JP4911082B2 - Display device and lighting device - Google Patents

Description

  The present invention relates to a display device and an illumination device, and more particularly to a light-emitting element using a nitride III-V compound semiconductor and a display device and an illumination device using a phosphor excited by light emitted from the light-emitting element. It is suitable for application.

  Since GaN-based semiconductors are direct transition semiconductors, and their forbidden band ranges from 1.9 eV to 6.2 eV, it is possible to realize a light-emitting element capable of emitting light from the visible region to the ultraviolet region. It has attracted attention and its development is actively underway.

  As an apparatus using such a GaN-based light emitting element, an all-color image display apparatus has been proposed (Japanese Patent Laid-Open No. 8-63119). In this all-color image display device, phosphors emitting three primary colors of red, green and blue are excited by a GaN-based light emitting diode array arranged on a substrate, respectively, or red and green are respectively emitted by a GaN-based light emitting diode array. A green phosphor is excited, and light emission of a GaN-based light emitting diode is used for blue.

  On the other hand, as a next-generation display device, high brightness and high resolution are desired. Of these, since the luminance is determined by the output of the light emitting diode and the quantum efficiency of the phosphor, a phosphor having a higher quantum efficiency is desired. In addition, since the resolution is determined by the size of the pixel, when the fluorescent screen is formed by applying a fluorescent material, the size of the phosphor crystal particles must be reduced in accordance with the size of the pixel.

JP-A-8-63119

  However, in general, near the phosphor crystal surface, non-radiative recombination due to surface states is dominant, and hardly contributes to light emission. For this reason, the quantum efficiency decreases as the crystal grains of the phosphor are made smaller. In particular, it is said that this decrease is remarkable when the particle diameter is about 1 μm or less.

  It is also possible to form a phosphor screen by forming a phosphor material by epitaxial growth, vacuum deposition, sputtering, etc., but with these methods, light propagates in a guided manner within the phosphor surface having a large refractive index. However, there is an inconvenience that light is not easily emitted outside.

  For the above reasons, it has been difficult to realize a high-luminance and high-resolution display device using a GaN-based light emitting element.

  Accordingly, an object of the present invention is to provide a display device with high brightness, high resolution, low power consumption, and a low profile.

  Another object of the present invention is to provide a high-luminance, low power consumption, thin, all-solid-state lighting device.

  When the crystal size is reduced to about the exciton Bohr radius (hereinafter such crystals are called “nanocrystals”), exciton confinement and band gap increase due to quantum size effects are observed (J. Chem. Phys. , Vol. 80, No. 9, p. 1984). Some semiconductors of this size have been reported to have high quantum efficiency in photoluminescence (Phys. Rev. Lett., Vol. 72, No. 3, p. 416, 1994, MRSbulletin Vol. .23, No. 2, p. 18, 1998 and US Pat. No. 5,455,489). This effect will be described by taking Mn-doped ZnS (ZnS: Mn) that is easy to compare because the emission wavelength does not change due to the quantum size effect. Table 1 shows a comparison of luminance of light emission when ZnS: Mn nanocrystals surface-treated with methacrylic acid and bulk ZnS: Mn particles having a particle diameter of 1 μm or more are excited by the same ultraviolet lamp. It can be seen from Table 1 that the ZnS: Mn nanocrystals have a luminance nearly five times higher than that of the bulk ZnS: Mn particles.

Table 1
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Nanocrystal bulk
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Luminance 69 cd / m ² 14.2 cd / m ²
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The physical relationship between the high quantum effect and the quantum size effect has not yet been clearly explained, but the increase in the oscillator strength due to the formation of electron-hole pairs and the energy level quantum This is thought to be related to a decrease in the density of states that does not contribute to light emission due to crystallization, the effect of changes in the crystal field near the light emission center due to crystal lattice distortion, crystal surface treatment, and the like. It is not clear which of these elements contributes effectively to the luminous efficiency, but an increase in luminous efficiency has been reported for crystals having a size less than the exciton Bohr radius described below. Here, the exciton Bohr radius indicates the spread of the existence probability of excitons, and 4πε ₀ h ² / me ² (where ε ₀ is the low-frequency dielectric constant of the material, h is the Planck constant, m is the electron and The converted mass obtained from the effective mass of holes, e is the charge of electrons). For example, the exciton Bohr radius of ZnS is about 2 nm.

  An example of the most typical quantum size effect is an increase in the band gap. FIG. 1 shows the crystal size dependence of the band gap of ZnS calculated based on the theory of L.E.Brus et al. Since the original band gap of ZnS is about 3.5 eV, it can be predicted that the quantum size effect will increase in a range smaller than about 8 nm in diameter. This diameter value corresponds to a crystal having a radius twice the exciton Bohr radius. Therefore, the contribution of the quantum size effect to light emission can be utilized by using a phosphor made of a crystal having a size of twice or less the exciton Bohr radius.

  On the other hand, in a crystal not subjected to surface treatment, electrons excited by dangling bonds of ions existing on the surface are captured and recombined without light emission, so that the emission intensity is remarkably reduced. For example, as shown in Table 2, in the case of ZnS: Mn nanocrystals surface-treated with acrylic acid, dangling bonds on the crystal surface are effectively terminated, and the emission intensity is remarkably increased as compared with a sample that is not surface-treated. ing. In addition, as shown in FIG. 2, in the CdSe nanocrystal capped with ZnS, not only dangling bonds on the crystal surface are terminated, but also the electron-hole pair is formed by taking a quantum well structure. It is strongly confined in the crystal and recombines. With this material, a luminous efficiency that is one digit higher than that of CdSe nanocrystals without capping is obtained, and a quantum efficiency of about 50% is obtained.

Table 2
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Surface treatment Acrylic acid
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Luminance 69 cd / m ² 9.4 cd / m ²
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A case where ZnSe quantum dots are used as the phosphor will be described. Originally, ZnSe has a band gap of 2.58 eV at room temperature, but when the crystal size is reduced to a grain size of about 8.5 ± 1.5 nm, the band gap increases to about 2.8 eV due to the quantum size effect, and the wavelength is around 435 nm. Band edge emission is observed at (Fig. 3). Since the exciton Bohr radius of ZnSe is about 4 nm, the crystal grain size of this phosphor is considered to be approximately the same. This phosphor induces a chemical reaction by irradiating ultraviolet rays, so that dangling bonds on the crystal surface can be terminated, and the reactants generated on the crystal surface serve as potential barriers, making it an ideal quantum well. A structure can be formed. For this reason, the light emission intensity can be remarkably increased by ultraviolet treatment as shown in FIG.

  FIG. 3 shows an excitation spectrum (excitation wavelength dependence of emission intensity) of this phosphor. From FIG. 3, peaks are observed at wavelengths of 270 nm and 370 nm. Of these, the peak at 370 nm on the long wavelength side corresponds to the band gap of GaN, so that this phosphor is excited by an ultraviolet light emitting diode using GaN or GaInN in which GaN is doped with In as an active layer material. High luminous efficiency can be obtained. Also, the half-value width of the emission peak is very narrow, about 20 nm for ZnSe quantum dots, compared to the ZnS: Ag of 60 nm with a particle size of several μm used in conventional blue phosphors. Can be realized.

On the other hand, for green and red phosphors, the band gap is reduced by using Zn _1-x Cd _x Se (where 0 <x ≦ 1) quantum dots in which part of ZnSe is substituted with Cd. be able to. In this Zn _1-x Cd _x Se quantum dot, light emission with a desired wavelength can be obtained by changing the composition ratio or crystal size of Zn and Cd. A full color display can be realized by using light emission of these direct interband transitions.

  Furthermore, by using a white phosphor in which a red phosphor, a green phosphor and a blue phosphor composed of nanocrystals as described above are mixed, the white phosphor is excited by the light of a GaN-based light emitting diode, thereby producing a white phosphor. A lighting device can be obtained.

As described above, there are phosphors made of microcrystals that exhibit quantum size effects, that is, nanocrystals, that exhibit very large quantum efficiency. Therefore, such phosphors can be excited with an ultraviolet light emitting element. Thus, an efficient display device and lighting device can be realized.
The present invention has been devised based on the above studies by the present inventors.

  That is, in order to achieve the above object, the first invention of the present invention has a light emitting element using a nitride III-V group compound semiconductor and a phosphor excited by light emitted from the light emitting element. In the display device, the phosphor is made of a crystal having a particle size not larger than twice the exciton Bohr radius.

  According to a second aspect of the present invention, there is provided a lighting device having a light emitting element using a nitride III-V compound semiconductor and a phosphor excited by light emitted from the light emitting element, wherein the phosphor is excited. It is an illuminating device characterized by comprising a crystal having a particle size not larger than twice the child Bohr radius.

In the present invention, preferably, dangling bonds on the surface of the crystal constituting the phosphor are terminated. Moreover, typically, the crystal constituting the phosphor has a quantum well structure.
In the present invention, the light emitting elements are typically arranged in a one-dimensional or two-dimensional array. Moreover, these light emitting elements are typically formed by growing a nitride III-V group compound semiconductor on a substrate such as a sapphire substrate, a SiC substrate, or a ZnO substrate.

  In the first aspect of the present invention, in a typical example, the phosphor includes a red phosphor, a green phosphor and a blue phosphor provided in the red light emitting portion, the green light emitting portion and the blue light emitting portion, respectively. A light emitting element is provided corresponding to each of the red phosphor, the green phosphor, and the blue phosphor, and the red phosphor, the green phosphor, and the blue phosphor are excited by light emitted from the light emitting element. Each is configured to emit red, green, and blue light. In another typical example, the phosphor is composed of a red phosphor and a green phosphor provided in the red light emitting portion and the green light emitting portion, respectively, and corresponds to each of the red phosphor and the green phosphor. The light emitting element is provided, the light emitting element is provided in the blue light emitting portion, and the red phosphor and the green phosphor are excited by the light emitted from the light emitting element to emit red and green, respectively, The light emitting element provided in the blue light emitting unit is configured to emit blue light directly.

  In the second aspect of the present invention, typically, the phosphor is a white phosphor in which a red phosphor, a green phosphor and a blue phosphor are mixed, and the white phosphor is constituted by light emitted from the light emitting element. The red phosphor, the green phosphor, and the blue phosphor are excited to emit red, green, and blue, respectively, thereby emitting white light.

In the present invention, the crystals constituting the red phosphor and the green phosphor are made of, for example, Zn _1-x Cd _x Se (where 0 <x ≦ 1), and the crystals constituting the blue phosphor are made of, for example, ZnSe.

  In this invention, the nitride-based III-V group compound semiconductor contains at least one group III element selected from the group consisting of Ga, Al, In and B, and at least N, and optionally further contains As or P. It consists of the V group element to contain. Specific examples of the nitride III-V group compound semiconductor include GaN, AlGaN, AlN, GaInN, AlGaInN, InN, and the like.

  According to the first invention of the present invention configured as described above, since the phosphor is made of a crystal having a particle size equal to or less than twice the exciton Bohr radius, the nitride III-V compound semiconductor is used. The quantum efficiency of the phosphor can be increased by exciting the phosphor with the light emitted from the light emitting element, and the resolution can be increased due to the extremely small size of the crystal constituting the phosphor. .

  According to the second invention of the present invention configured as described above, since the phosphor is made of a crystal having a particle size equal to or less than twice the exciton Bohr radius, a nitride III-V compound semiconductor is used. Exciting this phosphor with light emitted from the light emitting element can increase the quantum efficiency of the phosphor and obtain a more uniform illumination due to the extremely small size of the crystals constituting the phosphor. be able to.

According to the first aspect of the present invention, the phosphor is made of a crystal having a particle size equal to or less than twice the exciton Bohr radius, thereby realizing a high-luminance, high-resolution, low power consumption, thin display device. be able to.
According to the second aspect of the present invention, since the phosphor is made of a crystal having a particle size equal to or less than twice the exciton Bohr radius, a high-luminance, low power consumption, and thin lighting device can be realized. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings of the embodiments, the same or corresponding parts are denoted by the same reference numerals.

  FIG. 5 shows a color display device according to the first embodiment of the present invention. As shown in FIG. 5, in the color display device according to the first embodiment, GaN light emitting diodes 2 are arranged in a two-dimensional array on a sapphire substrate 1 having a size corresponding to the display area. . The emission wavelength of the GaN-based light emitting diode 2 is, for example, about 380 nm. For example, a sapphire substrate having a c-plane orientation is used. These GaN-based light emitting diodes 2 are separated from each other by a partition wall 3. An ultraviolet blocking filter 4 having the same size as that of the sapphire substrate 1 is provided in parallel with the sapphire substrate 1 so as to face the sapphire substrate 1 with the GaN-based light emitting diodes 2 interposed therebetween. On the main surface of the ultraviolet blocking filter 4 on the GaN-based light emitting diode 2 side, a phosphor is provided corresponding to each GaN-based light emitting diode 2. Specifically, three GaN-based light emitting diodes 2 adjacent to each other are taken as a set, and a red phosphor 5, a green phosphor 6 and a blue phosphor 7 are provided for each of these GaN-based light emitting diodes 2. Yes. Then, light emitted from the GaN-based light emitting diode 2 corresponding to each of the red phosphor 5, the green phosphor 6 and the blue phosphor 7 is irradiated and excited to emit red, green and blue, respectively. It is supposed to be. In this case, one pixel is formed by the set of red phosphor 5, green phosphor 6, and blue phosphor 7 and the corresponding set of GaN-based light emitting diodes 2.

An example of the structure of the GaN-based light emitting diode 2 is shown in FIG. As shown in FIG. 6, the GaN-based light emitting diode 2 includes a GaN buffer layer 21, an n-type GaN contact layer 22, an n-type AlGaN cladding layer 23, a Ga _1-x In _x N / Ga _1- on a sapphire substrate _1. The active layer 24, the p-type AlGaN cladding layer 25, and the p-type GaN contact layer 26 having a _y In _y N multiple quantum well structure are sequentially stacked. The n-type AlGaN cladding layer 23, the active layer 24, the p-type AlGaN cladding layer 25, and the p-type GaN contact layer 26 have a predetermined mesa shape. A p-side electrode 27 made of, for example, a Ti / Au film is in ohmic contact with the p-type GaN contact layer 26, and an n-side electrode 28 made of, for example, a Ti / Al film is formed on the n-type GaN contact layer 22 in ohmic contact. I'm in contact.

The formation of the GaN-based light emitting diode 2 is performed as follows. That is, after the GaN buffer layer 21 is grown on the sapphire substrate 1 at a temperature of, for example, about 560 ° C. by the metal organic chemical vapor deposition (MOCVD) method, the n-type is subsequently formed on the GaN buffer layer 21 by the MOCVD method. A GaN contact layer 22, an n-type AlGaN cladding layer 23, an active layer 24, a p-type AlGaN cladding layer 25, and a p-type GaN contact layer 26 are sequentially grown. Here, the growth temperature of the n-type GaN contact layer 22, the n-type AlGaN clad layer 23, the p-type AlGaN clad layer 25, and the p-type GaN contact layer 26, which are layers not containing In, is about 1000 ° C. The growth temperature of the active layer 24 of the Ga _{1 -x} In _x N / Ga _{1 -y} In _y N multiple quantum well structure is 700 to 800 ° C. Thereafter, the electrical activation of the n-type impurity and the p-type impurity doped in these layers, particularly the electrical activation of the p-type impurity doped in the p-type AlGaN cladding layer 25 and the p-type GaN contact layer 26 is performed. Heat treatment is performed. This heat treatment is performed at a temperature of 800 ° C. in a nitrogen gas atmosphere, for example. Next, after forming a resist pattern (not shown) having a predetermined stripe shape on the p-type GaN contact layer 26, the n-type GaN contact layer 22 is formed by, for example, reactive ion etching (RIE) using the resist pattern as a mask. Etch until reached. Thereafter, the resist pattern is removed. Next, a p-side electrode 27 is formed on the p-type GaN contact layer 26, and an n-side electrode 28 is formed on the n-type GaN contact layer 22. Next, after forming a resist pattern (not shown) having a predetermined stripe shape on the substrate surface, using this resist pattern as a mask, the GaN buffer layer 21, the n-type GaN contact layer 22, the n-type AlGaN cladding layer 23, Ga The active layer 24, p-type AlGaN cladding layer 25, and p-type GaN contact layer 26 having a _1-x In _x N / Ga _1-y In _y N multiple quantum well structure are etched. As described above, the GaN-based light emitting diodes 2 are formed in a two-dimensional array in a state of being separated from each other.

In this first embodiment, the red phosphor 5, for example, for example, x = 0.90 of particle size 6~10nm Zn _1-x Cd x Se consisting nanocrystal or Zn _1-x Cd x Se quantum dots Is used. As the green phosphor 6, for example, a nanocrystal made of Zn _1-x Cd _x Se having a particle diameter of 6 to 10 nm, for example, x = 0.38, or a Zn _1-x Cd _x Se quantum dot is used. . As the blue phosphor 6, a nanocrystal made of ZnSe having a particle diameter of about 6 to 10 nm or a ZnSe quantum dot is used.

  In the color display device according to the first embodiment configured as described above, a current corresponding to an input signal is injected into each GaN-based light-emitting diode 2, and red is generated by light generated from each GaN-based light-emitting diode 2. By exciting the phosphor 5, the green phosphor 6 and the blue phosphor 7, full color display can be performed.

  As described above, according to the first embodiment, the red phosphor 5, the green phosphor 6, and the blue phosphor 7 are both composed of crystals having a particle diameter equal to or smaller than the exciton Bohr radius, that is, nanocrystals. A full color flat display with high brightness, high resolution, and low power consumption can be realized.

  FIG. 7 shows a color display device according to a second embodiment of the present invention. As shown in FIG. 7, in the color display device according to the second embodiment, the blue phosphor 7 is not provided. The emission wavelength of the GaN-based light emitting diode 2 is about 460 nm. In this case, in the blue light emitting part, blue light emitted from the GaN-based light emitting diode 2 is directly emitted to the outside through the ultraviolet blocking filter 4. Others are the same as those of the color display device according to the first embodiment, and a description thereof will be omitted.

  According to the second embodiment, there are advantages similar to those of the first embodiment.

  FIG. 8 shows an illumination apparatus according to a third embodiment of the present invention. As shown in FIG. 8, in the illumination device according to the third embodiment, GaN-based light emitting diodes 2 are arranged in a two-dimensional array on a sapphire substrate 1 having a predetermined size. The emission wavelength of the GaN-based light emitting diode 2 is, for example, about 380 nm. As the sapphire substrate 1, for example, a c-plane substrate is used. These GaN-based light emitting diodes 2 are separated from each other by a partition wall 3. An ultraviolet blocking filter 4 having the same size as that of the sapphire substrate 1 is provided in parallel with the sapphire substrate 1 so as to face the sapphire substrate 1 with the GaN-based light emitting diodes 2 interposed therebetween. On the main surface of the ultraviolet blocking filter 4 on the GaN-based light emitting diode 2 side, a white phosphor 8 is provided corresponding to each GaN-based light emitting diode 2. The light emitted from the GaN-based light emitting diode 2 corresponding to the white phosphor 8 is irradiated and excited to emit white light.

  Since the structure and formation method of the GaN-based light emitting diode 2 are the same as those in the first embodiment, description thereof is omitted.

  In the third embodiment, as the white phosphor 8, three types of nanocrystals constituting the red phosphor 5, the green phosphor 6 and the blue phosphor 7 used in the first embodiment are mixed. What consists of things is used.

  According to the third embodiment, a flat illumination device with high brightness and low power consumption can be realized, and unlike a conventional illumination device, an illumination device that is all solid and has very high mechanical strength is realized. can do.

  As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, The various deformation | transformation based on the technical idea of this invention is possible.

  For example, the numerical values, structures, substrates, processes, and the like given in the first, second, and third embodiments described above are merely examples, and different numerical values, structures, substrates, processes, and the like may be used as necessary. It may be used.

It is a basic diagram which shows the crystal size dependence of the band gap energy of ZnS. It is sectional drawing and energy band figure which show a CdSe quantum dot. It is a basic diagram which shows the photo-luminescence spectrum and excitation spectrum which were measured at room temperature. It is an approximate line figure showing the photoluminescence intensity of a ZnSe quantum dot as a function of ultraviolet irradiation time. It is sectional drawing which shows the color display apparatus by 1st Embodiment of this invention. It is sectional drawing which shows the structural example of the GaN-type light emitting diode in the color display apparatus by 1st Embodiment of this invention. It is sectional drawing which shows the color display apparatus by 2nd Embodiment of this invention. It is sectional drawing which shows the illuminating device by 3rd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate, 2 ... GaN-type light emitting diode, 3 ... Partition, 4 ... Ultraviolet blocking filter, 5 ... Red fluorescent substance, 6 ... Green fluorescent substance, 7 ... Blue phosphor, 8 ... white phosphor

Claims (6)

A light emitting device that emits blue light using a nitride-based III-V compound semiconductor;
Having a phosphor excited by light emitted from the light emitting element,
The phosphor is made of a crystal made of Zn _1-x Cd _x Se (where 0 <x ≦ 1) having a particle diameter of 6 to 10 nm ,
The dangling bonds on the surface of the crystal are terminated,
The phosphor is composed of a red phosphor and a green phosphor provided in a red light emitting part and a green light emitting part, respectively, and the red phosphor and the green phosphor are excited by light emitted from the light emitting element, respectively. A display device configured to emit green light and to emit blue light from the light emitting element. The display device according to claim 1, wherein the crystal has a quantum well structure. The display device according to claim 1, wherein the light emitting elements are arranged in an array. A light emitting device that emits blue light using a nitride-based III-V compound semiconductor;
Having a phosphor excited by light emitted from the light emitting element,
Zn whose particle size is 6 to 10 nm _1-x Cd _x A crystal composed of Se (where 0 <x ≦ 1),
The dangling bonds on the surface of the crystal are terminated,
The phosphor is composed of a red phosphor and a green phosphor provided in a red light emitting part and a green light emitting part, respectively, and the red phosphor and the green phosphor are excited by light emitted from the light emitting element, respectively. An illumination device configured to emit green light and to emit blue light from the light emitting element. The lighting device according to claim 4, wherein the crystal has a quantum well structure. The lighting device according to claim 4 or 5, wherein the light emitting elements are arranged in an array.

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