JP3215180B2 - Semiconductor laser array - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-wavelength semiconductor laser array for wavelength-division multiplexed optical communication, and more particularly to a surface-emitting type semiconductor laser array.

[0002]

2. Description of the Related Art In recent years, with the increase in capacity of optical communication, attempts have been made to propagate multi-channel information over a single optical fiber. As one method of increasing the number of channels, wavelength multiplex communication has been proposed in which a plurality of laser beams having different oscillation wavelengths are used and one frequency corresponds to one channel. In order to realize this, a laser array in which a plurality of single wavelength lasers oscillating at different wavelengths are integrated is required.

[0003] Such an element is a DFB shown in FIG.
(Distributed Feed Back: distributed feedback) It has already been realized as a laser array. In the figure, 80 is an n-type substrate, 81, 8
2 is an optical waveguide layer, 83 is an n-type cladding layer, 84 is an active layer, 85 is a p-type cladding layer, 86 is a contact layer, 8
7, 88 are electrodes and 89 is a diffraction grating. In this device, the oscillation wavelength is determined by the period of the engraved diffraction grating. Therefore, in order to obtain different oscillation wavelengths for individual lasers, diffraction gratings having different periods must be imprinted on each laser.

At present, as a method of engraving such a diffraction grating, a two-beam interference exposure method utilizing interference between laser beams is used. In order to change the period of the interference pattern by this method, it is necessary to change the alignment of the optical system each time. Therefore, it is necessary to repeat exposure by the number of lasers to be arrayed, and there is a problem that productivity is extremely poor. In addition, since the resonator is formed in a direction parallel to the substrate, integration is limited to a one-dimensional method. There was also a problem that it became difficult.

[0005]

As described above, in the conventional multi-wavelength semiconductor laser array, the productivity is low because diffraction gratings having different periods must be stamped on individual lasers. was there. Further, there is a problem that it becomes difficult to couple with an optical fiber when the integration is high.

The present invention has been made in view of the above circumstances, and has as its object to perform a single lithography process.
An object of the present invention is to provide a multi-wavelength semiconductor laser array in which the oscillation wavelengths of a plurality of lasers can be determined by a process, and which can be easily coupled to an optical fiber even when highly integrated.

[0007]

The gist of the present invention is to use a vertical cavity surface emitting semiconductor laser having distributed reflection films above and below a light emitting region, and to change the cross sectional area of the resonator. It is to change the oscillation wavelength of the laser by changing the resonance wavelength. That is, the present invention provides a surface-emitting type multi-wavelength semiconductor laser array in which a plurality of electrically independent semiconductor light-emitting regions are formed on a substrate and sandwiched between two upper and lower distributed reflection films. It is composed of a plurality of semiconductor lasers that emit output light in a direction perpendicular to the substrate surface, divided into light emitting regions, and the light emitting region has a different cross-sectional area on a plane parallel to the substrate. And

According to the present invention, in addition to the above structure, the optical output of each semiconductor laser is made constant for a predetermined operating current.
To manner, characterized in that a structure for constricting a current in a portion of the light emitting region of each semiconductor laser.

[0009]

According to the present invention, the oscillation wavelength is changed by changing the sectional area of the waveguide portion of the vertical cavity surface emitting laser. To change the cross-sectional area of the waveguide portion, it is only necessary to change the size of the mask in photolithography, and the oscillation wavelength of a plurality of lasers can be determined by one lithography. By integrating vertical cavity surface emitting lasers having waveguides with different cross-sectional areas, a laser light source for wavelength division multiplexing optical communication that oscillates at multiple wavelengths can be obtained. Furthermore, because of the surface light emission, it is easy to couple with an optical fiber even when highly integrated.

Also, taking into account both an increase in gain due to current constriction, an increase in absorption loss and a decrease in optical confinement coefficient,
By providing an appropriate current confinement structure for each laser, it becomes possible to obtain a laser light source for wavelength division multiplexing optical communication that oscillates at multiple wavelengths and has uniform operating characteristics.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the embodiments, the basic principle of the present invention will be described. The vertical cavity surface emitting semiconductor laser which is a component of the present invention has a first distributed Bragg reflection film (Dist) in which a medium having a large refractive index and a medium having a small refractive index are alternately stacked.
ributedBragg Reflector (DBR) and the second DBR
A double hetero structure portion (light emitting region) of a semiconductor having an active layer is formed between the first and second DBRs, and at least a part of the first DBR has a columnar waveguide structure that stands perpendicular to the substrate. The oscillation wavelength λ for such a laser structure is defined as the axial propagation constant β of the waveguide mode of the columnar waveguide structure, the propagation constant β _{t in the} direction perpendicular to the axis, and the effective refractive index n _{eff of the} waveguide.
Using,

(2πn _eff / λ) ² = β ² + βt ² (1)

Is determined from the relationship Where β is DB
R optical long period T (= n ₁ T ₁ + n ₂ T ₂ ; n ₁ , n ₂₎
Is the refractive index of the medium constituting the DBR, and T ₁ and T ₂ are the respective layer thicknesses).

Β = β ₀ = π / T (2)

## EQU1 ## B _t is related to β by the cross-sectional shape, cross-sectional area, n _{eff of} the waveguide and the refractive index n _out of the medium outside the waveguide. For a circular section,

(Η ₁ + η ₂ ) (ε _eff η ₁ + ε _out η ₂ ) = n ² (1 / u ² + 1 / w ² ) (ε _eff / u ² + ε _out / w ² ) where u = β _{t a, w = α t a β} 2 = (2πn eff / λ) 2 - (u / a) 2 = (2πn eff / λ) 2 + (w / a) 2 η 1 = Jn (u) / uJn (u ) η ₂ = Kn (w) / wKn (w) (3)

Here, ε _eff = n _eff ² , ε _out = n
_out ² and a are the radius of the waveguide, Jn and Kn are n-order Bessel functions and modified Bessel functions, respectively, Jn and Kn are the derivatives of Jn and Kn, respectively, and n is the order of the Bessel function.

FIG. 7 summarizes these relationships. In this figure, for the waveguides having different diameters d ₁ , d ₂ and d ₃ , β of the HE ₁₁ mode, which is the lowest order waveguide mode, is shown.
A curve showing the relationship between the beta _t ((3) expression of relationship), the asymptotic value beta ₁ of beta _t, beta _2, shows a beta _3, and (2) beta ₀ obtained from the equation. The oscillation wavelength is inversely proportional to the distance from the intersections P ₁ , P ₂ , and P ₃ of the straight line of β = β ₀ and the three curves to the origin from the equation (1). Since the three curves become farther from the origin as the diameter becomes smaller, the laser having a waveguide with a smaller diameter oscillates at a shorter wavelength.

FIG. 8 shows a specific calculation example. The horizontal axis shows the waveguide diameter, and the vertical axis shows the shift amount from the asymptotic wavelength (850 nm) to the short wavelength side when the diameter is infinitely large. Note that n _eff = 3.38. As can be seen from this figure, a wavelength shift of 10 nm or more is possible with a laser having a diameter of 1 μm that can be manufactured by ordinary photolithography.

On the other hand, in order to suppress variations in threshold value and operating current between individual laser elements due to different diameters, the following method may be used. The gain (material gain) g _m of the active layer is a function of the current density. Therefore,
When the same current injection is performed for lasers having different diameters, the gains caused by the different current densities in the active layers of the respective lasers also differ, and the output light intensity varies as shown in FIG. 9A.

To suppress this variation, a current confinement structure may be provided for each laser so that the active regions have the same area. However, this alone causes an increase in the absorption loss in the current confining portion and a decrease in the optical confinement coefficient for each element, so that the output intensity also varies. Therefore, it is necessary to determine a constriction structure in consideration of both an increase in gain due to current confinement, an increase in absorption loss, and a decrease in optical confinement coefficient. The conditions for that are:

Ξηg _m (I / A, λ) −ξ (1-η) α = const. … (Four)

It is expressed by the following equation. Here, I is the injection current, A is the area of the active region, η is the light confinement coefficient, α is the absorption coefficient of the current confinement portion, and ξ is the gain increase coefficient due to the standing wave effect. Note that this condition can be expressed by a simple expression by performing appropriate approximation. First, assume that the gain increase factor does not depend on the cross-sectional area of the waveguide. Considering the linear gain that does not depend on the wavelength,

G _m = g ₀ (I / A−Jt) (5)

## EQU1 ## Here, g ₀ is a constant, and Jt is a current density required for inversion of the active layer to occur. Also, since the absorption coefficient α of the current constriction is equal to −g _m (0),

Α = g ₀ × Jt (6)

## EQU1 ## From these relations,

Η / A = const. … (7)

The following relational expression is obtained. That is, by making the ratio between the area A of the active region and the light confinement coefficient η equal between the individual elements, uniform oscillation characteristics can be obtained as shown in FIG. 9B.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing a schematic configuration of a multi-wavelength semiconductor laser array according to a first embodiment of the present invention, and FIG. 2 is a sectional view taken along line AA 'of FIG. In this embodiment, the diameter 12
A device combining surface emitting lasers 1 having a circular cross section of μm, 9 μm, 7 μm, and 6 μm, and oscillates at intervals of 0.1 nm. The sides are etched vertically until they reach the substrate 4,
It is planarized by polyimide 2. The upper surface of each laser 1 is covered with a p-electrode / reflection film 3. A hole for holding the optical fiber 6 is dug in the bottom of the substrate 4 to facilitate coupling with the laser light. An n-type electrode 5 is provided around the optical fiber hole.

FIG. 3 shows details of the sectional structure of each laser.
(A). The active layer 17 is made of In _0.2 Ga having a thickness of 8 nm.
_0.8 As quantum well, p and n cladding layers (barrier layers)
Reference numerals 16 and 18 denote GaAs having an optical length and a half wavelength thickness of the oscillation wavelength.
It is. The p and n DBRs 11 and 12 are formed by alternately laminating AlAs layers 15 and GaAs layers 14 each having an optical length and a thickness of a quarter of the oscillation wavelength. Substrate 4 for active layer 17
On the upper surface of the DBR 11 on the opposite side (upper side), a phase matching layer 13 having an optical length and a thickness of 0.3 times the oscillation wavelength is stacked to compensate for a phase shift generated at the time of reflection by the electrode / reflection film. ing. Since the oscillation wavelength is 980 nm which is transparent to the substrate 4, the output light is extracted from the substrate side. The device of this embodiment can be applied to a structure in which etching is stopped up to a part of the DBR 12 as shown in FIG. further,
It is also possible to apply to a structure in which only the DBR 11 is etched in a column shape.

Next, a method of manufacturing the device of the first embodiment will be described. First, as shown in FIG.
Molecular beam epitaxy (MBE) on As substrate 4
Or n-type D by metal organic chemical vapor deposition (MOCVD)
The BR 12, the n-type cladding layer 18, the active layer 17, the p-type cladding layer 16, the p-type DBR 11, and the phase matching layer 13 are sequentially stacked. Subsequently, the silicon dioxide (SiO ₂ ) film 2 is formed on the phase matching layer 13 by the atmospheric pressure chemical vapor deposition (CVD) or the like.
Form one. Then, circular patterns having different diameters are transferred to the resist 20 by ordinary photolithography, and the SiO ₂ film 21 is etched with an ammonium fluoride solution using the resist 20 as a mask.

Next, electrodes are deposited on the surface of the substrate having the resist mask in the order of silver and nickel, and portions other than the circular pattern are removed by lift-off with acetone.
When the remaining SiO ₂ film 21 is etched by the ammonium fluoride solution, as shown in FIG.
Two circular patterns remain. Here, silver functions as a reflective film having a high reflectance, and nickel functions as a mask for the next dry etching.

Next, using the metal film 22 as a mask, the phase matching layer 13 to the n-type DBR 12 are etched by reactive ion etching (RIE) or reactive ion beam etching (RIBE) to form a columnar structure. Subsequently, as shown in FIG. 4C, the portion removed by etching is filled with polyimide 2 to flatten it, and the metal film 22 is caught by reactive ion etching using oxygen.

Next, in the same manner as in the lift-off process described above, a gold p-type electrode 3 connected to the metal film 22 is formed, and an n-type electrode 5 in which a gold-germanium alloy and gold are laminated in this order on the back surface of the substrate is formed. After that, a hole for an optical fiber is finally formed on the back surface of the substrate by RIE or RIBE or ordinary wet etching, and the process is completed.

As described above, according to this embodiment, a plurality of semiconductor lasers having different wavelengths can be integrated on the substrate 4. In this case, the wavelength of each laser can be changed only by changing the size of the mask in photolithography. That is, the oscillation wavelengths of a plurality of lasers can be determined by one lithography, so that the manufacturing process can be facilitated and the productivity can be improved.
In addition, since the semiconductor lasers are integrated two-dimensionally, there is an advantage that the coupling with the optical fiber becomes easy even when the integration is high.

FIGS. 5A and 5B are views for explaining a schematic configuration of a multi-wavelength semiconductor laser array according to a second embodiment of the present invention, wherein FIG. 5A is a plan view, and FIG. BB '
It is sectional drawing. 1 and 2 are denoted by the same reference numerals, and detailed description thereof will be omitted. In this embodiment,
Basically, it is the same as the first embodiment, except that a current confinement structure 19 is provided. Current confinement is achieved by increasing the resistance of the active layer by proton implantation.

With such a configuration, it is possible to obtain the same effects as those of the first embodiment, as well as to suppress variations in the threshold current and the operating current between the laser elements due to the difference in diameter. And the output light intensity can be made uniform. 6A and 6B are views for explaining a schematic configuration of a multi-wavelength semiconductor laser array according to a third embodiment of the present invention, wherein FIG. 6A is a plan view, and FIG.
It is C 'sectional drawing. 1 and 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

This embodiment is an element in which lasers oscillating at 16 different wavelengths are integrated. In this embodiment, since the element area is relatively large, a lens structure is provided on the bottom surface of the fiber hole on the substrate side, so that laser oscillation light is condensed and guided to the fiber 6. Here, since the emission angle of the oscillation light emitted from the laser having a small diameter is widened due to the effect of diffraction, the laser having a small diameter is arranged at the center and the laser having a large diameter is arranged at the periphery to couple the laser 6 with the fiber 6. It was performed uniformly. The structure of other parts is the same as that of the first embodiment.

It is to be noted that the current confinement structure as in the second embodiment can be applied to this embodiment. Further, in the first to third embodiments, the thickness of each layer constituting the DBR does not necessarily have to be one-fourth the optical length of the oscillation wavelength, and β = β ₀ and three curves in FIG. Can be made thicker (to decrease β) or thinner (to increase β) so that the intersection of does not protrude from the gain band. Further, the light emitting region is not limited to the double hetero structure in which the active layer is sandwiched by the cladding layers, but can be appropriately changed to a single hetero structure, a quantum well, or another structure.

Next, another embodiment of the present invention will be described. Since a surface emitting laser can be integrated at a high density and two-dimensionally, it is suitable as a light emitting element for the purpose of optical communication, multiplexing of optical wiring, parallelization of optical operation, and the like. Semiconductor DB
A surface emitting laser having an R reflecting mirror has an excellent film thickness controllability.
Since it can be continuously formed by a crystal growth apparatus such as BE, a DBR reflector structure as designed can be easily manufactured (K. Tai et al., Appl. Phys. Lett. 55, 2473 (1989)).

As shown in FIG. 15, an element structure of the surface emitting laser is such that an n-type Al _0.3 Ga _0.7 As etch stop layer 30 is formed on an n-type GaAs substrate 301 as a layer structure.
2, Lower DBR of n-type AlAs / Al _0.1 Ga _0.9 As
Reflector layer 303, n-type Al _0.3 Ga _0.7 As carrier confinement layer 304, p-type GaAs active layer 305, p-type Al
_{0. 3} Ga _0.7 As carrier confinement layer 306, p-type Al
_{0.1 Ga 0.9 As / Al 0. 7} Ga 0.3 As upper DBR
Layer 307, Al _0.3 Ga _0.7 As phase matching layer 308, p
The GaAs contact layer 309 is formed in MBE.

The subsequent device manufacturing process is as follows. After the GsAs substrate 301 is thinly polished to about 100 μm, the Ge (40 nm) / Au (120 nm) electrode 3 is polished.
10 is deposited and contacts are made. Next, Ag (100 nm) of 15 μm diameter /
An Au (10 nm) electrode 311 is formed on the p-type GaAs contact layer 309, and a depth of 0.7 μm (to the p-type Al _0.3 Ga _0.7 As carrier confinement layer 306), an inner diameter of 15 μm, Diameter 60 μm
Is performed. In addition, the thickness 150
nm SiO ₂ insulating layer 312 and Au contact pad 3
13 is formed. A hole for extracting light is formed on the GaAs substrate 301 with an ammonia-based etchant.

With such a structure, the surface emitting laser can oscillate at room temperature. However, since the current is injected through the DBR layer, it is necessary to avoid the high resistance inherent in the semiconductor heterostructure. difficult. In other words, a large problem has been caused with respect to integration such as a large amount of current required for laser oscillation and large heat generation. To lower the resistance of the DBR layer, AlGaAs
A structure in which the composition of s is changed stepwise has been proposed (K. Tai et al., Appl. Phys. Lett. 56, 2496 (199019)).
However, there are drawbacks such as that the crystal growth becomes very complicated and the resistance cannot be sufficiently reduced.

As described above, in the conventional surface emitting laser having a DBR reflecting mirror made of a crystal, since current is injected through a DBR layer having a relatively high resistance, there are problems such as an increase in threshold current and an increase in heat generation. I was The main point of the present embodiment is that the injection of current is performed not by using a high-resistance DBR layer but by using a high mobility carrier in a semiconductor such as a two-dimensional electron gas. To this end, the active layer of the surface emitting laser is arranged near the conductive layer of the carrier so as not to lose the advantage of the high speed of the carrier, and a heterostructure is devised so that the carrier is effectively confined in the active layer. . Furthermore, in the semiconductor layer formed by continuous crystal growth, a device is devised so that a loss due to the radiative recombination of carriers in portions other than the surface emitting laser portion does not occur. In order to easily perform patterning for confining light and patterning for confining current with a single lithography process, a lithography method of inorganic resist, focused ion beam exposure, and dry etching development is used.

One example of the basic structure of a device that can be manufactured by implementing the present invention is shown in FIG.
Surface emitting laser region 101 having DBR reflector layers above and below
And a wiring region 102 having a channel layer of two-dimensional electron gas (2DEG). The layer structure of the semiconductor multilayer film is
Undoped AlA is formed on a semi-insulating GaAs substrate 103.
lower DBR 104 made of s and GaAs, n-type Al _0.3
Ga _0.7 As electron supply layer 105, undoped Al _0.3 G
a _0.7 As spacer layer 106, undoped GaAs channel / cladding layer 107, undoped InGaAs active layer 108, undoped AlAs etch stop layer 10
9, p-type GaAs cladding layer 110, undoped Al
An upper DBR reflector layer 111 made of As and GaAs and an undoped GaAs cap layer 112 (107 nm) are formed.

The undoped GaAs layer 107 serving as a 2DEG channel layer is adjacent to the undoped InGaAs active layer 108, and the lower end of the conduction band has a larger energy than that of InGaAs, so that electrons are confined in the active layer 108. Effectively done. Also,
In the wiring region, the portion up to the upper p-type GaAs cladding layer 110 is removed so that light emission recombination in the undoped GaAs channel layer hardly occurs.

A method for manufacturing an element having the basic structure shown in FIG. 10 will be described below. First, as shown in FIG. 11A, semi-insulating GaAs is formed by MBE or MO-CVD.
On the substrate 103, undoped AlAs (76.5n
m, 19 layers) / GaAs (63.4 nm, 18 layers) to form a lower DBR reflector layer 104, and furthermore, an n-type A
l _0.3 Ga _0.7 As electron supply layer 105 (121.7 n
m, n = 1 × 10 ¹⁸ cm ⁻³ ), undoped AlGaAs
Spacer layer 106 (2 nm), undoped GaAs channel / cladding layer 107 (20 nm), undoped In
_0.15 Ga _0.85 As active layer 108 (10 nm), undoped AlAs etch stop layer 109 (1.4 nm), p
Type GaAs cladding layer 110 (120.3 nm, p = 1
× 10 ¹⁸ cm ^-3 ) and undoped AlA
s (76.5 nm, 10 layers) / GaAs (63.4 n
An upper DBR reflector layer 111 composed of (m, 9 layers) and an undoped GaAs cap layer 112 (107 nm) are formed.

Then, as shown in FIG. 11B, a Si oxide mask layer 113 (400) is formed on the entire surface of the GaAs cap layer 112 by using a plasma CVD (P-CVD) method.
nm), using a focused ion beam (FIB), injecting Ga into a circular pattern having a diameter of 1 μm for a surface emitting laser of the Si oxide film 113, and reactive ion beam etching (RIBE) using CF ₄ gas. By this, the Si oxide film 113 other than the implantation region is removed. Since the etching rate of the region into which Ga is injected by the FIB is greatly reduced during the dry etching of the F-based gas, the Si oxide film 113 can be patterned as a negative resist.

Next, as shown in FIG.
P-type Ga by the RIBE method using _two gases and Ar gas.
Surface emitting laser region 10 halfway through As cladding layer 110
Other than 1 is removed by etching. Further, the p-type GaAs cladding layer 110 is completely removed by selective etching of reactive ion etching (RIE) using CCl ₂ F ₂ , and at the same time, the undoped AlAs etch stop layer 1 is removed.
At 11 the etching is stopped.

At this time, in the first etching, AlA
In order to vertically and smoothly etch a thick DBR layer composed of s / GaAs, ion etching was strengthened.
Dry etching with low selectivity and high etching rate is effective. Therefore, a Si oxide film that is resistant to Cl-based ionic etching is used as an etching mask. In the second etching, a large GaAs / AlAs etching selectivity for stopping the etching with an extremely thin AlAs layer can be obtained, and a highly reactive etching that causes less etching damage to the base remains. This is important for removing the p-type GaAs cladding layer 110.

Next, as shown in FIG. 12B, the Si oxide film mask 113 in the surface emitting laser region is removed by dry etching using F radicals, and then P-CVD.
The entire surface of the silicon nitride mask layer 114 (400
nm), Ga ions are implanted into the Si nitride film 114 in the pattern of the surface emitting laser region and the wiring region using FIB, and the Si nitride film 114 other than the implanted portion is removed by RIBE using CF ₄ gas. I do. At the time of this RIBE, a high resistance region 115 containing 2DEG is formed below the region where the Si nitride film 114 has been removed due to damage by the irradiated ions. As a result, the region through which electrons conduct is limited to the surface emitting laser region 101 and the wiring region 102.

Next, as shown in FIG. 13, after removing the Si nitride film 114 by dry etching of F radicals, an Si nitride film insulating layer 116 (100 nm) is again deposited on the entire surface by plasma CVD, and CF ₄ Deposited on the cylindrical side surface by isotropic dry etching using
By completely removing only the i-nitride film, depositing a p-type electrode 117 on the entire surface and making contact with the p-GaAs cladding layer 108, the basic structure of the integrated surface emitting device is completed.

In this embodiment, the wiring area of 2DEG is
If it is formed in a so-called quantum wire shape with a carrier confinement width of about the electron Fermi wavelength, the degree of freedom in the scattering direction of elastic scattering such as impurity scattering can be greatly reduced, so the scattering effect is greatly suppressed. can do. As a result, the mobility of electrons at low temperatures at which impurity scattering is dominant is significantly improved, and higher-speed control of carriers, that is, higher-speed device operation becomes possible. In the case where the wiring region is formed into a quantum wire, the number of injected carriers decreases. However, if a multiple quantum wire structure in which a plurality of quantum wires are arranged in parallel can be used, the number of injected carriers can be increased while maintaining the features of the quantum wire. . Furthermore, the wiring using multiple quantum wires has the effect of canceling out the universal fluctuation of the conductance characteristically appearing in the quantum wires, thereby increasing the controllability of carrier injection.

Since the 2DEG wiring region described in this embodiment has a layer structure similar to a typical HEMT structure of a GaAs / AlGaAs heterostructure, a part of the wiring region may be used as a switching element. Can,
It is possible to design a transmitting optoelectronic integrated circuit with a simple fabrication process. Further, since the semiconductor laser having a DBR can be used as a light receiving element having a wavelength filter, a receiving optoelectronic integrated circuit having a simple manufacturing process can be similarly designed.

2DEG of undoped GaAs channel layer
In order to inject electrons into the InGaAs active layer from, it is necessary to cross the potential peak due to the bending of the band, but by applying an appropriate bias voltage only to the surface emitting laser region, the electrons can be injected more efficiently. It can be carried out. Although the AlAs etch stop layer functions as a potential barrier against hole injection, the increase in resistance is negligibly small since the film thickness is as thin as several atomic layers.

In this embodiment, an example in which n-type carriers are injected by 2DEG with high mobility has been described.
Dimensional hole gas (2DHG) is also undoped GaAs
Since 2DHG can be formed at the hetero interface between the s layer and the p-type AlGaAs layer (including the undoped AlGaAs spacer layer), p-type carrier injection can be performed at a higher speed.
Wiring.

Although this embodiment includes several types of dry etching processes, it is important to select the etching conditions (apparatus, etching gas, etc.) from the viewpoint of etching damage. In other words, in the CF ₄ RIBE for selectively forming a high-resistance region in the 2DEG layer, ion species contributing to etching penetrate lightly and deeply into the substrate. Can be To etch the upper DBR layer and the like, a RIB using a mixed gas of Cl ₂ and Ar is used.
E is used, but the heavy ion species causes damage of only about 6 nm even at an ion energy of 400 eV, and hardly affects the underlying 2DEG layer. Furthermore, CC
The process of selective etching by RIE of l ₂ F ₂ is as follows.
2DE of base by etching with low ion energy
Since the p-type GaAs cladding layer can be removed without damaging the G layer, it is possible to prevent injection of p-type carriers into the wiring region. The pattern formation on the Si oxide film or the Si nitride film by the FIB Ga implantation is 30k.
It is performed by high energy ions of eV to 100 keV, but if the film thickness is about 400 nm, most of the implanted ions remain in the Si oxide film or Si nitride film and do not damage the base.

The active layer is made of InGaAs as in this embodiment.
In a surface emitting laser in which s and DBR are AlAs / GaAs and the substrate is GaAs, light can be extracted not only from the upper side but also from the substrate side. However, according to the conventional method of forming an electrode on a substrate and injecting carriers, it is necessary to form a large hole for extracting light in a substrate-side electrode, and it is difficult to perform effective carrier injection for a fine surface emitting laser. In this embodiment, effective carrier injection can be performed without any problem relating to light extraction. Therefore, an aperture structure for optical coupling with a fiber and a lens structure for spatial optical coupling can be freely formed on the substrate.

As described above, according to the present embodiment, high speed operation of the surface light emitting element utilizing the high speed of the carrier becomes possible, and reduction in power consumption and heat generation due to low resistance can be expected. Performance can be improved. Furthermore, since a high-performance integrated surface emitting device can be manufactured by a simple process, productivity can be improved.

The present invention is not limited to the above-described embodiments, but can be implemented in various modifications without departing from the scope of the invention.

[0062]

As described above, according to the present invention, a vertical cavity surface emitting semiconductor laser having distributed reflection films above and below a light emitting region is used, and the cross section of the resonator is changed to change the laser. Since the oscillation wavelength is changed, the oscillation wavelength of a plurality of lasers can be determined by one lithography process, and even when highly integrated, a multi-wavelength semiconductor laser array that can be easily coupled to an optical fiber. Can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a semiconductor laser array according to a first embodiment;

FIG. 2 is a sectional view taken along the line AA ′ of FIG. 1;

FIG. 3 is a diagram showing details of a laser cross section;

FIG. 4 shows a manufacturing process of the first embodiment element.

FIG. 5 is a diagram showing a schematic configuration of a semiconductor laser array according to a second embodiment;

FIG. 6 is a diagram showing a schematic configuration of a semiconductor laser array according to a third embodiment;

FIG. 7 is a diagram showing a relationship between an oscillation wavelength and a diameter of a waveguide;

FIG. 8 is a diagram showing a change amount of an oscillation wavelength when a diameter is changed;

FIG. 9 is a diagram showing oscillation characteristics with and without a current confinement structure;

FIG. 10 is a diagram showing a schematic configuration of an integrated surface light emitting device according to another embodiment;

FIG. 11 is a diagram showing a manufacturing process of the integrated surface-emitting element.

FIG. 12 is a diagram showing a manufacturing process of the integrated surface-emitting element.

FIG. 13 is a view showing a manufacturing process of the integrated surface-emitting element.

FIG. 14 is a diagram showing a conventional DFB laser array;

FIG. 15 is a diagram showing a schematic configuration of a conventional surface emitting element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Surface emitting laser, 2 ... Polyimide, 3 ... P-type electrode and reflection film, 4 ... Substrate, 5 ... N-type electrode, 6 ... Optical fiber, 11 ... p-type DBR (upper distributed reflection film), 12 ... n DBR (lower distributed reflection film), 13: phase matching layer, 16: p-type cladding layer (barrier layer), 17: active layer, 18: n-type cladding layer (barrier layer), 20: resist, 21: SiO ₂ film 22 metal film.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (2)

(57) [Claims] A plurality of electrically independent semiconductor light-emitting regions sandwiched between two upper and lower distributed reflection films on a substrate, wherein at least an upper distributed reflection film is divided for each light-emitting region; a plurality of semiconductor laser emitting an output light in a square line direction with respect to the substrate surface, Unlike the cross-sectional area of the substrate parallel to the plane of the light emitting region for each of the semiconductor laser, to and a predetermined operating current Each
Of each semiconductor laser to keep the optical output of the semiconductor laser constant.
A structure for confining current is provided in a part of the emission region of a semiconductor laser.
The semiconductor laser array, characterized in that only composed. 2. A current confinement structure provided in a part of the light emitting region.
Is used to implant a part of the active layer in the light emitting region with protons.
It is characterized by being formed by increasing the resistance.
The semiconductor laser array according to claim 1.