JP2013222810A - Semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser device which can emit with high extraction efficiency, a terahertz wave having a spread angle which is restricted in a two-dimensional direction.SOLUTION: A semiconductor laser device 1 comprises: a common electrode 3; an annular semiconductor laminate 4 provided on the common electrode 3; a plurality of split electrodes 5 provided on the semiconductor laminate 4 so as to be opposite to the common electrode 3 and circularly arranged; counter electrodes 7 which face the common electrode 3 and electrically connected to the split electrodes 5, respectively; and an insulation layer 6a provided between the common electrode 3 and the counter electrodes 7. The semiconductor laminate 4 has a quantum cascade laser structure and generates a terahertz wave by application of voltage between the common electrode 3 and the split electrodes 5. The semiconductor laminate 4 functions as a meta-material ring resonator together with the common electrode 3, the split electrodes 5, the counter electrodes 7 and the insulation layer 6a to emit the terahertz wave to the outside.

Description

  The present invention relates to a terahertz wave semiconductor laser device.

  The terahertz cascade laser is expected as a terahertz light source that is small and easy to drive. However, since the wavelength of the terahertz wave emitted from the emission end face of the terahertz cascade laser is very long with respect to the emission region at the emission end face, the influence of diffraction appears remarkably and the spread angle becomes large. It is difficult to increase the ratio (extraction efficiency) that can be effectively used as the oscillation light of the cascade laser.

  As a method for suppressing the spread angle of a terahertz wave, a method is known in which a ring-shaped diffraction grating structure is formed on the surface of a terahertz cascade laser and a higher-order diffraction mode emitted from the surface is used (non-patent document). Reference 1 and 2). As another method for suppressing the spread angle of a terahertz wave, a method of combining a terahertz cascade laser and a one-dimensional leaky wave antenna with a metamaterial structure is known (see Non-Patent Documents 3 and 4).

L. Mahler et al., "Distributed feedbackring resonators for vertically emitting terahertz quantum cascade lasers", Optics Express, 17, 13031 (2009). M. S. Vitiello et al., "High efficiency coupling of Terahertz micro-ring quantum cascade lasers to the low-loss opticalmodes of hollow metallic waveguides", Optics Express, 19, 1122 (2011). A. A. Tavallaee et al., "Zero-IndexTerahertz Quantum-Cascade Metamaterial Lasers", IEEE Journal of Quantum Electronics, 46, 1091 (2010). A. A. Tavallaee et al., "Terahertzquantum-cascade laser with active leaky-wave antenna", Applied PhysicsLetters, 99, 141115 (2011).

  However, in the methods described in Non-Patent Documents 1 and 2, since a higher-order diffraction mode is used, the terahertz wave extraction efficiency is not necessarily high. In the methods described in Non-Patent Documents 3 and 4, since the one-dimensional leaky wave antenna of the metamaterial structure is used, the spread angle of the terahertz wave can only be suppressed in the one-dimensional direction.

  Accordingly, an object of the present invention is to provide a semiconductor laser device that can emit a terahertz wave whose divergence angle is suppressed in a two-dimensional direction with high extraction efficiency.

  A semiconductor laser device according to the present invention includes a first electrode, an annular semiconductor laminate provided on the first electrode, and a semiconductor laminate that faces the first electrode and is arranged in an annular shape. A plurality of second electrodes, a third electrode facing the first electrode and electrically connected to each of the second electrodes, a first electrode and a third electrode; The semiconductor stacked body has a quantum cascade laser structure, and a voltage is applied between the first electrode and the second electrode, whereby terahertz In addition to generating a wave, it functions as a metamaterial ring resonator together with the first electrode, the second electrode, the third electrode, and the first insulating layer, and emits a terahertz wave to the outside.

  In this semiconductor laser device, a terahertz wave is generated in a semiconductor stacked body having a quantum cascade laser structure. At this time, since the semiconductor stacked body functions as a metamaterial ring resonator together with the first electrode, the second electrode, the third electrode, and the first insulating layer, the terahertz wave corresponds to the shape of the semiconductor stacked body. A ring-shaped pattern is emitted to the outside. In addition, since the semiconductor stacked body also serves as a part of the configuration of the metamaterial ring resonator, loss when the generated terahertz wave is emitted to the outside hardly occurs. Therefore, according to this semiconductor laser device, the terahertz wave whose divergence angle is suppressed in the two-dimensional direction can be emitted with high extraction efficiency.

  Here, the second electrodes may be arranged in a ring shape with a period of less than a quarter of the wavelength of the terahertz wave. According to this, as the metamaterial ring resonator with respect to the terahertz wave, the first electrode, the semiconductor stacked body, the second electrode, the third electrode, and the first insulating layer can function well.

  In addition, the first electrode, the semiconductor stacked body, the second electrode, the third electrode, and the first insulating layer are dispersed so that the metamaterial ring resonator has a unit structure exhibiting balanced dispersion characteristics. You may be comprised so that the phase constant of a characteristic may be set to 0. According to this, since the wavelength in the metamaterial ring resonator becomes infinite and does not depend on the frequency, the resonator length can be freely designed. Further, the spread angle of the terahertz wave can be more reliably suppressed in the two-dimensional direction.

  The semiconductor laser device of the present invention may further include a substrate that supports the semiconductor stacked body, and the first electrode may be provided on the substrate. According to this, each component of the semiconductor laser device can be stabilized.

  Further, the semiconductor stacked body may be circular. According to this, a terahertz wave forming a circular pattern can be emitted.

  The semiconductor laser device of the present invention is formed on the outer side surface of the semiconductor stacked body, and electrically connects the second electrode and the third electrode, the semiconductor stacked body, And a second insulating layer provided between the four electrodes. According to this, the structure for realizing the configuration in which the phase constant of the dispersion characteristic of the metamaterial ring resonator is 0 can be simplified.

  According to the present invention, it is possible to provide a semiconductor laser device that can emit a terahertz wave whose divergence angle is suppressed in a two-dimensional direction with high extraction efficiency.

1 is a plan view of a semiconductor laser device according to an embodiment of the present invention. FIG. 2 is a side view of the semiconductor laser device of FIG. 1. It is sectional drawing along the III-III line of FIG. FIG. 2 is an equivalent circuit diagram of a unit structure of a metamaterial ring resonator in the semiconductor laser device of FIG. 1. 2 is a graph showing dispersion characteristics of a unit structure of a metamaterial ring resonator in the semiconductor laser device of FIG. 1. It is a top view of the semiconductor laser apparatus of other embodiment of this invention.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same part or an equivalent part, and the overlapping description is abbreviate | omitted.

  As shown in FIGS. 1 to 3, the semiconductor laser device 1 includes a square plate-like substrate 2 made of InP. A common electrode (first electrode) 3 made of gold and indium is provided on the surface 2 a of the substrate 2. A circular annular semiconductor laminate 4 is provided on the surface 3 a of the common electrode 3. That is, the substrate 2 supports the semiconductor stacked body 4.

  The semiconductor stacked body 4 has a quantum cascade laser structure made of InGaAs / InAlAs. The semiconductor stacked body 4 is disposed at the center on the surface 2 a of the substrate 2. A plurality of divided electrodes (second electrodes) 5 made of gold are provided on the surface 4 a of the semiconductor stacked body 4 so as to face the common electrode 3 and are arranged in a ring shape. The semiconductor laminate 4 is sandwiched between the common electrode 3 and the divided electrode 5 to form a ring resonator using a metal waveguide, and a voltage is applied between the common electrode 3 and the divided electrode 5. Thus, a terahertz wave is generated.

  On the surface 3a of the common electrode 3, an insulating layer (first insulating layer) 6a made of a silicon nitride film is stacked in a region outside the region where the semiconductor stacked body 4 is provided. An insulating layer (second insulating layer) 6 b made of a silicon nitride film is also provided on the outer side surface 4 b of the semiconductor stacked body 4. The insulating layers 6a and 6b are integrally formed with each other. That is, the insulating layer 6 a extends on the surface 3 a of the common electrode 3, is bent along the side surface 4 b at a portion in contact with the outer side surface 4 b of the semiconductor stacked body 4, and continuously from there as the insulating layer 6 b. The side surface 4b is also covered. The upper end of the insulating layer 6 b covering the side surface 4 b is in contact with the surface of each divided electrode 5.

  A plurality of rectangular counter electrodes (third electrodes) 7 made of gold are provided on the surface 6 c of the insulating layer 6 a so as to face the common electrode 3. The number of the counter electrodes 7 is the same as the number of the divided electrodes 5, and each of the counter electrodes 7 extends along the ring so as to correspond to each of the divided electrodes 5 in the radial direction of the ring of the semiconductor stacked body 4. It is arranged in a ring.

  A plurality of connection electrodes (fourth electrodes) 8 made of gold are formed on the outer side surface 4b of the semiconductor stacked body 4 via an insulating layer 6b. Each connection electrode 8 electrically connects each divided electrode 5 and each counter electrode 7. In other words, each connection electrode 8 and each counter electrode 7 extend along the insulating layers 6b and 6a with each divided electrode 5 as a starting end.

  The divided electrodes 5 are arranged in a ring with a period of less than a quarter of the wavelength of the target terahertz wave. That is, the divided electrodes 5 are separated from each other by the gap 9 and have a metamaterial structure on the surface 4 a of the semiconductor stacked body 4. Thereby, the semiconductor stacked body 4 functions as a metamaterial ring resonator together with the common electrode 3, the divided electrode 5, the counter electrode 7, the connection electrode 8, and the insulating layers 6 a and 6 b, and the terahertz wave generated in the semiconductor stacked body 4 is Emits outside. Here, the period corresponds to the total value of the size of one divided electrode 5 and one gap 9 in the circumferential direction in which each divided electrode 5 and gap 9 are arranged. For example, it is a value obtained by dividing the length of the circumference passing through the center of the semiconductor stacked body 4 by the number of divided electrodes 5 (or gaps 9).

  Here, the semiconductor stacked body 4, the common electrode 3, the divided electrode 5, the counter electrode 7, the connection electrode 8, and the insulating layers 6 a and 6 b have a unit structure ΔZ that exhibits a dispersion characteristic of a balanced system as a metamaterial ring resonator. And the phase constant of the dispersion characteristic is set to zero. The dispersion characteristics of the metamaterial ring resonator will be described next.

FIG. 4 shows an equivalent circuit of a unit structure ΔZ of a part that functions as a metamaterial ring resonator in the semiconductor laser device 1. As shown in FIG. 4 (a), the equivalent circuit of the unit structure ΔZ includes a series capacitance C _L is formed between the divided electrodes 5 adjacent, and parallel inductance L _L corresponding to the connecting electrode 8, the counter electrode 7 and the first parallel capacitance C _g is formed between the common electrode 3, the divided electrode 5 and the second parallel capacitance C _R formed between the common electrode 3, corresponding to the divided electrodes 5 It consists of five elements of the series inductance L _R. This equivalent circuit can be considered as a left-hand / right-handed composite line, and can be said to have a so-called transmission line type metamaterial structure.

（式中、ωはテラヘルツ波の角周波数を示し、ｊは虚数単位を示す。） Here, the impedance Z constituted by the parallel inductance L _L and the first parallel capacitance C _g is expressed by the following equation (1).

(Wherein, ω represents the angular frequency of the terahertz wave, and j represents the imaginary unit.)

_If the value of C _g in Equation (1) is sufficiently large, the term including C _g can be ignored, and therefore the impedance Z can be considered to be composed of only the L _L term. That is, the equivalent circuit shown in FIG. 4 (a), may be as shown in FIG. 4 (b), regarded as an equivalent circuit in which the first parallel capacitance C _g is not present.

In this case, it can be said that the divided electrode 5 is virtually grounded to the common electrode 3 via the connection electrode 8. That is, although there is no insulating layer 6a between the counter electrode 7 and the common electrode 3, it is not connected as a DC circuit, but as an AC circuit having a frequency in the terahertz region, the counter electrode 7 and the common electrode 3 to are connected by a first parallel capacitance C _g is formed between, the alternating current circuit of the frequency of the terahertz range, split electrodes 5 via the connection electrode 8, the common electrode 3 power is connected It will be grounded. The reason why virtual grounding is used instead of direct grounding is that when the divided electrode 5 is connected to the common electrode 3 as a DC circuit, it becomes impossible to apply a voltage to the semiconductor stacked body 4 and generate terahertz waves. It is because it is not possible.

The virtual grounding can be realized as follows, for example. If the insulating layers 6a and 6b are silicon nitride films having a film thickness of 0.1 μm and a relative dielectric constant of 7, and the size of the counter electrode 7 is 30 μm × 30 μm, C _g = 560 fF. In the case of = 2 THz × 2π, the term including C _g can be ignored. Further, if the connection electrode 8 has a width of 2 μm and a length of 10 μm, L _L = about 5.7 pH, and in the case of ω = 2 THz × 2π in equation (1), L _L is two digits more than the term including C _g. the degree increases, it is possible to ignore the terms involving C _g. Therefore, the virtual grounding is possible.

When the virtual grounding is established, the metamaterial ring resonator adjusts the four elements (C _L , L _L , C _R , and L _R ) in the equivalent circuit shown in FIG. Can be controlled. Here, the dispersion characteristic is a characteristic representing the relationship between the phase constant β and the angular frequency ω of the terahertz wave, and is specifically represented by the graph shown in FIG. The phase constant β is obtained by the following equation (2).

Here, the shape and material of the members constituting the semiconductor laminate 4, the common electrode 3, the divided electrode 5, the counter electrode 7, the connection electrode 8, and the insulating layers 6a and 6b, and the distance between the adjacent divided electrodes 5 (that is, the width of the gap 9) by variously changing the like, metamaterial ring resonator equilibrium (i.e. ^{_{(C L · L R) (}} -1/2) = (C R · L L) (-1 / ²⁾ , the phase constant β of the dispersion characteristic can be zero. Alternatively, a desired angular frequency ω can be set in advance, and the metamaterial ring resonator can be configured so as to have the angular frequency ω when the phase constant β is zero.

For example, the height of the unit structure, width, and 10μm in length, respectively, if the width of the gap 9 0.2 [mu] m, a width of the connection electrode 8 to about 2 [mu] m, the angular frequency determined by the _{C L} and _{L R} omega _se If, and the C _R and L _L and the angular frequency omega _sh determined by match 2THz region (overlap on omega-axis in FIG. 5), shows the dispersion characteristic of the equilibrium system with beta = 0 there is no gap in the angular frequency omega A unit structure can be produced.

  As described above, in the semiconductor laser device 1, terahertz waves are generated in the semiconductor stacked body 4 having the quantum cascade laser structure. At this time, since the semiconductor stacked body 4 functions as a metamaterial ring resonator together with the common electrode 3, the divided electrode 5, the counter electrode 7, the connection electrode 8, and the insulating layers 6 a and 6 b, the terahertz wave is generated in the semiconductor stacked body 4. A circular pattern corresponding to the shape is emitted to the outside. Moreover, since the semiconductor laminate 4 also serves as a part of the configuration of the metamaterial ring resonator, a loss when the generated terahertz wave is emitted to the outside hardly occurs. Therefore, according to this semiconductor laser device 1, it is possible to emit a terahertz wave whose divergence angle is suppressed in the two-dimensional direction with high extraction efficiency.

  Here, the connection electrode 8 is formed on the outer side surface 4b of the semiconductor stacked body 4 to electrically connect each of the divided electrodes 5 and the counter electrode 7, and between the semiconductor stacked body 4 and the connection electrode. Since the insulating layer 6b is provided, the semiconductor laser device 1 can be said to have a simplified structure for realizing a configuration in which the phase constant of the dispersion characteristic of the metamaterial ring resonator is zero.

  In the semiconductor laser device 1, the divided electrodes 5 are arranged in a ring shape with a period of less than one quarter of the wavelength of the terahertz wave, so that the common electrode 3 and the semiconductor stacked body 4 are used as metamaterial ring resonators for the terahertz wave. The divided electrode 5, the counter electrode 7, the connection electrode 8, and the insulating layers 6a and 6b function well.

  Further, in the semiconductor laser device 1, the common electrode 3, the semiconductor stacked body 4, the divided electrode 5, the counter electrode 7, the connection electrode 8, and the insulating layers 6 a and 6 b are units in which the metamaterial ring resonator exhibits a balanced dispersion characteristic. Since it has a structure and is configured so that the phase constant of the dispersion characteristic is 0, the wavelength in the metamaterial ring resonator becomes infinite and does not depend on the frequency. It becomes possible to design freely. Further, the spread angle of the terahertz wave can be more reliably suppressed in the two-dimensional direction. That is, in a state where the phase constant is 0, the terahertz wave is emitted from the metamaterial ring resonator directly above (that is, in a direction perpendicular to the plane formed by the circular shape of the semiconductor stacked body 4).

  In addition, since the semiconductor laser device 1 further includes a substrate that supports the semiconductor stacked body 4 and the common electrode 3 is provided on the substrate, each component of the semiconductor laser device 1 is stabilized.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, in the above-described embodiment, the embodiment in which the annular shape of the semiconductor stacked body is a circular shape is shown. However, as shown in FIG. 6, the annular shape may be a hexagon or other polygons.

  Moreover, in the said embodiment, although the insulating layer 6a, 6b was shown in the form integrally formed, as long as the semiconductor laser apparatus 1 is comprised so that there may exist the effect of this invention, insulating layer 6a, 6b. May be separate members.

  Moreover, in the said embodiment, although the connection electrode 8 formed in the outer side surface 4b of the semiconductor laminated body 4 was shown as a means to electrically connect the division | segmentation electrode 5 and the counter electrode 7, wire connection or a through hole is shown. Connection or the like may be used.

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser apparatus, 2 ... Board | substrate, 3 ... Common electrode (1st electrode), 4 ... Semiconductor laminated body, 4b ... Outer side surface of semiconductor laminated body, 5 ... Divided electrode (2nd electrode), 6a, 6b: insulating layer (first insulating layer, second insulating layer), 7 ... counter electrode (third electrode), 8 ... connection electrode (fourth electrode).

Claims (6)

A first electrode;
An annular semiconductor stack provided on the first electrode;
A plurality of second electrodes provided on the semiconductor stacked body so as to face the first electrode and to be arranged in a ring shape;
A third electrode facing the first electrode and electrically connected to each of the second electrodes;
A first insulating layer provided between the first electrode and the third electrode,
The semiconductor stacked body has a quantum cascade laser structure, and generates a terahertz wave when a voltage is applied between the first electrode and the second electrode, and the first electrode, A semiconductor laser device that functions as a metamaterial ring resonator together with the second electrode, the third electrode, and the first insulating layer, and emits the terahertz wave to the outside.   2. The semiconductor laser device according to claim 1, wherein the second electrodes are arranged in a ring shape with a period of less than a quarter of the wavelength of the terahertz wave.   The first electrode, the semiconductor stacked body, the second electrode, the third electrode, and the first insulating layer have a unit structure in which the metamaterial ring resonator exhibits balanced dispersion characteristics. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is configured so that a phase constant of the dispersion characteristic is zero. A substrate for supporting the semiconductor laminate;
The semiconductor laser device according to claim 1, wherein the first electrode is provided on the substrate.   The semiconductor laser device according to claim 1, wherein the semiconductor stacked body has a circular shape. A fourth electrode formed on an outer side surface of the semiconductor stacked body and electrically connecting each of the second electrodes and the third electrode;
The semiconductor laser device according to claim 1, further comprising: a second insulating layer provided between the semiconductor stacked body and the fourth electrode.

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