JP3403915B2 - Semiconductor laser - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a long-wavelength semiconductor laser used for optical communication and the like, and more particularly to a high-wavelength semiconductor laser in which a side surface of a light emitting region is embedded with a semi-insulating semiconductor layer. The present invention relates to a resistance embedded semiconductor laser. 2. Description of the Related Art A long-wavelength semiconductor laser for optical communication and information processing has a structure in which a side surface of an active layer forming a light emitting region is processed into a mesa stripe shape and is embedded with a current confinement layer. Generally, the threshold current is reduced and the oscillation lateral mode is controlled. As such a buried type semiconductor laser, a pn buried structure in which a pn reverse junction is provided in a current confinement layer to perform current confinement, and a current confinement is performed by providing a semi-insulating semiconductor layer having high electric resistance in the current confinement layer. A high resistance embedded structure is well known. The former pn
Since the buried structure has a very good current blocking effect due to the pn junction, laser oscillation can be performed with high efficiency, and low threshold operation, high output operation and high temperature operation can be easily obtained. However, there is a problem that the parasitic capacitance of the pn junction current block layer is very large and is not suitable for high-speed modulation. On the other hand, in the latter high-resistance buried structure, although the parasitic capacitance of the buried layer is small and high-speed modulation is possible, there is a problem that the current blocking effect is not as strong as in the pn buried structure, and high-output operation and high-temperature operation are difficult. FIG. 6 shows a conventional example of a semiconductor laser having a high resistance buried structure (SUSUMU ASADA et.al, IEEE JOURNAL OF
QUANTUM ELECTRONICS, VOL25, NO.6 PP1362-1368, JUNE
1989). Reference numerals 601 to 607 in the figure denote n-type InP substrate (601) and non-doped InGaAs, respectively.
sP active layer (602), p-type InP cladding layer (60
3), non-doped InGaP barrier layer (604), Fe
Doped semi-insulating InP layer (605), p-side electrode (60
6), n-side electrode (607). Fe-doped semi-insulating InP has the effect of trapping electrons injected from the n-side in the deeper order formed in the forbidden band, and uses this to narrow the current. However, since the Fe-doped semi-insulating InP layer does not act as a trap for holes injected from the p-side, trapping occurs when holes are injected from the p-type cladding layer into the Fe-doped semi-insulating InP layer. The electrons are easily recombined with the electrons and a leakage current flows. This leakage current becomes particularly remarkable at the time of high current injection or high-temperature operation, and significantly lowers laser characteristics. Therefore, an InGaP barrier layer was introduced to prevent holes from being injected from the p-type cladding layer into the Fe-doped semi-insulating InP layer. InGaP is
If the band gap is larger than that of InP, for example, if the In composition is 0.5, the band discontinuity of the valence band with respect to InP is about 0.3 eV. Therefore, InGaP
The layer is composed of a Fe-doped semi-insulating I
It can be expected to function as a barrier layer that prevents holes from being injected into the nP layer. However, InGaP inserted between the p-type InP cladding layer and the Fe-doped semi-insulating InP buried layer has a larger band gap than InP and is expected to be effective as a barrier layer, but lattice mismatch with Inp is expected. There is a problem of being large. For example, In
InGaP having a composition of 0.5 has a sufficiently large band gap with respect to InP and a band discontinuity of a valence band of about 0.3 eV, but has a lattice constant of 3% as compared with InP.
Due to the above lattice mismatch, the thickness at which the crystal can be grown on the InP layer without generating misfit dislocations is 10 nm or less. In order to obtain a sufficient effect as a barrier layer, 20 n
m or more, a thickness of 10 nm or less
At present, a sufficient barrier effect cannot be obtained with a GaP layer. [0004] Further, if a larger InGaP having an In composition with a small lattice mismatch is used, a thicker InGaP layer can be grown, but a band gap difference from InP becomes small, so that a sufficient barrier effect cannot be obtained. . As described above, conventionally, in a semiconductor laser having a high resistance buried structure using a semi-insulating buried layer, holes are injected from the p-type cladding layer into the semi-insulating buried layer. There is a problem that the barrier layer inserted to prevent the barrier effect cannot obtain a sufficiently large barrier effect. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a high-resistance buried layer having a barrier layer having a sufficient effect capable of preventing hole injection into a semi-insulating buried layer. An object of the present invention is to provide a semiconductor laser having a structure. [0007] In order to solve the above problems, the present invention employs the following configuration. That is, the present invention is particularly directed to a semiconductor laser having a long-wavelength band high-resistance buried structure having an oscillation wavelength of 1 to 1.6 μm, wherein the barrier layer adjacent to the semi-insulating buried layer has a thickness of 50 nm or more. It is characterized by doing. this is,
As a barrier layer, a laser having a high resistance buried structure is realized by using a material having a band gap larger than that of the semi-insulating buried layer and the p-type clad layer and having sufficiently small lattice mismatch. Further, it is empirically found that the product of the thickness (nm) of the barrier layer and the height (eV) of the barrier is required to be 5 [nm · eV] or more in order to sufficiently exhibit the effect of the barrier layer. Therefore, if the thickness of the barrier layer is set to 50 nm or more, hole injection into the semi-insulating buried layer can be sufficiently prevented even when the height of the barrier is as small as about 0.1 eV. Here, preferred embodiments of the present invention include the following. (1) The semiconductor substrate is GaAs. (2) An active layer having an oscillation wavelength of 1 to 1.6 μm is formed of Ga
forming a semiconductor layer containing _{x In 1-x N y As} 1-y.
(0 <x ≦ 1,0 <y <1) (3) as the semi-insulating buried layer, a semiconductor containing at least Ga, for example, _{In u Ga 1-u As V} P 1-V mixed crystal used (0 ≦ u <1,0 <v ≦ 1) (4) a semiconductor containing at least Ga and InP as a barrier layer for preventing hole injection into the semi-insulating buried layer;
For example, the thickness is set to 50 nm or more using In _{m Gn} Al _1-mn P mixed crystal (0 <m ≦ 1, 0 <n ≦ 1, 0 <
m + n ≦ 1) In the high-resistance buried structure having the above configurations (1) to (4),
A semiconductor laser oscillating at a wavelength of 1 to 1.6 μm is formed on a GaAs substrate, and a band gap larger than the two layers between the semi-insulating buried layer and the cladding layer lattice-matched to the GaAs substrate is formed. A barrier layer lattice-matched (sufficiently small in lattice mismatch) can be inserted into the substrate. Therefore, the thickness of the barrier layer can be made sufficiently large, and the injection of holes into the semi-insulating buried layer can be more reliably prevented. Embodiments of the present invention will be described below in detail with reference to the drawings. (First Embodiment) FIG. 1 is a sectional view schematically showing an element structure of a semiconductor laser according to a first embodiment of the present invention. In the figure, 101 to 111 are n-type Ga
As substrate (101), n-type InGaAsP clad layer (102), non-doped GaAs light guide layer (10
3), undoped GaInNAs active layer (104), undoped GaAs light guide layer (105), p-type InGa
AsP cladding layer (106), p-type GaAs contact layer (107), non-doped InGaP barrier layer (10
8), Fe-doped InGaAsP semi-insulating buried layer (109), p-side electrode (110), n-side electrode (111)
It is. The outline of the manufacturing process of the semiconductor laser of FIG. 1 is as follows. First, an MOC is formed on an n-type GaAs substrate 101.
N-type InGaAs by VD method (metal organic chemical vapor deposition)
1.5 μm sP cladding layer 102, non-dove GaAs
0.1 μm, undoped GaIn
0.1 μm of NAs active layer (emission wavelength: 1.3 μm) 104
m, the undoped GaAs light guide layer 105 is 0.1 μm
m, p-type InInAsP cladding layer 106
Crystal growth of the m and p type GaAs contact layers 107 is performed in order of 0.2 μm. Next, etching is performed using the SiO ₂ film provided on the contact layer 107 as a mask to form a mesa stripe having a width of 1.5 μm and a depth of 4 μm. Next, the non-doped InGaP barrier layer 108 and the Fe-doped InGaAsP semi-insulating buried layer 109 are sequentially grown by MOCVD to a thickness of 0.2 μm and a thickness of 3.8 μm. Finally, a p-side electrode 110 and an n-side electrode 111 are formed, and cleaved at right angles to the stripe.
Is completed. Here, InGaAs
Both the sP layer and the InGaP layer are lattice-matched to the GaAs substrate, and have band gaps of about 1.6 eV and 1.
It was manufactured to be 9 eV. In the high-resistance buried semiconductor laser having the structure as shown in FIG. 1, a barrier layer having a band gap larger than the both and a sufficiently thick barrier layer is inserted between the semi-insulating buried layer and the p-type cladding layer. ing. Therefore, hole injection from the p-type cladding layer to the semi-insulating buried layer is completely suppressed. Therefore, the leakage current flowing through the buried layer during injection of a high current or high-temperature operation is very small, and a semiconductor laser having high output and excellent temperature characteristics can be obtained. In this embodiment, an n-type GaAs substrate is used as a semiconductor substrate. However, even when a p-type GaAs substrate is used, a similar structure can be realized by inverting the p-type layer and the n-type layer. It is. (Second Embodiment) FIG. 2 is a sectional view schematically showing an element structure of a semiconductor laser according to a second embodiment of the present invention. In the figure, reference numerals 201 to 212 denote an n-type GaAs substrate (201) and an n-type InGaAsP, respectively.
Cladding layer (202), undoped GaAs light guide layer (203), undoped GaInNAs active layer (20
4), non-doped GaAs light guide layer (205), p-type InGaAsP first cladding layer (206), Fe-doped InGaP semi-insulating buried layer (207), thickness 0.3
μm n-type InGaP barrier layer (208), p-type InG
An aAsP second cladding layer (209), a p-type GaAs contact layer (210), a p-side electrode (211), and an n-side electrode (212). In this embodiment, a so-called SI-PBH structure (Semiin
The present invention is applied to sulating-Planar Buried Heterostructure). (Third Embodiment) FIG. 3 shows a third embodiment of the present invention.
FIG. 4 is a cross-sectional view schematically showing an element structure of the semiconductor laser according to the embodiment. Reference numerals 301 to 313 in the figure denote n-type GaAs substrate (301) and n-type InGaAsP, respectively.
Cladding layer (302), undoped GaAs light guide layer (303), undoped GaInNAs active layer (30
4), non-doped GaAs light guide layer (305), p-type InGaAsP first cladding layer (306), Fe-doped InGaAsP semi-insulating buried layer (307), n-type I
nGaAsP intermediate layer (308), 0.3 μm thick n-type InGaP barrier layer (309), p-type InGaAsP second cladding layer (310), p-type GaAs contact layer (311), p-side electrode (312), n Side electrode (313)
It is. This embodiment is different from the second embodiment in that n-type In
Between the GaP barrier layer 309 and the Fe-doped InGaAsP semi-insulating buried layer 307, an n-type I
An nGaAsP intermediate layer 308 is added. This intermediate layer is effective for improving the reliability of the device. (Fourth Embodiment) FIG. 4 is a sectional view schematically showing an element structure of a semiconductor laser according to a fourth embodiment of the present invention. Reference numerals 401 to 413 in the figure denote n-type GaAs substrate (401) and n-type InGaAsP, respectively.
Cladding layer (402), non-doped GaAs light guide layer (403), non-doped GaInNAs active layer (40
4), undoped GaAs light guide layer (405), p-type InGaAsP first cladding layer (406), thickness 0.2
μm undoped InGaP barrier layer (407), Fe
Doped InGaAsP semi-insulating buried layer (408),
An n-type InGaP barrier layer (409) having a thickness of 0.3 μm,
p-type InGaAsP second cladding layer (410), p-type G
aAs contact layer (411), p-side electrode (412),
This is an n-side electrode (413). In this embodiment, in addition to the second embodiment, a non-doped InGaP barrier layer 407 is inserted. By adding this barrier layer, the Fe-doped InGaAsP semi-insulating buried layer and the p-type InGaP
The AsP cladding layer will be completely separated by the two InGaP barrier layers. Therefore, p-type InGa
Hole injection from the AsP cladding layer to the Fe-doped InGaAsP semi-insulating buried layer is further suppressed. (Fifth Embodiment) FIG. 5 is a sectional view schematically showing an element structure of a semiconductor laser according to a fifth embodiment of the present invention. In the figure, reference numerals 501 to 512 denote a p-type GaAs substrate (501) and a p-type InGaAsP, respectively.
Cladding layer (502), non-doped GaAs light guide layer (503), non-doped GaInNAs active layer (50
4), undoped GaAs light guide layer (505), n-type InGaAsP first cladding layer (506), thickness 0.2
μm undoped InGaP barrier layer (507), Fe
Doped InGaP semi-insulating buried layer (508), n-type InGaAsP second cladding layer (509), n-type GaAs
An s contact layer (510), an n-side electrode (512), and an n-side electrode (513). In this embodiment, p-type GaAs
The present invention is applied to a high resistance buried structure of an SI-PBH structure using a substrate. In this case, one In
The GaP barrier layer can separate the Fe-doped InGaAsP semi-insulating buried layer from the p-type InGaAsP cladding layer. In the first to fifth embodiments, the cladding layer and the semi-insulating buried layer 109 are made of InG.
Although aAsP and InGaP were used for the barrier layer, for example, InGaP was used for the cladding layer and the semi-insulating buried layer.
It goes without saying that the mixed crystal composition may be changed without departing from the spirit of the present invention, such as by using InGaAlP for the barrier layer. Further, although the GaInNAs layer is used for the active layer, a GaInNAs / GaInAsP quantum well structure can be used. As described in detail above, according to the present invention, p
By disposing a barrier layer having a band gap larger than the both and a sufficient thickness of 50 nm or more between the p-type cladding layer and the semi-insulating burying layer, Hole injection is completely suppressed.
Therefore, the leakage current flowing through the buried layer at the time of high current injection or high temperature operation is very small. This allows
Even in a high-resistance embedded structure excellent in high-speed operation, pn
As with the buried structure, a semiconductor laser having high output and excellent temperature characteristics can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an element structure of a semiconductor laser according to a first embodiment of the present invention. FIG. 2 is a sectional view showing an element structure of a semiconductor laser according to a second embodiment of the present invention. FIG. 3 is a sectional view showing an element structure of a semiconductor laser according to a third embodiment of the present invention. FIG. 4 is a sectional view showing an element structure of a semiconductor laser according to a fourth embodiment of the present invention. FIG. 5 is a sectional view showing an element structure of a semiconductor laser according to a fifth embodiment of the present invention. FIG. 6 is a sectional view showing an element structure of a conventional semiconductor laser. [Description of References] 101, 201, 301, 401 ... n-type GaAs substrate 102, 202, 302, 402, 506 ... n-type InG
aAsP cladding layers 103, 105, 203, 205, 303, 305, 4
03,405,503,505 ... non-doped GaAs light guide layers 104,204,304,404,504 ... non-doped GaInNAs ... active layers 106,204,306,406,502 ... p-type InG
aAsP cladding layers 107, 210, 311, 411... p-type GaAs contact layers 108, 407, 507... non-doped InGaP barrier layers 109, 207, 307, 408, 508. 412, 512, 606 ... p
Side electrodes 111, 212, 313, 413, 511, 607... N
Side electrodes 208, 309, 409 n-type InGaP barrier layer 308 n-type InGaAsP intermediate layer 501 p-type GaAs substrate 510 n-type GaAs contact layer 601 n-type InP substrate 602 non-doped InGaAsP active layer 603 p-type InP Cladding layer 604: non-doped InGaP barrier layer 605: Fe-doped semi-insulating InP buried layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-102600 (JP, A) JP-A-8-255950 (JP, A) JP-A 1-220490 (JP, A) JP-A-6-255 37355 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (1)

(57) Claims 1. A semiconductor substrate containing Ga and As, and an active layer containing Ga, As, and N as constituent elements.
Having, provided on the semiconductor substrate, the semiconductor substrate
Including a semiconductor layer forming a mesa stripe and a semi-insulating semiconductor layer containing Ga as a constituent element.
Only semi-conductive buried at least the mesa stripe side
Ga and I as constituent elements in the body buried layer and the semiconductor buried layer.
n and P, and the semi-insulating semiconductor layer
The forbidden band width is larger and thicker than any of the semiconductor substrates.
A semiconductor layer having a thickness of 50 nm or more.
Semiconductor laser.