JP3045098B2 - Tunable laser diode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser, and more particularly, to a tunable laser diode.

[0002]

2. Description of the Related Art Conventionally, a wavelength division multiplexing method has been studied to increase the communication capacity, and a wavelength tunable laser diode is used as a local light source or a signal light source.

FIG. 11 is a sectional view showing an example of the configuration of a conventional wavelength tunable laser diode.

As shown in FIG. 11, this conventional example includes an active layer region 1101 which is a light emitting region, and a wavelength control region 1102 for controlling a wavelength. The wavelength control region 1102 is composed of a p-type cladding layer 1103. , P-type light guide layer 1104, active layer 1105, n-type light guide layer 110
6 and an n-type cladding layer 1107.

In the tunable laser diode configured as described above, electrons and holes are accumulated in the active layer 1105 due to the injection of current from the outside, and the effective refractive index of the wavelength control region 1102 changes. And thereby
The oscillation wavelength of the laser is controlled (1994).
Year, IEICE Technical Report, Vol. 493, pages 25-30).

[0006]

In the conventional wavelength tunable diode as described above, electrons and holes recombine even in the wavelength control region, thereby consuming power and generating heat. Here, when heat is generated in the wavelength control region, the refractive index of the material changes, but the change in the refractive index of the material acts in a direction to cancel the change in the refractive index due to current injection.

For this reason, the conventional wavelength tunable diode as described above has problems that the controllability of the wavelength is deteriorated and the power consumption is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a tunable laser diode having low power consumption and high wavelength controllability. Aim.

[0009]

In order to achieve the above object, the present invention comprises an active layer region, which is a light emitting region, and a wavelength control region for controlling an oscillation wavelength, and a change in the refractive index in the wavelength control region. In the wavelength tunable laser diode in which the wavelength of the laser emitting light in the active layer region changes, the wavelength control region is formed on a second clad layer formed on a semiconductor substrate and on the second clad layer . ,
Graded layer of semiconductor mixed crystal with continuously changing composition
And a charge storage layer formed on the graded layer ;
The second comprises a cladding layer same conductivity type and has a first cladding layer formed on the charge storage layer, the grayed
The refractive indices of the radiated layer and the charge storage layer are higher than the refractive indices of the first cladding layer and the second cladding layer, and the potential of the first cladding layer for carriers is smaller than the potential of the charge storage layer for carriers. High and the gray
The potential of carriers in the charge storage layer
And the potential of the second cladding layer with respect to the carrier.
It is characterized by being equal to

[0010]

Further, the active layer region includes an active layer region which is a light emitting region and a wavelength control region for controlling an oscillation wavelength. The wavelength of the laser emitting light in the active layer region changes due to a change in the refractive index in the wavelength control region. In the wavelength tunable laser diode, the wavelength control region includes a second cladding layer formed on a semiconductor substrate, a charge storage layer formed on the second cladding layer, and a conductive layer identical to the second cladding layer. A charge supply layer formed on the charge storage layer, and a first clad layer formed on the charge supply layer having the same conductivity type as the second clad layer. The refractive indices of the charge storage layer and the charge supply layer are larger than the refractive indices of the first cladding layer and the second cladding layer, and the potential of the charge supply layer with respect to carriers is It is higher than the potential for carriers of serial charge storage layer.

In addition, a graded layer of a semiconductor mixed crystal having a continuously changed composition is provided between the second clad layer and the charge storage layer, and the refractive index of the graded layer is the first clad layer. And wherein the potential of the graded layer with respect to carriers is greater than the refractive index of the second cladding layer, and is equal to the potential of the charge storage layer and the second cladding layer with respect to carriers.

Further, the potential of the first cladding layer for carriers is equal to the potential of the charge supply layer for carriers.

(Operation) In the present invention configured as described above, since the potential of the first cladding layer for carriers is higher than the potential of carriers for the charge storage layer, electrons or holes are transferred from the first cladding layer to the carriers. It moves to the storage layer and is stored near the interface between the charge storage layer and the first cladding layer. Therefore, when a positive voltage is applied to the first cladding layer, electrons or holes move from the first cladding layer to the charge storage layer, and the amount of electrons or holes stored in the charge storage layer further increases. , The carrier density increases. When the carrier density changes, the refractive index changes, so that the reflectance of light from the wavelength control region changes, and the oscillation wavelength of the laser changes.

As described above, since carriers to be stored are either electrons or holes, recombination of electrons and holes generated at the pn junction does not occur, and current injected from outside is not generated. Power consumption is also reduced.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a sectional view showing a tunable laser diode according to a first embodiment of the present invention.

As shown in FIG. 1, the present embodiment comprises an active layer region 101 which is a light emitting region and a wavelength control region 102 for controlling an oscillation wavelength.
A semiconductor substrate 103; an n-type cladding layer 104 formed on the semiconductor substrate 103; an active layer 105;
Guide layers 106a and 106b formed so as to sandwich
And the p-type cladding layer 1 formed on the guide layer 106b
07, the p-type cladding layer 107, that is, the p-electrode 109 formed on the surface of the active layer region 101, and the surface of the active layer region 101 opposite to the surface on which the p-electrode 109 is formed. The wavelength control region 102 includes a semiconductor substrate 110 and a semiconductor substrate 11.
A second cladding layer 114 formed on the second cladding layer 114, a diffraction grating 113 formed on the second cladding layer 114, a charge storage layer 112 formed on the second cladding layer 114 via the diffraction grating 113, The first cladding layer 1 having the same conductivity type as the second cladding layer and formed on the charge storage layer 112
11, on the first cladding layer 111, that is, on the surface of the wavelength control region 102 opposite to the surface on which the first electrode 116 is formed, And the second electrode 115 formed.
Note that the refractive index of the charge storage layer 112 is higher than the refractive indexes of the first cladding layer 111 and the second cladding layer 114, and the potential of the first cladding layer 111 for carriers is higher than the potential of the charge storage layer 112 for carriers. high.

In the wavelength tunable laser diode formed as described above, when current is injected into the active layer region 101, light emission occurs in the active layer 105. At this time, in the wavelength control region 102, charge accumulation occurs. The refractive index of the layer 112 is the first clad layer 111 and the second clad layer 11
4, the wavelength control region 10
Light is propagated in 2. Then, light of a specific wavelength is reflected by the diffraction grating 113 to the active layer region 101, and laser oscillation of a specific wavelength is obtained.

FIG. 2 is a band lineup diagram of the wavelength tunable laser diode shown in FIG.

As shown in FIG. 2, the potential of the charge storage layer 112 with respect to carriers is lower than the potential of the first cladding layer 111 with respect to carriers.
Here, when the first cladding layer 111 is of the n-type conductivity type, the carriers become electrons 203, and the potential of the electrons 203 decreases at a portion where the conduction band edge 202 is low, and the electrons accumulate from the first cladding layer 111. It moves to the layer 112 and is stored near the interface between the charge storage layer 112 and the first cladding layer 111. In the first cladding layer 111, a depletion layer region 204 in which electrons do not exist is formed.

As shown in FIG. 2, the potential of the second cladding layer 114 with respect to the carriers is
12, the electrons 203 are accumulated at the interface with the second cladding layer 114 as in the interface with the first cladding layer 111, and the depletion layer is formed in the second cladding layer 114. An area 204 is formed. When the conduction band edge 202 is discontinuous between the second cladding layer 114 and the charge storage layer 112 and the bandwidth is small, the amount of electrons accumulated at the interface with the second cladding layer 114 is small. .

When a positive voltage is applied to the first electrode 116, the electrons 203 move from the first cladding layer 111 to the charge storage layer 112, and the electrons 203 in the charge storage layer 112
Increases the amount of storage. Carrier density is 1 × 10 ¹⁷ cm ^-3
To 1 × 10 ¹⁹ cm ⁻³ . At this time, the charge accumulation amount on the second cladding layer 114 side decreases, but the decrease amount is
It is about 1/10 to 1/100 of the amount of charge increase on the side, and can be ignored.

When the stacking direction of the semiconductor is taken on the x-axis, the refractive index distribution in the stacking direction is n (x), the normalized electric field profile of light is E (x), and the effective refractive index is n _eff. Is expressed by the subscript δ.

[0025]

(Equation 1) It can be expressed as.

Here, in the above equation, the contribution of the second term is small, and therefore, the change of the effective refractive index δn _eff is determined by the change of the refractive index in a region where the electric field profile E (x) of light is large. Since the refractive index of the charge storage layer 112 is larger than the refractive indexes of the first cladding layer 111 and the second cladding layer 114, the electric field profile of light increases in the charge storage layer 112. Therefore, as the charge density in the charge storage layer 112 increases, the refractive index of the charge storage layer 112 decreases and the effective refractive index of the waveguide decreases. Therefore, the diffraction grating 113
Changes the wavelength of the light reflected by the laser, thereby changing the oscillation wavelength of the laser.

When the first cladding layer 111 and the second cladding layer 114 are of the p-type conductivity type, the carriers become holes, and the potential becomes lower as the position of the valence band edge 201 becomes higher. By accumulating holes in the charge storage layer 112, the same effect as described above can be obtained.

Although the diffraction grating is formed on the second cladding layer 114, the diffraction grating may be formed just below the first cladding layer 111 in the wavelength control region or on the side surface of the charge storage layer 112 regardless of the shape and position of the diffraction grating. The same effect can be obtained even if it is configured.

In this embodiment, the first cladding layer 111
And the second cladding layer 114 have the same conductivity type, and use either carriers of electrons or holes.
No recombination of electrons and holes occurs at the junction, and no power is consumed.

(Second Embodiment) FIG. 3 is a sectional view showing a tunable laser diode according to a second embodiment of the present invention.

As shown in FIG. 3, the present embodiment comprises an active layer region 301 which is a light emitting region, and a wavelength control region 302 for controlling an oscillation wavelength.
A semiconductor substrate 303; an n-type cladding layer 304 formed on the semiconductor substrate 303; an active layer 305;
Guide layers 306a and 306b formed so as to sandwich
And the p-type cladding layer 3 formed on the guide layer 306b
07, a p-type electrode 309 formed on the p-type cladding layer 307, that is, on the surface of the active layer region 301, and a surface of the active layer region 301 opposite to the surface on which the p-electrode 309 was formed. The wavelength control region 302 is composed of a semiconductor substrate 310 and a semiconductor substrate 31.
A second cladding layer 314 formed on the second cladding layer 314, a diffraction grating 313 formed on the second cladding layer 314, a charge storage layer 312 formed on the second cladding layer 314 via the diffraction grating 313, The charge supply layer 317 having the same conductivity type as the second cladding layer and formed on the charge storage layer 312
And a first cladding layer 311 formed on the charge supply layer 317 and having the same conductivity type as the second cladding layer, and formed on the first cladding layer 311, that is, on the surface of the wavelength control region 302. The first electrode 316 and the wavelength control region 302
And the second electrode 315 formed on the surface opposite to the surface on which the first electrode 316 is formed. Note that the refractive index of the charge storage layer 312 and the charge supply layer 317 is larger than the refractive index of the first clad layer 311 and the second clad layer 314, and the potential of the charge supply layer 317 with respect to the carrier is higher than that of the charge storage layer 312. Higher than the potential for In addition, the charge supply layer 317
In the charge storage layer 312, light is transmitted to the wavelength control region 3
The layer thickness is designed so that the optical profile when propagating inside 02 is maximized near the interface between the charge supply layer 317 and the charge storage layer 312.

In the tunable laser diode formed as described above, since the refractive indices of the charge supply layer 317 and the charge storage layer 312 are larger than the refractive indices of the first cladding layer 311 and the second cladding layer 314, the wavelength is changed. Control area 3
02, an optical waveguide is formed and the active layer region 3
01 emitted from the active layer 305
Of the incident light, only the light of a specific wavelength out of the incident light is caused by the diffraction grating 313 to be the active layer region 301.
The laser beam of a specific wavelength is thereby obtained.

FIG. 4 is a band lineup diagram of the wavelength tunable laser diode shown in FIG.

As shown in FIG. 4, the potential of the charge storage layer 312 with respect to carriers is lower than the potential of the charge supply layer 317 with respect to carriers. Here, when the charge supply layer 317 is of the n-type conductivity type, the carriers are electrons 403, the potential of the electrons is lower at the portion where the conduction band edge 402 is low, and the electrons are
7 to the charge storage layer 312 and is stored near the interface between the charge storage layer 312 and the charge supply layer 317. In the charge supply layer 317, a depletion layer region 404 where electrons do not exist is provided.
Is formed. Here, similar charge transfer may occur at the interface between the first cladding layer 311 and the charge supply layer 317. However, since the difference in potential is small, the amount of charge transfer is limited to the interface between the charge supply layer 317 and the charge storage layer 312. Less than. When the potential of the first cladding layer 317 with respect to the carrier is equal to the potential of the charge supply layer 317 with respect to the carrier, the first cladding layer 311
No charge transfer occurs at the interface between the charge supply layer 317 and the charge supply layer 317.

As shown in FIG. 4, the potential of the second cladding layer 314 with respect to the carriers is
12 is higher than the potential for carriers, the charge storage layer 312
17, the electrons 403 are accumulated at the interface with the second cladding layer 314, and the second cladding layer 3
14, a depletion layer region 404 is formed. Note that as the bandwidth at which the conduction band edge 402 becomes discontinuous between the second cladding layer 314 and the charge storage layer 312 decreases, the amount of electrons accumulated at the interface with the second cladding layer 314 decreases, When the potential of the second cladding layer 314 is lower than the potential of the charge storage layer 312, no electrons are stored in the charge storage layer 312.

When a positive voltage is applied to the first electrode 316, electrons move from the charge supply layer 317 to the charge storage layer 312, and the amount of electrons stored in the charge storage layer 312 increases. Carrier density from 1 × 10 ¹⁷ cm ^-3 to 1 × 10 ¹⁹ c
It is possible to vary up to m ^-3 . At this time, although the amount of accumulated charges on the second cladding layer 314 side decreases,
The amount of decrease is about 1/10 to 1/100 of the amount of increase in charge on the charge supply layer 317 side, and can be ignored.

At the interface between the first cladding layer 311 and the charge supply layer 317, if the conduction band edge of the first cladding layer 311 is lower than the conduction band edge of the charge supply layer 317, the second cladding layer and the charge As with the interface with the supply layer 317, the amount of charge reduction can be neglected.

Conversely, when the conduction band edge of the first cladding layer 311 is higher than the conduction band edge of the charge supply layer 317, charges accumulate similarly to the interface between the charge accumulation layer 312 and the charge supply layer 317. The same effects as those of the first embodiment can be obtained.

As the charge density in the charge storage layer 312 increases, the effective refractive index of the waveguide decreases accordingly. Since the light profile is designed to be maximized in the vicinity of the interface between the charge supply layer 317 and the charge storage layer 312, the coupling between the refractive index change due to light and the stored electrons is increased, and this is shown in the first embodiment. The change in the effective refractive index of the accumulated carriers is larger than that of the laser, and a larger change in the oscillation wavelength of the laser can be obtained.

When the first cladding layer 311, the charge supply layer 317, and the second cladding layer 314 are of the p-type conductivity type, the carriers become holes, and the potential is higher at the position of the valence band edge 401. The lower the portion, the more the holes accumulate in the charge accumulation layer 312, and the same effect as above can be obtained.

Although the diffraction grating is formed on the second cladding layer 314, the shape and position of the diffraction grating are not limited, and the diffraction grating is located immediately below the first cladding layer 311 in the wavelength control region, the charge storage layer 312 and the charge supply layer. The same effect can be obtained by forming the layer on the side surface of the layer 317.

In this embodiment, the first cladding layer 311
And the charge supply layer 317 and the second cladding layer 314 have the same conductivity type and use either the electron carrier or the hole carrier. No recombination of electrons and holes occurs, and no current is consumed.

(Third Embodiment) This embodiment has basically the same structure as that shown in the first embodiment, except that the space between the charge storage layer and the second cladding layer is different. In addition, a graded layer of a semiconductor mixed crystal having a continuously changed composition is provided. Note that the refractive index of the charge storage layer and the graded layer is larger than the refractive index of the first clad layer and the second clad layer, so that light is confined in the charge storage layer and the graded layer. The second cladding layer and the first cladding layer have the same conductivity type.

FIG. 5 is a band lineup diagram of a wavelength tunable laser diode according to a third embodiment of the present invention.

As shown in FIG. 5, in the present embodiment, at the interface between the charge storage layer 505 and the first cladding layer 507, the potential of the charge storage layer 505 for carriers is lower than the potential of the first cladding layer 507 for carriers. It is lower. Here, the first cladding layer 50
When 7 is an n-type conductivity type, the carriers become electrons 503, the potential of the electrons decreases at the lower portion of the conduction band edge 502, and the electrons move from the first cladding layer 507 to the charge storage layer 505 to store the charge. It is accumulated near the interface between the layer 505 and the first cladding layer 507. In the first cladding layer 507, a depletion layer region 504 in which electrons do not exist is formed.

The potential of the charge storage layer 505 with respect to carriers is equal to the potential of the graded layer 506 with respect to carriers. Therefore, no carriers are accumulated at the interface between the charge storage layer 505 and the graded layer 506. Also, the second cladding layer 508
Potential for carriers is graded layer 5
06, the potential of the carrier is equal to that of the carrier, and therefore no carrier is accumulated at the interface between the graded layer 506 and the second cladding layer 508.

When a positive voltage is applied to the first cladding layer 507, the charge from the first cladding layer 507 to the charge storage layer 505 increases.
The electrons move to and the amount of stored electrons in the charge storage layer 505 increases. As the charge density in the charge storage layer 505 increases, the refractive index of the charge storage layer 505 decreases, and the effective refractive index of the waveguide decreases. Therefore, the oscillation wavelength of the laser can be changed as in the case of the first embodiment.

In this embodiment, the graded layer 50
The potential for the carrier 6 is equal to the potential for the carrier of the charge storage layer 505 and the potential for the carrier of the second cladding layer 508 on both sides thereof. Therefore, no voltage drop occurs at the interface between the graded layer 506 and the charge storage layer 505 and at the interface between the graded layer 506 and the second cladding layer 508, and the device can operate at a low voltage.

When the first cladding layer 507 and the second cladding layer 508 are of the p-type conductivity type, the carriers are holes, and the potential thereof decreases as the position of the valence band edge 501 increases. . Graded layer 506
Is equal to the potential for carriers of the charge storage layer 505 and the potential for carriers of the second cladding layer 508 on both sides thereof, the same effect as described above can be obtained.

As a material of this embodiment, for example, the first cladding layer 507 is formed of n-type Al _0.7 Ga _0.3 As,
05, undoped GaAs, graded layer 506 n continuously changed from GaAs to Al _0.7 Ga _0.3 As
Type or undoped AlGaAs graded layer,
Combinations using n-type Al _0.7 Ga _0.3 As for the second cladding layer 508, or similar first cladding layers 50
7, charge storage layer 505, graded layer 506, second
P-type AlGaAs as a combination of the cladding layer 508
/ GaAs / AlGaAs graded layer / p-type Al
GaAs, n-type ZnSe / CdSe / CdZnSe graded layer / n-type ZnSe, n-type ZnMgSSe / Z
nSSe / ZnMgSSe graded layer / n-type Zn
A material system such as MgSSe is conceivable.

The charge storage layer 505 and the second cladding layer
508 and the material system may be different from each other.
As the first cladding layer 507, n-type Zn_0.36Cd_0.34
Mg _0.3Se, undoped Zn in the charge storage layer 505_0.47
Cd_0.53Se, Zn in the graded layer 506_0.47Cd
_0.53Se to ZnSe_0.54Te_0.46Changed continuously until
N-type or undoped ZnCd lattice matched to InP
The SeTe graded layer and the second cladding layer 508 have n
Type Zn_0.36Cd_0.34Mg_0.3A set using each of Se
The first cladding layer 507 or the
The two cladding layers 508 are made of ZnMgSeTe or MgCdSS
e, or the first cladding layer 507,
The charge storage layer 505, the graded layer 506, the second
N-type MgCdSSe /
ZnCdMgSe / ZnCdMgSe graded layer
/ N-type MgCdSSe, p-type ZnCdMgSe / ZnT
e / ZnCdSeTe graded layer / p-type ZnCd
MgSe or the like can be considered.

In the above-described embodiment, the same material system is used for the first cladding layer 507 and the second cladding layer 508, but the material systems of the first cladding layer and the second cladding layer are different from each other. Is also good.

The above-described effect can be obtained even if the charge storage layer 505 is omitted as a limit of the structure in which the charge storage layer is thin and a graded layer is used as the charge storage layer.

(Fourth Embodiment) The present embodiment has basically the same structure as that shown in the third embodiment, except that the space between the charge storage layer and the second cladding layer is different. In addition, a graded layer of a semiconductor mixed crystal having a continuously changed composition is provided. Note that the refractive indices of the charge supply layer, the charge storage layer, and the graded layer are larger than the refractive indices of the first cladding layer and the second cladding layer, and light is confined in the charge supply layer, the charge storage layer, and the graded layer. It has a structure. The first cladding layer, the second cladding layer, and the charge supply layer have the same conductivity type.

FIG. 6 is a band lineup diagram of a tunable laser diode according to a fourth embodiment of the present invention.

As shown in FIG. 6, in the present embodiment, at the interface between the charge storage layer 605 and the charge supply layer 609,
The potential of the charge storage layer 605 with respect to carriers is lower than the potential of the charge supply layer 609 with respect to carriers. Here, when the charge supply layer 609 is an n-type conductivity type, the carriers are electrons 603 and the potential of the electrons is lower at a lower portion of the conduction band edge 602,
The electrons move from the charge supply layer 609 to the charge storage layer 605 and are stored near the interface between the charge storage layer 605 and the charge supply layer 609. In addition, a depletion layer region 604 where electrons do not exist is formed in the charge supply layer 609.

The potential of the charge storage layer 605 for carriers is equal to the potential of the graded layer 606 for carriers. Therefore, no carriers are accumulated at the interface between the charge storage layer 605 and the graded layer 606. Also, the second cladding layer 608
Potential for carriers is graded layer 6
Therefore, the carrier is not accumulated at the interface between the graded layer 606 and the second cladding layer 608.

When a positive voltage is applied to the first cladding layer 607, electrons move from the charge supply layer 609 to the charge storage layer 605, and the amount of electrons stored in the charge storage layer 605 increases. As the charge density in the charge storage layer 605 increases, the effective refractive index of the waveguide decreases accordingly. Since the light profile is designed to be maximized in the vicinity of the interface between the charge supply layer 609 and the charge storage layer 605, the coupling of the change in the refractive index due to light and the stored electrons becomes large, and this is shown in the second embodiment. The oscillation wavelength of the laser can be changed in the same manner as the above.

In this embodiment, the graded layer 60
The potential for carriers of No. 6 is equal to the potential of carriers of the charge storage layer 605 and the potential of carriers of the second cladding layer 608 on both sides thereof. Therefore, the interface between the graded layer 606 and the charge storage layer 605, the graded layer 606 and the second
No voltage drop occurs at the interface with the cladding layer 608, which allows the device to operate at a low voltage.

When the first cladding layer 607, the charge supply layer 609, and the second cladding layer 608 are of the p-type conductivity type, the carriers are holes, and the potential is at the position of the valence band edge 601. The higher part is lower. Since the potential of the graded layer 606 with respect to the carriers on both sides thereof is equal to the potential of the charge storage layer 605 with respect to the carriers and the potential of the second cladding layer 608 with respect to the carriers, the same effect as described above can be obtained.

The materials of the present invention include, for example, n-type Zn _0.7 Mg _0.3 Se _0.7 Te _0.3 for the first cladding layer 607, n-type ZnSe _0.54 Te _{0.46 for the} charge supply layer 609, and undoped Zn _0.47 Cd for the charge storage layer 605. _0.53 Se, Zn _0.47 Cd _0.53 Se from Zn _0.47 Cd _0.53 Se to graded layer 606
N-type or undoped ZnCdSeTe graded layer whose composition continuously changes to _0.54 Te _0.46 and is lattice-matched to InP, and n-type Zn _0.36 Cd as the second cladding layer 608
A combination using each of _0.34 Mg _0.3 Se and the combination of the second cladding layer 608 with the n-type ZnMgSe
Te or n-type MgCdSSe, or the first cladding layer 607, charge supply layer 609, charge storage layer 605, graded layer 606, second cladding layer 60
N-type ZnMgSe / n-type ZnTe
/ CdSe / ZnCdSe graded layer / n-type Zn
Se, n-type ZnSe / n-type AlGaAs / GaAs / G
aAsZnSe graded layer / n-type ZnSe, p-type ZnSe / p-type AlG group As / GaAs / GaAsZn
Se graded layer / p-type ZnSe, n-type MgCdS
Se / n type ZnSeTe / ZnMgCdSe / ZnMg
CdSe graded layer / n-type MgCdSSe, p-type ZnMgCdSe / p-type ZnCdSe / ZnSeTe /
ZnCdSeTe graded layer / p-type ZnCdMg
A material system such as Se may be used.

In the above-described embodiment, the same material is used for the first cladding layer and the second cladding layer.
The material systems of the cladding layer and the second cladding layer may be different from each other.

The effect of the present invention can be obtained even if the charge storage layer 605 is omitted as a limit of the structure in which the charge storage layer is thin and a graded layer is used as the charge storage layer.

(Fifth Embodiment) This embodiment has basically the same structure as that shown in the third embodiment.

FIG. 7 is a band lineup diagram of a wavelength tunable laser diode according to a fifth embodiment of the present invention. The first cladding layer 311, the second cladding layer 314, and the charge supply layer 317 are n-type conductive layers. Indicates a type.

In the present embodiment, the first cladding layer 311
The potential of the conduction band edge 702 for electrons at the interface between the semiconductor device and the charge supply layer 317 is equal, so that no voltage drop occurs at this interface, thereby enabling the device to operate at a low voltage.

When the first cladding layer 311, the charge supply layer 317, and the second cladding layer 314 are of the p-type conductivity type, the carriers are holes but the first cladding layer 311
Since the potential of the valence band edge 701 with respect to the holes is equal at the interface between the charge supply layer 317 and the charge supply layer 317, the same effect as described above can be obtained.

As the material of this embodiment, for example, the first cladding layer 311, the charge supply layer 317, the charge storage layer 312,
The second cladding layer 314 has n-type Zn _0.36 Cd _0.34 Mg _0.3
Se / n type ZnSe _0.54 Te _0.46 / Zn _0.47 Cd _0.53 S
e / n-type Zn _0.36 Cd _0.34 Mg _0.3 Se or a combination using each of them,
4 using n-type ZnMgSeTe or n-type MgCdSSe or p-type ZnCdMgSe / p-type ZnCdSe / Z
Combinations such as nSeTe / p-type ZnCdMgSe are conceivable.

This embodiment may be used in combination with the fourth embodiment.

[0070]

Embodiments of the present invention will be described below.

(Embodiment 1) The semiconductor substrate 10 shown in FIG.
3 using an n-type InP substrate and n-type cladding 104
InP (n = 5 × 10¹⁷cm^-3, Thickness 2μm), active layer
105 is an InGaAs / InGaAsP multiple quantum well;
The light guide layers 106a and 106b are formed of InGaAsP (thickness
0.07 μm) and the p-cladding layer 107 is formed of p-type InP (p
= 5x10 ¹⁷cm^{ー 3}, Thickness of 2 μm)
After growing the crystal by the growth method, the n-electrode 108 and the p-electrode
As 109, Au was formed by vacuum evaporation.

As the semiconductor substrate 110, a GaAs substrate is used.
The second cladding layer 114 is made of n-type Al _0.7Ga_0.3As
(N = 5 × 10¹⁷cm^-3, Organic metal as thickness 2μm)
Photolithography after crystal growth by vapor phase growth
And 1.55μm Bragg wavelength by chemical etching
Is formed, and the charge storage layer 112 is
Dove GaAs (0.10 μm thickness), 1st clad
111 is n-type Al_0.7Ga_{0 .3}AS (n = 5 × 10¹⁷cm
^-3, Thickness 2 μm).

As the first electrode 116 and the second electrode 115, A
u was formed by vacuum evaporation.

FIG. 8 is a graph showing the characteristics of the applied voltage and the carrier density in the first embodiment of the wavelength tunable laser diode of the present invention. FIG. 9 is a graph showing the characteristics of the first embodiment of the wavelength tunable laser diode of the present invention. 4 is a graph illustrating characteristics of an applied voltage and an oscillation wavelength in an example.

As shown in FIG. 8, the carrier concentration is 1 × 1
It varied from 0 ¹⁷ cm ⁻³ to 4 × 10 ¹⁹ cm ⁻³ .

Further, a current is injected into the active layer region 101,
When the voltage applied to the first electrode was changed, the oscillation wavelength changed from 1.564 μm to 1.553 μm as shown in FIG.

At this time, the current flowing through the wave control area 102 was 1 mA or less, and an element with very low power consumption was obtained.

In this embodiment, the active layer region 1
In the present invention, an InGaAsP-based material was used for Al.01, AlGaAs-based, AlGaAsP-based and Zn-based materials.
Another material system such as a CdMgSSe system may be used.

Further, the first cladding layer, the charge storage layer and the second cladding layer are made of n-type AlGaAs / GaAs / n-type Al
Although a GaAs structure was adopted, the present invention is not limited to this.
s / GaAs / p-type AlGaAs, n-type ZnSe / Cd
Se / n-type ZnSe, n-type ZnMgSSe / ZnSSe
/ N-type ZnMgSSe, n-type MgCdSSe / ZnCd
Other material systems such as MgSe / n-type MgCdSSe may be used.

Although the same AlGaAs-based material was used for the first cladding layer and the second cladding layer, n-type ZnMg
SeTe / ZnCdMgSe / n-type MgCdSSe, n
The material system of the first cladding layer and the material system of the second cladding layer may be different from each other, such as the type ZnMgSSe / ZnSSe / n-type ZnCdSSe.

Although different substrates are used for the active layer region and the wavelength control region, they may be monolithically grown using the same substrate.

(Embodiment 2) The semiconductor substrate 30 shown in FIG.
3, an n-type InP substrate was used, and the n-type
Type InP (n = 5 × 10 ¹⁷ cm ⁻³ , thickness 2 μm), the active layer 305 is InGaAs / InGaAsP multiple quantum well, and the light guide layers 306a and 306b are InGaASP.
(Thickness: 0.07 μm), the p-type cladding layer 307 is
Crystals were grown by metalorganic vapor phase epitaxy with nP (p = 5 × 10 ¹⁷ cm ⁻³ , thickness 2 μm).

The semiconductor substrate 310 is an n-type InP substrate
The second cladding layer 314 is formed by using a part of the semiconductor substrate 303.
With n-type Mg_0.3Cd_0.7S_0.57Se_0.43(N = 5 × 10¹⁷
cm ^-3, Thickness 2 μm) by molecular beam epitaxy.
After crystal growth, photolithography and dry etching
A circuit having a Bragg wavelength of 1.55 μm
Form a folded grating 313 and undoped the charge storage layer 312
Zn_0.47Cd_0.53Se (0.1 μm thickness), current supply layer
317 is n-type ZnSe_0.54Te_0.46(N = 5 × 10¹⁷c
m^-3, Thickness 0.1 μm), the first cladding 311 is made of n-type Z
n_0.7Mg_0.3Se_0.7Te_0.3(N = 5 × 10¹⁷cm^-3,
(Thickness: 2 μm) and regrown.

The n electrode 308, the p electrode 309, the first electrode 3
16. Au was formed as the second electrode 315 by vacuum evaporation.

The active layer region 301 and the wavelength control region 302 were formed monolithically on one substrate.

FIG. 10 is a graph showing the characteristics of the applied voltage and the oscillation wavelength in the second embodiment of the wavelength tunable laser diode according to the present invention.

In this embodiment, since the vicinity of the interface between the charge supply layer and the charge storage layer is designed at the position where the intensity of the light profile is maximum, as shown in FIG. It changed greatly from 553 μm to 1.545 μm.

At this time, the current flowing through the wavelength control region 302 was 1 mA or less, and an element with very low power consumption was obtained.

In this embodiment, the active layer region 3
Although the InGaAsP-based material was used for 01, the present invention is not limited to this, and AlGaAs-based, AlGaAsP-based, Zn
Other village materials such as CdMgSSe may be used.

The first cladding layer, the charge supply layer, the charge storage layer, and the second cladding layer are made of n-type ZnMgSeTe / n-type ZnSeTe / ZnCdSe / n-type MgCdSSe, but are not limited thereto. Type ZnT
e / CdSe / n-type ZnSe, n-type ZnSe / n-type Al
GaAs / GaAs / n-type ZnSe, p-type ZnSe / p
-Type AlGaAs / GaAs / p-type ZnSe, n-type ZnM
gSeTe / n type ZnSeTe / ZnMgCdSe / n
Other material systems such as type MgCdSSe may be used.

Although the same substrate is used in the active layer region and the wavelength control region, different substrates may be used.

[0092]

As described above, in the present invention,
Since the oscillation wavelength is changed by using the movement of carriers from the charge supply layer or the first cladding layer in the wavelength control region to the charge storage layer, almost no current injection from the outside of the device is required, thereby reducing power consumption. The power can be reduced. In addition, the amount of heat generated in the passive waveguide portion is reduced, and a change in the refractive index due to heat generation of the waveguide can be suppressed, thereby improving the controllability of the wavelength.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a wavelength tunable laser diode according to a first embodiment of the present invention.

FIG. 2 is a band lineup diagram of the wavelength tunable laser diode shown in FIG.

FIG. 3 is a sectional view showing a wavelength tunable laser diode according to a second embodiment of the present invention.

FIG. 4 is a band lineup diagram of the wavelength tunable laser diode shown in FIG. 3;

FIG. 5 is a band lineup diagram of a wavelength tunable laser diode according to a third embodiment of the present invention.

FIG. 6 is a band lineup diagram of a wavelength tunable laser diode according to a fourth embodiment of the present invention.

FIG. 7 is a band lineup diagram of a tunable laser diode according to a fifth embodiment of the present invention.

FIG. 8 is a graph showing characteristics of an applied voltage and a carrier density in the first embodiment of the wavelength tunable laser diode of the present invention.

FIG. 9 is a graph showing characteristics of an applied voltage and an oscillation wavelength in the first embodiment of the wavelength tunable laser diode of the present invention.

FIG. 10 is a graph showing characteristics of an applied voltage and an oscillation wavelength in a second embodiment of the wavelength tunable laser diode of the present invention.

FIG. 11 is a cross-sectional view showing one configuration example of a conventional tunable laser diode.

[Explanation of symbols]

101, 301 Active layer region 102, 302 Wavelength control region 103, 110, 303, 310 Semiconductor substrate 104, 304 N-type cladding layer 105, 305 Active layer 106a, 106b, 306a, 306b Guide layer 107, 307 P-type cladding layer 108 , 308 n-electrode 109, 309 p-electrode 111, 311, 507, 607 first cladding layer 112, 312, 505, 605 charge storage layer 113, 313 diffraction grating 114, 314, 508, 608 second cladding layer 115, 315 Two electrodes 116,316 First electrodes 201,401,501,601,701 Valence band edges 202,402,502,602,702 Conduction band ends 203,403,503,603 Electrons 204,404,504,604 Depletion layer Region 317,609 Charge supply layer 5 06,606 Graded layer

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 G02F 1/00-1/35 JICST file (JOIS)

Claims (4)

(57) [Claims] An active layer region, which is a light emitting region, and a wavelength control region for controlling an oscillation wavelength, wherein a change in the refractive index in the wavelength control region causes a change in the wavelength of a laser emitting in the active layer region. In the wavelength tunable laser diode, the wavelength control region includes a second cladding layer formed on a semiconductor substrate, and a second cladding layer formed on the second cladding layer.
A semiconductor mixed crystal graded layer, a charge storage layer formed on the graded layer , and a first clad formed on the charge storage layer, having the same conductivity type as the second clad layer. A refractive index in the graded layer and the charge storage layer is larger than a refractive index in the first cladding layer and the second cladding layer, and the potential of the first cladding layer for carriers is A potential higher than the potential of the charge storage layer with respect to the carriers, and
The potential of the carrier of the did layer is the electric charge.
Potentials for carriers in the storage layer and the second cladding layer
Tunable laser diode characterized by being equal to a tangential . 2. An active layer region, which is a light emitting region, and a wavelength control region for controlling an oscillation wavelength, and a change in a refractive index in the wavelength control region causes a change in a wavelength of a laser emitting in the active layer region. In the wavelength tunable laser diode, the wavelength control region includes: a second cladding layer formed on a semiconductor substrate; a charge storage layer formed on the second cladding layer; A charge supply layer formed on the charge storage layer, and a first clad layer formed on the charge supply layer and having the same conductivity type as the second clad layer. The refractive indices in the charge storage layer and the charge supply layer are larger than the refractive indices in the first cladding layer and the second cladding layer, and the potential of the charge supply layer with respect to carriers is higher than that of the first and second cladding layers. A tunable laser diode having a potential higher than the potential of the charge storage layer for carriers. 3. The tunable laser diode according to claim 2 , further comprising a semiconductor mixed crystal graded layer having a composition continuously changed between the second cladding layer and the charge storage layer. The refractive index in the graded layer is larger than the refractive index in the first clad layer and the second clad layer, and the potential of the graded layer with respect to the carrier is the potential of the charge storage layer and the second clad layer with respect to the carrier. A wavelength tunable laser diode, characterized in that: 4. The tunable laser diode according to claim 2 , wherein the potential of the first cladding layer for carriers is equal to the potential of the charge supply layer for carriers.