MEASURING DEVICE AND METHOD FOR OPERATING A MEASURING DEVICE

Abstract

Measuring device (100) for determining the value of at least one environmental parameter comprising - comprising an environmental sensor (1) - a semiconductor layer sequence (2) which is designed to form laser modes within the environmental sensor (1), - a cladding (4) whose refractive index changes as a function of the environmental parameter, - a first electrical contact (5) and a second electrical contact (6) for supplying current to the semiconductor layer sequence (2), where - the semiconductor layer sequence (2) has the shape of a general cylinder with a main axis (7), - in directions perpendicular to the main axis (7), the semiconductor layer sequence (2) is at least partially covered by the cladding (4), - the semiconductor layer sequence (2) has a refractive index which is greater than the refractive index of the cladding (4), such that ring modes can form within the semiconductor layer sequence (2) by total reflection at an interface between the semiconductor layer sequence (2) and the cladding (4) by impressing a current into the semiconductor layer sequence (2), - the environmental sensor (1) is designed such that, during its intended operation, a change in the refractive index of the cladding (4) causes a change in the electrical resistance of the semiconductor layer sequence (2) due to a change in the radiation losses within the semiconductor layer sequence (2), - a current source (105) which is designed to impress a constant current into the semiconductor layer sequence (2) via the electrical contacts (5, 6), - a voltmeter (110) coupled to the environmental sensor (1) and configured to measure an electrical voltage drop across the environmental sensor (1), - an evaluation device (120) which is designed to assign the value of the environmental parameter to be determined from a voltage drop measured by the voltmeter (110).

Description

[0001] A measuring device is specified. Furthermore, a method for operating a measuring device is specified.

[0002] US 7 749 748 B2 relates to a method for detecting biological or chemical substances using a microdisk laser and a biological or chemical detection element applied to the microdisk laser.

[0003] DE 10 2015 108 529 A1 relates to a semiconductor diode having a semiconductor layer sequence comprising an active zone, wherein the semiconductor layer sequence is cylindrical, a cylinder axis of the semiconductor layer sequence is perpendicular to a layer plane of the semiconductor layer sequence, and the semiconductor laser diode emits radiation generated during operation perpendicular to the cylinder axis of the semiconductor layer sequence.

[0004] The KR 10 1896 180 B1 relates to a microdisk for the formation of ring modes (whispering gallery modes), with a first coating and a second coating.

[0005] One object to be solved is, among other things, to provide a measuring device comprising an environmental sensor that can be designed to be particularly compact and has a high sensitivity for measuring at least one environmental parameter. Another object to be solved is, among other things, to provide a method for operating such a measuring device.

[0006] These objects are achieved by the subject matter and methods of the independent patent claims. Advantageous embodiments and further developments are the subject matter of the respective dependent patent claims.

[0007] The measuring device described here is particularly suitable for detecting at least one environmental parameter.

[0008] The measuring device includes an environmental sensor.

[0009] The environmental sensor comprises a semiconductor layer sequence. For example, the semiconductor layer sequence comprises a p-type region and an n-type region and an active zone arranged between these two regions. The active zone serves to generate electromagnetic radiation. The active zone contains, in particular, at least one quantum well structure in the form of a single quantum well, or SQW for short, or in the form of a multi-quantum well structure, or MQW for short. In addition, the active zone contains one, preferably several, secondary well structures. For example, during normal operation, electromagnetic radiation in the blue, green, or red spectral range, or in the UV or IR range, is generated in the active zone.

[0010] For example, the semiconductor layer sequence is based on a nitride compound semiconductor material, such as Al n In1-n-m Ga m N, or on a Phosphide compound semiconductor material, such as Al n In 1-n-m Ga m P, or on a Arsenide compound semiconductor material, such as Al n In 1-n-m Ga m As, where 0 ≤ n ≤ 1, 0 ≤ m ≤ 1, and m + n ≤ 1. The semiconductor layer sequence can contain dopants as well as additional components. For the sake of simplicity, however, only the essential components of the crystal lattice of the semiconductor layer sequence, i.e., Al, As, Ga, In, N, or P, are given, even if these may be partially replaced and / or supplemented by small amounts of other substances.

[0011] The environmental sensor comprises a casing. The casing is formed from a material whose refractive index changes as a function of an environmental parameter. In particular, the value of the environmental parameter can be unambiguously determined from the refractive index of the casing. The casing is formed, for example, from a dielectric material. All refractive indices mentioned here and below refer in particular to the radiation generated in the active zone at an operating temperature of the environmental sensor.

[0012] The environmental sensor comprises a first electrical contact and a second electrical contact for supplying current to the semiconductor layer sequence. The electrical contacts are arranged, in particular, on opposite outer surfaces of the semiconductor layer sequence, wherein the outer surfaces run parallel to the main extension plane of the semiconductor layer sequence and / or the active zone. The electrical contacts are formed, for example, with one of the following materials or with a mixture of the following materials: Au, Ag, Al, Ti.

[0013] The semiconductor layer sequence has the shape of a general cylinder with a main axis. The main axis runs, in particular, perpendicular to a main extension plane of the semiconductor layer sequence. In particular, the main axis runs perpendicular to a main extension plane of the active zone.

[0014] The term "general cylinder" refers specifically to the mathematical sense. Accordingly, a general cylinder is formed by a geometric base surface and a geometric top surface, with the top surface resulting from a parallel displacement of the base surface. In particular, the base surface and the top surface are congruent in the direction of the major axis. This means that the parallel displacement occurs primarily in the direction of the major axis. A lateral surface of the general cylinder connects the base surface and the top surface.

[0015] For example, the semiconductor layer sequence has the geometric shape of a right circular cylinder. For example, the semiconductor layer sequence is then circular in plan view. In particular, the main axis is a rotational symmetry axis of the semiconductor layer sequence. In a right circular cylinder, both the base surface and the top surface are formed from a circular disk. Here and in the following, plan view refers to a view of the semiconductor layer sequence in the direction of the main axis.

[0016] In the direction perpendicular to the main axis, the semiconductor layer sequence is at least partially covered by the cladding. Preferably, the semiconductor layer sequence is completely covered by the cladding in these directions. This means that in plan view, the cladding in particular completely encloses the semiconductor layer sequence. The semiconductor layer sequence has a refractive index that is greater than the refractive index of the cladding. “Refractive index of the semiconductor layer sequence” refers in particular to an average refractive index of the semiconductor layer sequence. Alternatively, “the semiconductor layer sequence has a refractive index” means that a layer, for example the active layer, or a region of the semiconductor layer sequence, for example a mode-guiding region, has a corresponding refractive index.

[0017] For example, a difference in the refractive index between the semiconductor layer sequence and the cladding, hereinafter also referred to as the refractive index difference, is at least 0.1% and at most 1%. In particular, even if the refractive index of the cladding changes, the refractive index difference still exists in this order of magnitude. For example, the difference in the refractive index is 1×10 -3 .

[0018] The semiconductor layer sequence is configured to form laser modes within the environmental sensor. Ring modes, also known as whispering gallery modes, can be generated in the semiconductor layer sequence. These modes run along an interface between the semiconductor layer sequence and the cladding. Due to total internal reflection at this interface, the modes within the semiconductor layer sequence are amplified, and laser modes are formed. During operation, a current can be injected into the semiconductor layer sequence via the electrical contacts, which current pumps the semiconductor layer sequence and excites the laser modes. A basic operating principle and examples of semiconductor laser diodes that form ring modes are described, for example, in the publication DE 102015108529 A1, the disclosure of which is hereby incorporated by reference.

[0019] The environmental sensor is configured so that, during its intended operation, a change in the refractive index of the cladding causes a change in the electrical resistance of the semiconductor layer sequence due to a change in the radiation losses within the semiconductor layer sequence. In other words, the electrical resistance of the semiconductor layer sequence or of the environmental sensor is a function of the environmental parameter. Since, during its intended operation, the generated laser modes run particularly at the interface between the semiconductor layer sequence and the cladding, and the generation of the laser modes is based on total internal reflection occurring at the interface, the refractive index of the cladding has a significant influence on radiation losses within the semiconductor layer sequence.

[0020] The environmental sensor comprises the semiconductor layer sequence, the cladding, whose refractive index changes as a function of the environmental parameter, as well as the first electrical contact and the second electrical contact, which serve to supply current to the semiconductor layer sequence. The semiconductor layer sequence has the shape of a general cylinder with a main axis. In the direction perpendicular to the main axis, the semiconductor layer sequence is at least partially covered by the cladding. The semiconductor layer sequence has a refractive index that is greater than the refractive index of the cladding. The semiconductor layer sequence is configured to form laser modes within the environmental sensor.Furthermore, the environmental sensor is designed such that, during its intended operation, a change in the refractive index of the cladding causes a change in the electrical resistance of the semiconductor layer sequence due to a change in the radiation losses within the semiconductor layer sequence.

[0021] The environmental sensor described here is based on the following technical features, among others. To create a particularly sensitive environmental sensor, a cylindrical semiconductor layer sequence is encased in a material whose refractive index reacts to changes in the environment. Through total internal reflection at an interface between the semiconductor layer sequence and the cladding, a ring mode formed in the semiconductor layer sequence is guided within the semiconductor layer sequence. During total internal reflection, a portion of the reflected laser radiation penetrates the cladding as an evanescent field. This, among other things, influences the refractive index of the cladding on the laser mode within the semiconductor layer sequence. In particular, optical properties are influenced.For example, the frequency at which the laser radiation exhibits its maximum intensity may shift, or a resonance of the laser radiation may be split into two resonances. These changes can be used as a measurement signal. This typically requires an evaluation of the optical properties of the laser radiation, for example, using a spectrometer. Such a measurement method is described, for example, in US Pat. No. 7,749,748 B2, the disclosure of which is incorporated by reference.

[0022] For example, in the publications Behringer M. (2007) High-Power Diode Laser Technology and Characteristics. In: Bachmann F., Loosen P., Poprawe R. (eds) High Power Diode Lasers. Springer Series in Optical Sciences, vol 128. Springer, New York, NY as well as Y. Mitsuhashi et al., IEEE J. of Quantum Electronics 17, 1216 ,1981, and AA Sahai et al., Optic Letters 39, 5630, 2014, it is described that the electrical resistance of a conventional semiconductor laser diode is a function of the reflectivity of the resonator end faces.

[0023] The environmental sensor utilizes, among other things, the idea of ​​using a functional relationship between an environmental parameter and the electrical resistance of the semiconductor layer sequence or the environmental sensor as a measured value. This allows a change in an environmental parameter to be determined via the electrical resistance of the environmental sensor.

[0024] Due to the change in the refractive index of the cladding, the conditions for total internal reflection at an interface between the semiconductor layer sequence and the cladding change, resulting in changes in radiation losses within the semiconductor layer sequence. This causes a change in the electrical resistance of the semiconductor layer sequence. Thus, there is a direct correlation between a voltage drop measured across the semiconductor layer sequence at a constant power supply and a change in an environmental parameter. If there is a functional relationship, in particular a one-to-one relationship, between the environmental parameter and the electrical resistance, absolute values ​​of the environmental parameter can also be recorded, for example, due to a calibration of the environmental sensor.

[0025] Advantageously, the environmental sensor described here does not require an additional readout device such as a spectrometer. Furthermore, cylindrical semiconductor laser diodes can advantageously be designed to be particularly compact. A further advantage arises from the fact that, due to the casing arranged on a lateral surface of the general cylinder, a particularly large portion of the outer surface of the environmental sensor can react sensitively to changes in the environment.

[0026] According to at least one embodiment of the environmental sensor or one of its embodiments described above, the environmental parameter is one of the following parameters: temperature, pressure, humidity, light intensity, magnetic field strength, pH value. For example, the refractive index of the casing changes due to a change in one of these parameters. In particular, a specific temperature value, pressure value, humidity value, light intensity, magnetic field strength, and / or pH value is assigned exactly one value of the refractive index of the casing. In other words, there is a one-to-one relationship between the environmental parameter and the refractive index of the casing, and thus in particular the electrical resistance of the environmental sensor.

[0027] According to at least one embodiment of the environmental sensor or one of its above-mentioned embodiments, the casing comprises at least one of the following materials: Bromophenol blue, polyvinyl alcohol, Fe 3 O 4 -Ferrofluid, lithium niobate, AlGaN.

[0028] For example, bromophenol blue reacts to a change in pH with a change in its refractive index. Polyvinyl alcohol reacts particularly to a change in humidity, such as the humidity of the ambient air of the environmental sensor, with a change in its refractive index. The refractive index of Fe 3 O 4For example, the refractive index of a ferrofluid is a function of light intensity and / or magnetic field strength. For example, the refractive index of lithium niobate is strongly dependent on temperature, such as the ambient temperature. The refractive index of AlGaN, for example, depends on pressure, such as ambient pressure. Preferably, radiation generated in the environmental sensor during operation is not absorbed by AlGaN.

[0029] According to at least one embodiment of the environmental sensor or one of its embodiments described above, the functional relationship between the refractive index of the casing and the at least one environmental parameter is linear. For example, the refractive index is a linear function of the environmental parameter to be detected.

[0030] According to at least one embodiment of the environmental sensor or one of its embodiments described above, a side of the casing facing away from the semiconductor layer sequence directly borders the environment to be monitored. This means, in particular, that the casing is exposed to the outside, i.e., no further materials and / or layers are arranged between the casing and the environment containing the at least one environmental parameter. Advantageously, this allows the environmental parameter to be detected particularly well, since environmental influences can be registered directly by the casing. In particular, for determining temperature, ambient pressure, humidity, and pH, the sensitivity of the environmental sensor can be increased by an outwardly exposed casing.

[0031] According to at least one embodiment of the environmental sensor or one of its embodiments described above, a passivation layer is arranged on a side of the casing facing away from the semiconductor layer sequence. The casing, in particular, can be protected by the passivation layer. Preferably, the passivation layer has no effect on the environmental parameter that is to be seen by the casing. For example, light intensity and / or magnetic field strength come into consideration as such environmental parameters. In this case, the passivation layer is preferably permeable to ambient light and / or magnetic fields. The passivation layer has, for example, a thickness measured perpendicular to the main axis of between 1 nm and 100 nm inclusive. The passivation layer is formed, for example, with an oxide, such as silicon oxide or aluminum oxide, or a nitride, such as silicon nitride.

[0032] According to at least one embodiment of the environmental sensor or one of its embodiments described above, the sheath has a thickness of at least 1 nm and at most 1 µm. In particular, the sheath has a thickness between 10 nm and 200 nm inclusive. Preferably, the thickness is between 90 nm and 110 nm inclusive. The thickness is measured in particular in the direction perpendicular to the main axis.

[0033] According to at least one embodiment of the environmental sensor or one of its embodiments described above, the semiconductor layer sequence has the shape of a prism. In particular, the environmental sensor has the shape of a prism. The semiconductor layer sequence and / or the environmental sensor each have, for example, the shape of a regular polygon in plan view. The regular polygon has, in particular, at least five, at least six, or at least eight corners. The prism is, in particular, a general cylinder in which the base and top surfaces are formed from a regular polygon. In particular, any prism that can form ring modes inside the semiconductor layer sequence is conceivable for the semiconductor layer sequence.If the semiconductor layer sequence is based on an InGaN material system, for example, a semiconductor layer sequence in the form of a prism with a hexagon as the base area can be realized particularly easily.

[0034] According to at least one embodiment of the environmental sensor or one of its embodiments described above, the environmental sensor has an extension perpendicular to the main axis of a maximum of 1000 µm or a maximum of 20 µm or a maximum of 5 µm. Alternatively or additionally, the extension is at least 500 nm or at least 1 µm or at least 5 µm. In the case of a semiconductor layer sequence in the form of a right circular cylinder, the extension is determined in particular by the diameter of the environmental sensor. An axis along which the extension is measured preferably runs through the main axis. The extension is in particular a maximum extension of the semiconductor layer sequence.

[0035] According to at least one embodiment of the environmental sensor or one of its embodiments described above, the semiconductor layer sequence comprises a mode-guiding region. The mode-guiding region includes, in particular, the active zone of the semiconductor layer sequence, which is configured to generate electromagnetic radiation. Furthermore, the mode-guiding region is preferably spaced apart from the first electrical contact and the second contact. In particular, the mode-guiding region comprises a first waveguide layer and a second waveguide layer, between which the active zone is arranged. In particular, radiation generated in the active zone is guided within the mode-guiding region. For example, the mode-guiding region limits the propagation of the radiation in a direction parallel to the main axis.For this purpose, regions of the semiconductor layer sequence that delimit the mode-guiding region in the direction of the main axis preferably have a lower refractive index than the mode-guiding region.

[0036] Due to the distance between the mode-guiding region and the electrical contacts, a disturbing influence of the electrical contacts or the outer surfaces on which the electrical contacts are arranged on the laser mode in the mode-guiding region can be advantageously reduced.

[0037] According to at least one embodiment of the environmental sensor or its just-described embodiment, the mode-guiding region has a larger extension in the direction perpendicular to the main axis than the remaining semiconductor layer sequence. This advantageously allows the influence of the electrical contacts or the top and bottom surfaces of the semiconductor layer sequence to be further reduced.

[0038] According to at least one embodiment of the environmental sensor or one of its embodiments described above, the environmental sensor has a substrate. The substrate is arranged in particular between the semiconductor layer sequence and the first electrical contact. The substrate is preferably formed from an electrically conductive material. The substrate comprises, for example, Si or GaAs or is formed from one of these materials. The substrate is, for example, a growth substrate of the semiconductor layer sequence. By leaving the semiconductor layer sequence on the growth substrate, the environmental sensor is relatively simple and cost-effective to manufacture.

[0039] The measuring device comprises a current source configured to inject a constant current into the semiconductor layer sequence via the electrical contacts. Furthermore, the measuring device comprises a voltmeter coupled to the ambient sensor and configured to measure an electrical voltage drop across the ambient sensor. Due to the constant power supply, the voltmeter can be used to determine the electrical resistance of the ambient sensor.

[0040] The measuring device further comprises an evaluation device configured to assign, for example, calculate, the value of the environmental parameter to be determined from a voltage drop measured by the voltmeter. For example, the evaluation device stores how a functional relationship between the voltage drop, which occurs due to the dependence of the refractive index of the cladding on the environmental parameter, is related to the at least one environmental parameter. Preferably, exactly one value of the environmental parameter is assigned to each value of the voltage drop, and vice versa. This thus involves, in particular, a bijective or one-to-one relationship between the environmental parameter and the voltage drop.

[0041] Furthermore, a method for operating a measuring device is specified.

[0042] In the method for operating the measuring device, a constant current is injected into the ambient sensor, which leads to the generation of laser modes in the semiconductor layer sequence. A current is injected such that, in particular, a current density in the semiconductor layer sequence is sufficient to operate the semiconductor layer sequence above a laser threshold. Preferably, a current of a constant value is injected into the semiconductor layer sequence via the electrical contacts throughout the entire method.

[0043] In a further process step, a voltage drop across the ambient sensor is measured. In particular, the voltage drop is measured using the voltmeter of the measuring device.

[0044] In a further process step, the measured voltage drop is assigned a value of an environmental parameter to be determined. This is done, in particular, using the evaluation device.

[0045] For example, the measuring device is calibrated before performing the method. This means that the voltage drop across the ambient sensor is measured for a known ambient parameter. This pair of values, consisting of the voltage drop and the value of the ambient parameter, is stored, for example, in a memory of the evaluation device. This is repeated, in particular, for a large number of values ​​of the ambient parameter. During the method for operating the measuring device, these stored pairs of values ​​are then used, for example, to determine the value of the ambient parameter from the measured voltage drop.

[0046] According to at least one embodiment of the method or one of its embodiments described above, a change in the at least one environmental parameter causes a change in the refractive index of the cladding of the environmental sensor. This change in the refractive index causes a change in electrical losses within the semiconductor layer sequence. This occurs in particular because the condition for total reflection at an interface between the semiconductor layer sequence and the cladding changes. Furthermore, a portion of the totally reflected radiation penetrates the cladding, for example in the form of an evanescent field, whereby the change in the refractive index of the cladding influences the laser mode in the semiconductor layer sequence. The change in losses within the semiconductor layer sequence causes a change in the measured voltage drop due to a change in the electrical resistance of the environmental sensor.For example, if higher losses occur within the semiconductor layer sequence due to a change in the refractive index of the cladding, the ambient sensor must be operated with higher electrical power. Due to the constant current, the voltage drop increases.

[0047] A change in at least one environmental parameter is determined from the change in the measured voltage drop. This makes it possible to determine not only a constant value of an environmental parameter, but also a change in its value.

[0048] According to at least one embodiment of the method or one of its aforementioned embodiments, a change in the refractive index of the cladding causes a change in the amount of light emitted by the ambient sensor. Due to the change in the refractive index of the cladding, in particular, the condition for total internal reflection at the interface between the semiconductor layer sequence and the cladding changes, which also changes the proportion of radiation reflected at the interface due to total internal reflection. If, for example, the condition shifts such that a smaller portion of the incoming radiation is totally reflected, a larger portion of the radiation leaves the ambient sensor in a direction perpendicular to the main axis. It is possible that the condition for total internal reflection changes such that no total internal reflection occurs at all. In this case, the amount of light emitted by the ambient sensor increases significantly.The amount of light can, for example, be registered by a human observer with the naked eye. The amount of light emitted represents an additional signal that can be used to detect a change in the environmental parameter. In particular, this signal is detectable by a human observer with the naked eye.

[0049] Further advantages and advantageous configurations and developments of the environmental sensor, the measuring device, and the method for operating a measuring device will become apparent from the exemplary embodiments presented below in conjunction with the schematic drawings. Identical, similar, and similarly acting elements are provided with the same reference numerals in the figures. The figures and the relative sizes of the elements shown in the figures are not generally to scale. Rather, individual elements may be exaggerated for clarity and / or clarity.

[0050] They show: Fig. 1 an embodiment of a measuring device in a perspective view, Fig. 2 to 5 examples of an environmental sensor in different views, and Fig. 6 and Fig. 7 the dependence of the refractive index of each material as a function of an environmental parameter.

[0051] In the embodiment of the measuring device 100 of the Fig. 1, an environmental sensor 1 comprises a semiconductor layer sequence 2 with a mode-guiding region 9. The environmental sensor 1 further comprises a cladding 4. The environmental sensor 1 and the semiconductor layer sequence 2 each have the shape of a right circular cylinder with a main axis 7. The main axis 7 is in particular a rotational symmetry axis of the environmental sensor 1. The cladding 4 completely covers the semiconductor layer sequence 2 in directions perpendicular to the main axis 7. The cladding 4 has a refractive index that changes as a function of an environmental parameter of a medium surrounding the environmental parameter 1. In particular, the cladding 4 is formed with a dielectric material, for example, consists entirely of a dielectric material.

[0052] The semiconductor layer sequence 2, in particular the mode-guiding region 9, has a refractive index that is greater than the refractive index of the cladding 4. Due to the difference in refractive index between the semiconductor layer sequence 2 and the cladding 4, electromagnetic radiation propagates at an interface 16 between the semiconductor layer sequence 2 and the cladding 4. In particular, due to the difference in refractive index, electromagnetic radiation is totally reflected at the interface 16. The electromagnetic radiation is generated in the active zone 3 during normal operation. A laser mode 11 is thus formed inside the semiconductor layer sequence 2. The laser mode 11 is particularly in the Fig. 3 is indicated as a dashed line. The refractive index difference is, for example, 1×10 -3 .

[0053] The semiconductor layer sequence 2 is based, for example, on a compound semiconductor material, such as InAlGaAs or InGaN. Examples of materials of the semiconductor layer sequence and the basic functioning that lead to the formation of laser modes within the semiconductor layer sequence 2 are described, for example, in the document DE 102015108529 A1.

[0054] The mode-guiding region 9 comprises the active layer 3 as well as a first waveguide 12 and a second waveguide 13. The active zone 3 is arranged between the waveguides 12, 13. The mode-guiding region 9 is arranged between a first cover layer 14 and a second cover layer 15. Electromagnetic radiation generated in the active zone 3 preferably propagates only in the mode-guiding region 9. For this purpose, the mode-guiding region 9 has, for example, a refractive index that is different from those of the first and second cover layers 14, 15. In particular, the cover layers 14, 15 each have a lower refractive index than the mode-guiding region 9. The first waveguide 12 and the first cover layer 14 are, in particular, n-doped, and the second waveguide 13 and the second cover layer 15 are, in particular, p-doped. Alternatively, the doping is selected to be the opposite, for example.

[0055] A substrate 10 is arranged on a surface of the first cover layer 14 facing away from the active zone 3. A first electrical contact 5 is arranged on a side of the substrate 10 facing away from the semiconductor layer sequence 2. The first electrical contact 5 is, in particular, an n-type contact. The substrate 10 is preferably formed from a semiconductor material and is electrically conductive. For example, the substrate 10 comprises one of the following materials: Si, Ga, As. The growth substrate 10 is, in particular, a growth substrate for the semiconductor layer sequence 2.

[0056] A second electrical contact 6 is arranged on a surface of the second cover layer 15 facing away from the active zone 3. The second electrical contact 6 is in particular a p-contact. The electrical contacts 5, 6 preferably comprise one of the following metals: Au, Pt, Ag, Al. During normal operation, the semiconductor layer sequence 2 is supplied with current via the electrical contacts 5, 6. For this purpose, the measuring device 100 comprises a current source 105, via which current is impressed such that laser modes are excited in the mode-guiding region 9. Furthermore, the measuring device 100 comprises a voltmeter 110, which is coupled to the ambient sensor 1 and via which a voltage drop across the ambient sensor 1 can be measured.

[0057] The measuring device 100 of the Fig. 1 is suitable both for determining an environmental parameter and for measuring a change in an environmental parameter. Since the refractive index of the cladding 4 is a function of the environmental parameter, the electrical resistance of the environmental sensor 1 is also a function of the environmental parameter. The reason for this is that a condition for total reflection at the interface 16 depends on the refractive index of the cladding 4. This means that the refractive index of the cladding 4 determines which proportion of the radiation generated in the active zone 3 is totally reflected at the interface 16. Among other things, this proportion determines the magnitude of the radiation loss within the semiconductor layer sequence 2 and thus the power with which the environmental sensor 1 must be operated so that laser modes 11 can continue to be excited in the mode-guiding region 9.This means that the electrical resistance of the environmental sensor 1 depends on the radiation losses within the semiconductor layer sequence 2 and thus on the refractive index of the cladding 4. Thus, the electrical resistance, in turn, depends on the environmental parameter to be determined.

[0058] The electrical resistance of the environmental sensor 1 can be determined via the voltage drop measured across the voltmeter 110, since the current source 105 injects a constant current into the semiconductor layer sequence 2 via the operation of the measuring device. An evaluation device 120 connected to the voltmeter 110 determines the value of the environmental parameter from the voltage drop.

[0059] Since a change in the environmental parameter causes a change in the refractive index of the casing 4, a changed voltage drop is measured at the environmental sensor 1 for the reasons just explained. This allows a change in the environmental parameter to be determined by means of the evaluation device 120.

[0060] For example, the coating 4 comprises bromophenol blue. In this case, the refractive index of the coating 4 is a function of the ambient pH. Thus, a pH measurement can be performed with the measuring device 100.

[0061] The example of the environmental sensor 1 of the Fig. 2 has essentially the same features as the environmental sensor 1 of the Fig. 1 with the difference that the mode-guiding region 9 has a greater extent perpendicular to the main axis 7 than the other regions of the semiconductor layer sequence 2. The other regions of the semiconductor layer sequence 2 are formed in particular by the first and second cover layers 14, 15.

[0062] The Fig. 3 shows a cross-section perpendicular to a main axis 7 of an environmental sensor 1. The cutting plane runs in particular through the active zone 3. The environmental sensor 1 is, for example, an environmental sensor 1 according to one of the Fig. 1 and Fig. 2. In the Fig. 3 shows how laser modes 11 form in the semiconductor layer sequence 2 due to total reflection at the interface 16.

[0063] The example of Fig. 4 shows essentially the same features as the examples of the environmental sensors of the Fig. 1 to 3, with the difference that the semiconductor layer sequence 2 and the environmental sensor 1 have the shape of a prism. In the cross section of the Fig. 4, this can be seen in the fact that the semiconductor layer sequence 2 and the environmental sensor 1 have the shape of a hexagon. In this case, the semiconductor layer sequence 2 is based, for example, on the InGaN material system. Due to the crystal structure of this material system, an environmental sensor 1 with a hexagon as its base area can be manufactured particularly easily.

[0064] Fig. 5 shows an environmental sensor 1 in a sectional view, with the cutting plane running parallel and along the main axis 7. The environmental sensor 1 of the Fig. 5 has essentially the same features as the environmental sensor 1 of Fig. 1 with the difference that a passivation layer 8 is present. The passivation layer 8 is arranged on a side of the casing 4 facing away from the semiconductor layer sequence 2. In particular, this side of the casing 4 is completely covered by the passivation layer 8. Such an environmental sensor 1 can be used, for example, to determine a light intensity of the environment or a magnetic field strength. For this purpose, the passivation layer 8 is preferably permeable to magnetic fields and / or electromagnetic fields. This means that the physical properties of these fields are not significantly influenced or not influenced at all by the passivation layer 8. The passivation layer 8 also protects the casing 4 and is made of silicon oxide, for example. A passivation layer 8 can also be present in all other embodiments of the environmental sensor 1.

[0065] Fig. 6 shows a refractive index of 30 for Fe 3 O 4 -Ferrofluid as a function of light power 31 in µW at different magnetic field strengths 32 (curves A to E). Fig. 6 is like the one mentioned below Fig. Figure 7 is taken from the publication MG Shlyagin et al., Int. J. for Light and Elec. Opt. 186, 418-422, 2019, the disclosure of which is hereby incorporated by reference. For curve A, the magnetic field strength 32 is 40 Oe, for curve B 70 Oe, for curve C 100 Oe, for curve D 130 Oe, and for curve E 0 Oe. The magnetic field strength 32 is given in Oersteds (Oe) in the cgs unit system.

[0066] Fig. 6 shows that with increasing light output 31 or light intensity the refractive index 30 of Fe 3 O 4-ferrofluid increases when a magnetic field is applied. Secondly, in this case, the refractive index 30 is essentially a linear function of the light output 31.

[0067] Fig. 7 illustrates the refractive index 30 of Fe 3 O 4 -Ferrofluid as a function of a magnetic field strength 32 in Oe (cgs unit system) for two light powers 31 (curves F and G). Fig. 7 is like Fig. 6 of the publication MG Shlyagin et al. It can be seen that the refractive index 30 increases with increasing magnetic field strength 32 at constant light output 31. Furthermore, in a range of magnetic field strength 32 from 40 Oe to 120 Oe, the functional relationship between magnetic field strength 32 and refractive index 30 is linear.

[0068] This means that using Fe 3 O 4-Ferrofluid as material for the casing 4, an environmental sensor 1 for determining light output 31 or light intensity and / or magnetic field strength 32 can be realized.

[0069] Unless otherwise indicated, the components shown in the figures preferably follow one another directly in the specified order. Layers that do not touch in the figures are preferably spaced apart from one another. Where lines are drawn parallel to one another, the corresponding surfaces are preferably also aligned parallel to one another. Likewise, unless otherwise indicated, the relative positions of the drawn components to one another are realistically represented in the figures. List of reference symbols 1 environmental sensor 2 Semiconductor layer sequence 3 active zones 4 Sheathing 5 first electrical contact 6 second electrical contact 7 Main axis 8 Passivation layer 9 fashion-leading area 10 Substrat 11 Laser mode 12 first waveguide 13 second waveguide 14 first top layer 15 second top layer 16 Interface 30 Refractive index of Fe 3 O 4 -Ferrofluid 31 Light output in µW 32 Magnetic field strength in µW 100 measuring device 105 Power source 110 voltmeters 120 Evaluation device A to G measurement curves

Claims

[1] Measuring device (100) for determining the value of at least one environmental parameter comprising - comprising an environmental sensor (1) - a semiconductor layer sequence (2) which is designed to form laser modes within the environmental sensor (1), - a cladding (4) whose refractive index changes as a function of the environmental parameter, - a first electrical contact (5) and a second electrical contact (6) for supplying current to the semiconductor layer sequence (2), where - the semiconductor layer sequence (2) has the shape of a general cylinder with a main axis (7), - in directions perpendicular to the main axis (7), the semiconductor layer sequence (2) is at least partially covered by the cladding (4), - the semiconductor layer sequence (2) has a refractive index which is greater than the refractive index of the cladding (4), such that ring modes can form within the semiconductor layer sequence (2) by total reflection at an interface between the semiconductor layer sequence (2) and the cladding (4) by impressing a current into the semiconductor layer sequence (2), - the environmental sensor (1) is designed such that, during its intended operation, a change in the refractive index of the cladding (4) causes a change in the electrical resistance of the semiconductor layer sequence (2) due to a change in the radiation losses within the semiconductor layer sequence (2), - a current source (105) which is designed to impress a constant current into the semiconductor layer sequence (2) via the electrical contacts (5, 6), - a voltmeter (110) coupled to the environmental sensor (1) and configured to measure an electrical voltage drop across the environmental sensor (1), - an evaluation device (120) which is designed to assign the value of the environmental parameter to be determined from a voltage drop measured by the voltmeter (110). [2] Measuring device (100) according to claim 1, wherein the environmental parameter is one of the following parameters: temperature, pressure, humidity, light intensity, magnetic field strength, pH value. [3] Measuring device (100) according to one of the preceding claims, wherein the sheath (4) comprises at least one of the following materials: bromophenol blue, polyvinyl alcohol, Fe 3 O 4 -Ferrofluid, lithium niobate, AlGaN. [4] Measuring device (100) according to one of the preceding claims, wherein the functional relationship between the refractive index of the cladding (4) and the at least one environmental parameter is linear. [5] Measuring device (100) according to one of the preceding claims, wherein a side of the casing (4) facing away from the semiconductor layer sequence (2) directly borders the environment to be monitored. [6] Measuring device (100) according to one of claims 1 to 4, wherein a passivation layer (8) is arranged on a side of the casing (4) facing away from the semiconductor layer sequence (2). [7] Measuring device (100) according to one of the preceding claims, wherein the sheath (4) has a thickness of at least 1 nm and at most 1 µm. [8] Measuring device (100) according to one of the preceding claims, wherein the semiconductor layer sequence (2) has the shape of a prism. [9] Measuring device (100) according to one of the preceding claims, wherein the environmental sensor (1) has an extension of a maximum of 20 µm perpendicular to the main axis (7). [10] Measuring device (100) according to one of the preceding claims, wherein - the semiconductor layer sequence (2) comprises a mode-guiding region (9), - the mode-guiding region (9) includes an active zone (3) of the semiconductor layer sequence (2), and - the mode-guiding region (9) is spaced apart from the first electrical contact (5) and the second electrical contact (6). [11] Measuring device (100) according to claim 10, wherein the mode-guiding region (9) has a greater extent in directions perpendicular to the main axis (7) than the remaining semiconductor layer sequence (2). [12] Measuring device (100) according to one of the preceding claims, wherein - the environmental sensor (1) has a substrate (10), - the substrate (10) is arranged between the semiconductor layer sequence (2) and the first electrical contact (5), - the substrate (10) is formed from an electrically conductive material. [13] Method for operating a measuring device (100) according to one of the preceding claims, in which - a constant current is impressed into the environmental sensor (1), which causes laser modes to be generated in the semiconductor layer sequence (2), - a voltage drop is measured at the environmental sensor (1), - the measured voltage drop is assigned a value of an environmental parameter to be determined. [14] The method of claim 13, wherein - a change in the at least one environmental parameter causes a change in the refractive index of the casing (4) of the environmental sensor (1), - the change in the refractive index of the cladding (4) causes a change in electrical losses within the semiconductor layer sequence (2), - the change in electrical losses within the semiconductor layer sequence (2) causes a change in the measured voltage drop, - a change in at least one environmental parameter is determined from the change in the measured voltage drop. [15] Method according to claim 13 or 14, wherein a change in the refractive index of the casing (4) causes a change in an amount of light emitted by the environmental sensor (1).

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