivation, and the pn that dramatically improves the light emission efficiency is achieved. It is presumed that the formation of a joint structure has occurred. On the other hand, even if the ammonia ratio is further reduced from 1%, no substantial change in output is observed. Therefore, for the purpose of improving the output of the LED, the ammonia ratio is preferably less than 2.5%, more preferably 1% or less.

  FIG. 3 shows the results of measuring Vf of the LEDs according to Examples 1 to 6 and Comparative Examples 1 to 3. Similar to FIG. 2, the horizontal axis of the figure represents the ratio of ammonia. As can be seen from this figure, Vf does not change much even when the ammonia ratio is decreased from 25% to 2.5%, but starts to decrease when the ammonia ratio falls below 2.5%. Even when the ratio is 1% or less, unlike the case of the output, it tends to decrease as the ratio of ammonia decreases. In FIG. 3, Vf shows the lowest value in Example 5 in which the ammonia ratio is 0.1%, and in Example 6 in which no ammonia was introduced, Vf started to increase. 4V or more. Therefore, for the purpose of lowering the Vf of the LED, it is preferable to make the ammonia ratio smaller than 2.5%. In addition, it is preferable to introduce a small amount of ammonia rather than not introducing ammonia at all.

  FIG. 4 shows the measurement results of Vr of the LEDs according to Examples 1 to 6 and Comparative Examples 1 to 3. Similar to FIGS. 2 and 3, the horizontal axis of the figure represents the ratio of ammonia. As can be seen from this figure, Vr also does not change much when the ammonia ratio is decreased from 25% to 2.5%, but decreases when the ratio falls below 2.5%. Begins, and the value decreases as the ammonia ratio decreases. Vr is maintained at a value of about 25 V even in Example 5 in which the ammonia ratio is lowered to 0.1%, but is reduced to about 5 V in the LED according to Example 6 that does not flow ammonia at all. Therefore, from the viewpoint of Vr, it is preferable to introduce a small amount of ammonia rather than not introducing ammonia at all. However, ammonia may not be introduced at all for the purpose of causing no problem even if Vr is low.

On the other hand, for the LEDs according to Comparative Examples 4 to 7, the following results were obtained.
First, regarding the output, a tendency similar to Comparative Examples 1 to 3 was observed, Comparative Example 4 in which the ammonia ratio was 25%, Comparative Example 5 in which the ammonia ratio was 4%, and the ammonia ratio was 2.5. %, There was almost no change in the output among the LEDs according to each of Comparative Examples 6 and the values thereof were similar to those of the LEDs according to Comparative Examples 1 to 3. On the other hand, the output of the LED according to Comparative Example 7 in which the ammonia ratio was 1% was a value higher by one digit or more than that of the LED according to Comparative Example 3, and was about the same as the LEDs of Examples 1-6. Therefore, regarding the output, Comparative Examples 4 to 7 in which the p-type contact layer was formed of GaN, and Comparative Examples 1 to 3 and Example 4 in which AlGaN was formed had a similar tendency. However, regarding Vf, the Vf of the LEDs according to Comparative Examples 4 to 7 were all about 6.5 V, and no significant change was observed even when the ammonia ratio was decreased from 25% to 1%. . In addition, the Vr of the LEDs according to Comparative Examples 4 to 7 was slightly lower than the LEDs of the examples and other comparative examples that were cooled under the same gas flow rate conditions except that the p-type contact layer was formed of AlGaN. It was.

Here, when Comparative Examples 1 to 3 and Example 1 are compared with Comparative Examples 4 to 7, even when the ammonia ratio is the same, when the semiconductor composition of the p-type contact layer is AlGaN, The Vf of the LED is different from that when the p-type contact layer is made of AlGaN, and the Vf is lower. In addition, as can be seen from Example 1, when the p-type contact layer is formed of AlGaN, when the ammonia ratio is reduced to 1%, the LED V
Although f shows a clear decreasing tendency, such a tendency is not observed when the p-type contact layer is formed of GaN. When the p-type contact layer is made of AlGaN, the elimination of nitrogen atoms on the surface is suppressed, and the effect of suppressing hydrogen passivation becomes obvious, and it is possible that the decrease in Vf appears.

Next, measurement results regarding the LEDs according to Examples 7 to 11 will be described.
FIG. 5 shows the results of measuring the output of the LEDs according to Examples 6-10. The horizontal axis of the figure is the ammonia stop temperature. As can be seen from FIG. 5, the output of the LED does not substantially change even when the ammonia stop temperature is changed between 400 ° C. and 950 ° C. Combined with the results of Examples 1 to 6 described above, the effect of reducing the amount of ammonia introduced into the growth furnace during the temperature lowering process seems to tend to saturate when the amount of ammonia is reduced to some extent.

  FIG. 6 shows the results of measuring Vf of the LEDs according to Examples 6-10. The horizontal axis of the figure is the ammonia stop temperature, as in FIG. As shown in FIG. 6, when the stop temperature of ammonia is raised to a temperature higher than 650 ° C., Vf is lowered. Therefore, for the purpose of lowering the Vf of the LED, it is preferable that the ammonia stop temperature is higher than 650 ° C. Although the details of the cause of the decrease in the LED Vf by increasing the ammonia stop temperature in this way are unclear, the type or state of atomic hydrogen that causes hydrogen passivation is not uniform, Some of them are unstable until the substrate temperature reaches 650 ° C., but stabilize at 650 ° C. or lower. If such atomic hydrogen is present, when the supply of ammonia is stopped at a temperature higher than 650 ° C., this atomic hydrogen escapes out of the crystal, so that hydrogen passivation is suppressed. In the present invention, since the p-type contact layer on the outermost surface of the GaN-based semiconductor layer is formed of AlGaN, desorption of nitrogen atoms is suppressed, so that such an effect of suppressing hydrogen passivation may become apparent. . In Example 6, the introduction of ammonia was stopped immediately after the growth of the p-type AlGaN contact layer 17, but the Vf of the LED according to Example 6 is higher than that of the LEDs according to Examples 8-10. This is considered to be because the adverse effect due to the desorption of nitrogen atoms increases under the condition where ammonia is not supplied at all after the growth of the semiconductor. Therefore, it is preferable to lower the temperature while supplying ammonia until the substrate temperature falls to 950 ° C.

  FIG. 7 shows the results of measuring the Vr of the LEDs according to Examples 7-11. The horizontal axis of the figure is the ammonia stop temperature, as in FIGS. As is clear from FIG. 7, Vr maintains a value of about 24 V to 25 V when the ammonia stop temperature is between 400 ° C. and 800 ° C., but rapidly decreases when the ammonia stop temperature is 800 ° C. or higher. Therefore, for the purpose of preventing the decrease in Vr, the ammonia stop temperature is preferably 800 ° C. or lower.

  Incidentally, as can be seen from FIG. 7, a large decrease in Vr does not occur when ammonia is supplied until the substrate temperature falls to 800 ° C. or lower after the growth of the p-type AlGaN contact layer 17. On the other hand, as shown in FIG. 6, when the ammonia stop temperature is set to 650 ° C. or higher, Vf is lowered. Therefore, if ammonia is stopped when the substrate temperature is 650 ° C. to 800 ° C., Vr is lowered. Vf can be reduced while preventing it.

Further, in order to promote a decrease in Vf while preventing a large decrease in Vr, when the substrate temperature is between 650 ° C. and 800 ° C. with the introduction of ammonia stopped, the temperature decrease rate is slowed down. Also good. Here, slowing the temperature decrease rate includes temporarily suspending the temperature decrease and maintaining it at a constant temperature. Also, due to temperature control factors, the substrate temperature is temporarily increased within a range not exceeding 800 ° C. It can also include warming. As shown in FIG. 6, when ammonia is stopped at a substrate temperature of 650 ° C. or higher, Vf tends to decrease. Therefore, the temperature lowering rate is slowed to allow the time for the substrate temperature to be kept at 650 ° C. or higher. Longer times promote this trend. In addition,
When the temperature lowering rate is changed in this manner, the temperature lowering rate is relatively fast when the substrate temperature is high, so that the time during which the semiconductor layer is exposed to high temperature does not increase, and 650 ° C. to 800 ° C. To the extent, problems due to thermal degradation of semiconductor layers including the InGaN layer and diffusion of Mg added as a p-type impurity to other layers are not so great. Rather, if the temperature drop rate is slowed when the substrate temperature is 650 ° C. to 800 ° C., a substrate made of a material having a different thermal expansion coefficient from that of a GaN-based semiconductor grown on the substrate is used. The strain between the semiconductor layer and the semiconductor layer is alleviated, and the effect of suppressing the generation of cracks and defects is brought about. In particular, as in the above example, when the irregular shape is processed and formed on the surface of the substrate, the area of the interface between the substrate and the GaN-based semiconductor layer is wider than in the case of a flat substrate, More effective. On the other hand, from FIG. 6, after the substrate temperature becomes lower than 650 ° C., even if the introduction of ammonia is stopped, a large decrease in Vf cannot be expected. The temperature lowering rate may be increased when the temperature falls below ℃.

  Since the substrate temperature during the GaN-based semiconductor growth and in the temperature lowering process after the growth is as high as several hundred degrees C., the substrate temperature naturally occurs even if the heating of the substrate is simply stopped. In order to further increase the temperature lowering rate, a cooling circuit may be provided in the susceptor to perform forced cooling. On the other hand, in order to slow down the temperature drop rate of the substrate, a predetermined susceptor heating means such as heater heating or high frequency heating may be operated, or the flow rate of gas introduced into the growth furnace may be reduced or temporarily. Alternatively, the introduction of gas may be stopped. It goes without saying that if the operation for slowing down the temperature drop rate of the substrate is canceled, the temperature drop rate of the substrate is increased again.

[Other embodiments]
(Examples 12 to 14)
Examples 12 to 14 are the same as those in Example 11 except that the flow rates of nitrogen gas and hydrogen gas introduced into the growth furnace as carrier gases when the p-type AlGaN contact layer 17 is grown are as shown in Table 3 below. The same method is used from the growth of the GaN-based semiconductor layer to device fabrication. For the LEDs according to Examples 12 to 14, Vf was measured in the same manner as in Example 11. Table 3 also shows the measurement result of Vf.

As shown in Table 3, when the p-type AlGaN contact layer 17 is grown, the ratio of the flow rate of nitrogen gas and hydrogen gas introduced into the growth furnace as a carrier gas ([flow rate of nitrogen gas] / [flow rate of hydrogen gas] ]) (Hereinafter also referred to as N ₂ / H ₂ ratio) increased, Vf tended to decrease. The lowest value was obtained when no hydrogen was contained in the carrier gas. Therefore, the preferable N ₂ / H ₂ ratio is 1 or more, more preferably 2 or more, and further preferably 3 or more. As can be seen from Table 3, favorable results are obtained even when hydrogen is not used as the carrier gas.

The effect of the N ₂ / H ₂ ratio on the Vf of the LED is speculated, but since hydrogen introduced as a carrier gas during the growth of the p-type layer contributes to hydrogen passivation, this supply amount It is thought that the generation of hydrogen passivation can be suppressed by reducing the amount of hydrogen. In the present embodiment, nitrogen and hydrogen are used as carrier gases during the growth of the p-type AlGaN contact layer 17, but other chemically stable gases can be used instead of nitrogen. “Chemically stable” means that during the growth of the p-type AlGaN contact layer 17, a chemical reaction occurs between a source gas introduced into the growth furnace, another carrier gas, a substrate, and a growing or grown nitride semiconductor. Is not substantially generated. Examples of such a gas include so-called noble gases such as argon, neon, and helium in addition to nitrogen. In addition, a plurality of these gases can be used at the same time. From the viewpoint of reducing the manufacturing cost, it is preferable to use inexpensive nitrogen gas.
As mentioned above, although embodiment of this invention was described using the Example, this invention is not limited to the said Example.

  In the above embodiment, the p-type AlGaN contact layer 17 is grown at a substrate temperature of 1000 ° C., but it may be grown at a higher temperature or at a lower temperature. It is considered that the electrical characteristics improve because the crystallinity of the p-type AlGaN contact layer 17 improves as the temperature grows higher. When grown at a low temperature, it is disadvantageous in terms of crystallinity, but there is an advantage that adverse effects due to deterioration of the InGaN layer and Mg diffusion are suppressed.

  In the above embodiment, ammonia and nitrogen gas are introduced into the growth furnace in the temperature lowering process after the growth of the p-type AlGaN contact layer 17, but all or part of this nitrogen gas is supplied to the GaN-based semiconductor. Other gases that are inert may be substituted. Inert to a GaN-based semiconductor means that it does not substantially affect hydrogen passivation or desorption of nitrogen atoms in or on the surface of the GaN-based semiconductor layer. Examples of such a gas include so-called noble gases such as argon, neon, and helium in addition to nitrogen gas. Hydrogen gas can also be used as an inert gas for GaN-based semiconductors under conditions that do not substantially affect hydrogen passivation and desorption of nitrogen atoms, for example, when the substrate temperature is sufficiently lowered. it can. In the present invention, it is not necessary to make the types of these gases flowing in the temperature lowering process constant, and they may be changed in the middle. In addition, a plurality of these gases can be used at the same time. From the viewpoint of reducing the manufacturing cost, it is preferable to use inexpensive nitrogen gas.

  The method of lowering the temperature of the substrate and the GaN-based semiconductor after the growth of the GaN-based semiconductor is not particularly limited, and it may be simply a natural temperature decrease caused by stopping the heating of the substrate, or by using forced cooling of the susceptor together. May be. On the contrary, if the susceptor heating means specified in the apparatus is operated, the temperature can be lowered at a temperature lowering rate slower than the natural temperature lowering. The case of changing the temperature drop rate is as described above.

Organic metal raw materials, gas raw materials, carrier gas types used for growth of GaN-based semiconductors by the MOVPE method, flow rates of raw materials and carrier gases introduced into the growth furnace during growth, substrate temperature during growth, growth time, these programs, For the adjustment method and the like, a conventionally known method may be referred to.
The present invention is characterized in that a p-type AlGaN contact layer, which is the uppermost layer, is grown by the MOVPE method when forming a laminated structure of a GaN-based semiconductor on a substrate. The method is not particularly limited, and conventionally known methods such as a hydride vapor phase epitaxy (HVPE) method and a molecular beam evaporation (MBE) method can be appropriately used in addition to the MOVPE method. From the viewpoint of manufacturing efficiency, it is preferable that the growth of the GaN-based semiconductor layer stacked on the substrate is performed consistently in one growth furnace by the MOVPE method up to the uppermost p-type contact layer.

About the structure of LED which concerns on implementation of this invention, it is not limited to the structure of FIG.
A structure obtained by omitting the structure shown in FIG. 1 or an additional structure added to the structure shown in FIG. 1 may be used. For the crystal composition of each GaN-based semiconductor layer constituting the LED structure, the design of dopant and its concentration, thickness, etc., the electrode material, shape, formation method, element isolation method, etc., refer to conventionally known techniques. It's okay.

  The present invention is useful as a method for manufacturing not only LEDs but also all GaN-based semiconductor elements having a p-type GaN-based semiconductor (light-emitting elements other than LEDs, light-receiving elements, electronic devices, etc.). In that case, refer to the well-known technology for the structure of the device and the technology required for its manufacture (eg, GaN-based semiconductor multilayer structure formation technology, patterning technology, electrode material technology, device isolation technology). Good.

DESCRIPTION OF SYMBOLS 11 Sapphire substrate 12 Undoped GaN foundation layer 13 n-type GaN contact layer 14 Active layer 15 p-type AlGaN cladding layer 16 p-type GaN high carrier concentration layer 17 p-type AlGaN contact layer 21 n-side electrode 22 p-side electrode

Claims (33)

Including a step of forming a laminated structure of a GaN-based semiconductor on a substrate,
(A) A raw material and a carrier gas are introduced into a growth furnace in which the substrate is installed, and a p-type contact layer made of Al _a Ga _1-a N (0 <a ≦ 1) is formed by the MOVPE method. Growing as the top layer,
(B) After completion of the step (A), ammonia and a first gas made of a gas inert to the GaN-based semiconductor are all introduced into the growth furnace. A step of lowering the temperature of the p-type contact layer while introducing a ratio f of the flow rate of ammonia in the flow rate such that 0 <f <0.025;
A method for manufacturing a GaN-based semiconductor device, comprising:   The manufacturing method according to claim 1, wherein the ratio f is 0.001 ≦ f ≦ 0.01. Forming the laminated structure of the GaN-based semiconductor on a substrate;
(C) After the step (B), the temperature of the p-type contact layer is lowered while introducing a second gas that is inert to the GaN-based semiconductor and does not contain ammonia into the growth furnace. Process to perform,
The manufacturing method of Claim 1 or 2 containing.   The manufacturing method according to claim 3, wherein switching from the step (B) to the step (C) is performed when the substrate temperature t is t ≦ 950 ° C. 5.   The manufacturing method according to claim 4, wherein switching from the step (B) to the step (C) is performed when the substrate temperature t is t ≦ 800 ° C. 6.   The manufacturing method according to claim 3, wherein the switching from the step (B) to the step (C) is performed when the substrate temperature t is t> 650 ° C. 6.   The manufacturing method according to claim 6, wherein, in the step (C), when the substrate temperature t is 650 ° C. <t ≦ 800 ° C., the temperature decreasing rate of the p-type contact layer is changed slowly.   The manufacturing method according to claim 7, wherein the method of slowly changing the temperature decrease rate of the p-type contact layer includes operating a susceptor heating unit.   9. The manufacturing according to claim 1, wherein, in the step (B) or (C), when the substrate temperature t is t ≦ 650 ° C., the temperature decreasing rate of the p-type contact layer is changed rapidly. Method.   The production method according to claim 1, wherein 0.01 ≦ a ≦ 0.2.   The manufacturing method according to any one of claims 1 to 10, wherein the first gas and the second gas include one or more kinds of gases selected from nitrogen gas and rare gases.   The manufacturing method in any one of Claims 1-11 whose thickness of the said p-type contact layer is 1 nm-50 nm. The manufacturing method according to claim 1, wherein Mg is added to the p-type contact layer at a concentration of 1 × 10 ¹⁹ cm ⁻³ to 1 × 10 ²¹ cm ⁻³ . The GaN-based semiconductor element includes a layer made of p-type GaN having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁸ cm ⁻³ adjacent to the p-type contact layer. The manufacturing method in any one.   The step of forming a laminated structure of the GaN-based semiconductor on the substrate includes a step of growing a layer made of undoped GaN on the substrate before the step (A). The manufacturing method of crab.   The manufacturing method according to any one of claims 1 to 15, wherein the substrate is a substrate having a concavo-convex shape formed on a surface thereof.   In the step (A), the carrier gas introduced into the growth furnace includes a first carrier gas made of a chemically stable gas and hydrogen gas, and the flow rate of the first carrier gas is hydrogen. The manufacturing method in any one of Claims 1-16 which is the same or larger than the flow volume of gas.   The manufacturing method according to claim 17, wherein the first carrier gas includes one or more kinds of gases selected from nitrogen gas and rare gases.   The manufacturing method in any one of Claims 1-16 in which the carrier gas introduce | transduced in the said growth furnace does not contain hydrogen gas in the process of (A). Including a step of forming a laminated structure of a GaN-based semiconductor on a substrate,
(D) A raw material and a carrier gas are supplied into a growth furnace in which the substrate is installed, and a p-type contact layer made of Al _b Ga _1-b N (0 <b ≦ 1) is formed by the MOVPE method. Growing as the top layer,
(E) After the completion of the step (D), the temperature of the p-type contact layer is lowered while introducing a third gas that is inert to the GaN-based semiconductor and does not contain ammonia into the growth furnace. A third temperature lowering step for performing
A method for manufacturing a GaN-based semiconductor device, comprising:   21. The manufacturing method according to claim 20, wherein, in the step (E), when the substrate temperature t is 650 ° C. <t ≦ 800 ° C., the temperature decreasing rate of the p-type contact layer is changed slowly.   The manufacturing method according to claim 21, wherein the method of slowly changing the temperature decrease rate of the p-type contact layer includes operating a susceptor heating unit.   23. The manufacturing method according to claim 20, wherein in the step (E), when the substrate temperature t is t ≦ 650 ° C., the temperature decreasing rate of the p-type contact layer is changed rapidly.   The manufacturing method in any one of Claims 20-23 which is 0.01 <= b <= 0.2.   The manufacturing method according to any one of claims 20 to 24, wherein the third gas includes one or more kinds of gases selected from nitrogen gas and rare gases.   The manufacturing method according to any one of claims 20 to 25, wherein a thickness of the p-type contact layer is 1 nm to 50 nm. 27. The manufacturing method according to any one of claims 20 to 26, wherein Mg is added to the p-type contact layer at a concentration of 1 × 10 ¹⁹ cm ⁻³ to 1 × 10 ²¹ cm ⁻³ . The GaN-based semiconductor element includes a layer made of p-type GaN having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁸ cm ⁻³ adjacent to the p-type contact layer. The manufacturing method in any one.   The step of forming the laminated structure of the GaN-based semiconductor on the substrate includes a step of further growing a layer made of undoped GaN on the substrate before the step (D). The manufacturing method of crab.   The manufacturing method according to any one of claims 20 to 29, wherein the substrate is a substrate having a concavo-convex shape formed on a surface thereof.   In the step (D), the carrier gas introduced into the growth furnace includes a second carrier gas made of a chemically stable gas and hydrogen gas, and the flow rate of the second carrier gas is hydrogen. The manufacturing method according to any one of claims 20 to 30, wherein the flow rate is the same as or larger than a flow rate of the gas.   32. The manufacturing method according to claim 31, wherein the second carrier gas contains one or more kinds of gases selected from nitrogen gas and rare gases.   The manufacturing method according to any one of claims 20 to 30, wherein the carrier gas introduced into the growth furnace in the step (D) does not contain hydrogen gas.

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