JP2007049062A - Semiconductor light emitting element, lighting system employing it, and process for fabricating semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance light take-out efficiency in a light emitting diode consisting of a plurality of nanocolumns. <P>SOLUTION: In the light emitting diode D1 where an n-type GaN nanocolumn layer 2, and a light emitting layer 3 are formed on a silicon substrate 1, and after growing a p-type GaN contact layer 4 epitaxially while enlarging the nanocolumn diameter, a translucent p-type electrode 5 is formed, the n-type GaN nanocolumn layer 2 is provided with a absorption/re-emission layer 6 achieved with a multiple quantum well structure or a double heterostructure. Light not entering the escape cone of the light emitting layer 3 but radiated therefrom in the axial direction of nanocolumn is absorbed by the absorption/re-emission layer 6 and light is re-emitted from that escape cone to the outside of the nanocolumn, and thereby the rate of light being absorbed by the silicon substrate 1 or the translucent p-type electrode 5 is reduced. Consequently, light confined in the nanocolumn can be taken out efficiently and light take out efficiency can be enhanced furthermore. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor light-emitting element that emits light by combining electrons and holes in a semiconductor, a lighting device using the same, and a method for manufacturing the semiconductor light-emitting element. In particular, the semiconductor light-emitting element has a columnar shape called a nanocolumn. The present invention relates to a structure having a plurality of crystal structures.

  In recent years, a quantum well is formed in a III-N compound semiconductor (hereinafter referred to as a nitride) or an oxide semiconductor, and an electric current is passed from outside to couple electrons and holes in the quantum well. The development of solid-state light-emitting elements that emit light by making them light is remarkable. However, the fabrication of these solid state light emitting devices has the following problems.

  For example, when referring to nitride, a fundamental problem that crystal growth has is that crystal growth on a dissimilar material substrate is the main. As a general growth model for nitride heteroepitaxial growth, three-dimensional nuclei are first formed on a low-temperature buffer layer that is thinly deposited on the substrate, and as the growth proceeds further, the nuclei become larger and combine with adjacent nuclei. And a flat surface is formed. Thereafter, the two-dimensional growth is continued while maintaining a flat surface. However, when adjacent nuclei are bonded, the respective nuclei are formed independently, so that the growth planes do not coincide completely, and after bonding, many defects are formed at the nuclear interface. Many of the defects reach the crystal surface as threading dislocations. This threading dislocation acts as a non-radiative recombination center and significantly reduces the luminous efficiency of the solid state light emitting device.

Conventionally, various efforts have been made to reduce threading dislocations against such problems. As a result, the dislocation that was initially about 10 ¹⁰ cm ⁻² in the nitride crystal has been reduced to about 10 ⁵ cm ⁻² .

  As a further technique for lowering dislocations, columnar crystal structures (hereinafter referred to as nanocolumns) have begun to attract attention. The nanocolumn has a diameter of about 100 nm and forms columnar crystals independently without bonding adjacent nuclei. Therefore, the nanocolumn hardly contains threading dislocations in the crystal, and a very high quality crystal can be obtained. In addition, since the nanocolumn has a significantly larger surface area than a thin film and has a cylindrical shape, an improvement in light extraction efficiency is expected as compared with a normal thin film light emitting element.

FIG. 6 shows the structure of Non-Patent Document 1 as an example of an attempt to manufacture a solid-state light emitting device using such a nanocolumn. According to the prior art, an n-type GaN nanocolumn layer 52 and a light emitting layer 53 are formed on a silicon substrate 51 by an RF-MBE (high frequency molecular beam epitaxy) apparatus, and the p-type GaN contact layer 54 is expanded while increasing the nanocolumn diameter. Is epitaxially grown, and Ni (2 nm) / Au (3 nm) to be a translucent p-type electrode 55 is formed.
Kikuchi, Nomura, Kishino “Development of New Functional Device Materials Using Nitride Semiconductor Nanocolumn Crystals” (Applied Physics Society 2004 Autumn Conference Proceedings Vol. 1 P-W-1)

  However, in the above-described conventional technology, the light emitted in the axial direction of the nanocolumn among the light generated in the light emitting layer 53 does not enter the escape cone shown in the light emitting layer 53, but the silicon substrate 51 or the p-type electrode. 55 will be absorbed. Therefore, the situation is that the light extraction efficiency has not been improved as expected.

  An object of the present invention is to provide a semiconductor light-emitting element that can suppress light absorption by a substrate or an electrode and efficiently extract light confined in a nanocolumn to the outside, a lighting device using the same, and a method for manufacturing the semiconductor light-emitting element Is to provide.

  The semiconductor light-emitting device of the present invention has a columnar shape in which an n-type nitride semiconductor layer or an n-type oxide semiconductor layer, a light-emitting layer, and a p-type nitride semiconductor layer or a p-type oxide semiconductor layer are sequentially stacked on a substrate. In a semiconductor light emitting device having a plurality of crystal structures, an absorption / relight emitting layer that absorbs light emitted from the light emitting layer and re-emits light in a region other than the light emitting layer in the columnar crystal structure. It is characterized by that.

  The method for manufacturing a semiconductor light emitting device of the present invention includes an n-type nitride semiconductor layer or an n-type oxide semiconductor layer, a light-emitting layer, a p-type nitride semiconductor layer or a p-type oxide semiconductor layer on a substrate. In the method for manufacturing a semiconductor light-emitting device having a plurality of columnar crystal structures laminated in order, the n-type nitride semiconductor layer or n-type oxide semiconductor layer and the p-type nitride semiconductor layer or p-type oxide semiconductor The step of growing at least one of the layers includes a step of growing an absorption / re-emission layer that absorbs light emitted from the light-emitting layer to re-emit light.

  According to the above configuration, the columnar crystal structure (nanocolumn) in which the n-type nitride semiconductor layer or the n-type oxide semiconductor layer, the light emitting layer, and the p-type nitride semiconductor layer or the p-type oxide semiconductor layer are sequentially stacked. ), The nanocolumn has a shape close to a cylindrical shape. Therefore, since the escape cone is formed in a ring shape from the light emitting layer in the circumferential direction of the nanocolumn, high extraction efficiency is expected. Therefore, an absorption / re-emission layer that absorbs and re-emits light emitted from the light-emitting layer in the axial direction of the nanocolumn without entering the escape cone is a region other than the nano-column light-emitting layer (pn junction). Provided.

  The absorption / re-emission layer should be realized with a multiple quantum well structure in which a plurality of heterostructures are stacked with a relatively thin well layer sandwiched between barrier layers, or a double heterostructure with a relatively thick well layer sandwiched between barrier layers. One or a plurality of absorption / relight emission layers are provided in at least one of the n-type nitride semiconductor layer or the n-type oxide semiconductor layer and the p-type nitride semiconductor layer or the p-type oxide semiconductor layer. Depending on the material of the double heterostructure and the quantum well layer, light having the same wavelength as the light from the light emitting layer may be regenerated, or light having a wavelength different from the light emitting wavelength of the light emitting layer may be regenerated. can do.

  Therefore, the light generated in the absorption / re-emission layer is emitted from the escape cone to the outside of the nanocolumn, and thus a part of the light emitted from the emission layer in the axial direction of the nanocolumn can be extracted. The rate at which light is absorbed by the substrate or electrode decreases. Thereby, the light confined in the nanocolumn can be efficiently extracted to the outside, and the light extraction efficiency can be further improved.

  Furthermore, the semiconductor light emitting device of the present invention has a p-type electrode formed by laminating a conductive material capable of making ohmic contact with the p-type nitride semiconductor layer or the p-type oxide semiconductor layer. It is characterized by that.

  According to the above configuration, in the semiconductor light emitting device having the plurality of nanocolumns, the p-type electrode to be provided on the tip end side of the nanocolumn is connected to the p-type nitride semiconductor layer or the p-type oxide semiconductor layer. Realized by bonding conductive materials that can be contacted. Specifically, after embedding an insulator between the nanocolumns, metal is deposited on the tips of the nanocolumns, or the tips of the nanocolumns are polished to make the height uniform and flat, and the conductive substrate is adhered, Bonding is performed by applying pressure and heating.

  Therefore, in the p-type electrode made of a conductive material, there is no threading dislocation that occurs when the p-type nitride semiconductor layer or the p-type oxide semiconductor layer is grown in the plane direction to form the p-type electrode. Further, it is possible to realize a more efficient semiconductor light-emitting device that takes advantage of the fact that the nanocolumn does not have threading dislocations inside.

  Moreover, the illumination device of the present invention is characterized by using the semiconductor light emitting element.

  According to the above configuration, a highly efficient semiconductor light emitting device with improved light extraction efficiency by the absorption / re-emission layer can be used to obtain the same luminous flux (brightness, illuminance), but with a small size and low power consumption. Can be realized.

  As described above, the semiconductor light emitting device and the manufacturing method thereof according to the present invention include an n-type nitride semiconductor layer or an n-type oxide semiconductor layer, a light-emitting layer, a p-type nitride semiconductor layer or a p-type oxide semiconductor layer, In the semiconductor light emitting device having a plurality of columnar crystal structures (nanocolumns) stacked in order, the nanocolumn has a shape close to a cylindrical shape, and therefore the escape cone is formed in a ring shape from the light emitting layer to the circumferential direction of the nanocolumn. Because it is formed and high extraction efficiency is expected, the nanocolumn has an absorption / re-emission layer that does not enter the escape cone and absorbs the light emitted from the light emitting layer in the axial direction of the nanocolumn and re-emits it. Provided in a region other than the light emitting layer (pn junction).

  Therefore, the ratio of light absorbed by the substrate or the electrode is reduced, the light confined in the nanocolumn can be efficiently extracted to the outside, and the light extraction efficiency can be further improved.

  In addition, as described above, the illumination device of the present invention uses the above-described highly efficient semiconductor light emitting element in which the light extraction efficiency is improved by the absorption / re-emission layer.

  Therefore, it is possible to realize a small-sized and low power consumption lighting device for obtaining the same luminous flux (brightness and illuminance).

[Embodiment 1]
FIG. 1 is a cross-sectional view schematically showing the structure of a light-emitting diode D1 which is a semiconductor light-emitting element according to the first embodiment of the present invention. An n-type GaN nanocolumn layer 2 and a light emitting layer 3 are formed on a silicon substrate 1 by an RF-MBE (high frequency molecular beam epitaxy) apparatus, and a p-type GaN contact layer 4 is epitaxially grown while increasing the nanocolumn diameter. Ni (2 nm) / Au (3 nm) to be a semitransparent p-type electrode 5 is formed. Thereafter, an n-type electrode is formed on the opposite side of the silicon substrate 1 from the nanocolumn, and a light-emitting diode D1 having the light extraction surface on the p-type electrode 5 side is fabricated. The above points are the same as those of the conventional nanocolumn manufacturing method shown in FIG.

  It should be noted that in the present invention, the n-type GaN nanocolumn layer 2 is provided with an absorption / re-emission layer 6. The absorption / re-emission layer 6 is a multi-quantum well structure as shown by the absorption / re-emission layer 6a in FIG. 2 (a) while maintaining the columnar structure, or the absorption / re-emission layer 6b in FIG. 2 (b). It can be realized with a double heterostructure as shown. In the multiple quantum well structure of FIG. 2 (a), a relatively thin, for example, 2 nm well layer 7a, 7b, 7c is hetero-heteromorphically sandwiched between n-type GaN nanocolumn layers 2a, 2b and 5 nm barrier layers 2c, 2d. It consists of multiple structures. On the other hand, the double hetero structure of FIG. 2B is configured by sandwiching a relatively thick, for example, 20 nm well layer 8 between the n-type GaN nanocolumn layers 2a and 2b.

  The absorption / re-emission layer 6 may be provided on the p-type GaN contact layer 4 side, or may be provided on both sides of the n-type GaN nanocolumn layer 2 as shown in FIG. As shown in (b), it may be provided at a plurality of locations. Depending on the material of the absorption / re-emission layer 6, light having the same wavelength as that of the light from the light-emitting layer 3 is regenerated, or light having a different wavelength longer than the emission wavelength of the light-emitting layer 3 is regenerated. can do.

  With such a configuration, the nanocolumn has a shape close to a cylindrical shape, and as shown in FIG. 4, the escape cone C1 is formed in a ring shape from the light emitting layer 3 in the circumferential direction of the nanocolumn, and high extraction efficiency is expected. Therefore, the absorption / re-emission layer 6 that does not enter the escape cone C1 and absorbs the light 9 emitted from the light emitting layer 3 in the axial direction of the nanocolumn and re-emits it is used as the nanocolumn light emitting layer. By providing in a region other than (pn junction) 3, a part of the light emitted from the light emitting layer 3 in the axial direction of the nanocolumn can be extracted, and the silicon substrate 1 and the p-type electrode 5 absorb the light. The rate of being reduced. Thereby, the light confined in the nanocolumn can be efficiently extracted to the outside, and the light extraction efficiency can be further improved. The light emitting layer 3 and the absorption / relight emitting layer 6 have an InGaN multiple quantum well structure, and when the emission wavelength is 460 nm, θ is about 23 to 24 °.

[Embodiment 2]
FIG. 5 is a cross-sectional view schematically showing the structure of a light-emitting diode D2 which is a semiconductor light-emitting element according to the second embodiment of the present invention. In the present embodiment, it is assumed that fabrication is performed by metal organic chemical vapor deposition (MOCVD). However, the nanocolumn growth method is not limited to this, and molecular beam epitaxy (MBE) or hydride vapor phase growth is possible. It is publicly known that nanocolumns can be produced using an apparatus such as (HVPE). Although a case where a nitride semiconductor with an emission wavelength of 460 nm is manufactured is described, the emission wavelength is not limited and may be an oxide semiconductor. Furthermore, the substrate 11 is not limited to sapphire, but silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga ₂ O ₃ ), silicon (Si), glass (SiO ₂ ), zirconium boride (ZrB). ₂ ), zinc oxide (ZnO), and the like are also listed as candidates.

  First, a low temperature AlN buffer layer is deposited on the sapphire substrate 11 by a well-known method, and then Si is added to form an n-type AlGaN underlayer 12 having a thickness of 2 μm. Here, the formation conditions of the n-type AlGaN underlayer 12 were a growth temperature of 1100 ° C. and a growth pressure of 76 Torr. The n-type AlGaN underlayer 12 may be any layer that does not absorb the light generated in the light emitting layer 16 and can have conductivity. Therefore, the material to be used is not limited to the AlGaN, but GaN, InGaN, AlN, ZnO, MgZnO, and the like are also candidates. The n-type AlGaN underlayer 12 may be composed of a plurality of layers. When the substrate 11 absorbs the light of the light emitting layer 16 on the n-type AlGaN foundation layer 12, a distributed Bragg reflector or a metal film such as rhodium may be formed.

Subsequently, the process proceeds to nanocolumn growth. First, a nucleus growth portion 13 is formed on the n-type AlGaN underlayer 12. The conditions at this time are as follows: trimethylgallium (TMGa; Ga (CH ₃ ) ₃ ) as a Ga source and ammonia (NH ₃ ) as a nitrogen source at a growth temperature of 500 ° C. and a growth pressure of 76 Torr. Crystalline GaN is formed. Thereafter, the temperature is heated to about 1050 ° C. to polycrystallize amorphous GaN. At this time, the height of the nucleus growth part 13 was about 20 nm.

  Next, the n-type nanocolumn GaN layer 14a is grown at a growth temperature of 1070 ° C. The n-type nanocolumn GaN layer 14a can be produced by ensuring n-type conductivity by adding Si as an impurity during the growth of the nanocolumn GaN. The height of the n-type nanocolumn GaN layer 14a was 2 μm. However, the material of the nanocolumn is not limited to GaN, and for example, InN, InGaN, AlGaN, AlN, ZnO, MgZnO, and the like can be listed as candidates.

  Subsequently, the absorption / re-emission layer 15a is formed by lowering the growth temperature to 700 ° C. and growing the InGaN / GaN multiple quantum well structure while maintaining the columnar structure. In the present embodiment, as shown in FIG. 2A, the well layers 7a, 7b, 7c have a thickness of 2 nm, and the barrier layers 2c, 2d have a thickness of 5 nm. did. The In composition of InGaN in the well layers 7a, 7b, and 7c was 17%.

  Next, the n-type nanocolumn GaN layer 14b is formed. The manufacturing conditions at this time are the same as the manufacturing conditions of the n-type nanocolumn GaN layer 14a used under the absorption / re-emission layer 15a. However, the thickness was 300 nm.

  Subsequently, the light emitting layer 16 is formed. The manufacturing conditions at this time are the same as those of the absorption / re-emission layer 15a. However, in the case of the quantum well, the emission wavelength of the light emitting layer 16 can be changed by changing the In composition. However, the material of the light emitting layer 16 is not limited to InGaN, and the above-mentioned InN, GaN, AlGaN, AlN, ZnO and the like are also candidates.

  Next, the p-type nanocolumn GaN layer 17a is formed. The growth conditions this time were the same as the conditions for forming the n-type nanocolumn GaN layers 14a and 14b. Similar to the n-type nanocolumn GaN layers 14a and 14b, the material of the p-type nanocolumn GaN layer 17a is not limited to GaN. The thickness was 30 nm. Subsequently, the absorption / re-emission layer 15b is formed. The manufacturing conditions are the same as those of the absorption / re-emission layer 15a. Next, the p-type nanocolumn GaN layer 17b is formed. The manufacturing conditions are the same as those for the p-type nanocolumn GaN layer 17a. However, the thickness was 20 nm. By performing the above steps, the absorption / re-emission layers 15a and 15b can be introduced into the n-type nanocolumn GaN layer 14 and the p-type nanocolumn GaN layer 17, respectively.

  Subsequently, SOG (Spin on Glass) which is an insulator is applied by spin coating, and the insulator 18 is filled in the gaps between the nanocolumns. Since the SOG is liquid, it penetrates into the gaps between the nanocolumns. By controlling the nanocolumn spacing, the viscosity of the SOG, etc., it is easy to penetrate from the p-type nanocolumn GaN layer 17b to the substrate 11 side. Thereafter, SOG is baked and solidified at 400 ° C., and the entire surface of the SOG is etched using buffered hydrofluoric acid so that the tip of the p-type nanocolumn GaN layer 17b is exposed. At least the p-type nanocolumn GaN layer 17b, SOG that is an insulator 18 is embedded so as to cover the absorption / re-emission layer 15 b and the light emitting layer 16. Then, for example, a Ni / Au transparent electrode is vapor-deposited to form a p-type electrode 19. In the case where light is extracted from the sapphire substrate 11 side, a metal having high reflectivity in the visible region such as rhodium, silver, or Al can be used for the p-type electrode 19.

  Further, pattern formation is performed using a normal photolithography technique, and a part of the nanocolumn is dry-etched and removed until the n-type AlGaN underlayer 12 is exposed. For example, Ti / Au or Al / Au (Al / Au) The n-type electrode 20 having higher reflectivity and promising) is formed. In this manner, the light emitting diode D2 of the present embodiment is manufactured.

  With this configuration, in Non-Patent Document 1 shown in FIG. 6 described above, crystals with different plane orientations grow in the p-type GaN contact layer 54 for forming the p-type electrode 55, even if nanocolumns are grown. Even if there are no threading dislocations, a large number of threading dislocations are generated in the p-type GaN contact layer 54, and much of the light generated in the light emitting layer 53 is absorbed. In this way, the p-type electrode 19 to be provided on the tip side of the nanocolumn is realized by laminating a transparent electrode capable of making ohmic contact with the p-type nanocolumn GaN layer 17b. A more efficient light-emitting diode can be realized that takes advantage of no threading dislocations inside.

  In the above-described light emitting diode D2, the p-type electrode 19 is embedded with an insulator 18 made of SOG so that the n-type nanocolumn GaN layer 14b and the p-type nanocolumn GaN layer 17a are not short-circuited with the light-emitting layer 16 interposed therebetween. Thereafter, although formed by vapor deposition, after the p-type nanocolumn GaN layer 17b is formed from the absorption / re-emission layer 15b, the tip of the p-type nanocolumn GaN layer 17b is used widely for manufacturing a multilayer semiconductor. A p-type electrode may be fabricated by stacking a p-type GaN substrate that has been flattened by polishing in the same manner, and then heating and pressurizing after the CMP technique is used to achieve uniform height by rotational polishing. .

  By using the light emitting diodes D1 and D2 configured as described above for the lighting device, it is possible to realize a small lighting device with low power consumption even when the same luminous flux (luminance, illuminance) is obtained.

It is sectional drawing which shows typically the structure of the light emitting diode which is a semiconductor light emitting element concerning the 1st Embodiment of this invention. It is sectional drawing which shows the structural example of the absorption and re-emission layer provided in the nanocolumn of this invention. It is sectional drawing which shows the example of arrangement | positioning of the said absorption and re-emission layer. It is a figure for demonstrating the light extraction angle | corner by the escape cone in a nanocolumn. It is sectional drawing which shows typically the structure of the light emitting diode which is a semiconductor light-emitting device based on the 2nd Embodiment of this invention. It is sectional drawing which shows typically the manufacturing process of the typical prior art semiconductor light-emitting device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2, 2a, 2b N-type GaN nanocolumn layer 2c, 2d Barrier layer 3 Light emitting layer 4 p-type GaN contact layer 5 p-type electrode 6, 6a, 6b Absorption / re-light emitting layer 7a, 7b, 7c Well layer 8 Well Layer 11 Sapphire substrate 12 AlGaN underlayer 13 Nucleus growth part 14, 14a, 14b N-type nanocolumn GaN layer 15a, 15b Absorption / re-emission layer 16 Light-emitting layer 17, 17a, 17b P-type nanocolumn GaN layer 18 Insulator 19 P-type electrode 20 n-type electrode C1, C2 escape cone D1, D2 light emitting diode

Claims (6)

A plurality of columnar crystal structures in which an n-type nitride semiconductor layer or an n-type oxide semiconductor layer, a light emitting layer, and a p-type nitride semiconductor layer or a p-type oxide semiconductor layer are sequentially stacked on a substrate; In a semiconductor light emitting device comprising:
A semiconductor light-emitting element comprising an absorption / re-emission layer that absorbs light emitted from the light-emitting layer and re-emits light in a region other than the light-emitting layer in the columnar crystal structure.   2. The semiconductor light emitting device according to claim 1, wherein the absorption / re-emission layer has a multiple quantum well structure.   2. The semiconductor light emitting device according to claim 1, wherein the absorption / re-emission layer has a double hetero structure.   4. The p-type electrode according to claim 1, wherein a p-type electrode is formed on the p-type nitride semiconductor layer or the p-type oxide semiconductor layer by bonding a conductive material capable of making ohmic contact therewith. The semiconductor light emitting element of any one of Claims.   An illumination device using the semiconductor light emitting element according to claim 1. A plurality of columnar crystal structures in which an n-type nitride semiconductor layer or an n-type oxide semiconductor layer, a light emitting layer, and a p-type nitride semiconductor layer or a p-type oxide semiconductor layer are sequentially stacked on a substrate; In a method for manufacturing a semiconductor light emitting device comprising:
At least one growth step of the n-type nitride semiconductor layer or n-type oxide semiconductor layer and the p-type nitride semiconductor layer or p-type oxide semiconductor layer absorbs light emitted from the light emitting layer. A method for producing a semiconductor light emitting device, comprising a step of growing an absorption / relight emission layer for re-emission.

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