JPH04105383A - Manufacture of optical semiconductor element - Google Patents

Abstract

PURPOSE:To make it possible to obtain a semiconductor optical integrated element with comparatively ease and with good controllability by a method wherein a dielectric thin film is formed on the flat surface of a semiconductor substrate and thereafter, the thin film is processed into the form of parallel two stripes, a crystal growth is performed selectively and a semiconductor layer, which is grown at the region pinched between the stripes, is used as an active layer, an optical waveguide or the like. CONSTITUTION:An SiO2 film 21 is deposited on the surface of an n-type InP substrate 1, parallel two stripes are formed and an Si-doped n-type InP clad layer 2, an InGaAsP active layer 3 and a Zn-doped p-type InP clad layer 4 are selectively grown. Then, the film 21 is once removed, an SiO2 film 21 is again formed on the whole surface, is formed in such a way as to cover an active region only and the unnecessary layers 4 and 3 are removed. After that, a p-type InP layer 5 is grown on the whole surface and thereafter, a p-type InP layer 6 and a p-type InGaAs cap layer 7 are selectively grown only on the region over the active region using again an SiO2 film and a P side pad electrode is formed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method of manufacturing an optical semiconductor element such as a semiconductor laser or an optical waveguide, or an integrated optical semiconductor element, which is used in optical communication, optical information processing, etc. .

[Conventional technology]

Optical semiconductor devices used for optical communication and optical information processing are required to have even higher performance and higher functionality. To this end, it is important not only to improve the performance and functionality of individual elements such as semiconductor lasers and photodiodes, but also to integrate these elements by combining them. Semiconductor photonic integrated devices (SPICs) are created by integrating various elements.
When manufacturing integrated circuits, it is important to consider how to arrange each element on a semiconductor substrate.
Also, it is important how to fabricate the structure as designed.

As a conventional example of a 5PIC, FIG. 9 shows a structure in which two semiconductor laser (LD) elements, a gold wave device, and an optical waveguide are integrated. Figure 9(a) is a plan view showing the outline of 5PIC, Figure 9(b)
) is a perspective view showing the structure of 5PIC. The active layer 3 is present only in the laser region, and the kite layer 10 is present throughout the laser region and the waveguide region. As an example, when InGaAsP with a wavelength of 1.55 and a film composition of m is used for the active layer 3,
The kite layer 10 has an InGaAsP composition with a wavelength of 1.3 μm.
is used. In order to pass current only to the laser region and to provide electrical insulation between the two laser elements, high resistance InP1 was used.
A high-resistance buried structure is used, and mesa etching is used.

The manufacturing process of this 5PIC will be described. Metal organic vapor phase epitaxy (MOVPE) is generally used for crystal growth. First, after growing an n-InGAsP guide layer 10, an InGaAsP active layer 3, and a p-InP cladding layer 4 on an n-InP substrate 1, the p-InP in the waveguide region is grown using the Si02 film as a selective mask. Cladding layer 4, InGa
The AsP active layer 3 is removed, and an InGaAsP guide layer and a p-InP cladding layer (not shown in the figure) are selectively grown. Next, mesa etching is performed using 5iO211 as a mask to form a Fe-topped high-resistance TnP layer 13. After removing S i 02 M, further
p~InP Cra-Sotho layer 5 and p"-1nGa on the entire surface
An As cap layer 7 is grown.

After forming insulating grooves between the laser region and the waveguide region and between the two laser elements by etching, a 5i02 film 21 is deposited on the entire surface, and a window is opened in the upper part of the laser region to form a p-side groove. A pass electrode 32 and an n-side electrode 33 are formed on the substrate side to complete the process. In this example, the oscillation wavelengths of the two laser elements cannot be controlled, but the distributed feedback (DF)
With the B) structure, a multi-wavelength light source can be obtained by changing the grating pitch or creating a multi-electrode structure.

[Problem to be solved by the invention]

In producing such a 5PIC, it is important to precisely control the layer structure forming the waveguide.

Although the layer thickness can be sufficiently controlled using a vapor phase growth method such as MOVPE, the waveguide width has conventionally been sublimated by mesa etching using a mask such as 5i02.
There were problems such as insufficient controllability due to side etching.

For example, the manufacturing process of a general buried structure semiconductor laser is shown in FIG.
nP cladding layer 2, r nGaAsP active layer 3, p-I
After growing the nP cladding layer 4 (FIG. 3(a)), the Si
○ Patterning the film 21 to a width of 2 μm (Figure 3(b))
, perform mesa etching (Fig. 3(C)). and p
-InP buried layer 8 and n-InP buried layer 9 are buried and grown (FIG. 3(d)), and finally p-In9 layer 5 and P"-In GaAs cap layer 7 are grown over the entire surface (FIG. 3(d)). e)). Fig. 4 shows the manufacturing process of a conventional buried ridge structure semiconductor laser. First, a double hetero (DH) structure in which the active layer 3 is sandwiched between the ground layers 2 and 4 is grown. After FIG. 4(a)), the striped SiO2 film 21 is completely etched (FIG. 4(b)), and after mesa etching (FIG. 4(C)), a cladding layer 5 and a cap layer 7 are grown on the entire surface. In FIG. 4(d)), a high resistance region 31 into which protons are implanted is formed around the active layer to constrict the current (FIG. 4(e)).

In these mesa etchings, the S i 02 film 21
Even if the width of the active layer is exactly 2 μm, the active layer width will vary due to variations in the mesa structure and side etching during active layer etching. Particularly in processes using large diameter wafers such as 2-inch substrates, variations within the wafer surface become large. Variations in the width of the active layer and waveguide affect device characteristics such as threshold current, oscillation wavelength, and beam pattern, which not only reduces device yield but also causes problems such as difficulty in achieving designed operation. There was a need for improvement.

[Means to solve the problem]

The method for manufacturing optical semiconductor devices to solve the above problems is to form a dielectric thin film such as SiO□ on a flat semiconductor surface and then process it into two parallel stripes to selectively grow crystals. This method of manufacturing an optical semiconductor device is characterized in that the semiconductor layer grown in the region sandwiched between the stripes is used as an active region, an optical waveguide, or the like.

[Effect]

The selective growth on a flat substrate, which is the basis of the present invention, is explained in the first part.
As shown in the figure. As shown in FIG. 1(a), a thin film 21 for selective growth is formed on a (100) oriented semiconductor substrate 1, and
When the thin film 21 is selectively removed in stripes in the <1> and <011> directions and a DH tank structure is grown by MOVPE, the side surfaces of the grown layer become <0 as shown in FIG. 1(b).
Along the 11> stripe, the (111) A side is also <
Along the <011> direction, a <111)B plane is formed.

Further, the surface of each grown layer forms a (100) plane, and the interface is also very flat. The composition of the mixed crystal is also uniform within the plane unless the stripe width of the thin film is extremely wide, and can be sufficiently applied to optical semiconductor elements and active layers and waveguide layers of 5PIC. Furthermore, since the side surfaces are (111) planes, if the patterning of the thin film 21 is precise, the controllability of the growth layer width will be very good.

Furthermore, in this selective growth, the thickness of the grown layer can be changed by changing the stripe width of the thin film. FIG. 7 shows an example of the results of measuring the relationship between stripe width and growth rate. The wider the stripe width, the higher the growth rate. This is because the amount of the growth layer that migrates from the thin film and reaches the semiconductor surface increases. This makes it possible to control the thickness of the selectively grown layer. By selectively growing a quantum well structure and changing the well layer thickness, it becomes possible to locally change the equivalent refractive index and emission energy of the quantum well structure, increasing the degree of freedom in 5PIC production.

〔Example〕

First, the results of fabricating the conventional buried ridge structure semiconductor laser shown in FIG. 4 using the present invention will be described. FIG. 2 shows the manufacturing process. (100
) orientation of the n-InP substrate using the CVD method.
An i02 film 21 (thickness of about 2,000 layers) was deposited, and two stripes with a width of 5 μm and a gap of 2 μm were formed using a photolithography method (FIG. 2(a)). Then, by low pressure MOVPE method, Si-doped n-nP cladding layer 2 (layer thickness 1000λ, carrier concentration 1×10”c
m' ), InGaAs P active layer 3 (1,55
μm composition, layer thickness 800 layers) - Zn-doped pInP cladding layer 4 (layer thickness 500 layers, carrier concentration 5 x 1017 CI
laL〉All selective growth (Fig. 2(b)). Layer thickness is Si
This is the value in the active region sandwiched between the O□ films 21, and the layer thickness was constant within this region. Next, all 2 of the Si○2 film 21
Once removed, a 5i02 film 21 is again formed on the entire surface.
It was formed so as to cover only the active region (FIG. 2(C)). Next, HC1 + H, PO4 mixed liquid, and H2s○4 + H2
Remove unnecessary InP cladding layer 4 and InGaAsP active layer 3 using O2 + H20 mixed solution (see Figure 2).
d)). After that, as shown in FIG. 2(e), a p-InP layer 5 (layer thickness 0.5 μm, carrier concentration 5×1
0'7cm'), then a p-InP layer 6 is grown only in a 15μm wide region above the active layer using the SiC2 film again.
(layer thickness: 1 μm, carrier concentration: 5 × 10 17 CIII) and a pInGaAs cap layer 7 (layer thickness: 0.3 tt-ram, carrier concentration: I × 10 cm) to form a p-side pad electrode. completed the laser.

Note that, as shown in FIG. 2(f), a current confinement structure using a proton implantation region 31 similar to the conventional example shown in FIG. 4 may be used.

When this semiconductor laser was evaluated with a cavity length of 300 ttm, the threshold current was an average of 12.3 mA with a standard deviation of 0.4
mA, slope efficiency average 0.21W/A, standard change 0
．． It was 05W/A. The active layer width is 1.83 μm on average.
The standard deviation was 0.12 μm. For comparison, as shown in Figure 4, the DH tank structure was first grown on the entire surface, and then the HC1+
H3PO4 mixture and H2SO4+H2O2+H20
InP cladding layer and InGaAsP using mixed solution
The active layer is selectively mesa-etched, and then the p-InP layer is formed on the entire surface, and then the p-InP layer is etched on the entire surface as in the embodiment of the present invention.
A semiconductor laser fabricated by selectively growing a P layer and a p-InGaAs cap layer was also evaluated. As a result, the threshold current was 12.1 mA on average, standard deviation 1.8 mA, efficiency was 0.18 W/A on average, standard deviation 0.09 W7'A, and active layer width was 162 μm on average, standard deviation 0. It was 25 μm. From this result, the semiconductor laser according to Yokomichi, in which the active layer of the present invention is selectively grown, can be obtained. It was confirmed that compared to the conventional structure in which the active layer is mesa-etched, the active layer width can be better controlled and the characteristics vary less. This method can be used for MOVP, which allows uniform growth over a large area.
By applying using E-growth, high yield,
It also becomes possible to manufacture low-cost semiconductor lasers. Although the active layer width was somewhat widened, the far-field pattern was unimodal, and the half-width was also standard at 32° in the direction perpendicular to the active layer and 28° in the parallel direction. By controlling the patterning width of SiO2 and the layer thickness of the n-InP layer, it is possible to further narrow the active layer width.

Next, as a second example, we will discuss the results of applying a distributed feedback (DFB) semiconductor laser having a multi-quantum well (MQW> structure active layer) and an electroabsorption semiconductor optical modulator to a 5PIC integrated into a monolink. Describe these 5 PIs.
C uses a modulator to oscillate and modulate the light generated by a semiconductor laser, and the light is emitted from the modulator side end facet. 〉It has the feature of being narrow,
Research and development is underway as a next-generation optical communication device. Conventionally, the active layer in the laser region (wavelength 1,55 μm composition)
After growing on the entire surface, the active layer in the modulator region was selectively etched and removed, and an absorbing layer (14 μm composition in terms of wavelength) was selectively grown. The active layer and absorption layer must be optically coupled to create a structure that reduces scattering at the junction, and it has been relatively difficult to create such a side channel by selective growth. On the other hand, if the present invention is used, the layer thickness of the selectively grown MQW structure can be changed by changing the width of the SiO2 film, so it is possible to grow the active layer and absorption layer at the same time, which will reduce the number of times of growth. Alternatively, it is possible to obtain a bond with high coupling efficiency. FIG. 8 shows the results of calculating the relationship between the well layer thickness and the emission wavelength of the MQW when the well layer of the MQW is InGaAs and the barrier layer is InGaAsP. This figure shows cases in which the InGaAs P of the barrier has a composition with a wavelength of 1.3 μm and a composition with a wavelength of 1.15 μm. From this figure, it can be seen that when the barrier has a composition of 1.15 μm, the wavelength becomes 1.55 μm when the well thickness is about 80 people, and 1.4 μm when the well thickness is about 30 people. Based on this calculation result and the relationship between the 5i02 stripe width and the growth rate shown in FIG. 7, the stripe width was set to 20 μm for the laser region and 2 μm for the modulator region.

FIG. 5(a) shows a selectively grown MQW structure. The grating is formed only in the laser region of the n-InP substrate 1, and an n-InGaAsP guide layer 1 is formed on it.
0 (wavelength 1.3ttm composition, carrier concentration 1×1018
CIl#, layer thickness 1000 people>, MQW active layer and absorption layer 1
1. p-InP rad layer 4 <carrier concentration 5 x 1
0"crn', layer thickness 500 people) selective growth.MQ
W is the number of wells 4, and the layer thickness is the laser region or InGa
AS well 478 people, 1.1.5 μm composition nG
The aAsP barrier thickness was 150 mm, the modulator area or well was 734 mm, and the barrier thickness was 66 mm. Also, the active layer width is 2
．． It was 0 μm. In order to suppress the reflectance of the modulator side end face, a window structure was adopted in which an ungrown region was provided on the end face.

Subsequently, a p-InP layer 5 (carrier concentration 5×1
017cm'', layer thickness 0.5μm), and further 5i
02 film in the laser cavity direction with a width of 10 μm and a spacing of 30 μm.
The p-InP layer 6 (carrier concentration I x 101
8 cm”, layer N10 μm) and p”-I nGa
As cap layer 7 (layer thickness 0.3 μm, carrier concentration I
X 1019C:m') was selectively grown to constrict the current and electric field to the active layer and absorption layer, and to electrically insulate the laser region and modulator region. Finally, S i 02 film 2 again
A window is formed on the top of the active layer and the absorption layer, and a ρ-side electrode 32 is formed in a bat shape, and an n-side electrode 3 is also formed on the substrate 1 side.
3 was formed. The completed drawing is shown in Figure 5(b).

The length of the cleaved laser region is 400 μm, and the length of the modulator region is 200 μm. In addition, the laser side end face has a reflectance of 80
% high reflective coating.

The oscillation threshold current of a typical device is 18 mA, with a maximum C
The W optical power was 25 mW. The oscillation wavelength is 1.545μ
m, and when -5V is applied to the modulation region, the extinction ratio is 2.
It was 5 dB. Furthermore, the coupling efficiency estimated from the extinction characteristics was as high as 95%. Thus, it was confirmed that a good coupled waveguide structure can be easily produced by the technique of simultaneously growing an active layer and an absorbing layer by selective growth of the present invention.

Finally, as a third example, we will discuss the results of fabricating a 5PIC integrated with the two-wavelength semiconductor laser array and optical waveguide shown in FIG. 9 using the selective growth of the present invention. Figure 6 (a> is 5 when the DH elliptical structure was first selectively grown)
This is the pattern of the i02 film 21. The width of the growth head surrounded by Si○2 stripes in each region is 2 μm, and 5i
The 02 stripe width was 15 μm in one laser region and 5 μm in the other laser region and waveguide region.

FIGS. 6(c) and 6(d) are cross-sectional views of the completed device (
The cutting direction is shown in FIG. 6(a)).

First, an n-InGaAsP guide layer 10 (wavelength 1.3 μm composition, carrier concentration I
n-InP etch stop layer 12 (carrier concentration 1×10′−1 layer thickness approx. 1017CTI+1, layer thickness 500λ) was grown. The number of MQW wells is 4, and the layer thickness is 70 I nGaAs well layers in the laser region on one side, I
The nGaAsP (wavelength 1.3 μm composition) barrier thickness was 150 layers, and the other laser region had a well thickness of 50 layers and a barrier thickness of 110 layers. Next, as shown in FIG. 6(b), the 5i02 film is patterned, and the p-I area other than the laser region is
nP cladding layer 4 and MQW active layer 11, n-InP
Processing: The stop layer 12 was selectively etched and soothed, and a non-doped InGaAsP waveguide layer 14 (wavelength 1.3 μm composition, layer thickness 1500 layers) was selectively grown. Next, as shown in FIG. 6<c) and (d), a p-1nP layer 5 (carrier concentration I x 10"cm', layer thickness 0.5 μm), p-
2 layers (carrier concentration I x 1018cm", /1f
fl 08m)- and p”-I n G a A
S cap layer 7 (layer thickness 0.3 μm, carrier concentration I
After selective growth of the 5i02 film 21 (X 1019 cm'), a p-side pad electrode 32 was formed on the upper surface of the apertured laser active layer of the 5i02 film 21, and an n-side electrode 33 was formed on the substrate side. The laser resonator length was 300 μm, the laser spacing was 50 μm, the waveguide length was 250 μm, and the output end face had a window structure.

The typical oscillation threshold current of this twin laser is 15m
In A, the oscillation wavelengths were 1.552 μm and 1528 μm. The maximum optical output from the waveguide end face was 20 mA.

In this way, by changing the stripe width, the MQW
The oscillation wavelength of the laser can be changed, and this technology can be applied to a variety of integrated optical devices.

In each of the above embodiments, a SiC2 film was used as a dielectric film serving as a mask for selective growth, or other dielectric films such as a Si3N4 film may be used.

〔Effect of the invention〕

As described above, if the manufacturing method of the present invention is used, mesa etching is not necessary, and a uniform active layer and waveguide width can be manufactured with good control. In addition, by changing the mask width, it is possible to change the growth layer thickness, and it is also possible to change the M-QW elliptical structure emission wavelength and effective refractive index. By using these techniques, it has become possible to manufacture various semiconductor optical integrated devices (SPICs), which conventionally required complicated processes, relatively easily and with good controllability.

[Brief explanation of drawings]

FIG. 1 is a structural diagram representing the concept of the present invention. FIG. 2 is a diagram showing the manufacturing process of a semiconductor laser manufactured using the present invention, and FIGS. 3 and 4 are diagrams showing the manufacturing process of a conventional semiconductor laser, respectively. FIG. 5 is a diagram showing the manufacturing method and element structure of a 5PIC that integrates a DFB semiconductor laser and a semiconductor optical modulator manufactured using the present invention,
FIG. 6 is a diagram showing a manufacturing method and device structure of an integrated device of a two-wavelength semiconductor laser and a guiding waveguide manufactured using the present invention. FIG. 7 is a diagram showing the relationship between stripe width and growth rate, and FIG. 8 is a diagram showing the relationship between MQW elliptical structure well thickness and emission wavelength. FIG. 9 is a diagram illustrating the structure of an integrated device of a two-wavelength semiconductor laser and a leading waveguide, which is the same as that shown in FIG. 6, by a conventional manufacturing method. In the figure, 1-n-I n P substrate, 2=-n-1nP cladding layer, 3...InGaAsP active layer, 4...p
-InP cladding layer, 5-p-InP layer, 6 ・pIn
P layer, 7-p''-I nGaAski'l = Tsubu layer,
8...p-InP buried layer, 9...n-InP buried layer, 10.-n-I nGaAs guide layer, 11
. . . MQW active layer, 12 . . . n-InPn fetch layer, 13 ・High resistance InP buried layer, 141r+
G a A s P waveguide layer, 21 ・= S i○
2 membrane, 3 proton injection region, 32... p-side electrode, 3
B - n-side electrode.

Claims (1)

[Claims] 1. After forming a dielectric thin film on a flat semiconductor surface, it is processed into two parallel stripes, and crystals are selectively grown in the region sandwiched between the stripes. A method for manufacturing an optical semiconductor device, which comprises processing a semiconductor layer into an active region, an optical waveguide, etc. 2. A method for manufacturing an optical semiconductor device according to claim 1, characterized in that the width of the stripes is varied.