JPH0654826B2 - Semiconductor laser manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an AlGaAs semiconductor laser manufactured using an MBE device.

(B) Conventional Technique FIGS. 3A, 3B, 3C and 3D are process explanatory diagrams showing a conventional method for manufacturing a semiconductor laser.

This semiconductor laser manufacturing method uses an MBE device,
A semiconductor laser is formed by performing MBE growth twice.

FIG. 3A shows a step of forming a first growth layer on the semiconductor substrate 1. The semiconductor substrate 1 made of N-type GaAs mounted in an MBE (Molecular Beam Epitaxy) apparatus is heated to evaporate the raw materials and impurities respectively put in the evaporation source in the form of a molecular beam, so that N-type Al _x Ga ₁ lower clad layer 21 made of _{-x As, Al x 'Ga 1} -x' active layer 22 made of As, P-type Al _x Ga _1-x As comprising the first upper cladding layer 23, N-type light of GaAs Absorption layer 24, N-type Al _x "G
An evaporation prevention layer 25 made of a _1-x ″ As is sequentially laminated on the surface of the semiconductor substrate 1 to form the first growth layer 2.

Next, FIG. 3 (B) shows a photo-etching step of forming stripe grooves in the first growth layer 2. The semiconductor substrate 1 having the first growth layer 2 formed thereon is taken out from the MBE apparatus, and the evaporation preventing layer 25 other than the portion where the stripe groove 3 is formed is covered with the photoresist 6. Using the photoresist 6 as a mask, the evaporation preventing layer 25 and the light absorbing layer 24 are etched so that the light absorbing layer 24 remains appropriately, and the stripe groove 3 having a desired width is formed.

Further, FIG. 3C shows a re-evaporation step of evaporating the remaining light absorption layer by forming the stripe groove. The semiconductor substrate (the substrate on which the first growth layer 2 has been formed) 1 from which the photoresist 6 has been removed is organically cleaned. Then, the semiconductor substrate 1 is mounted in the MBE device again. Here, the semiconductor substrate 1 is heated while applying As molecular beams to the semiconductor substrate 1 to evaporate impurities such as oxides attached to the surface of the semiconductor substrate 1 and the remaining light absorption layer 24. As a result, the light absorption layer 24 is also selectively evaporated, so that the first
The surface of the upper clad layer 23 is exposed.

FIG. 3D shows a step of forming the second growth layer 4 on the semiconductor substrate 1. On the surface of the semiconductor substrate 1 from which the impurities and the remaining light absorption layer 24 are evaporated, P-type Al _Y Ga
Second upper clad layer 41 consisting of _1-Y As and P ⁺ type GaA
The cap layer 42 made of s is sequentially laminated to form the second growth layer 4. Then, the N-type electrode 1 a is provided on the back surface of the semiconductor substrate 1, and the P-type electrode 42 a is provided on the front surface of the cap layer 42.

In the semiconductor laser thus obtained, population inversion (stimulated emission) occurs due to carrier injection, and coherent light is stimulated and emitted at the Pn junction.

(C) Problem to be Solved by the Invention In the conventional method for manufacturing a semiconductor laser, the P-type first upper cladding layer 23 and the P-type second upper cladding layer 41 are in contact with each other in the stripe groove portion. Formed to face. Therefore, when a current flows from the P-type electrode 42a side to the N-type electrode 1a side through the second growth layer 4 and the first growth layer 2, the current flows through the stripe groove 3, that is, the narrow groove portion. Therefore, the narrow stripe groove 3
The current confined by the first upper cladding layer 23
When, i.e., when the narrow stripe groove 3 is removed, a part of the current spreads laterally (parallel to the N-type electrode) in the first upper cladding layer 23, resulting in a reactive current. It has the disadvantage of increasing the threshold current. Therefore, it is difficult to manufacture a semiconductor laser having a low threshold current and a high current efficiency by the conventional method.

An object of the present invention is to solve the above problems and to provide a manufacturing method for obtaining a semiconductor laser having a low threshold current and high current efficiency.

(D) Means and Actions for Solving the Problems This semiconductor laser manufacturing method is a method for manufacturing a semiconductor laser manufactured by using an MBE device, in which a lower clad layer and an active layer are formed on the surface of a semiconductor substrate. Forming a first growth layer by sequentially stacking a first upper clad layer, an N-type or undoped layer, a light absorption layer and an evaporation prevention layer, and forming the first growth layer with an arbitrary width. A photo-etching step of forming a stripe groove having a depth that leaves a light absorbing layer; and ions of a P-type dopant are implanted into a portion of the light absorbing layer corresponding to the stripe groove to stripe the N-type or undoped layer. An ion implantation step of forming a P-type dopant ion implantation part in the groove corresponding part, and impurities and residual light absorption layer attached to the surface of the semiconductor substrate in which the stripe groove is formed. And re-evaporation step of evaporating, on a surface of a semiconductor substrate on which the light-absorbing layer is evaporated, and a step of forming a second growth layer and a second upper cladding layer and a cap layer are sequentially stacked.

In the method of manufacturing a semiconductor laser including such steps,
In the stripe groove, the N-type or undoped layer is interposed between the P-type first upper cladding layer and the P-type second upper cladding layer. Then, the P-type dopant ion implantation portion of the N-type or undoped layer is
It comes into contact with the P-type second upper cladding layer.

Therefore, when a current is passed from the P-type electrode side formed on the surface of the cap layer to the N-type electrode side formed on the back surface of the semiconductor substrate, the current flows through the stripe groove, that is, the narrow groove portion. The current confined by the narrow stripe groove is released from the confined state in the N-type or undoped layer and tries to spread laterally (parallel to the electrode) in the N-type or undoped layer. However, this layer is an N-type or undoped layer, and has a conductor pattern different from that of the P-type second upper cladding layer. Therefore, the lateral expansion is prevented. Therefore, the current flows to the P-type first upper cladding layer through the P-type ion implantation portion formed in the N-type or undoped layer, and the generation of the reactive current is significantly reduced. Therefore, the threshold current becomes low and a semiconductor laser having high current efficiency can be obtained.

(E) Example FIG. 1 (A), FIG. 1 (B), FIG. 1 (C) and FIG. 1 (D) are process explanatory views showing a method for manufacturing a semiconductor laser according to the present invention. .

In this semiconductor laser manufacturing method, an MBE apparatus (not shown) is used to form a semiconductor laser by performing MBE growth twice.

FIG. 1A shows a step of forming a first growth layer on the semiconductor substrate 1. The semiconductor substrate 1 made of N-type GaAs mounted in an MBE (Molecular Beam Epitaxy) apparatus is heated to evaporate the raw materials and impurities respectively put in the evaporation source in the form of a molecular beam, so that N-type Al _x Ga _{1 -xAs} lower clad layer 21, Al _x ′ Ga _1-x ′ As active layer 22, P-type Al _x Ga _1-x As first upper clad layer 23, and N-type or undoped layer 23a, and N type
A light absorption layer 24 made of GaAs and an evaporation prevention layer 25 made of N-type Al _x "Ga _{1 -x} " As are sequentially laminated on the surface of the semiconductor substrate 1 to form the first growth layer 2.

Next, FIG. 1 (B) shows a photo-etching step of forming a stripe groove in the first growth layer 2 and an ion implantation step which is a feature of the present invention. The semiconductor substrate 1 on which the first growth layer 2 has been formed is taken out from the MBE apparatus and covered with the evaporation preventing layer 25 photoresist 6 other than the portion where the stripe groove 3 is to be formed. Using the photoresist 6 as a mask, the evaporation preventing layer 25 and the light absorbing layer 24 are etched so that the light absorbing layer 24 is slightly left (about 1000 Å), and the stripe groove 3 having a desired width is formed.

In this state, the N-type layer (or undoped layer) 23a is exposed under the light absorption layer 24 slightly left on the bottom of the stripe groove 3. Further, in this state (a state in which the photoresist 6 is provided), ions that can serve as a P-type dopant, such as Zn ions and Be, are formed in the stripe groove 3.
Ions or Mg ions (Zn ions in the embodiment) are implanted. This implantation work consists of an ion source, an ion accelerator,
An ion implanter (not shown) including a mass separator, a beam scanning system, and a target changer is used.
That is, Zn ions generated by the ion source are accelerated by the lens system, converged, and enter the mass separator by the deflection electromagnet. Here, the ions are deflected and enter the scanning system. Then, the ions collide with the surface of the N-type layer (or undoped layer) 23a and are injected. As a result, the P-type dopant ion implantation portion 5 is formed in the portion of the N-type layer (or undoped layer) 23a corresponding to the stripe groove 3.

In this embodiment, this ion implantation process is performed twice. The implanted ions lose energy while repeatedly colliding with the atoms of the N-type layer 23a and stop. Therefore, the depth at which the ions stop differs depending on the collision direction of the ions with the crystal plane. Although there is a possibility that a predetermined concentration distribution may not be obtained in the depth direction in one implantation operation, in the present embodiment, the ion implantation operation is performed twice (broken line, broken line in FIG. 2), The ion concentration in the depth direction is designed to have a predetermined distribution [solid line in FIG. 2].

Further, FIG. 1 (C) shows a re-evaporation step of evaporating the remaining light absorption layer by forming the stripe groove 3. The semiconductor substrate (the substrate on which the first growth layer 2 has been formed) 1 from which the photoresist 6 has been removed is organically cleaned. Then, the semiconductor substrate 1 is mounted in the MBE device again. Here, the semiconductor substrate 1 is heated while applying As molecular beams to the semiconductor substrate 1 to evaporate impurities such as oxides and the like remaining on the surface of the semiconductor substrate 1 and the remaining light absorption layer. This allows
The surface of the P-type dopant ion implantation portion 5 is exposed at the bottom of the stripe groove 3.

FIG. 1D shows a step of forming the second growth layer 4 on the semiconductor substrate 1. On the surface of the semiconductor substrate 1 from which the impurities and the remaining light absorption layer 24 are evaporated, P-type Al _Y Ga
Second upper clad layer 41 consisting of _1-Y As and P ⁺ type GaA
The cap layer 42 made of s is sequentially laminated to form the second growth layer 4. Then, the N-type electrode 1 a is provided on the back surface of the semiconductor substrate 1, and the P-type electrode 42 a is provided on the front surface of the cap layer 42.

The semiconductor laser obtained by such a manufacturing method,
In the stripe groove, the P-type first upper cladding layer 2
3 and the P-type second upper clad layer 41, the N-type layer (or undoped layer) 23a is interposed. Then, the P-type dopant ion-implanted portion 5 of the N-type layer 23a comes into contact with the P-type second upper cladding layer 41.

Thereby, from the P-type electrode 42a side to the N-type electrode 1a side,
That is, when a current is passed in the vertical direction, the current flows through the stripe groove 3, that is, the narrow groove portion. The current confined by the narrow stripe groove 3 escapes from the confined state in the N-type layer (or undoped layer) 23a and is laterally (electrode 1) in the N-type layer (undoped layer) 23a.
a, 42a). However, this layer 23a is an N-type or undoped layer, and has a conductor pattern different from that of the P-type second upper cladding layer 41. Therefore, the lateral expansion is prevented. Therefore, the current flows through the P-type ion implantation portion 5 formed in the N-type layer (undoped layer) 23a to the P-type first upper cladding layer 23, and the generation of the reactive current is significantly reduced. To be done. Therefore, a semiconductor laser having a low threshold current and a high current efficiency can be obtained.

(F) Effects of the Invention As described above, in the semiconductor laser manufacturing method of the present invention,
An N-type or undoped layer is provided on the first upper cladding layer, and ions capable of becoming P-type dopants are implanted into the portions of the N-type or undoped layer corresponding to the stripe grooves to form P-type dopant ion implantation portions. Therefore, a part of the current confined by the stripe groove is
The mold layer prevents lateral expansion and allows smooth flow to the first upper cladding layer through the P-type dopant ion implant. Therefore, this manufacturing method has an excellent effect that the object of the invention is achieved, such that a reactive current is significantly reduced and a semiconductor laser having a low threshold current is obtained.

[Brief description of drawings]

1 (A), 1 (B), 1 (C) and 1 (D) are explanatory views showing the manufacturing process of the semiconductor laser according to the embodiment, and FIG. 1 (A) is FIG. 1 (B) is an explanatory view of forming a first growth layer, FIG. 1 (B) is an explanatory view of forming a stripe groove and a P-type dopant ion implantation portion, and FIG. FIG. 1 (D) is an explanatory diagram for forming the second growth layer, FIG. 2 is an explanatory diagram showing the relationship between the depth and the concentration of the ion implantation performed twice, FIG. 3 (A),
3 (B), 3 (C), and 3 (D) are explanatory views showing a manufacturing process of a conventional semiconductor laser, and FIG. 3 (A) forms a first growth layer. Explanatory diagram, FIG. 3 (B)
Is an explanatory view showing a photo-etching step, FIG. 3 (C) is an explanatory view showing a re-evaporation step, and FIG. 3 (D) is an explanatory view for forming a second growth layer. 1: semiconductor substrate, 2: first growth layer, 3: stripe groove, 4: second growth layer, 5: P-type dopant ion implantation part, 23: first upper cladding layer, 23a: N-type layer ( Or undoped layer).

Claims (1)

[Claims] 1. A method of manufacturing a semiconductor laser manufactured by using an MBE apparatus, comprising: a lower clad layer, an active layer, a first upper clad layer, an N-type or undoped layer, and an optical layer on a surface of a semiconductor substrate. A step of sequentially stacking an absorption layer and an evaporation prevention layer to form a first growth layer, and forming a stripe groove having a depth such that the light absorption layer is left in the first growth layer with an arbitrary width Photo-etching step, and ion implantation for implanting ions capable of becoming a P-type dopant into the stripe groove corresponding portion of the light absorption layer, and forming a P-type dopant ion implantation portion in the stripe groove corresponding portion of the N-type or undoped layer. A step of re-evaporating the impurities adhering to the surface of the semiconductor substrate having the stripe groove and the remaining light absorption layer, and a semi-evaporation step of evaporating the light absorption layer. On the surface of the body substrate, a semiconductor laser manufacturing method comprising a step of forming a second growth layer and a second upper cladding layer and a cap layer are sequentially stacked.