JP2017152637A - Heat radiation light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat radiation light source excellent in wavelength selectivity, and capable of controlling the intensity of light with high speed of responce.SOLUTION: A heat radiation light source 10 includes a tabular base 11 provided with an n-layer 112 composed of an n-type semiconductor and a p-layer 113 composed of a p-type semiconductor so as to sandwich a quantum well structure layer 111, i.e., a layer having a quantum well structure, a photonic crystal part 12 provided on the surface of the base 11, and formed of lone members (first lone member 121, second lone member 122) arranged periodically so that the light of a wavelength, corresponding to the transition energy between subbands in the quantum well of the quantum well structure layer 111 will resonate, and voltage application means (power supply 14) provided on the base 11, and applying a voltage to the quantum well structure layer 111.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heat radiation light source. A heat radiation light source is a device that uses an electromagnetic wave radiated by heat radiation as a light source, but can be regarded as a heat-light conversion device that receives heat and outputs light (electromagnetic waves). When this input heat is given by electromagnetic waves (infrared rays), it can also be regarded as a wavelength converter. Moreover, it can also be regarded as a device that generates thermal radiation by supplying electric energy instead of heat. The “thermal radiation light source” in the present invention targets both of them.

  The thermal radiation light source has an advantage that light can be obtained simply by applying heat to an object. The thermal radiation light source can be used as a light source for various sensors using infrared rays, for example, and is particularly suitable as a light source for converting engine waste heat into infrared rays for sensing in a gas sensor for analyzing components in engine exhaust gas. Can be used.

  An electromagnetic wave emitted from an object to which heat is applied has a spectrum extending in a wavelength range depending on the temperature. For example, the wavelength range of electromagnetic waves obtained by heating an object to several tens of degrees Celsius to several hundreds of degrees Celsius is several μm to several tens of μm, and the higher the temperature is, the wider the range is on the short wavelength side. However, since the above-described infrared sensor generally uses only infrared light having a specific wavelength, using such a heat radiation light source irradiates the object to be measured with unnecessary infrared light other than the specific wavelength, Adverse effects such as being heated occur. In addition, when heat radiation is generated by inputting electric energy, an increase in power consumption becomes a problem in a light source that generates broadband radiation.

  In order to solve such problems, Patent Document 1, Non-Patent Document 1, and Non-Patent Document 2 propose a heat radiation light source in which a quantum well structure is formed in a photonic crystal. A photonic crystal has a periodic refractive index distribution and can form a standing wave of light having a specific wavelength corresponding to the period. A quantum well structure is a structure in which a well-type energy potential (quantum well) is formed by laminating a plurality of semiconductor layers having a thickness of several nanometers to several tens of nanometers with different energy band gaps. Refers to the structure.

  In Patent Document 1, a photonic crystal in which holes are periodically provided in a slab (plate material) having a quantum well structure is mainly used. In this photonic crystal, since the slab and the holes have different refractive indexes, a periodic refractive index distribution is formed. On the other hand, Non-Patent Document 1 and Non-Patent Document 2 use a configuration in which a photonic crystal in which isolated members having a quantum well structure are periodically arranged is arranged on a base. Since the isolated member has a refractive index different from that of the surrounding space (air), a periodic refractive index distribution is formed together with the surrounding space. As the isolated member, a plurality of members extending upward from the upper surface of the base are isolated and arranged two-dimensionally, or a plurality of members that are long in a direction parallel to the upper surface of the base are isolated and parallel to each other. Some of them are arranged in a dimension (in the latter example, it can be said that the isolated member extends upward from the front of the base together with the direction parallel to the top surface of the base). Hereinafter, the photonic crystal described in Patent Document 1 is referred to as “hole-type photonic crystal”, and the photonic crystals described in Non-Patent Document 1 and Non-Patent Document 2 are referred to as “isolated member-type photonic crystals”.

  In the thermal radiation light source described in each of these documents, when heat is supplied from the heat source, transitions between multiple discrete energy levels (subbands) formed in the quantum well of the quantum well structure (between subbands) Transition) occurs, and light emission having a finite wavelength band centered on the wavelength corresponding to the transition energy occurs. In the photonic crystal provided with the quantum well structure, light having one wavelength determined by the period of the photonic crystal resonates and is amplified. Thereby, the thermal radiation light source described in each document can generate light having a wavelength spectrum having a sharp peak at the specific wavelength.

  Moreover, in the thermal radiation light source of patent document 1, the electrode is provided in the front and back both surfaces of the slab. In this thermal radiation light source, by applying a voltage to the quantum well structure using the electrode, the number of electrons or holes in the quantum well can be changed, thereby controlling the intensity of light of the specific wavelength. it can. The intensity of light changes depending on the intensity of heat applied to the quantum well structure, but the speed is extremely slow, and high-speed modulation operation reaching 1 MHz is possible only by controlling using voltage as in Patent Document 1. become.

International Publication WO2015 / 129668

Takuya Inoue et al., "Design of single-mode narrow-bandwidth thermal emitters for enhanced infrared light sources", Journal of the Optical Society of America B, (USA), Optical Society of America (American Optical Society), January 2013, Vol. 30, No. 1, pp. 165-172 Takuya Inoue et al., “Single-peak narrow-bandwidth mid-infrared thermal emitters based on quantum wells and photonic crystals”, Applied Physics Letters, (USA), published by American Institute of Physics, May 13, 2013, Vol. 102, No. 19, 191110-1 to 191110-4

  When calculations and experiments are performed with a thermal radiation light source using a hole-type photonic crystal and a thermal radiation light source using an isolated member type photonic crystal, the latter is narrower in the wavelength spectrum and the target Light emission close to a single wavelength is generated, which includes almost no unnecessary radiation peak other than the wavelength. This is because the direction of the electric field of the light generated by the intersubband transition of the quantum well coincides with the direction in which the isolated member physically extends because the isolated member extends upward, and as a result, the resonance wavelength of the photonic crystal This is because it becomes easy to control the radiation peak (set the resonance wavelength to a predetermined value) and to enhance the radiation peak generated by the resonance. Therefore, a thermal radiation light source using an isolated member type photonic crystal is more desirable in terms of wavelength selectivity. However, in the thermal radiation light source using the isolated member type photonic crystal described in Non-Patent Documents 1 and 2, voltage cannot be applied to the quantum well structure, and the light intensity can be controlled at a fast response speed. Can not.

  The problem to be solved by the present invention is to provide a thermal radiation light source that has excellent wavelength selectivity and can control the intensity of light with a fast response speed.

The thermal radiation light source according to the present invention made to solve the above problems is
a) a plate-like base provided with an n layer made of an n-type semiconductor and a p layer made of a p-type semiconductor so as to sandwich a quantum well structure layer which is a layer having a quantum well structure;
b) Photonics comprising isolated members arranged periodically so that light of a wavelength corresponding to the transition energy between subbands in the quantum well in the quantum well structure layer provided on the surface of the base resonates. A crystal part;
c) voltage applying means for applying a voltage to the quantum well structure layer connected to the base.

  Conventionally, in a thermal radiation light source using a photonic crystal, in order to amplify light of a specific wavelength generated by supplying heat to the quantum well structure, a quantum well structure is provided inside the photonic crystal that controls light resonance. It was thought that it was necessary to establish. However, as a result of verification by the present inventors through calculations and experiments, in a thermal radiation light source using an isolated member type photonic crystal, even if the quantum well structure is provided on the base outside the photonic crystal, the quantum inside the base is It was revealed that light of a specific wavelength generated from the well structure resonates in combination with the periodic refractive index distribution of the photonic crystal.

  In the present invention, the quantum well structure is provided in the base as described above, and the number of electrons or holes in the quantum well is changed by providing the base with voltage applying means for applying a voltage to the quantum well structure layer. Thereby, it is possible to control the intensity of light generated from the quantum well structure during the heating and resonating in the photonic crystal part.

  In the photonic crystal part (isolated member type photonic crystal), there are two-dimensionally arranged isolated members extending vertically from the surface of the base, or a plurality of members that are long in the direction parallel to the upper surface of the base. Thus, those arranged in a one-dimensional manner in parallel with each other can be used.

  In a photonic crystal in which a single isolated member is periodically arranged, the time for which light remains in the photonic crystal due to excessively strong light diffraction effects in free space due to resonance of all the isolated members in the same phase. May be shortened. Since the time during which light stays in the photonic crystal and the line width of the obtained emission spectrum are inversely proportional, in the case of the above structure, the emission line width may be widened. On the other hand, in photonic crystals in which two or more different types of isolated members are periodically arranged, it is possible to resonate light in opposite phases between different isolated members, and the light diffraction effect can be offset appropriately. Light is confined in the photonic crystal part for a long time, and an emission spectrum with a narrow line width is finally obtained. Therefore, it is desirable that the photonic crystal part has two or more types of isolated members having different shapes or sizes.

  In order to increase the intensity of light having a specific wavelength that is generated in the quantum well structure and resonates in the photonic crystal part, the surface side surface of the base of the quantum well structure layer is as close as possible to the surface. For example, it is desirable that the thickness be 100 nm or less.

In a thermal radiation light source having a quantum well structure, the output of light generated in the quantum well structure can be increased as the heating temperature is increased. In addition, the higher the heating temperature, the wider the wavelength band of light emission from the quantum well structure (especially on the short wavelength side), and the amplification by resonance by setting the period length of the photonic crystal part accordingly. The range of wavelengths to be selected can be widened. Therefore, in the thermal radiation light source according to the present invention, it is desirable to use a quantum well structure made of a nitride semiconductor having excellent heat resistance. By using a nitride semiconductor, the heating temperature can be increased to about 600 ° C. For example, compared with the case where GaAs (maximum heating temperature capable of voltage control is about 250 ° C) is used for the quantum well structure, The output can be increased about 10 times. In addition, by using a nitride semiconductor in the quantum well structure, the emission wavelength band can be set to a wide range of _{2 to 10} μm, so that CO ₂ (absorption wavelength 4.3 μm), CO (4.8 μm), CH ₄ (3.3μm) It can be used as a light source for sensing various gases and compounds. As the nitride semiconductor, GaN, InN, AlN, or a mixed crystal thereof can be used.

  The isolated member is preferably made of a semiconductor material that is not doped with electrons or holes. Thereby, unnecessary broadband light emission derived from free carrier absorption can be suppressed.

The element for heat radiation light source according to the present invention is:
a) a plate-like base provided with an n layer made of an n-type semiconductor and a p layer made of a p-type semiconductor so as to sandwich a quantum well structure layer which is a layer having a quantum well structure;
b) Photonics comprising isolated members arranged periodically so that light of a wavelength corresponding to the transition energy between subbands in the quantum well in the quantum well structure layer provided on the surface of the base resonates. And a crystal part.

  According to the present invention, it is possible to obtain a thermal radiation light source capable of controlling the intensity of light with a fast response speed using an isolated member type photonic crystal having excellent wavelength selectivity.

The perspective view (a) which shows one Embodiment of the thermal radiation light source concerning this invention, AA 'sectional drawing (b), and BB' sectional drawing (c) of a photonic crystal part. The figure which shows the energy state of the electron in the state (a) which has not applied the voltage between electrodes, and the state (b) which applied the thermal radiation light source which concerns on this invention. The graph which shows the result of having calculated | required the emissivity of the light in the state (solid line) and the state (dashed line) which have not applied the voltage between electrodes about the thermal radiation light source of this embodiment. For the thermal radiation light source using an isolated member made of the same material as the n layer of the base, the emissivity of light in the state where no voltage is applied between the electrodes (solid line) and in the state where it is applied (broken line) was calculated. The graph which shows a result. The graph which shows the result of having calculated | required the emissivity of light in the several example from which the thickness of n layer and p layer differs regarding the heat radiation light source of this embodiment. The perspective view (a) and CC 'sectional drawing (b) which show other embodiment of the thermal radiation light source which concerns on this invention. With respect to the heat radiation light source of another embodiment, the emissivity of light in a state where no voltage is applied between the electrodes (solid line) and in a state where the voltage is applied (broken line) is expressed as E _x polarized light (a) and E _y polarized light (b). The graph which shows the result calculated | required by dividing into.

  1 to 7 show an embodiment of a thermal radiation light source according to the present invention.

(1) Configuration of Embodiment of Thermal Radiation Light Source According to the Present Invention FIG. 1 shows an embodiment of a thermal radiation light source according to the present invention. This thermal radiation light source 10 has a base 11 and a photonic crystal portion 12 provided on the surface of the base 11, and electrodes (n layer 112 and A p-layer 113) is provided.

  The base 11 has a structure in which both front and back surfaces of a plate-like quantum well structure 111 are sandwiched between an n layer 112 made of an n-type semiconductor and a p layer 113 made of a p-type semiconductor. The n layer 112 is provided closer to the photonic crystal part 12 than the quantum well structure 111, and the p layer 113 is provided on the opposite side.

In this embodiment, the quantum well structure 111 includes a GaN layer in which electrons are doped (1 × 10 ¹⁸ cm ⁻³ ) in GaN, and Al _1-x Ga _x N (0 <x <1). A structure in which 50 layers of AlGaN layers made of Al _0.4 Ga _0.6 N with = 0.6 and not doped with electrons or holes are alternately stacked is used. The thickness of each GaN layer and AlGaN layer is 3 nm. GaN and Al _0.4 Ga _0.6 N have overlapping band gaps, and since GaN has a smaller band gap than Al _0.4 Ga _0.6 N, a quantum well with the GaN side at the bottom is formed, and a subband is formed in GaN. . Here, the number of Al atoms per N atom in the AlGaN layer (1-x) is not limited to the above value, but as the value of (1-x) increases (the value of x decreases) Since the difference in the size of the band gap increases, light emission with higher energy (short wavelength) can be obtained. On the other hand, if the value of (1-x) exceeds 0.4, dislocations and cracks may occur during production. Therefore, in the present embodiment, the value of (1-x) is set to 0.4.

In this embodiment, the n layer 112 is made of GaN doped with electrons (5 × 10 ¹⁸ cm ⁻³ ), and the p layer 113 is doped with holes (1 × 10 ¹⁸ cm ⁻³ ). Each made of GaN is used. The thickness d ₁ of the n layer 112 is 50 nm, and the thickness d ₂ of the p layer 113 is 250 nm. In contrast to the above embodiment, a p layer may be provided closer to the photonic crystal part 12 than the quantum well structure 111, and an n layer may be provided on the opposite side. The thickness of the semiconductor layer (n layer 112 in the example of FIG. 1) provided between the quantum well structure 111 and the photonic crystal portion 12 is preferably as small as possible, and is preferably 100 nm or less, for example.

The photonic crystal portions 12 are arranged in a square lattice shape having a periodic length a so that a columnar first isolated member 121 having a radius r ₁ and a thickness d is erected on the surface of the base 11, and has a radius r _2. Cylindrical second isolated members 122 having a thickness d are arranged in a square lattice with a periodic length a so as to stand on the surface. Each second isolated member 122 is disposed at a position shifted by a / 2 from the first isolated member 121 in each of two directions in which the first isolated member 121 is arranged at a lattice length of a square lattice with a periodic length a. In this embodiment, the period length a is 3.0 μm, the radius r ₁ is 0.23 a (= 0.69 μm), the radius r ₂ is 0.18 a (= 0.54 μm), and the thickness d is 1.2 μm. Both the first isolated member 121 and the second isolated member 122 are made of GaN that is not doped with electrons or holes.

  The n layer 112 is connected to the negative electrode of the power source 14, and the p layer 113 is connected to the positive electrode of the power source 14. The n layer 112 and the p layer 113 function as electrodes. The power supply 14 corresponds to the above-described voltage applying means. A switch 15 is provided in a circuit connecting the thermal radiation light source 10 and the power source 14.

(2) Operation of Thermal Radiation Light Source of the Present Embodiment Operation of the thermal radiation light source 10 of the present embodiment will be described with reference to FIG.
In the thermal radiation light source 10, since electrons are doped in the GaN layer corresponding to the bottom of the quantum well of the quantum well structure 111, the thermal radiation light source 10 is heated from the heat source with the switch 15 being OFF. Electrons transition between subbands formed in the quantum well, and light emission in a finite wavelength band centering on the wavelength corresponding to the transition energy is generated (FIG. 2 (a)). Of the light in this wavelength band, only light having a specific wavelength corresponding to the periodic length of the photonic crystal part 12 is resonated and amplified in the photonic crystal part 12 and emitted to the outside of the thermal radiation light source 10. The

  When the switch 15 is switched from OFF to ON, the electrons doped in the quantum well structure 111 move to the n layer 112, thereby reducing the number of electrons in the quantum well (FIG. 2 (b)). Thereby, the intensity of the light from the quantum well structure 111 is reduced, and the intensity of the light that is resonated and amplified by the photonic crystal portion 12 and emitted to the outside of the thermal radiation light source 10 is also reduced. In this way, the intensity of light emitted to the outside of the thermal radiation light source 10 by turning OFF / ON of voltage application between the n layer 112 and the p layer 113 (that is, to the quantum well structure 111) as electrodes. Can be controlled.

In the present embodiment, since the first isolated member 121 and the second isolated member 122 having different radii are arranged with the periodic length a, the in-medium wavelength λ _i corresponding to the periodic length a in the photonic crystal portion 12. Light having (= 3.0 μm) is amplified. The light having the wavelength has a wavelength λ of (n _eff λ _i / n _a ) in the air. Where n _eff is the effective refractive index felt by the light within the photonic crystal 12, the n _a is the refractive index of air (= 1). The effective refractive index n _eff depends on the refractive indexes of the materials of the first isolated member 121 and the second isolated member 122 and the volume ratio that they occupy in the photonic crystal portion 12. Further, when the photonic crystal portion 12 is thin, the refractive index of the base 11 may affect the effective refractive index n _eff . The effective refractive index n _eff is calculated (simulated) based on these parameters or obtained by conducting a preliminary experiment.

  In the present embodiment, since the first and second isolated members 121 and 122 having different radii are used, the light resonates between the different isolated members in an opposite phase, and the light diffraction effect is appropriately offset. Therefore, light is confined in the photonic crystal for a long time. As a result, an emission spectrum having a narrow line width is obtained.

For the thermal radiation light source 10 of the present embodiment, the emissivity of light to the outside in a state where no voltage is applied between the electrodes (OFF state) and an applied state (ON state) was obtained by calculation. The results are shown graphically in FIG. Here, the emissivity is a value obtained by normalizing the heat radiation intensity of the light source with the black body radiation intensity at the same temperature. The horizontal axis of the graph indicates the wave number of light in air (the reciprocal of the wavelength). From this result, there is a strong peak at a wave number of about 2500 cm ^-1 and a wavelength of about 4 μm in the OFF state, whereas in the ON state, the peak height at the same wave number (same wavelength) is slight. It can be confirmed that the intensity of the light is controlled by the voltage OFF / ON. The peak Q value when OFF is 105. It should be noted that there is a weak peak at a wave number other than about 2500 cm ⁻¹ , which is due to free carrier absorption of the n layer 112 and the p layer 113, and the intensity thereof is a heat radiation light source described in Patent Document 1. Weaker than.

  Next, the material of the first isolated member 121 and the second isolated member 122 is made of the same material as that of the n layer 112 (electron doped) instead of the above-described GaN not doped with electrons and holes (undoped GaN). The same calculation was performed for GaN). This configuration corresponds to the case where the first isolated member 121 and the second isolated member 122 and the n layer 112 are manufactured integrally. The calculation results are shown in FIG. In the OFF state, a similar strong peak exists at the same wave number as in the case of undoped GaN, whereas in the ON state, a stronger peak appears at the same wave number than in the case of undoped GaN, although it is weaker than the OFF state. This is considered to be caused by light emission due to free carrier absorption in the first isolated member 121 and the second isolated member 122. From this result, it can be said that it is desirable to use a semiconductor material that is not doped with electrons or holes for the isolated member in order to switch the intensity of light more clearly.

Next, assuming that the thickness of the n layer 112 is d ₁ nm, the thickness of the p layer 113 is d ₂ = (300−d ₁ ) nm, and the thickness of the quantum well structure 111 is constant (300 nm), d ₁ is 50 to 250 nm. Calculations were made for different cases within the range. The calculation results are shown in FIG. As the n layer 112 is thicker, that is, as the position of the quantum well structure 111 is further away from the photonic crystal portion 12, the light output becomes weaker. In particular, when d ₁ is 150 nm or more, the emissivity decreases significantly.

(3) Other Embodiment of Thermal Radiation Light Source According to the Present Invention FIG. 6 shows another embodiment of the thermal radiation light source according to the present invention. The thermal radiation light source 20 has a base 11 having the same configuration as described above. A photonic crystal portion 22 is provided on the surface of the base 11 on the n layer 112 side. The photonic crystal portion 22 is formed by alternately arranging parallelepiped rod-shaped first isolated members 221 and second isolated members 222 on the surface of the base 11. An interval (period length) a between adjacent first isolated members 221 and adjacent second isolated members 222 is 3.1 μm. The width W ₁ of the first isolated member 221 is 0.27a (= about 0.84 μm), and the width W ₂ of the second isolated member 222 is 0.18a (= about 0.56 μm). The heights of the first isolated member 221 and the second isolated member 222 from the base 11 are both 1.2 μm. The material of the first isolated member 221 and the second isolated member 222 is undoped GaN. These numerical values and materials are examples, and can be changed as appropriate.

For the heat radiation light source 20 of the present embodiment, the emissivity of light to the outside in the OFF state and the ON state was obtained by calculation. In this calculation, the first isolated member 221 and the second isolated member 222 have an infinite length. The calculation is based on polarized light whose electric field oscillates in the width direction of the first isolated member 221 and the second isolated member 222 (referred to as “E _x polarized light”) and polarized light whose electric field oscillates in the length direction (“E _y polarized light”). To go). The calculation results are shown in FIG. E _x polarization is strong peak is observed in the vicinity of wave number 2500 cm ^-1 (wavelengths 4 nm) in the OFF state, the peaks are weakened in the ON state. The Q value in the OFF state was 116. E _y polarization contrast, strong peaks at both the OFF and ON states was observed. As described above, the thermal radiation light source 20 can generate linearly polarized light ( _Ex polarized light) whose electric field oscillates in the width direction of the first isolated member 221 and the second isolated member 222 and can emit the light to the outside. The intensity of the light can be controlled.

DESCRIPTION OF SYMBOLS 10, 20 ... Thermal radiation light source 11 ... Base 111 ... Quantum well structure 112 ... n layer 113 ... p layer 12, 22 ... Photonic crystal part 121, 221 ... 1st isolation member 122, 222 ... 2nd isolation member 14 ... Power supply 15 ... Switch

Claims (8)

a) a plate-like base provided with an n layer made of an n-type semiconductor and a p layer made of a p-type semiconductor so as to sandwich a quantum well structure layer which is a layer having a quantum well structure;
b) Photonics comprising isolated members arranged periodically so that light of a wavelength corresponding to the transition energy between subbands in the quantum well in the quantum well structure layer provided on the surface of the base resonates. A crystal part,
c) A thermal radiation light source, comprising: a voltage applying means for applying a voltage to the quantum well structure layer connected to the base.   2. The thermal radiation light source according to claim 1, wherein the photonic crystal portion includes two or more kinds of the isolated members having different shapes or sizes.   The thermal radiation light source according to claim 1 or 2, wherein the surface of the base of the quantum well structure layer is located at a position separated from the surface by 100 nm or less.   The thermal radiation light source according to claim 1, wherein the quantum well structure layer is made of a nitride semiconductor.   The thermal radiation light source according to claim 4, wherein the quantum well structure layer includes GaN. 6. The heat according to claim 5, wherein the quantum well structure layer is formed by alternately laminating a layer made of GaN and a layer made of Al _1-x Ga _x N (0 <x <1). Radiation light source.   The thermal radiation light source according to claim 1, wherein the isolated member is made of a semiconductor material that is not doped with electrons or holes. a) a plate-like base provided with an n layer made of an n-type semiconductor and a p layer made of a p-type semiconductor so as to sandwich a quantum well structure layer which is a layer having a quantum well structure;
b) Photonics comprising isolated members arranged periodically so that light of a wavelength corresponding to the transition energy between subbands in the quantum well in the quantum well structure layer provided on the surface of the base resonates. A thermal radiation light source element comprising a crystal part.