JP2018088456A - Quantum cascade semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an end face emission type quantum cascade semiconductor laser having a structure in which an end face reflection film is not used for a high reflection mirror of a resonator.SOLUTION: A quantum cascade semiconductor laser comprises: a first semiconductor region that is provided on a first area and a second area of a substrate; and a semiconductor mesa that is provided on a third area of the substrate and extends in a direction of a first axis. The first area, the second area, the third area and a fourth area are successively arrayed in the direction of the first axis. The first semiconductor region includes a first photonic crystal structure, and the first semiconductor region includes multiple pores that are arrayed in such a manner that the first photonic crystal structure has a photonic band gap. The first photonic crystal structure includes a first photonic waveguide part in which the pores are thinned in a first direction and which is provided on the second area. The semiconductor mesa includes a core layer and a clad layer, and the semiconductor mesa includes an end face that is positioned on a boundary between the third area and the fourth area.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a quantum cascade laser.

  Patent Document 1 discloses an optical integrated circuit including a photonic crystal. Patent Document 2 discloses a surface emitting laser including a photonic crystal. Non-Patent Document 1 discloses a photonic band gap.

International Publication WO2008-084830 International Publication WO2010-140404

Optics 25, 7 pp409-415 (1996)

  The quantum cascade laser can generate 3 to 20 micrometers mid-infrared light using intersubband transition. Such light having a wavelength of 有用 is useful in a light source for laser processing or an optical gas detector. Examples of applications of quantum cascade lasers that require low power consumption operation include gas detector applications. By reducing the threshold current of the quantum cascade laser, low power consumption operation is possible. The threshold current can be reduced because the quantum cascade laser has a short cavity length. A short resonator length therefore requires the formation of an end-face reflective film for the resonator on the end surface of a small semiconductor chip. Handling a small semiconductor chip is complicated.

  According to the inventor's study, the element structure that eliminates the step of forming the end face reflection film on the laser bar makes it possible to avoid this handling.

  An object of one aspect of the present invention is to provide an end face emission type quantum cascade laser having a structure in which an end face reflection film is not used for a high reflection mirror of a resonator.

  A quantum cascade laser according to an aspect of the present invention includes a substrate including a main surface having a first area, a second area, a third area, and a fourth area, and the first area and the second area of the substrate. And a semiconductor mesa provided on the third area of the substrate and extending in the direction of the first axis, the first area, the second area, the third area The area and the fourth area are sequentially arranged in the direction of the first axis, the first semiconductor region includes a first photonic crystal structure, and the first semiconductor region includes the first photonic crystal structure. The first photonic crystal structure includes a plurality of holes arranged so that the body has a photonic band gap, and the holes are thinned out in the direction of the first axis and provided on the second area. First photonic Has a waveguide section, said semiconductor mesa comprises a core layer and a cladding layer, said semiconductor mesa has an end face positioned on the boundary between the third area and the fourth area.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to one aspect of the present invention, there is provided an edge emission type quantum cascade laser having a structure that does not use an edge reflection film for a high reflection mirror of a resonator.

FIG. 1 is a plan view schematically showing the quantum cascade laser according to this embodiment. FIG. 2 is a drawing showing the quantum cascade laser shown in FIG. 1 in several cross sections. FIG. 3 is a drawing showing the quantum cascade laser according to this embodiment in several cross sections. FIG. 4 is a drawing schematically showing main steps in the method for producing the quantum cascade laser according to the present embodiment. FIG. 5 is a drawing schematically showing main steps in the method of manufacturing the quantum cascade laser according to this embodiment. FIG. 6 is a drawing schematically showing main steps in the method of manufacturing the quantum cascade laser according to this embodiment.

  Some specific examples will be described.

  A quantum cascade laser according to a specific example includes: (a) a substrate including a main surface having a first area, a second area, a third area, and a fourth area; and (b) the first area and the first area of the substrate. A first semiconductor region provided on two areas; and (c) a semiconductor mesa provided on the third area of the substrate and extending in a direction of a first axis, the first area, the first The second area, the third area, and the fourth area are sequentially arranged in the direction of the first axis, the first semiconductor region includes a first photonic crystal structure, and the first semiconductor region includes the first semiconductor region, The first photonic crystal structure includes a plurality of holes arranged to have a photonic band gap, and the first photonic crystal structure has the second area in which the holes are thinned out in the first direction. First photo provided above Tsu has a click waveguide portion, said semiconductor mesa comprises a core layer and a cladding layer, said semiconductor mesa has an end face positioned on the boundary between the third area and the fourth area.

  According to the quantum cascade laser, the first semiconductor region includes an array of holes that enables the first photonic crystal structure. Since the first photonic crystal structure does not include the column arrangement, the first semiconductor region can increase the mechanical strength of the quantum cascade laser. The core layer of the semiconductor mesa generates light related to the quantum cascade laser. The photonic band gap of the first photonic crystal structure is matched to the wavelength of the laser light of the quantum cascade laser. The first photonic waveguide portion and the semiconductor mesa are aligned in the direction of the first axis, and the photonic band gap of the first photonic crystal structure is the first photonic waveguide from the semiconductor waveguide portion related to the semiconductor mesa. Light that enters the waveguide portion and propagates through the first photonic waveguide portion can be reflected. The reflected light propagates through the first photonic waveguide portion and enters the semiconductor waveguide portion. The first photonic crystal structure functions as an optical resonator mirror of the quantum cascade laser. The first photonic waveguide portion functions as a waveguide connected to the semiconductor mesa. The first photonic waveguide section makes it possible to provide one end of the laser waveguide in the quantum cascade laser at a position away from the edge of the first photonic crystal structure and the edge of the semiconductor mesa. By using the first photonic crystal structure, it is not necessary to deposit an end face reflecting film for the optical resonator mirror, and the quantum cascade laser has a cavity length resulting from the deposition of the end face reflecting film. It is released from the restrictions.

  In the quantum cascade laser according to the specific example, the first photonic crystal structure includes a dielectric provided in the hole.

  According to the quantum cascade laser, the dielectric in the hole of the first photonic crystal structure can increase the mechanical strength of the quantum cascade laser.

  The quantum cascade laser according to a specific example further includes a second semiconductor region provided on the fourth area, wherein the second semiconductor region includes a second photonic crystal structure, and the second semiconductor region includes The second photonic crystal structure includes a plurality of holes arranged to have a photonic band gap, and the second semiconductor region has the holes so that a spot size of light from the end surface can be changed. Is thinned out and extends in the direction of the first axis, and the second photonic waveguide portion is optically coupled to the end face of the semiconductor mesa.

  According to the quantum cascade laser, the second semiconductor region includes an array of holes that enables the second photonic crystal structure. Since the second photonic crystal structure does not include a column arrangement, the second semiconductor region can increase the mechanical strength of the quantum cascade laser. The photonic band gap of the second photonic crystal structure is matched with the oscillation wavelength of the quantum cascade laser. The second photonic crystal structure is optically coupled to the end face of the semiconductor mesa, and the photonic band gap of the first photonic crystal structure can confine light in the second photonic waveguide portion. The light from the end face of the semiconductor mesa propagates through the second photonic waveguide portion according to the second photonic waveguide portion that is not provided with a hole in the second semiconductor region.

  In the quantum cascade laser according to the specific example, the second semiconductor region has a third photonic waveguide portion in which the hole is thinned out in the direction of the first axis and extends in the direction of the first axis. The third photonic waveguide portion is optically coupled to the end face of the semiconductor mesa, and the third photonic waveguide portion is provided between the semiconductor mesa and the second photonic waveguide portion. It is done.

  According to the quantum cascade laser, the semiconductor mesa, the second photonic waveguide portion, and the third photonic waveguide portion are aligned in the direction of the first axis. The second photonic waveguide portion and the third photonic waveguide portion function as an external waveguide provided outside the optical resonator. The second photonic waveguide portion and the third photonic waveguide portion allow light from the other end of the laser waveguide in the quantum cascade laser to be output to the outside from the quantum cascade laser.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, embodiments relating to a quantum cascade laser and a method of manufacturing a quantum cascade laser will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

  FIG. 1 is a plan view schematically showing the quantum cascade laser according to this embodiment. Part (a) of FIG. 2 shows a cross section taken along the line IIa-IIa shown in FIG. Part (b) of FIG. 2 shows a cross section taken along the line IIb-IIb shown in FIG. (C) part of FIG. 2 shows the cross section taken along the IIc-IIc line | wire shown by FIG. (D) part of FIG. 2 shows the cross section taken along the IId-IId line | wire shown by FIG.

  The quantum cascade laser 11 includes a substrate 13, a first semiconductor region 15, and a semiconductor mesa 17. The substrate 13 includes a main surface 13a. The main surface 13a has a first area 13b, a second area 13c, a third area 13d, and a fourth area 13e. The first area 13b, the second area 13c, the third area 13d, and the fourth area 13e are They are arranged in order in the direction of one axis Ax1.

  The semiconductor mesa 17 is provided on the third area 13d of the substrate 13 and extends in the direction of the first axis Ax1. The semiconductor mesa 17 has an end face 17e located at the boundary 25 between the third area 13d and the fourth area 13e.

  As shown in FIGS. 1 and 2 (a) and (c), the first semiconductor region 15 is provided on the first area 13 b and the second area 13 c of the substrate 13. The first semiconductor region 15 includes a first photonic crystal structure 21. The first semiconductor region 15 includes a plurality of holes 23 arranged so that the first photonic crystal structure 21 has a photonic band gap.

  As shown in FIG. 2B, the semiconductor mesa 17 includes a core layer 17a (for example, an InGaAs / AlInAs superlattice, 2.282 μm thickness) and a cladding layer 17b (for example, n-type InP, 3 μm thickness). If necessary, a diffraction grating layer 17c (for example, n-type InGaAs layer, 500 nm thickness) and a contact layer 17d (for example, n-type InGaAs layer, 100 nm thickness) can be included. The core layer 17a, the cladding layer 17b, the diffraction grating layer 17c, and the contact layer 17d extend from the end surface 17e in the direction of the first axis Ax1, and are sequentially arranged in the normal direction of the main surface 13a of the substrate 13. ing. The upper surface of the diffraction grating layer 17c has a periodic structure (arrangement of protrusions and depressions) for wavelength selection. The core layer 17a of the semiconductor mesa 17 generates laser light related to the quantum cascade laser 11, and the wavelength of the laser light is, for example, in the range of 4 to 10 micrometers. If necessary, the semiconductor mesa 17 can include a cladding region 17f provided between the core layer 17a and the substrate 13. In this embodiment, the cladding region 17f is formed by the ridge structure 13r of the substrate 13. Provided. The mesa width WM of the semiconductor mesa 17 can be in the range of 3 to 5 micrometers, for example. In order to realize a short resonator, the length L of the semiconductor mesa 17 can be in the range of 300 to 500 micrometers.

  In the present embodiment, the semiconductor mesa 17 is buried with the buried semiconductor region 27 in the third area 13d. The quantum cascade laser 11 can include an insulating film 29, a first electrode 31a, and a second electrode 31b provided in the third area 13d. The insulating film 29 covers the upper surface on the embedded semiconductor region 27. And an opening 29 a located on the upper surface of the semiconductor mesa 17. The first electrode 31a is provided on the embedded semiconductor region 27 and the semiconductor mesa 17, and makes contact with the upper surface of the semiconductor mesa 17 through the opening 29a. The second electrode 31 b is in contact with the back surface 13 f of the conductive substrate 13.

  The embedded semiconductor region 27 is also provided in the first area 13b and the second area 13c. The first semiconductor region 15 includes a buried semiconductor region 27 having a periodic array of holes 23. The embedded semiconductor region 27 can comprise, for example, semi-insulating InP, the diameter of the hole 23 can be, for example, 1.81 micrometers, and the period of the arrangement of the holes 23 in the photonic crystal is, for example, 3. It can be 15 micrometers.

  Specifically, as shown in FIG. 1, in the first semiconductor region 15, the holes 23 are periodically arranged in two or three directions in the first area 13 b of the substrate 13 to form a photonic crystal. The lattice structure in the photonic crystal can be, for example, a square lattice, a triangular lattice, and a hexagonal lattice. In this embodiment, the holes 23 are periodically arranged in three directions to form a triangular lattice.

  As shown in FIG. 1 and FIG. 2C, the first photonic crystal structure 21 has a first photonic waveguide portion 21a provided on the second area 13c. The nick waveguide portion 21a includes a semiconductor waveguide portion 16a that is continuous in the direction of the first axis Ax1 with the holes 23 (24) thinned out in the direction of the first axis Ax1. On both sides of the semiconductor waveguide portion 16a, holes 23 are periodically arranged in two or three directions in the second area 13c of the substrate 13 to form a photonic crystal. In the first area 13b and the second area 13c, the first photonic crystal structure 21 has a first array A1RY of holes 23 provided to have a photonic band gap. The arrangement of the holes 23 (24) in the first arrangement A1RY is an exemplary structure for allowing light to propagate in the first photonic crystal structure 21 having a photonic band gap. If necessary, the semiconductor waveguide portion 16 a can include the same semiconductor stack as the semiconductor mesa 17.

  According to the quantum cascade laser 11, the first semiconductor region 15 includes a first array A1RY of a plurality of holes 23 that enables the first photonic crystal structure 21. Since the first photonic crystal structure 21 does not include an array of columns but includes an array of holes 23 (for example, holes), the first semiconductor region can increase the mechanical strength of the quantum cascade laser 11. . The core layer 17 a of the semiconductor mesa 17 generates light related to the quantum cascade laser 11. The photonic band gap of the first photonic crystal structure 21 is matched with the wavelength of the laser beam of the quantum cascade laser 11. The first photonic waveguide portion 21a and the semiconductor mesa 17 are aligned in the direction of the first axis Ax1, and the photonic band gap of the first photonic crystal structure 21 is the semiconductor waveguide portion 16b according to the semiconductor mesa 17. The light that enters the first photonic waveguide portion 21a (semiconductor waveguide portion 16a) and propagates through the semiconductor waveguide portion 16b can be reflected. The reflected light returns from the first photonic waveguide portion 21a (semiconductor waveguide portion 16a) to the semiconductor waveguide portion 16a. The first photonic crystal structure 21 functions as an optical resonator mirror of the quantum cascade laser 11. Further, the end face 17 e of the semiconductor mesa 17 functions as an optical resonator mirror of the quantum cascade laser 11. The first photonic waveguide portion 21 a functions as a waveguide connected to the semiconductor mesa 17. The first photonic waveguide portion 21 a is provided with one end 16 E of the laser waveguide 16 in the quantum cascade laser 11 at a position away from the edge E 21 of the first photonic crystal structure 21 and the edge E 17 of the semiconductor mesa 17. Enable. By using the first photonic crystal structure 21, it is not necessary to deposit an end face reflection film for the optical resonator mirror, and the quantum cascade laser 11 has a cavity length due to the deposition of the end face reflection film. Free from constraints.

  In the present embodiment, as shown in FIGS. 2A, 2 </ b> C, and 2 </ b> D, the hole 23 has a bottom 23 a located in the substrate 13. According to the quantum cascade laser 11, the first photonic crystal structure 21 has the hole 23 having a depth reaching the substrate 13. The arrangement of the deep holes 23 is effective for reflecting long wavelength light propagating through the semiconductor mesa 17.

  As shown in FIG. 1 and FIG. 2D, the quantum cascade laser 11 further includes a second semiconductor region 33 provided on the fourth area 13e. The second semiconductor region 33 includes a second photonic crystal structure 35, and the second semiconductor region includes a plurality of holes 23 arranged so that the second photonic crystal structure 35 has a photonic band gap. . The embedded semiconductor region 27 is also provided in the fourth area 13e. The second semiconductor region 33 includes a buried semiconductor region 27 having a periodic array of holes 23. The embedded semiconductor region 27 can comprise, for example, semi-insulating InP, the diameter of the hole 23 can be, for example, 1.81 micrometers, and the period of the arrangement of the holes 23 in the photonic crystal is, for example, 3. It can be 15 micrometers.

  The second semiconductor region 33 is a second photo that extends in the direction of the first axis Ax1 in the fourth area 13e, with the holes 23 (24) thinned out so that the spot size of light from the end face 17e can be changed. It has the nick waveguide part 35a. The second photonic waveguide portion 35 a is optically coupled to the end face 17 e of the semiconductor mesa 17. In the present embodiment, the second photonic waveguide portion 35a has a shape, for example, a fan shape, that is thinned out so that the number of thinned holes 23 (24) increases in the direction from the first area 13b to the fourth area e. have.

  According to the quantum cascade laser 22, the second semiconductor region 33 includes an array of a plurality of holes 23 that allow the second photonic crystal structure 35. Since the second photonic crystal structure 35 does not include the column arrangement, the second semiconductor region 33 can increase the mechanical strength of the quantum cascade laser 11. The photonic band gap of the second photonic crystal structure 35 is matched with the wavelength of the laser beam of the quantum cascade laser 11. The second photonic crystal structure 35 is optically coupled to the end face 17e of the semiconductor mesa 17, and the photonic band gap of the second photonic crystal structure 35 confines light in the second photonic waveguide portion 35a. Can do. The light from the end face 17e of the semiconductor mesa 17 propagates through the second photonic waveguide portion 33b according to the second photonic waveguide portion 33b in which the hole 23 in the second semiconductor region 33 is not provided, and the quantum cascade laser 11 To the outside.

  The second semiconductor region 33 includes a third photonic waveguide portion 35b extending in the direction of the first axis Ax1 with the holes 23 (24) thinned out in the direction of the first axis Ax1. The third photonic waveguide portion 35 b is optically coupled to the end face 17 e of the semiconductor mesa 17. The third photonic waveguide portion 35b makes it possible to provide the end face 17e of the semiconductor mesa 17 at a position away from the edge E35 of the second photonic crystal structure 35 and the edge E17 of the semiconductor mesa 17. The third photonic waveguide portion 35b can be provided between the semiconductor mesa 17 and the second photonic waveguide portion 35a.

  According to the quantum cascade laser 11, the semiconductor mesa 17, the third photonic waveguide portion 35b, and the second photonic waveguide portion 35a are aligned in the direction of the first axis Ax1. The second photonic waveguide portion 35a and the third photonic waveguide portion 35b function as waveguides (semiconductor waveguide portions 16c and 16d) provided on the substrate 13 outside the optical resonator. The second photonic waveguide portion 35a and the third photonic waveguide portion 35b enable light from the other end of the laser waveguide in the quantum cascade laser 11 to be output from the quantum cascade laser 11 to the outside. To do.

  The second photonic crystal structure 35 includes a second photonic waveguide portion 35a and a third photonic waveguide provided on the fourth area 13e as shown in FIG. 1 and FIG. 2 (d). The second photonic waveguide portion 35a and the third photonic waveguide portion 35b have a portion 35b, and the semiconductor is continuous in the direction of the first axis Ax1 with the holes 23 being thinned out in the direction of the first axis Ax1. It has waveguide parts 16c and 16d. On both sides of the semiconductor waveguide portions 16c and 16d, holes 23 are periodically arranged in two or three directions in the fourth area 13e of the substrate 13 to form a photonic crystal. In the fourth area 13e, the second photonic crystal structure 35 has a second array A2RY of holes 23 provided to have a photonic band gap. The thinning out of the holes 23 (24) in the second array A2RY is an exemplary structure for enabling light propagation and spot size conversion in the second photonic crystal structure 35 having a photonic band gap. .

  The (a) part, (b) part, (c) part, and (d) part of FIG. 3 correspond to the (a) part, (b) part, (c) part, and (d) part of FIG. 2, respectively. It is a section to do. As shown in (a) to (d) of FIG. 3, the first photonic crystal structure 21 and / or the second photonic crystal structure 35 includes a dielectric 37 provided in the hole 23. be able to. The dielectric 37 in the hole 23 of the first photonic crystal structure 21 and / or the second photonic crystal structure 35 can increase the mechanical strength of the quantum cascade laser 11. The dielectric 37 can include, for example, a silicon-based inorganic insulator such as silicon oxide, silicon nitride, or silicon oxynitride.

  A method of manufacturing the quantum cascade laser according to this embodiment will be described with reference to FIGS. Subsequent description will be made, where possible, using the reference numerals used in the above description for ease of understanding. Also, in each of FIGS. 4 to 6, an orthogonal coordinate system S is drawn in order to represent the direction of the product in each process. As shown in part (a) of FIG. 4, a semiconductor wafer such as an InP substrate (hereinafter referred to as “wafer W”) is prepared. A semiconductor superlattice (InGaAs / AlInAs) for the core layer 17a is grown on the wafer W, and a semiconductor layer for the diffraction grating layer 17c is grown on the semiconductor superlattice. By these growths, the lower stacked body 41a is formed. The growth is performed, for example, by metal organic vapor phase epitaxy or molecular beam epitaxy.

  As shown in FIG. 4B, a first mask 43 for the diffraction grating is formed on the lower stacked body 41a. The first mask 43 can include, for example, a 100 nm thick SiN film. The first mask 43 has a pattern including bridges 43a and openings 43b that are periodically arranged in the direction of the y-axis (first axis Ax1).

  Using this first mask 43, the lower stacked body 41 is etched using hydrobromic acid (etchant) to form a diffraction grating layer 17c including concave and convex portions. In the diffraction grating layer 17c, the depth D of the concave portion can be, for example, 100 to 200 nm, and the height H of the convex portion can be, for example, 100 to 200 nm. The processed lower laminated body 41b is formed by etching. After the etching is completed, the first mask 43 is removed.

  After the etching, as shown in FIG. 4C, a cladding layer 17b (n-type InP, 3 μm thick) is grown on the processed lower laminated body 41b on the wafer W, and the cladding A contact layer 17d (n-type InGaAs, 100 nm thick) is grown on the layer 17b. By these growths, the upper stacked body 41c is formed. The growth is performed, for example, by metal organic vapor phase epitaxy or molecular beam epitaxy.

  After this regrowth, as shown in FIG. 4D, a second mask 47 that defines a mesa is formed on the upper stacked body 41c. The second mask 47 can include, for example, a SiN film having a thickness of 500 to 1000 nm. The second mask 47 has a stripe pattern extending in the direction of the y-axis (first axis Ax1).

  Using the second mask 47, the upper stacked body 41c and the lower stacked body 41b are etched by dry etching using a halogen-based gas, so that the semiconductor mesa 17 is formed. The mesa width WM of the semiconductor mesa 17 can be, for example, 3 to 10 micrometers, and the mesa height HM can be, for example, 7 micrometers. In this embodiment, in order to form the semiconductor mesa 17, the wafer W is etched in addition to the upper stacked body 41c and the lower stacked body 41b. The stripes of the semiconductor mesa 17 are formed in the first area 13b, the second area 13c, and the third area 13d, but not in the fourth area 13e. Even after the etching is completed, the second mask 47 is left without being removed.

  With the second mask 47 left, selective growth is performed to embed the semiconductor mesa 17 in the embedded semiconductor region 27 as shown in FIG. The buried semiconductor region 27 includes, for example, Fe-doped InP. After the burying growth is completed, the second mask 47 is removed.

  After the buried growth, a third mask 49 is formed on the semiconductor mesa 17 and the buried semiconductor region 27 as shown in part (b) of FIG. The third mask 49 has a pattern for the first photonic crystal structure 21. The third mask 49 can include, for example, a 500 nm thick SiN film. The third mask 49 has a pattern including an array of openings for the photonic crystal on the first area 13b and the second area 13c.

  Using the third mask 49, the buried semiconductor region 27 on the first area 13b and the second area 13c, and if present, the semiconductor mesa 17 are etched by dry etching using a halogen-based gas to obtain a first photonic. A crystal structure 21 is formed. The diameter for the hole 23 of the first photonic crystal structure 21 may be, for example, 8 to 10 micrometers, and the depth DP1 of the hole 23 may be, for example, 8 micrometers. Specifically, the length GW of the waveguide having gain can be, for example, 500 micrometers, and the length GM is in the range of 300 to 500 micrometers.

  In this embodiment, in order to form the first photonic crystal structure 21. In addition to the semiconductor mesa 17 and the embedded semiconductor region 27, the wafer W is etched to form a hole 23 deeper than the etching of the semiconductor mesa 17. Desirably, the depth DP is greater than the mesa height HM, thereby blocking the waveguide of light from the substrate. After the etching is completed, the third mask 49 is removed.

  After the first photonic crystal structure 21 is formed, a fourth mask 51 is formed on the semiconductor mesa 17 and the embedded semiconductor region 27 as shown in FIG. 5C. The fourth mask 51 has a pattern for the second photonic crystal structure 35. The fourth mask 51 can include, for example, a 500 nm thick SiN film. The fourth mask 51 has a pattern including an array of openings for the photonic crystal on the fourth area 13e.

  Using the fourth mask 51, the embedded semiconductor region 27 on the fourth area 13e is etched by dry etching using a halogen-based gas to form the second photonic crystal structure 35. The diameter for the hole 23 of the second photonic crystal structure 35 may be 1 to 3 micrometers, for example, and the depth DP2 of the hole 23 may be 8 to 10 micrometers, for example.

  In this embodiment, in order to form the second photonic crystal structure 35. The buried semiconductor region 27 is etched to form the hole 23. The depth DP1 of the hole 23 of the second photonic crystal structure 35 is preferably equal to or greater than the depth DP2 of the hole 23 of the second photonic crystal structure 35, thereby blocking the light guide from the substrate. it can. After the etching is completed, the fourth mask 51 is removed. Prior to the formation of the first photonic crystal structure 21, the second photonic crystal structure 35 can be formed. Further, if possible, the first photonic crystal structure 21 and the second photonic crystal structure 35 may be formed together.

  As shown in part (a) of FIG. 6, a passivation film 53 is grown. The passivation film 53 can include, for example, SiN or SiON having a thickness of 300 nm. In order to prevent the passivation film 53 from being formed on the first photonic crystal structure 21 and the second photonic crystal structure 35, removal of the passivation film with buffered hydrofluoric acid can be used.

  As shown in part (b) of FIG. 6, an opening 53 a is formed in the passivation film 53. Photolithography and etching can be used for this formation. After forming the opening 53a, the first electrode 55 is formed on the passivation film 53 on the third area 13d. The first electrode 55 may have a Ti / Pt / Au structure.

  As shown in FIG. 6C, the back surface of the wafer W is polished to form a substrate having a thickness of 100 micrometers, and the second electrode 57 is formed on the back surface of the substrate. The second electrode 57 can have an AuGeNi / Au structure.

A wafer product was formed by these steps. The wafer product can be separated by cleavage to form a buried hetero quantum cascade laser. Since the quantum cascade laser has TM polarization, a wide photonic band gap can be obtained in the photonic crystal structure (21, 35). The semiconductor filling factor (definition: (SH) / ((DIS) ² × SQRT (3) / 4)) in the triangular lattice according to the present embodiment is 0.1, where the area of the hole is “SH”. And the hole spacing is represented as “DIS”. “SQRT (A)” represents the square root of A. In the example of the photonic crystal structure of the quantum cascade laser with a wavelength of 7 micrometers, the normalized frequency is 0.9 so that the TM polarized wave falls within the photonic band gap. The period of the triangular lattice determined from the oscillation wavelength and the normalized frequency is 3.15 micrometers. From the period of the triangular lattice and the semiconductor filling factor, the hole diameter of the photonic crystal structure is 1.81 micrometers. This diameter can be resolved using a reduction projection exposure apparatus. Furthermore, in the production of a quantum cascade laser in a wavelength region of 4 micrometers or less where a fine hole is required, a two-dimensional photonic crystal pattern can be formed using a nanoimprint method. In order to ensure selection of a single wavelength, the semiconductor mesa is preferably provided with a distributed feedback diffraction grating. Optical confinement in the lateral direction of the quantum cascade laser portion is performed by a high resistance semiconductor layer for current confinement. The distributed feedback embedded heterostructure quantum cascade laser according to the embodiment may have a resonator length of 500 micrometers or less.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

  As described above, according to the present embodiment, there is provided an end face emission type quantum cascade laser having a structure that does not use an end face reflection film for the high reflection mirror of the resonator.

DESCRIPTION OF SYMBOLS 11 ... Quantum cascade semiconductor laser, 13 ... Board | substrate, 13a ... Main surface, 13b ... 1st area, 13c ... 2nd area, 13d ... 3rd area, 13e ... 4th area, 15 ... 1st semiconductor region, 17 ... Semiconductor Mesa, 17a ... core layer, 17b ... clad layer, 17c ... diffraction grating layer, 17d ... contact layer, 17e ... end face, Ax1 ... first axis, 21 ... first photonic crystal structure, 23 ... hole, 25 ... boundary 27 ... Embedded semiconductor region, 33 ... Second semiconductor region, 35 ... Second photonic crystal structure.

Claims (4)

A quantum cascade laser,
A substrate including a main surface having a first area, a second area, a third area, and a fourth area;
A first semiconductor region provided on the first area and the second area of the substrate;
A semiconductor mesa provided on the third area of the substrate and extending in the direction of the first axis;
With
The first area, the second area, the third area, and the fourth area are sequentially arranged in the direction of the first axis,
The first semiconductor region includes a first photonic crystal structure,
The first semiconductor region includes a plurality of holes arranged so that the first photonic crystal structure has a photonic band gap;
The first photonic crystal structure has a first photonic waveguide portion in which the hole is thinned out in the direction of the first axis and provided on the second area,
The semiconductor mesa includes a core layer and a cladding layer,
The semiconductor semiconductor mesa is a quantum cascade laser having an end face located at a boundary between the third area and the fourth area.   The quantum cascade laser according to claim 1, wherein the first photonic crystal structure includes a dielectric provided in the hole. A second semiconductor region provided on the fourth area;
The second semiconductor region includes a second photonic crystal structure;
The second semiconductor region includes a plurality of holes arranged so that the second photonic crystal structure has a photonic band gap,
The second semiconductor region includes a second photonic waveguide portion in which the hole is thinned and extends in the direction of the first axis so that the spot size of light from the end face can be changed. 3. The quantum cascade laser according to claim 1, wherein the two-photonic waveguide portion is optically coupled to the end face of the semiconductor mesa. The second semiconductor region has a third photonic waveguide portion extending in the first axis direction with the hole being thinned out in the first axis direction, and the third photonic waveguide portion is , Optically coupled to the end face of the semiconductor mesa,
4. The quantum cascade laser according to claim 3, wherein the third photonic waveguide portion is provided between the semiconductor mesa and the second photonic waveguide portion.

Images