JP2012160524A - Semiconductor laser and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve optical output of a horizontal current injection type silicon laser and a germanium laser and to improve optical output of the horizontal current injection type laser regardless of elements of an active layer.SOLUTION: In the horizontal current injection type semiconductor laser, an active layer is a silicon thin film or a germanium thin film and is provided in the vicinity of a core layer or at least of its part is in the core layer, a reflectance of a first end face is higher than that of a second end face, a width of the core layer at the first end face is wider than a maximum core width which is present in only zeroth-order mode, a width of the core layer at the second end face is equal to or narrower than the maximum core width which is present in only zeroth-order mode, there is a part where its width changes along the propagation direction of the light in at least a part of the core layer, in the part where the core layer width changes, only the light having the intensity distribution of the zeroth-order mode is propagated without emitting, and the light having the intensity distribution of high order mode is emitted.

Description

  The present invention relates to a semiconductor laser and a manufacturing method thereof. In particular, the present invention relates to a horizontal current injection type semiconductor laser whose active layer is a silicon thin film or a germanium thin film and a method for manufacturing the same.

  In recent years, research on a technique called silicon photonics, which attempts to realize a short-distance optical wiring between silicon chips or within a chip with an optical element using silicon, has been actively conducted. This is because, if silicon photonics is realized, for example, higher density and higher speed and lower price of LSI can be expected.

  One of the most challenging issues in silicon photonics is the development of a laser as a light source. This is because silicon and germanium in a bulk state are indirect transition semiconductors and thus have extremely low luminous efficiency. In view of this, a method has been proposed in which silicon or germanium is directly transformed into a transition semiconductor in order to emit light with high efficiency. For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2007-294628) and Patent Document 2 (Japanese Patent Laid-Open No. 2008-205006), an electrode is directly connected to ultrathin single crystal silicon having a (100) plane on the surface, and the carrier is horizontally aligned with the substrate. A method for efficiently emitting ultra-thin single crystal silicon by injecting a silicon oxide is disclosed.

JP 2007-294628 A JP 2008-205006 A

  In addition to the above, various methods have been proposed by which silicon or germanium emits light to form a laser. However, in order to apply to silicon photonics, improvement of light output is a problem.

  Accordingly, an object of the present invention is to improve light output in a horizontal current injection type silicon laser and germanium laser in which carriers are injected in the horizontal direction with respect to a substrate. Another object of the present invention is to improve the light output of a horizontal current injection laser regardless of the elements of the active layer.

  That is, the object of the present invention is not only to improve the optical output of a semiconductor laser whose active layer is silicon or germanium, but also to improve the optical output of a semiconductor laser whose active layer is a III / V type semiconductor, for example.

  Among the inventions of the semiconductor laser disclosed in the present application, outlines of typical ones are as follows.

  An active layer for emitting light provided on the substrate; a first electrode having a first conductivity type electrically connected to one end of the active layer; and a first electrode electrically connected to the other end of the active layer. A second electrode having a conductivity type of 2 and a core layer that is provided on the active layer via a dielectric and guides the light, and is disposed between the first electrode and the second electrode with respect to the active layer. In a semiconductor laser in which current is injected in a horizontal direction substantially parallel to the substrate surface, and light emitted from the active layer resonates in a resonator provided between the first end face and the second end face The width of the core layer on the first end face side in the resonator is different from the width of the core layer on the second end face side.

  Alternatively, the active layer for emitting light provided on the substrate, the semiconductor layer provided on one main surface of the active layer, and the first electrode having the first conductivity type electrically connected to the active layer A second electrode having a second conductivity type electrically connected to the semiconductor layer, and carriers having the first conductivity type from the first electrode in a direction substantially parallel to the substrate surface with respect to the active layer A current is injected, carriers having the second conductivity type are injected from the second electrode in a direction substantially perpendicular to the substrate surface with respect to the active layer, and light emitted from the active layer is emitted from the first end face. In a semiconductor laser which resonates in a resonator provided between the second end surface, the width of the core layer on the first end surface side in the resonator and the width of the core layer on the second end surface side It is characterized by being different.

  In the above configuration, the active layer is a silicon thin film or a germanium thin film, and is provided in the vicinity of the core layer, or at least part of the active layer is in the core layer, and the reflectance of the first end surface is the reflection of the second end surface. The core layer width at the first end face is greater than the maximum core width where only the 0th order mode can be present, and the core layer width at the second end face is the maximum at which only the 0th order mode can exist There is a portion that is equal to or less than the core width, and at least part of the core layer has a width that changes along the light propagation direction, and only the light having the 0th-order mode intensity distribution is emitted at the portion where the core layer width changes The main feature of the semiconductor laser is a horizontal current injection type semiconductor laser, which propagates without being transmitted and emits light having a higher-order mode intensity distribution.

  According to the present invention, the optical output of a horizontal current injection type semiconductor laser, particularly a horizontal current injection type semiconductor laser using silicon or germanium as an active layer is improved.

The top view of the 1st example of the present invention. The band structure figure of the 1st example of the present invention. Sectional drawing of a conventional element. The top view of the 1st example of the present invention. The band structure figure when an active layer is expanded in the 1st Example of this invention. Sectional drawing when a core layer is expanded in the 1st Example of this invention. Sectional drawing when a core layer is narrow in a vertical current injection type element. Sectional drawing when a core layer is wide in a vertical current injection type element. The band structure figure of a perpendicular current injection type element. Sectional drawing of a conventional element. Sectional drawing of the 1st Example of this invention. Sectional drawing of the 1st Example of this invention. The top view of the 1st example of the present invention. 3A and 3B illustrate a manufacturing method of the first embodiment of the present invention. 3A and 3B illustrate a manufacturing method of the first embodiment of the present invention. 3A and 3B illustrate a manufacturing method of the first embodiment of the present invention. 3A and 3B illustrate a manufacturing method of the first embodiment of the present invention. 3A and 3B illustrate a manufacturing method of the first embodiment of the present invention. The top view of the 2nd example of the present invention. Sectional drawing of the 2nd Example of this invention. The top view of the 3rd example of the present invention. The top view of the 4th example of the present invention. The top view of the 5th example of the present invention. The top view of the 6th example of the present invention. The top view of the 7th example of the present invention. Sectional drawing of a conventional element. The top view of the conventional element.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition to the method introduced in this embodiment, it goes without saying that many changes such as changing the combination of materials and manufacturing processes are possible.

  Specific examples will be described below. The drawings described in the drawings are not necessarily drawn to scale accurately, and are drawn schematically with emphasis on important portions so that the logic is clear.

Examples of the horizontal injection laser using silicon or germanium material will be described in detail below. However, the present invention can also be applied to a horizontal injection laser using a III / V compound semiconductor material, for example.
First, before describing the present embodiment, the structure of the conventional example will be described for comparison. FIG. 14A is a cross-sectional view perpendicular to the substrate of an element as disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-294628. In this element, a silicon dioxide film 130, an active layer 110 made of a silicon thin film, a silicon dioxide film 180, and a core layer 100 made of a silicon nitride film are sequentially laminated on a silicon substrate 120, and an air layer 190 is formed thereon. is there. The active layer 110 made of a silicon thin film is bonded at both ends to the n-type silicon contact layer 140 and the p-type silicon contact layer 150.

  Further, the n-type silicon contact layer 140 and the p-type silicon contact layer 150 are provided with an n-type electrode 160 and a p-type electrode 170, respectively. Here, the operation of this element as a semiconductor laser is performed by injecting electrons and holes from the n-type electrode 160 and the p-type electrode 170, respectively. That is, the light injected by the electrons injected from the n-type electrode 160 and the holes injected from the p-type electrode 170 are recombined in the active layer 110 made of a silicon thin film, and emitted from the core layer 100 made of a silicon nitride film. Waveguide.

  Here, the active layer is a layer that generates light by current injection. The core layer is a layer sandwiched between clad layers having a refractive index lower than that of the core layer so that guided light is confined in the layer. In this element, the silicon dioxide film 180 and the air layer 190 are the lower and upper cladding layers, respectively. FIG. 14B is a top view of the device. Here, for simplicity, the air layer 190 and the silicon dioxide film 180 are omitted.

  In this element, the width of the active layer 110 made of a silicon thin film and the width of the core layer 100 made of a silicon nitride film are constant at Wa and Wc, respectively. Further, a rear end face side DBR (Distributed Bragg Reflector) area 200 and a front end face side DBR formed from a silicon nitride film are respectively provided after and before the region having the active layer 110 made of a silicon thin film and the core layer 100 made of a silicon nitride film. A region 210 is provided to form a resonator mirror.

  Therefore, the configuration of the resonator region 220 of this element is a region having an active layer 110 made of a silicon thin film and a core layer 100 made of a silicon nitride film, a rear end face side DBR region 200, and a front end face side DBR region 210. In the present device, for example, by providing the optical circuit portion 230 made of a silicon nitride film core, it can be used for optical wiring within or between chips.

  Next, Example 1 of the present invention will be described. The cross-sectional structure perpendicular to the substrate of this device is the same as that of the conventional device shown in FIG. 14A.

FIG. 1 shows a top view of the element of this embodiment. In the figure, the left side is the rear end surface and the right side is the front end surface. In this element, the width of the core layer 100 made of a silicon nitride film is wide on the rear end face side and narrower on the front end face side, and gradually changes between the rear end face and the front end face. Here, the width Wc (r) of the core layer 100 made of the silicon nitride film on the rear end face side is larger than the cut-off core width W _cutoff that can exist only in the 0th mode, and the core made of the silicon nitride film on the front end face side. The width Wc (f) of the layer 100 is equal to or less than W _cutoff . According to this structure, the laser beam output can be improved. The reason will be described below.

  There are two reasons why the laser output can be improved by this element structure. The first is because the gain can be improved by increasing the intensity of the stimulated emission light, and the second is because the improved gain can be concentrated on the light of a single waveguide mode. Hereinafter, these two points will be described in detail.

First, the reason why the stimulated emission light intensity can be increased will be described below.
FIG. 2A is a band structure diagram in the forward bias of the active layer 110, the n-type silicon contact layer 140, and the p-type silicon contact layer 150 made of a silicon thin film in the conventional element and the present element. In this structure, light emission generates spontaneous emission light 420 by recombining electrons 400 and holes 410 injected from the n-type silicon contact layer 140 and the p-type silicon contact layer 150, respectively, in the active layer 110 made of a silicon thin film. To be generated. At this time, the efficiency in which the electrons 400 and the holes 410 are recombined in the active layer 110 made of a silicon thin film to generate the spontaneous emission light 420 is proportional to Wa / (Vs * τ). Here, Wa is the width of the active layer 110 made of a silicon thin film. Vs is the saturation rate of electrons and holes, that is, carriers, and τ is the lifetime of carriers. In this band structure, the active layer 110 made of a silicon thin film having a larger band gap than the n-type silicon contact layer 140 and the p-type silicon contact layer 150 is sandwiched, and there is no carrier confinement structure. It depends.

  That is, since the carrier does not have a confinement structure, it can travel a maximum distance of Vs * τ until recombination, and the probability of recombination is considered to be constant regardless of the travel distance. The probability of recombination is obtained by dividing the active layer width Wa by the maximum travel distance Vs * τ. For this reason, when Wa is smaller than Vs * τ, the intensity of spontaneous emission light is uniform within Wa.

  FIG. 2B and FIG. 2C schematically show this. FIG. 2B shows a state in the forward bias of the A-A ′ section in the conventional element shown in FIG. 14B. For simplicity, the structure shows only the active layer 110 made of a silicon thin film, the n-type silicon contact layer 140, the p-type silicon contact layer 150, and the core layer 100 made of a silicon nitride film. In the active layer 110, spontaneous emission light generated by recombination of carriers injected from the contact layer exists uniformly. Of the spontaneous emission light 420, a portion that overlaps the guided light 440 by the core layer 100 made of a silicon nitride film becomes the stimulated emission light 430. The laser gain is proportional to the amount of the stimulated emission light 430. Next, the case of the present embodiment is shown in FIG. 2C. FIG. 2C shows a state in the forward bias of the A-A ′ cross section in the element of the embodiment shown in FIG. 1. From the figure, it can be seen that in this embodiment, the distribution of the guided light 440 is expanded by increasing the width of the core layer 100 and the stimulated emission light 430 increases.

  Therefore, the gain of the laser can be improved in the element of this embodiment. In the present invention, generally, the above effect can be obtained even if the width of the core layer 100 is equal to or larger than the active layer width Wa. However, in the structure of the present embodiment, when the width of the core layer 100 is greater than or equal to the active layer width Wa, the guided light is easily absorbed by the silicon contact layer and the electrodes. Therefore, in this embodiment, the width of the core layer 100 is narrower than the active layer width Wa. Furthermore, in order to increase the laser gain, the active layer width Wa and the core width may be increased. First, the intensity of spontaneous emission light generated in the active layer can be increased by increasing the active layer width Wa. This is because the intensity of spontaneous emission light generated in the active layer is proportional to the active layer width Wa when the active layer width Wa is within Vs * τ for the reason described above.

  FIG. 2D shows a band structure when the active layer width Wa is expanded to about Vs * τ. In this case, there is no carrier that reaches the contact layer on the opposite side before recombination as seen in FIG. 2A, and almost all the carriers are recombined in the active layer and the spontaneous emission light 420 is reduced. It will be released. Here, for convenience, non-radiative recombination is ignored and described.

  FIG. 2E is a cross-sectional view of the element in this case. It can be seen that by further increasing the width of the core layer 100, stimulated emission light intensity greater than that of FIG. 2C can be obtained. As described above, it can be understood that the laser gain can be improved by widening the core width in any active layer width.

  As described above, the effects of the present invention can be obtained with a horizontal current injection type semiconductor laser. Therefore, this effect is generally not obtained with a semiconductor laser using a normal III / V type semiconductor that is a vertical current injection type. However, if a horizontal current injection type is applied to a semiconductor laser using a III / V type semiconductor, the gain of the laser can be improved by widening the core width for the above reason, and this effect can be obtained. Here, the vertical current injection type semiconductor laser is a type of semiconductor laser that injects carriers along the stacking direction of the semiconductor layers. The reason why the above effect cannot be obtained with a vertical current injection type semiconductor laser is that there is generally a current confinement structure in the horizontal direction and that the active layer and the clad layer are usually the same. The details will be described below. In the description, the non-radiative recombination component is ignored for simplicity.

  First, FIG. 3A shows a layer structure of a vertical current injection type semiconductor laser when the core width is narrow. The layer structure of this laser is a p-type cladding layer 510, an active layer 110, and an n-type cladding layer 500 from the bottom. The active layer 110 and the n-type cladding layer 500 are sandwiched between current confinement layers 520, and an n electrode 160 and a p electrode 170 are provided above and below the element, respectively. In this structure, the active layer 110 also functions as a core layer. This is because the active layer 110 has a higher refractive index and a sufficient thickness than the cladding layer. In this structure, since the active layer is current-confined in the horizontal direction, all recombination occurs within the width of the active layer. In addition, since the active layer is the core layer at the same time, all the spontaneous emission light generated by recombination overlaps the guided light 440 in the core layer and becomes stimulated emission light 430.

  FIG. 3B shows a layer structure of a vertical current injection type semiconductor laser when the core width is wide. As in the case of FIG. 3A, all spontaneous emission light becomes stimulated emission light 430. In this way, because of the current confinement structure in the horizontal direction and the fact that the active layer and the cladding layer are the same, the optical output of a normal vertical current injection semiconductor laser does not depend on the core width when the injection current is constant. It becomes constant. In the vertical current injection type semiconductor laser using III / V type semiconductor, even if the active layer is made thick, the effect obtained when the core width is increased by the horizontal current injection type semiconductor laser cannot be obtained. This is due to the band structure.

  FIG. 3C shows a band structure of a vertical current injection type semiconductor laser using a III / V type semiconductor. The horizontal direction in the figure indicates the stacking direction. In this structure, the band gap of the active layer 110 is smaller than that of the cladding layer, and carriers are confined in the active layer 110. Therefore, even if the thickness of the active layer is small, carriers are not easily injected into the cladding layer having the opposite polarity. For this reason, in the vertical current injection type semiconductor laser using the III / V type semiconductor, when the current is constant, the optical output is constant regardless of the core thickness. As described above, in the vertical current injection type semiconductor laser using the III / V type semiconductor, the optical output is obtained when the core width is increased in the horizontal current injection type semiconductor laser even if the shape of the core layer is changed. Cannot be obtained. However, also in a semiconductor laser using a III / V type semiconductor, when the horizontal current injection type is applied, the gain of the laser can be improved by widening the core width as described above.

  In FIG. 2, it has been explained that the optical output can be improved by widening the core width for a horizontal current injection type semiconductor laser in which the core layer and the active layer are formed by different layers. The same effect can be obtained in a horizontal current injection type semiconductor laser that also functions as The reason will be described below.

  FIG. 4A shows a cross-sectional structure of such an element when the active layer width Wa, that is, the core width is narrow. In this element, the active layer also functions as a core layer at the same time, so that all spontaneous emission light generated in the active layer overlaps with the guided light 440. For this reason, all the spontaneous emission light becomes the stimulated emission light 430.

  FIG. 4B shows a cross-sectional structure of such an element when the active layer width Wa, that is, the core width Wa is wide. In the figure, Wa is about Vs * τ. Also in this case, all the spontaneous emission light generated in the active layer becomes the stimulated emission light 430 as in FIG. 4A. However, in FIG. 4B, since the intensity of spontaneous emission light increases in proportion to Wa, as a result, the intensity of stimulated emission light also increases and the light output of the laser increases. Thus, in the horizontal current injection type semiconductor laser in which the same layer functions as both a core layer and an active layer, the optical output of the laser can be improved by widening the core width.

  Even in an element in which only one of electrons or holes is injected horizontally into the active layer, the laser output can be improved by widening the core width. Examples of such elements include elements described in Non-Patent Document 1 (IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 15, NO. 3, MAY / JUNE 2009 pp.535-544). It is done.

  FIG. 5 shows an example of a layer structure of an element in which only one of the above-described electrons or holes is horizontally injected into the active layer. The layer structure of this element is, from the bottom, a silicon substrate 120, a silicon dioxide film 130, a core layer 900 made of silicon, an active layer 930 made of III / V semiconductor, and a p-type cladding layer 950 made of III / V semiconductor. . The core layer 900 made of silicon is separated from other silicon layers 910 by an air layer 920, and the p-type cladding layer 950 is sandwiched from both sides by a current confinement layer 940 made of III / V semiconductor. The electrons 400 travel horizontally through the active layer 930 from the right and left n-type electrodes 160 provided on the active layer 930. Holes are injected perpendicularly into the active layer 930 from the p-type electrode 170 provided on the p-type cladding layer 950.

  However, after this is also injected into the active layer 930, it proceeds horizontally to the layer in the same manner as the electrons and heads toward the n-type electrode 160. Therefore, the carrier behavior in the active layer is the same as that of the horizontal current injection type semiconductor laser as described with reference to FIG. Therefore, the ratio of spontaneous emission light generated by carrier recombination to stimulated emission light increases as the core width increases, and the laser light output improves as in the element described with reference to FIG. Therefore, the horizontal current injection type semiconductor laser that is the subject of the present invention may be considered as an element in which the n-type electrode and the p-type electrode are arranged apart from each other in the spreading direction of the active layer.

  As described above, in the horizontal current injection type semiconductor laser, even when the core layer and the active layer are formed as separate layers, or when one layer has the functions of the core layer and the active layer at the same time. It can be seen that the laser output can be improved by increasing the width of the core layer. In addition, from the above description, even in a vertical current injection type semiconductor laser, if the core layer and the active layer are formed of separate layers, the laser output may be improved by widening the width of the core layer. I understand.

  Therefore, the effect of this embodiment is that in the horizontal current injection type semiconductor laser, when the core layer and the active layer are formed by separate layers, and one layer functions as the core layer and the active layer at the same time. It can be obtained for both cases. The effect of this embodiment can also be obtained for a vertical current injection type semiconductor laser in which the core layer and the active layer are formed of separate layers.

  Next, the reason why the structure of this embodiment can concentrate the gain on the light of a single waveguide mode will be described. Before that, first, the reason why the laser output is improved when the gain is concentrated on the light of a single waveguide mode will be described. Here, a case where the core width is uniformly wide over the entire resonator is considered. In this case, since the core width is wide, there is an advantage that the stimulated emission light intensity is increased as described above.

  However, when the core width is wide, not only the light of the 0th-order guided eigenmode but also the light of the higher-order eigenmode is propagated, and each of them can be laser-oscillated. Also occurs. Here, the reason why the laser oscillation in a plurality of modes is a drawback is that the threshold gain increases. In other words, laser output does not occur until the gain exceeds the threshold gain, so when multiple modes laser oscillate, a gain equivalent to the threshold gain for the number of modes is required to obtain the optical output. It is because it becomes.

  Therefore, minimizing the gain consumed as the threshold gain increases the laser light output. For this purpose, it is sufficient to concentrate the gain on light of a single waveguide mode and oscillate only the single mode. Since only one mode of gain is consumed as the threshold gain, the laser light output can be increased. Next, the reason why the structure of this embodiment can concentrate the gain on the light of a single waveguide mode will be described.

  FIG. 6 is a diagram for explaining a waveguide mode of light propagating through the element of this embodiment. First, on the rear end face side having a wide core width, there are a waveguide eigenmode 300 of higher order and a waveguide eigenmode 310 of higher order as the waveguide modes of light that can propagate. However, only the 0th-order guided eigenmode 300 can exist on the front end face side where the core width is equal to or smaller than the cutoff core width. Therefore, even if a waveguide mode of light having a higher-order light intensity distribution in addition to the zeroth order occurs on the rear end face side, the higher-order mode is emitted when propagating to the front end face. On the other hand, the 0th-order mode can exist at any position although the spot size is different between the rear end face side and the front end face side.

  Therefore, if the change in the core width is moderated and the increase in propagation loss due to spot size conversion is sufficiently suppressed, the zero-order mode can propagate through the entire resonator with low loss. For this reason, a large propagation loss difference occurs between the 0th-order mode and the higher-order mode. Therefore, in the structure of the present embodiment, only the 0th mode can exist in the resonator as the light resonates. For this reason, only the 0th mode is oscillated, and the laser output can be improved for the reason described above. Here, since the spot size conversion of the present element is performed in a range where the core width is equal to or larger than the cut-off core width, even if the change rate of the core width is large, the increase in propagation loss due to the spot size is small. This is because when the core width is equal to or larger than the cut-off core width, light is hard to be radiated because light is strongly confined in the core.

  Therefore, the propagation loss accompanying the spot size conversion is almost negligible unlike a general spot size enlarged semiconductor laser. In general spot size-enhanced semiconductor lasers, spot size conversion is performed in order to increase the optical coupling efficiency with the single mode fiber, and the core width is performed within the cut-off width or less, resulting in an increase in loss. However, in the present invention, this loss increase is negligible, so that the laser light output can be increased. In the figure, the change in the core width is a straight line, but it may be changed in a curved line.

  Thus, in the element of the present invention, the gain is increased by having a region with a wide core width, and further, a single mode oscillation is realized by having a cutoff function of a higher-order mode in the laser resonator. Thus, the laser light output can be improved.

  Next, a method for manufacturing the element of this example will be described with reference to FIGS. 7A to 7E. First, as shown in FIG. 7A, after the silicon layer 600 is oxidized and the silicon dioxide film 610 is formed on an SOI (Silicon On Insulator) substrate in which the silicon dioxide film 130 and the silicon layer 600 are provided on the silicon substrate 120. Then, a silicon nitride film mask 620 having an opening obtained by processing the silicon nitride film by etching is provided.

  Next, as shown in FIG. 7B, the silicon layer 600 in the region where the silicon nitride film mask 620 is open is oxidized to produce an active layer 110 made of a silicon thin film. Next, as shown in FIG. 7C, the n-type silicon contact layer 140 and the p-type silicon contact layer 150 are formed by implantation except for the silicon nitride film mask 620. Next, as shown in FIG. 7D, a core layer 100 made of a silicon nitride film is formed. Then, as shown in FIG. 7E, when the n-type electrode 160 and the p-type electrode 170 are provided except for the silicon layer 600 on the n-type silicon contact layer 140 and the p-type silicon contact layer 150, this element is completed.

  Note that a horizontal current injection type semiconductor laser using a III / V type semiconductor is manufactured by a method described in, for example, Non-Patent Document 2 (OPTICS EXPRESS, Vol. 17, No. 15, 20 July 2009, pp. 12564-12570). it can. That is, a semiconductor layer connected to the active layer and the contact layer may be sequentially formed in the horizontal direction using etching and layer thickness control.

  In this embodiment, a structure of an element in which an active layer 110 made of a silicon thin film is arranged perpendicular to the substrate surface is disclosed. Since the top view of this element is the same as that of Example 1, only the cross-sectional structure perpendicular to the substrate will be described here.

  FIG. 8A shows a top view of the device. The shapes of the active layer 110 made of a silicon thin film and the core layer 100 made of a silicon nitride film are the same as those in the first embodiment. In the figure, for simplicity, electrodes and others are omitted as in the first embodiment.

  FIG. 8B shows a cross section taken along line A-A ′ shown in FIG. 8A. In this element, the active layer 110 made of a silicon thin film has a structure called a Fin structure in which a plurality of silicon thin films are erected vertically to the substrate. Although the figure shows a structure in which a silicon dioxide film 180 is filled between silicon thin films in the Fin structure and a core layer 100 made of a silicon nitride film is provided thereon, the silicon dioxide film 180 may be omitted. According to this structure, the overlap between the active layer 110 made of a silicon thin film and the guided light can be increased, and the laser light output can be further improved.

  FIG. 9 shows a top view of the third embodiment. Since the layer structure of this element is the same as that of Example 1, only the top view is shown here. In the drawing, Wa represents the width of the active layer 110, Wc (r) represents the width of the core layer 100 on the rear end face side, and Wc (f) represents the width of the core layer 100 on the front end face side. In this embodiment, the active layer 110, the n-type electrode 160, and the p-type electrode 170 are not provided in a region having a narrow core width. Here, the region where the electrode is provided becomes the current injection region 800 and gain is generated from the active layer 110, and the region where the active layer and the electrode are not provided becomes the non-current injection region 810 and no gain occurs. According to this structure, since the gain is lost in the region where the core width is narrow, it becomes easier to radiate higher-order modes. For this reason, the single mode selectivity of the laser resonator is increased, and the laser light output can be further improved. The active layer emits light as a gain medium when current injection is present, but light loss occurs as an absorption medium when current injection is absent. Therefore, the effect of providing the non-current injection region is peculiar to the structure of this embodiment in which the core layer and the active layer are separate layers, and the same layer functions as the core layer and the active layer. It cannot be obtained with a vertical current injection type semiconductor laser using a normal III / V semiconductor.

  FIG. 10 shows a top view of the fourth embodiment. In the figure, electrodes and others are omitted for simplicity. Further, since the layer structure of this element is the same as that of Example 1, only the top view is shown here. In this embodiment, the core layer 100 made of a silicon nitride film has a curved shape in a narrow region. It is desirable that this curved shape propagates without emitting the 0th-order guided light mode, and the higher-order guided light mode has a curvature to emit. According to this structure, it becomes easier to radiate the next mode. For this reason, the single mode selectivity of the laser resonator is increased, and the laser light output can be further improved.

  FIG. 11 shows a top view of the fifth embodiment. In the figure, electrodes and others are omitted for simplicity. Further, since the layer structure of this element is the same as that of Example 1, only the top view is shown here. In the present embodiment, the width of the core layer 100 made of a silicon nitride film is significantly reduced from the cut-off core width. Thereby, the single mode property is further improved, and the laser light output is further improved. When this element is coupled to the optical circuit 230 made of a silicon nitride film outside the resonator, it is preferable to provide a tapered region whose width narrows toward the tip in the optical circuit. This is because the width of the optical circuit is usually narrowed by the cut-off core width or slightly smaller than that in order to increase the optical confinement and reduce the allowable radius of curvature.

Therefore, in the case of the present embodiment optically coupled to the core width W _f was significantly narrower than the cutoff core width W _cutoff, it is desirable to reduce the coupling loss by introducing tapered.

  FIG. 12 shows a top view of the sixth embodiment. In the figure, electrodes and others are omitted for simplicity. Further, since the layer structure of this element is the same as that of Example 1, only the top view is shown here. In the embodiments so far, the width of the active layer 110 made of a silicon thin film is constant in the element, but it is not necessarily required to be constant. For the purpose of reducing electrical resistance or optimizing the layout in the LSI, the active layer width may be modulated in the resonator direction.

  FIG. 13 shows a top view of the seventh embodiment. In the figure, electrodes and others are omitted for simplicity. Further, since the layer structure of this element is the same as that of Example 1, only the top view is shown here. In the embodiments so far, the case where all the widths of the core layer 100 made of the silicon nitride film are narrowed on the front end face has been described.

  However, in the present invention, it is not generally necessary to reduce the width of the core layer 100 only on the front end face. Certainly, if the core width is narrowed at the front end face, even if higher-order modes occur in the wide core area due to non-uniform distribution of current, etc., the laser light is taken out from the front end face. There is an advantage that the light intensity distribution can be easily made into a single mode. However, in order to optimize the coupling with an optical circuit having a wide core width, it may be narrowed at a place other than the front end face as shown in FIG.

  In each of the above embodiments, the substrate is described using a silicon substrate, that is, a substrate made of a semiconductor material. However, a dielectric material can be applied as the substrate. When a dielectric material is used as the substrate, it is possible to expect an effect that guided light is strongly confined in the active layer and the efficiency of stimulated emission is further increased. By using a dielectric for the substrate, the effect of improving the laser light output according to the present invention, that is, the effect of improving the gain by increasing the intensity of stimulated emission light, and the improved gain can be achieved with a single waveguide. The effect of concentrating on the mode light is not impaired.

100 ... core layer,
110 ... active layer,
120 ... silicon substrate,
130 ... silicon dioxide film,
140 ... n-type silicon contact layer,
150 ... p-type silicon contact layer,
160 ... n-type electrode,
170 ... p-type electrode,
180 ... silicon dioxide film,
190 ... Air layer,
200 ... rear end face side DBR region,
210 ... front end face side DBR region,
220 ... resonator region,
230: optical circuit section,
400 ... Electronic,
410 ... holes,
420 ... spontaneous emission,
430 ... Stimulated emission light,
440 ... guided light,
500 ... n-type cladding layer,
510 ... p-type cladding layer,
520 ... current confinement layer,
600 ... silicon layer,
610 ... silicon dioxide film,
620 ... Silicon nitride mask,
900 ... core layer,
910 ... Silicon layer,
920 ... Air layer,
930 ... active layer,
940 ... current confinement layer,
950: p-type cladding layer.

Claims (13)

An active layer for emitting light provided on a substrate;
A first electrode having a first conductivity type electrically connected to one end of the active layer;
A second electrode having a second conductivity type electrically connected to the other end of the active layer;
A core layer provided on the active layer via a dielectric to guide the light, and
A carrier having a first conductivity type and a carrier having a second conductivity type are injected from each of the first electrode and the second electrode in a horizontal direction substantially parallel to the substrate surface with respect to the active layer. A semiconductor laser in which light emitted from the active layer resonates in a resonator provided between the first end face and the second end face, and amplified light is emitted from the second end face side In
The semiconductor laser according to claim 1, wherein the core layer has regions having different widths along a resonance direction of light in the resonator. The semiconductor laser according to claim 1, wherein
A semiconductor laser characterized in that the width of the core layer in at least a partial region between the first end face and the second end face is narrower than the width of the core layer on the first end face side in the resonator. . The semiconductor laser according to claim 1, wherein
The reflectivity of the first end face is greater than the reflectivity of the second end face;
The width of the core layer at the first end face is greater than the maximum core width in which only the zeroth-order mode can exist,
The width of the core layer at the second end face is less than or equal to the maximum core width in which only the zeroth mode can exist;
At least a part of the core layer has a region where the width of the core layer changes along the light propagation direction;
In the region where the width of the core layer changes, only the light having the 0th-order mode intensity distribution propagates without being emitted, and the light having the higher-order mode intensity distribution is emitted. . The semiconductor laser according to claim 1, wherein
2. The semiconductor laser according to claim 1, wherein the first and second electrodes and the active layer are not provided in at least a part of a region where the width of the core layer is not maximum. The semiconductor laser according to claim 1, wherein
At least a portion of the core layer has a curved shape in a plane horizontal to the substrate surface;
The curvature of the curved shape is set so that only light having the intensity distribution of the 0th mode propagates without being emitted, and light having the intensity distribution of the higher order mode is emitted. The semiconductor laser according to claim 1. The semiconductor laser according to claim 1, wherein
2. The semiconductor laser according to claim 1, wherein the core layer is formed of a layer different from the active layer. The semiconductor laser according to claim 1, wherein
2. The semiconductor laser according to claim 1, wherein the core layer is formed of the same layer as the active layer. The semiconductor laser according to claim 1, wherein
The active layer is composed of a silicon thin film or a germanium thin film,
The active layer is provided in the vicinity of the core layer, or at least a part of the active layer is provided in the core layer. The semiconductor laser according to claim 8, wherein
A semiconductor laser, wherein the active layer is provided so as to extend parallel to the substrate surface. The semiconductor laser according to claim 8, wherein
The semiconductor laser according to claim 1, wherein the active layer is provided so as to extend in a direction perpendicular to the substrate surface. An active layer for emitting light provided on a substrate;
A semiconductor layer provided on one main surface of the active layer;
A first electrode having a first conductivity type electrically connected to the active layer;
A second electrode having a second conductivity type electrically connected to the semiconductor layer;
Carriers having the first conductivity type are injected from the first electrode into the active layer in a direction substantially parallel to the substrate surface,
Carriers having the second conductivity type are injected from the second electrode into the active layer in a direction substantially perpendicular to the substrate surface,
In a semiconductor laser in which light emitted from the active layer resonates in a resonator provided between a first end face and a second end face, and amplified light is emitted from the second end face side ,
The semiconductor laser according to claim 1, wherein the core layer has regions having different widths along a resonance direction of light in the resonator. Forming an active layer on a semiconductor layer via a first insulator on a substrate;
A first contact layer having a first conductivity type so as to be connected to one end of the active layer, and a second contact type opposite to the first conductivity type so as to be connected to the other end of the active layer. Forming a second contact layer having a conductivity type of:
Depositing a dielectric on the active layer via a second insulator;
Patterning the dielectric to form a core layer;
Forming the electrodes of the first conductivity type and the second conductivity type on the first contact layer and the second contact layer,
In the patterning of the core layer, a photomask having a pattern whose width changes along the longitudinal direction is used. Preparing an SOI substrate provided with a silicon dioxide film and a silicon layer on a silicon substrate;
Depositing a silicon nitride film on the silicon dioxide film after oxidizing the silicon layer to form a silicon dioxide film;
Forming an opening in the silicon nitride film by etching and forming a silicon nitride film mask;
Oxidizing the region where the silicon layer is exposed at the opening of the silicon nitride mask to form an active layer made of a silicon thin film;
The silicon nitride mask is removed, and a silicon contact layer having a first conductivity type and a silicon contact layer having a second conductivity type opposite to the first conductivity type are formed on the silicon layer. Process,
Depositing a silicon nitride film on the silicon dioxide film, and forming a core layer by patterning the silicon nitride film;
Removing the silicon layer on the silicon contact layer having the first conductivity type and the silicon contact layer having the second conductivity type to form electrodes of the first conductivity type and the second conductivity type; ,
In the patterning of the core layer, a photomask having a pattern whose width changes along the longitudinal direction is used.

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