JP2002222991A - Semiconductor light emitting device - Google Patents

Abstract

(57) [Problem] A white LED is attracting attention as a light source replacing an incandescent lamp or a fluorescent lamp because it has better luminous efficiency, generates less heat, and consumes less power than an incandescent lamp or a fluorescent lamp. Although it is already used for backlights of mobile phones and the like, it is desired to be able to produce a large area more efficiently and simply in order to spread it more widely. In order to solve this problem, a ZnO-based semiconductor and a GaN-based semiconductor are joined together to easily produce a white LED that emits light with emission characteristics extremely close to a human visibility curve without using a phosphor. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white semiconductor light emitting device which emits light with light emission characteristics very close to a human visibility curve.

[0002]

2. Description of the Related Art At present, a white light emitting device (L) using a semiconductor is known.
As ED), there are two methods. These are shown in FIG.
This will be described with reference to FIG. White LED first appeared
(Refer to FIG. 2) is that the blue LED is covered with a yellow-emitting phosphor, and the blue light transmitted from the blue LED through the yellow-emitting phosphor and directly reaches the outside and the blue light from the blue LED are once yellow-emitting. Is synthesized with the yellow light that is absorbed by the phosphor and emitted therefrom. However, in this method, the efficiency is reduced because the light is absorbed once by absorbing the blue light. In addition, in the manufacturing process, the number of steps is larger than that of a normal LED by the amount of the phosphor. Next, the white LED of the second type (see FIG. 3) is ZnSe of the blue ZnSe LED.
This is a white LED using the fluorescence from the substrate, and the efficiency of the white LED is also reduced by using the fluorescence from the substrate.

[0003]

As compared with incandescent lamps and fluorescent lamps, white LEDs have attracted attention as light sources replacing incandescent lamps and fluorescent lamps, because they have better luminous efficiency, generate less heat, and consume less power. Although it is already used for backlights of mobile phones and the like, it is desired to be able to produce a large area more efficiently and simply in order to spread it more widely.

[0004]

[Means for solving the problem] Therefore, ZnO based semiconductors and G
A white LED that emits light with a light emission characteristic extremely close to a human luminosity curve due to a junction structure with an aN-based semiconductor is simply manufactured without using a phosphor. Here, ZnO
Based semiconductors are ZnO, ZnCdO, ZnMgO, ZnCdMgO, ZnOSe, ZnO
ZnCdMgOSSe which is S or the like and a combination thereof. GaN-based semiconductors include GaN, GaInN, AlGaN and AlGaI.
nN.

[0005]

The LED of the present invention emits light according to the following principle. Conventional semiconductor light-emitting devices all have a structure in which light is emitted by a pn junction of a p-type semiconductor and an n-type semiconductor, which are all the same semiconductor. The light emitting principle of the present invention is a new principle of emitting light by a pn junction of a p-type semiconductor and an n-type semiconductor of different semiconductors. The hetero structure used in the conventional double hetero structure is a hetero structure in which the refractive index and the forbidden band width are different from each other. However, in reality, it is only a structure in which the mixed crystal ratio of a homologous semiconductor is changed. In the conventional technology, even the one that changed the mixed crystal ratio of the family semiconductor was revolutionary,
The heterostructure of the present invention is a heterostructure completely formed by a junction between heterogeneous semiconductors, and it has been conventionally difficult to manufacture a light emitting device.

FIG. 1 shows an example of a light emitting device in which a p-type GaN semiconductor and an n-type ZnO semiconductor are joined. In addition, at present,
Only GaN semiconductors have realized wide-bandgap semiconductors and practical p-type semiconductors.
And since there is no other example in which a lattice constant is as close as GaN and ZnO in a heterogeneous semiconductor, it is unlikely that the white semiconductor light emitting device will be a white semiconductor light emitting element even in a combination other than a combination of a p-type GaN semiconductor and an n-type ZnO semiconductor. Seem.

[0007] White light emission is called a heterogeneous (hetero) semiconductor junction (or a heterogeneous (hetero) semiconductor junction).
May be accurate. ) Is generated using a new principle that utilizes the levels in the forbidden band. The following sub-band formation is considered as a mechanism for forming a sub-level. In semiconductors different from the 2-6 group and the 3-5 group, there is an excess or deficiency in the number of electrons bonded at the junction interface.
An attempt is made to compensate for excess or deficiency of electrons by creating electrons (dangling bonds) that are not excessively bonded or holes that are not enough to open holes (vacancies) at the bonding interface. Such a phenomenon is considered to be a cause of forming a subband.
Although the contribution is considered to be small, it is considered that the following effects are also included. In other words, even if the band gap is the same, that is, even if the difference between the valence band and the conduction band is the same, it is considered that the actual positions of the valence band and the conduction band are slightly different. It is considered that a step (band offset) occurs, which forms a new light-emitting recombination process like a sub-band, and emits light with energy in the band gap.

[0008] This eliminates the need for a phosphor or a fluorescent agent. Further, as described above, formation of dangling bonds and the like at the junction interface between heterogeneous semiconductors can be performed in an infinite number of combinations in terms of spatial structure in order to compensate for excess or deficiency of electrons, and an unspecified number of sub-levels are formed. Therefore, the interface states are continuously distributed. For this reason, light emission having a white light emission spectrum that is very close to a human visibility curve can be obtained.

The n-type semiconductor portion includes a ZnO-based semiconductor and p-type semiconductor.
The use of a CaN-based semiconductor for the n-type semiconductor portion and, in particular, the use of a ZnO-based semiconductor that is easy to etch for the n-type semiconductor portion has the characteristic of improving the processability of the device.

[0010]

An embodiment of the present invention will be described with reference to FIG. In FIG. 1, as a p-type layer, a p-type GaN layer is laminated on a sapphire (0001) plane substrate by doping Mg using a MOCVD method. On the p-GaN layer, an n-type ZnO layer was prepared,
Form an n-junction. Here, heterojunction fabrication techniques of different families are required. First, the p-GaN layer is etched by irradiation with hydrogen plasma in an ultra-high vacuum to prepare for excellent interface formation. After the hydrogen plasma surface treatment,
A ZnO layer is grown. In the device of the embodiment, an i-ZnO layer to which no impurity is added is introduced as the light emitting layer. As the laminating method, the MBE method was used. Ultra-high-purity Zn (purity 7N) was supplied from a K cell, and an oxygen source was supplied from an RF radical cell using plasma of high-purity oxygen (purity 6N), and an extremely thin i-ZnO layer of about 10 nm was grown. The growth temperature is about 450 to 600 ° C., and the degree of vacuum in the growth chamber during growth is about 10 −6 Torr.

Finally, an n-type ZnO layer heavily doped with Ga is grown on the extremely thin i-ZnO layer. This is also i-ZnO
Using MBE method for the layer, ultra-high purity Zn (purity 7N)
From the cell, the oxygen source was supplied from an RF radical cell using a plasma of high purity oxygen (purity 6N), and the ultra high purity Ga (purity 7N) for doping was supplied from a K cell. The grown film thickness is about 200 nm. The growth temperature is slightly lower than the i-ZnO layer, about 350-450 ° C, and the growth chamber vacuum during growth is 10 −6
It is about rr.

In order to form an electrode structure, an i-ZnO layer and an nZ
Etch the nO layer with hydrochloric acid. One of the advantages of the light emitting element manufacturing process of the present invention is that wet etching can be used for etching. With a hydrochloric acid-based etchant, a ZnO-based oxide semiconductor is etched well, and a GaN-based nitride semiconductor is not etched at all. This not only has a great advantage in the manufacturing process, but also in the future, when fabricating a complex device such as a semiconductor laser using this heterojunction between heterogeneous semiconductors,
Selective etching is easy, and various structures can be formed in a ZnO-based semiconductor portion easily etched with hydrochloric acid. In the case of a device having a complex structure of a semiconductor laser class, since there are numerous forms of the structure even today, a new world of structural operation of a short wavelength laser diode is opened. The structure of the current nitride semiconductor laser is naturally limited due to its difficulty in etching, hindering the development of a short wavelength laser structure. In that sense, the heterojunction between ZnO / GaN heterogeneous semiconductors of the present invention opens up new possibilities.

Finally, a negative electrode is taken on the n-ZnO layer growth surface, and a positive (+) electrode is taken on the p-GaN layer exposed after etching. Indium is used for the negative electrode metal and gold is used for the positive electrode.

In the above description, the substrate underlying the p-type GaN layer does not necessarily have to be the sapphire (0001) plane substrate described above, but rather a SiC substrate or a conductive substrate.
Even on a recently developed GaN substrate or the same sapphire substrate, the characteristics may be improved when fabricated on a GaN layer applying technology such as ELOG (epitaxial lateral pver growth) .

Further, a p-AlGaN layer may be formed on the p-GaN layer as a partial carrier electron overflow prevention layer.

When actually manufacturing a light emitting device, more layers such as quantum well layers are required. A ZnCdO mixed crystal semiconductor is a candidate for a light-emitting layer called an active layer. In this case, the light emission characteristics can be controlled by the content of Cd.

FIG. 4 shows light emission characteristics when the LED of FIG. 1 of the present invention is actually manufactured and driven by current. FIG. 4 shows a light emission intensity characteristic and a voltage characteristic when a current flows through the pn junction. Despite the hetero pn junction between different kinds of semiconductors, the rectification characteristics and LED characteristics normally found in semiconductor pn junctions are obtained. The emission threshold voltage is about 4V and the injection current density is about
It was 50 A / cm2.

FIG. 5 shows the result of wavelength characteristic evaluation of the LED of FIG. 1 of the present invention actually produced and emitted. FIG. 5 shows what wavelength light is emitted at what intensity. The black part of the background in the figure is the visibility curve of human vision. The conventional white LED uses both blue light emission and fluorescent light emission, so it has two peaks as shown in FIG. 6 and does not overlap with the luminosity curve, but in the LED of the present invention,
An emission spectrum having a smooth and continuous curve and close to a luminosity curve can be obtained by the interface levels of the heterojunction distributed continuously.

The n-type semiconductor portion, which is a feature of the present invention, has Z
In the case of a hetero-pn junction light-emitting device using a GaN-based semiconductor for the nO-based semiconductor and the p-type semiconductor, LEDs with different light-emitting characteristics as shown in Fig. 7 are controlled by controlling the interface state. It is also possible to produce. FIG. 7 shows the result of actually producing a blue-green LED and emitting light. As described above, in the LED of the present invention, the emission color can be changed by controlling the interface states of the heterojunction distributed from the ultraviolet region to the entire visible light region and the infrared wavelength region.

[0020]

Since the semiconductor light emitting device of the present invention has a continuous white light emission curve very close to the human visibility curve, it can be widely used as a lighting in a new era replacing incandescent lamps and fluorescent lamps. There is. In addition, by using new semiconductor ZnO, low power consumption white L
The spread of ED can be improved, and it can contribute to environmental measures and energy saving. Furthermore, by using a ZnO-based semiconductor that can be produced by spin coating or sputter deposition, high production efficiency can be obtained.
A large area and low cost can be achieved, and a high penetration rate can be expected when it is widely used as lighting for a new era replacing incandescent lamps and fluorescent lamps.

[Brief description of the drawings]

FIG. 1 shows a ZnO / GaN heterojunction white LED according to the present invention.
FIG.

FIG. 2 is a schematic view of a conventional InGaN-based white LED.

FIG. 3 is a schematic view of a conventional ZnSe-based white LED.

FIG. 4 is a light emission characteristic diagram of the white LED according to the present invention.

FIG. 5 is an emission spectrum of the white LED of the present invention.

FIG. 6 is an emission spectrum of a conventional InGaN-based white LED.

FIG. 7 is an emission spectrum of the blue-green LED according to the present invention.

Claims (5)

[Claims] 1. A semiconductor light emitting device wherein a ZnO-based semiconductor is used for an n-type semiconductor portion and a GaN-based semiconductor is used for a p-type semiconductor portion. 2. The semiconductor light-emitting device according to claim 2, wherein an interface state of a junction structure between the ZnO-based semiconductor and the GaN-based semiconductor is used as the light-emitting level in the light-emitting portion. . 3. A semiconductor light emitting device formed by laminating a ZnO-based semiconductor as an n-type semiconductor on a p-type GaN-based semiconductor. 4. A semiconductor light emitting device formed by laminating a ZnO-based semiconductor as an n-type semiconductor on a p-type GaN-based semiconductor by spin coating or sputter deposition. 5. The light-emitting device according to claim 4, wherein a part of the n-type semiconductor is removed by etching, and a p-type electrode is formed in the removed part.