JP5400001B2 - III-nitride semiconductor deep ultraviolet light emitting device structure - Google Patents

Description

  The present invention relates to a deep ultraviolet light emitting element structure, and more particularly to a deep ultraviolet light emitting element structure using a group III nitride semiconductor.

  When fabricating a deep ultraviolet light emitting device using an aluminum gallium nitride (AlGaN) -based semiconductor, which is a group III nitride semiconductor, an AlGaN multiple layer comprising an AlGaN well layer and an AlGaN barrier layer having a higher Al composition as the active layer. Quantum well structures have been used. However, in AlGaN multiple quantum well deep ultraviolet light emitting devices, many crystal defects such as point defects and dislocations are likely to be introduced into the AlGaN well layer, and it is generally used as a growth surface as the Al composition increases (0001). Light emission in the surface direction is weak, the emission wavelength is likely to be non-uniform due to fluctuations in the mixed crystal composition of AlGaN, and the difference in band gap between the AlGaN well layer and the AlGaN barrier layer is small. There are problems such as low.

A deep ultraviolet light emitting device using an AlGaN multiple quantum well structure for the light emitting layer is described below. A report by Khan et al. (See Non-Patent Document 1) will be described. FIG. 1 shows the structure of a deep ultraviolet light emitting device 100 using a reported AlGaN multiple quantum well structure. In this report example, a light-emitting diode (LED) is manufactured by a metal organic chemical vapor deposition (MOCVD) method. An Al ₂ O ₃ (0001) surface 101 is used for the substrate. First, an AlN buffer layer 102, an undoped AlN / AlGaN superlattice layer 103, an n-type AlGaN layer 104, and an AlGaN multiple quantum well layer 105, a p-type AlGaN layer 106, and a p-type GaN layer 107 were grown as a light emitting layer. A mesa structure is formed by dry etching, and an n-type electrode 108 is formed on the n-type AlGaN layer 104 and a p-type electrode 109 is formed on the p-type GaN layer 107. The luminous efficiency in the deep ultraviolet region with a wavelength of 280 nm or less is as low as 1% or less.

  H. As reported by Hirayama et al. (See Non-Patent Document 2), the AlGaN barrier layer 102 of the AlGaN multiple quantum well layer 105 has an Al composition that is only about 15% higher than the AlGaN well layer 104, and therefore has a band offset. Since it is small and carriers cannot be sufficiently confined, the light emission efficiency is low. Further, the higher the Al composition of the AlGaN multiple quantum well structure 105, that is, the shorter the emission wavelength, the lower the light emission efficiency. Thus, the conventional structure using the AlGaN multiple quantum well 105 has a high luminous efficiency and cannot produce a deep ultraviolet light emitting device with a short wavelength.

Asif Khan, et al., ‘‘ Ultraviolet light-emitting diodes based on group three nitrides, ’’ Nature Photonics, Vol. 2, pp. 77-84 (2008). Hideki Hirayama, et al., '' 231-261 nm AlGaN deep-ultraviolet light-emitting diodes fabricated on AlN multilayer buffers grown by ammonia pulse-flow method on sapphire, '' Appl. Phys. Lett. 91, 71901 (2007) .

  An object of the present invention is to provide a group III nitride semiconductor deep ultraviolet light emitting element structure capable of obtaining high luminous efficiency.

In order to solve the above problems, a deep ultraviolet light emitting device structure of a group III nitride semiconductor according to claim 1 of the present invention includes an AlGaN / GaN short-period superlattice layer comprising an AlGaN barrier layer and a GaN well layer. A group III nitride semiconductor deep ultraviolet light emitting device having an emission wavelength of 220 to 280 nm, comprising an n-type AlGaN layer and a p-type AlGaN layer arranged so as to sandwich the AlGaN / GaN short period superlattice layer above and below The AlGaN / GaN short-period superlattice layer has an Al composition of the AlGaN barrier layer, an Al composition of the n-type AlGaN layer, and an Al composition of the p-type AlGaN layer of 70% or more. the thickness of the GaN well layer of GaN short period superlattice layer is characterized der Rukoto below 0.75 nm.

  A deep ultraviolet light-emitting device structure in which an AlGaN / GaN short-period superlattice layer composed of an AlGaN barrier layer and a GaN well layer is sandwiched between an n-type AlGaN layer and a p-type AlGaN layer has a large band offset in the GaN well layer serving as the light-emitting layer A short period superlattice is formed by the AlGaN barrier layer. For this reason, it is possible to use a GaN well layer with few defects, strong light emission in the (0001) plane direction and no mixed crystal composition fluctuation as a light emitting layer, and a large GaN well layer and AlGaN barrier layer. By making it possible to strongly confine carriers by the band offset, it becomes possible to manufacture a deep ultraviolet semiconductor light emitting element having a wavelength of 220 to 280 nm and having a high light emission efficiency.

  As described above, the group III nitride semiconductor deep ultraviolet light emitting device structure of the present invention has an AlGaN / GaN short-period superlattice layer composed of an AlGaN barrier layer and a GaN well layer sandwiched between an n-type AlGaN layer and a p-type AlGaN layer. With this configuration, a deep ultraviolet light-emitting element structure with a wavelength of 220 to 280 nm with high luminous efficiency can be manufactured.

It is a structural diagram showing a deep ultraviolet light emitting element structure using a conventional AlGaN multiple quantum well layer. As an example of the group III nitride semiconductor of the deep ultraviolet light-emitting device structure according to a first embodiment of the present invention, it is a structural diagram showing a deep ultraviolet light-emitting device structure using AlN / GaN short periodic superlattice layer. FIG. 3 is a structural diagram showing a deep ultraviolet light emitting element structure using an AlGaN multiple quantum well layer produced for comparison in Example 1. It is the schematic of the energy band of (A) AlGaN multiple quantum well and (B) AlN / GaN short period superlattice. The deep ultraviolet light-emitting device structure using a deep ultraviolet emitting device structure is AlGaN / GaN short periodic superlattice layer of the group III nitride semiconductor according to the second embodiment of the present invention is a structural diagram showing. It is a figure which shows the relationship between Al composition of a AlGaN barrier layer, an n-type, and a p-type AlGaN layer, and luminous efficiency. It is a figure which shows the relationship between the film thickness of a GaN well layer, and the light emission wavelength of a deep ultraviolet light emitting element. It is a figure which shows the relationship between the film thickness of a GaN well layer, and the luminous efficiency of a deep ultraviolet light emitting element.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Example 1>
First, Embodiment 1 of the present invention will be described with reference to FIGS.
FIG. 2 shows an example of a group III nitride semiconductor deep ultraviolet light emitting device structure according to Example 1 of the present invention, in which an AlN barrier layer of an AlGaN / GaN short period superlattice 204 is formed with an AlN layer 202 and an n-type AlGaN layer. FIG. 6 is a structural diagram when a p-type AlN layer 205 is used for an n-type AlN layer 203 and a p-type AlGaN layer.

The deep ultraviolet light emitting element 200 using the AlN / GaN short period superlattice shown in FIG. 2 was produced by metal organic chemical vapor deposition (MOCVD). Trimethylaluminum (TMA) was used as the Al source, trimethylgallium (TMG) was used as the Ga source, and ammonia (NH ₃ ) was used as the N source. Silane (SiH ₄ ) was used as a silicon (Si) raw material for impurity doping, and biscyclopentadienyl magnesium (Cp ₂ Mg) was used as an Mg raw material.
First, an undoped AlN buffer layer (film thickness 1 μm) 202 is formed on a sapphire (0001) substrate 201 at 1300 ° C. 202 and an n-type Si-doped AlN layer (film thickness 1 μm, Si concentration 1 × 10 ¹⁹ cm ⁻³ ) 203 at 1200 ° C. 203. , A 30-period AlN / GaN short-period superlattice layer 204 composed of an AlN barrier layer (film thickness 1.8 nm) and a GaN well layer (film thickness 0.48 nm) at 1000 ° C., and a p-type Mg-doped AlN layer at 1200 ° C. Epitaxial growth was performed in the order of film thickness 20 nm, Mg concentration 1 × 10 ¹⁹ cm ⁻³ ) 205. The GaN well layer 204 is epitaxially grown coherently with respect to the AlN barrier layer and the n-type Si-doped AlN layer, and defects such as misfit dislocations do not occur, and a large compressive strain is inherent in the GaN well layer. In the n-type Si-doped AlN layer 203 and the p-type Mg-doped AlN layer 205, the residual oxygen concentration is reduced to 5 × 10 ¹⁷ cm ⁻³ or less in order to obtain good electrical conductivity. Subsequently, a mesa structure is formed by dry etching using chlorine gas. A Ni / Au electrode 207 was formed on the p-type Mg-doped AlN layer 205 above the mesa, and a Ti / Al / Ti / Au electrode 206 was formed on the exposed n-type Si-doped AlN layer 203. The emission wavelength of this element is 256 nm. In the AlN / GaN short period superlattice, the emission wavelength can be controlled only by the film thickness of the AlN barrier layer and the GaN well layer.

For comparison, a deep ultraviolet light emitting device 300 having a wavelength of 256 nm using a conventional AlGaN multiple quantum well was fabricated. FIG. 3 shows the structure of the manufactured deep ultraviolet light emitting element 300. The manufacturing method is the same as described above. First, on an sapphire (0001) substrate 301, an undoped AlN buffer layer (film thickness 1 μm) 302 at 1300 ° C., and an n-type Si-doped AlGaN layer (Al composition 80%, film thickness 1 μm, Si concentration 1 × 10 ¹⁹ at 1200 ° C.). cm ⁻³ ) 303, 1000 ° C., AlGaN barrier layer (Al composition 80%, film thickness 2.5 nm) and AlGaN well layer (Al composition 60%, film thickness 1.5 nm) 10 periods AlGaN multiple quantum well layer At 304 and 1200 ° C., a p-type Mg-doped AlGaN layer (Al composition 80%, film thickness 20 nm, Mg concentration 1 × 10 ¹⁹ cm ⁻³ ) 305 was epitaxially grown in this order. In the n-type Si-doped AlGaN layer 303 and the p-type Mg-doped AlGaN layer 305, the residual oxygen concentration is reduced to 5 × 10 ¹⁷ cm ⁻³ or less in order to obtain good electrical conductivity. Subsequently, a mesa structure is formed by dry etching using chlorine gas. A Ni / Au electrode 307 was formed on the p-type Mg-doped AlGaN layer 305 above the mesa, and a Ti / Al / Ti / Au electrode 306 was formed on the exposed n-type Si-doped AlGaN layer. In the case of the AlGaN multiple quantum well 304, it is difficult to control the emission wavelength because the Al composition and film thickness of the AlGaN barrier layer and the Al composition and film thickness of the AlGaN well layer and many parameters are adjusted.

  By using the AlGaN / GaN short-period superlattice of the present invention as an active layer compared to the conventional AlGaN multiple quantum well, the luminous efficiency is increased about 5 times. In this embodiment, the sapphire (0001) plane is used for the substrate, but the luminous efficiency is also increased when an AlN (0001) plane or SiC (0001) plane is used.

  The reason why high luminous efficiency can be obtained by using the AlN / GaN short period superlattice of the present invention for the active layer of the deep ultraviolet light emitting device than the conventional AlGaN multiple quantum well will be described. FIG. 4 shows a schematic diagram of energy bands of (A) AlGaN multiple quantum well and (B) AlN / GaN short period superlattice. In the case of the AlGaN multiple quantum well (A), light is emitted by radiative recombination of electrons and holes which are carriers in the AlGaN well layer. In AlGaN, as the Al composition is higher, crystal defects such as point defects and dislocations are more likely to occur. Since these defects cause non-radiative recombination of carriers, the emission efficiency decreases if there are many of these defects. In addition, in an AlGaN multiple quantum well that requires a high Al composition for deep ultraviolet light emission, light emission in the (0001) plane direction becomes weaker as the Al composition becomes higher. Furthermore, in the AlGaN multiple quantum well, the band offset of the conduction band and the band offset of the valence band are small, so that the confinement of carriers (electrons and holes) in the well layer is weak, so the carriers do not emit light and the well layer does not emit light. Escape outside. For example, in the AlGaN multiple quantum well layer 256 nm deep ultraviolet light emitting device of this example, the band offset of the conduction band is as small as 0.3 eV and the band offset of the valence band is as small as 0.1 eV.

  On the other hand, in the case of the AlN / GaN short-period superlattice (B), light is emitted by radiative recombination of electrons and holes which are carriers in the GaN well layer. GaN is a binary material that does not contain Al, and crystal defects such as point defects and dislocations are unlikely to occur. In addition, GaN emits more light in the (0001) plane direction than AlGaN. Furthermore, since the AlN / GaN short period superlattice uses GaN with a small band gap for the well layer, the band offset of the conduction band is 1.95 eV and the band offset of the valence band is as large as 0.65 eV. Since carriers are strongly confined in the layer, light is emitted efficiently. For this reason, high luminous efficiency can be obtained by using an AlN / GaN short period superlattice. As described above, according to the present invention, a deep ultraviolet light emitting element structure with high luminous efficiency is realized.

<Example 2>
Next, a second embodiment of the present invention will be described with reference to FIGS.
FIG. 5 shows an AlGaN barrier layer 502 of an AlGaN / GaN short-period superlattice layer 504, an n-type AlGaN layer 503, p, as an example of a group III nitride semiconductor deep ultraviolet light emitting device structure according to Example 2 of the invention. The relationship between the Al composition of the type AlGaN layer 505 and the light emission characteristics will be described. It is a structural diagram of the manufactured deep ultraviolet light emitting element structure. The manufacturing procedure is the same as that in the first embodiment.

  FIG. 6 shows the relationship between the Al composition of the AlGaN barrier layer of the AlGaN / GaN short-period superlattice layer 504, the n-type AlGaN layer 503, and the p-type AlGaN layer 505, and the luminous efficiency of the deep ultraviolet light device. As can be seen from FIG. 6, the luminous efficiency increases as the Al composition increases. This is because the higher the Al composition, the stronger the carrier confinement in the AlGaN / GaN short period superlattice region. In the AlGaN / GaN short-period superlattice, higher light emission efficiency than that of the conventional AlGaN multiple quantum well can be obtained at a high Al composition that enables deep ultraviolet light emission. In particular, when each Al composition is 70% or more, the same high luminous efficiency as that when the Al composition is 100% can be obtained. Even when the AlGaN barrier layer 502, the n-type AlGaN layer 503, and the p-type AlGaN layer 505 have different Al compositions, high luminous efficiency can be obtained as long as the Al composition is 70% or more.

  Next, the Al composition and emission wavelength of the AlGaN barrier layer 502, the n-type AlGaN layer 503, and the p-type AlGaN layer 505 of the AlGaN / GaN short period superlattice layer 504 will be described. When the Al composition is 70% or more, the emission wavelength hardly depends on the Al composition. This is because when the Al composition is 70% or more, the band offset between the AlGaN barrier layer and the GaN well layer is sufficiently large, so that the change in the quantum level due to the Al composition is small and the change in the emission wavelength is small. is there. Thus, in the AlGaN / GaN short-period superlattice layer 504, even if the Al composition changes, the change in the emission wavelength is small and the controllability of the emission wavelength is high. On the other hand, in the conventional AlGaN multiple quantum well 105, the emission wavelength strongly depends on the Al composition of the AlGaN well layer and the barrier layer. Therefore, when the Al composition changes, the change of the emission wavelength is large and it is difficult to control the emission wavelength. is there.

<Example 3>
Next, Embodiment 3 of the present invention will be described with reference to FIGS.
First, the relationship between the film thickness of the GaN well layer and the light emission characteristics of the deep ultraviolet light emitting element will be described. In this embodiment, an AlN barrier layer (Al composition 100%) 202 is used as the AlGaN barrier layer of the AlGaN / GaN short-period superlattice layer 204 shown in FIG. 2, and an n-type AlN layer (Al composition 100%) 203 is used as the n-type AlGaN layer. The case of a p-type AlN layer (Al composition 100%) 205 as the p-type AlGaN layer will be described as an example. The manufacturing procedure is the same as that in the first embodiment.

  FIG. 7 shows the relationship between the film thickness of the GaN well layer of the AlN / GaN short period superlattice layer and the emission wavelength of the deep ultraviolet light emitting element. As can be seen from FIG. 7, when the film thickness of the GaN well layer is 0.75 nm or less, deep ultraviolet light emission with a wavelength of 280 nm or less is obtained. As the thickness of the GaN well layer decreases, the emission wavelength decreases. When the film thickness of the GaN well layer is 0.15 nm, deep ultraviolet light emission with a wavelength of 220 nm is obtained. Thus, in the AlN / GaN short period superlattice, the emission wavelength can be adjusted only by the film thickness of the GaN well layer, and therefore the controllability of the emission wavelength is high.

  FIG. 8 shows the relationship between the film thickness of the GaN well layer of the AlN / GaN short period superlattice layer and the luminous efficiency of the deep ultraviolet light emitting element. As can be seen from FIG. 8, when the film thickness of the GaN well layer is 1 nm or less, the luminous efficiency is higher than that of the conventional structure. In particular, high luminous efficiency can be obtained when the film thickness of the GaN well layer is 0.75 nm or less. On the other hand, when the film thickness of the GaN well layer is 0.75 nm or more, the light emission efficiency rapidly decreases as the film thickness of the GaN well layer increases. Furthermore, when the film thickness of the GaN well layer is 0.75 nm or more, in addition to deep ultraviolet light emission between the quantum levels of the AlN / GaN short period superlattice layer, light emission derived from defects occurs in the near ultraviolet or visible region. As a result, the monochromaticity of the emission peak deteriorated. Thus, in the AlN / GaN short-period superlattice layer, light emission with excellent monochromaticity can be obtained by making it thinner than the thickness of the well layer used in the conventional AlGaN multiple quantum well. In addition, since the carrier can be confined in the GaN well layer when the film thickness of the AlGaN barrier layer is 0.24 nm or more, deep ultraviolet light emission with high emission efficiency and good monochromaticity can be obtained.

  From the X-ray diffraction measurement, when the thickness of the GaN well layer is 0.75 nm or less, the GaN well layer is epitaxially grown coherently with respect to the AlN barrier layer and the n-type Si-doped AlN layer, and the GaN well layer has a large thickness. It was confirmed that compression strain was inherent. Moreover, the growth surface was flat from the optical microscope observation. On the other hand, when the film thickness of the GaN well layer is 0.75 nm or more, defects such as misfit dislocations are generated, so that the GaN well layer is lattice-relaxed. Further, from observation with an optical microscope, it was found that a three-dimensional island was formed on the growth surface and the flatness was poor.

  In this example, when the Al composition of the AlGaN barrier layer of the AlGaN / GaN short period superlattice is 100% (ie, AlN barrier layer), the Al composition of the n-type AlGaN layer is 100% (ie, n-type AlN layer). The deep ultraviolet light emitting device structure in the case where the Al composition of the p-type AlGaN layer is 100% (that is, the p-type AlN layer) has been described as an example, but the Al composition of the AlGaN barrier layer of the AlGaN / GaN short period superlattice, the n-type When the Al composition of the AlGaN layer and the Al composition of the p-type AlGaN layer are 70% or more, the same emission wavelength and emission efficiency can be obtained. Even when the AlGaN barrier layer, the n-type AlGaN layer, and the p-type AlGaN layer of the AlGaN / GaN short-period superlattice layer have different Al compositions, the same emission wavelength and emission efficiency can be obtained.

200, 300, 500 Deep ultraviolet light emitting device structure 201, 301, 501 Sapphire (0001) substrate 202, 302, 502 AlN buffer layer 203, 303, 503 n-type AlN layer 204, 304, 504 AlN / GaN short period superlattice layer 205,305,505 p-type AlN layer 206,306,506 n-type electrode 207,307,507 p-type electrode

Claims (1)

An AlGaN / GaN short period superlattice layer comprising an AlGaN barrier layer and a GaN well layer;
A deep ultraviolet light emitting element structure of a group III nitride semiconductor having an emission wavelength of 220 to 280 nm, comprising an n-type AlGaN layer and a p-type AlGaN layer disposed so as to sandwich the AlGaN / GaN short period superlattice layer vertically Because
Al composition of the AlGaN barrier layer of the AlGaN / GaN short period superlattice layer, Al composition of the n-type AlGaN layer, Al composition of the p-type AlGaN layer is 70% or more,
The AlGaN / GaN short period thickness of the GaN well layer of the superlattice layers of the group III nitride semiconductor, characterized in der Rukoto less 0.75nm deep-UV light emitting device structure.

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