Method for manufacturing non-classical light source device, non-classical light source device, single photon source device, and random number generator

Abstract

To provide a non-classical light source device that emits non-classical light with a simple configuration and a method for manufacturing the same.SOLUTION: A method for manufacturing a non-classical light source device includes the steps of preparing a semiconductor structure having a first semiconductor region having first impurities of the first conductivity type, which is one of p-type and n-type, and a second semiconductor region having second impurities of the second conductivity type, which is the other of p-type and n-type; and irradiating the semiconductor structure with a laser beam while passing a forward current through the semiconductor structure to diffuse second impurities, with the semiconductor structure in thermal contact with a cooling substrate at a temperature greater than -40°C but less than 15°C.SELECTED DRAWING: Figure 4D

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a non-classical light source device, a non-classical light source device, a single photon source device, and a random number generator.

Background Art

[0002] In recent years, non-classical light that cannot be described as a classical electromagnetic field has attracted attention in the fields of basic research and applications. For example, Patent Document 1 discloses a single photon source that emits a single photon, which is an example of non-classical light, using quantum dots. The single photon source is expected to be applied to, for example, quantum key distribution. If a non-classical light source device that can emit non-classical light with a simple configuration can be realized, it will be useful for the practical application of devices using non-classical light.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] There is a need for a non-classical light source device that can emit non-classical light with a simple configuration and a method for manufacturing the same.

Means for Solving the Problems

[0006] In one embodiment, a method for manufacturing a non-classical light source device according to the present disclosure includes a step of preparing a semiconductor structure having a first semiconductor region having a first impurity of a first conductivity type, which is one of p-type and n-type, and a second semiconductor region having a second impurity of a second conductivity type, which is the other of p-type and n-type; and a step of irradiating the semiconductor structure with light while passing a forward current through the semiconductor structure in a state where the semiconductor structure is thermally contacted with a cooling substrate greater than -40°C and less than 15°C to diffuse the second impurity.

[0007] In one embodiment, a non-classical light source device according to the present disclosure includes a first semiconductor region having a conductivity type of one of p-type and n-type, a second semiconductor region having a conductivity type of the other of p-type and n-type, a pn junction located between the first semiconductor region and the second semiconductor region, and a plurality of light-emitting regions discretely distributed along the pn junction, each emitting non-classical light; and a semiconductor structure; and an electrode structure for applying a voltage to the pn junction. The base materials of the first semiconductor region and the second semiconductor region are formed from an indirect transition type semiconductor. When viewed from a direction perpendicular to the pn junction using a camera with a spatial resolution of 10 μm at a predetermined frame rate, each light emitted from the plurality of light-emitting regions is observed to be separated.

Advantages of the Invention

[0008] According to an embodiment of the present disclosure, a non-classical light source device that emits non-classical light with a simple configuration and a method for manufacturing the same can be realized.

Brief Description of the Drawings

[0009]

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MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, with reference to the drawings, a non-classical light source device and a method for manufacturing the same according to embodiments of the present disclosure will be described in detail. Parts denoted by the same reference numerals in the plurality of drawings indicate the same or equivalent parts.

[0011] Furthermore, the following is an exemplification for embodying the technical idea of the present invention and does not limit the present invention thereto. Also, descriptions of the dimensions, materials, shapes, relative arrangements, etc. of the components are not intended to limit the scope of the present invention thereto, but are intended to be illustrative. The sizes and positional relationships of the members shown in each drawing may be exaggerated for ease of understanding.

[0012] In this specification or the claims, when there are a plurality of corresponding components with respect to a certain component and they are to be distinguished and expressed separately, "first" and "second" may be appended to the head of the component for distinction. When the objects and viewpoints for distinction are different between this specification and the claims, the same appended notation may not refer to the same object between this specification and the claims.

[0013] (Embodiment) <Non-classical light source device> The non-classical light source device according to an embodiment of the present disclosure includes a first semiconductor region having one conductivity type of p-type and n-type, a second semiconductor region having the other conductivity type of p-type and n-type, a pn junction located between the first semiconductor region and the second semiconductor region, and a plurality of light-emitting regions that are discretely distributed along the pn junction and each emits non-classical light, and a semiconductor structure, and an electrode structure that applies a voltage to the pn junction, wherein the base materials of the first semiconductor region and the second semiconductor region are formed from an indirect-transition semiconductor, and when viewed from a direction perpendicular to the pn junction using a camera with a spatial resolution of 10 μm at a predetermined frame rate, the lights emitted from the plurality of light-emitting regions are observed to be separated.

[0014] With such a non-classical light source device, non-classical light can be emitted with a simple configuration. Non-classical light refers to light that satisfies the relationship of g (2) (τ) such that g (2) (0) < g (2) (τ) (τ ≠ 0) and represents anti-bunching of photons. Note that the intensity correlation function g (2) (τ) represents the temporal correlation between two photons.

[0015] The non-classical light source device according to this embodiment has a plurality of light-emitting regions. Focusing on each of the plurality of light-emitting regions, the light-emitting region emits non-classical light having a plurality of photons as pulsed light at a certain pulse frequency by using dressed photons, which are a kind of near-field light. The dressed photons are considered to be virtual photons representing a state in which electrons and holes existing in a semiconductor interact with photons. The dressed photons, which are virtual photons, can exist as dressed photon phonons via, for example, phonons representing lattice vibrations in a crystal, particularly coherent phonons. When the dressed photon phonons decay into photons and phonons, the momentum of the photons has an uncertainty component corresponding to the phonons, and its magnitude is as large as the momentum of the phonons. Therefore, even in an indirect-transition semiconductor, the dressed photon phonons can compensate for the difference in momentum between the highest energy of the valence band and the lowest energy of the conductor, and it becomes possible to emit light having an energy lower than the bandgap of the indirect-transition semiconductor.

[0016] Coherent phonons can stably exist, for example, in dopant pairs formed by impurities doped into a semiconductor. Such dopant pairs can be formed by a special annealing called dressed photon phonon-assisted annealing (hereinafter referred to as "DPP annealing"). DPP annealing is a method in which a semiconductor having impurities is irradiated with light having a predetermined peak wavelength while flowing a forward current through the semiconductor. Details of DPP annealing will be described later.

[0017] Hereinafter, with reference to FIG. 1, a basic configuration example of a non-classical light source device according to an embodiment of the present disclosure will be described. In the following description, for simplicity, the non-classical light source device is simply referred to as a "light source device".

[0018] FIG. 1 is a perspective view schematically showing the configuration of a light source device 100 according to an exemplary embodiment. In the drawing, for reference, an X-axis, a Y-axis, and a Z-axis orthogonal to each other are schematically shown. The direction of the arrow on the X-axis is referred to as the +X direction, and the opposite direction is referred to as the -X direction. When the ±X directions are not distinguished, it is simply referred to as the X direction. The same applies to the Y-axis and the Z-axis. In this specification, for ease of explanation, the +Z direction is referred to as "upward", and the -Z direction is referred to as "downward". Also, a portion located "upward" is referred to as the "upper part", and a portion located "downward" is referred to as the "lower part". This does not limit the orientation of the light source device 100 during use, and the light source device 100 can be used in any orientation.

[0019] The light source device 100 shown in FIG. 1 includes a semiconductor structure 10, a lower electrode 20a, and an upper electrode 20b. Below, the configurations of the semiconductor structure 10, the lower electrode 20a, and the upper electrode 20b will be described.

[0020] [Semiconductor structure 10] The semiconductor structure 10 has a first semiconductor region 12 and a second semiconductor region 14 whose base material is formed from an indirect transition type semiconductor. The first semiconductor region 12 has a first impurity of a first conductivity type, which is one of p-type and n-type. The second semiconductor region 14 has a second impurity of a second conductivity type, which is the other of p-type and n-type. The semiconductor structure 10 has a pn junction 16 located between (at the interface of) the first semiconductor region 12 and the second semiconductor region 14. The pn junction 16 can be parallel to, for example, the XY plane. The semiconductor structure 10 has a back surface 10s1 in the first semiconductor region 12 and a front surface 10s2 in the second semiconductor region 14. The back surface 10s1 and the front surface 10s2 can be parallel to, for example, the XY plane.

[0021] [First semiconductor region 12] The first semiconductor region 12 is formed from an indirect semiconductor. The base material of the first semiconductor region 12 can be at least one semiconductor selected from the group consisting of, for example, silicon (Si) germanium (Ge), silicon carbide (SiC), gallium phosphide (GaP), or diamond. A preferred base material of the first semiconductor region 12 is Si. When the base material is Si, the first semiconductor region 12 has, as a first impurity, at least one type of atom selected from the group consisting of phosphorus (P) atoms, arsenic (As) atoms, antimony (Sb) atoms, boron (B) atoms, and aluminum (Al) atoms. When the first conductivity type is n-type, the first impurity is preferably an As atom or an Sb atom. The concentration of the first impurity is, for example, 1.0×10 14 cm -3 or more and 1.0×10 20 cm -3 or less. Note that the first semiconductor region 12 may be an n-type silicon substrate, or may include an n-type silicon semiconductor layer provided on the n-type silicon substrate in addition to the n-type silicon substrate.

[0022] [Second Semiconductor Region 14] The second semiconductor region 14 is formed from an indirect semiconductor. The base material of the second semiconductor region 14 can be the same as the base material of the first semiconductor region 12. The second impurity can have a concentration gradient in a direction perpendicular to the surface 10s2. When the base material of the first semiconductor region 12 is Si and the second conductivity type is p-type, the second impurity is preferably a B atom or an Al atom. The concentration distribution of the second impurity can have a peak at a certain depth from the surface 10s2. The peak concentration of the second impurity in the depth direction is, for example, 1.0×10 16 cm -3 or more and 1.0×10 20 cm -3 or less.

[0023] The concentrations of the first and second impurities can be analyzed, for example, by secondary ion mass spectroscopy (SIMS) or three-dimensional atom probe.

[0024] The high-concentration impurities near the surface can reduce the contact resistance with the upper electrode.

[0025] [Lower electrode 20a and upper electrode 20b] The lower electrode 20a is provided on the back surface 10s1, and the upper electrode 20b is provided on the surface 10s2. A voltage is applied to the pn junction 16 via the lower electrode 20a and the upper electrode 20b. In this specification, the lower electrode 20a and the upper electrode 20b are also collectively referred to as the "electrode structure". The upper electrode 20b has, for example, a plurality of through holes as a light-transmitting region. The plurality of through holes may be formed, for example, by making the upper electrode 20b into a mesh shape. By applying a steady DC voltage to the pn junction 16, non-classical light is generated inside the semiconductor structure 10, and the non-classical light is emitted to the outside from the surface 10s2 through the light-transmitting region of the upper electrode 20b. The upper electrode 20b can be, for example, a single-layer or multi-layer structure containing at least one metal such as copper (Cu), chromium (Cr), aluminum (Al), gold (Au), titanium (Ti), platinum (Pt), and silver (Ag). When the upper electrode 20b is a light-transmitting electrode, since the light-transmitting electrode itself has a light-transmitting region, the upper electrode 20b does not need to have a plurality of through holes. The transmittance of the non-classical light in the light-transmitting region can be, for example, 60% or more, preferably 80%. At this time, the upper electrode 20b can be a light-transmitting electrode such as ITO.

[0026] The lower electrode 20a reflects upward the non-classical light generated inside the semiconductor structure 10 and going downward. Thereby, the extraction efficiency of the non-classical light can be improved. The lower electrode 20a can be, for example, a single-layer or multi-layer structure containing at least one metal such as Cu, Cr, Al, Au, Ti, Pt, and Ag.

[0027] Next, with reference to FIG. 2, it will be explained where non-classical light is generated inside the semiconductor structure 10. FIG. 2 is a cross-sectional view obtained by cutting the second semiconductor region 14 shown in FIG. 1 along the dashed line. The cut surface is located along the pn junction 16 and is parallel to the XY plane. As shown in FIG. 2, the light source device 100 has a plurality of light-emitting regions 30a with different dimensions and non-light-emitting regions 30b surrounding each light-emitting region 30a in the second semiconductor region 14. The plurality of light-emitting regions 30a are discretely distributed along the pn junction 16 shown in FIG. 1. In this specification, "the plurality of light-emitting regions 30a are discretely distributed" includes both the case where the plurality of light-emitting regions 30a are regularly distributed via the non-light-emitting regions 30b and the case where they are irregularly distributed. The plurality of light-emitting regions 30a are considered to be located in the vicinity of the depletion layer formed by the pn junction 16. Each light-emitting region 30a emits non-classical light having a plurality of photons as an optical pulse at a certain pulse frequency. Each light-emitting region 30a actually has a three-dimensional shape rather than the planar shape shown in FIG. 2, spreads relatively large in the XY plane, and spreads relatively small in the Z direction. In this specification, the light-emitting region is defined by a region where the light intensity is 2 equal to or greater than 1 / e of the peak intensity. e is the base of the natural logarithm. Each light-emitting region 30a shown in FIG. 2 has an elliptical shape, but may actually have a more complex shape.

[0028] When viewed from a direction perpendicular to the pn junction 16, the area of each light-emitting region 30a can be, for example, 25 μm 2 or less. Each light-emitting region 30a can exist, for example, inside a virtual square with a side length of 5 μm. Also, when using a camera with a spatial resolution of 10 μm and at a predetermined frame rate, when viewed from a direction perpendicular to the pn junction, each light emitted from the plurality of light-emitting regions is observed separately. The predetermined frame rate can be, for example, 16.7 milliseconds. Also, when viewed from a direction perpendicular to the pn junction 16, the shortest distance between two adjacent light-emitting regions among the plurality of light-emitting regions 30a can be, for example, 10 μm or more. Preferably, the shortest distance between a certain light-emitting region 30a and another light-emitting region 30a adjacent thereto closest can be, for example, 10 μm or more. That the shortest distance between two adjacent light-emitting regions is 10 μm or more means that when viewed from a direction perpendicular to the pn junction at a predetermined frame rate using a camera with a spatial resolution of 10 μm, it suffices to confirm that each light emitted from the plurality of light-emitting regions is observed separately.

[0029] The principle by which non-classical light having a plurality of photons is emitted from each light-emitting region 30a is speculated as follows. Each light-emitting region 30a has a plurality of dopant pairs. The dopant pairs are formed by pairs of second impurities. The non-light-emitting region 30b is a region that does not have such dopant pairs or a region that does not have a sufficient amount of dopant pairs for the generation of non-classical light. When a steady forward voltage is applied to the pn junction 16 by the electrode structure, dressed photon phonons are generated in the dopant pairs. Thereby, the light-emitting region 30a can emit photons. When a photon is emitted from one of the plurality of dopant pairs in a certain light-emitting region 30a, other dopant pairs are induced by the photon to also emit photons. By such stimulated emission, a plurality of photons are synchronously emitted as non-classical light from the above-described light-emitting region 30a. The plurality of photons emitted synchronously have the same quantum state (for example, polarization state). Therefore, each light-emitting region 30a functions as a local oscillator without a resonator structure. Note that the light-emitting region 30a that emits light using dressed photon phonons can be referred to as a "near-field light formation region".

[0030] The number of dopant pairs in each of at least two of the plurality of light-emitting regions 30a can be different from each other. Therefore, the areas of the at least two light-emitting regions can be different from each other. Due to the difference in the number of dopant pairs, the number of photons emitted from the at least two light-emitting regions can also be different from each other. In other words, when a certain light-emitting region 30a behaves as a state defined by n photons, at least one of the other light-emitting regions 30a can behave as a state defined by m photons (n≠m). For example, if a certain light-emitting region 30a is in a photon number state |n> with a photon number of n, another light-emitting region 30a can be in a photon number state |m>, (n≠m). Alternatively, in a certain light-emitting region 30a, n single photons are generated from a plurality of dopant pairs included in the light-emitting region 30a, and m single photons (n≠m) can be generated from at least one of the other light-emitting regions 30a. This can be inferred from the fact that the emission intensities in a predetermined integration time can be different in at least two of the plurality of light-emitting regions 30a. Among the plurality of light-emitting regions 30a, two adjacent light-emitting regions are separated by a certain distance via a non-light-emitting region 30b. Therefore, the dressed photon phonons generated in one light-emitting region 30a emit a plurality of photons at independent timings without affecting the other light-emitting region 30a.

[0031] The energy of each of the above photons depends on the energy of the irradiation light during DPP annealing. When the energy of the irradiation light during DPP annealing is lower than the energy of the bandgap of the indirect-transition semiconductor, the energy of each photon becomes lower than the energy of the bandgap of the indirect-transition semiconductor. Depending on the conditions of DPP annealing, the energy of each photon may coincide with the energy of the irradiation light during DPP annealing, or may deviate from the energy of the irradiation light during DPP annealing. The polarization direction of each photon coincides with the polarization direction of the irradiation light during DPP annealing.

[0032] Next, with reference to FIG. 3, the principle by which non-classical light is emitted from each light-emitting region 30a at a pulse frequency will be described. FIG. 3 is a diagram schematically showing the current-voltage characteristics of the semiconductor structure 10 in the present embodiment. The dashed-dotted line represents voltage values V1 and V2, and the broken line represents a certain voltage value between them. The two arrows shown in FIG. 3 represent the intersections of the current-voltage characteristics and the broken line. As shown in FIG. 3, as the current I increases, the voltage V increases monotonically and then decreases monotonically. The semiconductor structure 10 exhibits a negative resistance in which the correlation between the current I and the voltage V becomes negative.

[0033] When a steady DC voltage is applied to the semiconductor structure 10 by the electrode structure, when the voltage V is 0 or more and less than V1, the current I shows one value, and when the voltage V is V1 or more and less than V2, the current I shows two values. When the voltage of the broken line shown in FIG. 3 is applied, relaxation oscillation occurs in which the current I alternately changes between two values (see the arrows). Due to this relaxation oscillation, it is considered that the light source device 100 is periodically driven and non-classical light is emitted at a pulse frequency. After the emission of non-classical light, the current changes from a high value to a low value. Assuming that each light-emitting region 30a has an electrically connected resistor R and capacitor C in series, the pulse frequency can be determined by f = 1 / (2πCR). The electrical resistance R can be different before and after the emission of the optical pulse reflecting the negative resistance. The capacitance C is determined by the dimensions of each light-emitting region 30a. The pulse frequency can be, for example, 100 MHz or more and 10 GHz or less. The pulse frequencies of at least two of the plurality of light-emitting regions 30a can be different from each other due to differences in the dimensions of the light-emitting regions 30a.

[0034] As described above, the light source device 100 according to the present embodiment can emit non-classical light having a plurality of photons as optical pulses at a certain pulse frequency from each of the plurality of light-emitting regions 30a with a simple configuration of the semiconductor structure 10 and the electrode structure.

[0035] <Method for manufacturing non-classical light source device> A method for manufacturing a non-classical light source device according to an embodiment of the present disclosure includes a step of preparing a semiconductor structure having a first semiconductor region having a first impurity of a first conductivity type which is one of p-type and n-type, and a second semiconductor region having a second impurity of a second conductivity type which is the other of p-type and n-type, and a step of irradiating the semiconductor structure with light while flowing a forward current through the semiconductor structure in a state where the semiconductor structure is thermally contacted with a cooling substrate having a temperature greater than -40°C and less than 15°C to diffuse the second impurity. By such a method for manufacturing a non-classical light source device, a non-classical light source device that emits non-classical light with a simple configuration can be manufactured.

[0036] Hereinafter, a method for manufacturing a non-classical light source device according to an embodiment of the present disclosure will be described with reference to FIGS. 4A to 4F. FIGS. 4A to 4F are diagrams for explaining an example of steps in the method for manufacturing a non-classical light source device according to the present embodiment. In the method for manufacturing a non-classical light source device of the present disclosure, a plurality of non-classical light source devices can be manufactured by singulating a semiconductor wafer. Therefore, mass production of non-classical light source devices is possible.

[0037] [Step of preparing semiconductor structure 10A] As shown in FIG. 4A, a wafer-like semiconductor structure 10A having a first semiconductor region 12A and a second semiconductor region 14A is prepared. The semiconductor structure 10A has a back surface 10AS1 in the first semiconductor region 12A and a front surface 10AS2 in the second semiconductor region 14A. The first semiconductor region 12A has a first impurity of a first conductivity type, which is one of p-type and n-type. The second semiconductor region 14A has a second impurity of a second conductivity type, which is the other of p-type and n-type. In this step, the first impurity is activated, but the second impurity is not activated. The base materials of the first semiconductor region 12A and the second semiconductor region 14 are formed from an indirect-transition semiconductor. The base material can be at least one semiconductor selected from the group consisting of, for example, Si, Ge, SiC, GaP, or diamond. The dimension of the first semiconductor region 12A in the Z direction is, for example, 10 μm or more and 1000 μm or less, and the dimension of the second semiconductor region 14A in the Z direction can be, for example, 2 μm or more and 10 μm or less. Note that the semiconductor structure 10A may be wafer-like as shown in FIG. 4A, but is not limited thereto. For example, a pre-individualized state may be used as the semiconductor structure 10A.

[0038] The semiconductor structure 10A can be formed by the following two methods. The first method is a method of ion-implanting a second impurity of a second conductivity type, which is the other of p-type and n-type, into a semiconductor substrate containing a first impurity of a first conductivity type, which is one of p-type and n-type. Among the semiconductor substrate, the ion-implanted region is the second semiconductor region 14A, and the other region is the first semiconductor region 12A. The second method is a method of forming a semiconductor layer of a first conductivity type by chemical vapor deposition on a semiconductor substrate containing a first impurity of a first conductivity type, which is one of p-type and n-type, and ion-implanting a second impurity, which is the other of p-type and n-type, on the surface of the semiconductor layer of the first conductivity type. The semiconductor substrate is, for example, a semiconductor single crystal substrate, and the semiconductor layer can be, for example, a semiconductor epitaxial growth layer. Among the semiconductor layer, the ion-implanted region is the second semiconductor region 14A, and the other region of the semiconductor layer and the entire region of the semiconductor substrate are the first semiconductor region 12A.

[0039] There is no particular limitation on how the first impurity is distributed inside the first semiconductor region 12A. However, it is preferable that the first impurity is uniformly distributed inside the first semiconductor region 12A in order to reduce the resistivity of the first semiconductor region 12A. As a result, when performing DPP annealing, Joule heat generated in the first semiconductor region 12A can be suppressed to a low level, facilitating heat dissipation. The concentration of the first impurity is, for example, 1.0×10 14 cm -3 or more and 1.0×10 20 cm -3 or less. When the base material of the first semiconductor region is Si, the first impurity is, for example, at least one type of atom selected from the group consisting of P atoms, As atoms, Sb atoms, B atoms, and Al atoms. When the first conductivity type is n-type, the first impurity is preferably an As atom or an Sb atom. When the semiconductor structure 10A is obtained by the first method, the first semiconductor region 12A consists of a semiconductor substrate. In this case, the concentration of the first impurity contained in the first semiconductor region 12A is preferably 1.0×10 14 cm -3 or more and 1.0×10 20 cm -3 or less. When the semiconductor structure 10A is obtained by the second method, the first semiconductor region 12A consists of a semiconductor layer of the first conductivity type provided by chemical vapor deposition on a semiconductor substrate in addition to the semiconductor substrate. In this case, the concentration of the first impurity contained in the semiconductor substrate is 1.0×10 14 cm -3 or more and 1.0×10 20 cm -3 or less, and the concentration of the first impurity contained in the semiconductor layer in the first semiconductor region 12A is preferably 1.0×10 14 cm -3 or more and 1.0×10 20 cm -3 or less. The concentration of the first impurity contained in the semiconductor layer is more preferably 1.0×10 14 cm -3 or more and 1.0×10 16 cm -3 or less.

[0040] The impurity concentration of the semiconductor structure 10A can be estimated, for example, with reference to the relationship between the impurity concentration and the electrical resistivity shown in John C. Irvin, “Resistivity of bulk silicon and of diffused layers in silicon”, The Bell System Technical Journal, 41, 387 (1962).

[0041] The second impurity has a concentration gradient in the depth direction, and the concentration distribution of the second impurity may have a peak at a certain depth from the surface. The peak concentration of the second impurity in the depth direction is, for example, 1.0×10 16 cm -3 or more and 1.0×10 20 cm -3 or less. The concentration distribution of the second impurity may have a relatively high concentration in a region in a plane perpendicular to the depth direction and a relatively low concentration in a region outside the region. When the base material of the first semiconductor region is Si, the second impurity is, for example, an atom capable of forming a second semiconductor region of a second conductivity type different from the first conductivity type among P atoms, As atoms, Sb atoms, B atoms, and Al atoms. When the second conductivity type is the p-type, the second impurity is preferably a B atom or an Al atom. When the atom of the second impurity is lighter than the atom of the first impurity, the second impurity can be diffused by DPP annealing described later to form the light-emitting region 30a formed by the population of dopant pairs.

[0042] [Step of forming the lower electrode 20A and the upper electrode 20B] In the next step, as shown in FIG. 4B, a lower electrode 20A is formed on the back surface 10AS1 of the semiconductor structure 10A, and an upper electrode 20B is formed on the surface 10AS2. The upper electrode 20B has a light-transmitting region that transmits the irradiation light during DPP annealing. The transmittance of the light-transmitting region with respect to the irradiation light is, for example, 60% or more, and preferably 80% or more. The formation of the lower electrode 20A and the upper electrode 20B can be performed, for example, by sputtering. When a plurality of through holes are provided as the light-transmitting region in the upper electrode 20B as described later, patterning by etching can be further performed, for example.

[0043] The lower electrode 20A and / or the upper electrode 20B can be formed of a metal selected from at least one selected from the group consisting of Cu, Cr, Al, Au, Ti, Pt, and Ag. Alternatively, the lower electrode 20A and / or the upper electrode 20B can be a light-transmitting electrode formed of, for example, ITO.

[0044] Regardless of whether the lower electrode 20A is formed of a metal or a light-transmitting electrode, it can have, for example, a flat plate shape. On the other hand, when the upper electrode 20B is formed of a metal, it can have, for example, a mesh shape. The mesh shape has, for example, a plurality of through holes two-dimensionally arranged along the surface 10AS2. The irradiation light during DPP annealing can pass through the plurality of through holes and be incident on the surface 10AS2 of the semiconductor structure 10A. When the upper electrode 20B is a light-transmitting electrode, since the light-transmitting electrode itself has a light-transmitting region, the upper electrode 20B can be formed over the entire surface of the surface 10AS2. As a result, the current can be spread over the entire semiconductor structure 10A, and it becomes possible to efficiently generate Joule heat. In the following description, it is assumed that the upper electrode 20B is formed of a metal and has a mesh shape.

[0045] By forming a high-concentration impurity region on the back surface 10AS1 of the semiconductor structure 10A, the contact resistance with the lower electrode 20A can be reduced. Similarly, by forming a high-concentration impurity region on the surface 10AS2 of the semiconductor structure 10A, the contact resistance with the upper electrode 20B can be reduced.

[0046] [Step of singulating] In the next step, as shown in FIG. 4C, the configuration including the semiconductor structure 10A, the lower electrode 20A, and the upper electrode 20B is singulated along a plurality of broken lines arranged in the X direction and the Y direction. The hatched portion shown in FIG. 4C schematically represents the portion taken out by singulation. By singulation, as shown in FIG. 4D, a configuration including the semiconductor structure 10a, the lower electrode 20a, and the upper electrode 20b is obtained. Singulation is performed, for example, by dicing or laser scribing. The semiconductor structure 10a has a first semiconductor region 12a that is a part of the first semiconductor region 12A and a second semiconductor region 14a that is a part of the second semiconductor region 14A. The dimensions in each of the X direction and the Y direction of the singulated configuration are, for example, 10 μm or more and 5000 μm or less, and the dimension in the Z direction can be, for example, 10 μm or more and 1000 μm or less.

[0047] [Step of performing DPP annealing] In the next step, as shown in FIG. 4E, while the semiconductor structure 10a is in thermal contact with a cooling substrate 40 at a temperature greater than -40°C and less than 15°C, a forward current is passed through the semiconductor structure 10a and the semiconductor structure 10a is irradiated with light 62 to thermally diffuse the second impurity. That is, DPP annealing is performed. Thereby, the second impurity can be thermally diffused while making it easier to exhaust the heat applied to the semiconductor structure 10a by the application of the forward current. Therefore, not only is electrical energy consumed by the induced emission using dressed photon phonons, but while Joule heat is dissipated by the cooling substrate, the thermal diffusion of the second impurity proceeds. Through this step, the semiconductor structure 10 shown in FIG. 1 is obtained. That is, the second impurity is activated by DPP annealing, and a pn junction 16 is formed at the interface between the first semiconductor region 12 and the second semiconductor region 14 in the semiconductor structure 10 as shown in FIG. 1. Further, since the temperature of the cooling substrate is relatively low, the thermal diffusion and activation of the second impurity by DPP annealing proceed discretely, and a plurality of light-emitting regions 30a that are discretely distributed are formed as shown in FIG. 2. The temperature of the cooling substrate 40 may preferably be -30°C or higher and 10°C or lower, may be -25°C or higher and 5°C or lower, and may be -25°C or higher and -5°C or lower. More preferably, it is -20°C or higher and -5°C or lower, and particularly preferably -20°C or higher and -10°C or lower. Thereby, the cooling substrate 40 can promote the thermal diffusion of the second impurity by DPP annealing while more efficiently dissipating the Joule heat generated by the application of the forward current.

[0048] The cooling substrate 40 includes, for example, a Peltier element 42 and a heat sink 44. The Peltier element 42 is disposed on the heat sink 44. The upper surface of the Peltier element 42 is in thermal contact with the semiconductor structure 10a via the lower electrode 20a. By passing a current in a specific direction through the Peltier element 42, heat can be moved from the upper surface to the lower surface of the Peltier element 42. The transferred heat is released to the outside through the heat sink 44.

[0049] In the example shown in FIG. 4E, the first semiconductor region 12a is located closer to the cooling substrate 40 than the second semiconductor region 14a, and the second semiconductor region 14a is irradiated with light 62. With such a configuration, the semiconductor structure 10 heated by Joule heat can be efficiently cooled, and the second impurity that is thermally diffused can be efficiently irradiated with the light 62.

[0050] The lower electrode 20a and the upper electrode 20b are electrically connected to the power supply 50. The power supply 50 has wires 52a, 52b. One wire 52a is electrically connected to the lower electrode 20a, and the other wire 52b is electrically connected to the upper electrode 20b. The power supply 50 applies a voltage between the lower electrode 20a and the upper electrode 20b to cause a steady DC forward current to flow through the semiconductor structure 10a. The maximum value of the current density is, for example, 1.0 A / cm 2 Up to 400 A / cm 2 Or less. By energizing under the maximum value of this current density and the conditions of the concentrations of the first and second impurities described above, the second impurity can be efficiently thermally diffused by Joule heat, and the heated semiconductor structure 10a can be efficiently cooled. Further, the maximum value of the current density is preferably 10 A / cm 2 Or more and 100 A / cm 2 Or less. Thereby, while reducing damage to the semiconductor structure 10a and / or the lower electrode 20a and the upper electrode 20b, the second impurity can be efficiently thermally diffused by Joule heat.

[0051] While a forward current is flowing, the light source 60 emits light 62 toward the surface 10as2 of the semiconductor structure 10a. The surface 10as2 of the semiconductor structure 10a is irradiated with the light 62 that has passed through the light-transmitting region of the upper electrode 20B. The light 62 has a peak energy, and the peak energy is lower than the energy of the band gap of the indirect-transition semiconductor that is the base material of the semiconductor structure 10a. In other words, the light 62 has a peak wavelength, and the peak wavelength is longer than the wavelength corresponding to the magnitude of the band gap of the indirect-transition semiconductor that is the base material of the semiconductor structure 10a. When the base material is silicon, the peak wavelength of the light 62 can be, for example, 1.1 μm or more and 4.0 μm or less, preferably 1.2 μm or more and 3.0 μm or less. The output density of the light 62 is, for example, 0.5 W / cm 2 or more and 100 W / cm 2 or less.

[0052] The light 62 is preferably laser light. The full width at half maximum of the spectrum of the laser light is, for example, narrower than that of the spectrum of an LED. Irradiating the surface 10as2 with laser light makes it easier to control the light-emitting characteristics of the manufactured light source device than using an LED as the light source of the light 62. The time of DPP annealing can be, for example, 10 minutes or more and 36 hours or less.

[0053] Due to energization, Joule heat is generated in the semiconductor structure 10a, and the second impurity thermally diffuses in the second semiconductor region 14a. Due to the irradiation with the light 62, dressed photons and dressed photon phonons are generated at the position of the second impurity. Also, due to the population inversion caused by the forward current, light having an energy corresponding to the peak energy of the light 62 is induced to emit. Due to this induced emission, the second impurity loses energy. Compared with the case where the second impurity diffuses only by heat, the diffusion of the second impurity is suppressed by the local cooling accompanying the energy loss due to the induced emission. As a result, it is considered that the second impurities form dopant pairs and are self-organizedly distributed along the interface between the first semiconductor region 12a and the second semiconductor region 14a.

[0054] When performing DPP annealing at room temperature, a plurality of dopant pairs are distributed throughout the region of the second semiconductor region 14a that is located along the interface between the first semiconductor region 12a and the second semiconductor region 14a. In contrast, when performing DPP annealing on the cooling substrate 40, since the Joule heat is rapidly taken away by the cooling substrate 40, a region where the second impurity is not sufficiently diffused is generated. In such a region, it is considered that at least a sufficient amount of dopant pairs of the second impurity that contribute to light emission are not formed. As a result, a plurality of near-field light forming regions each having a plurality of dopant pairs are discretely distributed along the interface between the first semiconductor region 12a and the second semiconductor region 14a. The near-field light forming region corresponds to the light emitting region 30a shown in FIG. 2. When the temperature of the cooling substrate 40 becomes -40°C or lower, the second impurity hardly thermally diffuses in the second semiconductor region 14a, and the near-field light forming region is not formed. The light source device 100 shown in FIG. 1 can be manufactured by the above-described steps described with reference to FIGS. 4A to 4E.

[0055] [Modification Example] As shown in FIG. 4F, a configuration including the semiconductor structure 10A, the lower electrode 20A, and the upper electrode 20B is arranged on the cooling substrate 40, and after performing DPP annealing, it is diced to obtain the non-classical light source device 100. The conditions for DPP annealing can be the same as the above-described conditions. By dicing after performing DPP annealing in this way, the production efficiency is improved. The hatching and broken lines shown in FIG. 4F schematically represent the regions diced and taken out. By connecting the wires 52a and 52b outside the region diced and taken out, the tip portions of the wires that are likely to be deteriorated by the forward current can be selectively excluded, and the non-classical light source device 100 can be taken out. Thereby, the yield is improved. The Peltier element 42 of the cooling substrate 40 may be one or a plurality may be arranged side by side. Although the semiconductor structure 10A shown in FIG. 4F is illustrated in a wafer form, it is not limited thereto.

[0056] [Application Example] Next, with reference to FIGS. 5A to 5C, an application example of the light source device 100 according to the present embodiment will be described. For example, by using the light source device 100 according to the present embodiment, a single photon source that emits single photons can be realized. FIG. 5A is a diagram schematically showing the configuration of a single photon source device 200 according to an exemplary embodiment. The single photon source device 200 shown in FIG. 5A includes the light source device 100 shown in FIG. 1 and a dimming member 210 that dims a part of a plurality of photons emitted from the light source device 100 to emit single photons. The dimming member 210 dims a part of a plurality of photons emitted from the light source device 100 to single photons, for example, by absorption, reflection, or scattering. The dimming member 210 can be, for example, a glass substrate having a metal or an oxide of the metal formed on its surface, or a glass substrate containing the metal or the oxide of the metal inside. The metal can be appropriately selected according to the light having the wavelength to be dimmed. For example, when dimming light having energy corresponding to a wavelength of 1300 nm, Cr can be used. In the example shown in FIG. 5A, the dimming member 210 is arranged away from the upper electrode 20b, but may be arranged on the upper electrode 20b of the light source device 100. In the example shown in FIG. 5A, out of 7 photons emitted from the light source device 100, 6 photons are absorbed, reflected, or scattered by the dimming member 210, and 1 photon is emitted from the dimming member 210. The arrows shown in FIG. 5A represent the traveling directions of the photons. The emission of a single photon may be confirmed by satisfying the intensity correlation function g (2) (0)<g (2) (τ) and g (2) (0)=0. Note that even if the optical pulses of coherent light emitted from a conventional mode-locked laser at a certain pulse frequency are dimmed, single photons cannot be obtained.

[0057] As another application example, the single photon source device 200 according to the present embodiment may be used in a quantum key distribution device. FIG. 5B is a diagram schematically showing the configuration of a quantum key distribution device 300 according to an exemplary embodiment. The quantum key distribution device 300 shown in FIG. 5B includes a single photon source device 200, a key generator 310, and a modulator 320 on the information transmission side (Alice), an observation device 330 on the information reception side (Bob), and an optical fiber 340 between the information transmission side and the information reception side.

[0058] In the quantum cryptographic communication device 300, a bit string in which the quantum state of a single photon is regarded as one bit is used for the exchange of encryption keys. On the information transmission side, the encryption key generator 310 generates an encryption key, and the modulator 320 modulates the quantum state of each single photon in the single photon train emitted from the single photon source device 200 based on the encryption key. The optical fiber 340 delivers the single photon train having the information of the encryption key. On the information reception side, the observation device 330 observes the single photon train having the information of the encryption key.

[0059] The above exchange of information is called quantum key distribution, which enables communication that is difficult to eavesdrop on. When a bit string in which the quantum state of a plurality of photons rather than a single photon is regarded as one bit is transmitted from a sender to a receiver, even if a third party extracts a part of the plurality of photons, the remaining photons will reach, so the receiver will not notice that they are being eavesdropped on. In contrast, if it is a bit string in which the quantum state of a single photon is regarded as one bit, when a third party extracts a photon, the photon will not reach, so the receiver can notice that they are being eavesdropped on. It is also conceivable that a third party observes the extracted photon and transmits the observed photon to the receiver so that the eavesdropping cannot be detected. However, the quantum state of the photon changes due to the observation, and the third party cannot transmit the photon in the original quantum state to the receiver. Alternatively, it is also conceivable that a third party copies the extracted photon without observing it and transmits the extracted photon as it is to the receiver. However, such copying is impossible due to the no-cloning theorem that an unknown quantum state cannot be copied. Quantum key distribution that uses a bit string in which the quantum state of a single photon is regarded as one bit as a key for encrypting or decrypting information can realize communication that is difficult to eavesdrop on. In this specification, quantum cryptographic communication is not limited to quantum key distribution, but means a communication technology that uses the properties of quantum mechanics to improve the confidentiality of communication.

[0060] As yet another application example, the non-classical light source device 100 according to the present embodiment may be used as a light source for an optical coherence tomography (OCT). Optical coherence tomography is used for diagnostic imaging of the retinal tissue of the fundus of the eye, as well as the eye and its surrounding tissues, and is also expected to be applied to the diagnosis of the superficial tissues of the digestive tract and trachea. Since the non-classical light emitted from the non-classical light source device 100 has the property of having a smaller photon number fluctuation compared to classical light, the noise in the interferometric measurement can be reduced.

[0061] FIG. 5C is a diagram schematically showing the configuration of an optical coherence tomography device 400 according to an exemplary embodiment. The optical coherence tomography device 400 shown in FIG. 5C includes a non-classical light source device 100, a beam splitter 410, a reference mirror 420, and a sensor 430. An object 440 is shown in FIG. 5C. The beam splitter 410 transmits a part of the light emitted from the non-classical light source device 100 toward the object 440 and reflects the remaining part toward the reference mirror 420. The beam splitter 410 reflects the light reflected back from the object 440 toward the sensor 430 and transmits the light reflected back from the reference mirror 420 toward the sensor 430. The sensor 430 detects the superimposed light in which the light reflected back from the object 440 and the light reflected back from the reference mirror 420 interfere with each other. Since the light emitted from the non-classical light source device 100 has little fluctuation in the number of photons, the tomography of the object 440 can be measured more accurately by optical interference with less noise.

[0062] The non-classical light source device 100 and the single photon source device 200 in this embodiment can also be used in a random number generator. FIG. 5D is a diagram schematically showing the configuration of a random number generator 500 according to an exemplary embodiment. The random number generator 500 shown in FIG. 5D includes a non-classical light source device 100, a beam splitter BS1 that transmits and / or reflects photons emitted from the non-classical light source device 100 to at least one of two paths, a detector D1 that detects photons passing through one path, and a detector D2 that detects photons passing through the other path. A plurality of photons emitted from the non-classical light source pass through and / or are reflected by the beam splitter BS1 and pass through at least one path. Since at least one or more photons are emitted from the non-classical light source device 100, one or more photons are detected by at least one of the detector D1 or the detector D2. FIG. 5 illustrates a state in which n1 photons are detected by the detector D1 and n2 photons are detected by the detector D2. Since the number of photons split by the beam splitter is random, random numbers can be generated with the configuration shown in FIG. 5. In addition, since the non-classical light source device 100 can emit photons with a pulse period of 100 MHz or more and 10 GHz or less, random numbers can be generated at high speed. Further, in the non-classical light source device 100, since the emission timings of photons emitted from each light emitting region 30a are independent of each other, the randomness of the random numbers can be enhanced.

[0063] FIG. 5E is a diagram schematically showing another configuration of the random number generator 600 according to an exemplary embodiment. The random number generator 600 shown in FIG. 5E is different from the random number generator 500 shown in FIG. 5D in that the light source is the single photon source device 200. The single photon source device 200 can have a configuration as shown in FIG. 5A. The random number generator 600 transmits or reflects a single photon emitted from the single photon source device 200 to at least one of two paths by the beam splitter BS1. A single photon is detected by either the detector D1 or the detector D2. That is, by using the random number generator 600 as shown in FIG. 5E, a binary random number can be generated. FIG. 5E illustrates a case where one single photon is detected by the detector D1 and no single photon is detected by the detector D2. In the random number generators shown in FIGS. 5D and 5E, by arranging one or more sets of beam splitters and detectors in at least one of the paths after transmission or reflection by the beam splitter BS1, more complex random numbers can be obtained.

[0064] In addition to the above application examples, by adjusting the number of photons emitted from the non-classical light source device 100 according to the present embodiment by the light attenuation member, it is also possible to transmit information by the number of photons. This can be used, for example, in a quantum computer using light.

[0065] <Example 1> Next, Example 1 of the non-classical light source device 100 according to the present embodiment will be described. Hereinafter, the non-classical light source device 100 will be simply referred to as the light source device 100. The light source device according to Example 1 was manufactured by the process described with reference to FIGS. 4A to 4E. In the example shown in FIG. 4A, the semiconductor structure 10A was formed by ion-implanting B atoms twice on the surface of an n-type silicon substrate having Sb atoms as n-type impurities. The electrical resistivity of the n-type silicon substrate was 5 Ωcm. The first ion implantation was performed under the conditions of a dose amount of 2.7×10 14 / cm 2 and an energy of 700 keV, and the second ion implantation was performed under the conditions of a dose amount of 5.3×10 14 / cm2 and was carried out under the condition of energy of 10 keV. As a result, the peak concentration of B atoms was 1.0×10 18 cm -3 at a depth of 1.5 μm from the surface, and 5.0×10 19 cm -3 at a depth of 50 nm from the surface.

[0066] In the example shown in FIG. 4C, the fragmentation was performed by dicing using a diamond blade. In the example shown in FIG. 4E, the temperature of the cooling substrate during DPP annealing was -15°C. The irradiated laser light was continuous-wave laser light with a wavelength of 1.31 μm and an output of 10 W / cm 2 . The forward current was a steady DC current, and the maximum current value was 600 mA. The time of DPP annealing was 3 hours.

[0067] The light source device according to Example 1 manufactured as described above has the configuration shown in FIG. 1. The dimensions of the light source device according to Example 1 in each of the X direction and the Y direction were 1 mm, and the dimension in the Z direction was 150 μm. Among the semiconductor structures 10, the dimension of the second semiconductor region 14 in the Z direction was 2 μm. The lower electrode 20a was formed of a stacked structure of Cr / Al / Au in order from the side closer to the semiconductor structure 10, and the thicknesses of Cr, Al, and Au were 30 nm, 200 nm, and 300 nm, respectively. The upper electrode 20b had a mesh shape and was formed of a stacked structure of Cr / Au in order from the side closer to the semiconductor structure 10. The thicknesses of Cr and Au were 30 nm and 200 nm, respectively.

[0068] FIG. 6 is a photograph of the upper surface of the light source device according to the example. A mesh-shaped upper electrode is provided on the surface of the semiconductor structure, and one wire each is electrically connected vertically and three wires each are electrically connected horizontally to the upper electrode for power supply. A lower electrode is provided on the back surface of the semiconductor structure, and the lower electrode is electrically connected to the wiring of an AlN ceramic wiring board having a high thermal conductivity.

[0069] <Comparative Example 1> The light source device according to Comparative Example 1 was fabricated under the same conditions as in Example 1 except for the following conditions. The temperature of the cooling substrate during DPP annealing was 20°C.

[0070] <Comparative Example 2> The light source device according to Comparative Example 2 was fabricated under the same conditions as in Example 1 except that the temperature of the cooling substrate during DPP annealing was -40°C.

[0071] <Experimental Results> Next, with reference to FIGS. 7A and 7B, the results of photographing the light emission states of the light source devices according to Example 1 and Comparative Example 1 will be described. Light emission was confirmed when a steady DC voltage of 42 V was applied to the light source device according to Example 1. Also, light emission was confirmed when a steady DC voltage of 40 V was applied to the light source device according to Comparative Example 1. Since infrared light is emitted from the light source devices according to Example 1 and Comparative Example 1, an infrared camera was used for this photographing. The spatial resolution of the infrared camera was 10 μm. Also, the frame rate of the infrared camera was 16.7 milliseconds.

[0072] FIG. 7A is a photograph showing the light emission state of the light source device according to Example 1. In FIG. 7A, a part of the portion where light emission was confirmed is shown enlarged. FIG. 7B is a photograph showing the light emission state of the light source device according to Comparative Example 1. As shown in FIG. 7A, in the light source device according to Example 1, a plurality of discrete light emission regions appeared as the portion where light emission was confirmed. The white arrows shown in FIG. 7A represent a part of the plurality of light emission regions. The area of each light emission region shown in FIG. 7A was 25 μm 2The distance between the two adjacent light-emitting regions was 50 μm or more. It was confirmed that each light-emitting region blinks repeatedly by applying a steady DC voltage. In contrast, as shown in FIG. 7B, in the light source device according to Comparative Example 1, a plurality of light-emitting regions distributed discretely could not be confirmed. In the light source device according to Comparative Example 1, the entire surface steadily emitted light, and the emission intensity was higher at the periphery than at the center. Since the resolution of the infrared camera is 10 μm, even if a plurality of light-emitting regions distributed discretely exist, the gap between the two adjacent light-emitting regions is less than 10 μm. Note that the white spots seen on the entire surface in FIG. 7B are camera noise and are not light-emitting regions of the light source device. In addition, the light emission state was also observed in Comparative Example 2 in the same manner, but neither a plurality of light-emitting regions distributed discretely nor a light-emitting region in which the entire surface emits light could be observed. It is considered that the near-field light forming region was hardly formed in Comparative Example 2.

[0073] Next, with reference to Figs. 8A to 8C, the results of measuring the intensity correlation function of the light emitted from the light source devices according to Example 1 and Comparative Example 1 will be described. This measurement was performed using a Hanbury Brown-Twiss experimental system shown in Fig. 10. Details of Fig. 10 will be described later. A part of the light emitted from the light source devices according to Example 1 and Comparative Example 1 was detected by a superconducting single-photon detector 76 via an optical fiber. The superconducting single-photon detector 76 can detect a single photon of infrared light with high sensitivity. The time resolution in the measurement was 50 picoseconds.

[0074] FIG. 8A is a graph showing the relationship between the intensity of light emitted from the light source device according to Example 1 and time. The intensity of light is represented by a photon count value. As shown in FIG. 8A, a light pulse having a plurality of photons is emitted, and the peak intensity of the light pulse increases almost monotonically with time in the time range of 0 nanoseconds to 50 nanoseconds. In the example shown in FIG. 8A, since the pulse frequencies of the light pulses emitted from the plurality of light-emitting regions may differ from each other, it was presumed that light pulses of various pulse frequencies are mixed.

[0075] 8B is a graph showing the relationship between time and the intensity of light emitted at a period of 1.1 nanoseconds (pulse frequency of 900 MHz) from the light source device according to Example 1. As shown in FIG. 8B, it can be seen that a light pulse is emitted at a pulse frequency of 900 MHz from one of the multiple light-emitting regions.

[0076] In addition, by changing the period and measuring the light intensity at a predetermined integration time, it can be confirmed that the intensities of the light emitted from at least two light-emitting regions are different from each other. In this way, in addition to the example shown in Figure 8B, light with pulse frequencies of 800 MHz and 2 GHz was also confirmed. In other words, it was suggested that the pulse frequencies in at least two of the multiple light-emitting regions may be different from each other.

[0077] Fig. 8C is a graph showing the relationship between time and the intensity of the light emitted from the light source device according to Comparative Example 1. As shown in Fig. 8C, light of a nearly constant intensity was steadily measured in the light source device according to Comparative Example 1. On the other hand, no light pulses were measured.

[0078] Next, referring to FIG. 9, the current-voltage characteristics of the semiconductor structure in the embodiment will be described. FIG. 9 is a graph showing the current-voltage characteristics of the semiconductor structure according to the embodiment 1. The current-voltage characteristics were obtained by measuring the voltage difference between the lower electrode and the upper electrode caused by injecting a constant current. As the current I increased, the voltage V monotonically increased and then exhibited a monotonically decreasing negative resistance. As shown in FIG. 9, when the voltage was 0 V or more and less than 35 V, the current I exhibited one value, and when the voltage V was 35 V or more and 60 V or less, the current I exhibited two values. For example, when a voltage of 50 V (see dashed line) was applied, it was presumed that the light source device was periodically driven due to relaxation oscillation in which the current I alternately changed between two values ​​(see arrows), and light pulses were emitted from each light-emitting region at a certain pulse frequency.

[0079] Next, with reference to Fig. 10 to Fig. 12, it will be described that the light emitted from the light source device according to the first embodiment is non-classical light. (2)FIG. is a diagram schematically showing a Hanbury Brown-Twiss experimental system for measuring (τ). The experimental system shown in FIG. 10 includes a light source device 100 according to Example 1, lenses 72a and 72b, an optical fiber 74a for transmitting photons collected by the lens 72a, an optical fiber 74b for transmitting photons collected by the lens 72b, a superconducting single-photon detector 76, and a time-correlation measuring device 78. The superconducting single-photon detector 76 in FIG. 10 can be 4ch-mounted, and a single superconducting single-photon detector can detect photons passing through the optical fibers 74a and 74b, respectively. In this experiment, instead of using a beam splitter, lenses and optical fibers are used to separate a plurality of photons emitted from the light source device 100 so that they travel along the paths of the lens 72a and the optical fiber 74a and the paths of the lens 72b and the optical fiber 74b. Photons traveling along each path were detected by a single superconducting single-photon detector 76. The superconducting single-photon detector 76 output a signal corresponding to the number of detected photons. The time-correlation measuring device 78 output the time correlation of the signals output from the superconducting single-photon detector 76. The intensity correlation function g (2) (τ) is the time integral of the product of the light intensities with a time difference of τ for the light traveling along two paths (i.e., the time correlation). τ represents shifting the light intensities in the two paths by a time τ.

[0080] Whether the light is classical light or non-classical light can be determined by examining the intensity correlation function g (2) (τ). This will be specifically described with reference to FIGS. 11A and 11B. FIGS. 11A and 11B are diagrams schematically showing the behavior of the ideal intensity correlation function g (2) (τ) of classical light (e.g., thermal light source and laser light) and non-classical light (e.g., photon number state). FIG. 11A shows the time correlation in the case of continuous wave, and FIG. 11B shows the time correlation in the case of periodic optical pulses. When the light is treated as a classical electromagnetic wave like a thermal light source, as shown by the dashed-dotted line in FIGS. 11A and 11B, the intensity correlation function g (2) (τ) satisfies g (2) (0) ≧ g (2)It satisfies the relation (τ)(τ≠0). This represents photon bunching. Also, in the case of a coherent state such as laser light, as shown by the dotted lines in FIGS. 11A and 11B, g (2) (0)=g (2) (τ). Note that the g (2) (τ) of the laser light shown in FIG. 11B shows a discrete time correlation with a value of 1. On the other hand, when the light is in a non-classical state, as shown by the solid lines in FIGS. 11A and 11B, the intensity correlation function g (2) (τ) satisfies the relation g (2) (0)<g (2) (τ)(τ≠0). This represents photon anti-bunching. Thus, whether the light is in a non-classical state can be confirmed by checking whether the intensity correlation function g (2) shows the behavior of g (2) (0)<g (2) (τ)(τ≠0). Note that in the examples shown in FIGS. 11A and 11B, at |τ|→∞, g (2) (τ) is normalized to 1. When qualitatively confirming the behavior of photon bunching and anti-bunching, normalization is not necessary. That is, it is sufficient to examine the magnitude relationship of the intensity correlation functions in the cases of τ = 0 and τ≠0 observed in the Hanbury Brown-Twiss experimental system.

[0081] FIG. 12 is a graph of the intensity correlation function of the light emitted from the light source device 100 according to Example 1 at a period of 1.1 nanoseconds (pulse frequency 900 MHz). As shown in FIG. 12, the intensity correlation function satisfies the relation g (2) (0)<g (2) (τ) and shows photon anti-bunching. For classical light, g (2) (0)≧g (2) (τ). Therefore, it can be seen that the light emitted from the light source device 100 according to Example 1 is non-classical light. Furthermore, since g (2) (0)>0, it is speculated that the non-classical light is in a photon number state with two or more photons, a state in which multiple single photons are generated, or a non-classical state close to them.

Industrial Applicability

[0082] The non-classical light source device of the present disclosure can be applied to, for example, a device that utilizes the particle nature of light.

Description of Reference Numerals

[0083] 10, 10a, 10A Semiconductor structure 12, 12a, 12A First semiconductor region 14, 14a, 14A Second semiconductor region 16 pn junction 20a, 20A Lower electrode 20b, 20B Upper electrode 30a Light emitting region 30b Non-light emitting region 40 Cooling substrate 42 Peltier element 44 Heat sink 50 Power supply 52a, 52b Wire 60 Light source 62 Light 72a, 72b Lens 74a, 74b Optical fiber 76 Superconducting single photon detector 78 Time correlation measurement device 100 Non-classical light source device 200 Single photon source device 210 Light attenuation member 300 Quantum key distribution communication device 310 Encryption key generator 320 Modulator 330 Observation device 340 Optical fiber 400 Optical coherence tomography device 410, BS1 Beam splitter 420 Reference mirror 430 Sensor 500, 600 Random number generator D1, D2 Detector

Claims

1. A step of preparing a semiconductor structure having a first semiconductor region having a first impurity of a first conductivity type, which is one of p-type and n-type, and a second semiconductor region having a second impurity of a second conductivity type, which is the other of p-type and n-type; A step of irradiating the semiconductor structure with light while flowing a forward current through the semiconductor structure in a state where the semiconductor structure is thermally contacted with a cooling substrate at -25°C or higher and -5°C or lower to diffuse the second impurity; A method for manufacturing a non-classical light source device, including the above steps.

2. The first semiconductor region is located closer to the cooling substrate than the second semiconductor region, The second semiconductor region is irradiated with the light. The method for manufacturing a non-classical light source device according to Claim 1.

3. The concentration of the first impurity is 1.0×10 １４ cm －３ or more and 1.0×10 ２０ cm －３ or less, and The concentration of the second impurity is 1.0×10¹⁶ cm －３ or more and 1.0×10 ２０ cm －３ or less, and The maximum value of the current density of the forward current is 1.0 A / cm ２ or more and 400 A / cm ２ or less. A method for manufacturing a non-classical light source device according to claim 1 or 2.

4. The base material of the semiconductor structure is an indirect transition type semiconductor, The light has a peak wavelength, and the peak wavelength is longer than the wavelength corresponding to the magnitude of the band gap of the indirect transition type semiconductor. The method for manufacturing a non-classical light source device according to any one of Claims 1 to 3.

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