JP5761853B2 - Semiconductor device, multi-wavelength semiconductor laser, multi-wavelength semiconductor laser module, gas sensing system, and semiconductor device manufacturing method - Google Patents

Description

  The present invention relates to a semiconductor device, a multi-wavelength semiconductor laser, a multi-wavelength semiconductor laser module, a gas sensing system, and a semiconductor device manufacturing method used as a light source for optically detecting gas.

  It is known that the presence or absence of gas can be detected by utilizing the fact that a laser beam with a specific wavelength is easily absorbed by a certain gas (a specific wavelength that is easily absorbed is called an absorption line). Optical sensing technology is widely used in industrial measurement and pollution monitoring. Such a detection technique based on laser spectroscopy has advantages such as excellent molecular selectivity and high-speed detection. Further, absorption spectroscopy using a semiconductor laser as a light source has practical features such as being small and light, easy to maintain, and relatively inexpensive.

  When a gas absorption line is detected by changing the wavelength of the laser light, the laser light is required to have a narrower line width than the gas absorption line. In semiconductor lasers, by adopting a distributed feedback (DFB) structure or a distributed reflection (DBR) structure, single longitudinal mode oscillation is possible, and the line width is narrower than the absorption line. Can be easily realized.

  In addition, in order to detect gas with high sensitivity, the selection of the wavelength is also important. It is known that the absorption line of gas has a large absorption in the mid-infrared region due to its molecular structure. However, in the wavelength region of 3 μm or more, it is difficult to realize a semiconductor laser (light source) and a light receiver that operate at room temperature, which is not practical. On the other hand, in the wavelength region of 3 μm or less, it is possible to use a semiconductor laser or light receiver that operates at room temperature based on the technology of an InP semiconductor device for optical communication. For example, Patent Document 1 discloses a semiconductor laser using InAs as a quantum well layer having an oscillation wavelength in a 2 μm wavelength band (2.0 to 2.8 μm). Also, as shown in FIG. 1, there are many gas absorption lines in the 2 μm wavelength band. That is, from the viewpoint of practicality and high sensitivity, it is desirable to use the 2 μm wavelength band for gas sensing by absorption spectroscopy.

JP 2009-059843 A

  Since gas detection by absorption spectroscopy is excellent in molecular selectivity, there is an advantage that only a desired gas can be detected with high sensitivity even in a situation where many kinds of gases are mixed. Therefore, it is also possible to detect a plurality of gases at the same time from many types of gases. However, since absorption spectroscopy uses an absorption line specific to a gas type, a semiconductor laser having a different oscillation wavelength is required for each gas. For example, even when measuring the same location, three semiconductor laser modules having different oscillation wavelengths are required to detect three types of gases. Further, when each laser beam is used in a separate optical path, a number of light receivers corresponding to the laser beams is also required. Further, even when a plurality of laser beams are received by a single light receiver, a mechanism for multiplexing the plurality of laser beams is required.

  Even when a plurality of semiconductor laser chips having different oscillation wavelengths are mounted in one module, it is impossible to avoid complication of the optical system such as lens arrangement.

  In other words, in the conventional technique, when a plurality of gases are detected by absorption spectroscopy, there is a problem that the system becomes large and expensive due to an increase in the number of components such as a semiconductor laser and a light receiver and a complicated structure of the device. there were.

  The present invention has been proposed in view of the above problems, and its object is to provide a semiconductor device that can oscillate at a plurality of wavelengths in the 2 μm wavelength band and a multi-wavelength semiconductor laser that matches the absorption lines of various gases. Another object of the present invention is to provide a multi-wavelength semiconductor laser module, a gas sensing system, and a method for manufacturing a semiconductor device.

A method for manufacturing a semiconductor device according to a first invention for solving the above-described problems is as follows.
Growing a quantum well structure comprising an InAs well layer and an InGaAs barrier layer on an InP substrate;
Laminating a cap layer on top of the quantum well structure;
Thinning a part of the cap layer;
Forming a dielectric film on a surface where the cap layer is thinned and a part of the surface where the cap layer is not thinned;
Forming another quantum well structure in which the quantum well structure under the dielectric film is disordered by heat-treating the quantum well structure together with the cap layer and the dielectric film, and
By the disordering, the wavelength of the light emitted from the light emitting layer having the other quantum well structure is made shorter than the wavelength of the light emitted from the light emitting layer having the quantum well structure .

A semiconductor device according to a second invention for solving the above-mentioned problems is as follows.
A semiconductor element having a light emitting layer that emits light of a plurality of wavelengths on an InP substrate,
The light emitting layer is composed of a quantum well structure including an InAs well layer and an InGaAs barrier layer, and another quantum well structure in which a part of the quantum well structure is disordered.
It was made by the manufacturing method of the first invention .

Wavelength semiconductor lasers according to a third invention for solving the above-
A multi-wavelength semiconductor laser using the semiconductor device according to the second invention,
The single-mode oscillation wavelength of the light-emitting layer having the quantum well structure and the single-mode oscillation wavelength of each of the light-emitting layers having the other quantum well structures are matched with different gas absorption lines , To do.

A multiwavelength semiconductor laser module according to a fourth invention for solving the above-mentioned problems is as follows.
The multi-wavelength semiconductor laser according to the third aspect of the invention is mounted, and the output optical axis is made one .

A gas sensing system according to a fifth invention for solving the above-described problem is
The multiwavelength semiconductor laser according to the third invention or the multiwavelength semiconductor laser module according to the fourth invention is used as a light source .

  According to the present invention, in a 2 μm wavelength band suitable for gas sensing, a semiconductor laser capable of oscillating at a plurality of wavelengths from a single laser element can be easily provided, and the gas detection system using absorption spectroscopy can be reduced in size. This is extremely useful for reducing the cost and price.

It is a figure which shows the wavelength of the absorption line of many gas. It is sectional drawing explaining the manufacturing process of the 1st Example of this invention. It is sectional drawing explaining the manufacturing process of the 1st Example of this invention. It is a graph which shows the X-ray-diffraction measurement result before and behind disordering of the quantum well structure of 1st Example of this invention. In the 1st Example of this invention, it is a graph which shows PL spectrum before disordering, after disordering, and without disordering. It is a graph which shows PL spectrum before and behind disordering of an InGaAsP / InGaAsP multiple quantum well structure. It is a graph which shows PL spectrum before and after disordering of an InGaAlAs / InGaAlAs multiple quantum well structure. In the 1st Example of this invention, it is a graph which shows PL peak light emission wavelength at the time of changing heat processing temperature. In the 1st Example of this invention, it is a graph which shows PL peak light emission wavelength when changing the thickness of a cap layer. It is sectional drawing explaining the preparation procedure of the ridge type FP laser which has two stripes as an application example of the 1st Example of this invention. It is a perspective view which shows the ridge type | mold FP laser which has two stripes as an application example of the 1st Example of this invention. It is sectional drawing explaining the preparation procedure of the ridge type DFB laser which has two stripes as another application example of the 1st Example of this invention. FIG. 5 is a perspective view showing a ridge type DFB laser having two stripes as another application example of the first embodiment of the present invention. It is a perspective view which shows the ridge type DFB laser which has one stripe as 2nd Example of this invention. It is sectional drawing explaining the preparation procedure of the ridge type DFB laser which has three stripes as 3rd Example of this invention. It is sectional drawing explaining the preparation procedure of the ridge type DFB laser which has three stripes as 4th Example of this invention. It is a schematic block diagram which shows the conventional laser module. It is a schematic block diagram which shows a laser module as 5th Example of this invention. It is a schematic block diagram which shows a gas sensing system as the 6th Example of this invention. It is the spectrum of the carbon dioxide measured using the gas sensing system shown in FIG. It is the spectrum of carbon monoxide measured using the gas sensing system shown in FIG. It is a figure explaining wavelength modulation spectroscopy.

  A preferred embodiment of the present invention is described below.

[Example 1]
As a first embodiment of the present invention, a semiconductor laser capable of oscillating at a plurality of wavelengths in the 2 μm wavelength band will be described. Here, description will be made with reference to FIGS. 2 to 13, but first, the manufacturing process of this embodiment will be described with reference to FIGS. 2 and 3.

In the present invention, the MOVPE method in which the reactor is decompressed to 50 Torr is used for crystal growth. Trimethylindium (TMIn) and triethylgallium (TEGa) were used as Group III materials, and phosphine (PH ₃ ) and arsine (AsH ₃ ) were used as Group V materials. Diethylzinc (DEZn) was used as the Zn source material that becomes the p-type impurity, and monosilane (SiH ₄ ) was used as the Si source material that becomes the n-type impurity. An X-ray diffractometer manufactured by Philips was used to evaluate the structural characteristics of the sample. For the evaluation of optical characteristics, photoluminescence (PL) measurement using a laser having a wavelength of 532 nm as a light source was performed at room temperature (25 ° C.).

FIG. 2 shows a separate confinement type multiple quantum well structure which becomes an active layer (light emitting layer) of the manufactured laser. An n-type InP clad layer 12 (film thickness: 500 nm) doped with Si at a concentration of 1 × 10 ¹⁸ cm ³ is grown on the n-type InP (100) substrate 11, and subsequently, an undoped band gap wavelength λg = InAs / InGaAs multiple quantum well structure comprising a 1.3 μm InGaAsP optical confinement layer 13 (film thickness: 100 nm), six InAs well layers (film thickness: 5 nm), and seven InGaAs barrier layers (film thickness: 20 nm) (MQW) 14a, non-doped band gap wavelength λg = 1.3 μm InGaAsP optical confinement layer 15 (film thickness: 100 nm), non-doped band gap wavelength λg = 1.1 μm InGaAsP optical confinement layer 16 (film thickness: 100 nm) P-type InP cap layer 17 (film thickness: 50 nm) doped with Zn at a concentration of 5 × 10 ¹⁷ cm ³ These are sequentially formed by crystal growth.

After crystal growth of the above layer structure, it is taken out from the MOVPE growth furnace, immersed in sulfuric acid at room temperature for 1 minute to clean the surface of the p-type InP cap layer 17, and then a 300 nm SiO ₂ layer 18 is formed on the wafer by sputtering (800W). Form on the entire surface. Thereafter, as shown in FIG. 3, the SiO ₂ layer 18 is patterned using photolithography. After the patterning of the SiO ₂ layer 18, the surface of the p-type InP cap layer 17 is again cleaned by immersion in sulfuric acid at room temperature for 1 minute, and then introduced into a MOVPE growth furnace, and heat treatment is performed at 680 ° C. for 1 hour in a PH ₃ atmosphere. I do. As a result, disordering occurs in the multiple quantum well structure 14b below the portion where the SiO ₂ layer 18 is formed, and the emission wavelength is shortened.

FIG. 4 shows the X-ray diffraction measurement results of the quantum well structure before and after disordering. In the quantum well structure before disordering, the compressive strain of the quantum well layer is 3.2%, indicating that the quantum well layer is InAs. On the other hand, in the disordered quantum well structure, the amount of compressive strain in the quantum well layer is reduced to 1.9%. This is because the interdiffusion of group III atoms (specifically, Ga atoms) occurs between the well layer and the barrier layer of the quantum well structure, and the amount of strain is reduced by Ga diffusing into the InAs well layer. Show. This interdiffusion of group III atoms between the well layer and the barrier layer and the change in the characteristics of the quantum well structure is called disordering. A mechanism in which disordering occurs by forming the SiO ₂ layer 18 and performing heat treatment will be described. When the SiO ₂ layer 18 is formed on the semiconductor, group III vacancies that are crystal defects are generated at the interface between the SiO ₂ layer 18 and the semiconductor. This group III vacancies diffuse to the quantum well structure by heat treatment, causing interdiffusion of group III atoms between the well layer / barrier layer.

In this example, in order to prevent the laser characteristics from being deteriorated due to crystal defects caused by phosphorus removal from the InP surface, heat treatment was performed in a MOVPE growth furnace in a PH ₃ atmosphere. However, as the heat treatment, rapid thermal annealing (RTA) is used. ) Can also be used.

FIG. 5 shows a PL spectrum of a portion where the SiO ₂ layer 18 is formed and heat-treated and a portion where the SiO ₂ layer 18 is removed and heat-treated. For reference, the PL spectrum of the wafer immediately after crystal growth (before heat treatment) is also shown. The PL peak wavelength of the portion where the SiO ₂ layer 18 is removed, that is, the region of the multiple quantum well structure 14a is 2350 nm, which is almost unchanged from that before the heat treatment. On the other hand, it can be seen that the PL peak wavelength of the portion where the SiO ₂ layer 18 is formed and heat-treated, that is, the region of the multiple quantum well structure 14b is 2050 nm, and the wavelength is shortened by 300 nm.

For comparison, FIGS. 6 and 7 show changes before and after disordering for multiple quantum well structures of different materials. Here, FIG. 6 shows a multiple quantum well structure (band gap wavelength: 1532 nm, InP cap layer thickness: 100 nm, which is made of an InGaAsP well layer having a compressive strain of 1% and an unstrained InGaAsP barrier layer fabricated on an InP substrate. ) Is the result of performing the same treatment as above (heat treatment by forming SiO ₂ ). FIG. 7 shows a multiple quantum well structure (band gap wavelength 1519 nm, InP cap layer thickness: 100 nm) made of an InGaAlAs well layer having a compressive strain of 1% and an unstrained InGaAlAs barrier layer fabricated on an InP substrate. This is the result of performing the same treatment as above (heat treatment by forming SiO ₂ ). As shown in FIGS. 6 and 7, the wavelength shift amounts of the InGaAsP / InGaAsP multiple quantum well structure and the InGaAlAs / InGaAlAs multiple quantum well structure are 20 nm and 4 nm, respectively, indicating that the wavelength shift is not greatly greater than 100 nm. .

  FIG. 8 shows a graph plotting the PL peak emission wavelength when the heat treatment temperature is changed using the quantum well structure sample composed of the InAs well layer. It can be seen that the shift amount of the emission wavelength is increased by increasing the heat treatment temperature. A wavelength shift of 150 nm is obtained at a heat treatment temperature of 620 ° C., 300 nm at 680 ° C., 400 nm at 720 ° C., and 470 nm at 800 ° C. However, at temperatures exceeding 800 ° C., light emission cannot be obtained. From this, it can be said that the heat treatment temperature in the range of 600 ° C. to 800 ° C. is effective.

  FIG. 9 shows a graph plotting the PL peak emission wavelength when the heat treatment conditions are the same (680 ° C., 1 hour) and the thickness of the p-type InP cap layer 17 having the above layer structure is changed. It can be seen that the shift amount of the emission wavelength is increased by reducing the thickness of the InP cap layer 17. In order to obtain a large amount of wavelength shift, it is desirable that the InP cap layer 17 is thin. However, if it is 300 nm or less, it is possible to obtain a sufficient amount of wavelength shift.

Further, when the thickness of the SiO ₂ layer 18 is changed, there is no significant difference in the emission wavelength shift amount. Therefore, the thickness of the SiO ₂ layer 18 is not limited to 300 nm, and there is no problem even if it is in the range of 50 nm to 1000 nm that maintains the strength as the SiO ₂ layer 18 and maintains the patterning accuracy.

In this embodiment, the SiO ₂ layer 18 is used as a mask for disordering the quantum well, but a dielectric film such as SiN _x or TiO ₂ can also be used.

In this embodiment, sputtering is used to form the SiO ₂ layer 18 that becomes a dielectric film, but there is no problem if it is formed by other methods such as plasma CVD.

  Conventionally, in a 1.55 μm band InGaAsP-based or InGaAlAs-based semiconductor laser used for optical communication, in order to control the emission wavelength over a wide range of 300 nm or more by quantum well disordering, it is about 800 ° C. It was necessary to perform heat treatment at a high temperature. Therefore, the Zn atom which is a p-type dopant diffuses to the quantum well structure, causes Auger recombination and absorption between valence bands, and causes deterioration of laser characteristics. As shown in FIGS. 6 and 7, the oscillation wavelength cannot be controlled (shifted) by heat treatment at a low temperature of 680 ° C. (700 ° C. or less) that can suppress Zn diffusion.

  However, in the present invention, wavelength control over a wide range of 300 nm or more is possible at a heat treatment temperature of 700 ° C. or less by using InAs having a large compressive strain in the quantum well layer. Therefore, it is possible to suppress the diffusion of Zn, which has been a problem in the past. Since Auger recombination and valence band absorption increase as the emission wavelength increases, suppressing the diffusion of Zn in a 2 μm wavelength band semiconductor laser is very important in preventing deterioration of the laser characteristics.

  In this example, since the InAs quantum well layer having a thickness of 5 nm was used for the active layer, the wavelength before the heat treatment was 2350 nm, but in order to increase the wavelength, the thickness of the InAs quantum well layer was increased. It ’s fine. If the thickness of the InAs quantum well layer is 7 nm, light emission at 2.7 μm can be obtained when the thickness is 2.5 μm and 10 nm. Further, since the amount of wavelength shift due to quantum well disordering does not depend on the film thickness of the quantum well layer, it is apparent that even if the quantum well layer thickness is changed, the same tendency as in FIGS.

(Application example 1)
Using quantum well disordering, active layers (light emitting layers) having different emission wavelengths in the 2 μm wavelength band are fabricated in a semiconductor laser chip, and a ridge-type Fabry-Perot (FP) laser is fabricated. As an example, a manufacturing procedure of a ridge type FP laser that oscillates at two wavelengths of 2350 nm and 2050 nm will be described with reference to FIGS. The active layer and the optical confinement layer have the same structure as described above, and the same reference numerals are given to the same structure.

  First, similarly to the multiple quantum well structure shown in FIG. 2, an n-type InP cladding layer 12, an InGaAsP optical confinement layer 13, an InAs / InGaAs multiple quantum well structure 14a, an InGaAsP optical confinement layer 15 are formed on an n-type InP substrate 11. The InGaAsP optical confinement layer 16 and the p-type InP cap layer 17 are sequentially formed by crystal growth (FIG. 10A).

Next, the SiO ₂ layer 18 is formed in the half of the region to be the chip, for example, in the region of 400 μm if the chip width is 800 μm, in parallel with the laser beam emission direction (FIG. 10B). Thereafter, the emission wavelength of the quantum well structure 14b is shortened by quantum well disordering by heat treatment (FIG. 10C). The p-type InP cap layer 17 at this time was 50 nm, and the heat treatment conditions were 680 ° C. and 1 hour. At this time, the PL peak wavelength in the region without the SiO ₂ layer 18 was 2346 nm, and the PL peak wavelength in the region in which the SiO ₂ layer 18 was formed was 2053 nm. Thereafter, the SiO ₂ layer 18 is removed with hydrofluoric acid (FIG. 10D).

Thereafter, the p-type InP cladding layer 19 and the p-type InGaAsP contact layer 20 are sequentially formed by crystal growth by introducing into a MOVPE growth furnace (FIG. 10E). Thereafter, using a SiO ₂ film as a mask, dry etching and wet etching are used together to produce a mesa stripe structure having a width of 2.0 μm in each region of 2346 nm (stripe 1) and 2053 nm (stripe 2). (FIG. 10 (f)). The distance between the two stripes was 400 μm. Thereafter, an SiO ₂ film 21 is formed beside the stripe, and a p-type electrode 22 is deposited on each. The n-type electrode 23 on the back surface was shared by the two lasers (FIGS. 10G to 10H). Thereafter, the ridge type FP laser structure having two stripes having different oscillation wavelengths as shown in FIG. 11 is produced by cleaving to a resonator length of 900 μm.

  The laser shown in FIG. 11 is capable of multimode oscillation at a wavelength of 2344 nm for stripe 1 and a wavelength of 2052 nm for stripe 2 in continuous operation at room temperature. The threshold currents are both about 30 mA and the optical output is about 5 mW. It is.

(Application example 2)
When a gas absorption line is detected by changing the wavelength of the laser light, the laser light is required to have a narrower line width than the gas absorption line. In semiconductor lasers, by adopting a distributed feedback (DFB) structure or a distributed reflection (DBR) structure, single longitudinal mode oscillation is possible, and the line width is narrower than the absorption line. Can be easily realized. Therefore, using quantum well disordering, active layers (light emitting layers) having different emission wavelengths in the 2 μm wavelength band are fabricated in a semiconductor laser chip, and a ridge type DFB laser that oscillates in a single mode is fabricated. As an example, a procedure for manufacturing a ridge type DFB laser that oscillates at two wavelengths of 2350 nm and 2050 nm will be described with reference to FIGS. The active layer and the optical confinement layer have the same structure as described above, and the same reference numerals are given to the same structure.

  First, similarly to the multiple quantum well structure shown in FIG. 2, an n-type InP cladding layer 12, an InGaAsP optical confinement layer 13, an InAs / InGaAs multiple quantum well structure 14a, an InGaAsP optical confinement layer 15 are formed on an n-type InP substrate 11. The InGaAsP optical confinement layer 16 and the p-type InP cap layer 17 are sequentially formed by crystal growth (FIG. 12A).

Next, in parallel with the laser beam emission direction, the SiO ₂ layer 18 is formed in a half of the chip region, for example, in a 400 μm region if the chip width is 800 μm (FIG. 12B). Thereafter, the light emission wavelength of the quantum well structure 14b is shortened by disordering the quantum well by heat treatment (FIG. 12C). The p-type InP cap layer 17 at this time was 50 nm, and the heat treatment conditions were 680 ° C. and 1 hour. At this time, the PL peak wavelength in the region without the SiO ₂ layer 18 was 2346 nm, and the PL peak wavelength in the region in which the SiO ₂ layer 18 was formed was 2053 nm. Thereafter, the SiO ₂ layer 18 is removed with hydrofluoric acid (FIG. 12D).

  Further, the p-type InP cap layer 17 on the entire surface is also removed with an etchant mixed with hydrochloric acid and phosphoric acid. Thereafter, a diffraction grating 24 is formed on the InGaAsP light confinement layer 16 having a band gap wavelength of 1.1 μm by using electron beam exposure and wet etching (FIG. 12E). At this time, the period of the diffraction grating 24 was changed between the place where the disordering was performed and the place where the disordering was not performed, and the periods were 318 nm and 366 nm, respectively.

Thereafter, the p-type InP cladding layer 19 (carrier concentration: 5 × 10 ¹⁷ cm ³ ) and the p-type InGaAsP contact layer 20 (1 × 10 ¹⁹ cm ³ ) are sequentially formed by crystal growth. (FIG. 12 (f)). Thereafter, using a SiO ₂ film as a mask, dry etching and wet etching are used together to produce a mesa stripe structure having a width of 2.0 μm in each region of 2346 nm (stripe 1) and 2053 nm (stripe 2). (FIG. 12 (g)). The distance between the two stripes was 400 μm. Thereafter, an SiO ₂ film 21 is formed beside the stripe, and a p-type electrode 22 is deposited on each. The n-type electrode 23 on the back surface was shared by the two lasers (FIGS. 12H to 12I). Thereafter, cleavage to a resonator length of 900 μm is performed, thereby producing a ridge type DFB laser structure having two stripes having different oscillation wavelengths as shown in FIG.

  In the laser shown in FIG. 13, the single mode oscillation wavelength in the room temperature continuous operation is 2337 nm for stripe 1 and 2052 nm for stripe 2, the line width is narrower than the gas absorption line, and the threshold current is 30 mA for both. The optical output is about 5 mW. In any laser, the wavelength change of 10 nm or more is possible by controlling the injection current and the operating temperature. These two wavelengths coincide with the absorption lines of carbon monoxide and carbon dioxide, respectively, and are useful as light sources for gas sensors by absorption spectroscopy.

  The oscillation wavelengths of the two-wavelength laser of this example are around 2350 nm and 2050 nm, but it is clear that any wavelength from 1900 nm to 2700 nm can be realized by selecting the thickness of the InAs quantum well layer and the quantum well disordering condition. It is.

The inter-chip mesa stripe interval of this example is 400 μm, but the region of 5 μm in the vicinity of the interface between the non-quantum well disordered region and the disordered region is used for the active layer because the composition of the quantum well structure is not uniform. However, since a uniform composition is obtained in a region 5 μm or more away from the interface, the mesa stripe interval is set to an arbitrary interval as long as it is 5 μm or more away from the interface between the non-disordered region and the disordered region. can do. The width of the SiO ₂ layer 18, in order to avoid uneven areas of the composition of the SiO ₂ layer 18 at both ends 5μm wide, it is desirable that the above width 10 [mu] m.

  Here, a DFB laser having a ridge structure is manufactured. However, it is only necessary that the emission wavelength of the active layer can be controlled in the present invention, and the effect is not dependent on the structure of the laser. That is, it is obvious that the present invention can also be applied to a pn buried structure in which p-type InP and n-type InP are alternately buried, or a buried structure DFB laser buried in semi-insulating InP. In this embodiment, a straight waveguide is used. However, a curved waveguide in which the exit ends of the respective lasers are close to each other or a separate waveguide layer is provided, and a single exit end (1) is obtained by a multiplexer. It is obvious that the present invention can also be applied to a structure with two outgoing optical axes.

[Example 2]
In the first embodiment, a plurality of stripes are formed in parallel with the laser light emission direction. However, the present embodiment is characterized in that a single stripe is used to connect the lasers in series. In this embodiment, the laser element itself has a single exit end, that is, one exit optical axis.

  Hereinafter, the laser manufactured in this example will be described with reference to FIG. The active layer and the optical confinement layer have the same structure as that described in the first embodiment, and the same reference numerals are given to the similar structures.

  First, similarly to the multiple quantum well structure shown in FIG. 2, an n-type InP cladding layer 12, an InGaAsP optical confinement layer 13, an InAs / InGaAs multiple quantum well structure 14a, an InGaAsP optical confinement layer 15 are formed on an n-type InP substrate 11. The InGaAsP optical confinement layer 16 and the p-type InP cap layer 17 are sequentially formed by crystal growth.

Next, a SiO ₂ layer 18 (see FIGS. 3, 10, and 12) is formed in a region on the laser beam emitting side in a region to be a chip, and light emission of the quantum well structure 14b is performed by quantum well disordering by heat treatment. Shorten the wavelength. The p-type InP cap layer 17 (see FIGS. 2, 10, and 12) at this time was 50 nm, and the heat treatment conditions were 680 ° C. and 1 hour. At this time, the PL peak wavelength in the region without the SiO ₂ layer 18 was 2349 nm, and the PL peak wavelength in the region in which the SiO ₂ layer 18 was formed was 2051 nm. Thereafter, the SiO ₂ layer 18 is removed with hydrofluoric acid.

  Further, the p-type InP cap layer 17 on the entire surface is also removed with an etchant mixed with hydrochloric acid and phosphoric acid. Thereafter, a λ / 4 shift diffraction grating 24 is formed on the InGaAsP optical confinement layer 16 having a band gap wavelength of 1.1 μm by using electron beam exposure and wet etching. At this time, the period of the diffraction grating 24 is changed in a region where the PL peak wavelength is different. The period of the diffraction grating 24 was set to 318 nm and 366 nm, respectively, at the place where the disordering was performed and the place where the disordering was not performed.

Thereafter, the p-type InP cladding layer 19 and the p-type InGaAsP contact layer 20 are sequentially formed by crystal growth by introducing into a MOVPE growth furnace. Thereafter, a mesa stripe structure having a width of 2.0 μm is formed so as to straddle the region of 2349 nm and the region of 2051 nm by using dry etching and wet etching together with the SiO ₂ film as a mask. Thereafter, a SiO ₂ film 21 is formed on the stripe side, and a p-type electrode 22 is deposited on the 2349 nm region and the 2051 nm region, respectively. The n-type electrode 23 on the back surface is common. Then, it is cleaved to a total length of 1200 μm. At this time, the region of 2349 nm and the region of 2051 nm were designed to be equal by 600 μm. After cleaving, anti-reflective coating was applied to both end faces. As described above, a ridge type DFB laser structure composed of one stripe in which lasers having different oscillation wavelengths are integrated as shown in FIG. 14 is manufactured.

  In the laser of this example, the single mode oscillation wavelength in the room temperature continuous operation is 2049 nm when the laser beam emission side is operated, and 2340 nm when the other side is operated. The threshold current of the DFB laser at the oscillation wavelength of 2350 nm is about 30 mA, and at 2050 nm, it is about 50 mA. The optical outputs are all about 5 mW. In any laser, the wavelength can be changed by 6 nm or more by controlling the injection current and the operating temperature. These two wavelengths coincide with the absorption lines of carbon monoxide and carbon dioxide, respectively, and are useful as light sources for gas sensors by absorption spectroscopy.

  In this embodiment, the oscillation wavelengths are 2350 nm and 2050 nm, but it is apparent that any wavelength from 1900 nm to 2700 nm can be realized by selecting the thickness of the InAs quantum well layer and the quantum well disordering conditions.

[Example 3]
In this embodiment, a multi-wavelength laser capable of oscillating at three wavelengths with one element will be described with reference to FIG.

  The active layer and the optical confinement layer have the same structure as that described in the first embodiment, and the same reference numerals are given to the similar structures.

  First, similarly to the multiple quantum well structure shown in FIG. 2, an n-type InP cladding layer 12, an InGaAsP optical confinement layer 13, an InAs / InGaAs multiple quantum well structure 14a, an InGaAsP optical confinement layer 15 are formed on an n-type InP substrate 11. The InGaAsP optical confinement layer 16 and the p-type InP cap layer 17 are sequentially formed by crystal growth (FIG. 15A). Here, the thickness of the p-type InP cap layer 17 is 300 nm.

Next, a mask 25 made of SiO ₂ or the like is formed on the p-type InP cap layer 17 in a part of a region to be a chip (here, a region of about 1/3 of the chip width), and the p-type InP cap layer 17 is formed. The thickness is reduced to 50 nm by wet etching (FIG. 15B). SiO ₂ layers 18a and 18b are formed in a thin region of the p-type InP cap layer 17 and a portion of the non-thin region (FIG. 15C). Thereafter, heat treatment is performed at 680 ° C. for 1 hour in the MOVPE apparatus. By performing the heat treatment in such a structure, the emission wavelength of the quantum well structures 14b and 14c is shortened, and the quantum well structure in which the p-type InP cap layer 17 is thin as shown in the graph of FIG. 14b has the shortest emission wavelength. As a result, three regions having different emission wavelengths can be produced in the same element. The emission wavelengths of the three regions manufactured in this example are 2050 nm, 2200 nm, and 2350 nm. Thereafter, the SiO ₂ layers 18a and 18b are removed with hydrofluoric acid (FIG. 15D).

  Further, the p-type InP cap layer 17 on the entire surface is also removed by an etchant mixed with hydrochloric acid and phosphoric acid, and then a diffraction grating is formed on the InGaAsP optical confinement layer 16 having a band gap wavelength of 1.1 μm using electron beam exposure and wet etching. 24 is formed (FIG. 15E). At this time, the period of the diffraction grating 24 was set to periods of 318 nm, 343 nm, and 366 nm in the regions of the emission wavelengths of 2050 nm, 2200 nm, and 2350 nm, respectively.

Thereafter, the p-type InP cladding layer 19 (carrier concentration: 5 × 10 ¹⁷ cm ³ ) and the p-type InGaAsP contact layer 20 (1 × 10 ¹⁹ cm ³ ) are sequentially formed by crystal growth. (FIG. 15 (f)). Then, using the SiO ₂ film as a mask, dry etching and wet etching are used together, and 2.0 μm each for a 2050 nm region (stripe 1), a 2200 nm region (stripe 2), and a 2350 nm region (stripe 3). A mesa stripe structure having a width is produced (FIG. 15G). The stripe interval was 200 μm. Thereafter, an SiO ₂ film 21 is formed beside the stripe, and a p-type electrode 22 is deposited on each. The n-type electrode 23 on the back surface was shared by the three lasers (FIGS. 15H to 15I). Thereafter, the ridge type DFB laser structure having three stripes each having a different oscillation wavelength is produced by cleaving to a resonator length of 900 μm.

In the laser of this example, the single mode oscillation wavelength in the continuous operation at room temperature is 2059 nm for stripe 1, 2203 nm for stripe 2, 2335 nm for stripe 3, the threshold current is about 30 mA, and the optical output is any. Is about 5 mW. In any laser, the wavelength change of 10 nm or more is possible by controlling the injection current and the operating temperature. These three wavelengths coincide with absorption lines of carbon dioxide (CO ₂ ), nitrous oxide (N ₂ O), and carbon monoxide (CO), respectively, and are useful as light sources for gas sensors by absorption spectroscopy.

  In the present embodiment, a three-wavelength laser has been described. However, it is apparent that a laser having an oscillation wavelength of four or more wavelengths can be manufactured by manufacturing a desired number of regions having different thicknesses of the p-type InP cap layer 17. is there.

  The oscillation wavelength of the three-wavelength laser of this example is in the vicinity of 2050 nm, 2200 nm, and 2350 nm, but by selecting the thickness of the InAs quantum well layer and the quantum well disordering condition, an arbitrary wavelength from 1900 nm to 2700 nm can be realized. Is clear.

  In this example, a DFB laser having a ridge structure was manufactured. However, it is only necessary that the emission wavelength of the active layer can be controlled in the present invention, and the effect is not dependent on the laser structure. That is, it is obvious that the present invention can also be applied to a pn buried structure in which p-type InP and n-type InP are alternately buried, or a buried structure DFB laser buried in semi-insulating InP. In this embodiment, a straight waveguide is used. However, a curved waveguide in which the exit ends of the respective lasers are close to each other or a separate waveguide layer is provided, and a single exit end (1) is obtained by a multiplexer. It is obvious that the present invention can also be applied to a structure with two outgoing optical axes.

[Example 4]
In this embodiment, a multi-wavelength laser that can oscillate at three wavelengths with one element and has a different manufacturing method for disordering from Embodiment 3 will be described with reference to FIG.

  The active layer and the optical confinement layer have the same structure as that described in the first embodiment, and the same reference numerals are given to the similar structures.

  First, similarly to the multiple quantum well structure shown in FIG. 2, an n-type InP cladding layer 12, an InGaAsP optical confinement layer 13, an InAs / InGaAs multiple quantum well structure 14a, an InGaAsP optical confinement layer 15 are formed on an n-type InP substrate 11. The InGaAsP optical confinement layer 16 and the p-type InP cap layer 17 are sequentially formed by crystal growth (FIG. 16A). Here, the thickness of the p-type InP cap layer 17 is 50 nm.

Next, the chip width is divided into a plurality of regions (here, divided into three), and the SiO ₂ layer 18 and the SiN _x layer 26 are respectively formed on the p-type InP cap layer 17 in two of the three divided regions. Is formed (FIG. 16B). Thereafter, heat treatment is performed at 680 ° C. for 1 hour in the MOVPE apparatus. By performing the heat treatment in such a structure, the light emission wavelength of the quantum well structures 14b and 14c is shortened, and the stress on the semiconductor layer depends on the type of the dielectric film (SiO ₂ layer 18 and SiN _x layer 26). Since the wavelength shift amounts are different due to the difference between the two, three regions having different emission wavelengths can be fabricated in the same element. The emission wavelengths of the three regions manufactured in this example are 2050 nm, 2100 nm, and 2350 nm. Thereafter, the dielectric film (SiO ₂ layer 18, SiN _x layer 26) is removed (FIG. 16C).

  Further, the p-type InP cap layer 17 on the entire surface is also removed by an etchant mixed with hydrochloric acid and phosphoric acid, and then a diffraction grating is formed on the InGaAsP optical confinement layer 16 having a band gap wavelength of 1.1 μm using electron beam exposure and wet etching. 24 is formed (FIG. 16D). At this time, the period of the diffraction grating 24 was set to 318 nm, 326 nm, and 366 nm, respectively, in the region of the emission wavelengths of 2050 nm, 2100 nm, and 2350 nm.

Thereafter, the p-type InP cladding layer 19 (carrier concentration: 5 × 10 ¹⁷ cm ³ ) and the p-type InGaAsP contact layer 20 (1 × 10 ¹⁹ cm ³ ) are sequentially formed by crystal growth. (FIG. 16 (e)). After that, using the SiO ₂ film as a mask, dry etching and wet etching are used together, and 2.0 μm each for 2050 nm region (stripe 1), 2100 nm region (stripe 2), and 2350 nm region (stripe 3). A mesa stripe structure having a width is produced (FIG. 16F). The stripe interval was 200 μm. Thereafter, an SiO ₂ film 21 is formed beside the stripe, and a p-type electrode 22 is deposited on each. The n-type electrode 23 on the back surface was shared by the two lasers (FIGS. 16G to 16H). Thereafter, the ridge type DFB laser structure having three stripes each having a different oscillation wavelength is produced by cleaving to a resonator length of 900 μm.

In the laser of this example, the single mode oscillation wavelength in the continuous operation at room temperature is 2059 nm for stripe 1, 2103 nm for stripe 2, 2335 nm for stripe 3, the threshold current is about 30 mA, and the optical output is Both are about 5 mW. In any laser, the wavelength change of 10 nm or more is possible by controlling the injection current and the operating temperature. These three wavelengths coincide with absorption lines of carbon dioxide (CO ₂ ), nitrous oxide (N ₂ O), and carbon monoxide (CO), respectively, and are useful as light sources for gas sensors by absorption spectroscopy.

  In this embodiment, the three-wavelength laser has been described. However, it is apparent that a laser having an oscillation wavelength of four wavelengths or more can be manufactured by manufacturing a desired number of regions for forming the dielectric film. Also, in combination with the manufacturing method shown in Example 3, the thickness of the p-type InP cap layer 17 is changed and the type of dielectric film is changed to produce a multi-wavelength laser corresponding to the desired number of wavelengths. Also good.

  The oscillation wavelength of the three-wavelength laser of this example is in the vicinity of 2050 nm, 2200 nm, and 2350 nm, but by selecting the thickness of the InAs quantum well layer and the quantum well disordering condition, an arbitrary wavelength from 1900 nm to 2700 nm can be realized. Is clear.

  In this example, a DFB laser having a ridge structure was manufactured. However, it is only necessary that the emission wavelength of the active layer can be controlled in the present invention, and the effect is not dependent on the laser structure. That is, it is obvious that the present invention can also be applied to a pn buried structure in which p-type InP and n-type InP are alternately buried, or a buried structure DFB laser buried in semi-insulating InP. In this embodiment, a straight waveguide is used. However, a curved waveguide in which the exit ends of the respective lasers are close to each other or a separate waveguide layer is provided, and a single exit end (1) is obtained by a multiplexer. It is obvious that the present invention can also be applied to a structure with two outgoing optical axes.

[Example 5]
In the present embodiment, the multi-wavelength semiconductor laser module described in the first to fourth embodiments will be described.

  Conventionally, in order to use as a light source for sensing various types of gases, it is necessary to incorporate the same number of single wavelength lasers as the number of gases to be detected and lenses for making the same number of laser beams into parallel light in the module. . For example, when the number of gases to be detected is two, it is necessary to incorporate two single wavelength lasers 31a and 32b and one lens 32a and 32b into the module 30 as shown in FIG.

  On the other hand, when the multi-wavelength semiconductor laser described in the first to fourth embodiments is used, a plurality of laser beams are emitted from one laser element 41 as shown in FIG. Only one lens 42 is required for parallel light. Furthermore, since the alignment (optical axis alignment) between the laser element 41 and the lens 42 is only once, the module 40 can be easily manufactured.

  According to the present invention, the number of members for manufacturing the laser module 40 can be reduced, and the manufacturing process can be simplified.

[Example 6]
In the present embodiment, a gas sensor system using the multiwavelength laser module described in the fifth embodiment will be described.

  A system for simultaneously detecting carbon monoxide and carbon dioxide using a two-wavelength laser module having oscillation wavelengths of 2050 nm and 2340 nm will be described with reference to FIG.

  Laser light emitted from the laser module 40 is received by the light receiver 53 through the gas cell 51 containing carbon monoxide and carbon dioxide. First, the laser of 2050 nm is operated, and the operating temperature is changed by the control device 52 to manipulate the oscillation wavelength. As a result, a transmission spectrum as shown in FIG. 20 can be obtained on the monitor 54. Since the wavelength with a small transmittance coincides with the absorption line of carbon dioxide, it indicates that carbon dioxide can be detected. Thereafter, by operating the 2340 nm laser in the same manner, the absorption line of carbon monoxide as shown in FIG. 21 can be detected. The wavelength with a low transmittance coincides with the absorption line of carbon monoxide. Thus, a plurality of gases can be easily detected by the system of the present invention.

  Furthermore, wavelength modulation spectroscopy capable of improving gas detection sensitivity can be used by using this module. The wavelength modulation spectroscopy will be described with reference to FIG. Wavelength modulation spectroscopy is used to detect weak absorption by gas with high sensitivity. In this method, the oscillation wavelength of the semiconductor laser is modulated by the injection current. Since the change in the absorptance can be converted into the change in the transmitted light intensity by the wavelength modulation, the absorption spectrum can be measured with high sensitivity by performing lock-in detection on the light receiver output using the modulation frequency as a reference signal. Further, if the center of wavelength modulation is stabilized at the center of the absorption spectrum, a signal (2f signal) obtained using the second harmonic of the modulation frequency f as a reference wave is proportional to the absorption peak value, so that weak absorption is obtained. Can be detected at high speed and high sensitivity (2f detection method).

  The present invention is suitable for absorption spectroscopy using a semiconductor laser as a light source.

11 InP substrate 14a Multiple quantum well layer 14b, 14c disordered multiple quantum well layer 17 cap layer 18, 18a, 18b SiO ₂ layer 25 SiN _x layer

Claims (5)

Growing a quantum well structure comprising an InAs well layer and an InGaAs barrier layer on an InP substrate;
Laminating a cap layer on top of the quantum well structure;
Thinning a part of the cap layer;
Forming a dielectric film on a surface where the cap layer is thinned and a part of the surface where the cap layer is not thinned;
Forming another quantum well structure in which the quantum well structure under the dielectric film is disordered by heat-treating the quantum well structure together with the cap layer and the dielectric film, and
A method of manufacturing a semiconductor device, wherein the wavelength of light emitted from the light emitting layer comprising the other quantum well structure is made shorter than the wavelength of light emitted from the light emitting layer comprising the quantum well structure by disordering. A semiconductor element having a light emitting layer that emits light of a plurality of wavelengths on an InP substrate,
The light emitting layer is composed of a quantum well structure including an InAs well layer and an InGaAs barrier layer, and another quantum well structure in which a part of the quantum well structure is disordered.
A semiconductor device manufactured by the manufacturing method according to claim 1. A multi-wavelength semiconductor laser using the semiconductor device according to claim 2 ,
The single-mode oscillation wavelength of the light-emitting layer having the quantum well structure and the single-mode oscillation wavelength of each of the light-emitting layers having the other quantum well structures are matched with different gas absorption lines, Multi-wavelength semiconductor laser. A multi-wavelength semiconductor laser module comprising the multi-wavelength semiconductor laser according to claim 3 and a single output optical axis. Gas sensing system characterized by using a multi-wavelength semiconductor laser module according to a multi-wavelength semiconductor laser or claim 4 according to claim 3 as a light source.

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