JP2001244551A - Pulsation laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To certainly cause a pulsation laser to perform pulsation operation, to facilitate its design and manufacture, and to increase the reliability and yield rate. SOLUTION: A semiconductor lamination structure 5 having a first conductivity type first clad layer 2, an active layer 3, and a second conductivity type second clad layer 4 is constituted. On the current injecting region of the structure 5, a second conductivity type electrode contact layer 6 is formed. Covering and bridging this layer 6 and the second layer 4, a first electrode 11 is attached. The first electrode 11 is brought into ohmic contact with the layer 6, and is brought into contact with the layer 4 forming Schottky barriers. Phototransistors containing these barriers SB are arranged on both outsides of the active region 3a of the active layer 3 interposing the active region region 3a between. The phototransistors are switched by irradiation with a laser beam and pulsation operation is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a pulsation laser.

[0002]

2. Description of the Related Art A pulsation laser, that is, a self-sustained pulsation laser, is suitable for use as a light source in various light sources, for example, an optical pickup of an optical disk, because it can effectively avoid return light noise.

A typical example of a conventional pulsation laser is a so-called SAL (Saturable Absorbing Layer).
And a so-called WI (Weakly Index Guide) type laser. SAL type pulsation laser
As shown in a schematic sectional view of FIG.
An n-type AlGaAs is formed on a semiconductor substrate 101 made of As.
, An AlGaAs active layer 103 having a smaller bandgap than the cladding layer, a second cladding layer 104 of p-type AlGaAs having a larger bandgap than the active layer,
4, a saturable absorption layer (SAL) 105 of AlGaAs having the same band gap as the active layer 103 and the opposing active layer 103 is formed. Also, n-type Ga
A pair of current blocking regions 106 that perform current constriction by As
These current blocking regions 1 are formed while maintaining a required interval.
6, a stripe-shaped current injection region 107 extending in a direction perpendicular to the paper of FIG. 9 is formed. A first electrode 111 serving as an anode in this example is ohmically applied over the current injection region 107 and the current blocking region 106, and
On one side, a second electrode 112 serving as a cathode electrode in this example is ohmicly adhered.

The current blocking region 106 has a thickness of, for example, 1 μm to 1.5 μm.
The leak of current to 04 is prevented.

[0005] The pulsation laser having this configuration is
By applying a required operating voltage between the first and second electrodes, a current is injected into the active layer 103 at a central portion below the current injection region 109, so that laser emission is performed. The laser light is absorbed by the saturable absorption layer 105, and carriers, that is, electrons are lifted from the ground state to the conduction band, so that the number of carriers is reduced and the laser light enters a saturable absorption state. Due to this decrease in carriers, injection of carriers into the active region decreases, and laser emission stops. When laser emission stops in this way,
Laser light absorption in the saturable absorption layer 105 is reduced,
The electrons fall to the ground state, generate photons, and increase in electrons, so that injection of electrons into the active region of the active layer becomes large, thereby causing laser emission. This phenomenon, that is, the interaction between light and carrier, causes intermittent laser emission, that is, pulsation.

Further, a WI type pulsation laser is
As shown in a schematic cross-sectional view in FIG. 10, the saturable absorption layer in FIG. 9 is not provided, and a saturable region is formed in the active layer 103. 10, parts corresponding to those in FIG. 9 are denoted by the same reference numerals, and redundant description will be omitted.
In this configuration, for example, a laser beam is absorbed by the current constriction region 106 to cause a difference in the refractive index between the central portion of the active layer 103 and both sides thereof, whereby an appropriate lateral confinement is performed in the active layer. An active region 103A for emitting laser light is formed at the same time, and saturable regions 103S are formed on both sides thereof.

[0007]

However, in the case of the above-mentioned SAL type, there is a problem in the pulsation operation at high temperature and high output, and the impurity concentration in the saturable absorption layer is relatively high. Impact, that is, changes over time and reliability. Further, in the WI type, it is necessary to set a delicate refractive index difference, so that the degree of freedom in design is small. In addition, since the gain guide-like configuration is used, quantum noise at a low output is slightly poor. There's a problem.

As described above, in both the SAL type and the WI type, the conventional general pulsation laser has a large temperature dependency because of the saturable absorption mechanism, and suppresses pulsation during high-temperature operation. If there is a problem, high accuracy is required for design and manufacturing to ensure pulsation operation with the desired characteristics, saturable absorption region is likely to be unstable, reliability, manufacturing There is a problem with the yield.

According to the present invention, a pulsation is generated by a new mechanism, and the temperature dependency is small.
The pulsation operation can be performed stably,
It is an object of the present invention to provide a pulsation laser which has high reliability, is easy to manufacture, has high yield, and can be manufactured at low cost.

[0010]

According to the pulsation laser of the present invention, a phototransistor is formed in the laser to perform a pulsation operation. That is, the pulsation laser according to the present invention has a semiconductor multilayer structure having at least a first cladding layer of the first conductivity type, an active layer, and a second cladding layer of the second conductivity type. An electrode contact layer of the second conductivity type is formed on the component of the current injection region of the semiconductor laminated structure, and the electrode contact layer and the second cladding on both sides of the electrode contact layer with the electrode contact layer interposed therebetween. A first electrode is applied across the layers. The first electrode is in ohmic contact with the electrode contact layer, is in contact with the second cladding layer by forming a Schottky barrier, and a phototransistor including the Schottky barrier sandwiches the active region of the active layer. To be arranged on both outer sides.

That is, in the present invention, a phototransistor is formed in a laser, the phototransistor is turned on by light irradiation by laser emission, and an injection current to be originally injected into a current injection region is transmitted to another portion. That is, leakage to both outer sides reduces current injection into the active region of the active layer, and stops laser emission. When the laser emission stops, the phototransistor is turned off by stopping light irradiation on the phototransistor. When the phototransistor is turned off, the injection current to the original current injection region increases, the current injection to the active region of the active layer increases, and laser emission is performed again. The intended pulsation operation is performed by repeating this phenomenon. That is, the pulsation laser according to the present invention has a gain-guided configuration, and the present invention avoids the provision of a saturable absorber and semi-forcedly pulsates the built-in phototransistor. It causes a sation.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A pulsation lay according to the present invention.
An example of the embodiment of the present invention will be described with reference to the schematic sectional view of FIG.
I will tell. In this example, an AlGaAs pulsation is used.
This is a case where a laser is configured. In this case, GaAs
A first conductivity type, for example, n-type Al_x1G
a_1-X1A first cladding layer 2 made of As, for example, GaAs
Active layer 3 of the second conductivity type, for example, p-type Al_x1 G
a_1-X1Semiconductor product having second cladding layer 4 made of As
The layer structure 5 is formed. And this semiconductor laminated structure
5, on the component of the current injection region, ie, of the active layer 3,
For example, in FIG. 1, a strike extending in a direction
On the portion opposed to the formation portion of the lip-shaped active region 5a,
2-conductivity type, for example, p-type, for example, Al_x0Ga _1-X0As for example
GaAs (x₀= 0).
It is formed in a lip shape.

The electrode contact layer 6 and the electrode
On the second cladding layer 4 on both sides of the tact layer 6
The first electrode 11 is applied over the entire surface. This first electrode 11
Represents an ohmic contact with the electrode contact layer 6.
And the Schottky barrier S is applied to the second cladding layer 4.
It is assumed that a contact for forming B is made. This second
The one electrode 11 forms, for example, Ti, Pt, and Au sequentially.
It is constituted by. At the same time, in the present invention,
Second cladding layer 4 with which first electrode 11 is in contact
And each Al composition (atomic ratio) x of contact layer 6₁And x
₀To x₁> X ₀And For example, x₁= 0.4-0.
5 and x₀= 0.

In this manner, a structure in which a Schottky barrier type phototransistor constituted by a Schottky barrier SB is arranged on both sides of the active region 3a of the active layer 3 in between. That is, the Schottky barrier SB
And the second cladding layer 4 and the first cladding layer 2 immediately below these constitute a phototransistor.

The formation portion of the Schottky barrier SB, that is, the formation portion of the phototransistor is a limited region having a required width W on both sides of the formation portion of the contact layer 6.
That is, the Schottky barrier SB is connected to the semiconductor laminated structure 5.
Are limitedly formed at positions excluding both outer edges. On the back surface of the substrate 1, a second electrode 12 is formed.

The height φ _B of the Schottky barrier SB is:
Although the injection current from the first electrode 11 is blocked and the current is condensed in the contact layer forming portion, that is, the active region 3 a of the active layer 3, the height of the barrier is reduced. The height is selected to be low enough to be turned on by the laser light from No. 3, for example, about 0.3 eV to 0.5 eV.

The pulsation laser according to the present invention has a configuration in which the above-mentioned phototransistor TR is connected in parallel with a semiconductor laser LD, as shown in an equivalent circuit diagram in FIG. In this configuration, when a required forward voltage is supplied between, for example, the anode terminal A of the first electrode 11 and the cathode terminal K of the second electrode 12, for example, the current is narrowed by the Schottky barrier SB,
The current is intensively injected into the center of the active layer 3, and the center becomes the active region 3a to emit laser light. This laser emission is absorbed by the phototransistor TR, and the Schottky barrier SB is turned on. That is, the phototransistor TR is turned on. Thus, the phototransistor T
When R is turned on, since the current confinement effect is reduced by this, the injected current spreads, since the reactive current is increased, the threshold current I _th is increased, the active area 3
The laser emission operation at a stops. When the laser emission stops, the phototransistor TR is turned off by reducing the irradiation light to the phototransistor TR. As a result, the current constriction effect becomes large, and current is intensively injected again into the component 6 of the current injection region, and current is intensively injected into the active region 3 a of the active layer 3. Light emission occurs. Pulsation is generated by repeating such operations repeatedly and continuously.

Thus, the on / off state of the phototransistor is
The pulsation is generated semi-forced, so to speak, by the switching effect, which is OFF.

In the example shown in FIG. 1, the first electrode 11 is formed on the second cladding layer 4 to have a width W and a width W.
Although the configuration is such that the formation position of the Schottky barrier SB is limited to avoid unnecessary current spreading, in this case, the width of the first electrode 11 is restricted. Since the first electrode 11 is electrically connected to wire bonding and other terminal portions, it may be desired to configure the first electrode 11 to be wide. In this case, the width W of the Schottky barrier SB is regulated by setting the insulating layer made of SiN or SiO ₂ on the cladding layer 4 of the semiconductor laminated structure 5 as shown in FIG. 7 is formed. In this case, by forming the first electrode 11 over the insulating layer 7, the first electrode 11 can be formed to be wide and the Schottky barrier SB can be limited to a predetermined width W.

Alternatively, as shown in a schematic sectional view of another example in FIG. 4, instead of the insulating layer of FIG. 2, a second conductive layer for forming a Schottky barrier higher than the Schottky barrier SB on the first electrode 11 is formed. It is possible to form a Schottky barrier control layer 8 of, for example, AlGaAs. In this case, the Schottky barrier control layer 8 may have an Al composition larger than that of the second cladding layer 4. For example, the cladding layer
Al _x1 Ga _{1 -X1} As, and the Schottky barrier control layer 8 is made of A
When l _x3 Ga _{1 -X3} As, x ₁ = 0.4 and x
₃ = 0.6.

In the above example, the second cladding layer 4
Is a single layer, but as shown in FIG. 5, a schematic cross-sectional view of one example thereof shows that the second cladding layer 4 is formed with a Schottky barrier SB of, for example, 100 nm to 20 nm.
As a configuration including the surface layer 41 having a thickness of 0 nm and the internal layer 42 disposed on the active layer side, the degree of freedom in selecting the height of the Schottky barrier by selecting, for example, the Al concentration of the surface layer 41. Can be enhanced. At this time,
The inner layer 42 is Al _x1 Ga _{1 -X1} As, and the surface layer 41 is A
_{l x2 Ga 1- X2 As (x} 2 atomic ratio), the contact layer A
When l _x0 Ga _1−X0 As, x ₁ > x ₂ > x ₀ , for example, x ₁ = 0.4 to 0.5, x ₂ = 0.2, x ₀
= 0.

In the laser having any of the structures shown in FIGS. 3 to 5, the pulsation operation is performed by the same operation as that described with reference to FIGS. That is, a pulsation laser is formed.

Next, an example of a method for producing a pulsation according to the present invention will be described with reference to FIGS. This example is also a case where an AlGaAs-based pulsation laser is formed. In this case, as shown in FIG.
A substrate of a first conductivity type, for example, n-type A
a first cladding layer 2 of l _x1 Ga _1-X1 As, an active layer 3 of, for example, GaAs, and a second conductivity type, for example, p-type A
A second cladding layer 4 of l _x1 Ga _1-X1 As and an etching stopper layer 10 thereon are further formed of, for example, M
OCVD (Metalorganic Chemical Vapor Deposition:
The semiconductor multilayer structure 5 is formed by a metal organic chemical vapor deposition method. Further, following the film formation of the semiconductor laminated structure 5, a contact layer 6 of, for example, GaAs is formed by, for example, the MOCVD method. Also in this case, the second cladding layer 4 and the Al
Although the compositions x ₁ and x ₀ satisfy x ₁ > x ₀ , the Al composition x ₃ of the etching stopper layer 10 also becomes x ₁ > x ₃
For example, 0.2. Thereafter, a mask layer 20 is finally formed on the constituent part of the current injection region of the contact layer 6. The mask layer 20 can be formed, for example, by pattern exposure and development of a photoresist layer.

Next, as shown in FIG.
Of the contact layer 6 and the stopper layer 10 thereunder are removed by using, for example, an ammonia-based etchant. In this case, the etching property of the stopper layer 10 is low because the Al concentration is selected to be higher than that of the cladding layer 4 therebelow, so that the etching is stopped when the etching property changes. Etching to a predetermined depth can be performed.

After that, as shown in FIG. 8, the contact layer 6 other than the constituent part of the current injection region is removed, and the remaining contact layer 6 and the second cladding layer 4 exposed by etching on both outer sides thereof are removed. For example, Ti,
The first electrode 11 is formed by sequentially depositing Pt and Au by, for example, vapor deposition, sputtering, or the like, and forming a desired pattern by photolithography. Also, substrate 1
The second electrode 12 is ohmicly adhered to the back surface of. In this way, a pulsation laser can be formed. In the manufacture of this pulsation laser, a plurality of lasers can be simultaneously formed on a common base 1 and divided to form a large number of pulsation lasers at the same time, or a multi-beam structure can be adopted. .

In each of the above examples, an AlGaAs pulsation laser has been described.
Any of nP-based and GaN-based configurations can be used.
For example, in an AlGaInP-based laser, the second cladding layer 4 or its inner layer 42 is formed of (Al _x1 Ga _1-X1 ).
In _0.5 P _0.5 and the surface layer 41 was (Al _x2 Ga _{1 -X2} )
In _0.5 P _0.5 and the contact layer 6 can be GaAs. In this case, the Al composition of the contact layer 6 when the x _0, and _{x 1> x 2> x 0} ,
For example, by setting x ₀ = 0, x ₁ = 0.5, and 0 <x ₂ <0.5, the same pulsation laser as described above can be formed.

For example, in a GaN-based laser, the second cladding layer 4 or its inner layer 42 is formed of (Al
_x1 Ga1 _-X1 ) N, and the surface layer 41 is ( _{Alx2Ga1 -X2} ).
N, and the contact layer 6 can be GaN.
Also in this case, the Al composition of the contact layer 6 is set to x ₀
X ₁ > x ₂ > x ₀ , for example, x = 0,
By setting x ₁ = 0.3 and 0 <x ₂ <0.3, the same pulsation laser as described above can be configured.

As described above, in the pulsation laser according to the present invention, a phototransistor is formed in the laser, and the phototransistor is turned on by light irradiation by laser emission, thereby injecting current into the active region of the active layer. The laser light emission is stopped, the laser emission stops, the light emission to the phototransistor stops, the phototransistor turns off, the current injection into the active region of the active layer increases, and the laser emission is repeated. The pulsation operation is performed.

That is, in the present invention, since the conventional formation of a saturable absorber is avoided, problems associated with the instability, low production yield, and reliability can be avoided. Improvement is also achieved, and pulsation can be stably generated even during high-temperature, high-output operation.

In the above-described example, the first conductivity type is the n-type and the second conductivity type is the p-type. However, these may be of the opposite conductivity type. Further, the present invention is not limited to the above-described structure, and can be applied to a configuration in which, for example, the active layer has a multiplex structure.

[0031]

As described above, in the pulsation laser according to the present invention, a phototransistor is formed in the laser and a pulsation generating mechanism is formed by this switching, so that the pulsation operation is semi-forced. This enables stable pulsation in a wide range of temperatures from low to high as compared with the conventional structure in which pulsation is caused by the interaction between light and delicate carriers due to saturable absorption. Further, the pulsation operation can be stably performed even in a wide range of power, that is, in a high output operation. Further, since a configuration for obtaining a subtle refractive index difference as in the WI type described above is not required, the applicable range of the laser is wide, and for example, adaptation from an index guide to a gain guide is possible.

Also, the manufacturing method does not increase the number of steps, and a more reliable pulsation can be manufactured with good yield and therefore at low cost.

As mentioned above, the pulsation laser according to the present invention has many advantages not available with conventional pulsation lasers.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an example of a pulsation laser according to the present invention.

FIG. 2 is an equivalent circuit diagram of the pulsation laser of FIG.

FIG. 3 is a schematic sectional view of another example of the pulsation laser according to the present invention.

FIG. 4 is a schematic sectional view of another example of the pulsation laser according to the present invention.

FIG. 5 is a schematic sectional view of another example of the pulsation laser according to the present invention.

FIG. 6 is a schematic cross-sectional view in one step of an example of a method of manufacturing an example of a pulsation laser according to the present invention.

FIG. 7 is a schematic cross-sectional view in one step of an example of a method of manufacturing an example of a pulsation laser according to the present invention.

FIG. 8 is a schematic cross-sectional view in one step of an example of a method of manufacturing an example of a pulsation laser according to the present invention.

FIG. 9 is a schematic sectional view of a conventional pulsation laser.

FIG. 10 is a schematic sectional view of a conventional pulsation laser.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Base, 2 ... 1st clad layer, 3 ... Active layer, 3a ... Active area, 4 ... 2nd clad layer, 5 ...
..Semiconductor laminated structure, 6 ... contact layer 7 ...
Insulating layer, 10 ... etching stopper layer, 11 ...
1st electrode, 12 ... 2nd electrode, 20 ... mask layer,
SB: Schottky barrier, LD: Laser, TR
..Phototransistor, 20... Mask, 41.
・ Surface layer, 42 ・ ・ ・ Inner layer, 101 ・ ・ ・ Base, 10
2 ... first cladding layer, 103 ... active layer, 103
A: active region, 103S: saturable absorption region, 10
4 ... second cladding layer, 105 ... saturable absorption layer,
106: current blocking region, 107: current injection region, 111: first electrode, 112: second electrode

Claims (9)

[Claims] 1. A semiconductor laminated structure having at least a first cladding layer of a first conductivity type, an active layer, and a second cladding layer of a second conductivity type. An electrode contact layer of the second conductivity type is formed on the constituent part of the implantation region, and the electrode contact layer and the second clad layer of the semiconductor multilayer structure part on both sides of the electrode contact layer with the electrode contact layer interposed therebetween. A first electrode is deposited, the first electrode is in ohmic contact with the electrode contact layer, and is in contact with the second cladding layer by forming a Schottky barrier; A pulsation laser, wherein the transistor is formed on both sides of the active region of the active layer with the active region interposed therebetween. 2. A Schottky barrier for the second cladding layer constituting the phototransistor is limited to a portion adjacent to a portion where the electrode contact layer is formed, except for both outer edges of the semiconductor laminated structure, with a required width. 2. The pulsation laser according to claim 1, wherein the pulsation laser is formed in a uniform manner. 3. The pulsation according to claim 2, wherein an insulating layer is formed outside a region where the Schottky barrier is limitedly formed, and a position where the Schottky barrier is formed is regulated. laser. 4. The method according to claim 1, wherein the cladding layer comprises a surface layer on which the Schottky barrier is formed and an inner layer disposed on the active layer side from the surface layer, and the height of the Schottky barrier is selected. The pulsation laser according to claim 1, wherein 5. A Schottky barrier control layer for forming a barrier higher than the Schottky barrier between the second electrode and the first electrode, in addition to the Schottky barrier forming portion for the second cladding layer. The pulsation laser according to claim 1, wherein 6. The pulsation laser according to claim 1, wherein the pulsation laser is AlGa.
The pulsation laser according to claim 1, wherein the pulsation laser is an As-based semiconductor laser. 7. The pulsation laser according to claim 1, wherein the pulsation laser is AlGa.
2. An InP-based semiconductor laser.
2. A pulsation laser according to 1. 8. The pulsation laser according to claim 1, wherein the pulsation laser is a GaN-based semiconductor laser. 9. A structure in which the cladding layer includes a surface layer on which the Schottky barrier is formed and an inner layer disposed on the active layer side from the surface layer, and the height of the Schottky barrier is selected by the surface layer. The Al composition ratio of the constituent material of the lower cladding layer is x
₁ (atomic ratio), the Al composition ratio of the constituent material of the upper cladding layer is x ₂ (atomic ratio), and the Al composition ratio of the constituent material of the contact layer is x ₀ (atomic ratio).
Pulsation laser of claim 1, wherein the selecting the _1> x _2> x _0.