JP4872096B2 - PHOTONIC CRYSTAL LIGHT EMITTING ELEMENT AND LIGHT EMITTING DEVICE - Google Patents

Description

  The present invention relates to a light emitting element such as a light emitting diode (LED) or a semiconductor laser (LD) that emits light by injecting carriers into an active medium arranged in a three-dimensional photonic crystal.

  A conventional general semiconductor light emitting device includes an electrode, a carrier conduction path, and an active layer. Hole carriers are injected from the p-type electrode and guided to the active layer via the p-type carrier conduction path. Electron carriers are injected from the n-type electrode and guided to the active layer via the n-type conduction path. Both injected carriers are combined in the active layer and emit spontaneous emission light having energy corresponding to the energy gap of the active layer. In particular, when a resonator is formed so as to include an active layer by a cleavage plane or the like, stimulated emission light is generated by light amplification by the resonator, and laser light is generated.

  However, not all carriers injected from the electrode contribute to light emission. It is consumed by non-radiative recombination, such as surface recombination, or by recombination that emits light of a wavelength other than the desired wavelength, and these are losses that reduce efficiency.

  In particular, as a method for reducing the loss due to recombination that emits light other than a specific wavelength, a method has been proposed in which spontaneous emission is controlled by a photonic crystal to obtain highly efficient light emission (Non-Patent Document 1). A photonic crystal is a structure in which a dielectric constant distribution is formed with a period having a length equal to or shorter than the wavelength of light. The method according to Non-Patent Document 1 suppresses spontaneous emission light other than a desired wavelength by limiting the wavelength range of light that can exist in the vicinity of the active layer, using the photonic band gap property of the photonic crystal. Is. Thus, in order to control spontaneous emission and obtain highly efficient light emission, a three-dimensional photonic crystal in which a dielectric constant distribution is three-dimensionally formed is desirable.

  Several structures have been proposed as three-dimensional photonic crystals (see Patent Documents 1 and 2). A configuration of a three-dimensional photonic crystal laser has been proposed (see Patent Document 3). In the three-dimensional photonic crystal laser disclosed in Patent Document 3, an active portion is formed in the three-dimensional photonic crystal, and a carrier is introduced into the photonic crystal from a metal electrode provided outside the photonic crystal via a contact layer. Inject. The injected carriers are conducted through the photonic crystal and are guided to the active part via the carrier conduction path formed by the linear defects. The carrier conduction path also serves as an optical waveguide, and light generated by carrier coupling in the active portion is extracted out of the photonic crystal through the optical waveguide.

Other three-dimensional photonic crystal light emitting elements are disclosed in Patent Documents 4 and 5.
US Pat. No. 5,335,240 JP 2005-292787 A JP 2001-257425 A US Pat. No. 5,406,573 US Pat. No. 5,998,298 Physical Review Letters, Vol. 58, pp. 2059, 1987

  In the structure disclosed in Patent Document 1, carriers injected from an electrode conduct in a three-dimensional photonic crystal formed by stacking a plurality of layers each having a columnar structure arranged in a cross-beam shape. As described above, when the carriers conduct in the cross beam structure, the cross-sectional area of the path through which the carriers conduct is smaller and the length is longer than that of the conventional semiconductor light emitting device, so that the series resistance of the conduction path with respect to the carrier is large. When the series resistance is large, the carrier is changed to heat or the like during conduction to cause loss, and the carrier injection efficiency is lowered.

  In addition, since the light extraction part to the outside of the light emitting element is a part corresponding to one of the columnar bodies constituting the photonic crystal, the mode diameter is smaller than the length of the emission wavelength, and the external optical element such as an optical fiber is connected. The optical coupling efficiency is very small.

  The present invention provides a three-dimensional photonic crystal light-emitting element that has high optical coupling efficiency with an external optical element and can efficiently inject carriers into an active portion (resonator).

  A three-dimensional photonic crystal light-emitting device according to one aspect of the present invention includes a point defect resonator formed in a photonic crystal and including an active medium, a first electrode for injecting carriers into the resonator, and a first electrode The second electrode is connected to the first electrode in the photonic crystal, and carriers are guided from the first electrode to the resonator, and light generated by the resonator is guided to the first electrode having translucency. And a conduction path. The conduction path is a tapered conduction path whose cross-sectional area increases from the resonator side toward the first electrode side.

  Note that a light-emitting device having the three-dimensional photonic crystal light-emitting element and voltage applying means for applying a voltage to the first and second electrodes also constitutes another aspect of the present invention.

  According to the present invention, it is possible to realize a highly efficient light-emitting element that has high optical coupling efficiency with an external optical element and can efficiently inject carriers into the resonator.

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

  FIG. 1 shows a cross-sectional structure of a three-dimensional photonic crystal light emitting device (hereinafter simply referred to as a light emitting device) that is Embodiment 1 of the present invention.

  The light-emitting element 10 includes a three-dimensional photonic crystal 20, a p-type electrode (first electrode) 30, a tapered carrier conduction path (tapered conduction path) 40, a p-type region 50, an active portion 60, It has an n-type carrier conduction region 70, an n-type electrode (second electrode) 80, and an insulating part 90.

  The active portion 60 is a point defect resonator formed as a point defect including an active medium in the three-dimensional photonic crystal 20.

  The p-type electrode 30 for injecting hole carriers (p-type carriers) into the active part 60 has translucency. In the following description, the p-type electrode is referred to as a p-type transparent electrode.

  A voltage is applied between the p-type transparent electrode 30 and the n-type electrode 80 for injecting electron carriers into the active part 60 by an electric circuit 110 as voltage applying means. The light emitting device 10 and the electric circuit 110 constitute a light emitting device. Although not shown, this is the same in other embodiments described later.

  In this embodiment, the p-type transparent electrode 30 is described as the first electrode, but the n-type electrode 80 may be used as the first electrode. In the present embodiment, the case where only the p-type transparent electrode 30 has translucency will be described. However, the n-type electrode 80 may also have translucency.

  The tapered carrier conduction path 40 is formed as a line defect having a tapered structure (tapered shape) connected to (in contact with) the p-type electrode 30 in the three-dimensional photonic crystal. The tapered carrier conduction path 40 functions as an optical waveguide that guides carriers from the p-type transparent electrode 30 to the active part 60 and guides light generated at the active part 60 to the p-type transparent electrode 30.

  In the tapered carrier conduction path 40, the cross-sectional area on the p-type electrode side is larger than the cross-sectional area on the active part side (resonator side) (the cross-sectional area is from the active part side to the p-type electrode side (first electrode side)). It has a taper structure (increasing toward).

  The three-dimensional photonic crystal 20 has a structure in which a dielectric constant distribution is formed in a three-dimensional direction with a period equal to or less than the wavelength of light. For example, the three-dimensional photonic crystal 20 has a structure disclosed in Patent Documents 1 and 2.

  Specifically, in the three-dimensional photonic crystal 20, a plurality of first structures each extending in the first direction are periodically arranged in a second direction orthogonal to the first direction at intervals. Having a first layer and a third layer. In addition, a plurality of second structures each extending in the second direction includes a second layer and a fourth layer that are periodically arranged in the first direction at intervals. The first to fourth layers, which are a plurality of layers having these two-dimensional periodic structures, are stacked in this order.

  The first structure included in the first layer and the first structure included in the third layer are arranged with a half-cycle shift in the second direction, and the second structure included in the second layer The second structure included in the fourth layer is arranged with a half-cycle shift in the first direction.

  The first to fourth layers may sandwich an additional layer including at least one layer in which the third structures are discretely arranged in a plane parallel to each layer. The third structure is arranged at a position where the first structure and the second structure intersect three-dimensionally (a position corresponding to the intersection).

  Of the three-dimensional photonic crystal, the first and second structures (and the third structure) are formed of the first medium, and the portions other than these structures are more than the first medium. It is formed of a second medium (such as air) having a low refractive index.

  As the first medium, a semiconductor such as InP, GaAs, GaN, or TiO 2 is used. The p-type region and the n-type region are formed by doping the first medium. Zn, Mg, or the like is used as the p-type dopant, and Si, S, or the like is used as the n-type dopant. When TiO2 is used as the first medium, the p-type region is formed by strong reduction. For increasing the resistance, methods such as oxidation and nitriding are used.

  The tapered carrier conduction path 40 is formed to extend in the stacking direction of the first to fourth layers, and the cross-sectional area changes in the stacking direction as described above.

  The active medium is selected according to the wavelength to be oscillated. For example, it can be selected from InGaAsP, AlGaAs, AlGaInP, AlGaN, InGaN, ZnSe, ZnS-based multiple quantum well structure or multiple quantum dot structure, an organic material, and the like.

  Hole carriers injected from the p-type transparent electrode 30 are guided to the active part 60 via the tapered carrier conduction path 40 and the p-type region 50. In addition, the electron carriers injected from the n-type electrode 80 are guided to the active part 60 through the n-type carrier conduction region 70 to form an inversion distribution.

  The insulating part 90 forms a current confinement structure and efficiently injects carriers into the active part 60.

  In the active portion 60, hole carriers and electron carriers are combined to generate spontaneously emitted light having energy corresponding to the energy gap of the active medium. This light resonates in the active part 60 as a resonator, so that stimulated emission occurs, and amplified laser light is generated from the active part 60.

  Laser light generated in the active portion 60 is optically coupled to the tapered carrier conduction path 40 and propagates through the tapered carrier conduction path 40. The laser light passes through the p-type transparent electrode 30 and is emitted to the outside of the light emitting element 10.

  A carrier conduction path formed with a basic structure that does not include defects of a conventional photonic crystal has a small cross-sectional area of the conduction path and a long distance. The series resistance value in the conduction path is proportional to the length and inversely proportional to the cross-sectional area. For this reason, in the conventional structure, the series resistance value for carrier conduction is very high, the consumption of carriers in the conduction path is large, and the carrier injection efficiency is low.

  On the other hand, when the tapered carrier conduction path 40 is used as in the present embodiment, the length of the conduction path can be shortened and the cross-sectional area can be increased. Therefore, the series resistance value for carrier conduction can be reduced, and the carrier injection efficiency can be increased.

  Furthermore, since the tapered carrier conduction path 40 also functions as a tapered optical waveguide, the mode diameter of light emitted from the light emitting element can be increased. Thereby, the optical coupling efficiency with external optical elements, such as an optical fiber, can be improved.

  Here, a specific example in which the series resistance value and the carrier injection efficiency are improved in this embodiment will be described. For example, if the mode diameter of light emitted from the light emitting element is expanded to about 6 μm, which is the same as that of a single mode fiber, by the taper structure of the tapered carrier conduction path 40, the cross-sectional area of the conduction path is about 10 times that of the conventional structure. The length is about 1/3. Thereby, the series resistance value by a conduction path becomes about 1/30.

  Further, since the tapered carrier conduction path 40 is connected to the p-type transparent electrode 30 on the terminal side having a large cross-sectional area, the contact area with the electrode is about three times larger than the conventional structure. Therefore, coupled with the small series resistance value in the conduction path, carrier injection efficiency about 90 times that of the conventional carrier injection efficiency can be realized.

  As described above, in this embodiment, carriers are injected into the active part 60 through the n-type transparent electrode 30 and the tapered carrier conduction path 40, and the light generated in the active part 60 functions as an optical waveguide. The light-emitting element 10 is taken out through the tapered carrier conduction path 40. As a result, it is possible to obtain a light emitting element that has high optical output efficiency with respect to the injected current and good optical coupling efficiency with the external optical element.

  In this embodiment, the case where the tapered carrier conduction path 40 is provided in the p-type region 50 has been described. However, a similar tapered carrier conduction path may be formed in the n-type region. However, in particular, it is more desirable to use as a carrier conduction path in the p-type region 50 having low carrier mobility and high resistance to carrier conduction.

  In the present embodiment, the case where stimulated emission is caused by resonance in the active portion 60 to cause laser oscillation has been described. However, the light-emitting element of the present invention does not necessarily have to be a laser element, and has a broadened wavelength. You may apply to small resonator type LED.

  FIG. 2 shows a cross-sectional structure of a light emitting device that is Embodiment 2 of the present invention.

  In the light emitting device 11 of the present embodiment, reference numeral 51 denotes a portion (tapered carrier conduction path) between the tapered carrier conduction path 40 and the active portion 60 in the p-type region 50 in which the tapered carrier conduction path 40 is formed. 40 and a portion for connecting the active part 60). In the present embodiment, the portion 91 of the p-type region 50 other than the portion 51 is formed of a medium having a higher resistance to carrier conduction than the medium forming the tapered carrier conduction path 40. And different.

  In this example, the same reference numerals as those in Example 1 are given to portions having the same functions as those of the light emitting element 10 in Example 1, and the description thereof is omitted.

  Thus, by increasing the resistance of the portion 91 of the p-type region 50, a current confinement structure can be formed and hole carriers can be efficiently injected into the active portion 60. In particular, the tapered carrier conduction path 40 has a large contact area with the n-type transparent electrode 30, and can suppress the expansion of the carrier accompanying conduction of hole carriers. For this reason, hole carriers can be concentrated in the vicinity of the active portion 60. Thereby, the loss of carriers in the region other than the active portion 60 can be suppressed, and the optical output with respect to the injected current can be increased.

  When the tapered carrier conduction path is formed in the n-type region corresponding to the n-type carrier conduction region 70, the part other than the part between the carrier conduction path and the active part 60 in the n-type region is subjected to carrier conduction. You may form with the medium whose resistance value is higher than the medium which forms a path | route.

  In the first and second embodiments, the case where the tapered carrier conduction path 40 is formed so as to extend in the stacking direction of a plurality of layers constituting the photonic crystal has been described. However, as in the light emitting element 12 illustrated in FIG. , And may be formed to extend in a direction parallel to each layer. In this case, the p-type transparent electrode 30 and the n-type electrode 80 are also formed on both sides of the photonic crystal 20 in a direction parallel to each layer.

  FIG. 4 shows a cross-sectional structure of a light-emitting element that is Embodiment 3 of the present invention. In the light emitting element 10 of Example 1, the case where optical coupling is directly performed between the active portion 60 and the tapered carrier conduction path 40 has been described. On the other hand, in the light emitting element 13 of this embodiment, optical coupling is performed via the line defect waveguide 52.

  In this example, the same reference numerals as those in Example 1 are given to portions having the same functions as those of the light emitting element 10 in Example 1, and the description thereof is omitted.

  The line defect waveguide 52 is formed as a line defect in the three-dimensional photonic crystal 20 and functions as an optical waveguide and a carrier conduction path. By appropriately setting the shape and position of the line defect, the line defect is guided as an optical waveguide that propagates light in a single guided mode and propagates light having a waveguide mode pattern close to unimodality. The waveguide 52 can function. As a result, the line defect waveguide 52 converts the mode pattern of light by coupling the resonance mode of the point defect resonator constituting the active portion 60 to a waveguide mode close to unimodality.

  Thereafter, the line defect waveguide 52 couples light to the tapered carrier conduction path (tapered optical waveguide) 40, and gradually increases the mode diameter as the light propagates. Thereby, a unimodal emission light pattern can be obtained.

  As described above, since the mode pattern of light can be controlled by the line defect waveguide 52, the active portion 60 that is a point defect resonator and the tapered carrier conduction path 40 that is a tapered waveguide are directly optically coupled. Compared with the case of making it, a unimodal emission light pattern can be easily obtained. This increases the degree of freedom in the resonant mode of the point-defect optical resonator and the guided mode of the tapered waveguide and increases the degree of freedom in designing each structure, enabling a stronger light confinement effect and efficient light extraction. It becomes.

  Like the light emitting element 11 of Example 2, like the light emitting element 14 shown in FIG. 5, the waveguide 52, of the p-type region 50 in which the tapered carrier conduction path 40 and the line defect waveguide 52 are formed, The portion 92 other than the portion 53 between the waveguide 52 and the active portion 60 may be increased in resistance. Thereby, a current confinement structure can be formed, and hole carriers can be efficiently injected into the active portion 60.

  FIG. 6 shows a cross-sectional structure of a light-emitting element that is Embodiment 4 of the present invention. The light emitting element 15 of this embodiment has an antireflection structure (antireflection film) 100 including the p-type transparent electrode 30.

  In this example, the same reference numerals as those in Example 1 are given to portions having the same functions as those of the light emitting element 10 in Example 1, and the description thereof is omitted.

  The antireflection structure 100 includes a first thin film formed of a medium having a first refractive index, and a second thin film formed of a medium having a second refractive index lower than the first refractive index. Are stacked alternately or in a specific pattern. The p-type transparent electrode 30 constitutes a part of the first and second thin films.

  By using such an antireflection structure 100, reflection at the interface between the light emitting element 15 and the outside can be suppressed, and highly efficient light extraction can be realized.

  The antireflection structure 100 may be formed as a single-layer antireflection film in which the optical thickness of the p-type transparent electrode 30 is set to ¼ of the emission wavelength.

  Next, a method for manufacturing a tapered carrier conduction path of the light emitting element described in each of the above embodiments will be described.

  First, as shown in FIG. 7A, the basic structure 110 of a photonic crystal that does not include a defect structure disclosed in Patent Document 1 or Patent Document 2 is disclosed in Patent Document 4 or Patent Document 5. The method is used.

  The basic structure 110 is formed of a medium 120 that constitutes a photonic crystal and a sacrificial medium 130 that is removed in a later process described later. The sacrificial medium 130 suppresses the influence of mechanical damage in the laminating process and the processing process described later.

  Next, as shown in FIG. 7B, the region corresponding to the tapered carrier conduction path is removed by ablation using an energy beam such as FIB or GCIB, or a multiphoton absorption process by an ultrashort pulse laser, and the holes 140 are removed. Form.

  Next, as shown in FIG. 7C, the tapered carrier conduction path 150 is collectively formed by filling the holes 140 by MOCVD, MBE, sputtering, or the like.

  Thereafter, the sacrificial medium 130 is removed by wet etching or the like, whereby the tapered carrier conduction path 150 can be formed in the photonic crystal.

  By forming the taper structure in a lump, as shown in FIG. 8, the two-dimensional pattern 160 including the taper structure cross section is formed and laminated, as compared with the case where the taper structure 170 is formed. Contact failure can be avoided and resistance can be reduced. Thereby, an increase in the series resistance of the carrier conduction path can be suppressed, and more efficient carrier injection can be performed.

  However, the present invention includes a case where the tapered carrier conduction path is formed so that the cross-sectional area changes stepwise as shown in FIG.

  Also, when the line defect waveguide shown in FIGS. 4 and 5 is included in the photonic crystal, contact failure at the stacked interface is avoided by forming the taper type carrier conduction path and the line defect waveguide in a lump. Therefore, more efficient carrier injection is possible.

  Further, in the light-emitting element described in each embodiment, a tapered structure that functions as a carrier conduction path and an optical waveguide is provided in the stacking direction in a three-dimensional photonic crystal formed by stacking layers including a two-dimensional periodic structure. The light is extracted in the stacking direction. Thus, a uniform p-type semiconductor or n-type semiconductor can be used as a material (medium) constituting each layer. For this reason, when forming each layer, complicated processes such as selective growth and partial ion implantation are not required, and it is possible to form a film in a lump or to form a periodic structure. Can be easily.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

1 is a cross-sectional view of a three-dimensional photonic crystal light-emitting element that is Embodiment 1 of the present invention. Sectional drawing of the three-dimensional photonic crystal light-emitting element which is Example 2 of this invention. Sectional drawing which shows the modification of the three-dimensional photonic crystal light emitting element of Example 2. FIG. Sectional drawing of the three-dimensional photonic crystal light-emitting element which is Example 3 of this invention. Sectional drawing which shows the modification of the three-dimensional photonic crystal light emitting element of Example 3. FIG. Sectional drawing of the three-dimensional photonic crystal light-emitting element which is Example 4 of this invention. The figure explaining the manufacturing method of the three-dimensional photonic crystal light emitting element demonstrated as Example 5 of this invention. The figure explaining the said manufacturing method. The figure explaining the said manufacturing method. The figure which shows the case where a taper structure is formed by laminating | stacking a two-dimensional pattern.

Explanation of symbols

10 to 15 3D photonic crystal light emitting device 20 3D photonic crystal 30 p-type transparent electrode 40 tapered carrier conduction path 50 p-type region 60 active part (resonator)
70 n-type carrier conduction region 80 n-type electrode 90 insulating portion

Claims (7)

A light emitting device using a three-dimensional photonic crystal,
A point defect resonator formed in the photonic crystal and containing an active medium;
A first electrode and a second electrode for injecting carriers into the resonator;
Connected to the first electrode in the photonic crystal, guides carriers from the first electrode to the resonator, and guides light generated by the resonator to the first electrode having translucency. A conduction path,
The three-dimensional photonic crystal light-emitting element, wherein the conduction path is a tapered conduction path whose cross-sectional area increases from the resonator side toward the first electrode side. Having a line defect waveguide formed in the photonic crystal;
2. The three-dimensional photonic crystal light emitting device according to claim 1, wherein the line defect waveguide and the tapered conductive path guide light generated by the resonator to the first electrode. 3. The first electrode is a p-type electrode;
3. The three-dimensional photonic crystal light emission according to claim 1, wherein p-type carriers are injected from the first electrode into the resonator through the tapered conduction path. element. In the p-type region or the n-type region where the tapered conductive path is formed in the photonic crystal, a portion other than the portion between the tapered conductive path and the resonator constitutes the tapered conductive path. 4. The three-dimensional photonic crystal light-emitting element according to claim 1, wherein the three-dimensional photonic crystal light-emitting element is formed of a medium having a higher resistance value to carrier conduction than a medium to perform. The three-dimensional photonic crystal is configured by laminating a plurality of layers including a two-dimensional periodic structure,
5. The three-dimensional photonic crystal light-emitting element according to claim 1, wherein the tapered conductive path is formed so as to extend in a stacking direction of the plurality of layers. 6. The three-dimensional photonic crystal light-emitting element according to claim 1, further comprising an antireflection structure including the first electrode. A three-dimensional photonic crystal light-emitting device according to any one of claims 1 to 6,
A light emitting device comprising voltage applying means for applying a voltage to the first and second electrodes.