JP2980302B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having a high light output and a stable transverse mode.

[0002]

[Prior art]

(1) In recent years, as a high-power AlGaInP-based semiconductor laser, a structure as shown in FIG.
No. and Japanese Journal of Applied Physics (Japanese Journal of Applied Physics)
of Applied Physics, vol. 32, page 609 (S. Kawanak).
a, T .; Tanaka, H .; Yanagisawa,
S. Yanoand S. Minagawa). n-type G
n-type (Al _0.7 Ga _0.3 ) _0.5 I
n _0.5 P cladding layer 32, n-type (Al _0.5 Ga _0.5 )
_0.5 In _0.5 P outer guide layer 33, n-type (Al _0.7 Ga
_0.3 ) _0.5 In _0.5 P inner cladding layer 34, (Al _0.5
Ga _0.5 ) _0.5 In _0.5 P inner guide layer 35, GaI
nP active layer 36 (strain 0.3 to 0.9%, thickness 20 to 3)
0 nm) and a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 37 is formed. A stripe-shaped mesa is formed in the p-side semiconductor layer, and the mesa side is buried with an n-type GaAs block layer 39. By using the above structure for a semiconductor laser, the light intensity distribution in the direction perpendicular to the active layer spreads toward the n-type semiconductor layer, and the relative light intensity in the active layer can be reduced.
This means that the optical output that causes optical damage at the end face is high, and high-output operation is possible. The stripe-shaped mesa structure buried with p-side GaAs is for forming an optical waveguide, controlling the transverse mode, and confining the current. With this structure, a lateral mode control type high power AlGaInP based semiconductor laser can be manufactured.

(2) Japanese Patent Laid-Open No. 2-1288 discloses a semiconductor laser having a structure similar to that of the semiconductor laser of the present invention described later.
No. 5 discloses this. This semiconductor laser is shown in FIG.
As shown in the figure, the cladding layer has a double structure consisting of an inner cladding layer having a lower refractive index and an outer cladding layer having a higher refractive index, and the composition and material of the inner cladding layer and the outer cladding layer are changed. The vertical emission angle can be controlled to an arbitrary value by appropriately selecting the value.

[0004]

(1) In a structure in which an optical waveguide is formed by a stripe-shaped mesa to control a transverse mode in a waveguide form, the stability of the transverse mode is determined by the difference in the refractive index between the mesa portion and the mesa side portion. Is deeply related to the current.
The output at which the linearity of the optical output characteristic is disturbed, that is, the so-called kink is determined. In the above conventional structure (FIG. 5), n
The active layer 3 has a higher refractive index than the cladding layers 32 and 34 on the side.
Since the outer guide layer 33 having a refractive index smaller than 6 is provided to bias the light distribution on the end face to the n side in both the mesa portion and the mesa side portion, the difference in the refractive index between the mesa portion and the mesa side portion is reduced. small, there is a disadvantage that the light output occurs Kin click is small. Actually, in the structure described in (1) of the conventional technology,
The thickness of the p-type cladding layer is 1 μm, the thickness of the active layer is 40 nm, the thickness of the inner guide layer is 0 nm, and the thickness of the n-type inner cladding layer is 57.5 n.
m, and the thickness of the outer cladding layer is 0.95 μm. When the outer guide layer is changed and the refractive index difference between the mesa portion and the mesa side portion is calculated, a solid line shown in FIG. 4B is obtained. In order to obtain stable fundamental transverse mode oscillation, 1 × 10 ⁻³ to 1 × 10
^-2 refractive index difference is required, but the calculation result shows that the guide thickness is 4
If it is 50 nm or more, it will be 1 × 10 ⁻³ or less. In order to achieve high output, the guide thickness must be increased,
It can be seen that there is a trade-off between high output and transverse mode stability, and it is difficult to achieve both. In other words, even if a desired refractive index difference is obtained at a guide layer thickness of 300 nm, the laser beam will be broken by the time the output power of the end face breakdown is low and the output power of the kink light is high even if the output power is high.

An object of the present invention is to solve the above-mentioned drawbacks and to provide a laser having a large difference in refractive index between a mesa portion and a mesa side portion, high transverse mode stability, and a large optical output in which kink is generated.

(2) The structure disclosed in Japanese Patent Laid-Open No. 2-188585 is a structure for controlling the vertical radiation angle, and is similar to the present semiconductor laser described later. The problems of this semiconductor laser will be described so as to clarify the difference from the present invention. As shown in FIG. 6, the structure is such that a layer having a higher refractive index than the inner cladding layer is used as the outer cladding layer. Therefore, the light distribution in the thickness direction extends to the electrode contact layer sandwiching the double hetero structure including the cladding layer and the active layer. For this reason, when a GaAs layer capable of reducing the contact resistance with the electrode is used as the electrode contact layer, the electrode contact layer becomes a layer that absorbs the oscillating laser light due to the narrow band gap of GaAs, and the internal loss is large. Disadvantage. Actually, the active layer is Ga _0.5 In _0.5 P, and the inner cladding layer is (Al _0.7 Ga
_0.3 ) _0.5 In _0.5 P, outer cladding layer (Al _0.5 G
a _0.5 ) _0.5 In _0.5 P, GaAs electrode contact layer
The thickness of the active layer is 40 nm, and the thickness of the inner cladding layer is 57.5.
When a GaAs buried refractive index guided laser having a thickness of 1.55 μm and an outer cladding layer thickness of 5 μm and a stripe width of 5 μm is manufactured, the internal loss of the laser is calculated to be 20 cm ⁻¹ or more.

An object of the present invention is to solve the above-mentioned drawbacks and to achieve a high kink output with a laser having a low internal loss, which does not reach the electrode contact layer.

[0008]

A semiconductor laser according to the present invention has a mesa-type stripe structure for controlling a transverse mode.
The active layer has at least a double heterostructure composed of a cladding layer having a lower refractive index than the active layer, and both cladding layers have a high refractive index optical guiding layer and a low refractive index cladding layer.
The light guide layer has a triple structure sandwiched between
And characterized in that forming part of the mesa stripe, and the mesa side portions are embedded by a current blocking layer having a band gap capable of absorbing laser light of the current blocking layer or oscillation of the low-refractive index than the cladding layer I do.
Also, the layer between the active layer and the current blocking layer is
The cladding layer has a small refractive index .

[0009]

FIG. 3 shows the refractive index distribution of the layer structure of the semiconductor laser of the present invention divided into a mesa portion and a mesa side portion. The refractive index distribution of the mesa portion (A) is symmetric about the active layer, and the light naturally spreads symmetrically on the p-side and the n-side. on the other hand,
In the mesa side portion (B), the p-side guide layer is removed and GaAs is formed.
It has been replaced by an s layer. Therefore, the n-side guide layer pulls the light distribution and the loss in the GaAs layer pushes the light to the n-side. As a result, light has a distribution biased toward the n side in the mesa side portion. The distribution of light between the mesa portion and the mesa side portion is largely different, that is, the refractive index difference is large between the mesa portion and the mesa side portion.

FIG. 4 shows an example of the result of the refractive index difference obtained by calculation.
Shown in In the figure, the solid line (a) shows the calculated refractive index difference when the thickness of the guide layer on both sides of p and n is changed while maintaining the same for the present invention. (B) corresponds to the case of the conventional semiconductor laser as described above. First, in the present invention, a large difference in refractive index can be obtained as compared with the related art. In particular, when gradually increasing the thickness of the guide layers for high output, in the conventional structure will become insufficient value for 1 × 10 ^-3 or less and a transverse mode control but, 1 × 10 ^-2 in the present invention A value of about 5 × 10 ⁻³ is maintained. As a result, the optical output at which kink occurs can be increased.

Further, as can be seen from the refractive index distribution of the mesa portion in FIG. 3, the semiconductor laser of the present invention has a structure in which a low refractive index layer is introduced between the GaAs layer and the guide layer. It has become. This low refractive index layer rapidly reduces light towards the GaAs layer. Therefore, when the GaAs layer capable of reducing the contact resistance with the electrode is used as the electrode contact layer, the light distribution in the layer thickness direction extends to the electrode contact layer sandwiching the double hetero structure composed of the cladding layer and the active layer. The laser light is not absorbed by the contact layer, and the internal loss can be reduced. When the internal loss of the laser having the structure shown in the example was actually calculated, it was 15 cm ^-1 . This value is smaller than the value of the internal loss of the conventional example of 20 cm ⁻¹ or more.

[0012]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a laser chip showing one embodiment of the semiconductor laser of the present invention, and FIG.

First, an n-type GaAs substrate 1 (Si-doped; n = 2 × 10
^The next layer is formed successively with matching the lattice constant on ¹⁸ cm ^-3 ).

N-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P
Outer cladding layer 2 (n = 5 × 10 ¹⁷ cm ⁻² ; thickness 1 μm)
), N-type (Al _0.5 Ga _0.4 ) _0.5 In _0.5 P guide layer 3 (800 nm thick), n-type (Al _0.7 Ga _0.3 ) _0.5
In _0.5 P inner cladding layer 4 (50 nm thick), four G layers
a _0.5 In _0.5 P well (10 nm thick) and three (Al
_A multiple quantum well active layer 5 (undoped) of _0.7 Ga _0.3 ) _0.5 In _0.5 P barrier (5 nm thick), p-type (A
l _0.7 Ga _0.3 ) _0.5 In _0.5 P inner cladding layer 6 (50 nm thick), p-type (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P
Guide layer 7 (800 nm thick), p-type (Al _0.7 G
a _0.3 ) _0.5 In _0.5 P outer cladding layer 8 (p = 5 × 1
0 ¹⁷ cm ⁻³ ; thickness 1 μm), p-type Ga _0.5 In _0.5 P buffer layer 9 and p-type GaAs cap layer 10.

The growth temperature is 660 ° C. and the pressure is 70 Torr.
r, V / III ratio = 150, and the total flow rate of carrier gas (H ₂ ) was 15 l / min. As raw materials, trimethyl indium (TMI: (C ₂ H ₅ ) ₃ In), triethyl gallium (TEG: (C ₂ H ₅ ) ₃ Ga), trimethyl aluminum (TMA: (CH ₃ ) ₃ Al), arsine (AsH) ₃ ), phosphine (PH ₃ ), n-type dopant: disilane (Si ₂ H ₆₎ , p-type dopant: dimethyl zinc (DMZn: (CH ₃ ) ₂ Zn).

An SiO ₂ film 1 on a stripe having a width of 5 μm is formed on the wafer thus grown by photolithography.
One mask was formed (FIG. 2A). Next, this Si
Using a O ₂ mask 11, the p-type GaAs cap layer 10 is etched in a mesa shape with a phosphoric acid-based etchant,
Subsequently, a p-type (Al _0.7 Ga
_0.3 ) Etch the _0.5 In _0.5 P outer cladding layer,
Similarly, a p-type (Al _0.5 G
The a _0.4 ) _0.5 In _0.5 P guide layer was etched into a mesa shape up to a position where the remaining thickness beside the p-type mesa was 0.25 μm from the p-side interface of the active layer (FIG. 2B). Next, a _second growth is performed by the reduced pressure MOVPE method with the SiO ₂ mask 11 attached, and the n-type GaAs block layer 1 is formed.
2 is formed, and after the SiO ₂ mask 11 is removed,
The third growth was performed by the OVPE method to form a p-type GaAs contact layer 13 (FIG. 2C). Finally p,
The n electrodes are respectively connected to the p-type contact layer 13 and the n-type GaAs.
After being formed on the s-substrate 1 and cleaved to a cavity length of 700 μm, the laser end face has a front surface reflectance of 5% and a back surface reflectance of 95%.
%, Coated with Al ₂ O ₃ , separated into individual chips, and fused to a Si heat sink to complete a semiconductor laser.

In the above manufacturing process, the p-type (Al _0.5 G
a _0.5 ) The mesa width of the _0.5 In _0.5 P guide layer 7 is 5 at the bottom.
μm.

The light output of the thus obtained laser of the present invention at which kink occurs was measured at room temperature during continuous oscillation and found to be 100 mW. When the internal loss of the laser was measured, it was 15 cm ^-1 . In addition, since a sufficient difference in the refractive index was obtained, stable fundamental transverse mode oscillation was obtained.

In the embodiment described above, the active layer is made of GaIn.
The multiple quantum well composed of P and AlGaInP, the cladding layer was (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, and the guide layer was (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P. A composition and a material that can sufficiently confine the carrier and the carrier in the mesa stripe portion may be selected, and a composition and a material of the guide layer may be selected so that the refractive index is higher than that of the cladding layer. Further, although the block layer is made of GaAs, the composition of the block layer may be selected from a composition having a lower refractive index than the cladding layer, a material or a composition having a band gap capable of absorbing oscillating laser light. Depending on the characteristics required for the laser, an SCH structure or the like can be used. If the etching stopper layer is used, the remaining thickness of the mesa side guide layer can be more strictly controlled.

[0020]

According to the present invention, the transverse mode stability is high,
A semiconductor laser having a high optical output in which a kink having a low internal loss occurs can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a manufacturing process of the semiconductor laser of the present invention.

FIG. 3 shows an active layer, a cladding layer, and a semiconductor laser of the present invention.
It is the figure which represented the refractive index of the guide layer typically.

FIG. 4 is a diagram showing calculation results obtained by comparing the refractive index difference between a mesa portion and a mesa side portion between the present invention and a conventional example.

FIG. 5 is a diagram showing a conventional semiconductor laser.

FIG. 6 is a diagram for explaining a structure of a conventional example.

[Explanation of symbols]

Reference Signs List 1 n-type GaAs substrate 2 n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P outer cladding layer 3 n-type (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P guide layer 4 n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P inner side Cladding layer 5 multiple quantum well active layer 6 p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P inner cladding layer 7 p-type (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P guide layer 8 p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P outer cladding layer 9 p-type Ga _0.5 In _0.5 P buffer layer 10 p-type GaAs cap layer 11 SiO ₂ mask 12 n-type GaAs block layer 13 p-type GaAs contact layer 31 n-type GaAs substrate 32 n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P outer cladding layer 33 n-type (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P outer guide layer 34 n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P inner cladding layer 3 5 (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P inner guide layer 36 GaInP active layer 37 p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 38 p-type Ga _0.5 In _0.5 P buffer layer 39 n-type GaAs block layer 40 p-type GaAs cap layer 41 p-type GaAs contact layer

Claims (2)

(57) [Claims] 1. A mesa-shaped stripe for controlling a transverse mode.
Having at least a double hetero structure comprising a cladding layer having a smaller refractive index than the active layer with the active layer interposed therebetween, and both cladding layers sandwiching a high-refractive-index optical guide layer with a low-refractive-index cladding layer. The light has a triple structure
Guide layer forms part of the mesa stripe, and the
A semiconductor laser mesa side portion is characterized in that it is filled with the current blocking layer having a band gap capable of absorbing laser light of the current blocking layer or oscillation of the low-refractive index than the cladding layer. 2. The semiconductor laser according to claim 1, wherein the layer between the active layer and the current blocking layer is a clad layer having a smaller refractive index than the active layer.