JPH10112567A - Semiconductor laser and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multiwavelength simultaneously oscillating semiconductor laser in which the interference between oscillation modes is little and which is easy of manufacture. SOLUTION: In a semiconductor laser which has a quantum box and oscillates with the resonance wavelength of a resonator, the luminous spectra a of a group of quantum boxes and the sizes of quantum boxes are put in unimodal distribution, and it is oscillated with a plurality of wavelengths within the range of spectra width. For the quantum box of such distribution, the object arising naturally by the dispersion of manufacture, for example, the dispersion of accumulation can be made use of, and the manufacture is easy Furthermore, by providing plural groups of quantum boxes, unimodal distribution is superposed to make luminous spectra flat over a wide range of wavelength, thus multiwavelength oscillation in wide wavelength zone is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-wavelength simultaneous oscillation semiconductor laser capable of simultaneously oscillating a plurality of lights having different wavelengths.

[0002] In wavelength multiplex optical communication, a multi-wavelength light source that simultaneously generates light of different wavelengths is required. As such a multi-wavelength light source, a multi-wavelength simultaneous oscillation semiconductor laser capable of simultaneously generating light of many different wavelengths by one semiconductor laser is suitable from the viewpoint of ease of manufacture and handling. Among them, a semiconductor laser containing a quantum box in the active layer has the advantage that the interaction between the oscillation modes having different wavelengths is small, so that the loss is small and the optical output of each wavelength can be adjusted independently. It is expected as a light source for lighting.

However, in a semiconductor laser having a quantum box in the active layer, it is necessary to make the wavelength of the transition light emission of the quantum box coincide with the resonance wavelength of the optical resonator. Therefore, unless the dimensions of the quantum box are precisely formed. It is extremely difficult to manufacture.

Therefore, there is a strong demand for a multi-wavelength simultaneous oscillation semiconductor laser which uses a quantum box formed in an active layer as a light emitting source and is easy to manufacture.

[0005]

2. Description of the Related Art Conventionally, a multi-wavelength light source using a semiconductor laser has a method in which a plurality of semiconductor lasers having different oscillation wavelengths are arranged individually or in an array and their outputs are combined. It has been realized by a method of superimposing a high frequency to make a multi-mode operation and simultaneously exciting a plurality of wavelengths of oscillation.

However, in the method of arranging a plurality of semiconductor lasers individually, it is necessary to select semiconductor lasers having a constant oscillation wavelength interval and uniform light emission characteristics and to assemble them on the same substrate. Requires a lot of labor and precise assembly technology. Further, in a method of incorporating an array of semiconductor lasers having a predetermined oscillation wavelength interval into an optical integrated circuit, laser arrays having different oscillation wavelengths must be precisely manufactured, which is difficult to manufacture. In particular, when a short wavelength interval, for example, a wavelength interval of about 1 nm is required, the dimensions of the semiconductor laser must be strictly controlled on the order of 0.1 nm, and individual or array-shaped semiconductor lasers are manufactured and sorted. It becomes extremely difficult to do so.

Further, in the method using the high frequency superposition method, it is necessary to modulate the drive current of the semiconductor laser at a frequency corresponding to the oscillation wavelength interval, and there is a problem that the modulation frequency becomes high when the oscillation wavelength interval is long. For example, wavelength 1.
When a wavelength interval of 1 nm is required in the 55 μm band, modulation at a high frequency of 100 GHz is required, and it is difficult to perform modulation with a normal semiconductor laser.

In order to avoid the drawbacks of the conventional multi-wavelength light source combining a plurality of semiconductor laser outputs, a multi-wavelength simultaneous oscillation semiconductor laser having an active layer provided with a quantum box has been developed. It is described in Japanese Patent Publication No. 63-213384. Hereinafter, the semiconductor laser will be described.

FIG. 12 is a sectional view of a conventional example, showing the structure of a conventional multi-wavelength simultaneous oscillation semiconductor laser having an active layer provided with a quantum box. 12 (a) and 12 (b)
Represents semiconductor lasers having different active layer structures.

Referring to FIG. 12, this semiconductor laser
It has a double hetero junction structure including an active layer 2 sandwiched between cladding layers 3 and 4 on the upper and lower sides. The active layer 2 includes first to third regions 2a and 2 divided into three along the optical axis or up and down.
b, 2c. These first to third regions 2a, 2
In b and 2c, quantum boxes of different sizes are formed for each region. For example, the first region 2a has 18 nm,
20 nm for the second region 2b and 22 nm for the third region 2c
Is provided. As a result, a wavelength of 1.51 μm corresponding to the emission wavelength of the quantum box of each size.
A multi-wavelength simultaneous oscillation semiconductor laser in which oscillations of m, 1.53 μm, and 1.55 μm are simultaneously excited and oscillation lights of three wavelengths are simultaneously output is realized.

A semiconductor laser utilizing the light emission of such a quantum box has an emission wavelength of the quantum box, in other words, an absorption wavelength takes discrete values, and the movement of carriers between quantum boxes is extremely restricted. Therefore, there is no interference between three different wavelengths, the oscillation is stable, and the absorption is small, which is a characteristic suitable for wavelength multiplexed optical communication.

However, the above-mentioned conventional multi-wavelength simultaneous oscillation semiconductor laser using a quantum box has the following problems due to the operation principle. FIG. 13 is a diagram for explaining the operation principle of the conventional multi-wavelength simultaneous oscillation semiconductor laser, and shows the relationship between the gain of the active layer having the quantum box and the resonance wavelength of the resonator.
The gain of an active layer having a quantum box mainly comes from the quantum box. The size of the quantum box usually has a unimodal distribution, for example, a normal distribution, corresponding to the manufacturing accuracy. Therefore, FIG.
Referring to (a), the active layer has a gain distribution having peaks at wavelengths Λa, Λb, and Λc corresponding to quantum boxes of three different sizes. The wavelengths Λa, Λb, and Λc are emission wavelengths associated with the emission transition of the quantum box having a size corresponding to the distribution peak of each of the three types of quantum boxes. When the three resonance wavelengths λa, λb, and λc of the resonator match or are close to the peak wavelengths Λa, Λb, and Λc of the gain, the oscillations of the three wavelengths λa, λb, and λc are simultaneously excited, and the multi-wavelength simultaneous oscillation operation is performed. Is performed.

On the other hand, referring to FIG. 13B, the interval between the peak wavelengths Λa, Λb and Λc of the gain corresponding to the size of the quantum box coincides with the interval between the resonance wavelengths λa, λb and λc of the resonator. Otherwise, even if one of the peak wavelengths Λb matches one of the resonance wavelengths λb, the remaining peak wavelengths Λa and Λb
c does not match the resonance wavelengths λa and λc. In such a case, no oscillation occurs at the wavelengths λa and λc, and only one wavelength of the wavelength λb oscillates.

As described above, in the conventional multi-wavelength simultaneous oscillation semiconductor laser using the quantum box, the size of the quantum box is precisely controlled so that the emission wavelength interval of the quantum box matches the resonance wavelength interval of the resonator. Need to be manufactured. As described above, if the size of the quantum box deviates from the design value, the peak wavelength of the gain of the active layer deviates, the oscillation intensity differs depending on the wavelength, and it becomes impossible to oscillate at multiple wavelengths.
However, since the quantum box is very small, it is extremely difficult to manufacture the quantum box by precisely controlling its size, and there is a possibility that the simultaneous oscillation operation of multiple wavelengths does not occur. In particular, in the above-described conventional semiconductor laser, quantum boxes having one size are formed in different regions using molecular beam epitaxy and a focused ion beam. Therefore, a quantum box of a required size must be manufactured independently for each region, and it is more difficult to accurately manufacture the difference in the size of the quantum box between the regions as designed.

The second problem of the conventional semiconductor laser described above arises from the fact that the quantum box is processed by lithography, for example, by a focused ion beam method. Since the quantum box is small, the ratio of the surface area to the volume is large. For this reason, when a quantum box is manufactured by lithography that generates a surface defect, the optical defects and the optical and electrical characteristics of the quantum box are likely to be greatly affected by the surface defect.

The third problem of the conventional semiconductor laser occurs when an active layer having a multilayer structure is formed. Referring to FIG. 12B, in the conventional multi-wavelength simultaneous oscillation semiconductor laser, N
In order to oscillate the number of wavelengths, it is necessary to provide the same number N of active layers as the number of wavelength multiplexing. However, when the number of wavelength multiplexing is large, the number of active layers is increased and the active layer becomes thick. As a result, the mode in the thickness direction of the active layer cannot be limited to a single mode, and a multi-mode operation in the thickness direction occurs, resulting in increased noise and unstable operation. Therefore, there is a problem that the number of wavelengths that can be oscillated is limited in order to prevent the multi-mode operation in the thickness direction. The problem that the number of wavelength multiplexes is limited is described with reference to FIG. 12A, in which the in-plane region of the active layer is divided into regions of the number of wavelength multiplexes, and quantum regions having different sizes for each of the divided regions The same applies to the semiconductor laser forming the box. In this case, if the number of wavelength division multiplexing is large, the area of each divided region becomes small, and it is not possible to provide a quantum box having a sufficient gain for oscillation. Therefore, the number of wavelength multiplexing is limited to obtain the required gain.

[0017]

As described above, in a conventional multi-wavelength simultaneous oscillation semiconductor laser in which a quantum box having a different size is formed for each divided region of an active layer in a plane, the size of the quantum box is reduced. There is a problem that it must be manufactured precisely and is difficult to manufacture. Further, when the number of wavelengths to be multiplexed is large, multimode operation in the thickness direction occurs or the gain is reduced, so that the number of wavelengths that can be multiplexed is limited. Further, there is a problem that the optical and electrical characteristics of the quantum box are deteriorated due to surface defects due to lithography.

According to the present invention, the size of the quantum box is distributed so that the gain spectrum of the active layer having the quantum box is distributed over a plurality of resonance wavelengths of the optical resonator. It is an object of the present invention to provide a multi-wavelength simultaneous oscillation semiconductor laser having a large number of multiplexed wavelengths, which does not require a large size control, and which can be manufactured without using lithography.

[0019]

FIG. 1 is an explanatory view of the structure of a semiconductor laser according to the present invention, showing the structure of a multi-wavelength simultaneous oscillation semiconductor laser having a quantum box in an active layer. Note that FIG.
1A is a perspective view, and FIG. 1B is an enlarged view of a portion A in FIG. 1A. FIG. 3 is an emission spectrum of the quantum box, and shows an emission spectrum attributable to a light emission transition of the quantum box included in the active layer according to the present invention. 6 to 8 are manufacturing process diagrams of the first embodiment of the present invention, and show a method of manufacturing a group of quantum boxes having a single-peak emission spectrum. FIG. 9 is a manufacturing process diagram of the second embodiment example of the present invention.
FIG. 4 illustrates another method of fabricating a group of quantum boxes having a single-peak emission spectrum. FIG. 10 is a manufacturing process diagram of the third embodiment of the present invention. A method of manufacturing a plurality of quantum boxes having a single-peak emission spectrum and manufacturing a quantum box group having a double-peak emission spectrum is shown. Represents.

In order to solve the above problem, a first configuration of the present invention comprises an active layer 2 including a quantum box 2d and an optical resonator, as shown in FIGS. In a semiconductor laser that oscillates at the resonance wavelength of the resonator, the emission spectrum a associated with the emission transition of the group of quantum boxes 2d included in the active layer 2 has a single-peak spectral distribution, and the plurality of resonances of the optical resonator Referring to FIG. 1, the second configuration includes an active layer 2 including a quantum box 2d, and an optical resonator, and a resonance wavelength of the optical resonator. A semiconductor laser that oscillates at a plurality of resonance wavelengths of the optical resonator, and has a group of quantum boxes 2d having a single-peak distribution in size. 1 and 3, the active layer 2 including the quantum box 2d and the optical A semiconductor laser that oscillates at the resonance wavelength of the optical resonator. A semiconductor having a lattice constant different from that of the barrier layer 2a is vapor-phased on the surface of the barrier layer 2a constituting a part of the active layer 2. A group of quantum boxes 2d manufactured by deposition by a deposition method; and an optical resonator that oscillates at a plurality of resonance wavelengths by emitting light from the group of quantum boxes 2d. The fourth configuration is shown in FIG.
In the method of manufacturing a semiconductor laser having the first or second configuration, a second semiconductor having a different lattice constant from the first semiconductor layer 8 is formed on the first semiconductor layer 8 by a vapor deposition method. The method is characterized in that it has a step of depositing to form the quantum box 2d.
Referring to (b), in a semiconductor laser including an active layer 2 including a quantum box 2d and an optical resonator, and oscillating at a resonance wavelength of the optical resonator, the active layer 2 emits light due to light emission transition. Includes a plurality of groups of quantum boxes 2d forming a single-peak emission spectrum a, b, c, and the light emission accompanying the light emission transition of the plurality of quantum boxes 2d has different center wavelengths Λa, Λb, Λc. The single-peak emission spectrums a, b, and c are characterized by having a plurality of emission spectra in which a plurality of emission spectra are overlapped with each other. In a semiconductor laser that includes an active layer 2 containing 2d and an optical resonator and oscillates at the resonance wavelength of the optical resonator, a plurality of quantum boxes 2d whose distributions of sizes differ from each other at different center sizes are different. It has a multi-peak distribution with peak distributions superimposed, and emits at multiple resonance wavelengths of the optical resonator. The seventh configuration is characterized in that the seventh configuration is formed on the first semiconductor layer 8 in the method of manufacturing a semiconductor laser having the fifth or sixth configuration with reference to FIGS. Forming a mask 9 for selective vapor deposition having a plurality of openings 9a of different sizes exposing the surface of the first semiconductor layer 8; A second semiconductor having a lattice constant different from that of the second semiconductor layer 8 is selectively deposited on the first semiconductor layer 8 exposed in the opening 9a.
forming a d, then removing the mask 9, and then depositing a third semiconductor layer 10 burying the quantum box 2 d on the first semiconductor layer 8. Is configured as a feature.

FIG. 1A shows a semiconductor laser according to the present invention.
, An active layer 2 and an optical resonator are provided. Active layer 2
Includes a group of quantum boxes 2d, and the gain of the active layer 2 is mainly caused by the light emission transition of the group of quantum boxes 2d. The optical resonator has a resonance mode in which light having a plurality of different wavelengths to be wavelength-multiplexed resonates. Such a resonator is, for example, a Fabry-Perot optical resonator having a reflection surface at an end face perpendicular to the active layer 2 in the double heterojunction semiconductor laser shown in FIG. 1A, and above and below the active layer 2 in the surface emitting semiconductor laser. This can be realized by using a reflection layer parallel to the provided active layer 2 as a reflection surface.

In the first configuration of the present invention, a group of quantum boxes 2 d is provided in the active layer 2. This group of quantum boxes 2d
Are formed such that the emission spectrum associated with the emission transition of the group of quantum boxes 2d forms a single-peak spectral distribution. That is, referring to FIG. 3A, the emission spectrum a associated with the emission transition of the group of quantum boxes 2d included in the active layer is the emission spectrum having a very narrow peak width associated with the emission transition of each quantum box 2d. The distribution, that is, the envelope of the peak of the emission spectrum of each quantum box forms a single peak. The difference between the wavelengths of the emission spectra of the individual quantum boxes 2d occurs due to, for example, a difference in the size or composition of each quantum box. It should be noted that a group of quantum boxes having such a single-peak emission spectrum naturally occurs due to variations in manufacturing conditions when manufacturing many identical quantum boxes. If necessary, the quantum box can be formed by selecting the manufacturing conditions such that the size or composition of the quantum box or other factors that determine the wavelength of the emission spectrum increase.

Further, in the first configuration, oscillation occurs at a plurality of resonance wavelengths of the optical resonator. FIG. 4 is a diagram (part 1) for explaining the principle of the present invention, and illustrates the operating principle of the semiconductor laser having the first to third configurations. Since the emission spectrum associated with the emission transition of the active layer 2 roughly corresponds to the gain spectrum of the active layer 2, referring to FIG. 4, the active layer 2 includes a group of quantum boxes 2 d having a single-peak emission spectrum having a central wavelength Λa. Is
It has a single-peak gain spectrum a having a center wavelength Λa. Since the emission spectrum associated with the emission transition of the group of quantum boxes 2d included in the active layer 2 and the gain spectrum of the active layer 2 have substantially the same distribution, the same symbols are given to all the speckles. In the first configuration, the resonance wavelength λ _1,
λ _2, ··· λ _k, at the same time oscillating at two or more of the wavelength of the .... Such a condition means that the width of the gain spectrum a of the active layer is sufficiently larger than the resonance wavelength interval, and the difference between the gains of the active layer at a plurality of resonance wavelengths that oscillate simultaneously is small. Therefore, oscillation usually occurs at a resonance wavelength close to the peak wavelength of the gain. As is well known, oscillation also involves the gain of the optical resonator, so that the oscillation wavelength may not coincide with the beak wavelength of the gain of the active layer.

As described above, in the semiconductor laser having the first configuration of the present invention, when the optical resonator has a plurality of resonance wavelengths near the peak wavelength of the gain spectrum of the active layer, the plurality of resonance wavelengths are simultaneously used. It oscillates and outputs wavelength-multiplexed light. Therefore, it is not necessary to make the gain spectrum of the active layer, that is, the beak wavelength of the emission spectrum of the quantum box, coincide with each resonance wavelength of the optical resonator as in the conventional multi-wavelength simultaneous oscillation semiconductor laser using the quantum box. Therefore, strict processing accuracy is not required in the production of the quantum box, and the production is easy.

In the first configuration, since the interval between the resonance wavelengths of the optical resonator can be reduced and a large number of resonance wavelengths can be included in the wavelength range where the gain of the active layer is large, the wavelength interval is short. Light can be easily multiplexed in large quantities.
Even if the wavelength interval of the oscillating light is shortened in this way, since the emission spectrum width of each quantum box is significantly narrower than the wavelength interval of the oscillating light, no optical interference occurs between the wavelengths. Further, by arranging the quantum boxes more discretely than the diffusion length of the carriers, it is possible to avoid electrical interference between the oscillation modes of each wavelength. Therefore, even if the wavelength interval of the oscillating light is shortened, interference between the oscillation modes does not occur. Therefore, when the conventional semiconductor laser is operated in multiple modes, no modal noise occurs due to the interference between the oscillation modes. Noise is small. Also, the difference and fluctuation of the oscillation intensity between the wavelengths are small.

In the second configuration of the present invention, the quantum boxes are formed such that the size of a group of quantum boxes included in the active layer forms a unimodal distribution. For such a distribution, a variation in the production of the quantum box, for example, a distribution that naturally occurs when the quantum box is produced by depositing a semiconductor can be used. The gain spectrum of such an active layer becomes a single-peak gain spectrum similar to that of the active layer of the first configuration according to the size distribution of the quantum box.
Further, in the second configuration, oscillation occurs at a plurality of resonance wavelengths of the optical resonator, as in the first configuration. Therefore, the semiconductor laser of the present configuration operates and performs the same function as the semiconductor laser of the first configuration, so that it is easy to multiplex at a narrow wavelength interval. In addition, noise is small, and the difference and fluctuation in oscillation intensity between the wavelengths are small. Furthermore, it is not necessary to strictly match the size of the quantum box with the resonance wavelength, so that the fabrication is easy.

In the third structure of the present invention, referring to FIG. 1, quantum box 2d is formed by depositing another semiconductor by vapor deposition on the surface of barrier layer 2a forming a part of the active layer. It is made with. That is, when a semiconductor having a lattice constant different from that of the barrier layer 2a is deposited by a vapor deposition method, the deposited semiconductor aggregates on the surface of the barrier layer 2a to form a quantum box. Further, a quantum box embedded layer 2b is deposited to form an active layer in which the quantum box is embedded. The quantum box made by this method is
The distribution of the size constitutes a group of quantum boxes forming a unimodal distribution. Therefore, in the semiconductor laser of the third configuration, since a group of quantum boxes having the same size distribution as the second configuration is formed in the active layer, the same operation and effect as the second configuration are obtained. Play. Note that a group of quantum boxes in which the composition distribution of the quantum boxes forms a single peak may be formed by the above-described vapor deposition method. Since the emission spectrum of the group of quantum boxes associated with the emission transition has a single-peak emission spectrum, the same operation and effect as those of the first configuration are obtained. In the third configuration, by selecting the deposition conditions, it is possible to vary the size, composition, or other factors that change the light emission level of the quantum box, and widen the gain spectrum width of the active layer. , It is easy to manufacture quantum boxes.

In the fourth configuration, referring to FIG. 7, a second semiconductor having a lattice constant different from that of the first semiconductor layer 8 is deposited on the first semiconductor layer 8 by vapor deposition, for example, chemical vapor deposition. Law (CV
D method) or a deposition method of irradiating a molecular beam to form a group of quantum boxes 2d. This group of quantum boxes has a single-peak emission spectrum due to variations in size, composition, or other factors. Therefore, the semiconductor laser having the above-described first or second configuration can be manufactured by the deposition method, so that the manufacturing is easy. Further, in the semiconductor lasers according to the fourth configuration and the third configuration described above, since quantum boxes are formed by deposition, surface defects of the quantum boxes due to processing do not occur as in the case of lithography. Therefore, the light emission characteristics of the quantum box are hardly deteriorated, and the light emission efficiency of the semiconductor laser is excellent.

In the fifth configuration, referring to FIG.
A plurality of quantum boxes having a single-peak emission spectrum are provided in the active layer. The single-peak emission spectra a, b, and c associated with the emission transitions of the group of quantum boxes have different center wavelengths, and are formed so that the tails of the emission spectra overlap each other. Therefore, the emission spectrum associated with the emission transition of the quantum boxes of the plurality of groups as a whole is composed of a single-peaked emission spectrum a, b, and c, and a multi-peaked spectrum distribution that is shifted and superposed, and forms a flat emission spectrum over a wide wavelength range. . Note that the difference between the peak and the valley of the multi-peak spectrum can be reduced by overlapping the tails of the single-peak spectrum. Since the gain spectrum of the active layer also has a flat distribution over a wide wavelength range, the semiconductor laser of this configuration can extremely widen the wavelength range of simultaneous oscillation, and can multiplex many lights or have a wide wavelength interval. Multiplexing of light can be realized.

FIG. 5 is a diagram (2) for explaining the principle of the present invention.
The operating principles of the semiconductor lasers of the fifth and sixth configurations are shown.
doing. As described above, the active layer according to the fifth configuration
The gain spectrum is a multiple of the center wavelengths Λa to Λe, respectively.
The emission spectrum of peaks a to e is superimposed and flat.
Distribution. Therefore, the resonance wavelength λ of the optical resonator₁~ Λ _n
Are shifted from the peak wavelengths of the single-peak emission spectra a to e.
Even_,Oscillation of the same intensity is excited at all resonance wavelengths
You. Therefore_,The quantum box according to this configuration is_,Emission of quantum boxes of each group
You only have to control the difference between the peak wavelengths of the optical spectrum_,That
Easy production because there is no need to strictly control the peak wavelength
It is.

In the sixth configuration of the present invention, a plurality of groups of quantum boxes having a unimodal size are provided in the active layer. Each of these groups has a different center size and a flat bimodal distribution as a whole. Therefore, the quantum box according to this configuration has an emission spectrum similar to that of the quantum box according to the above-described fifth configuration. For this reason, the semiconductor laser of the present configuration has the same functions and effects as the semiconductor laser of the fifth configuration.

The seventh configuration relates to a method of manufacturing the semiconductor laser according to the fifth or sixth configuration. In this configuration, referring to FIG. 9 and FIG. 10, the second vapor deposition method is used by using a selective vapor deposition mask 9 having a plurality of openings 9 a formed on the first semiconductor layer 8. Is selectively deposited on the first semiconductor layer 8 exposed in the opening 9a.

In the seventh configuration, since the first semiconductor layer 8 and the second semiconductor have different lattice constants, the second semiconductor deposited on the surface of the first semiconductor layer 8 aggregates to form the quantum box 2d. To form On the other hand, the quantum box 2 d is selectively formed in the opening 9 a of the mask 9. The size of the opening 9a is
This is one of the factors that define the central value of the size of the quantum box 2d. Therefore, by arranging the openings 9a having different sizes, it is easy to arrange the quantum boxes having different sizes at the positions of the openings 9a. Further, since the deposition conditions are uniform in all the openings 9a, the difference in size is mainly determined by the size of the openings. Therefore, it is possible to easily form a quantum box in which the center of the size distribution or the difference between the centers is precisely controlled. Therefore, it is possible to easily manufacture a semiconductor laser in which the intensity of simultaneously oscillating light is uniform. In this configuration, a plurality of quantum boxes may be formed in one opening 9a.

The above-described semiconductor laser of the present invention has the structure shown in FIG.
Referring to (b), at least one active layer including a quantum box is provided. The quantum boxes may be distributed at random positions in the active layer, or may be arranged on one plane. Furthermore, since there are two or more types of quantum boxes, the semiconductor lasers of the fifth and sixth configurations having an active layer having quantum peaks having a bimodal emission spectrum or a bimodal size distribution are also similarly used. The quantum boxes can be randomly or planarly distributed.

Further, the active layer may be provided with two or more quantum box burying layers 2b in which quantum boxes are buried. FIG. 2 is an explanatory view of another semiconductor laser structure according to the present invention.
3 shows a cross section including an active layer of a portion A. Referring to FIG. 2, a plurality of quantum box embedded layers 2b are provided separated from each other by a barrier layer 2c. This barrier layer is provided to prevent optical and electrical interaction between the quantum box buried layers 2b.

In general, the increase in the gain of the active layer saturates as the number of quantum boxes included in one quantum box buried layer 2b increases. For this reason, the gain cannot be increased with a single quantum box buried layer 2b. On the other hand, by providing a plurality of embedded quantum box layers 2b, the same gain of the active layer can be obtained even if the number of quantum boxes in one of the embedded quantum box layers 2b is small. As a result, saturation of the gain of the active layer can be avoided, and a semiconductor laser having a constant oscillation intensity or a constant threshold value can be easily manufactured.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first embodiment of the present invention relates to the manufacture of a multi-wavelength simultaneous oscillation DH (double heterojunction) semiconductor laser in which a group of quantum boxes having a single-peak emission spectrum is provided in an active layer.

First, referring to FIG. 6A, the substrate 1
Si (2 × 10 ¹⁸ cm ⁻³⁾ and a thickness of 300 μm (00
An n-type GaAs substrate having 1) as a main surface was used. On this substrate 1, a buffer layer 1a made of n-type GaAs having a thickness of 0.5 μm and containing 2 × 10 ¹⁸ cm ^{−3 of} Si by a vapor deposition method, for example, an MBE method (molecular beam epitaxial growth method).
Was deposited. As the vapor deposition method, an MOVPE method (metal organic chemical vapor deposition) can be used. Then,
Referring to FIG. 6B, 1 × 1 of Si is formed by MBE.
0 ¹⁸ cm ^-3 doped n-type Al _0.3 Ga _0.7 A 1 μm thick
s was deposited at a deposition temperature of 580 ° C.

Next, referring to FIG. 7C, a barrier layer 2a made of non-doped GaAs having a thickness of 100 nm is formed as a first semiconductor layer 8 by MBE at a deposition temperature of 510 ° C.
Deposited.

Next, referring to FIG. 7D, InAs corresponding to a 1.8 atomic layer was deposited as a second semiconductor at a deposition temperature of 510 ° C. by the MBE method. As a result, GaAs
A quantum box 2d of InGaAs having a volume filling factor of 2 × 10 ¹⁰ cm ⁻³ and a surface coverage of 15% was formed on the surface of the barrier layer 2a made of InGaAs. The center value of the size distribution of the quantum box 2d corresponds to a diameter of 20 nm and a height of 5 nm. The size and physical properties of the quantum box manufactured by the vapor deposition method and their distribution vary depending on the deposition conditions, for example, the amount of InAs deposited and the deposition temperature. Further, it changes depending on the standing time until the third semiconductor layer 10 is deposited after the deposition. Therefore, by selecting these conditions, the central value and the distribution width of the characteristics of the quantum box can be controlled.

Next, referring to FIG. 7E, a barrier layer 2c made of non-doped GaAs having a thickness of 100 nm is formed as a third semiconductor layer 10 by MBE at a deposition temperature of 510.
Deposited at ° C. The quantum box 2d is embedded by the third semiconductor layer 10 constituting the barrier layer 2c, and the quantum box
b (see FIG. 1). In this embodiment, the lower part of the barrier layer 2c constitutes the quantum box buried layer 2.

Next, referring to FIG. 8F, the MB is formed on the active layer 2 including the barrier layers 2a and 2c and the quantum box 2d.
1 μm thick with 1 × 10 ¹⁸ cm ^{−3 of} Be added by E method
Second cladding layer 4 made of p-type Al _0.3 Ga _0.7 As
Was deposited at a deposition temperature of 580 ° C.

Next, referring to FIG. 8 (g), a thickness of 0.5 μm to which Be was added at 2 × 10 ¹⁹ cm ⁻³ was applied by MBE.
The contact layer 5 made of p-type GaAs is deposited at a deposition temperature of 58.
Deposited at 0 ° C. Next, a thickness of 0.
2 μm Ti, 0.3 μm thick Pt, 3 μm thick A
u is sequentially deposited and patterned to form a p-side electrode 6. On the back surface of the substrate 1, a 50 nm thick AuG
e, 3 μm thick Au is sequentially deposited and patterned,
An n-side electrode 6 is formed.

Next, the substrate was divided along a cleavage plane perpendicular to the active layer 2 to form an optical resonator having a length of 900 μm. This optical resonator has a wavelength difference of about 50 around 1.15 μm at room temperature.
It has longitudinal resonance modes at nm intervals, and simultaneous continuous oscillation of multiple wavelengths was confirmed.

FIG. 11 is an explanatory diagram of the effect of the present invention, and shows the output light spectrum of the semiconductor laser according to the first embodiment. The operating temperature is 60 K, and the numerical values in FIG. 11 represent the excitation current. Referring to FIG. 11, the emission intensity shows a gentle single-peak spectrum distribution having a peak at 1000 to 1100 nm, and emission accompanying laser oscillation was observed at an excitation current of 18 mA. The light emission accompanying the laser oscillation is composed of a number of peaks having a narrow width smaller than the resolution of the spectroscope. This is oscillation corresponding to the longitudinal mode of the optical resonator, and clarifies that oscillation light of each mode oscillates at the same time. The difference between the center wavelength of light emission and that at room temperature is mainly due to the change in the forbidden band width of the quantum box due to the temperature difference.

The second embodiment of the present invention is a single-peak light emitting switch.
Fabricating a group of quantum boxes with spectra using a mask
And a method for manufacturing a semiconductor laser. In this embodiment example
Is the same as that of the first embodiment described above with reference to FIG.
Barrier layer 2 as first semiconductor layer 8 on first cladding layer
This is the same up to the step of depositing a. Then, FIG.
Referring to (a), a 100 nm thick S layer is formed on the barrier layer 2a.
iO _TwoAn opening with a diameter of 1 μm is deposited by etching a film.
Open 9a and have openings 9a arranged in a grid
A mask 9 is formed.

Then, InAs is deposited at a deposition temperature of 510 ° C. by a vapor deposition method, for example, an MBE method. This deposited InAs aggregates to form a quantum box 2d in the opening 9a.

Next, after the mask 9 is removed by etching, a barrier layer, a second cladding layer, other semiconductor layers and electrodes are deposited and cleaved as in the first embodiment, and the semiconductor laser is cut. Complete.

In this embodiment, the size of the quantum box depends on the opening diameter of the mask. Also, the arrangement of the quantum boxes can be precisely controlled. Therefore, in the quantum box manufactured according to the present embodiment, the central value of the size and the arrangement are precisely controlled, so that a semiconductor laser having uniform characteristics can be manufactured.

The third embodiment of the present invention relates to a method for forming a quantum box having a bimodal emission spectrum. FIG.
Numeral 0 is a manufacturing process diagram of the third embodiment of the present invention, and represents a vapor deposition mask used for forming a quantum box.

In this embodiment, referring to FIG. 7C, the steps up to the step of depositing the barrier layer 2a as the first semiconductor layer 8 on the first clad layer of the first embodiment described above will be described. The same is true. Next, referring to FIG. 10, barrier layer 2a
A SiO ₂ film having a thickness of 100 nm is deposited thereon, and openings 9 a having different diameters, for example, openings 9 a having three kinds of diameters are opened by etching, and a mask 9 for vapor deposition is formed.

Next, the opening 9a is formed in the same manner as in the second embodiment.
A quantum box is formed inside. In these quantum boxes, a group of quantum boxes of a size defined by the diameter is formed in the opening 9a of each diameter. The groups vary in their characteristics due to variations in the manufacturing conditions, and give a single-peak distribution to the emission spectrum of the group of quantum boxes. After that, a barrier layer made of a non-doped GaAs layer, and Zn of 1 × 10 ¹⁸ cm
^A second cladding layer 4 made of p-type Al _0.3 Ga _0.7 As with a thickness of ³ μm and a contact layer 5 made of p-type GaAs with a thickness of 0.5 μm and 2 × 10 ¹⁹ cm ^{3 of} Zn added
Are sequentially deposited, an electrode 6 is formed and cleaved to manufacture a semiconductor laser.

According to this embodiment, even if the center of the size distribution of the quantum box fluctuates due to the change of the growth condition, the difference between the centers of the size distribution does not change much. Therefore, it is easy to manufacture the quantum box so that the emission spectrum of the entire quantum box becomes flat.

[0054]

According to the present invention, if a plurality of resonance wavelengths of an optical resonator exist in the range of the emission spectrum distribution width of the quantum box, simultaneous multi-wavelength oscillation is excited. There is no need to strictly match the spectra, and manufacturing is easy. Further, since the quantum box is used, there is no mutual interference even when oscillating at a narrow wavelength interval, the mode noise is small, and the intensity difference between the oscillation modes is small. Further, by forming a quantum box by a deposition method, a quantum box having excellent quality can be formed, and thus a semiconductor laser having excellent characteristics can be realized. Therefore, the semiconductor laser according to the present invention can provide an extremely wavelength-multiplexed light source, and greatly contributes to optical communication technology.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the structure of a semiconductor laser according to the present invention.

FIG. 2 is an explanatory view of another semiconductor laser structure of the present invention.

Fig. 3 Emission spectrum of quantum box

FIG. 4 is a diagram illustrating the principle of the present invention (part 1).

FIG. 5 is a diagram illustrating the principle of the present invention (part 2).

FIG. 6 is a process chart of the first embodiment of the present invention (part 1).

FIG. 7 is a process diagram of the first embodiment of the present invention (part 2).

FIG. 8 is a process diagram of the first embodiment of the present invention (part 3).

FIG. 9 is a process diagram of the second embodiment of the present invention.

FIG. 10 is a process diagram of a third embodiment of the present invention.

FIG. 11 is a diagram illustrating the effects of the present invention.

FIG. 12 is a sectional view of a conventional example.

FIG. 13 is a diagram illustrating the operation principle of a conventional multi-wavelength simultaneous semiconductor laser.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Active layer 2a, 2c Barrier layer 2b Quantum box burying layer 2d Quantum box 3 First cladding layer 4 Second cladding layer 5 Contact layer 6, 7 Electrode 8 First semiconductor layer 9 Mask 9a Opening 10 Third semiconductor layer

Claims (7)

[Claims] 1. A semiconductor laser comprising: an active layer including a quantum box; and an optical resonator, wherein the semiconductor laser oscillates at a resonance wavelength of the optical resonator. A semiconductor laser having an emission spectrum having a single-peak spectrum distribution and oscillating at a plurality of resonance wavelengths of the optical resonator. 2. A semiconductor laser comprising: an active layer including a quantum box; and an optical resonator. The semiconductor laser oscillates at a resonance wavelength of the optical resonator. And a semiconductor laser oscillating at a plurality of resonance wavelengths of the optical resonator. 3. A semiconductor laser comprising: an active layer including a quantum box; and an optical resonator, wherein the semiconductor laser oscillates at a resonance wavelength of the optical resonator. A group of quantum boxes manufactured by depositing a semiconductor having a lattice constant different from that of a barrier layer by a vapor deposition method; and an optical resonator oscillating at a plurality of resonance wavelengths by emitting light from the group of quantum boxes. A semiconductor laser, comprising: 4. The method for manufacturing a semiconductor laser according to claim 1, wherein a second semiconductor having a different lattice constant from the first semiconductor layer is deposited on the first semiconductor layer by a vapor deposition method. A method for manufacturing a semiconductor laser, comprising a step of forming the quantum box. 5. A semiconductor laser comprising an active layer including a quantum box and an optical resonator, and oscillating at a resonance wavelength of the optical resonator. And a plurality of the quantum boxes constituting the plurality of groups, and the light emission accompanying the emission transition of the quantum boxes constituting the plurality of groups overlaps a plurality of the single-peak emission spectra having different center wavelengths by partially overlapping each other. A semiconductor laser having a light emission spectrum. 6. A semiconductor laser having an active layer including a quantum box and an optical resonator, and oscillating at a resonance wavelength of the optical resonator, wherein the size distribution of the quantum box is such that the sizes of the centers are mutually different. A semiconductor laser having a bimodal distribution in which a plurality of different monomodal distributions are superimposed, and oscillating at a plurality of resonance wavelengths of the optical resonator. 7. The method for manufacturing a semiconductor laser according to claim 5, wherein a plurality of openings of different sizes exposing the surface of the first semiconductor layer are opened on the first semiconductor layer. Forming a mask for vapor deposition, and then selectively depositing a second semiconductor having a lattice constant different from that of the first semiconductor layer on the first semiconductor layer exposed at the opening by vapor deposition. Forming the quantum box mainly composed of the second semiconductor, removing the mask, and then embedding the quantum box on the first semiconductor layer. A step of depositing three semiconductor layers.