JP2012009784A - Semiconductor element and method of reducing dislocation of semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a dislocation density of a semiconductor element having a laminated structure of a group III nitride-based semiconductor, which can be used as a light-emitting diode, etc., to improve the crystallinity.SOLUTION: A semiconductor element is constituted of a base layer composed of a first group III nitride semiconductor and a functional layer which is composed of a second group III nitride semiconductor having a composition of AlGaInN (0≤X≤1, 0≤Y≤1, 0<Z≤1, X+Y+Z=1), and exhibits a periodic superlattice structure.

Description

  The present invention relates to a semiconductor element having a laminated structure of a group III nitride semiconductor that can be used as a light emitting element (light emitting diode).

  Light-emitting diodes are rapidly expanding in various fields such as backlights for liquid crystal displays, mobile phones, information terminals, and indoor / outdoor advertisements. In addition, light emitting diodes have long life and high reliability, and have features such as low power consumption, impact resistance, high purity display color, lightness, thinness, and so on. Application is also being attempted.

  Currently, Group III nitride semiconductors such as GaN and AlGaInN having a relatively low AlN molar fraction are used for light emitting diodes, particularly light emitting diodes that emit light in the green to blue region. For example, in Patent Document 1, after forming a buffer layer on a sapphire substrate, an n-type GaN layer, an AlGaN active layer, and a p-type GaN layer are sequentially formed on the buffer layer to produce a light emitting diode. It was. However, when the light emitting diode is manufactured by such a method, there is a problem that sufficient device characteristics cannot be exhibited.

  This is because, for example, misfit dislocations generated at the interface between the sapphire substrate and the n-type GaN layer propagate through the n-type GaN layer and reach the surface thereof. This is because the dislocation propagates also in the AlGaN active layer and the p-type GaN layer formed in this manner, and the crystallinity of the semiconductor layer constituting the light emitting diode is deteriorated.

  As a fabrication technique for reducing the dislocation density in semiconductors, ELO technology in “Japanese Journal Applied Physics, 36 (1997) L899”, “MRS internet Journal Nitride Semicond. Res.4S1, G3.37 (1999)” PENDEO epitaxy technology and periodic groove structure technology in “The 46th Autumn Meeting on Applied Physics Related Lectures No.1 (1999) p416” have been proposed.

In the ELO technology, after forming a low-temperature buffer layer on a sapphire substrate, a GaN layer is formed on the buffer layer, and a striped layer made of a dielectric material having selectivity such as SiO ₂ is formed on the GaN layer. Form. Thereafter, this is a technique for forming, for example, a GaN semiconductor with low dislocations by selective growth from this layer in the lateral direction.

  In the PENDEO epitaxy technique, a low-temperature buffer layer is formed on a sapphire substrate, and then a GaN layer is formed on the buffer layer. Then, a recess having a striped bottom surface penetrating to the sapphire substrate is formed in the GaN layer. Then, for example, a GaN semiconductor is formed by lateral growth so as to fill the step of the recess. Then, since the part above the said recessed part of a GaN semiconductor is a low dislocation, this part is used as a board | substrate.

  Further, in the periodic groove structure technology, after forming a low-temperature buffer layer on the sapphire substrate, a GaN layer is formed on the buffer layer. Then, a stripe-shaped step is formed on the main surface of the GaN layer, and, for example, a GaN semiconductor is formed so as to fill the step. Then, since the part above the level | step difference of a GaN semiconductor is a low dislocation, this part is used as a board | substrate.

However, these dislocation reduction techniques require an extra operation when forming a stripe-like layer made of SiO _{2 in} addition to the process of forming each layer constituting the light emitting diode, which is necessary for manufacturing the light emitting diode. There is a problem that the process becomes complicated and the manufacturing cost increases accordingly.

JP 2000-196196 A

Japanese JournalApplied Physics, 36 (1997) L899 MRS internet Journal Nitride Semicond. Res.4S1, G3.37 (1999) The 46th Autumn Meeting on Applied Physics Lecture Proceedings No.1 (1999) p416

  An object of the present invention is to reduce the dislocation density and improve the crystallinity of a semiconductor element having a laminated structure of a group III nitride semiconductor that can be used as a light emitting diode or the like.

In order to achieve the above object, the present invention provides an underlayer made of a first group III nitride semiconductor, Al _X Ga _Y In _ZN (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 <Z ≦ 1). , X + Y + Z = 1), and a functional layer made of a second group III nitride semiconductor having a periodic superlattice structure.

The inventors of the present invention have intensively studied to achieve the above object. As a result, when a predetermined semiconductor element is formed by forming a functional layer also made of a group III nitride semiconductor on a base layer made of a predetermined group III nitride semiconductor, the functional layer is made of Al _X Ga _Y In by configuring as _{Z N (0 ≦ X ≦ 1,0} ≦ Y ≦ 1,0 <Z ≦ 1, X + Y + Z = 1) becomes periodic superlattice structure from the second group III nitride semiconductor having a composition, the It has been found that the dislocation density in a semiconductor element can be reduced and its crystallinity can be improved.

  That is, according to the semiconductor element of the present invention, even when misfit dislocations are generated between the base layer and the functional layer and further dislocations are generated in the functional layer, these dislocations cause the functional layer to The surface layer portion of the functional layer is in a low dislocation state without penetrating. Therefore, the crystallinity of the surface layer portion of the functional layer is improved, and even when a predetermined layer such as a conductive layer is formed on the functional layer according to the use application of the semiconductor element, this layer is located below. It is not affected by dislocations in the functional layer. As a result, the crystallinity of the entire semiconductor element is improved, and the characteristics of the target semiconductor element and a device using the semiconductor element can be sufficiently exhibited.

  Note that the functional layer functions as an active layer (light emitting layer) in a light emitting diode, for example, and also functions as an active layer (light emitting layer) in a light emitting element. In the high electron mobility transistor, it functions as a conductive layer. That is, the functional layer is a layer for the semiconductor element to exhibit its original function, and is an essential element in the semiconductor element.

Therefore, according to the present invention, in addition to the process of forming each layer constituting the semiconductor element, an extra process for forming a striped layer made of SiO ₂ or the like is not required, and the process for manufacturing the semiconductor element is eliminated. Complexity and increase in manufacturing cost can be avoided.

Note that the "III-nitride semiconductor" in the present invention, is represented by the general formula _{Al P Ga Q In R N (} 0 ≦ P ≦ 1,0 ≦ Q ≦ 1,0 ≦ R ≦ 1, P + Q + R = 1) In addition, a case where a donor such as Si or P or an acceptor such as Mg is contained is included as necessary.

  In an example of the present invention, the thickness of the functional layer can be 200 nm or more. As a result, the above-described effects can be more remarkably exhibited, the dislocation density in the semiconductor element can be reduced, and the crystallinity can be improved. The upper limit of the thickness of the functional layer is not particularly limited, but can be set to 300 nm, for example. Even if the thickness of the functional layer is greater than 2000 nm, it no longer contributes to the above-described effects.

  In one example of the present invention, the functional layer has a periodic superlattice structure in which the first layer and the second layer are alternately stacked, and the thickness of the first layer is 0.25 nm. The thickness of the second layer can be set to 0.25 nm to 20 nm. Even in this case, the crystallinity can be improved by reducing the dislocation density in the semiconductor element.

According to the present invention, the dislocation density in the surface layer portion of the functional layer can be reduced to 1/100 or less as compared to the case where the above-described periodic superlattice structure is not provided. ⁷ / cm or less.

  The surface layer portion of the functional layer means a region having a depth of approximately several tens of nanometers from the surface of the functional layer, depending on the thickness of the functional layer.

  As described above, according to the present invention, it is possible to reduce the dislocation density and improve the crystallinity of a semiconductor element having a laminated structure of a group III nitride semiconductor that can be used as a light emitting diode or the like. .

It is a figure which shows roughly the structure of a light emitting element (light emitting diode) as an example of the semiconductor element of this invention. It is a figure which shows schematically the structure of the conventional light emitting element (light emitting diode). It is a cross-sectional TEM photograph of the light emitting element in an Example. It is a cross-sectional TEM photograph of the light emitting element in a comparative example.

  Hereinafter, the present invention will be described based on embodiments.

  FIG. 1 is a diagram schematically showing a configuration of a light emitting element (light emitting diode) as an example of a semiconductor element of the present invention.

In the light emitting device 10 shown in FIG. 1, an n-type GaN layer 12 having a thickness on the order of μm, a GaInN active layer 13 and a p-type GaN layer 14 having a thickness on the order of μm are sequentially formed on a GaN substrate 11. It becomes. The GaInN active layer 13 has a periodic superlattice structure, and includes a first layer 131 having a composition of Ga _{1 -S} In _S N and a second layer 132 having a composition of Ga _{1 -T} In _T N (S > T) are alternately and periodically stacked.

  In the light emitting device 10 shown in FIG. 1, the composition ratio X of the first layer 131 constituting the GaInN active layer 13 is in the range of 0.05 to 0.25, and the composition ratio Y of the second layer 132 is 0.35. In the range of ˜0.50, the light emitting element 10 emits red light, the composition ratio X of the first layer 131 constituting the GaInN active layer 13 is in the range of 0.05 to 0.25, and When the composition ratio Y of the second layer 132 is in the range of 0.25 to 0.35, the light emitting element 10 emits green light. The composition ratio X of the first layer 131 constituting the GaInN active layer 13 is in the range of 0.05 to 0.20, and the composition ratio Y of the second layer 132 is in the range of 0.15 to 0.25. In this case, the light emitting element 10 emits blue light.

  The red light here means light having an emission peak in the wavelength range of 620 nm to 750 nm, and the green light generally has an emission peak in the wavelength range of 495 nm to 570 nm. It means light, and blue light generally means light having an emission peak in the wavelength region of 450 nm to 495 nm.

  For example, when a sapphire substrate is used as the substrate, the n-type conductive layer, the active layer, and the p-type conductive layer can be made of an AlGaN-based group III nitride semiconductor or an AlGaInN-based nitride semiconductor. Also in this case, it is possible to emit red light to blue light by appropriately adjusting the composition ratio of these group III nitride semiconductors.

  In the light emitting element 10 shown in FIG. 1, since the GaInN active layer 13 which is a functional layer has a periodic superlattice structure, its dislocation density can be reduced and its crystallinity can be improved.

  That is, even when misfit dislocations occur at the interface between the n-type GaN layer 12 and the GaInN active layer 13 and further dislocations occur in the GaInN active layer 13, these dislocations penetrate the GaInN active layer 13. The surface layer portion of the GaInN active layer 13 is in a low dislocation state. Therefore, the crystallinity of the GaInN active layer 13, particularly the surface layer portion, is improved, and the p-type GaN layer 14 formed thereon also exhibits good crystallinity without being affected by dislocations. As a result, the crystallinity of the entire light emitting element 10 is improved, and characteristics such as light emission efficiency can be improved.

The GaInN active layer 13 is a layer for the light emitting element 10 to exhibit its original function, and is an essential element. Therefore, in addition to the process of forming each layer constituting the light emitting element 10, an extra process for forming a stripe-like layer made of SiO ₂ in the ELO technique or the like is not necessary, and the process for manufacturing the light emitting element 10 is not necessary. Complexity and increase in manufacturing cost can be avoided.

  In the present embodiment, the GaInN active layer 13 of the light emitting element 10 has a periodic superlattice structure in which the first layers 131 and the second layers 132 are alternately stacked. By setting the thickness to 0.25 nm to 20 nm and the thickness of the second layer 132 to 0.25 nm to 20 nm, the dislocation density in the surface layer portion of the GaInN active layer 13 and the p-type GaN layer 14 thereon is further increased. It can be reduced and the crystallinity can be improved.

  Furthermore, if the thickness of the GaInN active layer 13 is 200 nm or more, the above-described effects can be more remarkably exhibited. The upper limit value of the thickness of the GaInN active layer 13 can be 2000 nm.

  The surface layer portion of the GaInN active layer 13 means a region having a depth of approximately several tens of nanometers from the surface of the GaInN active layer 13 depending on the thickness of the GaInN active layer 13.

  FIG. 2 is a diagram showing a schematic configuration of a conventional light emitting device in which the GaInN active layer does not have a periodic superlattice structure.

  2, an n-type GaN layer 22 having a thickness on the order of μm, a GaInN active layer 23 and a p-type GaN layer 24 having a thickness on the order of μm are sequentially formed on a GaN substrate 21. It becomes. The GaInN active layer 23 is formed as a single layer without exhibiting a periodic superlattice structure. Similar to the light emitting element 10 shown in FIG. 1, by controlling the composition ratio in the GaInN active layer 23, it is possible to emit red light to blue light.

  In the light emitting device 20 shown in FIG. 2, since the GaInN active layer 23 does not exhibit a periodic superlattice structure, misfit dislocations are generated at the interface between the n-type GaN layer 22 and the GaInN active layer 23, and the GaInN active layer When dislocations are generated in 23, these dislocations penetrate the GaInN active layer 23 and are exposed on the surface of the GaInN active layer 23. Therefore, the crystallinity of the GaInN active layer 23 is lowered, and the p-type GaN layer 14 formed thereon is also affected by the dislocation, so that the crystallinity is lowered. As a result, the crystallinity of the entire light emitting element 20 is lowered, and characteristics such as light emission efficiency cannot be improved.

For example, when comparing the dislocation density of the surface layer portion of the GaInN active layer 13 of the light emitting device 10 of FIG. 1 with the dislocation density of the GaInN active layer 23 of the light emitting device 20 of FIG. It can be at least 1/100 or less, specifically 2 × 10 ⁷ / cm or less.

(Example)
In the light emitting device 10 shown in FIG. 1, the GaInN active layer 13 has a period in which the first layer 131 is Ga _0.9 In _0.1 N and the second layer 132 is Ga _0.8 In _0.2 N. The dislocation state of the obtained light-emitting element 10 was observed with a TEM. Note that the periodic superlattice structure was a periodic superlattice structure (thickness 300 nm) with a total of 50 periods, with the thickness of each of the first layer 131 and the second layer 132 being 3 nm. The thicknesses of the n-type GaN layer 12 and the p-type GaN layer 14 were 3 μm, respectively.

Each layer was formed by MOCVD using trimethylgallium (TMG), trimethylindium (TMI), and ammonia (NH ₃ ) as source gases.

  FIG. 3 is a cross-sectional TEM photograph of the light-emitting element 10. As is clear from FIG. 3, in the light emitting device 10 of this example, it is recognized that dislocations are generated in the interface between the n-type GaN layer 12 and the GaInN active layer 13 and in the GaInN active layer 13. It can be seen that dislocations do not escape to the surface of the GaInN active layer 13. Therefore, since dislocations do not propagate to the GaInN active layer 13 and the p-type GaN layer 14 thereon, the dislocation density existing in the surface layer portion of the GaInN active layer 13 and the p-type GaN layer 14 can be sufficiently reduced. It can be seen that the performance can be improved.

Actually, TEM observation revealed that the dislocation density of the surface layer portion of the GaInN active layer 13 was 2 × 10 ⁻⁷ / cm.

(Comparative example)
In the light-emitting element 20 shown in FIG. 2, the GaInN active layer 23 is a Ga _0.8 In _0.2 N single layer having a thickness of 300 nm, and the dislocation state of the obtained light-emitting element 20 was observed by TEM. The thicknesses of the n-type GaN layer and the p-type GaN layer were 3 μm, respectively.

Each layer was formed by MOCVD using trimethylgallium (TMG), trimethylindium (TMI), and ammonia (NH ₃ ) as source gases.

  FIG. 4 is a cross-sectional TEM photograph of the light emitting element 20. As is clear from FIG. 4, in the light emitting device 20 of this example, it is recognized that dislocations are generated in the interface between the n-type GaN layer 22 and the GaInN active layer 23 and in the GaInN active layer 23. Since the GaInN active layer 23 does not have a periodic superlattice structure, it is understood that the dislocation penetrates the GaInN active layer 23 to the surface and further propagates to the p-type GaN layer 24 thereon. . Therefore, in this comparative example, due to the fact that the GaInN active layer 23 does not exhibit a periodic superlattice structure, the dislocation density existing in the GaInN active layer 23 and the p-type GaN layer 24 cannot be sufficiently reduced, It turns out that these crystallinity falls.

Actually, TEM observation revealed that the dislocation density of the surface layer portion of the GaInN active layer 23 is 1 × 10 ⁻¹⁰ / cm. Therefore, it can be seen that the dislocation density is 100 times or more as compared with the above examples. In other words, it can be seen that the dislocation density in the above example is 1/100 or less compared to the dislocation density in the comparative example.

  The present invention has been described in detail with specific examples. However, the present invention is not limited to the above contents, and various modifications and changes can be made without departing from the scope of the present invention.

  For example, in the above specific example, the GaInN active layer 23 is formed as thick as 300 nm. However, even if the GaInN active layer 23 is about 100 nm, the dislocation density in the GaInN active layer 23 can be sufficiently reduced, and the light emitting layer The function as can be fully achieved.

  In the above specific examples, the semiconductor element has been mainly described. However, the semiconductor element of the present invention can be applied not only to a light emitting element but also to a light receiving element, a high electron transfer transistor, a solar cell, and the like.

10, 20 Light emitting device 11, 21 GaN substrate 12, 22 n-type GaN layer 13 GaInN active layer (periodic superlattice structure)
14, 24 p-type GaN layer 23 GaInN active layer (single layer)

Claims (7)

An underlayer made of a first group III nitride semiconductor;
A periodic superlattice structure composed of a second group III nitride semiconductor having a composition of Al _X Ga _Y In _ZN (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 <Z ≦ 1, X + Y + Z = 1) A functional layer exhibiting
A semiconductor device comprising:   The semiconductor element according to claim 1, wherein the functional layer has a thickness of 200 nm or more.   The functional layer has a periodic superlattice structure in which a first layer and a second layer are alternately stacked, and the thickness of the first layer is 0.25 nm to 20 nm. The thickness of the layer of 2 is 0.25 nm-20 nm, The semiconductor element of Claim 1 or 2 characterized by the above-mentioned.   4. The semiconductor according to claim 1, wherein a dislocation density in a surface layer portion of the functional layer is 1/100 or less as compared with a case where the periodic superlattice structure is not provided. element. The semiconductor element according to claim 4, wherein a dislocation density of the surface layer portion of the functional layer is 2 × 10 ⁷ / cm or less.   The semiconductor element according to claim 1, wherein the base layer is a conductive layer, the functional layer is an active layer, and the semiconductor element constitutes a light emitting diode. A first layer having a composition of Al _X Ga _Y In _ZN (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 <Z ≦ 1, X + Y + Z = 1) is formed on the first group III nitride semiconductor underlayer. Comprising a step of forming a semiconductor element by forming a functional layer having a periodic superlattice structure, comprising a group III nitride semiconductor of 2;
A dislocation reduction method for a semiconductor device, wherein a dislocation density in a surface layer portion of the functional layer is 1/100 or less as compared with a case where the functional layer does not have the periodic superlattice structure.