JP2000091702A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize high output and high temperature in operational temperature in a buried semiconductor laser. SOLUTION: This semiconductor laser contains n-type clad layers 21 and 22 formed like a mesa, an active layer 23 formed like a stripe thereon, first buried layers 27 and 29 which are formed on both sides of the n-type clad layers 21 and 22 and are made of InP containing a p-type impurities, a second buried layer 28 which is formed in the first buried layers 27 and 29 and is made of AlaInbGacAsdPe (0<=a, b, c, d, e<=1) mixed crystal semiconductor containing a p-type impurities of higher concentration than that of the first buried layers 27 and 29, an n-type current block layer 30 which is on the side of the active layer 23 and is formed on the second buried layer 28, and p-type clad layers 24 and 32 formed on the n-type current block layer 30 and active layer 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a semiconductor laser. In recent years, the development of optical communication technology based on semiconductor lasers and optical fibers has been remarkable, and optical fibers have almost replaced electric cables in trunk-line communication paths. In the future, with the increase in the amount of information communication, it is required to establish a technology for producing a large number of semiconductor laser modules at a lower cost. In order to reduce the price of the semiconductor laser module, a semiconductor laser having good temperature characteristics, high output, and requiring no cooling device is required.

[0002]

2. Description of the Related Art As a typical example of a buried type semiconductor laser, an FBH (Flat Buried Heterostructure) structure and an SI
PBH (Semi-Insulating layer Planar Buried Hetero
structure) will be described. The semiconductor laser having the FBH structure has, for example, a cross-sectional structure shown in FIG.

In FIG. 1, an InGaAsP multiple quantum well (MQ) is formed on a mesa 1a formed on an n-InP substrate 1.
W) A layer 2 and a first p-InP cladding layer 3 are formed. Further, on both sides of a layer extending from the mesa 1a to the first p-InP cladding layer 3, a p-InP buried layer 4 and an n-InP The buried layer 5 is formed in order. Further, the first p-InP cladding layer 3 and the n-InP
The buried layer 5 is covered with a second p-InP cladding layer 6, and a p-side electrode 8 is formed on the second p-InP cladding layer 6 via a p-InGaAsP contact layer 7. . An n-side electrode 9 is formed on the lower surface of the n-InP substrate 1.

A semiconductor laser having the SIPBH structure has, for example, a sectional structure as shown in FIG. 2, and in FIG. 2, the same reference numerals as those in FIG. 1 denote the same elements. That SIPBH
The semiconductor laser having the structure has a structure in which the p-InP buried layer 4 is replaced with an Fe-doped high-resistance InP buried layer 4a, and the other structure is the same as the FBH structure.

A general manufacturing process of such a semiconductor laser is as follows. That is, InGaAsP is formed on the n-InP substrate 1 by the metal organic chemical vapor deposition (MOVPE) method.
After forming the MQW layer 2 and the first p-InP cladding layer 3 in this order, a stripe-shaped mask (not shown) made of SiO ₂ is formed on the first p-InP cladding layer 3. Then,
A mesa stripe 1a is formed by sequentially etching from the first p-InP cladding layer 3 existing in a region not covered by the mask to the upper portion of the n-InP substrate 1. After this, the p-InP is placed on the n-InP substrate 1 in the etched portions on both sides of the mask.
A P buried layer 4 and an n-InP buried layer 5 are grown by MOVPE. After removing the mask, a second p-InP cladding layer 6 and a p-InGaAsP contact layer 7 are formed by MOVPE. Thereafter, a p-side electrode 8 is formed on the p-InGaAsP contact layer 7, and an n-side electrode 9 is formed below the n-InP substrate 1.

[0006]

In a semiconductor laser, holes are supplied from a p-side electrode 8 and electrons are supplied from an n-side electrode 9, and holes and electrons are generated and recombined in the active layer 2. When there is a leakage current path bypassing the active layer 2, the current flowing therethrough becomes an ineffective component that does not contribute to light emission, and as a whole, the threshold current required for laser oscillation increases, and the light emission efficiency decreases. Become.

In the FBH semiconductor laser shown in FIG. 1, the p-InP cladding layer 6, the p-InP buried layer 4, and the n-type InP
A leakage current path i ₁ of the path of the substrate 1, and the leakage current path i ₂ of the p-InP cladding layer 6 and the n-InP buried layer 5 and the p-InP buried layer 4 and the n-InP substrate 1 of path Exists. Among them, low-current injection region in the vicinity of the threshold current is a major leak current path is the leakage current path _1, a current path i ₂ leakage current limits the output at high bias or when high temperature leakage. Higher output of the semiconductor laser and for the high temperature of the operating temperature is necessary to reduce the leakage current through the leakage current path i _2.

In order to reduce the leakage current flowing through the leakage current path i ₂ , it is necessary to increase the turn-on voltage of the npnp thyristor structure as viewed from the n-InP substrate 1 side. In order to improve the turn-on voltage, the n-InP substrate 1
In order to suppress the injection of electrons into the n-InP buried layer 5 via the P buried layer 4, it is necessary to increase the p-type impurity concentration of the p-InP buried layer 4 and increase its thickness. It is valid.

However, in the conventional semiconductor laser, Zn,
Doping of p-type impurities into InP using Cd is limited to at most about 2.0 × 10 ^{18 to} 3.0 × 10 ¹⁸ atoms / cm ³ , and it is impossible to further increase the impurity concentration.
In addition, the increase in the thickness of the p-InP buried layer 4 is not realistic because the manufacturing process of the semiconductor laser becomes extremely difficult. On the other hand, according to the SIPBH structure laser, there is an advantage that the capacity of the element can be reduced and high-speed modulation is advantageous without forming an npnp structure by the high-resistance InP buried layer 4a.

However, in the SIPBH structure laser,
The maximum doping concentration of iron (Fe), which is a deep acceptor impurity doped to increase the resistance of the buried layer 4a, is at most 1.0 × 10 ¹⁷ at on the (100) plane.
oms / cm ^3, which is inferior to the FBH laser in terms of the ability to suppress the injection of electrons from the InP substrate 1 into the n-InP buried layer 5, and has high output power and poor operating performance at high temperatures. SUMMARY OF THE INVENTION It is an object of the present invention to provide a semiconductor laser having a new structure of a buried layer, and to provide a semiconductor laser capable of achieving high output and high operating temperature.

[0011]

Means for Solving the Problems (1) The above-mentioned problems are:
As illustrated in FIGS. 5 and 8, an n-type formed in a mesa shape
Cladding layers 21 and 22;
2, a stripe-shaped active layer 23 formed on
Formed on both sides of the n-type cladding layers 21 and 22 and
First embedded layers 27 and 29 made of InP containing pure substance
(27a, 29a) and the first buried layers 27, 29 (2
7a, 29a) and the first buried layer 2
7,29 (27a, 29a) higher concentration of p-type impurity
Al containing material_aIn _bGa_cAs_dP_e(0 ≦ a, b, c, d,
e ≦ 1) second buried layer 28 (2
8a) and the second buried layer on the side of the active layer 23
N-type current blocking layer formed on layer 28 (28a)
30, the n-type current blocking layer 30 and the active layer 2
3 and p-type cladding layers 24 and 32 formed on
The problem is solved by a semiconductor laser characterized by the following.

In the above-described semiconductor laser, the second
The buried layer 28 (28a) is the mesa-shaped n-type clad layer 2
It is characterized in that it is in contact with the sides 1 and 22. In the semiconductor laser described above, the second buried layer 28 (28
The concentration of the p-type impurity contained in a) is 3.0 × 10
It is characterized by being higher than ¹⁸ atoms / cm ³ . In the semiconductor laser described above, the band gap of the _{Al a In b Ga c As d} P e mixed crystal semiconductor second constituting buried layer 28 (28a) is characterized by a band gap than InP is small.

In the above-described semiconductor laser, the p-type impurity is a group II element or carbon. (2) As shown in FIGS. 6 and 9,
N-type cladding layers 21 and 22 formed in a mesa shape, stripe-shaped active layer 23 formed on n-type cladding layers 21 and 22, and formed on both sides of n-type cladding layers 21 and 22. Buried layers 37, 39 (37a, 39) made of InP and containing deep acceptor impurities.
a) and the first buried layers 37, 39 (37a, 39a)
Al _a formed in and includes a p-type impurity or deep acceptor impurity of _{In b Ga c As d P e} (0 ≦ a, b, c,
d, e ≦ 1), a second buried layer 28 (28a) made of a mixed crystal semiconductor or InP containing a p-type impurity, and the second buried layer 28 ( 28a) and an n-type current blocking layer 30 formed on the n-type current blocking layer 30 and the active layer 23.
The problem is solved by a semiconductor laser having the mold cladding layers 24 and 31.

In the above-described semiconductor laser, the second
The buried layer 28 (28a) is formed of the n-type clad layers 21 and 22.
Is characterized by being in contact with the side of In the semiconductor laser described above, the p-type impurity or the deep acceptor impurity contained in the second buried layer 28 (28a) is the deep acceptor contained in the first buried layers 37 and 39 (37a, 39a). It is characterized by a higher concentration than impurities.

In the above-mentioned semiconductor laser, the second
The p-type impurity contained in the buried layer is 1.0 × 10 ¹⁷ atom
It is characterized by having a concentration higher than s / cm ³ . In the above-described semiconductor laser, the mixed crystal semiconductor is InGaAs, InAl.
It is characterized by being As. In the above-described semiconductor laser, the second buried layer 28 (28a) and the first buried layer 28 are arranged in the vertical direction of the second buried layer 28 (28a).
Between (28a), an undoped InP layer or undoped
Al _a In _b Ga _c As _{d Pe} (0 ≦ a, b, c, d, e ≦ 1)
It is characterized in that a mixed crystal semiconductor is inserted.

In the above-described semiconductor laser, the second
The mixed crystal semiconductor forming the buried layer contains a deep acceptor impurity in addition to the p-type impurity. In the above-described semiconductor laser, the p-type impurity is a group II element or carbon.

The figures and reference numerals described above are provided to facilitate understanding of the present invention, and the present invention is not limited thereto. Next, the operation of the present invention will be described. According to the present invention, in the first buried layer made of InP into which a p-type impurity or a deep acceptor impurity is introduced,
A second buried layer made of a mixed crystal semiconductor capable of introducing a p-type impurity or a deep acceptor impurity at a higher concentration than nP is formed.

Therefore, it is possible to reduce the leakage current flowing between the n-type substrate and the current block layer, thereby increasing the output of the semiconductor laser and increasing the operating temperature. In addition, the second buried layer made of the mixed crystal semiconductor is replaced with the first buried layer made of InP.
Since the second buried layer is not formed to be in contact with the n-type substrate by being formed in the buried layer, a mixed crystal semiconductor having a band gap smaller than that of InP is formed in the second buried layer. Even if it is used as a constituent material, the built-in potential of the substrate and the buried layer does not lower than before.

In order to increase the resistance by introducing a deep acceptor impurity into the first buried layer, an undoped layer may be introduced between the first buried layer and the second buried layer, or
When a deep acceptor impurity is introduced into the buried layer in addition to a group II element (for example, Zn or Cd), rapid diffusion of the group II element introduced into the second buried layer into the first buried layer is prevented.

[0020]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. (First Embodiment) FIGS. 3 and 4 are cross-sectional views showing steps of manufacturing a semiconductor laser having an FBH structure according to a first embodiment of the present invention.

First, as shown in FIG.
According to the method, an n-type (n-)
InP buffer layer 22, MQ made of undoped InGaAsP
W (multi-quantum well) active layer 23, p-type (p-) InP
The cladding layer 24 is formed in order. Those layers are MOVP
It grows by E method. InP is grown using trimethylindium (TMIn) and phosphine (PH ₃ ) as source gases, and InGaAsP is grown using TMIn, PH ₃ , arsine (AsH ₃ ), and triethylgallium (TEGa) as source gases. You. Further, dimethyl zinc (DMZn) is used as a p-type dopant, and silane (SiH ₄ ) is used as an n-type dopant.

The well layer forming the MQW active layer 23 is made of InGaAsP having a composition corresponding to an emission wavelength of 1.30 μm, and the barrier layer is formed of InGaP having a composition corresponding to an emission wavelength of 1.10.
Consists of AsP. The impurity concentration of the n-InP buffer layer 22 is 5 × 10 ¹⁷ atoms / cm ³ , and the impurity concentration of the p-InP cladding layer 24 is 5 × 10 ¹⁷ atoms / cm ³ .

The n-InP under the active layer 23 functions as an n-type cladding layer. After completing the first film growth as described above, a SiO ₂ film is formed on the p-InP clad layer 24 by C
It is formed to a thickness of 0.3 μm by the VD method. And
As shown in FIG. 3B, the SiO ₂ film is patterned into a stripe shape having a width of 2.0 μm by photolithography and used as a mask 25.

Next, as shown in FIG.
The mesa portion 26 is formed under the mask 25 by etching the portion not covered by the p-InP cladding layer 24 to the upper portion of the n-InP substrate 21 to a depth of about 3.0 μm. The etching is performed by reactive ion etching (RIE: Reac
tive Ion Etching) and uses ethane-based gas.

Thereafter, the process proceeds to the second film growth step.
First, as shown in FIG. 3D, etching of the InP substrate 1 is performed.
P-InP first buried layer 27 on the surface and the side surface of the mesa portion 26.
It is grown to a thickness of 0.5 μm by MOVPE. p-In
P The growth condition of the first buried layer 27 is as follows.
n, PH_ThreeAnd DMZn as a gas for p-type dopant
And a growth temperature of 600 ° C. DMZn in this case
The gas flow rate is such that the p-type impurity concentration of the InP first buried layer 27 is about
1.0 × 10 ¹⁸ atoms / cm^ThreeIs set so that
You.

Subsequently, as shown in FIG. 4A, p ⁺ -InG is formed on a surface of the p-InP first buried layer 27 substantially parallel to the substrate surface.
aAs second buried layer 28 is formed to a thickness of 0.5 μm by MOVPE.
Formed to a thickness of The growth conditions for the p ⁺ -InGaAs second buried layer 28 are as follows: TMIn, TEGa, and AsH ₃ are used as source gases.
DMZn is used as the gas for the p-type dopant, and the growth temperature is 550 ° C. In this case, the flow rate of the DMZn gas is such that the p-type impurity concentration of the second embedded layer 28 is about 2.0 × 10 ¹⁹ atom.
The amount is set to be as high as s / cm ³ .

Further, as shown in FIG.
The p-InP third layer is formed on the InGaAs second buried layer 28 by the E method.
The buried layer 29 and the n-InP current blocking layer 30 are formed to a thickness of 1.5 μm and 0.5 μm, respectively. p-
The growth conditions for the InP third buried layer 29 are as follows.
In, PH ₃ is used, DMZn is used as a dopant gas, and the growth temperature is 600 ° C. In this case, the gas of DMZn has a p-type impurity concentration of the InP third buried layer 29 of about 1.0.
The flow rate is set so as to be × 10 ¹⁸ atoms / cm ³ .

The growth conditions for the n-InP current blocking layer 30 are as follows: TMIn and PH ₃ are used as source gases, silane (SiH ₄ ) is used as a dopant gas, and the growth temperature is 600 ° C. In this case, the SiH ₄ gas is n-InP
The current blocking layer 30 has an n-type impurity concentration of about 2.0 × 10
^The flow rate is set so as to be ¹⁸ atoms / cm ³ . Note that p-
In order to planarize the InP buried layer 29 and the n-current blocking layer 30, methyl chloride (CH ₃ C
l) is added.

Next, after removing the mask used to prevent the growth of the compound semiconductor with hydrofluoric acid, the process proceeds to the third film growth step. First, as shown in FIG. 4C, a p-InP cladding layer 31 having a p-type impurity concentration of 1.0 × 10 ¹⁸ atoms / cm ³ and a film thickness of 1.0 μm and a p-type impurity concentration of 2.0 × 10 ¹⁸ atoms / cm ^3. 10 ¹⁸ atoms / cm ³ with a film thickness of 0.2 μm
p-InGaAsP intermediate layer 32, p-type impurity concentration 2.0 × 10 ¹⁹
A p-InGaAs contact layer 33 of atoms / cm ³ and a thickness of 0.5 μm is sequentially formed. In this case, InGaAsP constituting the intermediate layer 32 has a wavelength corresponding to the band gap of 1.
The composition is 3 μm.

The growth conditions for the p-InP cladding layer 31 are such that TMIn and PH ₃ are used as source gases and DMZn is used as a p-type dopant gas. The growth conditions for the p-InGaAsP intermediate layer 32 are TMIn, PH ₃ , AsH ₃ , TE
Ga is used, and DMZn is used as a p-type dopant gas. Further, the growth conditions of the p-InGaAs contact layer 33 are as follows:
TMIn, AsH ₃ , and TEGa are used as source gases, and DMZn is used as a p-type dopant gas.

After completing the third film growth step as described above, a p-side electrode 34 made of a Ti / Pt / Au film is formed on the contact layer 33 as shown in FIG. later,
An n-side electrode 35 made of AuGe / Au is formed on the lower surface of the InP substrate 21. As shown in FIG. 5, the semiconductor laser having the FBH structure formed by the above steps has a p-type impurity concentration of
The buried layer 28 of InGaAs, which can be made higher than InP, is p-In
It is formed in the P buried layers 27 and 29, and has an impurity concentration higher than 3.0 × 10 ¹⁸ atoms / cm ³ .

Therefore, electrons injected from the n-InP substrate 21 are prevented from being injected into the n-InP buried layer 30 by the InGaAs buried layer 28. As a result, the leakage current is reduced through the path i ₂ shown in FIG. 5 turn-on voltage of the thyristor structure of npnp formed on both sides of the mesa portion 26 becomes high,
This prevents an increase in leakage current when a high bias voltage is applied or under high temperatures.

By the way, when the buried layer 28 is formed of a material having a composition whose band gap is smaller than that of InP in such a mixed crystal semiconductor layer, the n-type InP
Since the built-in potential of the pn junction with the substrate 21 is reduced, the current flowing through the pn junction increases, and as a result, the total leakage current may increase.

Therefore, if the second buried layer 28 is arranged at a position not in contact with the n-InP layer, that is, at a position above the p-InP first buried layer 27, its built-in potential may be reduced. Absent. With respect to the characteristics of the semiconductor laser having the above-described structure, the maximum output at room temperature in the state where the element length is 300 μm and both end faces are cleaved is 25 to 35 mW of the conventional element (FIG. 1).
It could be increased by 5 mW to mW. In addition, the maximum oscillation temperature under the same conditions was increased from 100 ° C. of the conventional device (FIG. 1) to 1 °.
The temperature was increased by 10 ° C to 10 ° C. (Second Embodiment) In the first embodiment described above, F
Although the semiconductor laser having the BH structure has been described, an SIPBH structure as shown in FIG. 6 may be used. In the semiconductor laser having the SIPBH structure, as shown in FIG. 5, a deep acceptor impurity (for example, iron) is doped instead of p-InP forming the first buried layer 27 and the third buried layer 29 of the FBH structure semiconductor laser. High-resistance InP may be used, and an embodiment thereof is shown in FIG.

In FIG. 6, a high resistance In doped with iron is shown.
The first buried layer 37 is formed by MOCVD instead of the first buried layer 27 shown in FIG.
The same source gas as that of the p-InP first burying layer 27 is used, and ferrocene (Fe (C ₅ H ₅ ) ₂ ) is used as an iron dopant. Further, on the high resistance InP first buried layer 37, FIG.
After forming the p ⁺ -InGaAs second buried layer 28 in the same manner as (a), instead of the third buried layer 29 shown in FIG.
A high resistance InP third buried layer 29 doped with iron is formed by the VD method. During the growth of the high resistance InP third buried layer 29, the same source gas as that of the p-InP third buried layer 29 is used, and Fe (C ₅ H ₅ ) ₂ is used as an iron dopant.

SIPBH structure having the above structure
High impurity concentration in the buried layer
P⁺-InGaAs second buried layer 28 is provided,
The leakage current from the block layer 30 to the InP substrate 21 is reduced.
You. In this embodiment, the constituent materials of the second embedded layer 28
InGaAs other than InGaAs containing p-type impurities
InP may be included. In this case, the second impurity layer
The impurity concentration of the first buried layer 37 and the third buried layer 3
Since the impurity concentration can be made higher than that of FIG.
Path i than the conventional semiconductor laser shown in FIG. _TwoLeakage current
The flow can be reduced. (Third Embodiment) In the first embodiment, the p-InP
(1) A buried layer 27 is also formed on the side surface of the mesa portion 26 to form a sectional shape.
Is substantially L-shaped, the mesa portion 26 and the second buried layer
28, there is a first buried layer 27 having a low impurity concentration.
You.

In order to extend the second buried layer 28 to the side surface of the mesa portion 26, a process as shown in FIG. That is, after the mesa portion 26 is formed, DMIn, PH ₃ , DMZn
In addition, when p-InP is grown using CH ₃ Cl, as shown in FIG. 7A, the p-InP first buried layer 27a hardly grows on the side surface of the mesa portion 26 and n- It is formed on the InP substrate 21.

Therefore, the p ⁺ -In formed on it
When the GaAs second buried layer 28a is grown under the same conditions as the p ⁺ -InGaAs layer 28 of the first embodiment, as shown in FIG.
The p ⁺ -InGaAs second buried layer 28a comes into contact with the buffer layer 22 or the n-InP substrate 21 in the mesa section 26. Subsequently, as shown in FIG. 7 (c), after forming the p ⁺ -InGaAs second buried layer 28a, the p-InP third buried layer 2 is formed thereon.
9a is formed. The growth condition is the p-In of the first embodiment.
P The conditions are the same as the growth conditions for the third buried layer 29.

Thereafter, when the n-InP current blocking layer 30 and the like are formed on the p-InP third buried layer 29 in the same manner as in the first embodiment, a semiconductor laser having an FBH structure as shown in FIG. Complete. In this semiconductor laser, since the p ⁺ -InGaAs _second buried layer 28a having a high impurity concentration extends to the n-InP layer, the leakage current of the path i2 passing through the npnp junction is further reduced. (Fourth Embodiment) In the above third embodiment, F
The semiconductor laser having the BH structure has been described, but the semiconductor laser may have a SIPBH structure as shown in FIG.

The semiconductor laser having the SIPBH structure is shown in FIG.
8, the first buried layer 2 of the semiconductor laser having the FBH structure
7a and p-InP forming the third buried layer 29a instead of p-InP
It uses iron-doped InP. The iron shown in FIG.
The buried high resistance InP first buried layer 37a is shown in FIG.
Instead of the first buried layer 27a
The same source as the p-InP first buried layer 27a.
Source gas and Fe (C _FiveH_Five)
_TwoUse

As shown in FIG. 7B, the p ⁺ -InGaAs second
After forming the buried layer 28a, an iron-doped high-resistance InP third buried layer 39a is formed by MOCVD instead of the third buried layer 29a shown in FIG. 7C. Its high resistance In
During the growth of the P third buried layer 39a, the p-InP third buried layer 2
The same source gas as in 9a is used, and Fe (C ₅ H ₅ ) ₂ is used as an iron dopant.

The semiconductor laser of the SIPBH structure having the above-described structure also has a high impurity concentration of p ⁺ -InGaA.
s Since the second buried layer 28a is in contact with the n-InP of the mesa portion 26, the leakage current passing through the buried layer can be further reduced as compared with the third embodiment. In this embodiment, the second buried layer 28a may be made of InP containing p-type impurities in addition to InGaAs containing p-type impurities. In this case, the impurity concentration of the second impurity layer 28a is
It is possible to increase the impurity concentration than 7a and the third burying layer 39a, can reduce the leakage current of the path i ₂ through the buried region than a semiconductor laser of the prior art structure shown in FIG. Was used InGaAs in the second buried layer of the embodiment described (Other Embodiments) _{Other, Al a In b Ga c As} d P
_A mixed crystal semiconductor composed of _e (0 ≦ a, b, c, d, e ≦ 1) may be used. Carbon (C) may be used as the p-type impurity of such a mixed crystal semiconductor, whereby the impurity concentration can be increased. For example, InGaAs can be doped with about 5 × 10 ¹⁹ atoms / cm ³ of carbon.

In particular, when InAlAs is used as the mixed crystal semiconductor constituting the second buried layer, the band gap can be made larger than in the case where InP is employed, so that it is difficult for electrons to move from the substrate to the current blocking layer. Furthermore, in addition to the p-type impurity concentration of the second buried layer in the second and fourth embodiments, iron (deep acceptor impurity) may be doped, and the mixed crystal semiconductor layer contains more iron than InP. can be contained, it is possible to reduce the leakage current of the path i _2.

In the first to fourth embodiments, Zn is used as the p-type impurity, but cadmium (Cd) or another group II element may be used. Note that the p-type impurity concentration of the second buried layer in the second and fourth embodiments may be lower than the p-type impurity concentration of the second buried layer in the first and third embodiments. Preferably, the p-type impurity concentration of the second buried layer in the second and fourth embodiments is higher than the impurity concentration of at least the first buried layer and the third buried layer having high resistance, that is, 1 × 10 ¹⁷ If it is higher than atoms / cm ³ , the leakage current of the path i ₂ passing through the buried region can be made smaller than that of the conventional semiconductor laser shown in FIG.

[0045]

As described above, according to the present invention, InP doped with a p-type impurity or a deep acceptor impurity is used.
Since the second buried layer made of a mixed crystal semiconductor capable of introducing a p-type impurity or a deep acceptor impurity at a higher concentration than InP is formed in the first buried layer, the n-type substrate and the current block are formed. It is possible to increase the output of the semiconductor laser and increase the operating temperature by reducing the leakage current flowing between the layers.

In addition, the second buried layer made of a mixed crystal semiconductor is
By forming the second buried layer in the first buried layer made of InP, the second buried layer does not have a structure in contact with the n-type substrate. 2 Even if it is used as a constituent material of the buried layer, the built-in potential of the substrate and the buried layer does not lower than before.

According to the present invention, when a deep acceptor impurity is introduced into the first buried layer to increase the resistance, an undoped layer is introduced between the first buried layer and the second buried layer. Alternatively, since a deep acceptor impurity is introduced into the second buried layer in addition to a group II element (for example, Zn or Cd),
Rapid diffusion of the group II element introduced into the buried layer into the first buried layer can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a conventional semiconductor laser having an FBH structure.

FIG. 2 is a cross-sectional view showing a conventional semiconductor laser having a SIPBH structure.

FIG. 3 is a cross-sectional view (No. 1) showing a step of manufacturing the semiconductor laser having the FBH structure according to the first embodiment of the present invention.

FIG. 4 is a sectional view (part 2) showing a step of manufacturing the semiconductor laser having the FBH structure according to the first embodiment of the present invention;

FIG. 5 is a sectional view showing a semiconductor laser having an FBH structure according to the first embodiment of the present invention.

FIG. 6 is a sectional view showing a semiconductor laser having a SIPBH structure according to a second embodiment of the present invention.

FIG. 7 is a cross-sectional view illustrating a main part of a manufacturing process of a semiconductor laser having an FBH structure according to a third embodiment of the present invention.

FIG. 8 is a sectional view of a semiconductor laser having an FBH structure according to a third embodiment of the present invention.

FIG. 9 is a sectional view of a semiconductor laser having a SIPBH structure according to a fourth embodiment of the present invention.

[Explanation of symbols]

21 ... n-InP substrate, 22 ... n-InP buffer layer, 23 ... In
GaAsP MQW active layer, 24 ... p-InP clad layer, 25 ...
Mask, 26 ... mesa portion, 27, 27a ... p-InP first buried layer, 28 ... p ⁺ -InGaAs second buried layer, 29, 29a ...
p-InP third buried layer, 30... n-InP current blocking layer, 31
... p-InP cladding layer, 32 ... p-InGaAsP intermediate layer, 33 ... p
-InGaAs contact layer, 34 ... p-side electrode, 35 ... n-side electrode, 37, 37a ... High-resistance InP first buried layer, 39,39
a: High resistance InP third buried layer.

Claims (10)

[Claims] 1. An n-type cladding layer formed in a mesa shape, a stripe-shaped active layer formed on the n-type cladding layer, and a p-type impurity formed on both sides of the n-type cladding layer. A first buried layer made of InP containing Si and Al _a In _b Ga _c As formed in the first buried layer and containing _a p-type impurity having a higher concentration than the first buried layer _d P
_e (0 ≦ a, b, c, d, e ≦ 1) a second buried layer composed of a mixed crystal semiconductor, and formed on the second buried layer at a side of the active layer. A semiconductor laser comprising: an n-type current blocking layer; and a p-type cladding layer formed on the n-type current blocking layer and the active layer. 2. The semiconductor laser according to claim 1, wherein said second buried layer is in contact with a side of said mesa-shaped n-type cladding layer. 3. The semiconductor laser according to claim 1, wherein the concentration of said p-type impurity contained in said second buried layer is higher than 3.0 × 10 ¹⁸ atoms / cm ³ . 4. The Al _a In _b Ga constituting the second buried layer.
_c As _d P band gap of the _e mixed crystal semiconductor, a semiconductor laser according to claim 1, wherein a band gap than InP is small. 5. An n-type clad layer formed in a mesa shape, a stripe-shaped active layer formed on the n-type clad layer, and a deep acceptor impurity formed on both sides of the n-type clad layer. _{Al a in b Ga c as d} P e (0 ≦ including but the first embedded layer composed of InP, which is contained, the p-type impurity or the deep acceptor impurity are formed in said first buried layer
a, b, c, d, e ≦ 1) a second buried layer made of a mixed crystal semiconductor or InP containing a p-type impurity, and a second buried layer on the side of the active layer. A semiconductor laser comprising: an n-type current blocking layer formed thereon; and a p-type cladding layer formed on the n-type current blocking layer and the active layer. 6. The semiconductor laser according to claim 5, wherein said second buried layer is in contact with a side of said n-type cladding layer. 7. The p-type impurity or the deep acceptor impurity contained in the second buried layer has a higher concentration than the deep acceptor impurity contained in the first buried layer. 5. The semiconductor laser according to 5. 8. The semiconductor laser according to claim 5, wherein said p-type impurity contained in said second buried layer has a concentration higher than 1.0 × 10 ¹⁷ atoms / cm ³ . 9. During the second buried layer and said first buried layer a vertical direction of the second buried layer is undoped InP layer or an undoped _{Al a In b Ga c As d} P e (0 ≦ a, b,
6. The semiconductor laser according to claim 5, wherein a mixed crystal semiconductor is inserted therein. 10. The semiconductor laser according to claim 5, wherein said mixed crystal semiconductor forming said second buried layer contains a deep acceptor impurity in addition to said p-type impurity.