JP2012178477A - Semiconductor light-emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the wavelength separation of a semiconductor light-emitting device that can change emission wavelength by directions of a bias.SOLUTION: A semiconductor light-emitting device has a sapphire substrate 10. The sapphire substrate 10 includes an n-GaN layer 11, an n-GaN layer 12, a p-GaN layer 13, a first light-emitting layer 14, a second light-emitting layer 15, a p-GaN layer 16, an n-GaN layer 17, and an n-GaN layer 18 sequentially stacked. A first electrode 19 is formed on the n-GaN layer 18. A trench reaching the n-GaN layer 11 is formed in a region on a surface of the n-GaN layer 18, and a second electrode 20 is formed on the n-GaN layer 11 exposed by the trench. A wavelength separation layer 21 having a larger band gap than the first light-emitting layer 14 and the second light-emitting layer 15 is provided between the first light-emitting layer 14 and the second light-emitting layer 15.

Description

  The present invention relates to a semiconductor light emitting device that can have different emission wavelengths depending on the direction of bias.

  Patent Document 1 discloses a semiconductor light-emitting element that can emit light regardless of the bias direction. The semiconductor light emitting device of Patent Document 1 has a structure in which a light emitting layer is provided in a p layer of an npn junction structure, each pn junction is a tunnel junction, and an electrode is provided in each n layer. Further, it is described that the light emitting layer can be made of two layers having different light emission wavelengths, and the light emission wavelength can be different depending on the bias direction. Furthermore, it is described that the separation of the emission wavelength is further increased by inserting an n layer between the two light emitting layers.

JP 2001-36141 A

  However, in the semiconductor light emitting device described above, the separation of the emission wavelength is not sufficient, and it has been a problem to further improve the separation.

  Further, in a normal group III nitride semiconductor light emitting device, the emission wavelength can be changed by current, but the change amount is 10 nm or less, and the emission wavelength cannot be changed greatly.

  Accordingly, an object of the present invention is to improve the separation of the emission wavelength in a semiconductor light emitting device having a different emission wavelength depending on the bias direction.

  The first invention includes a light emitting layer, two p-type layers positioned on both sides of the light emitting layer, and two p-type layers positioned on opposite sides of the light-emitting layer side and tunneling with the p-type layer. In a semiconductor light emitting device having an n-type layer and two electrodes in contact with the n-type layer and capable of emitting light in any bias direction, the light-emitting layer includes a first light-emitting layer having a different emission wavelength and The second light-emitting layer has two wavelength separation layers having a band gap larger than that of the first light-emitting layer and the second light-emitting layer between the first light-emitting layer and the second light-emitting layer. It is a semiconductor light emitting device.

The wavelength separation layer may be non-doped but is preferably n-type. This is because the separation of the emission wavelength can be further improved. When the wavelength separation layer is n-type, the impurity concentration is desirably 1 × 10 ¹⁷ to 1 × 10 ¹⁹ / cm ³ . Wavelength separation can be further improved. The thickness of the wavelength separation layer is desirably 1 to 10 nm. Similarly, the separation of the emission wavelength can be further improved. More desirably, it is 2 to 7 nm.

  An electron blocking layer that is a semiconductor layer having a larger band gap than the p-type layer may be provided between the light-emitting layer and the p-type layer.

The electron blocking layer can improve the light emission efficiency by suppressing the overflow of electrons to the outside of the light emitting layer. The electron blocking layer may be non-doped or may be doped with a p-type impurity at a low concentration, for example, about 1 × 10 ¹⁷ to 1 × 10 ¹⁸ / cm ³ . The thickness of the electron blocking layer is desirably 3 to 100 nm. The effect of suppressing the overflow of electrons is further increased, and the light emission efficiency can be further improved. More desirably, it is 5 to 30 nm.

  A second invention is a semiconductor light emitting device according to the first invention, further comprising an electron block layer having a band gap larger than that of the p type layer between the p type layer and the light emitting layer.

  A third invention is the semiconductor light emitting device according to the first invention or the second invention, wherein the wavelength separation layer has a thickness of 1 to 10 nm.

  A fourth invention is a group III nitride semiconductor light emitting device according to the first to third inventions.

  When a voltage is applied to the semiconductor light emitting device of the first invention, the light emitting layer closer to the positive electrode of the first light emitting layer and the second light emitting layer mainly emits light due to the difference in mobility between electrons and holes. Therefore, in the semiconductor light emitting device of the first invention, either the first light emitting layer or the second light emitting layer can selectively emit light depending on the bias direction, and the emission wavelength can be changed. Here, since the wavelength separation layer is provided between the first light emitting layer and the second light emitting layer, holes move to the light emitting layer closer to the negative electrode of the first light emitting layer and the second light emitting layer. Is suppressed, the light emission in the light emitting layer near the negative electrode is suppressed, and the light emission efficiency in the light emitting layer near the positive electrode is improved. Therefore, according to the first invention, it is possible to improve the separation of the emission wavelength.

  In addition, as in the second invention, when the electron blocking layer is provided, it is possible to prevent the electrons from overflowing to the outside of the light emitting layer, so that the light emission efficiency of the semiconductor light emitting element can be improved.

  In addition, according to the third invention, it is possible to further improve the light wavelength separation.

  In addition, as in the fourth invention, the present invention can be applied to the case where a group III nitride semiconductor material is used, and it is possible to realize a large change in the emission wavelength, which has been difficult in the past, with one element.

FIG. 3 shows a configuration of a semiconductor light emitting element of Example 1. 3 is a diagram showing a band structure of the semiconductor light emitting element of Example 1. FIG. FIG. 5 shows a configuration of a semiconductor light emitting element of Example 2.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

FIG. 1 is a diagram showing the configuration of the semiconductor light emitting device of Example 1. The semiconductor light emitting device of Example 1 has a sapphire substrate 10, and an n-GaN layer 11, an n ⁺ -GaN layer 12, a p ⁺ -GaN layer 13, a first light emitting layer 14, and a second sapphire substrate 10. The light emitting layer 15, the p ⁺ -GaN layer 16, the n ⁺ -GaN layer 17, and the n-GaN layer 18 are stacked in this order. A first electrode 19 is formed on the n-GaN layer 18. Further, a groove having a depth reaching the n-GaN layer 11 is formed in a partial region of the surface of the n-GaN layer 18, and the second electrode 20 is formed on the n-GaN layer 11 exposed by the groove. Yes. Further, a wavelength separation layer 21 is provided between the first light emitting layer 14 and the second light emitting layer 15.

The n ⁺ -GaN layer 12 and the p ⁺ -GaN layer 13 and the n ⁺ -GaN layer 17 and the p ⁺ -GaN layer 16 are configured to be tunnel-junctioned. That is, the thickness and impurity concentration of each layer are designed so that a tunnel current is generated during reverse bias. For example, the thickness of the n ⁺ -GaN layer 12 and the n ⁺ -GaN layer 17 is 20 nm, the Si concentration is 1 × 10 ²⁰ / cm ^3, and the thickness of the p ⁺ -GaN layer 13 and the p ⁺ -GaN layer 16 is 20 nm and Mg concentration are 1 × 10 ²⁰ / cm ³ . Thereby, the n ⁺ -GaN layer 12 and the p ⁺ -GaN layer 13 and the n ⁺ -GaN layer 17 and the p ⁺ -GaN layer 16 can be tunnel-joined, respectively. Further, the material of the p ⁺ -GaN layer 13 and the p ⁺ -GaN layer 16 may be changed from GaN to InGaN to reduce the band gap, thereby facilitating tunnel junction.

  The first light-emitting layer 14 and the second light-emitting layer 15 have an MQW structure in which well layers and barrier layers are alternately and repeatedly stacked, and have different emission wavelengths. For example, the first light-emitting layer 14 has an MQW structure with an emission wavelength of 450 nm in which 3 pairs of 3 nm InGaN and 3 nm GaN are stacked as a pair, and the second light-emitting layer 15 includes 3 nm InGaN and 3 nm. This is an MQW structure having an emission wavelength of 480 nm in which three pairs of GaN are laminated repeatedly.

  The wavelength separation layer 21 is made of AlGaN having a larger band gap than the first light emitting layer 14 and the second light emitting layer 15.

  The first electrode 19 and the second electrode 20 are made of a material conventionally used for an n electrode of a group III nitride semiconductor light emitting device. For example, Ni / Au, V / Al, Ti / Al, etc. The first electrode 19 and the second electrode 20 are preferably made of the same material. This is because the first electrode 19 and the second electrode 20 can be formed at the same time, and the manufacturing process can be simplified. Further, a transparent electrode such as ITO may be provided on almost the entire surface of the n-GaN layer 18 and the first electrode 19 may be provided on the transparent electrode.

  In the semiconductor light emitting device of Example 1, the voltage was applied using the first electrode 19 as the positive electrode and the second electrode 20 as the negative electrode, and conversely the voltage applied using the first electrode 19 as the negative electrode and the second electrode 20 as the positive electrode. Thus, the emission wavelength can be changed. Hereinafter, the operation of the semiconductor light emitting device of Example 1 will be described in more detail.

  FIG. 2 is a diagram showing a band structure of the semiconductor light emitting device of Example 1. 2A is a band diagram in a non-bias state, FIG. 2B is a band diagram when voltage is applied with the first electrode 19 as a negative electrode and the second electrode 20 as a positive electrode, and FIG. FIG. 5 is a band diagram when voltage is applied with the first electrode 19 as a positive electrode and the second electrode 20 as a negative electrode.

As shown in FIG. 2B, when a voltage is applied with the first electrode 19 as a negative electrode and the second electrode 20 as a positive electrode, the pn junction between the n ⁺ -GaN layer 12 and the p ⁺ -GaN layer 13 is reverse-biased, n ⁺ The pn junction between the −GaN layer 17 and the p ⁺ -GaN layer 16 is forward biased. Here, since the n ⁺ -GaN layer 12 and the p ⁺ -GaN layer 13 are designed to form a tunnel junction, a tunnel current is generated even in reverse bias, and holes are injected into the p ⁺ -GaN layer 13. It diffuses into one light emitting layer 14. On the other hand, electrons are injected from the n ⁺ -GaN layer 17 to the p ⁺ -GaN layer 16, and the electrons diffuse from the p ⁺ -GaN layer 16 to the second light emitting layer 15 and the first light emitting layer 14. Holes have a lower mobility than electrons, and the wavelength separation layer 21 serves as a barrier, so that diffusion into the second light emitting layer 15 is suppressed. As a result, most of the bonding between electrons and holes occurs in the first light emitting layer 14 and emits light at a wavelength of 450 nm.

Further, as shown in FIG. 2C, when a voltage is applied with the first electrode 19 as the positive electrode and the second electrode 20 as the negative electrode, the forward bias is applied to the pn junction between the n ⁺ -GaN layer 12 and the p ⁺ -GaN layer 13. The pn junction between the n ⁺ -GaN layer 17 and the p ⁺ -GaN layer 16 is reverse-biased, and the operation is opposite to that in the case of FIG. In other words, the diffusion of the holes to the first light emitting layer 14 is suppressed because the wavelength separation layer 21 serves as a barrier. Therefore, most of the bonding between electrons and holes occurs in the second light emitting layer 15 and emits light at a wavelength of 480 nm.

  As described above, in the semiconductor light emitting device of Example 1, by providing the wavelength separation layer 21 between the first light emitting layer 14 and the second light emitting layer 15, the light emitting wavelength was changed by changing the bias direction. The separation of the emission wavelength is improved.

  The wavelength separation layer 21 may be non-doped or n-type, but is preferably an n-type layer in order to further improve the light wavelength separation. Similarly, in order to further improve the separation of the emission wavelength, the thickness of the wavelength separation layer 21 is desirably 1 to 10 nm, and more desirably 2 to 7 nm. Similarly, in order to further improve the separation of the emission wavelength, the difference in band gap between the first light-emitting layer 14 and the second light-emitting layer 15 and the wavelength separation layer 21 is desirably 30 to 1000 meV.

FIG. 3 is a diagram showing the configuration of the semiconductor light emitting device of Example 2. The semiconductor light emitting device of Example 2 is the same as the semiconductor light emitting device of Example 1, except that the electron blocking layers 100 and 101 are further provided. The electron blocking layers 100 and 101 are provided between the p ⁺ -GaN layer 13 and the first light emitting layer 14 and between the second light emitting layer 15 and the p ⁺ -GaN layer 16, respectively. The electron blocking layers 100 and 101 are layers made of a group III nitride semiconductor having a band gap larger than that of the p ⁺ -GaN layers 13 and 16, respectively. For example, AlGaN.

By providing the electron block layers 100 and 101 in this way, electrons overflow from the first light emitting layer 14 to the p ⁺ -GaN layer 13 or from the second light emitting layer 15 to the p ⁺ -GaN layer 16. Can be suppressed. As a result, the luminous efficiency can be improved.

In order to more effectively suppress the overflow of electrons, the electron blocking layers 100 and 101 are desirably 3 to 100 nm. More desirably, the thickness is 5 to 30 nm. The electron blocking layers 100 and 101 may be doped with Mg at a low concentration. For example, the Mg concentration may be about 1 × 10 ¹⁷ to 1 × 10 ¹⁸ / cm ³ . The difference in band gap between the p ⁺ -GaN layers 13 and 16 and the electron block layers 100 and 101 is preferably 30 to 1000 meV. This is to suppress the overflow of electrons more effectively.

  In Examples 1 and 2, a semiconductor light emitting device made of a group III nitride semiconductor was shown. However, other III-V group semiconductors such as GaAs and InP, and II-VI groups such as ZnO are used. The present invention can be realized even if a compound semiconductor such as a semiconductor is used as a material. In addition, the semiconductor light emitting devices of Examples 1 and 2 have a configuration in which two electrodes are provided on the same surface side. However, the surface is obtained by using a conductive substrate as a growth substrate or removing the growth substrate by laser lift-off. It is good also as a structure which each provides an electrode in the side and a back surface side, and takes continuity in the vertical direction.

  The semiconductor light emitting device of the present invention can be used as a light source for display devices, lighting devices, optical communications, and the like.

10: Sapphire substrate 11: n-GaN layer 12: n ⁺ -GaN layer 13: p ⁺ -GaN layer 14: first light-emitting layer 15: second light-emitting layer 16: p ⁺ -GaN layer 17: n ⁺ -GaN layer 18: n-GaN layer 19: first electrode 20: second electrode 21: wavelength separation layer 100, 101: electron blocking layer

Claims (4)

A light-emitting layer, two p-type layers located on both sides of the light-emitting layer, and two n-types located on opposite sides of the p-type layer from the light-emitting layer side and tunnel-junction with the p-type layer In a semiconductor light emitting device having a layer and two electrodes that are in contact with each of the n-type layers and capable of emitting light in any bias direction,
The light emitting layer is a first light emitting layer and a second light emitting layer having different light emission wavelengths from each other,
Between the first light emitting layer and the second light emitting layer, there is a wavelength separation layer having a larger band gap than the first light emitting layer and the second light emitting layer,
A semiconductor light emitting element characterized by the above.   2. The semiconductor light emitting device according to claim 1, further comprising an electron block layer having a band gap larger than that of the p type layer between the p type layer and the light emitting layer.   The semiconductor light emitting element according to claim 1, wherein the wavelength separation layer has a thickness of 1 to 10 nm.   The semiconductor light emitting device according to any one of claims 1 to 3, wherein the semiconductor light emitting device is a group III nitride semiconductor light emitting device.

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