JPH03174792A - Semiconductor laser device - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a semiconductor laser device, and particularly to a highly efficient semiconductor laser device in which a current blocking layer is disposed around an active layer used in optical communication systems and the like. [Prior Art] A semiconductor laser currently in practical use consists of a double heterostructure light-emitting region sandwiched between cladding layers of P-type and n-type layers with a wide forbidden band from below the active layer. In order to enhance the current confinement effect in the active region, a structure in which a current blocking layer is provided around the active layer is used. BC (Burj, ed. Crescent) type laser (Journal ``Bright Wave Technology'' J) in which p-type InP and n-type InP are alternately formed as current blocking layers.
, of Light++aveTechnolog
y, Vol. LT-3, pp. 978-9843, 1985) or on the semi-insulating current blocking layer and on the sidewalls of the mesa forming the light emitting region, a strained semiconductor having a bandgap larger than that of the InP of the substrate or cladding. A structure with a certain InGaP layer is also used.
Heterostructure) type laser (eye
IEEE Journal of Quantum Electronics “IEEE J, of Quantum
Electronics” Volume QE-25 Volume 1362
~page 1368 (King 989) is known.

[Problem to be solved by the invention]

In conventionally known semiconductor lasers, the leakage current component increases and the luminous efficiency decreases at high temperatures, so the upper limit of the usable temperature is generally limited to about 80'C. In the BH type laser having the strained layer described above, the strained layer is also provided on the side of the mesa. However, usually on the mesa side or
It is difficult to form a strained layer of a predetermined thickness at the corner formed by the mesa and the substrate, and as a result, defect levels are generated within the forbidden band and the current blocking function is lost. Additionally, if such a defective layer exists in contact with the active layer, lattice defects will occur in the active layer itself, preventing proper recombination of electrons and genuine tags, generating heat and inhibiting laser oscillation. be. The main object of the present invention is to solve the problem described in item 1 and to realize a semiconductor laser capable of highly efficient continuous oscillation even at high temperatures of 80° C. or higher. 1. Means for Solving the Problem] In order to achieve the above object, a light emitting region including an active layer that emits light, and an electrode for injecting current into the active layer and emitting light are provided on a semiconductor substrate. In a semiconductor laser in which a current blocking layer for blocking current is formed in a peripheral area of the active layer in order to effectively inject the current into the active layer, at least a part of the current blocking layer has a forbidden band. A semiconductor layer having a width larger than the forbidden band width of the semiconductor substrate or the semiconductor constituting the light emitting region was formed as a flat layer on the outer periphery of the light emitting region. Here, the term "flat layer" means that the layer does not have a bent part and is perpendicular to the substrate described in -]2. ” 1. A preferable semiconductor for forming the flat layer is InP.
InGaAlAs or InA lattice matched to
There are QAs. Alternatively, it may be a strained layer or a strained superlattice whose lattice constant is different from that of the semiconductor substrate. I n G as the above strained layer or strained superlattice
Strained layer of a A Q A s or In A Q A s or InGaAlAs or InA Q
A strained superlattice containing As is effective. Also, G n
A Q A s, InGaAsP, InGaAQ, P
, a strained superlattice of InGaP or InAnP. Furthermore, similar effects can be obtained with ■-■ group semiconductors. Further, the current blocking layer may be composed only of the flat layer, or may be combined with another semiconductor layer having a current blocking function. As the semiconductor layer having the above-mentioned current blocking function, a layer formed of a semiconductor having a p-type conductivity type and a semiconductor having an n-type conductivity type to form a pnpn type current blocking structure can be applied. In addition, in order to solve the above object, the present invention makes the layer with a wide forbidden band non-contact with the active layer, thereby preventing stress due to strain from being applied to the active layer and appropriately controlling the operation of the active layer. I made it possible to do it. The shape of the light emitting region is a semiconductor substrate, in which a mesa type 1 to live light emitting region is formed, and a current blocking layer including the flat layer is formed as a buried layer on both sides of the mesa stripe. A so-called BC with a circular layer plane and a vertical light irradiation direction, and a so-called BC with a curved cross-sectional shape of the active layer.
(Buried Crescent Burj, e d
Crescent) type may also be used.

[Operation] FIG. 2 is a schematic cross-sectional view of a conventional BC type laser. In this structure, at high temperatures, the n-InP cladding layer 9
Electrons were injected into the n-1nP current blocking layer 2 through the -I nP current blocking layer 3, resulting in an increase in leakage current. In the structure of the present invention, as shown in the construction drawing, n-In
In order to block electron injection from the P cladding layer 9 to the p-InP current blocking layer 2, a semiconductor layer, a strained layer, or a strained superlattice 4 whose forbidden band width is larger than InP is provided. As a result, laser oscillation can be performed with high efficiency even at high temperatures with a small leakage current component. As an m-■ flag conductor material with a larger MIll band width than InP, (A (l x Ga 1-X)Y I n , -YA
S or (A Q x G a 1-X) Y I n , -
Examples include YP. Figures 3 and 4 are Cayce (H, C0Ca5ey)
and "Heteros H Structure Lasers, Part B No. 44N4" by Vanish (M, B, Pan1sh)
Page 5 (Heterostructure La5er
+; Part B pp, 44-45). (A Q x G at-X) Y I n 1-vA,
This figure shows the composition dependence of the forbidden band width and lattice constant of s and (A, Q ”1.y:o, 48 that is I n o+
5□A1□4! In IAs, the forbidden band width is maximum, and its value is 1. ．． It is about 50 eV, which is the forbidden band width of InP 1
．． It can be seen that 0.15 eV is much larger than 35 eV. Moreover, in I n , vA Q YA S, y>0.
Although lattice mismatch occurs in 48, the forbidden band width can be further increased. This lattice mismatch I n 1-yA f
l yA s can be grown without producing defects by forming a single layer film or a strained superlattice in which each layer has a thickness of about 10 nm or less. Also, Figure 4 shows (A
QxG a, -x) vI nI Yp system, but
A composition with a larger forbidden band width than InP will have a lattice mismatch with InP, but this can be achieved by creating a strained superlattice as described above. In Figure 5, the vertical axis shows the difference between the forbidden band width Eg of In□-xA Q This is a calculated value of the tensile strain when a semiconductor is grown. In the figure, changes in the forbidden band width due to strain and the effect of separating heavy hole bands and light hole bands are taken into consideration. InGaP is disadvantageous compared to InA-filled As because the rate of increase in the forbidden band width due to composition changes is small, and GaP has a small lattice constant and large tensile strain. On the other hand, Figure 6 shows the model of Matthews et al.
Of Crystal Growth (J, Crystal
Growth), Vol. 27, pp. 118-125, 19
The relationship between the lattice mismatch rate and critical film thickness hc for InP calculated by 1974 is shown. Although this model does not necessarily agree with experiments, it at least shows that it is not desirable to use a semiconductor with a lattice mismatch rate of 4% or more as a single film. Further, using FIGS. 7 and 8, computer simulation results showing that the structure of the present invention is effective in reducing current leakage are shown. FIG. 7 shows the current distribution of the conventional BC laser at 85° C. and 1.3 μm as a streamline. It is clear that a large amount of current leaks to areas other than the active layer. FIG. 8 shows In OH5□Afl with a thickness of 0.1 μm. This is a current distribution in a semiconductor laser of the present invention in which a 111As current blocking layer 4 is introduced. Although the temperature was 85° C., the voltage was 1.3 V, and the optical output was 6 mW, no current leakage was observed. Embodiments Embodiment 1 FIG. 1 shows a plan view of a first embodiment of a semiconductor laser according to the present invention. This example is a BC type semiconductor laser, and is a p-type I
A p-InP cladding layer 7, a crescent-shaped active M8 made of InGaAsP, and a part of an n-InP current blocking layer 9 are formed in the center (groove 6) of the nP substrate 1. The light-emitting regions constitute stripes extending perpendicular to the plane of the paper. On both sides of the groove 6, that is, the light emitting region, and on the upper surface of the substrate 1, n-InP layers 2. p-1nP layer 3
, p I na +g2 A Qo , 411A
A current blocking layer consisting of S4 and n-InP layer 5 is implemented. p-I nll,,=□A fl. ,,
llAs 4 is a semiconductor layer having a wider forbidden band width than the light emitting region 7.8 and the substrate 1, and forms a planar layer on both sides of the groove 6. Moreover, it is formed separately from the active layer. On the 1,000th side of the p-type InP substrate, there are 12 lower electrodes,
An upper electrode 11 is partially formed on the upper surface of the cladding layer 9 with a 1MA film 10 interposed therebetween. A method for manufacturing the semiconductor laser shown in FIG. 1 will be described. 1- N-InP is deposited on p-type InP substrate 1 by MOCVD method.
Current blocking layer 2 (donor concentration No=IX 10”c
m-', thickness 0.8 pm), p-InP current blocking layer 3 (acceptor concentration N^=IX101Bcm-3, thickness 1.0 pm), P-In0-52AQ, . As current block 14 (acceptor concentration NA: I x 10
"cm-3, thickness 0.1 μm), n-InP layer 5 (donor concentration No = I x 10" cm-3 thickness 0.1 μm)
m) are sequentially formed. Subsequently, using the oxide film as a mask, grooves 6 are formed by etching by a normal wet etching method until the n-InP current block 9M2 passes through. After that, the p-InP cladding layer 7 is formed using a liquid phase growth method.
(NA=IX101Bam-3), undoped InGaAsP active layer 8 (bandgap wavelength λg=1.3μm, center film thickness Q, 16μm),
n-InP clad M9 (No=IX101
11cm-3) as shown in the figure. After that, S
After shaping the i○2 insulating film 10 using the CVD method and forming contact holes, the n-type electrode 11 and the p-type 2 are finally formed using the vapor deposition method.
- By forming the electrode 12, the semiconductor laser device of the example shown in FIG. 1 was manufactured. In the device of the above embodiment, CW oscillation is performed up to 170°C, and 1. Efficiency at O0℃ is 0.10mW/mA
Met. In the conventional example, the CW oscillation limit temperature is around 130° C., and the efficiency at 100° C. is about 0.03 mW/mA, and the characteristics are significantly improved. Embodiment 2 FIG. 9 shows a cross-sectional structure of a second embodiment of a semiconductor laser according to the present invention. The main difference from Example 1 is that the light emitting region is p-
InP cladding M22, undoped InGa
A s P active layer 23. The n-InP cladding layer 24 has a mesa structure, and the layer 27 having a wide forbidden band and forming part of the current blocking layer is made of p-InA or As. The manufacturing method of this example will be explained. p-I is formed on the p-type InP substrate 21 by the MOCVD method.
n P clad N22 (thickness 1 μm), undoped I
nGaAsP active layer 23 (thickness 0.14μ
m) After sequentially growing an n-InP cladding layer 24 (thickness: 0.3 μm), a mesa is formed by a normal wet etching method. After that, p-InP was grown using liquid phase growth method.
Layer 25, n-InP current current clock 9 layer 26 l n
. +62A n 06411” S current blocking layer 27
, n-InP buried layer 28 are sequentially grown as shown in the figure. Thereafter, a 5 in 2 insulating film 29 is formed by the CVD method, contact holes are provided, and finally an n-type electrode 30 and an n-type electrode 31 are formed by using a vapor deposition method. The semiconductor laser of this example performs CW oscillation up to 160°C, and the efficiency at 100°C is 0.08nW/m.
It was A. Example 3 Next, a third example of the semiconductor laser according to the present invention will be described. The cross-sectional structure and manufacturing method of the semiconductor laser are basically the same as those of the first embodiment (FIG. 1). In this example, the current blocking layer is made of p-In. ,,2An
. , , , The feature is that a strained superlattice is used instead of As. The strained superlattice has a thickness of 5 nm, I n (1*3A
fl. , 7As and 5 nm InP were alternately formed for 10 periods. In addition, this strained superlattice is doped with P-type impurities at 1×1011
Dope to 1 cm-3. The rest is the same as in Example 1. In this example, CW oscillation is performed up to 200°C, and the efficiency at 100°C is 0.12mW/mA
Met. Embodiment 4 FIG. 10 shows a cross-sectional view of a fourth embodiment of a semiconductor laser according to the present invention. A striped active layer 42 with a diameter of ↓μm is formed on an n-type InP substrate 41 using undoped InGaAsP, and current blocks N45 having the same thickness as the active layer 42 are formed on both sides of the active layer 42 using InA. nA s as a buried layer, and a p-InP cladding layer 43 and a p-InP cladding layer 43 are formed thereon.
-I n Ga As P caps [44 are stacked in sequence. The manufacturing method of this example will be described. n-type InP substrate 4
1, an undoped InGaAsP active layer 425- (band gap wavelength λg = 1.3 μm, thickness 0.1
5 μm), p-InP cladding layer 43 (acceptor concentration l×1018CI11-3 thickness 1.5 μm), p-I
n G a A s P character layer 44 (λ□=1
．． 2 μm, acceptor concentration 2 X 10”cm-3,
0.5 μm thick) are sequentially formed. Subsequently, using the oxide film as a mask, etching is performed by a normal wet etching method until the active layer 42 is reached, thereby forming a mesa of @5 μm. Next, using a mixture of sulfuric acid, hydrogen peroxide and water,
By selectively side-etching the active layer 42 made of InGaAsP from both sides by about 2 μm, the width of the active layer 42 is made narrower than the cladding layer 43 to about lttm. Then, using the MOCVD method again, undoped In(1*
52AQ, 0. As buried layers 45 are provided on both sides of the active layer 142 with a thickness of 1 μm. Finally, the n-type electrode 46 and the n-type electrode 4
By vapor depositing 7, the semiconductor laser of this embodiment is manufactured. In the above example, the differential efficiency for light from the front facet at 50°C was 0.20 mW/mA, and a 10 GHz band was obtained at 50°C and an optical output of 10 mW. Embodiment 5 FIG. 11 shows the manufacturing process of a fifth embodiment of a semiconductor laser according to the present invention. On a p-type InP substrate 51, an undoped InGaAsP active layer 52 (with a thickness of 0.5 mm) is formed by MOCVD.
1μm, forbidden bandwidth wavelength 1.537zm), undoped
InGaAsP light guide M53 (thickness 0
1 .mu.m, forbidden band width wavelength 1.27 .mu.m). Next, using the oxide film 54 as a mask, the optical guide layer 53 made of InGaAsP and the active J'i 52 are selectively etched by a normal wet etching method, thereby increasing the width of the active layer 52. The thickness should be approximately 1 μm. Thereafter, using the MOCVD method again, p-type InP (acceptor concentration I x 1017 cm-3) 55 and In
,, 7Gao, 3F (40 people thick) 56 are provided almost flat on both sides of the mesa stripe. Next, the oxide film 54
After removing the n-InP cladding layer 57 (donor concentration 7×1017 Cm-3, thickness 2
μm), and finally, the n-type electrode 58 and the p-type electrode 59
The semiconductor laser of this example is fabricated by vapor-depositing. ” In the first embodiment, CW oscillation is performed up to 140,
The efficiency at 100°C was 0.06 mW/mA. Example 6 Next, a sixth example of the present invention will be described. The configuration and manufacturing method of the sixth embodiment are basically the same as those of the fifth embodiment (Figure 1). In this example, the InGaP current blocking layer 5 shown in Fig.
Instead of 6, I nolA Qo, 6A s (1
(% 100%) and n-InP (thickness 500 Å) (However, In., 4A fl., and 6A s are grown first)
This embodiment is characterized by the use of a two-layer structure, and is otherwise the same as the fifth embodiment. In this example, CW oscillation is performed up to 2000C, and 1. Efficiency at O0℃ is 0.13m
It was W/mA. Example 7 Next, a seventh example of the present invention will be described. The construction method of configuration 1 of the seventh embodiment is basically the same as that of the fifth embodiment (FIG. 11). This embodiment is characterized in that Zn5eTe, which is lattice-matched to InP, is used instead of the InGaP current blocking layer 56. The rest is the same as in Example 5 (Fig. 1↓). In this example, CW oscillation was performed up to 200°C, and the efficiency at 100°C was 0.12 mW/mA. In addition to this example, ZnSTe, CdSeTe, Cd5
■-■ group semiconductors such as Te can also be applied. Further, it does not necessarily have to be lattice matched to InP, and may be a strained layer or a strained superlattice. Note that the present invention is also effective for structures other than those shown in the above-mentioned embodiments. For example, a semiconductor with a wider bandgap than the substrate or a strained superlattice can be used for part or all of the n-type blocking layer. Further, it may be used for the entire p-type and n-type current blocking layers. Further, the current blocking layer combined with the current blocking layer having a wider forbidden band width than the semiconductor substrate or the cladding layer can have the same effect even if it is undoped or semi-insulating (Fe-doped, etc.). Further, the conductivity type of the substrate is not limited to p-type, but also n-type, a structure using a semi-insulating substrate and having an electrode on the upper part is also effective. Further, the present invention is applicable to semiconductor devices having a current blocking layer structure (current confinement structure), such as a distributed feedback (DFB) laser, a Bragg reflection type (DBR) laser, a wavelength tunable laser, a laser with an external cavity, and a vertical cavity laser. It can also be applied to vessel-shaped surface emitting lasers, light emitting diodes, optical modulators, and optical switches. Further, the wavelength is not limited to 1.3 μm, and the invention is applicable to all materials in the wavelength range that can be oscillated by a semiconductor laser.

【Effect of the invention】

According to the present invention, the leakage current component is reduced even at high temperatures of 80°C or higher, which was conventionally considered the practical temperature limit, and continuous (
(CW) oscillation, it is effective in improving the efficiency of semiconductor lasers, expanding the usable temperature range, and improving reliability. Further, by providing the current blocking layer both perpendicular and horizontal to the substrate plane, it is possible to prevent problems caused by tensile strain due to lattice defects.

[Brief explanation of drawings]

0- Fig. 1, Fig. 9, Fig. 10, and Fig. 1-1 are all cross-sectional views of an embodiment of the semiconductor laser according to the present invention, and Fig. 2 is a cross-sectional view of a conventional BC type semiconductor laser. Figure 3 is a map diagram showing the relationship between the forbidden band width and lattice constant, Figure 4 is a map diagram showing the relationship between the forbidden band width and lattice constant, and Figure 5 is a map diagram showing the relationship between the forbidden band width and lattice constant.
A calculation diagram of the relationship between the lattice mismatch rate and critical film thickness of Q A s and InGaP, Figure 6 is a diagram showing the relationship between the lattice mismatch rate and critical film thickness of InP, and Figure 7 is a diagram showing the relationship between the lattice mismatch rate and critical film thickness of InP. Current Distribution Diagram Based on Computer Simulation Results of Semiconductor Laser FIG. 8 shows a current distribution diagram based on computer simulation results in one embodiment of the semiconductor laser according to the present invention. 1... p-InP substrate, 2... 9 layers of n-InP current and current blocks... 9 layers of p-InP current and current blocks...
p-I n A Q A s current blocking layer, 5-n
-InP layer, 6...groove, 7...p-InP cladding layer, 8...InGaAsP active layer, 9...n
-I n P cladding layer, 10...insulating film, 11...
n electrode, 12...p electrode, 21- p -I n P
Substrate, 22-p-I nP cladding layer, 23-I
nGaAsP active layer, 24- nInP cladding layer, 2
5- p -I n P layer, 26...n-InP current current clock 9 layer 7- p -I n A QAsAs current clock 9 layer 8... n-InP buried layer, 29...
Insulating film, 30...n electrode, 31...n electrode, 4l-
n-TnP substrate, 42-InGaAsP
Active layer, 43 ・p-InP cladding layer, 44...p
I n Ga As P carapace layer, 45-I
n A Q A s buried layer, 46...n electrode, 47
...n electrode, 51...p-InP substrate, 52-I
n G a A s P active layer, 53...I n G
a A s P light guide layer, 54... oxide film, 55
-p-InPM, 56-InGaP current blocking layer, 57...rs -InP Clarado layer, 5
8...n electrode, 59...n electrode.

Claims (1)

[Claims] 1. A first semiconductor that is laminated on a semiconductor substrate and forms a light emitting region together with an active layer, an electrode that injects current into the active layer, and an electrode that blocks current in the periphery of the light emitting region. a current blocking layer, at least a part of the current blocking layer is a semiconductor having a forbidden band width wider than the forbidden band width of the semiconductor substrate or the first semiconductor, and has only a flat portion parallel to the substrate; A semiconductor laser device comprising a second semiconductor layer. 2. A first semiconductor layered on a semiconductor substrate and forming a light emitting region together with an active layer, an electrode for injecting current into the active layer, and a current blocking layer for blocking current in a peripheral area of the light emitting region. , at least a part of the current blocking layer is made of a semiconductor having a forbidden band width wider than the forbidden band width of the semiconductor substrate or the first semiconductor, and is formed without contact with the active layer. Semiconductor laser equipment. 3. The semiconductor laser device according to claim 1 or 2, wherein the current blocking layer further includes p-type and n-type semiconductor layers. 4. The semiconductor laser device according to claim 1 or 2, wherein the light emitting region is circular and the light emitted is emitted in a direction perpendicular to the semiconductor substrate. 5. In claim 1 or 2, the light emitting region is formed of a mesa stripe, the light emitting region and the upper part of the current blocking layer have a larger forbidden band width than the active layer, and the forbidden band width of the second semiconductor layer is larger than that of the active layer. A semiconductor laser device characterized in that it is formed of a third semiconductor layer having a forbidden band width smaller than a band width. 6. The semiconductor laser device according to claim 1, 2 or 3, wherein the active layer has a cross-sectional shape of a crescent BC type. 7. Claims 1, 2, 3, 4, 5, or 6, wherein the second semiconductor layer is a strained layer or a strained superlattice having a lattice constant different from the lattice constant of the semiconductor substrate. A semiconductor laser device comprising: 8. In claim 7, the semiconductor substrate is InP.
The second semiconductor layer is InGaAlAs, InAl
strained layer of As or GaAlAs or InGaAlAs,
A semiconductor laser device characterized by having a strained superlattice containing InAlAs or GaAlAs. 9. Claim 7, wherein the second semiconductor layer is I
nGaAsP, InGaAlP, InGaP or InA
A semiconductor laser device characterized in that it is an lP. 10. The semiconductor laser device according to claim 1, second, third, fourth, fifth, or sixth, wherein the second semiconductor layer is InGaAlAs or InAlAs lattice-matched to InP. 11. The semiconductor laser device according to claim 1, second, third, fourth, fifth or sixth, wherein the second semiconductor layer is a II-VI group semiconductor.