JPS63205982A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a laser whose active layer is narrow, whose oscillation mode is stable and whose threshold electric current is low by a method wherein an inverted-mesa-shaped part is formed by using a first etching solution and, in succession, a vertical-shaped part and a forward-mesa-shaped part are formed by using a second etching solution. CONSTITUTION:A p-type InP clad layer 12, an InGaAsP active layer 13 and an n-type InP clad layer 14 are formed on a p-type InP substrate 11. A stripe-shaped SiO2 film 23 to be used for a mask is formed on the layer 14; an etching process is executed up to the clad layer 12 over the active layer 13 by using a solution of Br2-CH3OH as a first etching solution so as to form an inverted-mesa-shaped part 20; then, another etching process is executed up to an intermediary part of the substrate 11 by using another solution of hydrochloric acid as a second etching solution so as to form a vertical-shaped part 21 and a forward-mesa- shaped part 22. Then, a p-type buried layer 15, an n-type buried layer 16 and a p-type buried layer 17 are formed in succession at the circumference of these mesa stripes. If the etching process is executed in such a way that the active layer 13 is situated near the part connecting the inverted-mesa-shaped part 20 to the vertical-shaped part 12 the width W of the active layer can be narrowed. By this setup, it is possible to stabilize an oscillation mode of a laser beam and to lower a threshold electric current while a high output is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor laser, and more particularly to a method for manufacturing a buried structure semiconductor laser using a p-type semiconductor as a substrate.

[Prior Art] In recent years, various semiconductor lasers have been developed for applications such as light sources in optical communications.
A semiconductor laser with a buried structure using a molded semiconductor as a substrate has been developed.

FIG. 6 is a cross-sectional view of a semiconductor laser using n-type 1nP as a p-type semiconductor substrate. In other words, 1 in the figure is n-type 1
On this n-type 1nP substrate 1, there is also a cladding layer 2 of n-type 1nP and an active layer 3 made of InGaAsP. An n-type 1nP (7) cladding layer 4 is laminated. And laminated cladding! 2. Active layer 3.
Clad l! 14 is surrounded by an n-type 1nP buried layer 5 and a p-type 1
It is covered with an nP buried layer 6. And electrodes 7 on both sides,
8 is installed.

A method for manufacturing a semiconductor laser having such a structure is to form a p-type InP cladding 12 on an n-type 1nP substrate 1 by epitaxial growth, as described in, for example, Japanese Patent Laid-Open No. 57-206082. N-type 1nP cladding! An active layer 3 of ln Ga As P is grown roughly on top of the active layer 13 by the same epitaxial growth method.
A cladding I4 of n-type InP is formed thereon by epitaxial growth. After that, this n-type 1nP cladding layer 4
An insulating layer of SiO2 is formed at the stripe forming pattern position, and using this insulating layer as a mask, the epitaxially grown layer is etched in the (110) direction into an inverted mesa shape until it reaches the ρ-type 1nP substrate 1. Thereafter, an n-type InP buried layer 5 is epitaxially grown on the mesa-etched portion, and an n-type 1nPjl buried layer 6 is epitaxially grown on this n-type InP buried layer 115. Thereafter, the insulating layer of SiO2 is removed and electrodes 7 and 8 are deposited on both sides.

In this case, the n-type 1nPM which becomes the current limiting layer! Including layer 5 and p
By locating the pn junction 9 with the W1nP buried layer 6 below the active layer 3, the leakage current shown by the dotted line in the figure that does not pass through the active layer 113 is transferred to the p-type I with high resistivity.
Since it passes through n PI6, its value is reduced, and a semiconductor laser with high efficiency and high output can be realized.

[Problems to be solved by the invention] However, with the above manufacturing method! IJ built 6th
The semiconductor laser shown in the figure still has the following problems. That is, in order to obtain a stable laser beam and a low threshold current in a semiconductor laser, the width W of the active layer 3 is made as narrow as possible so that light is emitted in a single oscillation mode in the lateral direction. It is necessary to control. However, in the semiconductor laser having the structure shown in FIG. 6, the width W of the active layer 3 is always larger than the width d of the constriction of the inverted mesa structure. Therefore, in order to narrow the width W of the active layer 3, it is necessary to make the width d of the constriction part as narrow as possible. However, if the width d of the constriction is narrowed, the current path shown by the solid line becomes narrower, and the resistance in the vertical direction increases rapidly, causing heat generation, resulting in the problem that high output cannot be obtained. For example, depending on the required wavelength of the laser beam, there may be cases where it is desirable to control the width W of the active layer 3 to 2- or less, but in the semiconductor laser of FIG. 6 manufactured by the above-mentioned manufacturing method, The width W of active 13 is 2-
If it is less than 2, it is necessary to further narrow the width d of the constriction, so as a practical matter, it is very difficult to reduce the width of the active layer 3 to 2- or less.

Note that it is possible to move the active layer 3 closer to the constriction, but if the active layer 3 and the constriction are brought too close together, problems may arise in relation to dimensional accuracy in the etching process and the epitaxial growth process of the buried layer. There is a problem that the yield of manufactured products decreases due to the high number of non-defective products.

The present invention was made in view of these circumstances, and
The purpose of this is to reduce the width of the active layer by etching it vertically to eliminate the constriction, and to use the same p-type layer as the substrate as the first buried layer to reduce the series resistance. An object of the present invention is to provide a method for manufacturing a semiconductor laser that makes it possible to stabilize the oscillation mode of a laser beam and lower the threshold current while maintaining high output.

[Means for Solving the Problems] The method for manufacturing a semiconductor laser of the present invention includes forming a multilayer structure wafer in which semiconductor layers including at least an InGaAsP active layer are laminated on a p-type semiconductor substrate. 1st
Epitaxial growth process: Forming a band-shaped insulating film on the surface of a multilayer film structure wafer, making absolutely no difference! A first etching step in which the multilayer film structure wafer on which A is formed is etched into an inverted mesa shape with a first etching solution until it reaches the active layer; a second etching solution is used to form a vertical and forward mesa shape below the active layer; a second etching step of etching into a p-type first etching shape; The second epitaxial growth step includes a second epitaxial growth step of forming a buried layer, a second n-type buried layer, and a third p-type buried layer in this order.

[Function] With such a semiconductor laser manufacturing method, the multilayer film structure wafer created in the first epitaxial growth process is etched into an inverted mesa shape in the first etching process until it reaches the active layer, and then the multilayer structure wafer is etched in the first etching process until it reaches the active layer. In the second etching step, the portion below the active layer is etched into a vertical shape and a forward mesa shape. As a result, the multilayer structure wafer is etched into a mesa stripe in which an inverted mesa shape, a vertical mesa shape, and a forward mesa shape are successive from above. Then, buried layers are formed in this mesa stripe in pn-p order. As a result, the conventional constricted portion is eliminated, and the width of the active layer can be made approximately equal to the width of the vertical portion. Furthermore, the series resistance below the active layer can be reduced.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of a semiconductor laser manufactured by the semiconductor laser manufacturing method of the example. As shown in the figure, n-type 1n
On the P substrate 11, there is also an n-type 1nP cladding layer 12. I
An active layer 113 made of nGaAsP and cladding 8!14 made of n-type InP are laminated. Laminated cladding layer 12. Active 113° clad! 114 is surrounded by p-type In
P buried 1l115 and n type 1nP buried 1116 and p type In
It is covered with a P buried layer 17. And electrodes 18 on both sides
．． 19 is installed.

In such a structure, clad! 114 and active layer 1
3 to form an inverted mesa-shaped portion 20, and the cladding layer 12 and p
A vertical portion 21 is formed with the upper end of the In type PM board 11, and a forward mesa portion 22 is formed with the upper portion of the n-type 1nP substrate.

Next, a method for manufacturing the semiconductor laser shown in FIG. 1 will be explained using FIG. 2.

First, as shown in FIG. 2(a), Zn is made into one impurity (carrier concentration 5×10ca
) plane with a thickness of 2.0− with Zn as an impurity (carrier concentration 2XIOtx”)
p-type InP cladding 112. The active layer 13°3n of n-type 1 n + - x G axA S t-1/p V with a thickness of 0.1- with Zn as an impurity (carrier concentration 2x10 α°3) as an impurity (carrier concentration 7x10a II
-3) An n-type InP cladding layer 14 having a thickness of 2.0 mm is sequentially grown to each of the above dimensions by a normal liquid phase epitaxial growth method. Then, a multilayer film structure wafer is obtained. However, 0≦x≦0.47.0≦y≦1.

Next, as shown in FIG. 2(b), insulating! ! As 23, silicon oxide (Si
02) or silicon nitride (Si3N4)
Form into a strip. After that, as shown in Figure 2 (C),
Brome-methanol solution (Sr
2-CH30H) with activity exceeding 1113 and slightly p
Type! Etching is performed until the nP cladding layer 12 is reached, and an inverted mesa-shaped portion 20 ((111) A plane) is formed.

Next, as shown in FIG. 2(d), a second etching agent Toshite salt MFB solution (HCI: H20-4: 1)
For example, for about 35 seconds at room temperature, the n-type 1nP substrate 1
Etch to the middle position of 1. Then, as shown in the figure, a vertical portion 21 ((01〒) plane) and a forward mesa portion 22 ((
111) 8 sides) are formed.

Finally, from top to bottom, the inverted mesa-shaped portion 20° and the vertical-shaped portion 21. A mesa stripe with continuous mesa-shaped portions 22 is obtained. Note that the height of the vertical portion 21 is approximately 2.0 mm.

Next, as shown in FIG. 2(e), in order to bury the periphery of the mesa stripe, a first burying layer with a supersaturation temperature of 1.
7n as an impurity (carrier concentration 2X10ffi°) at 2℃
3) An n-type 1nP buried layer 115 is grown by epitaxial growth. In this case, the upper end of the n-type 1nP buried portion 115 is positioned slightly above the middle portion of the vertical portion 21 of the mesa stripe. Next is this first embedding! ! Next to 15, Sn is added as an impurity (carrier concentration l
An n-type TnP buried layer 16 of x10"c°3) is grown by a two-phase melt method. In this case, the upper end of the n-type InP buried layer 16 is placed directly below the active layer 13 of the vertical portion 21. Finally, as a third buried layer, Zn is added as an impurity (carrier concentration 2
p-type InP buried layer 1 with
7 is grown to the height of the insulation 823 at a supersaturation temperature of 12°C.

Thereafter, as shown in FIG. 2(f), the insulating layer 23 is removed and an n-type 1nP cladding [114 and p-type 1nP buried! ! Au-Ge-Ni is vapor-deposited on the surface of the p-type 1nP substrate 17 to form an n-side electrode 18, and Au-Ge-Ni is deposited on the back surface of the p-type 1nP substrate 11.
-Zn is deposited to form the n-side electrode 19. Thus, a semiconductor laser having the structure shown in Section 1 is obtained.

Next, when a voltage is applied between the electrodes 18 and 19 of the semiconductor laser manufactured by such a manufacturing method, the current flows from the p-type 1nP substrate 11 to the mesa-shaped product 22. It passes through the vertically shaped portion 21 and flows into the active layer 13 . In addition to the current shown by the solid line, as shown by the dashed-dotted line arrow in the figure, pPJ! Current through the lnP implant 1115 also flows into the active layer. Therefore, the active layer 13 is excited by these currents.

In this case, the width W of the active layer 13 is approximately equal to the width W of the vertical shaped portion 21. That is, the dimensional relationship between the width W of the active layer 13 and the width W of the vertical portion 21 is the width W of the active layer 3 and the width d of the constriction portion of the conventional semiconductor laser shown in FIG.
The dimensional relationship between Therefore, even if the width W of the active layer 13 is narrowed, since there is no width d of the constriction narrower than this width W, the width of the current path is not limited, and the series resistance increases significantly. Never. In addition, since current also flows through the p-type 1nP buried M15, the series resistance further decreases. the result,
By narrowing the width W of the active layer 13 while maintaining high output, it becomes possible to stabilize the oscillation mode of the laser beam and lower the threshold current.

3 and 4 are characteristic diagrams of the semiconductor laser having the structure of the embodiment shown in FIG. 1, and are shown in comparison with the semiconductor laser having the conventional structure shown in FIG. 6. However, the width W of the active layer 113.3 of the semiconductor laser of the example structure and the conventional structure is both 1.
．． 5tI! ! The case where t is shown is shown. In this case, the width W of the vertical shaped portion 21 in the example structure is 1.5. In contrast, the width d of the constriction in the conventional structure is 0.5 mm. As is clear from FIG. 3, in the example structure, since there is no constriction, the vertical resistance is small, so the voltage rise is small with respect to the current increase, and the voltage characteristics are excellent. It can be understood.

Furthermore, it can be seen from FIG. 4 that the output of the laser beam can be increased for the same 'R flow value.

Furthermore, since the width W of the vertically shaped portion 21 and the width W of the active layer 13 are approximately the same dimension, when obtaining the same active layer width W, the width W of the active layer 13 can be controlled in accordance with the conventional structure shown in FIG. The width Wi of the active layer 3 can be easily controlled during manufacturing compared to the width Wi of the active layer 3 shown in FIG. Further, the minimum width to be controlled during the etching process is the width d of the constriction in the conventional structure shown in FIG. 6, whereas it is the width W of the active layer 13 in this embodiment. Therefore, if the minimum width that can be controlled is restricted by etching accuracy, the active width ~1 can be set narrower than in the conventional structure.

Furthermore, as shown in FIG. 5(a), since the forward mesa-shaped portion 22 is formed by etching so that the (111) 8 plane is exposed, the p-type 1nP buried layer 15 is grown epitaxially at a supersaturation temperature of 12°C. In this case, crystal growth occurs smoothly. As a result, each embedment in the vicinity of the forward mesa-shaped portion 22 and the vertical-shaped group portion 21! ! The dimensional accuracy of 15.16 can be greatly improved.

Incidentally, if the structure is made up of only vertical portions without forming a mesa-shaped portion as shown in FIG. The crystals do not grow smoothly, and breaks often occur at the interface.

In addition, a mesa stripe is formed by the inverted mesa shape portion 20, the vertical shape portion 21 having the (011) plane, and the forward mesa shape portion 22 having the <111)8 plane, and the active 1! ! 13
Since it is located directly above the connection part with the vertical shape part 21 in the inverted mesa shape part 2o, n-type 1nP is buried by using the epitaxial growth method using the two-phase melt method!
! It is easy to stop the tip of the active layer 13 directly below the active layer 13. Therefore, n-type 1nP embedded W! Since the boundary pn junction between the active layer 16 and the p-type 1nP buried layer 17 can be formed directly under the active layer 13, leakage current can be further reduced.

[Effects of the Invention] As explained above, according to the method of manufacturing a semiconductor laser of the present invention, since etching is performed in a vertical shape so as to eliminate the constriction, the width of the active layer can be narrowed. Furthermore, since the first buried layer is of the same type as the substrate, it is possible to stabilize the initiation mode of the laser beam and lower the threshold current while maintaining high output. Further, since the lower part of the vertical shape is etched into a mesa shape, the dimensional accuracy of the buried layer can be improved, and the yield of the product can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a semiconductor laser manufactured by a semiconductor laser manufacturing method according to an embodiment of the present invention, FIG. 2 is a diagram showing each manufacturing process of the manufacturing method of the embodiment, and FIGS. Figure 4 is a characteristic diagram showing the effects of the manufacturing method of the example, Figure 5 is a diagram for explaining the dimensional accuracy of the manufacturing method of the example, and Figure 6 is a cross section of a semiconductor laser manufactured by the conventional manufacturing method. It is a diagram. 11 - n-type 1nP substrate, 12-n-type 1nP cladding layer, 13... active layer, 14... n-type 1nP cladding layer, 15... p-type 1nP buried layer, 16...n Type I
nP buried layer, 17-D type 1nP buried layer, 18°19...
- Electrode, 2o... Inverted mesa shape part, 21... Vertical shape part, 22... Forward mesa shape part, 23... Insulating layer, W.
...Active layer width, d...Width of the constriction. Applicant's agent Patent attorney Takehiko Suzue (a) (b)
(c) (d) (e)
(f) 19 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] a first epitaxial growth step of forming a multilayer structure wafer in which semiconductor layers including at least an InGaAsP active layer are laminated on a p-type semiconductor substrate; forming an insulating film in a strip shape on the surface of the multilayer structure wafer; a first etching step of etching the wafer with a multilayer film structure formed thereon in an inverted mesa shape until it reaches the active layer using a first etching solution; a second etching step of etching into a mesa shape; Manufacturing a semiconductor laser comprising a second epitaxial growth step of burying a first buried layer, an n-type second buried layer, and a p-type third buried layer in this order. Method.