JPH0945989A - Semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the internal loss and the electric resistance of an element by performing modulation doping such that the second clad layer in an n-type and p-type clad layer is doped heavier than the first clad layer thereby confining the carriers surely in an active layer. SOLUTION: An n-type and p-type clad layer comprises first clad layers 12, 16 and second clad layers 11, 17 formed sequentially starting from an active layer 14. Assuming π is a circle ratio, λ is oscillation wavelength, N1 is the maximum refractive index of first clad layers 12, 16 including the active layer 14 and carrier block layers 13, 15, N2 is the refractive index of second clad layers 11, 17, and d1 is the effective thickness between the second clad layers, the standardization frequency V defined by formula I satisfies a relationship V>π/3. The n-type and p-type carrier block layers 13, 15 are doped heavier than the first clad layers 12, 16 in n-type and p-type clad layer. The second clad layer is doped heavier than the first clad layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device which is suitable for use in communications, laser printers, laser medical treatments, laser processing, etc., and which can operate with high efficiency and high output.

[0002]

2. Description of the Related Art For the purpose of increasing the output of a semiconductor laser device, by providing a carrier block layer having a large forbidden band width and a thin thickness on both sides of an active layer, a forbidden clad layer formed outside the carrier block layer is forbidden. There has been proposed a semiconductor laser device having a wide band width. In such a structure, the carrier block layer has a function of efficiently confining the injected carriers in the active layer, and since the carrier block layer is thinly formed, light generated in the active layer passes through the carrier block layer. And can easily leak to the outer cladding layer. Therefore, it is possible to prevent instantaneous optical damage caused by local concentration of laser light on the emission end face of the semiconductor laser device, and to increase the end face destruction level, thus realizing high output operation.

FIG. 7A is a sectional view showing an example of such a semiconductor laser device, FIG. 7B is a distribution diagram of a forbidden band width corresponding to each layer, and FIG. 7C is a refraction corresponding to each layer. It is a distribution chart of a rate. The structure shown in FIG. 7 is a well-known separate confinement heterostructure (SCH, Separate Confinement Heteros).
tructure), perfect separation confinement structure (Perfect
SCH) (International Publication WO93 / 16513).

In FIG. 7A, a second n-type clad layer (n-AlGaAs) 1 and a first n-type clad layer (n-) are sequentially formed on a semiconductor substrate (not shown) made of n-GaAs.
AlGaAs) 2, n-type carrier block layer (n-Al
GaAs) 3, active layer (GaAs / AlGaAs multiple quantum well layer) 4, p-type carrier block layer (p-AlG)
aAs) 5, first p-type cladding layer (p-AlGaAs)
6, the second p-type cladding layer (p-AlGaAs) 7 is formed.

As shown in FIG. 7B, the forbidden band width of each carrier block layer 3, 5 is formed so as to be larger than that of any of the active layer 4 and each of the cladding layers 1, 2, 6, 7. As a result, the injected carriers are efficiently injected into the active layer 4
Trapped in. Therefore, the number of carriers that contribute to laser oscillation increases, and the oscillation efficiency improves.

Further, when the carrier block layer and the active layer are sufficiently thin and the influence on the guided mode can be ignored, the effective refractive index distribution is from the first n-type cladding layer 2 as shown in FIG. 7 (c). Since each layer up to the first p-type cladding layer 6 is a high refractive index portion and the second n-type cladding layer 1 and the second p-type cladding layer 7 are low refractive index portions, a slab waveguide structure is formed, so that the active layer 4 is formed. The light generated in 2 spreads and propagates in the high refractive index portion. Therefore, the peak intensity of the guided mode is reduced, optical damage is less likely to occur at the exit end face, and higher output can be achieved.

In addition to this, an MQW (Multiple Quantum Well) -DCH (Decoupled Confinement Heteros) provided with a hole barrier layer.
An InGaAsP / InP semiconductor laser device having a tructure structure has been reported. (IEEE journal of quantum el
ectronics, vol.29, No.6, JUNE.1993, p1596 ~ 1600)

[0008]

In order to achieve high efficiency and high output in a semiconductor laser device, it is important to efficiently confine injected carriers in the active layer and reduce internal loss due to free carrier absorption.

In the semiconductor laser device having a complete isolation confinement structure, the injected carriers are close to the active layer and are confined in the active layer by the carrier block layer having the largest forbidden band width among the layers. This carrier block layer is usually added in an amount of 0.01 to 0.01 to facilitate light leakage into the cladding layer.
It is formed to an extremely thin thickness of about 0.03 μm. If the doping concentration of the carrier block layer having a large forbidden band width and formed extremely thin is insufficient, depletion of the entire carrier block layer occurs and carrier confinement in the active layer becomes insufficient. Therefore, it is necessary to form a high doping concentration in the carrier block layer with a doping element (dopant) having high doping efficiency and low diffusivity. However, since zinc, which is conventionally generally used as a p-type dopant, is an element that is very easily diffused in the bulk, the diffusion length of zinc during the manufacturing process becomes an order of magnitude larger than the thickness of the carrier block layer. It was not possible to form a high doping concentration in the extremely thin carrier block layer.

The efficiency of the semiconductor laser device largely depends on the internal loss due to absorption of free carriers. This free carrier absorption is determined by the doping concentration of each layer through which light propagates, and the higher the doping concentration, the larger the internal loss. Therefore, the doping concentration of each layer through which light propagates needs to be formed as low as possible.

However, if the doping concentration of each layer is suppressed to be too low, the electric resistance of the element increases and the amount of self-heating increases, which causes problems such as output saturation at low output and accelerated deterioration of the element. It was

The object of the present invention is to ensure carrier confinement in the active layer, suppress the internal loss to a lower level, and reduce the electric resistance of the device, thereby achieving a highly efficient, high output and highly reliable semiconductor laser device. Is to provide.

It is another object of the present invention to provide a semiconductor laser device which suppresses optical damage on the emitting end face which is an obstacle to higher output and further facilitates higher output.

[0014]

According to the present invention, n-type and p-type clad layers are provided on both sides of an active layer, and a forbidden band having a forbidden band width of the active layer or both of the clad layers is provided in the vicinity of the active layer. In a semiconductor laser provided with an n-type carrier block layer and a p-type carrier block layer each having a band width, the n-type and p-type clad layers each include a first clad layer and a second clad layer in the order of being closer to the active layer. Is the circular constant, λ is the oscillation wavelength, the maximum refractive index of the active layer, the carrier block layer and the first cladding layer is N1, the refractive index of the second cladding layer is N2, and the effective thickness between the second cladding layers is d1. And the normalized frequency V is defined as V = (π · d1 / λ) · (N1 ² −N2 ² ) ^0.5 , V> π / 3 holds, and the n-type and p-type carrier block layers are doped. Quantity is The doping concentration of the n-type and p-type cladding layers is higher than that of the first cladding layer, and the doping amount of the second cladding layers of the n-type and p-type cladding layers is higher than that of the first cladding layer. The semiconductor laser device is characterized by being applied. Here, when the refractive index of the first cladding layer is constant, the maximum refractive index N1 has the constant value, but when the refractive index has a distribution in the first cladding layer, it means the maximum value. The effective thickness d1 is Nw (x), which is the refractive index at an arbitrary position (x) between the two second cladding layers, and x is the position of the interface of the second n-type cladding layer near the active layer.
When the position of the interface between the first and second p-type cladding layers near the active layer is x2, it is expressed by the following formula.

[0015]

[Equation 1]

The present invention also provides an n-type and p-type carrier loop.
The doping amount of the lock layer is 1 × 10 ¹⁸cm^-3Above, n
Of the first cladding layer of the p-type and p-type cladding layers
The amount is 3 × 10¹⁷cm^-3Below, n-type and p-type cladding
The doping amount of the second cladding layer of the layer is 1 × 10¹⁸cm^-3
Make sure that the modulation doping is applied as described above.
Features. The present invention also relates to the p-type carrier block layer.
Specially, the dopant is carbon or magnesium.
Sign. The present invention also provides a carrier block layer and
The first and second cladding layers are III-V compound semiconductors.
It is characterized by being formed by the body. The present invention also provides
Carrier block layer and first and second cladding layers
Is made of AlGaAs compound semiconductor
It is characterized by.

[0017]

According to the present invention, the n-type and p-type clad layers are composed of a plurality of clad layers of the first and second clad layers, and further, the active layer, the carrier block layer and the first clad layer.
The normalized frequency V of the optical waveguide layer composed of the clad layer is π / 3
By forming it to a larger size, it is possible to realize guided-mode laser oscillation in a substantially Gaussian type. Then, the peak intensity of the guided mode is reduced, and the optical damage level at the emission end face of the semiconductor laser device can be increased. Note that the normalized frequency V is preferably 2π or less in order to prevent the waveguide modes from becoming multiple.

Further, the doping amount of the n-type and p-type carrier block layers is set to the first amount of the n-type and p-type clad layers.
Since the modulation doping is performed so that the concentration is higher than that of the cladding layer, free carrier absorption in the first cladding layer can be reduced while maintaining the carrier blocking function.
Therefore, it is possible to form a low-loss slab waveguide that does not disturb the guided mode.

Since the doping amount of the second cladding layers of the n-type and p-type cladding layers is higher than that of the first cladding layer, the modulation doping is performed to reduce the electric resistance of the entire device. Therefore, self-heating can be reduced.

The details will be described below. FIG. 1A is a graph showing the forbidden band width of each layer in the completely separated confinement structure, and FIG. 1B is a graph showing the guided mode when the normalized frequency V = π. As shown in the graph, most of the guided modes are the active layer 14 and the carrier block layer 1.
It can be seen that the light propagates through the optical waveguide layer composed of 3, 15 and the first clad layers 12, 16 and a small portion of the skirt leaks to the second clad layers 11, 17. In this way, the guided mode is expanded and its peak intensity is reduced, so that it is possible to increase the optical damage level at the exit end face of the device, thereby reducing the optical internal loss. In particular, it is preferable to lower the carrier concentration of the first cladding layers 12 and 16. In addition, it is preferable that the second cladding layers 11 and 17 in which light propagation is small have a high carrier concentration to reduce the electric resistance of the device.

FIG. 2 is a graph showing the change in the optical propagation rate of the optical waveguide layer with respect to the normalized frequency V in the slab waveguide structure. The normalized frequency V is such that π is the circular constant, λ is the oscillation wavelength, the maximum refractive index of the active layer 14, the carrier block layers 13 and 15 and the first cladding layers 12 and 16 is N1, and the maximum refractive index of the second cladding layers 11 and 17 is V = (π · d) where N2 is the refractive index and d1 is the effective thickness between the second cladding layers 11 and 17.
1 / λ) · (N1 ² −N2 ² ) ^0.5 .

When the standardized frequency V is small, the width of the guided mode becomes larger than the thickness of the optical waveguide layer, and the light propagation rate in the optical waveguide layer decreases. On the contrary, when the standardized frequency V is large, the width of the guided mode becomes smaller than the thickness of the optical waveguide layer, and the light propagation rate increases. Therefore, it is preferable that the normalized frequency V is higher than π / 3 in the semiconductor laser having the complete isolation and confinement structure, and thus the light propagation rate is 70%.
% Or more can be secured. As described above, when V becomes larger than π / 3 and the light propagation rate becomes large, the propagation of light to the second cladding layer becomes small. Therefore, even if the doping of the second cladding layer is made high, this is caused. Internal loss due to free carrier absorption is reduced. Further, the normalized frequency V is 2π in order to suppress the occurrence of multi modes other than the fundamental mode.
It is preferably smaller, and the single transverse mode can be stably maintained in combination with the gain guiding effect in the active layer.

According to the invention, the doping amount of the n-type and p-type carrier block layers is 1 × 10 ¹⁸ cm ⁻³ or more, and the doping amount of the first cladding layers of the n-type and p-type cladding layers is 3 ×. The doping amount of the second cladding layers of the n-type and p-type cladding layers is 1 × 10 ¹⁸ or less at 10 ¹⁷ cm ⁻³ or less.
By performing the modulation doping so as to be cm ⁻³ or more, it is possible to sufficiently exhibit the carrier confinement function and sufficiently suppress the internal loss of light.

Each carrier block layer and each second layer
Since excessive doping of the clad layer causes an increase in free carrier absorption and deterioration of crystallinity, the upper limit of the doping amount is preferably 1 × 10 ¹⁹ cm ⁻³ . Further, the lower limit of the doping amount of each first cladding layer is preferably 1 × 10 ¹⁶ cm ^{−3 in} order not to increase the electric resistance so much.

Further, according to the present invention, by using carbon or magnesium having a high doping efficiency and a low diffusivity as a dopant for the p-type carrier block layer, the dopant can be added at a high concentration in the manufacturing process. Therefore, even if the carrier block layer is extremely thin, the diffusion of the dopant generated during the manufacturing process can be suppressed to a practically negligible level. That is, since carbon and magnesium are elements that are difficult to diffuse in the bulk, the diffusion length of each element during the manufacturing process is practically negligible smaller than the thickness of the carrier block layer. As a result, a high doping concentration can be formed even with an extremely thin carrier block layer.

In this way, each carrier block layer 13, 1
By making the doping concentration of 5 high,
Since depletion of the carrier block layers 13 and 15 as a whole is suppressed and a sufficient potential barrier height can be maintained,
The injected carriers can be efficiently confined in the active layer 14.

By the way, conventionally, it was general to use zinc as the p-type dopant, but since zinc is an element which is very easily diffused in the bulk, the diffusion length of zinc during the manufacturing process is the carrier block layer. The thickness is orders of magnitude larger than the thickness, and as a result, a high doping concentration cannot be formed in the ultrathin carrier block layer.

The potential barrier of the carrier block layer can be further increased by using carbon or magnesium as the dopant of the p-type carrier block layer.

FIG. 3 is a graph showing acceptor levels of various p-type dopants in AlGaAs. In this graph, the horizontal axis represents the change in Al composition x. Zinc tends to have a deeper acceptor level as the Al composition increases, whereas carbon and magnesium are elements that form a shallower acceptor level than zinc as a whole even if the Al composition x changes. The potential barrier of the p-type carrier block layer 15 can be increased, and the carrier confinement action is increased. Therefore, it is possible to form a high doping concentration necessary for preventing the depletion of the entire carrier block layer while preventing the diffusion of the dopant into the active region, and it is possible to form a high potential barrier by the shallow acceptor level.

In particular, the carrier block layer is, for example, 0.0
Even when it is formed to a very thin thickness of about 1 to 0.03 μm, the above-mentioned modulation doping can be easily realized by using carbon or magnesium having a low diffusibility as a dopant. Therefore, since the effect of the carrier block is sufficiently exerted, the reactive current that does not contribute to the radiative recombination is significantly reduced, the temperature dependence (characteristic temperature) of the oscillation threshold is improved, and the laser oscillation efficiency is improved.

Incidentally, the diffusion constant of each element in GaAs is determined.
The number is 1 × 10 carbon C under certain conditions^-15cm²/ Sec
(900 ° C.) (Reference 1), magnesium Mg is 1.4 ×
10 ^-13cm²/ Sec (900 ° C) (reference 2)
There are precedents. (Reference 1: Journal Vacuum Science Techn
ology A. Vol8, No3, May / Jun 1990 p2980, Reference 2: Jour
nal Appl. Phys. 59 (4), 15 (1986) 1156). Thus carbon
Is more preferred. The diffusion length is the square root of the diffusion constant.
For example.

Further, since the carrier block layer and the first and second cladding layers are made of a III-V group compound semiconductor, the diffusivity of carbon or magnesium is kept lower, so that the doping of the carrier block layer is performed. A high concentration can be formed.

Further, it is preferable that the carrier block layer and the first and second cladding layers are made of AlGaAs compound semiconductor. In that case, as shown in FIG.
Since the acceptor level formed by carbon and magnesium becomes shallow, the potential barrier of the carrier block layer can be increased. Moreover, the doping concentration of the carrier block layer can be increased due to the high doping efficiency and the low diffusivity.

[0034]

【Example】

 (Embodiment 1) FIG. 4A shows the configuration of Embodiment 1 of the present invention.
4B is a cross-sectional view of the dopin corresponding to each layer.
It is a distribution diagram of the black concentration. In this semiconductor laser,
On the conductor substrate (n-GaAs) 20, the second n-type mask is sequentially formed.
Rad layer (n-Al_0.48Ga_0.52As, donor concentration: 1
× 10¹⁸cm^-3, Thickness: 0.7 μm) 11, first n-type
Rad layer (n-Al_0.31Ga_0.69As, donor concentration: 3
× 10¹⁷cm^-3, Thickness: 0.4 μm) 12, n-type carrier
Block layer (n-Al_0.60Ga_0.40As, Donor
Degree: 1 x 10¹⁸cm^-3, Thickness: 0.014 μm) 13,
Active layer (DQW: double quantum well, GaAs / Al_0.31G
a_0.69As, without doping) 14, p-type carrier block
Layer (p-Al_0.50Ga_0.50As, acceptor thick
Degree: 1 x 10¹⁸cm^-3, Thickness: 0.021 μm) 15,
First p-type cladding layer (p-Al_0.31Ga_0.69As, Ac
Scepter concentration: 3 x 10 ¹⁷cm^-3, Thickness: 0.4 μm)
16, second p-type cladding layer (p-Al_0.48Ga_0.52A
s, acceptor concentration: 1 × 10¹⁸cm^-3, Thickness: 0.
7 μm) 17, current confinement layer (n-GaAs, donor concentration)
Degree: 1 x 10¹⁸cm^-3, Thickness: 0.3 μm) 18, p-type
Contact layer (p-GaAs, acceptor concentration: 3x)
10¹⁷cm^-3~ 1 × 10¹⁹cm^-3, Thickness: 2 μm) 19
Are formed by MOCVD (metal organic chemical vapor deposition)
You. Here, Se (selenium) is doped as a donor,
C (carbon) except the p-type contact layer as an acceptor
And the p-type contact layer is doped with Zn (zinc)
doing.

Ohmic electrodes 21 and 22 are formed on the upper surface of the p-type contact layer 19 and the lower surface of the semiconductor substrate 20, respectively. The optical resonator is formed in the direction perpendicular to the paper surface,
Laser oscillation occurs due to reflection on both end faces of the device.

The point to be noted is that as shown in FIG. 4B, the donor concentration and p of the n-type carrier block layer 13 are set.
Type carrier block layer 15 has an acceptor concentration of 1 × 1
It is formed to a high concentration of 0 ¹⁸ cm ^-3 or more, and the donor concentration of the first n-type cladding layer 12 and the acceptor concentration of the first p-type cladding layer 16 are formed to a low concentration of 3 × 10 ¹⁷ cm ^-3 or less. The second n-type cladding layer 11
That is, the donor concentration and the acceptor concentration of the second p-type cladding layer 17 are set to a high concentration of 1 × 10 ¹⁸ cm ⁻³ or higher, and so-called modulation doping is performed.

As described above, the n-type carrier block layer 13 and the p-type carrier block layer 15 are subjected to modulation doping so that the doping amounts thereof are higher than those of the first n-type cladding layer 12 and the first p-type cladding layer 16. Therefore, the free carrier absorption in the second n-type cladding layer 11 and the second p-type cladding layer 17 can be reduced while maintaining the carrier blocking function. Therefore, it is possible to form a low-loss slab waveguide that does not disturb the guided mode.

Further, the second n-type cladding layer 11 and the second
Since the doping amount of the p-type clad layer 17 is modulation-doped so as to be higher than those of the first n-type clad layer 12 and the first p-type clad layer 16, the electric resistance of the entire device can be reduced, and Can reduce fever.

The normalized frequency V of the first embodiment is π. Therefore, the light propagation rate in the optical waveguide layer is increased, and further, the optical damage on the emission end face is suppressed, and the higher output is further facilitated.

(Comparative Example 1) FIG. 5A is a sectional view showing the structure of Comparative Example 1, and FIG. 5B is a distribution diagram of the doping concentration corresponding to each layer. In this semiconductor laser device, the second n-type clad layer (n-Al _0.48 Ga _0.52 As, donor concentration: 1 × 10 ¹⁸ cm ⁻³ , thickness: 0.7 μm) is sequentially formed on the semiconductor substrate (n-GaAs) 20. 11, first n-type cladding layer (n-Al _0.31 Ga _0.69 As, donor concentration: 1 × 10 ¹⁸ cm ⁻³ , thickness: 0.4 μm) 12, n
Type carrier block layer (n-Al _0.60 Ga _0.40 As, donor concentration: 1 × 10 ¹⁸ cm ⁻³ , thickness: 0.014 μm)
13. Active layer (DQW: double quantum well, GaAs / Al
_0.31 Ga _0.69 As, no doping 14, p-type carrier block layer (p-Al _0.50 Ga _0.50 As, acceptor concentration: 1 × 10 ¹⁸ cm ⁻³ , thickness: 0.021 μm) 1
5, the first p-type cladding layer (p-Al _0.31 Ga _0.69 As,
Acceptor concentration: 1 × 10 ¹⁸ cm ⁻³ , thickness: 0.4 μ
m) 16, the second p-type cladding layer (p-Al _0.48 Ga _0.52
As, acceptor concentration: 1 × 10 ¹⁸ cm ⁻³ , thickness:
0.7 μm) 17, current confinement layer (n-GaAs, donor concentration: 1 × 10 ¹⁸ cm ⁻³ , thickness: 0.3 μm) 18, p
-Type contact layer (p-GaAs, acceptor concentration: 3)
× 10 ¹⁷ cm ^-3 to 1 × 10 ¹⁹ cm ^-3 , thickness: 2 μm) 1
9 are each formed by MOCVD.

Here, the difference from the first embodiment is that, as shown in FIG. 5B, the carrier block layer 1
3 and 15, the first cladding layers 12 and 16 and the second cladding layers 11 and 17 are all doped at a high concentration of 1 × 10 ¹⁸ cm ⁻³ .

Comparative Example 2 FIG. 6A is a sectional view showing the structure of Comparative Example 2, and FIG. 6B is a distribution diagram of the doping concentration corresponding to each layer. In this semiconductor laser device, a second n-type clad layer (n-Al _0.48 Ga _0.52 As, donor concentration: 3 × 10 ¹⁷ cm ⁻³ , thickness: 0.7 μm) is sequentially formed on the semiconductor substrate (n-GaAs) 20. 11, first n-type cladding layer (n-Al _0.31 Ga _0.69 As, donor concentration: 3 × 10 ¹⁷ cm ⁻³ , thickness: 0.4 μm) 12, n
Type carrier block layer (n-Al _0.60 Ga _0.40 As, donor concentration: 1 × 10 ¹⁸ cm ⁻³ , thickness: 0.014 μm)
13. Active layer (DQW: double quantum well, GaAs / Al
_0.31 Ga _0.69 As, no doping 14, p-type carrier block layer (p-Al _0.50 Ga _0.50 As, acceptor concentration: 1 × 10 ¹⁸ cm ⁻³ , thickness: 0.021 μm) 1
5, the first p-type cladding layer (p-Al _0.31 Ga _0.69 As,
Acceptor concentration: 3 × 10 ¹⁷ cm ⁻³ , thickness: 0.4 μ
m) 16, the second p-type cladding layer (p-Al _0.43 Ga _0.57
As, acceptor concentration: 3 × 10 ¹⁷ cm ⁻³ , thickness:
0.7 μm) 17, current confinement layer (n-GaAs, donor concentration: 1 × 10 ¹⁸ cm ⁻³ , thickness: 0.3 μm) 18, p
-Type contact layer (p-GaAs, acceptor concentration: 3)
19 × 10 ¹⁷ cm ⁻³ , thickness: 2 μm) 19 is formed by MOCVD.

Here, the difference from the first embodiment is that, as shown in FIG. 6B, the carrier block layer 1
3 and 15 are doped at a high concentration of 1 × 10 ¹⁸ cm ⁻³ , and the first cladding layers 12 and 16 and the second cladding layer 1 are doped.
1 and ¹⁷ are doped at a low concentration of 3 × 10 ¹⁷ cm ⁻³ .

Comparative Example 3 The structure of Comparative Example 3 is the same as that of Comparative Example 1 of FIG.
The difference is that (zinc) is used.

Comparative Example 4 The structure of Comparative Example 4 is the same as that of Comparative Example 2 of FIG.
(Zinc) The difference is that it is used. Example 1
In order to compare Comparative Examples 1 to 4 with the characteristic temperature of the element, the result of measuring the internal loss, and the value obtained by simulating the electrical resistance from the n-type second cladding layer excluding the active layer to the p-type cladding layer are shown below ( It is shown in Table 1). The semiconductor laser element has the same cavity length of 700 μm, current injection stripe width of 50 μm, and no optical coating.

[0046]

[Table 1]

As a result, it was confirmed that the characteristic temperature showing the temperature dependence of the oscillation threshold in Example 1 was improved to 140K as compared with Comparative Examples 3 and 4. This is because the carrier block layer can be maintained at a desired concentration by using carbon, which has a significantly lower diffusivity than zinc, as a dopant, and therefore carriers are more reliably confined in the active layer than in the case of zinc. It is thought that this was possible.

Further, it can be seen that Example 1 has substantially the same characteristic temperature as Comparative Example 1, but the internal loss is greatly improved to 1/5. It is considered that this is because the doping concentration of the first cladding layer becomes low and the free carrier absorption decreases.

In addition, the first embodiment has a second comparison with the second comparison.
Since the doping concentration of the clad layer is high, the electric conductivity of that portion is improved and the electric resistance can be reduced.

As described above, the characteristic temperature can be improved by making the carrier block layer highly doped, and the optical internal loss can be improved by making the first cladding layer lightly doped, and the second cladding layer can be made high. The doping can improve the electrical resistance of the device.

In the above description, an example in which the AlGaAs semiconductor is used as the material of the semiconductor laser device is shown, but the present invention can be applied as long as carbon or magnesium is a material that functions as a p-type dopant.

[0052]

As described above, according to the present invention, n
The doping amount of the n-type and p-type carrier block layers is n
Since the modulation doping is performed so that the concentration of the p-type and p-type clad layers is higher than that of the first clad layer, the internal loss can be reduced while maintaining the carrier block function.

Further, since the doping amount of the second clad layer of the n-type and p-type clad layers is modulated so as to be higher than that of the first clad layer, the electric resistance of the entire device is reduced. Therefore, self-heating can be reduced.

Since optical damage at the exit end face can be suppressed, higher output can be achieved in combination with the above effect.

Furthermore, by using carbon or magnesium as the p-type dopant, a sufficient doping concentration can be realized even in a thin layer. Therefore, carrier confinement in the active layer is surely performed by the carrier block layer, which contributes to improvement of the characteristic temperature.

Thus, in the semiconductor laser device having the complete separation / confinement structure, higher efficiency and higher output can be achieved.

[Brief description of drawings]

FIG. 1 (a) is a graph showing a forbidden band width of each layer in a completely separated confinement structure, and FIG. 1 (b) is a graph showing a guided mode when a normalized frequency V = π.

FIG. 2 is a graph showing a change in optical propagation factor of an optical waveguide layer with respect to a normalized frequency V in a slab waveguide structure.

FIG. 3 is a graph showing acceptor levels of various p-type dopants in AlGaAs.

FIG. 4A is a cross-sectional view showing the configuration of the first embodiment of the present invention, and FIG. 4B is a distribution diagram of the doping concentration corresponding to each layer.

5A is a cross-sectional view showing the structure of Comparative Example 1, and FIG. 5B is a distribution diagram of doping concentration corresponding to each layer.

6 (a) is a cross-sectional view showing the structure of Comparative Example 2, and FIG. 6 (b) is a distribution diagram of the doping concentration corresponding to each layer.

7A is a cross-sectional view showing an example of a conventional semiconductor laser device, FIG. 7B is a distribution diagram of a forbidden band width corresponding to each layer, and FIG. 7C is corresponding to each layer. It is the distribution map of the refractive index which was done.

[Explanation of symbols]

 11 second n-type clad layer 12 first n-type clad layer 13 n-type carrier block layer 14 active layer 15 p-type carrier block layer 16 first p-type clad layer 17 second p-type clad layer 18 current confinement layer 19 p-type contact layer 20 semiconductor Substrate 21,22 Ohmic electrode

Claims (5)

[Claims] 1. An n-type carrier block having n-type and p-type clad layers provided on both sides of an active layer and having a forbidden band width equal to or greater than the forbidden band widths of the active layer and the both clad layers adjacent to the active layer. In a semiconductor laser having a p-type carrier block layer and a p-type carrier block layer, the n-type and p-type clad layers each include a first clad layer and a second clad layer in the order of being closer to the active layer. With the oscillation wavelength, the maximum refractive index of the active layer, the carrier block layer and the first cladding layer is N1,
When the refractive index of the second cladding layer is N2, the effective thickness between the second cladding layers is d1, and the normalized frequency V is defined as V = (π · d1 / λ) · (N1 ² −N2 ² ) ^0.5 , V> π / 3 holds, and the doping amounts of the n-type and p-type carrier block layers are
The doping concentration of the second cladding layers of the n-type and p-type cladding layers is higher than that of the first cladding layers of the n-type and p-type cladding layers. A semiconductor laser device characterized by being applied. 2. The doping amount of the n-type and p-type carrier block layers is 1 × 10 ¹⁸ cm ⁻³ or more, and the doping amount of the first cladding layers of the n-type and p-type cladding layers is 3 × 10.
^The modulation doping is performed so that the doping amount of the second cladding layers of the n-type and p-type cladding layers is ¹⁷ cm ^-3 or less and 1 × 10 ¹⁸ cm ^-3 or more. The described semiconductor laser device. 3. The semiconductor laser device according to claim 1, wherein the dopant of the p-type carrier block layer is carbon or magnesium. 4. The semiconductor laser device according to claim 1, wherein the carrier block layer and the first and second cladding layers are made of a III-V group compound semiconductor. 5. The semiconductor laser device according to claim 4, wherein the carrier block layer and the first and second cladding layers are made of an AlGaAs compound semiconductor.