Group lll nitride semiconductor light-emitting device

Abstract

The present invention provides a Group III nitride semiconductor light-emitting device exhibiting improved emission performance without increasing driving voltage. The Group III nitride semiconductor light-emitting device includes at least an n-type-layer-side cladding layer, a light-emitting layer, and a p-type-layer-side cladding layer, each of the layers being formed of a Group III nitride semiconductor. The n-type-layer-side cladding layer is a superlattice layer having a periodic structure including an InyGa1-yN (0<y<1) layer, an AlxGa1-xN (0<x<1) layer, and a GaN layer. The AlxGa1-xN (0<x<1) layer has such a thickness that electrons tunnel through the AlxGa1-xN layer and holes are confined in the light-emitting layer.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a Group III nitride semiconductor light-emitting device which suppresses an increase in driving voltage and which exhibits improved emission performance.[0003]2. Background Art[0004]Hitherto, various known Group III nitride semiconductor light-emitting devices are known, and some of them are disclosed in Japanese Patent Application Laid-Open (kokai) Nos. H11-191639 and 2007-180499. Japanese Patent Application Laid-Open (kokai) No. H11-191639 discloses a Group III nitride semiconductor light-emitting device having a structure in which a light-emitting layer is stacked on n-type layers; i.e., a third layer bonded to the light-emitting layer, a second layer bonded to the third layer, and a first layer bonded to the second layer. The second layer has a superlattice structure formed of two layers (AlGaN layer and GaN layer) or a superlattice structure formed of two layers (AlGaN layer and InG...

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Benefits of technology

[0007]The present invention has been accomplished for solving such a problem. An object of the present invention is to improve emission performance without increasing driving voltage, by effectively confining holes in a light-emitting layer without causing an increase in resistance to electrons.

[0010]In a second aspect of the present invention, the AlxGa1-xN (0<x<1) layer has such a thickness that electrons tunnel through the AlxGa1-xN layer and holes are confined in the light-emitting layer. Among the InyGa1-yN (0<y<1) layer, the AlxGa1-xN (0<x<1) layer, and the GaN layer, which form the periodic structure, the AlxGa1-xN (0<x<1) layer acts as a barrier against holes contained in the light-emitting layer, and exhibits the effect of confining holes in the light-emitting layer. However, when electrons are injected from the n-type contact layer provided below the n-type-layer-side cladding layer into the light-emitting layer, the AlxGa1-xN (0<x<1) layer acts as a barrier against electrons. Since the de Broglie wavelength of electrons is greater than that of holes, electron tunneling length is larger than hole tunneling length. Therefore, the thickness of the AlxGa1-xN (0<x<1) layer can be adjusted to such a level that electrons can tunnel therethrough and holes cannot tunnel therethrough. Thus, electrons can be effectively injected from the n-type contact layer into the light-emitting layer, and the AlxGa1-xN (0<x<1) layer can act as a barrier layer for holes injected from the p-contact layer into the light-emitting layer, whereby holes can be effectively confined in the light-emitting layer. As a result, emission performance can be improved without increasing driving voltage.

[0013]In a fifth aspect of the present invention, the p-type-layer-side cladding layer is formed of a superlattice layer including an AlzGa1-zN (0<z<1) layer, and the AlxGa1-xN (0<x<1) layer of the n-type-layer-side cladding layer has a compositional proportion x of ½ or more of the compositional proportion z of the AlzGa1-zN (0<z<1) layer of the p-type-layer-side cladding layer. With this configuration, holes pass through the p-type-layer-side cladding layer, and passage of holes is blocked by the AlxGa1-xN (0<x<1) layer (i.e., barrier layer) of the n-type-layer-side cladding layer. In contrast, electrons pass through the n-type-layer-side cladding layer, and passage of electrons is blocked by the p-type-layer-side cladding layer. Thus, electrons and holes are effectively confined in the light-emitting layer without increasing driving voltage, and emission performance is improved.

[0015]In a seventh aspect of the present invention, the light-emitting layer is formed directly on the n-type-layer-side cladding layer. With this configuration, electrons can be effectively injected into the light-emitting layer, and holes can be effectively confined in the light-emitting layer.

[0016]In an eighth aspect of the present invention, the p-type-layer-side cladding layer is a superlattice layer having a periodic structure including an InwGa1-xN layer and an AlzGa1-zN (0<z<1) layer. With this configuration, electrons can be effectively confined in the light-emitting layer, and holes can be effectively injected into the light-emitting layer, resulting in improvement of emission performance.

[0017]In a ninth aspect of the present invention, the n-type-layer-side cladding layer has a four-layer periodic structure including a second GaN layer interposed between the InyGa1-yN (0<y<1) layer and the AlxGa1-xN (0<x<1) layer. With this configuration, the difference in lattice constant between adjacent layers can be reduced, and the crystallinity of the AlxGa1-xN (0<x<1) layer or the InyGa1-yN (0<y<1) layer can be improved. In addition, formation of an AlxGa1-x-yInyN (0<x<1, 0<y<1, 0<x+y<1) layer is prevented between adjacent layers. Thus, the light-emitting device exhibits improved characteristics.

Problems solved by technology

In addition, since the AlGaN layer acts as a barrier against electrons, resistance to electrons is not reduced, and confinement of holes in the light-emitting layer is not improved.

In the device disclosed in Japanese Patent Application Laid-Open (kokai) No. 2007-180499, the light-emitting layer exhibits improved crystallinity, but confinement of holes in the light-emitting layer fails to be attained, and resistance to electrons is not reduced.

Thus, these conventional devices fail to achieve both reduction of driving voltage and improvement of emission performance.

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