JP3466972B2 - Organic semiconductor light emitting device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic semiconductor light emitting device capable of changing emission wavelength over a wide range.

[0002]

2. Description of the Related Art Surface emitting laser device type structures composed of semiconductors for both inorganic and organic lasers are known as VGKo.
zlov et al., J. Appl. Phys., 848 (1998). In addition, many examples of DFB (distributed feedback) lasers are
For example, Y. Suematsu et al., Chtp 4 Semiconductors a
nd Semimetals, Vol.22, Academic Press, San Diego 1
985 (editor RK Willardson AC Beer), especially in InP material systems. However,
All of these structures are limited by the fact that once manufactured, the laser wavelength is limited to one wavelength.

Therefore, various efforts have been made today to change the emission wavelength of laser light. However, the current state of the art is that the methods and materials used are generally very limited. Extending the wavelength range in which continuous tuning is achievable, mainly by using the variable absorption region in the middle of the device, despite other methods used to vary the output wavelength, is DF
In the case of B device, it is limited to 3 to 4 nm at most. DB
In the case of R (Distributed Bragg Reflector) devices, the tuning capability due to the problem of such devices being manufactured vertically has not been specifically studied.

FIG. 8 is a diagram showing an example of a conventional typical surface emitting semiconductor laser diode. In the figure, reference numeral 1 denotes an n-type substrate, and on the main surface of the n-type substrate 1, an n-type contact region 2, an n-type DBR layer 3, an n-type cladding layer 4,
An active layer 5, a p-type clad layer 6, a p-type DBR layer 71, and a p-type contact layer 72 are sequentially stacked. A p-type metal contact 73 is selectively formed on the p-type contact layer 72. On the back surface of the n-type substrate 1,
An n-type metal contact 12 is formed.

In this surface emitting laser diode,
The DBR structures (p-type DBR layer 3 and n-type DBR layer 71) formed on the upper side and the lower side of the active layer 5 are both conductive, and the p-type contact layer 72 is generally compared with the resistance of the DBR laminated structure. And has a very low specific resistance. As a result, a uniform current is injected into the active layer 5, and uniform surface emission of laser light is obtained. However, when the emission area of the laser light is larger than 10 μm, there is a problem that the laser light is not emitted uniformly.

In the example shown in FIG. 7, the emission wavelength of the laser light is fixed by the band gap of the active layer 5 and the DBR structure. Of course, the emission wavelength can be changed by changes in temperature, but it is very difficult to control this parameter, that is, temperature in a normal device.

[0007]

As described above, in the conventional semiconductor light emitting device, for example, when the surface emission type structure is taken as an example, the emission wavelength of the emitted laser light depends on the band gap of the active layer and the DBR structure. Fixed to only one. Therefore, it is possible to change the emission wavelength of the laser light by changing the temperature, but it is very difficult to control the temperature with an ordinary device.

The present invention has been made to solve the above problems, and an object thereof is to provide an organic semiconductor light emitting device capable of changing the emission wavelength of laser light in a wide range.

[0009]

An organic semiconductor light emitting device according to the present invention comprises an organic active layer composed of an organic material, and a lower part which is formed on the lower surface of the organic active layer and supplies carriers to the organic active layer. A carrier diffusion layer and an upper carrier diffusion layer formed on the upper surface of the organic active layer and supplying carriers having a conductivity type opposite to that of the lower carrier diffusion layer to the organic active layer, and formed on the upper carrier diffusion layer. An organic active layer comprising an insulating layer and a conductive layer formed on the insulating layer and made of a transparent conductive material, wherein an electric current is passed between the lower carrier diffusion layer and the upper carrier diffusion layer. The organic active layer is characterized by generating light therein and applying a voltage between the lower carrier diffusion layer and the conductive layer.

Desirably, the lower carrier diffusion layer and the upper carrier diffusion layer of the organic active layer are each made of a conductive polymer oriented parallel to the interface with the organic active layer.

[0011]

[0012]

(Function) In the present invention, the active layer functioning as the light emitting region is made of an organic material, and the upper carrier diffusion layer and the insulating layer are laminated on the active layer, and the active layer is formed on the insulating layer. Provide a conductive layer to generate strain.
Then, by applying a voltage between the lower carrier diffusion layer formed under the active layer and the electrode formed under the lower carrier diffusion layer, the Coulomb force is used to distort the active layer. The band gap or refractive index changes. By changing this band gap or refractive index,
It is possible to change the wavelength of the light emitted from the active layer.

[0014]

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a sectional view showing the overall structure of an organic semiconductor light emitting device according to the first embodiment of the present invention. This semiconductor light emitting device is characterized in that the wavelength of emitted light is changed.

In the figure, 1 is an n-type substrate, and on the main surface of the n-type substrate 1, an n-type contact layer 2, an n-type DBR (dispersive Bragg reflector) layer 3, an n-type cladding layer 4, and an organic active layer. The layer 5 and the p-type clad layer 6 are sequentially laminated and formed.
Then, the SiO ₂ block layer 7 and the high-conductivity bias layer 8 are sequentially stacked and selectively formed on the p-type cladding layer 6, and the surfaces of both end portions of the p-type cladding layer 6 are exposed. A clad layer contact 9 is formed on the exposed surface of the p-type clad layer 6.

Further, the non-conductive DBR layer 10 is selectively formed on the high-conductivity bias layer 8, and both end surfaces of the high-conductivity bias layer 8 are exposed. A bias layer contact 11 is formed on the exposed surface of the highly conductive bias layer 8. On the back surface of the n-type substrate 1,
The n-type metal contact layer 12 is formed.

The n-type DBR layer 3 has a DBR mirror structure formed by alternately laminating two different semiconductor layers 3a and 3b, and the non-conductive DBR layer 10 has the same structure.
This is a structure formed by alternately stacking two different semiconductor layers 10a and 10b.

The feature of this embodiment is that SiO is formed between the non-conductive DBR layer 10 having a DBR mirror surface structure and the active layer 5.
₂ block layer 7 and high conductivity bias layer 8 are formed,
Moreover, the bias layer contact 11 is formed on the exposed surface of the highly conductive bias layer 8. The SiO ₂ block layer 7 is an electrically insulated region.

In order to have such a characteristic point, the following substance species and manufacturing method are used for each constitution.

The n-type DBR layer 3 is made of a material having a low resistance so that a sufficient bias is applied to the organic active layer 5 and sufficient strain is generated.

Clad layer 4 provided as a current injection layer
For this, a conductive and highly anisotropic substance is used. As a result, the current injected from the clad layer contact 9 provided on the side portion uniformly flows in the p-type clad layer 4, and uniform current injection into the organic active layer 5 that emits light is performed.

The substance which is a conductive material and exhibits sufficiently high anisotropy is a long-chain polymer which is an organic semiconductor.

Generally, conductive polymers used for our purposes include polyacetylene (PA), poly (p-phenylene sulfide) (PPP), polyurethane, poly (p-phenylene) (PPS), polypyrrole ( PPY), polythiophene (Pth), etc. are used,
Doping with a material such as I ₃ ⁻ , AsF ₆ ⁻ , BF ₄ ⁻ , K ⁺ gives a polycrystalline thin film whose chains are oriented parallel to the film. Therefore, all chains are oriented in the same direction, and a highly anisotropic conductive material is obtained.

Therefore, in the cladding layer 4, the organic active layer 5
The orientation of the atoms is controlled so that the chains are oriented in the direction parallel to the interface with. As a result, the cladding layer 4 having high conductivity is obtained in the direction parallel to the interface with the organic active layer 5. The material species, characteristics, etc. used for the clad layer 4 are also common to the clad layer 6.

Various candidates for the organic active layer 5 formed on the clad layer 4 exist depending on the required emission wavelength, but for example, Alq3 (tris doped with DCM (or other dye)). -(8-Hydroxyquinoline aluminum), couramin47 (and other dyes) -doped 4,4'-di (N-carbazole) biphenol, PP
V (poly (p-phenylene vinylene)) is doped,
Or PBD (2- (4-biphenyl) -5- (4-t-
Butylphenyl) -1,3,4-oxadiazole) is doped in polyurethane. The substance species of the organic active layer 5 are not limited to those listed above.

Thus, by sandwiching the organic active layer 5 which is a light emitting region between the two clad layers 4 and 6 which are conductive and highly anisotropic, the organic active layer 5 and the clad layers 4 and 6 are sandwiched. Conductivity is highest along the direction of the interface with
A sufficient current flows in the direction parallel to the interface, and uniform emission light is obtained in the organic active layer 5.

As the highly conductive bias layer 8, a transparent conductive polymer having an electron donating property is used.
i thin film etc. are mentioned.

The material of the clad layer contact 9 is determined by its function. Formed on the upper side of the organic active layer 5,
The contact 9 to the clad layer 6 which functions as a hole injection region can be easily obtained from ITO, Au / Zn, or another material normally used as a p-type contact.
The material of the bias layer contact 11 is Au.
Etc. are used.

In the organic semiconductor light emitting device configured as described above, when a voltage is applied between the clad layer contact 9 and the n-type metal contact layer 12, the p-type clad layer 6 is formed as in a normal semiconductor laser device. From the hall,
Holes are supplied from the n-type cladding layer 4 to the organic active layer 5. In the organic active layer 5, light is generated by recombination of these holes and holes. This light is a non-conductive DB
It is repeatedly reflected between the R layer 10 and the n-type DBR layer 3, amplified, and emitted as laser light from the upper surface of the non-conductive DBR layer 10.

During this light emission, the bias layer contact 1
By applying a voltage to the organic active layer 5 by applying a voltage to the 1 and n-type metal contacts 12, a Coulomb force is generated between the contacts, which causes strain in the organic active layer 5. Due to the strain generated in the organic active layer 5, the band gap or the refractive index of the organic active layer 5 changes. As a result, the wavelength of the emitted laser light changes.

FIG. 2 shows the relationship between the electric field formed by the bias layer contact 11 and the n-type metal contact layer 12 and the wavelength change amount of the emitted light. The horizontal axis is the electric field,
The vertical axis represents the amount of wavelength change with respect to the case where no bias is applied.

As shown in FIG. 2, as the electric field formed between the bias layer contact 11 and the n-type metal contact layer 12 increases, the voltage applied between the bias layer contact 11 and the n-type metal contact layer 12 increases. The magnitude of the strain generated will also increase. When the magnitude of this strain increases,
The amount of change with respect to the wavelength of the emitted laser light when the bias is not applied is also large.

As described above, according to this embodiment, the active layer is made of the organic material, and the organic active layer can be strained by applying a bias to the organic active layer. Due to this strain, the band gap or the refractive index of the organic active layer changes, and the wavelength of the laser light emitted by this can be controlled.

(Second Embodiment) FIG. 3 is a sectional view showing the overall structure of an organic semiconductor light emitting device according to a second embodiment of the present invention. This embodiment relates to a modification of the first embodiment,
It relates to an embodiment in which the DBR layers formed above and below the organic active layer 5 are each non-conductive.

In the figure, 21 is a substrate, and a buffer layer 22, a non-conductive DBR layer 23,
The n-type clad layer 24 is sequentially laminated and formed. The organic active layer 25 is formed on the n-type cladding layer 24.
The p-type cladding layer 26 and the p-type cladding layer 26 are sequentially laminated and selectively formed, and the surfaces of both end portions of the n-type cladding layer 24 are exposed. A clad layer contact 27 is formed on the exposed surface of the n-type clad layer 24.

On the p-type clad layer 26, a SiO ₂ block layer 28 and a highly conductive bias layer 29 are sequentially laminated and selectively formed, and both end surfaces of the p-type clad layer 26 are exposed. ing. A clad layer contact 30 is formed on the exposed surface of the p-type clad layer 26.

The clad layer contact 30 provided on the clad layer 26 which is the p-type region is easily formed similarly to the p-type clad layer 6 of the first embodiment, but the n-type clad which is the electron supply layer is formed. The formation of the cladding layer contact 27 provided on the layer 24 is difficult. The clad layer contact 27 is made of Mg / Ag, Mg / Au, Li / Ag,
It is formed using a contact material such as Li / Au or LiF / Al.

A non-conductive DBR layer 31 is selectively formed on the high-conductivity bias layer 29, and both end surfaces of the high-conductivity bias layer 29 are exposed. A bias layer contact 32 is formed on the exposed surface of the highly conductive bias layer 29.

The non-conductive DBR layer 23 has a DBR mirror structure formed by alternately stacking two different semiconductor layers 23a and 23b, and the non-conductive DBR layer 31.
Similarly, it has a structure formed by alternately stacking two different semiconductor layers 31a and 31b.

The same material and manufacturing method are used for the same structure as the first embodiment.

The first characteristic point of the present embodiment is the non-conductivity D.
A SiO ₂ block layer 28 and a highly conductive bias layer 29 are formed between the BR layer 31 and the active layer 25, and a bias layer contact 32 is formed on the exposed surface of the highly conductive bias layer 29. It is in. This point is similar to the first embodiment, but the way to apply the bias for distorting the organic active layer 5 is different. In the first embodiment, a bias is applied between the n-type metal contact 12 formed on the back surface of the substrate 1 and the bias contact 11 via the n-type DBR layer 3 formed below the organic active layer 5. However, in this embodiment, a bias is applied between the cladding layers 24 and 26 without the intermediary of the electrically non-conductive DBR layer 23 formed below the organic active layer 25.

The second feature of this embodiment is that the DBR layer formed under the organic active layer 25 is also non-conductive. In the first embodiment, the DBR layer formed under the organic active layer 25 is a conductive layer, but it can be replaced with the non-conductive DBR layer 23 as in the present embodiment.
As described above, even if the DBR layer below the organic active layer 25 is used as a non-conductive layer, the current can be uniformly injected into the organic active layer 25.

As described above, according to this embodiment, even when both the DBR layers formed on the upper side and the lower side of the organic active layer 25 are made non-conductive layers, the same effect as that of the first embodiment can be obtained. Play.

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

As described above in detail, according to the present invention, it is possible to obtain a light emitting device capable of generating a light wavelength that can be tuned in a wavelength range larger than that obtained by the conventional device structure.

[Brief description of drawings]

FIG. 1 is a sectional view showing an overall configuration of an organic semiconductor light emitting device according to a first embodiment of the invention.

FIG. 2 is a diagram showing a relationship curve between an electric field and a wavelength change amount according to the same embodiment.

FIG. 3 is a diagram showing an overall configuration of an organic semiconductor light emitting device according to a second embodiment of the invention.

FIG. 4 is a cross-sectional view showing the overall configuration of a conventional surface emitting semiconductor laser.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... n-type substrate 2 ... n-type contact layer 3 ... n-type DBR layer 4 ... n-type clad layer 5 ... organic active layer 6 ... p-type clad layer 7 ... SiO ₂ block layer 8 ... highly conductive bias layer 9 ... clad Layer contact 10 ... Non-conductive DBR layer 11 ... Bias layer contact 12 ... N-type metal contact layer 21 ... Substrate 22 ... Buffer layer 23 ... Non-conductive DBR layer 24 ... Clad layer 25 ... Clad layer contact 26 ... Clad layer 27 ... Cladding layer contact 28 ... SiO ₂ blocking layer 29 ... Highly conductive bias layer 30 ... Cladding layer contact 31 ... Non-conducting DBR layer 32 ... Bias layer contact

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 33/00 H05B 33/00-33/28 H01S 5/00-5/50

Claims (2)

(57) [Claims] 1. An organic active layer made of an organic material, a lower carrier diffusion layer formed on the lower surface of the organic active layer and supplying carriers to the organic active layer, and formed on the upper surface of the organic active layer. An upper carrier diffusion layer for supplying carriers having a conductivity type opposite to that of the lower carrier diffusion layer to the organic active layer, an insulating layer formed on the upper carrier diffusion layer, and an insulating layer formed on the insulating layer. A conductive layer made of a transparent conductive material, wherein light is generated in the organic active layer by passing a current between the lower carrier diffusion layer and the upper carrier diffusion layer, An organic semiconductor light emitting device, characterized in that a strain is applied to the organic active layer by applying a voltage between a carrier diffusion layer and the conductive layer. 2. The organic semiconductor light emitting device according to claim 1, wherein each of the lower carrier diffusion layer and the upper carrier diffusion layer is made of a conductive polymer oriented parallel to an interface with the organic active layer. apparatus.