JP6410679B2 - Gas sensor - Google Patents

Description

  The present invention relates to a gas sensor, and more particularly to a gas sensor capable of correcting the temperature of the concentration of a measurement gas more easily than in the past.

  Conventionally, as a gas sensor that measures the concentration of the gas to be measured in the atmosphere, the non-dispersed red is used to measure the concentration of the gas by detecting the amount of absorption by utilizing the difference in the wavelength of the infrared rays absorbed by the type of gas. An external absorption type (NDIR-Dispersive Infrared, NDIR type) gas sensor is known. As a gas concentration measurement device using this principle, for example, an infrared light source, a filter (transmission member) that transmits infrared light limited to a wavelength at which the measurement target gas has an absorption characteristic, and an infrared sensor are combined, and the amount of infrared absorption is reduced. A gas concentration can be measured by measuring (Patent Document 1).

JP-A-9-33431

However, in the NDIR gas sensor, the light emission amount of a light source that emits light including infrared rays and the output of the infrared sensor vary depending on the ambient temperature of the surroundings. In particular, compound semiconductor diodes that are attracting attention as light sources and sensors for small NDIR gas sensors are known to have large changes in light emission intensity and light receiving sensitivity due to temperature. When measuring the gas concentration using the output of the infrared sensor, it is necessary to correct the output change due to the ambient temperature of the light source and the infrared sensor, but generally 3 to 4 points or more are required to correct the change. Therefore, it is necessary to perform output correction using the calibration environment, and the burden of both testing time and cost is large.
The present invention has been made in view of such problems, and an object of the present invention is to provide a gas sensor capable of temperature correction of the concentration of the measurement gas more easily than in the past.

According to a first aspect of the present invention, there is provided a gas cell, a light emitting diode disposed in the gas cell, and an electric signal that is disposed in the gas cell and outputs an electrical signal corresponding to the amount of light including infrared rays from the light emitting diode. 1 photodiode, a second photodiode that outputs a reference signal of the output of the first photodiode and that has the same semiconductor laminated structure as the first photodiode, and is disposed in the gas cell, An optical filter that narrows the wavelength of light incident on the first photodiode to an absorption band of a measurement target gas; and an arithmetic unit to which outputs from the first and second photodiodes are input . The output of the first photodiode is corrected using the output of the second photodiode, and the output of the first photodiode is corrected based on the corrected output of the first photodiode. The gas sensor for detecting the concentration, Ri said light emitting diode and the active layer is _{Al x In (1-x)} Sb (0.004 ≦ x ≦ 0.100) der each of the first and second photodiodes, The peak of the spectrum obtained by multiplying the emission intensity of the light emitting diode and the spectral sensitivity of the second photodiode when the wavelength at the long wavelength end of the half width of the transmission characteristic of the optical filter is the maximum value in the operating temperature range of the gas sensor. The gas sensor is shorter than the wavelength .

  According to the present invention, it is possible to realize a gas sensor whose temperature is corrected more simply than in the past.

It is a block diagram for demonstrating embodiment of the gas sensor which concerns on this invention. It is process drawing (the 1) for demonstrating the manufacturing method of the gas sensor which concerns on a present Example. It is process drawing (the 2) for demonstrating the manufacturing method of the gas sensor which concerns on a present Example. It is process drawing (the 3) for demonstrating the manufacturing method of the gas sensor which concerns on a present Example. It is process drawing (the 4) for demonstrating the manufacturing method of the gas sensor which concerns on a present Example. It is process drawing (the 5) for demonstrating the manufacturing method of the gas sensor which concerns on a present Example. It is a block diagram for demonstrating embodiment of the gas sensor which concerns on this embodiment.

Hereinafter, modes for carrying out the present invention (hereinafter referred to as the present embodiment) will be described. The following embodiments do not limit the invention according to the claims. In addition, not all the combinations of features described in the embodiments are essential for the solving means of the invention.
<Gas sensor>
The gas sensor of the present embodiment includes a gas cell, a light emitting diode disposed in the gas cell, a first photodiode that is disposed in the gas cell and outputs an electrical signal corresponding to the amount of light including infrared light from the light emitting diode, , An optical filter disposed in the gas cell, for narrowing the wavelength of light incident on the first photodiode to the absorption band of the measurement target gas, a reference signal output from the first photodiode, and the first photo A gas sensor comprising: a second photodiode having a semiconductor structure identical to the diode; and an arithmetic unit to which outputs from the first and second photodiodes are input. The active layer of each photodiode is Al _x In _(1-x) Sb (0.004 ≦ x ≦ 0.100), and the optical filter is 4. The wavelength having the maximum transmittance between 1 and 4.4 μm and the wavelength having the maximum transmittance is shorter than the maximum value of the spectral sensitivity characteristics of the first and second photodiodes. The wavelength is 5 μm or less, and the temperature is corrected from the correlation between the correction signal obtained by correcting the output of the first diode and the temperature using the output of the second diode as a reference sensor, and the gas concentration It is a gas sensor which outputs.

According to the gas sensor according to the present embodiment, it is possible to provide a gas sensor capable of correcting the temperature with high accuracy with a smaller number of test points than before. Further, in the gas sensor of the present embodiment, the measurement target gas may be carbon dioxide. Since the light emitting diode and photodiode of the present invention are excellent in light emission intensity and light receiving sensitivity in the vicinity of 4.3 μm, which is the peak of light absorption of carbon dioxide gas, the influence of absorption by carbon dioxide can be detected with high S / N. It is possible to measure the gas concentration with high accuracy.
<Gas cell>
In the gas sensor of the present embodiment, the gas cell is not particularly limited as long as the gas to be detected can be introduced. In other words, it only has to have an inlet for the gas to be detected. From the viewpoint of improving the accuracy of real-time detection of the gas to be detected, it is preferable to provide an outlet in addition to the inlet. The introduction port and the discharge port may be provided with a filter that prevents intrusion of dust and the like and does not block gas in / out. The material constituting the gas cell is not particularly limited. For example, materials such as metal, glass, ceramics, and stainless steel can be used, but not limited thereto. From the viewpoint of improving detection sensitivity, a material having a low absorption coefficient of light output from the light emitting diode and a high reflectance is preferable. Specifically, a metal case made of aluminum, an alloy containing aluminum, gold, silver, or a resin case coated with a laminate of these is preferable. From the viewpoint of reliability and change with time, a resin casing coated with gold or an alloy layer containing gold is preferable.

<Light emitting diode>
In the gas sensor according to the present embodiment, the light emitting diode outputs light including a wavelength absorbed by the measurement target gas, and the active layer is a diode having a PIN structure of Al _x In _1-x Sb, The Al composition of the layer satisfies 0.004 ≦ x ≦ 0.100. Here, when the Al composition of the active layer of the light emitting diode is in the range of 0.004 ≦ X ≦ 0.100, it has a strong emission intensity near 4.3 μm that is the peak of light absorption of carbon dioxide gas, At the same time, it is possible to obtain a light source suitable for a gas concentration measuring device capable of easily correcting the temperature of the concentration of the measuring gas. In addition, the upper limit of the Al composition of the active layer of the light emitting diode is preferably X ≦ 0.090, more preferably X from the viewpoint of having a stronger emission intensity in the vicinity of 4.3 μm, which is the light absorption peak of carbon dioxide gas. ≦ 0.080, more preferably X ≦ 0.070, more preferably X ≦ 0.060, more preferably X ≦ 0.050, and even more preferably X ≦ 0.040.

  In addition, the n layer and the p layer are compound semiconductors including at least one group III atom selected from the group consisting of In, Al, and Ga and at least one group V atom selected from the group consisting of Sb and As. Is preferable, and InSb or AlInSb is more preferable. As a result, it is possible to realize a light emitting diode having more suitable light emission characteristics near the light absorption peak of carbon dioxide gas of 4.3 μm.

  In addition, the light emitting diode may be formed on a substrate, and in the light emitting diode element of the present invention, the substrate is not particularly limited as long as a desired semiconductor laminated portion can be formed thereon. An example is crystal growth on a Si, GaAs, GaP, or InP substrate, but is not limited thereto. The crystal plane has (100), (111), (110) directions, and the like. In the infrared region, a substrate such as GaAs or Si is suitable as a substrate used in the present invention because it exhibits a high transmittance with respect to the absorption wavelength of the gas to be measured. When AlInSb is used as the material of the semiconductor stacked portion, GaAs is preferable as the substrate. It is also preferable that the light emitting diodes are connected in series or in parallel by wiring in order to increase the light emission intensity.

  The driving of the light emitting diode is not particularly limited as long as the signal of the photodiode as the light receiving sensor can be appropriately obtained. Specifically, it can be controlled by current, voltage, power or the like. In addition, since the light emitting diode generates heat during light emission, and the heat generation can be an acceleration factor for deterioration, it is preferable to drive under conditions that do not generate heat as much as possible by intermittent driving such as pulse driving. When pulse driving is performed, a photodiode signal with less noise can be obtained by obtaining a photodiode signal synchronized with the driving frequency of the light emitting diode.

<Photodiode>
In the gas sensor according to the present embodiment, the photodiode is a diode whose active layer has a PIN structure of Al _x In _1-x Sb, and the Al composition of the active layer has a relationship of 0.004 ≦ x ≦ 0.100. And outputs an electrical signal corresponding to the received infrared ray. Here, when the Al composition of the active layer of the photodiode is in the range of 0.004 ≦ X ≦ 0.100, it has a strong light receiving sensitivity in the vicinity of 4.3 μm that is the peak of light absorption of carbon dioxide gas, At the same time, it is possible to obtain a light source suitable for a gas concentration measuring device capable of easily correcting the temperature of the concentration of the measuring gas. In addition, the upper limit of the Al composition of the active layer of the photodiode is preferably X ≦ 0.090, more preferably X from the viewpoint of having higher light receiving sensitivity in the vicinity of 4.3 μm, which is the peak of light absorption of carbon dioxide gas. ≦ 0.080, more preferably X ≦ 0.070, more preferably X ≦ 0.060, more preferably X ≦ 0.050, and even more preferably X ≦ 0.040. Here, for the sake of convenience, the Al composition of the active layer of the light emitting diode and the Al composition of the active layer of the photodiode are represented by the same letter x, but each is within the range of 0.004 ≦ X ≦ 0.100. Either value may be adopted separately or may have the same composition. Further, the photodiode preferably has the same laminated structure and material as the light emitting diode. Thereby, it is possible to realize a photodiode more suitable for detection in the vicinity of 4.3 μm, which is the peak of light absorption of carbon dioxide gas.

  The photodiode may be formed on a substrate, and in the photodiode element of the present invention, the substrate is not particularly limited as long as a desired semiconductor laminated portion can be formed thereon. An example is crystal growth on a Si, GaAs, GaP, or InP substrate, but is not limited thereto. The crystal plane has (100), (111), (110) directions, and the like. In the infrared region, a substrate such as GaAs or Si is suitable as a substrate used in the present invention because it exhibits a high transmittance with respect to the absorption wavelength of the measurement target gas. When AlInSb is used as the material of the semiconductor stacked portion, GaAs is preferable as the substrate. The second photodiode that outputs the reference signal may be formed on the same substrate as the light-emitting diode. The shape of the photodiode is not particularly limited as long as sufficient S / N (signal / noise) can be obtained. It is also preferable that a plurality of units are connected in series for noise reduction.

<Optical filter>
In the gas sensor according to the present embodiment, the optical filter transmits infrared rays in a wavelength region where absorption of infrared rays by the measurement target gas occurs. The optical filter may be an interference filter made of a multilayer film of materials having different refractive indexes. As a specific example of the optical filter, an interference structure in which materials having different refractive indexes (for example, Ge, ZnSe, ZnS, SiO2, etc.) are alternately laminated on a substrate transparent to infrared rays can be used. Depending on the wavelength, the incident light can be strengthened or weakened by the interference phenomenon, and only specific light can be strongly reflected. These laminated structures may be formed on both sides of the substrate of the optical filter, or may be on one side. Specific examples of this substrate include GaAs, Si, and sapphire. A specific example of the interference filter is an interference filter in which a thin film of Ge and ZnS is alternately stacked on both surfaces of a Si substrate having a high transmittance and several cycles to several tens of cycles are stacked. By using such a structure, it is possible to realize a strong reflectance (for example, 80% or more) only at some wavelengths and a structure that transmits other wavelengths.

When the detection target gas is carbon dioxide, the wavelength at which the optical filter has the maximum transmittance is preferably 4.1 to 4.4 μm.
Here, the optimum wavelength range in which the filter has the maximum transmittance has been described. However, depending on the design of the gas cell, the incident angle of the light transmitted through the filter may or may not be vertical. On the other hand, the wavelength having the maximum transmittance may vary depending on the incident angle depending on the structure, material, design, and temperature of the optical filter. Needless to say, the “wavelength having the maximum transmittance” described in the present invention takes into consideration the incident angle determined by the optical path design of the gas cell. For example, when the incident angle is 30 degrees with respect to the vertical, the wavelength indicates the maximum transmittance at the incident angle of 30 degrees.

<Temperature measurement unit>
The gas sensor according to the present embodiment may further include a temperature measurement unit (not shown) that measures the temperature of the measurement target gas and outputs it as temperature information. The temperature measurement unit is not particularly limited as long as it can measure the temperature of the measurement target gas. Specifically, a thermistor or a platinum resistor can be used.

  The temperature information output from the temperature measurement unit may be temperature information calculated from the resistance value of a diode (light source or sensor). The resistance of the diode varies with temperature. In particular, a semiconductor material containing In or Sb in the active layer generally has a large resistance change due to temperature, and therefore, even a minute temperature change can be monitored. Therefore, the temperature can be measured with high accuracy by using the temperature information calculated from the resistance value of the photodiode. The resistance of the diode can be measured, for example, by applying a current or applying a voltage to the photodiode.

<Calculation unit>
In the gas sensor according to the present embodiment, the calculation unit (not shown) is not particularly limited as long as it can perform calculation in gas concentration calculation. For example, an analog IC, a digital IC, a CPU (Central Processing Unit), and the like are included. Is preferred. An output signal from the sensor may be taken out by wiring and connected to an external calculation unit. In addition, the calculation unit may include a function for controlling the light emitting diode.

<Derivation of correction signal>
In the gas sensor according to the present embodiment, the correction signal S is obtained by using the output S1 of the first photodiode and the output S2 of the second photodiode that is a reference sensor. S = S1 / S2
It is represented by In the range of 0.004 ≦ x ≦ 0.04 in the present embodiment, the temperature characteristic of S1 / S2 at 0 to 50 ° C. decreases as the temperature rises, so output at two temperatures (for example, 10, 40 ° C.). Can be improved with a straight line to improve the accuracy of the gas sensor. Further, when 0.01 ≦ x ≦ 0.035, the linearity of S is further improved, so that the correction accuracy of the temperature characteristic can be further improved even in the test at two temperatures. In addition, with the configuration of the above-described light emitting diode, photodiode, and optical filter, good linearity of the output signal can be obtained in the temperature range of 0 to 50 ° C., but the emission spectrum, light reception spectrum, filter transmission spectrum When the relative positional relationship on the wavelength axis is the same, the same effect can be obtained in other wavelength bands.

<About drive temperature>
Although the temperature range of 0 to 50 ° C. has been described above, a gas sensor that operates in a wider temperature range (for example, −40 to 85 ° C.) may be designed depending on the application. As in the present invention, the light emission intensity of the light emitting diode 11 is multiplied by the spectral sensitivity of the second photodiode 14 when the wavelength at the long wavelength end of the half-value width of the transmission characteristic of the optical filter is the maximum value in the operating temperature range of the gas sensor. If the configuration is shorter than the peak wavelength of the spectrum, a gas sensor that can be used within the range of the heat-resistant temperature of the component can be manufactured. However, since the deterioration of the light emitting diode and the photodiode is accelerated under a high temperature environment, the use at 150 ° C. or lower is preferable. Generally, temperatures of about 100 ° C. are required for in-vehicle use and about 85 ° C. for consumer use, but use under these environmental temperatures is also preferable.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<Embodiment>
FIG. 1 is a configuration diagram for explaining an embodiment of a gas sensor according to the present invention.
The gas sensor 100 according to this embodiment includes a gas cell 10, a light emitting diode 11 disposed in the gas cell 10, a first photodiode 12, an optical filter 13, and a second photodiode 14. Reference numeral 21 denotes a gas inlet and 22 denotes a gas outlet.

The first photodiode 12 is disposed in the gas cell 10 and outputs an electrical signal corresponding to the amount of light including infrared rays from the light emitting diode 11. The optical filter 13 is disposed in the gas cell 10 and narrows the wavelength of light incident on the first photodiode 12 to the absorption band of the measurement target gas.
The second photodiode 14 outputs a reference signal output from the first photodiode 12 and has the same semiconductor structure as that of the first photodiode 12. In addition, outputs from the first and second photodiodes 12 and 14 are input to a calculation unit (not shown).

With such a configuration, the gas sensor 100 of the present embodiment has an active layer of the light emitting diode 11 and the first and second photodiodes 12 and 14 with Al _x In _(1-x) Sb (0.004 ≦ x ≦ 0.04), and the optical filter 13 has a maximum transmittance between 4.1 and 4.4 μm, and the wavelength having the maximum transmittance is the light emission intensity of the light emitting diode 11 and the second photodiode 14. The wavelength is shorter than the peak wavelength of the spectrum obtained by multiplying the spectral sensitivities and the end on the long wavelength side of the half-value width is 4.5 μm or less.

Further, it is preferable that the light emitting diode 11 and the first photodiode 12 have the same semiconductor structure.
Further, the active layers of the light emitting diode 11 and the first photodiode 12 are preferably made of Al _x In _1-x Sb (0.01 ≦ x ≦ 0.035), respectively.
That is, as shown in FIG. 1, the gas sensor 100 of this embodiment includes a light emitting diode 11, a first photodiode 12, an optical filter 13, and a second photodiode 14 in a gas cell 10. The light emitted from the light emitting diode passes through the optical filter 13 and reaches the first photodiode 12, and reaches the second photodiode 14 without passing through the filter.

The light emitting diode 11 and the first and second photodiodes 12 and 14 are diodes whose active layer has a PIN structure of Al _x In _1-x Sb, and the Al composition of the active layer is 0.004 ≦ x ≦ 0. .04 relationship is satisfied. The wavelength of the optical filter 13 having the maximum transmittance of the optical filter is 4.1 to 4.4 μm. The current signals generated by the first and second photodiodes 12 and 14 are taken out from the electrodes by wiring, converted into voltage signals as they are or by an I / V conversion operational amplifier or the like, and S = S1 / S2 is calculated. Can do.
Next, the gas sensor of this embodiment is demonstrated based on each Example.

2 to 6 are process diagrams for explaining a method of manufacturing a light emitting diode and a photodiode element according to this embodiment. Hereinafter, the manufacturing process of the light emitting diode will be described, but the same applies to the first and second photodiodes. The laminated structure of these diodes is produced by the MBE method.
That is, first, an InSb layer 41a, which is an n-type semiconductor doped with Sn at a concentration of 1 × 10 ¹⁹ [cm ⁻³ ], was formed as a buffer layer on the GaAs substrate 40 by 0.5 μm. An Al _0.05 In _0.95 Sb layer 41b, which is an n-type semiconductor doped with Sn at a concentration of 1 × 10 ¹⁹ [cm ⁻³ ], was formed to 0.5 μm thereon. Further, an Al _0.22 In _0.78 Sb barrier layer 42 doped with Zn at a concentration of 1 × 10 ¹⁹ [cm ⁻³ ] was formed to 20 nm thereon.

Further, an i-type semiconductor Al _0.05 In _0.95 Sb layer was formed thereon with a thickness of 2 μm as an active layer 43. Here, i-type indicates that no dopant is intentionally added. Further, an Al _0.22 In _0.78 Sb barrier layer 44 doped with Zn at a concentration of 1 × 10 ¹⁸ [cm ⁻³ ] was formed to 20 nm thereon. Furthermore, an Al _0.05 In _0.95 Sb layer 45 of p-type semiconductor doped with Zn at a concentration of 1 × 10 ¹⁸ [cm ⁻³ ] was formed to a thickness of 0.5 μm. The structure from the n-type semiconductor layer 41a to the p-type semiconductor layer 45 forms a photodiode structure with a PIN junction.

Next, a resist pattern was formed on the compound semiconductor laminated portion. And the compound semiconductor laminated body was etched using this resist pattern as a mask. As a result, a mesa type compound semiconductor stacked portion 50 having a mesa structure having a top portion 51 and a bottom portion 52 as shown in FIG. 3 was formed on the substrate 40. Next, as shown in FIG. 5, 3000 ＳｉＯ of SiO ₂ was formed as the first protective layer 61 and 2,000 Ｓｉ of SiN was formed as the second protective layer 62 on the entire surface of the mesa compound semiconductor stacked portion 50. Next, a resist pattern was formed by opening a part on the top part 51 and a part on the bottom part 52 of the mesa compound semiconductor multilayer part 50 and covering the other regions. Then, the SiN film and the SiO ₂ film were dry etched using this resist pattern as a mask. Thereby, as shown in FIG. 4, the top part 51 and the bottom part 52 of the mesa compound semiconductor laminated part 50 were exposed from under the SiN film and the SiO ₂ film, respectively.

Further, as shown in FIG. 5, in order to form the first electrode portion 71 and the second electrode portion 72, a resist pattern is formed above the substrate 40, Ti is 1000 mm, Pt is 200 mm, Au is 3000 mm, Vapor deposition was performed in this order, and then lift-off was performed. Furthermore, as shown in FIG. 6, the infrared light emitting diode element 100 was obtained by rough-grinding the thickness from the back surface of the GaAs substrate 40 where the element was not processed to a thickness of 230 μm and vapor-depositing a TiO ₂ film 81 of 1500 mm. That is, the boundary A between the substrate 40 and the TiO ₂ film 81 is a rough surface.

FIG. 7 is a diagram illustrating the structure of the gas sensor according to the present embodiment.
The light-emitting diode 11 manufactured as described above, and the first photodiode 12 and the second photodiode 14 manufactured by the same method are sealed with the mold resin 90 and combined with the optical filter 13 as shown in FIG. The gas sensor was prepared. As the optical filter, an optical filter having a maximum transmittance of 4.21 μm and an upper end of the full width at half maximum of 4.42 μm is used. In this embodiment, the light emitting diode 11 and the second photodiode 14 that outputs a reference signal are formed on the same GaAs substrate, and the second photodiode emits light from the light emitting diode and reflects the light reflected in the GaAs substrate. The signal is output as S2. On the other hand, the first photodiode 12 is installed adjacent to the substrate on which the light emitting diode 11 and the second photodiode are formed, and the light reflected by the gas cell 10 after passing through the optical filter 13 is transmitted. Light is received and signal S1 is output. Although not shown in the drawings, the gas sensor according to the present embodiment is formed with holes for inflow and outflow of the measurement target gas.

と定義するΨ²を評価したところ、０．９９９となり、温度特性が一次関数で良く表せている結果となった。ただし、Ｓ_iは各温度でのＳ、ｆ（ｘ_i）は一次関数の回帰モデル、μはＳの平均値である。 Obtain correction signal S = S1 / S2 at 0 to 50 ° C.

Ψ ² defined as ## EQU3 ## was 0.999, and the temperature characteristics were well represented by a linear function. Here, S _i is S at each temperature, f (x _i ) is a regression model of a linear function, and μ is an average value of S.

A gas sensor was produced in the same manner as in Example 1 except that the active layers of the light emitting diode and the photodiode were respectively Al _0.005 In _0.995 Sb. The correction signal S = S1 / S2 at 0 to 50 ° C. was obtained, and when Ψ ² defined by [Equation 1] was evaluated for S, it was 0.975.

A gas sensor was produced in the same manner as in Example 1 except that the active layers of the light emitting diode and the photodiode were respectively Al _0.035 In _0.965 Sb. The correction signal S = S1 / S2 at 0 to 50 ° C. was obtained, and Ψ ² defined by [Equation 1] was evaluated for S, which was 0.992.

[Comparative Example 1]
A gas sensor was fabricated in the same manner as in Example 1 except that the active layers of the light emitting diode and the photodiode were respectively Al _0.003 In _0.997 Sb. The correction signal S = S1 / S2 at 0 to 50 ° C. was obtained, and when Ψ ² defined by [Equation 1] was evaluated for S, it was 0.03.

  As mentioned above, although embodiment of this invention was described, the technical scope of this invention is not limited to the technical scope as described in embodiment mentioned above. It is possible to add various changes or improvements to the above-described embodiments, and it is possible to add such changes or improvements to the technical scope of the present invention. it is obvious.

  The present invention is suitable as a gas sensor for gas that generates infrared absorption typified by carbon dioxide.

10 gas cell 11 light emitting diode 12 first photodiode 13 optical filter 14 second photodiode 21 gas inlet 22 gas outlet 40 GaAs substrate 41a InSb layer 41b n-type AlInSb layer 42 n-type barrier layer 43 active layer 44 p-type Barrier layer 45 p-type AlInSb layer 50 Mesa-type compound semiconductor laminated portion 51 Top portion 52 Bottom portion 61 First protective layer 62 Second protective layer 71 First electrode portion 72 Second electrode portion 81 TiO ₂ film 90 Mold resin 100 Gas sensor

Claims (7)

A gas cell;
A light emitting diode disposed in the gas cell;
A first photodiode that is disposed in the gas cell and outputs an electrical signal corresponding to the amount of light including infrared rays from the light emitting diode;
A second photodiode that outputs a reference signal of the output of the first photodiode and has the same semiconductor stacked structure as the first photodiode;
An optical filter disposed in the gas cell and narrowing the wavelength of light incident on the first photodiode to the absorption band of the measurement target gas;
And an arithmetic unit to which outputs from the first and second photodiodes are input , the output of the first photodiode is corrected using the output of the second photodiode, and the corrected A gas sensor for detecting a gas concentration based on an output of a first photodiode ,
The light emitting diode and the active layer are each _{Al x In (1-x)} Sb (0.004 ≦ x ≦ 0.100) of the first and second photodiodes der is,
The peak of the spectrum obtained by multiplying the emission intensity of the light emitting diode and the spectral sensitivity of the second photodiode when the wavelength at the long wavelength end of the half width of the transmission characteristic of the optical filter is the maximum value in the operating temperature range of the gas sensor. A gas sensor that is shorter than the wavelength . The active layers of the first and second photodiodes are Al _x In _(1-x) Sb (0.004 ≦ x ≦ 0.04), and the optical filter is 4.1 to 4.4 μm. The gas sensor according to claim 1 having a maximum transmittance therebetween. The gas sensor according to claim 1 or 2 , wherein an end of the optical filter on a long wavelength side of a half-value width has a wavelength of 4.5 µm or less. The gas sensor according to any one of claims 1 to 3 , wherein the light emitting diode and the first photodiode have the same semiconductor stacked structure. 2. The gas sensor according to claim 1, wherein active layers of the light emitting diode and the first photodiode are each made of Al _x In _1-x Sb (0.01 ≦ x ≦ 0.035). The gas sensor according to any one of claims 1 to 4 , wherein the gas sensor detects carbon dioxide. The maximum value of the said use temperature range is 150 degreeC, The gas sensor as described in any one of Claims 1-6 .

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