JP3296917B2 - Semiconductor laser device and method of manufacturing the same - 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 device, and more particularly to a semiconductor laser device having a surface emitting semiconductor laser suitable for a light source for optical information processing or optical communication.

[0002]

2. Description of the Related Art A surface-emitting type semiconductor laser has any advantage that a two-dimensional array can be integrated, and is being developed as a light source for optical information processing or optical communication. In a surface-emitting type semiconductor laser in which a resonator (abbreviated as a vertical resonator) is formed in a direction in which a crystal grows on a semiconductor substrate, and output light is in a direction perpendicular to a semiconductor substrate field surface, room temperature excited by current injection is applied. Continuous oscillations have been reported. For example, literature
The Institute of Electronics, Information and Communication Engineers, 1993, vol. 4, p. 179.

[0003]

The conventional surface-emitting type semiconductor laser device has a very large laser device resistance. Therefore, in a configuration in which laser oscillation is obtained only by direct current injection, a current density is required to cause oscillation. Is very high. The technique described in the above-mentioned document describes a continuous-wave oscillation at room temperature of a surface-emitting type semiconductor laser excited by directly injecting current into an active layer. However, the threshold current density at which light can be emitted is still 10 kA / cm. ^{Since the} resistance is as high as ² or more and the resistance of the laser element is extremely large, heat is remarkably generated and heat dissipation is required. Although the heat dissipation characteristics are improved by providing a reflector made of a high thermal conductive material, sufficient characteristics for practical use are still obtained for high-temperature operation above room temperature and high output avoiding thermal saturation of light output. Not. In addition, there is no description about measures against these problems or element structures.

An object of the present invention is to realize a semiconductor laser device having a high current density and a reduced device resistance due to the device structure of a conventional surface emitting semiconductor laser.

[0005]

In order to achieve the above object, a semiconductor laser device according to the present invention comprises a surface emitting semiconductor laser oscillating by light injection pumping, and a lateral light emitting laser for performing light injection pumping on the surface emitting semiconductor laser. A lateral cavity type semiconductor laser having a directional cavity structure was integrated and formed on the same semiconductor substrate.

In a preferred embodiment of the semiconductor laser device according to the present invention, the forbidden band width of the active layer of the surface emitting semiconductor laser is smaller than the forbidden band width of the active layer of the semiconductor laser having the lateral cavity structure. The energy of the active layer of the lateral cavity semiconductor laser is larger than the energy between the pseudo-Fermi levels of the carrier distribution accumulated by injection into the active layer of the surface emitting semiconductor laser, and is preferably set to 60 meV or more. .

Further, it is desirable that the active layer of the above-mentioned surface emitting semiconductor laser and the above-mentioned semiconductor laser having the lateral resonator structure have a multiple quantum well structure having a lattice strain which causes a compressive or tensile strain.

Further, in order to increase the light pumping efficiency and efficiently extract the laser light in the direction perpendicular to the substrate,
Distributed feedback (DFB) in which a first-order diffraction grating is formed between an active layer and a substrate of the above-mentioned lateral cavity type semiconductor laser.
ed Feedback) structure, forming a second-order diffraction grating between the active layer of the surface-emitting type semiconductor laser and the substrate, and having a component for separating the laser light in the horizontal direction vertically from the distributed Bragg reflection ( DBR: Distributed Blagg Reflector)
Set the structure. In addition, an electrode may be provided for a portion forming a surface-emitting type semiconductor laser so that current can be directly injected as well as optical excitation by the lateral resonator type semiconductor laser. The electrodes are provided so that they can be driven independently of the current injection electrodes.

In order to produce the semiconductor laser device of the present invention, in particular, to form active layers having different characteristics on a single semiconductor substrate as described above, utilizing the crystal selectivity of the vapor deposition method, The active layer is grown by either metal organic chemical vapor deposition or gas source molecular beam epitaxy.

[0010]

According to the present invention, the oscillation of the surface emitting laser is excited by light injection from a lateral cavity semiconductor laser formed on the same substrate, or is excited by light injection together with current injection. Threshold current density can be reduced. Hereinafter, the principle of performing light injection excitation on a surface emitting laser and extracting laser light from the surface emitting laser at a low threshold will be described.

FIG. 2 shows an energy band structure when a semiconductor laser (region I) having a lateral resonator is arranged on both sides of a surface emitting semiconductor laser (region I). The forbidden band width Eg (1) of the quantum well active layer in the region I is set to be larger than the forbidden band width Eg (0) of the quantum well active layer in the region II, thereby promoting light absorption in the region II and increasing excitation efficiency. . Actually, a pseudo-Fermi level is formed with respect to the carrier distribution accumulated by injection in the active layer in the region II, so that Eg (2) is larger than the energy Eg (2) between the pseudo-Fermi level in the conduction band and the valence band. The energy corresponding to 3) can be obtained as the energy between quasi-Fermi levels in region I.
At this time, Eg (3) is desirably larger than Eg (2) by at least 60 meV, and smaller than the energy height of the barrier layer achieves efficient light injection excitation. In other words, in order to realize efficient optical excitation in the region I without being disturbed by the region II, stimulated emission having oscillation energy when the surface emitting laser oscillates requires light absorption in the active layer of the lateral cavity laser. It is necessary that the laser light energy from the region I be efficiently absorbed in the region II so that the carrier inversion distribution is not disturbed and the characteristics of the lateral resonator laser are fluctuated. Region II is almost transparent to region I,
As a result of conducting an experiment on light absorption characteristics in consideration of no light absorption loss, a material having a large forbidden band energy is almost transparent and ignored when it has a difference of 60 meV or more than a material having a small forbidden band energy. It has been found that the obtained light absorption loss can be suppressed.

In order to set the difference between the energy widths Eg (3) and Eg (2) corresponding to the regions I and II, the active layer of the multiple quantum well structure is formed by utilizing the crystal selectivity of the vapor phase growth method. grow up.
In the region II, by using an insulating film such as SiO ₂ or SiN to form a narrow pattern surrounding only one direction or surrounding the periphery, selective growth can be performed by the vapor phase growth method. In this region selective growth, the element does not grow on the insulating film, and the migration speed of the element in the pattern is increased by migration, so that the quantum well width of the active layer having the multiple quantum well structure can be increased. At this time, since the material composition of the mixed crystal quantum well layer using an element of three or more elements changes, the band gap is effectively affected as the quantum well width changes. In other words, by controlling the pattern width, the growth rate of the quantum well layer, and the material composition inside and outside the pattern of the insulating film, a difference can be made in the forbidden band width of the region, and the energy difference is set to 60 meV or more. be able to.

[0013]

【Example】

<Embodiment 1> FIGS. 1A and 1B are views showing the structure of an embodiment of a semiconductor laser device according to the present invention. FIGS. 1A and 1B are a perspective view and a cross-sectional view taken along the line AA ', respectively. . As shown in the figure, a surface emitting semiconductor laser (region II) having a vertical cavity structure oscillating by light injection pumping in the center portion on a semiconductor substrate 1 and performing light injection pumping on the surface emitting semiconductor laser. Four semiconductor lasers (region I) having a lateral resonator structure are arranged and integrated so as to sandwich the surface emitting semiconductor laser (region II).

The detailed structure of this embodiment will be described in connection with a manufacturing process.

The plane orientation (511) in which the substrate plane orientation is off by 15.8 ° from (100) in the [011] or [0-1-1] direction (the minus sign indicates a negative direction in the crystal axis coordinates). on the n-type InP substrate 1, n-type InP buffer layer 2 (thickness d = 0.5 [mu] m ^{_{layer, n D = 1 × 10 18}} cm ~ 3), n -type I
_{n 0. 4 Ga 0. 6} As layers _{(d = 0.108μm, N D =} 1 × 1
0 ¹⁸ cm ~ ³⁾ and n-type _{In 0. 52 Al 0. 48} As layer (d = 0.
115 μm, N _D = 1 × 10 ¹⁸ cm ^-3 ) 40 cycles of alternating reflection of DBR structure 3, n-type InP layer 4
_{(D = 0.15~0.2μm, N D =} 7 × 10 17 cm ~ 3)
Grow sequentially.

Thereafter, the oscillation wavelength is 1.55 μm in region I.
A first-order diffraction grating is formed, and a mask is formed by photolithography in the region II so as to form a second-order diffraction grating with respect to the above-mentioned oscillation wavelength, and furthermore, 50 to 70 nm by chemical or dry etching. Form a periodic groove of depth. Next, the InGaAsP layer 5 (λ =
_{1.05μm, d = 0.3~0.5μm, N D} = 5~7 × 1
By growing 0 ¹⁷ cm ~ ³ ), the steps of the diffraction gratings in the regions I and II are buried flat. Thereafter, an insulating film SiN mask is formed so as to surround the region II, and n-type InGaAs is formed.
P light separation confinement layer 6 (λ = 1.05 μm, d = 0.1-
0.15 μm, N _D = 3-5 × 10 ¹⁷ cm- ³ ) and InGa
AsP quantum barrier layer 6 (λ = 1.15 μm, d = 10n
m) and the tensile strained InGaAs quantum well layer 7 (λ = 1.55)
μm, d = 10 nm) for 10 periods. At this time,
In the region I, the thickness d of the InGaAs quantum well layer is 7 nm, and a difference larger than the energy between quantum levels in the quantum well layer in the region II by 60 meV or more can be provided.

Subsequently, the p-type InGaAsP light separation / confinement layer 8 (λ = 1.05 μm, d = 0.1-0.15 μm)
_{m, N D = 3~5 × 10} 17 cm ~ 3), p -type InP waveguide layer _{9 (d = 1.5~2.0μm, N D} = 5 × 10 17 ~1 ×
10 ¹⁸ cm ~ ³ ), p-type InGaAsP contact layer 10
(Λ = 1.05μm, d = 0.1~0.2μm , N D = 4 ×
10 ^{18 to} 9 × 10 ¹⁸ cm ³ ) are sequentially epitaxially grown. Next, after forming an insulating film mask pattern by photolithography and etching it in a mesa shape, p-type In
A buried layer 11 in which a P layer and an n-type InP layer are alternately repeated twice.
Are formed selectively. Next, a high reflection film 12 having a dielectric DBR structure in which SiO ₂ and Si are alternately repeated is formed on the upper surface of the region II.

Further, a p-side electrode 13 is formed by lift-off by photolithography, a mask is formed by photolithography, and elements and electrodes in regions I and II are separated by dry etching. 14 is deposited. Finally, the substrate is scribed and cut into the element shape shown in FIG. In the above embodiment, the n-type I
As the plane orientation of the nP substrate 1, a plane orientation (511) in which the substrate plane orientation was off by 15.8 ° from (100) in the [011] or [0-1-1] direction was used. Is from 0 ° to 54.7 from the (100) plane in the [011] [0-1-1] direction or the [0-11] [01-1] direction (-sign indicates a negative direction in the crystal axis coordinates). The angle may be in the range of °.

According to this embodiment, the surface emitting laser having the vertical cavity in the region II can be easily and continuously operated at room temperature by light injection excitation of the lateral cavity DFB laser in the region I. Here, the high device resistance of 10 to 20 Ω or more, which has conventionally been a problem in the surface emitting laser only by current injection, does not flow because the surface emitting laser in the region II is excited by light injection, so that the problem disappears. The overall device resistance depends on the lateral cavity DFB laser in region I and is in the range of 2-5Ω. Further, in contrast to a threshold current density as high as 10 kA / cm ² or more in the conventional surface emitting laser, in the present embodiment, 1 kA / cm in the lateral cavity DFB laser is used.
0.5 to 0.9 kA / cm with a threshold current density lower than cm ²
The range was ² .

Conventionally, high-temperature operation at room temperature or higher and light output have been limited due to heat generation due to high element resistance and current density. However, these were able to be improved by this example. That is, with respect to the high-temperature operation, the lateral cavity DFB laser in the region I was able to operate to a temperature at which oscillation was possible, and the surface emitting semiconductor laser in the region II achieved continuous operation up to 100 ° C.

The threshold and light output of the surface emitting laser by light injection pumping are as follows. When pumped by two transverse cavity DFB lasers in contiguous region I, 5 transverse cavity DFB lasers at room temperature
When a current of 10 to 10 mA was injected, the threshold value at which the surface emitting laser in the region II oscillated reached 20 mA or less in total. When excited by two pairs of opposite DFB lasers in region I, the threshold value of the surface emitting laser in region II was reached with a total of 15 mA or less. The light output of the surface emitting laser is a continuous operation of 10 to 20 mW at room temperature when excited by a pair of opposite DFB lasers, and 40 to 50 mW when excited by two opposite pairs of DFB lasers. Operation was possible.

<Embodiment 2> Another embodiment of the present invention will be described. It is manufactured in exactly the same manner as in Example 1, except that an electrode is provided on the p side adjacent to the DBR structure high reflection film 12 made of a dielectric film in the region II. In the second embodiment, in addition to obtaining the effects of the first embodiment, the lateral resonance laser is difficult to directly modulate the surface emitting laser because the element resistance and the current density are high due to the conventional direct current injection alone. High-speed modulation has been made possible by the external modulation with light injection pumping of the DFB laser.

When current was injected only into region II, continuous operation was obtained at room temperature with a threshold current of 20 to 30 mA, but the modulation frequency of 3 dB down during direct modulation was 5 dB.
GHz was the highest. On the other hand, by injecting a current equal to or less than the threshold value into the region II and inputting a modulated optical signal of the lateral cavity DFB laser in the region I as external modulation, the surface emitting laser having a low threshold value of 10 to 15 mA in total. High-speed modulation was possible. The modulation frequency of 3 dB down obtained at the time of modulation is 15 GHz, and the extinction ratio of the modulated optical signal is 2 GHz.
0 dB or more.

[0024]

According to the present invention, the problem that the device resistance and the current density are high in the conventional surface emitting laser can be solved by the light injection excitation of the lateral cavity DFB laser provided in the peripheral portion of the surface emitting laser. As device characteristics that did not exist, a high temperature operation of 100 ° C. or higher and an optical output of 40 to 50 mW were achieved. Further, by using the lateral cavity DFB laser as the external modulation, the modulation frequency, which was not realized by the conventional surface emitting laser, can be increased to 15 GHz or more, and the extinction ratio of the modulated optical signal can be increased to 20 dB or more.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of an embodiment of a semiconductor laser device according to the present invention.

FIG. 2 is a diagram showing a relationship between an active layer forbidden band width in a structural region of a semiconductor laser device of the present invention.

[Explanation of symbols]

1: n-type InP substrate 2: n-type InP buffer layer 3: n-type InGaAs / InAlAs layer DBR structure high reflection film 4: n-type InP buffer layer 5: p-type InGaAsP layer 6: n-type InGaAsP light separation / confinement layer 7: Undoped InGaAs / InGaAsP tensile strained multiple quantum well structure active layer 8: p-type InGaAsP optical isolation confinement layer 9: p-type InP optical waveguide layer 10: p-type InGaAsP contact layer 11: p-type InP / n-type InP buried layer 12: SiO / Si dielectric DBR structure high reflection film 13: p-side electrode 14: n-side electrode

Claims (9)

(57) [Claims] 1. Oscillation by current injection or light injection excitation
A vertical cavity surface emitting semiconductor laser and the above surface
Lateral cavity structure for light injection pumping of a light emitting semiconductor laser
Lateral cavity type semiconductor laser with the same semiconductor base
The surface emitting type semiconductor laser is formed integrally on a plate.
The forbidden band width of the active layer is larger than that of the above-mentioned lateral cavity type semiconductor laser.
The surface emitting type is set to be smaller than the forbidden band width of the active layer.
Capacitors accumulated by injection into the active layer of a conductor laser
Lateral than the energy between the pseudo-Fermi levels of the rear distribution
High active layer energy of directional cavity semiconductor laser
A semiconductor laser device characterized by being set well. 2. The semiconductor laser device according to claim 1, wherein
Injection into the active layer of the above-mentioned surface emitting semiconductor laser.
Energy between pseudo-Fermi levels of carrier distribution accumulated from
From the active layer of the lateral cavity semiconductor laser
That the energy is set higher than 60 meV
Characteristic semiconductor laser device. 3. The semiconductor laser device according to claim 1, wherein
Of the active layer of the lateral cavity type semiconductor laser.
Energy is in the active layer of the above surface emitting semiconductor laser.
From energy between quasi-Fermi levels of injected carrier distribution
Large and smaller than the energy of the optical waveguide layer and the barrier layer
A semiconductor laser device characterized by being within a range. 4. A semiconductor laser element according to claim 1, 2 or 3.
The lateral cavity type semiconductor laser and the surface
The active layer structure of a light-emitting semiconductor laser causes compression or tensile strain.
Characterized by a multi-quantum well structure with resulting lattice strain
Semiconductor laser device . 5. The semiconductor laser according to claim 1, 2, 3, or 4.
In the device, the surface emitting semiconductor laser and the lateral
-Cavity type semiconductor lasers can be driven independently.
Semiconductor laser element characterized by having separated electrodes
Child . 6. The semiconductor according to claim 1, 2, 3, 4 or 5.
In the laser device, the semiconductor substrate has a substrate plane orientation.
[011] [0-1-1] direction from [00] plane or [0-1]
1] Tilt in the range of 0 ° to 54.7 ° in [01-1] direction
A semiconductor laser device having an inclined substrate surface. 7. The semiconductor laser according to claim 1, wherein:
In the device, the above-mentioned lateral cavity semiconductor laser is
Multiple differences in bandgap of active layer of surface emitting semiconductor laser
Quantum well layer thickness and quantum well layers in quantum well structures
Characterized by being set by the material composition forming
Semiconductor laser device. 8. The semiconductor laser according to claim 1, wherein:
In the method of fabricating the element, the lateral resonator type semiconductor
Multiple quantum well structure of laser and the above surface emitting semiconductor laser
Crystal in the vapor phase growth method for each active layer
Of the quantum well layer of the multiple quantum well structure
And controlling the material composition forming the multiple quantum well layer,
The lateral cavity semiconductor laser and the surface emitting semiconductor
Set different active layers and band gaps depending on the laser area.
A method for producing a semiconductor laser device, comprising: 9. A method of manufacturing a semiconductor laser device according to claim 8.
In the method, the crystal layer on the semiconductor substrate is
Either growth method or gas source molecular epitaxy
Fabrication of semiconductor laser device characterized by growing more
Method.