NITRIDE SEMICONDUCTOR WAFER AND MANUFACTURING METHOD THEREOF
20170141259 ยท 2017-05-18
Assignee
Inventors
Cpc classification
H10H20/8215
ELECTRICITY
H10H20/01335
ELECTRICITY
International classification
H01L33/00
ELECTRICITY
H01L33/06
ELECTRICITY
Abstract
Provided is a nitride semiconductor wafer in which, above a nitride semiconductor template having a nitride semiconductor layer as a top layer thereof, a light emitting layer having a multiple quantum well structure that is formed by a regrown nitride semiconductor and a p-type nitride semiconductor layer are stacked. Here, when the light emitting layer having a multiple quantum well structure includes a plurality of well layers and one of the well layers that is the closest to the p-type nitride semiconductor layer is referred to as a top well layer, a distance t from a regrowth interface of the nitride semiconductor layer of the nitride semiconductor template to the top well layer is 1 m or less, and the top well layer has an oxygen concentration of 5.010.sup.16 cm.sup.3 or less.
Claims
1. A nitride semiconductor wafer in which, above a nitride semiconductor template having a nitride semiconductor layer as a top layer thereof, a light emitting layer having a multiple quantum well structure that is formed by a regrown nitride semiconductor and a p-type nitride semiconductor layer are stacked, wherein when the light emitting layer having a multiple quantum well structure includes a plurality of well layers and one of the well layers that is the closest to the p-type nitride semiconductor layer is referred to as a top well layer, a distance t from a regrowth interface of the nitride semiconductor layer of the nitride semiconductor template to the top well layer is 1 m or less, and the top well layer has an oxygen concentration of 5.010.sup.16 cm.sup.3 or less.
2. The nitride semiconductor wafer as set forth in claim 1, wherein the distance t is 500 m or less.
3. The nitride semiconductor wafer as set forth in claim 1, further comprising an n-type nitride semiconductor layer between the nitride semiconductor layer and the light emitting layer having a multiple quantum well structure.
4. The nitride semiconductor wafer as set forth in claim 1, wherein the light emitting layer having a multiple quantum well structure is positioned immediately above the nitride semiconductor layer.
5. A method of manufacturing a nitride semiconductor wafer in which, above a nitride semiconductor template having a nitride semiconductor layer as a top layer thereof, a light emitting layer having a multiple quantum well structure that is formed by a regrown nitride semiconductor and a p-type nitride semiconductor layer are stacked, the method comprising above the nitride semiconductor layer of the nitride semiconductor template, regrowing in order the light emitting layer having a multiple quantum well structure and the p-type nitride semiconductor layer, wherein when the light emitting layer having a multiple quantum well structure includes a plurality of well layers and one of the well layers that is the closest to the p-type nitride semiconductor layer is referred to as a top well layer, the regrowing is performed in such a manner that a distance t [nm] from a regrowth interface of the nitride semiconductor layer of the nitride semiconductor template to the top well layer and a maximum value of a growth temperature T.sub.MAX [ C.] for the regrowing satisfy a relation expressed by t3.68210.sup.6 exp{E.sub.a/k(T.sub.MAX+273)} and the distance t is 1 m or less, where E.sub.a is set to 0.915 [eV] and k denotes the Boltzmann's constant.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0037]
[0038]
EXEMPLARY EMBODIMENTS OF THE INVENTION
One Embodiment of the Invention as Set Forth Herein
[0039] The following describes one embodiment of the invention as set forth herein.
[0040] (1) Nitride Semiconductor Wafer
[0041] To start with, a nitride semiconductor wafer relating to one embodiment is described with reference to
[0042] A nitride semiconductor wafer 1 relating to the present embodiment is formed using a nitride semiconductor template 10 having a substrate 11 and a nitride semiconductor layer 12 grown on the substrate 11, and more specifically, manufactured by regrowing a light emitting section 20 on the nitride semiconductor layer 12. In other words, the nitride semiconductor layer 12 and the light emitting section 20 are not formed using the continuous growth technique but formed separately by growing the nitride semiconductor layer 12 and subsequently regrowing the light emitting section 20.
[0043] In the nitride semiconductor wafer 1 relating to the present embodiment, as shown in
[0044] The template 10 is manufactured by growing a nitride semiconductor on the substrate 11 and structured in such a manner that the substrate 11 and the nitride semiconductor layer 12 are stacked.
[0045] The substrate 11 is not particularly limited as long as it can be formed by growing the nitride semiconductor layer 12 on the surface thereof. The substrate 11 can be, for example, a sapphire substrate, a ZnO substrate, a SiC substate, a Si substrate, a GaAs substrate, a GaN substrate, a AlN substrate, a AlGaN substrate or the like. From among these, a sapphire substrate is preferable. More specifically, a patterned sapphire substrate (PSS) that is obtained by forming projections and depressions on the surface of a sapphire substrate is preferably used for LEDs.
[0046] The nitride semiconductor layer 12 is formed on the substrate 11 and has a regrowth interface 12a on which the light emitting section 20 is regrown. The nitride semiconductor layer 12 is made of, for example, gallium nitride (GaN), aluminum nitride (AlN), aluminum gallium nitride (AlGaN), indium aluminum gallium nitride (InAlGaN) or the like. In addition, a buffer layer may be provided between the substrate 11 and the nitride semiconductor layer 12. The buffer layer is, for example, a GaN or AlN layer grown at low temperature, an AlN layer grown at high temperature, or the like. The nitride semiconductor layer 12 may contain n-type impurities such as silicon (Si) and germanium (Ge), or may be a n-type semiconductor layer. The amount of the n-type impurities contained is selected as appropriate in accordance with how the template is used or depending on other factors.
[0047] The thickness of the nitride semiconductor layer 12 is not particularly limited and can be, for example, no less than 2 m and no more than 50 m. The nitride semiconductor layer 12 achieves improved crystallinity due to having a predetermined thickness and contributes to improve the crystallinity of the light emitting section 20 to be regrown on the regrowth interface 12a. The technique used to grow the nitride semiconductor layer 12 is not particularly limited. The HVPE technique, which exhibits a high growth rate, is preferable but the MOVPE technique or the like can be also used. As described above, the regrowth interface 12a is oxidized when the template 10 is exposed to the air and has an oxide film (not shown) foil led thereon.
[0048] The light emitting section 20 is formed by regrowth on the regrowth interface 12a of the nitride semiconductor layer 12. In the present embodiment, as the light emitting section 20, the n-type nitride semiconductor layer 21 made of a nitride semiconductor, the light emitting layer 22 having a multiple quantum well structure and the p-type nitride semiconductor layer 23 are regrown in the stated order. The light emitting section 20 is grown using MOVPE, which can form a thin semiconductor layer of several nanometers under great controllability and can achieve excellent crystallinity.
[0049] The n-type nitride semiconductor layer 21 is formed on the regrowth interface 12a of the nitride semiconductor layer 12. As the n-type nitride semiconductor layer 21, an n-type GaN layer is grown, for example. The n-type nitride semiconductor layer 21 contains a predetermined concentration of predetermined n-type impurities. The n-type impurities can be, for example, silicon (Si), selenium (Se), tellurium (Te) and the like. The thickness of the n-type nitride semiconductor layer 21 is not particularly limited and can be, for example, no less than 0 m and no more than 1 m.
[0050] The light emitting layer 22 having a multiple quantum well structure has a laminate structure in which well layers 24 and barrier layers 25 are alternately grown on the n-type nitride semiconductor layer 21. In the laminate structure, one of the well layers 24 that is the closest to the p-type nitride semiconductor layer 23 is referred to as a top well layer 24. The well layers 24 are, for example, InGaN layers and the barrier layers 25 are, for example, GaN layers. The thickness of each of the well layers 24 constituting the light emitting layer 22 can be, for example, no less than 1 nm and no more than 5 nm, and the thickness of each of the barrier layers 25 can be, for example, no less than 5 nm and no more than 30 nm. A plurality of pairs of the well layer 24 and the barrier layer 25 are formed to achieve desired light emission.
[0051] The p-type nitride semiconductor layer 23 is formed on the light emitting layer 22 having a multiple quantum well structure and above the top well layer 24 of the light emitting layer 22 having a multiple quantum well structure. The p-type nitride semiconductor layer 23 is, for example, a p-type AlGaN layer or p-type GaN layer. As the p-type nitride semiconductor layer 23, a p-type AlGaN layer and a p-type GaN layer may be grown in the stated order on the regrowth interface 12a, for example. The p-type nitride semiconductor layer 23 contains a predetermined concentration of predetermined p-type impurities. The p-type impurities can be, for example, magnesium (Mg), zinc (Zn), carbon (C) or the like. The thickness of the p-type nitride semiconductor layer 23 is not particularly limited and can be, for example, no less than 200 nm and no more than 1000 nm.
[0052] In the nitride semiconductor wafer 1 relating to the present embodiment, by regrowing a nitride semiconductor on the regrowth interface 12a of the nitride semiconductor layer 12, the n-type nitride semiconductor layer 21, the light emitting layer 22 having a multiple quantum well structure and the p-type nitride semiconductor layer 23 are formed, as the light emitting section 20. The distance t from the regrowth interface 12a of the nitride semiconductor layer 12 to the top well layer 24 of the light emitting layer 22 having a multiple quantum well structure is 1 m or less. In other words, the sum of the thickness t.sub.1 of the n-type nitride semiconductor layer 21 and the thickness t.sub.2 of the light emitting layer 22 excluding the top well layer 24 is equal to 1 m or less. Preferably, the distance t is 500 nm or less, more preferably no less than 200 nm and no more than 500 nm. This can shorten the time required to grow the light emitting section 20 and improve the productivity of the manufacturing process of the nitride semiconductor wafer 1.
[0053] The top well layer 24 of the light emitting layer 22 having a multiple quantum well structure has an oxygen concentration of 5.010.sup.6 cm.sup.3 or less, which indicates that the amount of the oxygen introduced by the diffusion is reduced. For this reason, in the top well layer 24, the degradation of the crystallinity is reduced, and the drop in the light emission characteristics is reduced.
[0054] Here, the oxygen concentration is measured in the thickness direction of the top well layer 24 using, for example, secondary ion mass spectrometry (SIMS).
[0055] In the present embodiment, the thickness t.sub.1 of the n-type nitride semiconductor layer 21 and the thickness t.sub.2 of the light emitting layer 22 excluding the top well layer 24 are not particularly limited and the thicknesses t.sub.1 and t.sub.2 can be changed as appropriate provided their sum is 1 m or less.
[0056] (2) Method of Manufacturing Nitride Semiconductor Wafer
[0057] The following describes a method of manufacturing the above-described nitride semiconductor wafer 1. In the present embodiment, the template 10 is formed and the template 10 is then used to manufacture the nitride semiconductor wafer 1.
[0058] <Preparation of Substrate 11>
[0059] To start with, the substrate 11, for example a sapphire substrate is prepared.
[0060] <Growth of Nitride Semiconductor Layer 12>
[0061] Following this, the substrate 11, for example, the sapphire substrate is loaded into a HVPE apparatus. In the HVPE apparatus, a predetermined source gas is fed onto the substrate 11 or sapphire substrate to grow a GaN layer having a predetermined thickness (for example, no less than 2 m and no more than 50 m) as the nitride semiconductor layer 12. In this way, the template 10 is obtained.
[0062] <Transport of Template 10>
[0063] Subsequently, the template 10 is transported from the HVPE apparatus to a MOVPE apparatus. Alternatively, the template 10 may be stored for a predetermined period of time and then transported from the HVPE apparatus to a MOVPE apparatus. Since the template 10 is exposed to the air during the transport, the GaN layer of the nitride semiconductor layer 12 is oxidized and an oxide film is formed on the regrowth interface 12a of the nitride semiconductor layer 12.
[0064] <Regrowing Step of Light Emitting Section 20>
[0065] After this, in the MOVPE apparatus, a regrowing step is performed to regrow the light emitting section 20 on the nitride semiconductor layer 12. During the regrowing step, the regrowth is controlled in such a manner that the distance t [nm] from the regrowth interface 12a of the nitride semiconductor layer 12 to the top well layer 24 and the maximum value of the growth temperature T.sub.MAX [ C.] for the regrowth satisfy the following Expression (1) and the distance t can be 1 m or less.
tt.sub.min=3.68210.sup.6exp{E.sub.a/k(T.sub.MAX+273)}(1)
[0066] In Expression (1), E.sub.a is set to 0.915 [eV] and k denotes the Boltzmann's constant.
[0067] Specifically speaking, for the regrowing step, the conditions for growing the light emitting section 20 are determined based on Expression (1) and the light emitting section 20 is regrown based on the determined regrowth conditions. The following describes Expression (1) used to determine the growth conditions, how to determine the growth conditions based on Expression (1) and the regrowth of the light emitting section 20 based on the growth conditions.
[0068] (Expression (1))
[0069] Expression (1) is set up based on the Arrhenius plot between the minimum distance t.sub.min that does not cause the drop in the light emission characteristics of the light emitting element and the maximum value of the growth temperature T.sub.MAX, which are obtained through experiments (working examples described later).
[0070] In Expression (1), the distance t denotes the growth thickness from the regrowth interface 12a of the nitride semiconductor layer 12 to the top well layer 24 of the light emitting layer 22. In other words, the distance t denotes the thickness of the grown film that is actually grown on the regrowth interface 12a until the top well layer 24 is formed (the growth thickness). As shown in
[0071] In Expression (1), the distance t.sub.1, denotes the minimum distance that does not cause the drop in the light emission characteristics of the light emitting element and is equivalent to the theoretical value of the diffusion distance of the oxygen at a predetermined temperature. The minimum distance t.sub.min can be obtained based on the Arrhenius plot against the maximum value of the growth temperature T.sub.MAX as described above. In other words, as indicated in Expression (1), the minimum distance t.sub.min is a function of the maximum value of the growth temperature T.sub.MAX and can be calculated from the maximum value of the growth temperature T.sub.MAX.
[0072] In Expression (1), the maximum value of the growth temperature t.sub.MAX denotes the highest one of the growth temperatures at which the respective layers of the light emitting section 20 are grown. The growth temperatures for the respective layers of the light emitting section 20 range as follows, for example. The growth temperature for the n-type nitride semiconductor layer 21 is no less than 800 C. and no more than 1000 C., the growth temperature for the light emitting layer 22 is no less than 600 C. and no more than 900 C., and the growth temperature for the p-type nitride semiconductor layer 23 is no less than 700 C. and no more than 1000 C. Therefore, the maximum value of the growth temperature T.sub.MAX is at least 800 C. On the other hand, the maximum value of the growth temperature T.sub.MAX is at most 1000 C. If the maximum value of the growth temperature T.sub.MAX is higher than 1000 C., the diffusion of the oxygen is further encouraged and the distance t.sub.min exceeds 1 m. Therefore, when the maximum value of the growth temperature T.sub.MAX is higher than 1000 C., it is difficult to achieve a distance t of 1 m or less.
[0073] (How to Determine Growth Conditions)
[0074] Based on the above-described Expression (1), the conditions under which the light emitting section 20 is regrown are determined. In order to determine the growth conditions, the maximum value of the growth temperature T.sub.MAX for the regrowth is first determined. Subsequently, the distance t.sub.min corresponding to the determined maximum value of the growth temperature T.sub.MAX is calculated based on Expression (1). The calculated distance t.sub.min is used to determine the distance t.
[0075] Specifically speaking, the maximum value of the growth temperature T.sub.MAX is first determined. The maximum value of the growth temperature T.sub.MAX is determined by the growth temperatures for the respective layers of the light emitting section 20. The light emitting section 20 is constituted by the n-type nitride semiconductor layer 21, the light emitting layer 22 and the p-type nitride semiconductor layer 23, and the growth temperatures for the respective layers are selected as appropriate within the predetermined range of temperatures. From among the growth temperatures for the respective layers, the maximum temperature is treated as the maximum value of the growth temperature T.sub.MAX.
[0076] Subsequently, the distance t.sub.min is obtained in accordance with the determined maximum value of the growth temperature T.sub.MAX. The distance t.sub.min is calculated by substituting the determined maximum value of the growth temperature T.sub.MAX into Expression (1). As mentioned above, the distance t.sub.min is equivalent to the theoretical value of the diffusion distance of the oxygen at a predetermined temperature and indicates the minimum distance that does not cause the drop in the light emission characteristics of the light emitting element.
[0077] Subsequently, the obtained distance t.sub.min is used to determine the distance t. The distance t denotes the growth thickness of the films that are actually grown on the regrowth interface 12a up to the top well layer 24, as described above. In the case shown in
[0078] For example, the growth conditions are determined as follows. When the respective layers of the light emitting section 20 are regrown with the growth temperature of the n-type nitride semiconductor layer 21 set to 890 C., the growth temperature of the light emitting layer 22 set to 700 C. and the growth temperature of the p-type nitride semiconductor layer 23 set to 800 C., the maximum value of the growth temperature T.sub.MAX is 890 C. Based on Expression (1), the distance t.sub.min for this maximum value of the growth temperature T.sub.MAX (890 C.) is calculated as 350 nm. Based on the calculated distance t.sub.min (350 nm), the distance t is determined to be equal to or longer than 350 nm. Since the distance t is equal to the sum of the thickness t.sub.1 of the n-type nitride semiconductor layer 21 and the thickness t.sub.2 of the light emitting layer 22 excluding the top well layer 24, the thicknesses t.sub.1 and t.sub.2 are respectively determined so that their sum (t.sub.1 +t.sub.2) is 350 nm or more. The thicknesses t.sub.1 and t.sub.2 are not particularly limited. For example, the thickness t.sub.1 can be 200 nm and the thickness t.sub.2 can be 150 nm. Since the thicknesses t.sub.1 and t.sub.2 can be respectively changed as appropriate so that their sum is equal to or larger than 350 nm, the thickness t.sub.1 can be 50 nm and the thickness t.sub.2 can be 300 nm.
[0079] (Regrowth of Light Emitting Section 20)
[0080] Subsequently, in the MOVPE apparatus, the light emitting section 20 is regrown under the growth conditions determined in the above-described manner. The light emitting section 20 is regrown at a growth temperature that does not exceed the maximum value of the growth temperature T.sub.MAX determined as one of the growth conditions (for example, 890 C.).
[0081] A predetermined source gas is fed onto the regrowth interface 12a of the nitride semiconductor layer 12 to grow a n-type GaN layer having the thickness t.sub.1 (for example, 200 nm) as the n-type nitride semiconductor layer 21. During the growth of this layer, the oxygen contained in the oxide film diffuses and enter the n-type nitride semiconductor layer 21.
[0082] Following this, a predetermined source gas is fed onto the n-type nitride semiconductor layer 21 to alternately grow InGaN layers as the well layers 24 and GaN layers as the barrier layers 25. As a result, the light emitting layer 22 having a multiple quantum well structure and a predetermined thickness is formed. During the growth of the light emitting layer 22, the top well layer 24 starts to be grown once the sum of the thickness t.sub.1 of the n-type nitride semiconductor layer 21 (for example, 200 nm) and the thickness t.sub.2 of the light emitting layer 22 excluding the top well layer 24(for example, 150 nm) reaches the distance t.sub.min (for example, 350 nm) or more. In other words, the top well layer 24 is foiled above the regrowth interface 12a with the n-type nitride semiconductor layer 21 and the light emitting layer 22 placed therebetween and positioned away from the regrowth interface 12a by the distance t (the thickness t.sub.1 +the thickness t.sub.2).
[0083] During the regrowth of the light emitting layer 22, the oxygen contained in the oxide film on the template diffuses, and the oxygen that has diffused and entered the n-type nitride semiconductor layer 21 further diffuses and enters part of the light emitting layer 22. According to the present embodiment, however, the top well layer 24 is positioned away from the regrowth interface 12a by the distance t.sub.min (the theoretical value of the diffusion distance of the oxygen at a predetermined temperature) or more, and the oxygen can be prevented from entering the top well layer 24 as a result of the diffusion during the regrowing step.
[0084] Subsequently, a predetermined source gas is fed onto the top well layer 24 of the light emitting layer 22 to grow and form a p-type GaN layer as the p-type nitride semiconductor layer 23. Although the oxygen may diffuse during the regrowth of the p-type nitride semiconductor layer 23, the oxygen is prevented from diffusing into the top well layer 24 since the distance t is equal to or more than the distance t.sub.min. As a result, the top well layer 24 exhibits an oxygen concentration of 5.010.sup.16 cm.sup.3 or less.
[0085] <Unloading of Nitride Semiconductor Wafer 1>
[0086] After the regrowing step, the nitride semiconductor wafer 1 is unloaded out of the MOVPE apparatus and the nitride semiconductor wafer 1 of the present embodiment can be obtained.
Effects Produced by the Present Embodiment
[0087] The present embodiment produces the following one or more effects.
[0088] According to the present embodiment, in the nitride semiconductor wafer, the distance t from the regrowth interface to the top well layer is 1 m or less, and the top well layer exhibits an oxygen concentration of 5.010.sup.16 cm.sup.3 or less. Thus, the growth thickness is small and the productivity is high. The top well layer, which greatly influences the light emission characteristics, exhibits a low oxygen concentration. This means that the drop in the light emission characteristics caused by the entrance of the oxygen into the top well layer is prevented.
[0089] According to the present embodiment, the light emitting section is regrown in such a manner that the distance t from the regrowth interface to the top well layer and the maximum value of the growth temperature T.sub.MAX for the regrowth satisfy a predetermined relation and that the distance t is 1 m or less. As a result, when the light emitting section is regrown on the template, the oxygen can be prevented from diffusing into the top well layer, which greatly influences the light emission characteristics. In addition, since the growth temperature can determine the minimum distance (the growth thickness) that does not cause the drop in the light emission characteristics, the regrowing step is performed according to the thus determined growth thickness, which can resultantly reduce the growth thickness and improve the productivity.
Other Embodiments
[0090] One embodiment of the invention as set forth herein has been specifically described. The invention as set forth herein, however, is not limited to the above-described embodiment, which can be modified in various manners without departing from the principle of the invention as set forth herein.
[0091] According to the above-described embodiment, the nitride semiconductor wafer further includes the n-type nitride semiconductor layer between the nitride semiconductor layer and the multiquantum well layer. The present invention, however, is not limited to such. According to the present invention, the light emitting layer may be provided immediately above the nitride semiconductor layer of the template without the n-type nitride semiconductor layer. In other words, the thickness t.sub.1 of the n-type nitride semiconductor layer may be set to 0 and only the light emitting layer may be formed. In this case, the thickness t.sub.2 of the light emitting layer excluding the top well layer is set to be equal to or larger than the distance t.sub.min.
[0092] According to the above-described embodiment, the fabrication of the template by performing a growing step using HVPE is followed by a regrowing step using MOVPE in the manufacturing process of the the nitride semiconductor wafer. The present invention, however, is not limited to such. According to the present invention, the drop in the light emission characteristics caused by the diffusion of the oxygen can be prevented even if, for example, MOVPE is used to fabricate the template, the template is then unloaded, and MOVPE is again used to manufacture the nitride semiconductor wafer.
[0093] (Working Examples)
[0094] The following describes the working examples of the invention as set forth herein. The following working examples are shown as examples of the nitride semiconductor wafer relating to the present invention. The present invention is not limited by the following working examples.
[0095] According to one working example, a nitride semiconductor wafer was manufactured and used to fabricate an LED element. Specifically speaking, on a sapphire substrate having a thickness of 650 m and a diameter of 100 mm, an aluminum nitride (AlN) layer of 150 nm was grown at high temperature as a buffer layer using HYPE. After this, an n-type gallium nitride (GaN) layer of 8 m was grown as a nitride semiconductor layer, which was to serve as a template layer. In this way, a template was fabricated. On the template, as a light emitting section, an n-type GaN layer (having a thickness t.sub.1), an InGaN/GaN light emitting layer having a multiple quantum well structure (having a thickness of 78 nm), and a p-type nitride semiconductor layer (having a thickness of 300 nm) constituted by a p-type AlGaN layer and a p-type GaN contact layer were regrown using MOVPE. In this manner, a nitride semiconductor wafer was manufactured.
[0096] According to first to fifth working examples and first and second comparative examples, nitride semiconductor wafers were manufactured in such a manner that the maximum value of the growth temperature T.sub.MAX was set at various values for the regrowth of the light emitting section and the thickness t.sub.1 was set at various values when the regrowth was performed at each of the values of the maximum value of the growth temperature T.sub.MAX. On the manufactured nitride semiconductor wafers, electrodes were formed and other treatments were performed to fabricate LED elements, and the light emitted by the LED elements when applied with 20 mA was measured. In order to evaluate the light emitted from these LED elements, the ratio of the light emitted from each of the LED elements of the first to fifth working examples and the first and second comparative examples when 20 mA was applied to the light emitted from the LED element having the same structure but manufactured using the continuous growth technique when 20 mA was applied was calculated. In addition, the minimum distance t.sub.min was determined that can result in a ratio of approximately 50% or does not cause the drop in the light emission characteristics of the LED elements.
[0097] In the first working example, T.sub.MAX=820 C. and t.sub.min=240 nm. In the second working example, T.sub.MAX=890 C. and t.sub.min=350 nm. In the third working example, T.sub.MAX=950 C. and t.sub.min=500 nm. In the fourth working example, T.sub.MAX=980 C. and t.sub.min=800 nm. In the fifth working example, T.sub.MAX=1020 C. and t.sub.MAX=1000 nm. In the first comparative example, T.sub.MAX=1050 C. and t.sub.min=1400 nm. In the second comparative example, T.sub.MAX=1120 C. and t.sub.min=2000 nm.
[0098]
[0099] While the embodiments of the present invention have been described, the technical scope of the invention is not limited to the above described embodiments. It is apparent to persons skilled in the art that various alterations and improvements can be added to the above-described embodiments. It is also apparent from the scope of the claims that the embodiments added with such alterations or improvements can be included in the technical scope of the invention.
[0100] The operations, procedures, steps, and stages of each process performed by an apparatus, system, program, and method shown in the claims, embodiments, or diagrams can be performed in any order as long as the order is not indicated by prior to, before, or the like and as long as the output from a previous process is not used in a later process. Even if the process flow is described using phrases such as first or next in the claims, embodiments, or diagrams, it does not necessarily mean that the process must be performed in this order.
DESCRIPTION OF REFERENCE NUMERALS
[0101] 1 . . . nitride semiconductor wafer [0102] 10 . . . template [0103] 11 . . . substrate [0104] 12 . . . nitride semiconductor layer [0105] 20 . . . light emitting section [0106] 21 . . . n-type nitride semiconductor layer [0107] 22 . . . light emitting layer [0108] 23 . . . p-type nitride semiconductor layer [0109] 24 . . . well layer [0110] 24 . . . top well layer