JPH02222590A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To simplify a manufacture process and to obtain a semiconductor laser of this design free form the contamination of photoresist by a method wherein a distributed feedback type(DFB) and distributed reflection type(DBR) semiconductor laser is provided, where a diffraction grating inside a laser is selectively grown in crystal by irradiation with light rays. CONSTITUTION:First, the selective growth of an N-type InP is made as an InP substrate 1 is irradiated with light rays, and in succession, a non-doped GaInAsP layer 3 of an optical guide layer, a non-doped GaInAsP layer 4 of an active layer, a P-type InP layer 5, and a P-type GaInAsP electrode layer 6 are continuously grown in crystal without the irradiation with light rays. Then, a thin film of SiO2, SiN, or the like is formed on the whole face of the P-type GaInAsP 6, which is etched to form an inverted mesa-shaped laminated body. Next, a P-type InP layer 7 and an N-type InP layer 8 are grown on the part removed through etching in a buried manner for the current construction and the lateral mode control. As mentioned above, the formation of a diffraction grating is carried out through crystal growth whereby pollutants are prevented from mixing in a process.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a light emitting element used as a light source in an optical communication system using glass fiber, and is a distributed feedback type light emitting element that oscillates in a single longitudinal mode even during high speed modulation. We will discuss a method for manufacturing a distributed reflection semiconductor laser.

(Prior Art) A semiconductor laser used as a light source for optical communication is required to have a two-wavelength oscillation mode that is stable even during high-speed modulation. Semiconductor lasers that meet these requirements have a semiconductor crystal layer (so-called diffraction grating) in which the thickness of the semiconductor crystal layer changes periodically, and the refractive index changes periodically due to this periodic structure. The so-called distributed feedback type (hereinafter referred to as D
(hereinafter referred to as FB) semiconductor laser and distributed reflection type (hereinafter referred to as DB)
A semiconductor laser (referred to as R) is known.

(1ia to be solved by the invention) The manufacturing method of these DFB and DBR semiconductor lasers involves forming (0) an active layer in order to form a diffraction grating directly on an InP or GaAs substrate. In the grown heterostructure, a photoresist is formed and a light source such as an Ar laser is used to form a diffraction grating on the GalnAsP layer or GaAIAa layer, which has a larger band gap than the active layer and serves as a light guide layer on the active layer. The diffraction grating pattern is transferred onto the photoresist by interfering with light, and the diffraction grating is used as a mask to etch the substrate or light guide layer with a slow etchant such as a bromine-based etchant. Forming a lattice is carried out. After that, (A) or (E
By growing crystals again on the substrate on which the diffraction grating was formed, a heterostructure sea urchin with a DFB or DBR function was obtained. I was facing a big problem. That is, since it is difficult to remove contamination caused by photoresist or the like, it has been impossible to obtain a high-quality crystal growth layer on the diffraction grating.

Furthermore, when the diffraction grating is etched for the purpose of removing contamination, the difference in height between the concave and convex portions of the diffraction grating becomes small, resulting in a disadvantage that a sufficient coupling coefficient cannot be obtained.

Furthermore, in order to form a diffraction grating, it is necessary to divide the crystal growth into two steps, which adds to the problem of contamination and the complexity of crystal growth.

Moreover, this drawback is more pronounced in DFB lasers, which require the formation of a diffraction grating inside a hetero-grown structure.

The present invention was proposed to solve these drawbacks, and consists of (a) InP or GaAs g board, (U)G
I was deposited on the AlnAsP or GaAlAs optical guide layer by the organometallic molecular beam epitaxy (hereinafter referred to as MOMBB) method, which has a selective crystal growth function by irradiating Ar laser light.
The nP layer or the GaAs layer is selectively grown depending on the required pitch of the diffraction grating, and the diffraction grating is formed by crystal growth. Furthermore, it has become possible to obtain a multilayer structure including an active layer in a single crystal growth process.

That is, an object of the present invention is to provide a method for manufacturing a semiconductor laser which has a simplified process and is free from contamination caused by photoresist.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides InP and GaA
A method for manufacturing a buried distributed feedback type and distributed reflection type semiconductor laser having an S-layer double heterostructure, the method comprising selectively growing crystals of a diffraction grating in the laser by light irradiation. This is the gist of the invention.

In other words, the main feature of the present invention is that a diffraction grating having DFB and DBR functions is formed by crystal growth.

(Function) According to the present invention, when forming a diffraction grating, there is no contamination that inhibits crystal growth, and therefore a high-quality crystal growth layer can be obtained. It also has the effect of allowing continuous crystal growth without interrupting the selective growth of the diffraction grating and the crystal growth of the multilayer structure including the active layer.

In comparison, when forming a conventional diffraction grating, (a)
(0) Ga1nAsP on InP or GaAs substrate
Alternatively, since photowork is required to form an organic resist on the GaAlAs optical guide layer, contamination may occur, making it difficult to obtain a high-quality crystal growth layer when growing crystals on the diffraction grating. Since a process step is required to form the crystal, the crystal growth is interrupted midway and the second
It is necessary to divide the process into several batches, which makes the manufacturing method complicated.

(Example) Next, an example of the present invention will be described. It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements may be made without departing from the spirit of the present invention.

【Example! ]

Figures 1 (a), (b), and (C) show a 1nP/Ga1nAsP system fabricated using the present invention with a wavelength of 1.3 m! D
This figure shows an FB laser, in which (a) is a plan view, (b) is a cross-sectional view, and (c) is a cross-sectional view of the light extraction surface.

To fabricate the above element, a semiconductor thin film forming apparatus shown in FIG. 6 is used.

In the figure, 31 is the main body of the MOMBE device, 32 is a laser source, 33 is an optical element such as a mirror, lens, diffraction grating, etc.
4 is a vibration isolation table, 35 is a light entrance window, 36 is a raw material supply line, 37 is a vacuum exhaust system, 38 is a substrate, 0MOMBE apparatus body 31, and a laser 32. The optical element 33 is a vibration isolation table 34
They are fixed at the top to prevent their positional relationship from shifting due to vibration or the like. The light entrance window 35 is open to face the base Fi 38 in the MOMBB apparatus, and allows laser light irradiation during the growth of the semiconductor thin film. Vacuum exhaust system 3
7 is a raw material supply line 3 that can eliminate vibrations generated in the MOMBB device by using a diffusion pump.
By using a flexible part such as 6, which is connected to the outside of the vibration isolation table, it is possible to prevent vibrations generated outside from being transmitted to the vibration isolation table.

For example, when the substrate 38 is irradiated with a laser beam that has been narrowed down to a minute extent, the diameter of the beam at its narrowest point (focal point) that has been narrowed down by a lens is proportional to the focal length of the lens. Therefore, it is preferable to use a lens with a focal length as short as possible, and it is desirable to place the light entrance window 35 and the substrate 38 as close as possible.

With this structure, by combining mirrors, lenses, masks, etc. on the vibration isolation table, it is possible to irradiate a minute pattern onto the substrate inside the MOMBE device, and it is also possible to irradiate the substrate inside the MOMBE device. It is also possible to scan the substrate with a minute laser beam focused by a lens by moving it on a vibration isolation table. Furthermore, by utilizing the coherence of laser light and using various mirrors and diffraction gratings, it is possible to project a diffraction pattern or an interference pattern onto a substrate. Therefore, it is possible to grow a semiconductor thin film having a pattern on the micron order, which was impossible with conventional techniques.

For the selective growth of the InP layer, an Ar laser is used as a light source with an oscillation wavelength of 514. Snm, an Ar laser is interfered with the substrate in the chamber by the two-beam method using an optical output of 2 W, and the period is 4.
Adjustments were made so that a 40n InP diffraction grating could be formed. As raw material sources, triethyl gallium (TEG), arsine (85os), triethyl gallium (TM I
), phosphine (Pus), and the like were supplied using a mass flow controller. The n-type dopant is tetraethyl Sn or hydrogen sulfide (his),
For the p-type, dimethyl zinc (DMZn) was used and similarly supplied using a mass flow controller.

In producing the device shown in FIG.
Selective growth 2 of n-type 1nP is performed while irradiating light onto the nP substrate 1, and then non-doped GaI is grown as a light guide layer.
nAsP layer (λ-1, In)3. G of non-doped active layer
alnAsP layer (λ-1, 31All) 4, 9 type 1nP layer 5. p-type GafnAsP electrode layer (λ=1.In
) 6, crystal growth was performed continuously without light irradiation. After that, Si
The p-type Ga1nA3P or a thin film of SiN, etc.
After forming on the entire surface of 6, photoetching technology is used to
After forming stripes along the 110> direction with a radius of 4 to 5μ, each layer of 6.5.4.3.2 was formed using a 4% bromethanol solution using this SiO□ thin film or SiN stripe thin film as a mask. A p-type 1nP layer 7 and an n-type 1nP layer 8 are etched until they reach the substrate 1 to form an inverted mesa-shaped stacked layer.A p-type 1nP layer 7 and an n-type 1nP layer 8 are formed in the portions removed by etching using liquid phase epitaxy (LPE) as zero-order buried growth. Embedded growth was performed for current interpolation and transverse mode control.

On the upper surface of the wafer obtained in this way, Au-Zn
A p-type ohmic electrode 10 is formed with a width of 2°n only near the top of the active layer using photoetching technology, and a p-type ohmic electrode 10 with a width of 2°n is formed on the substrate side until the total thickness is about 80nm.
After polishing, Au-Ge-Ni was deposited to form an n-type ohmic electrode 9 on the entire surface. The structure of each layer of the device thus obtained is as follows in the state shown in FIG.
Each crystal layer matches the lattice constant of InP.

1: Sn-doped n-type 1nP substrate, thickness Son, carrier density 3 XIO"cm-"+E P 05 X10'
cs+-”2: n-type 1nP selective growth layer, thickness 0.1n+
Carrier density 5 x 10"cm-' 3! Non-doped Ga1nAsP optical guide layer, thickness O,1
5n.

Carrier density I XIO"cm-" 4: Non-doped Ga1nAsP active layer, thickness 0.1B,
Carrier density I x 10'? C-2, active layer width 1
．． 8n5: P-type 1nP crystal layer, thickness 1.5n+ carrier density 5X10'1cm-" 6: P-type Ga1nAsP electrode layer, thickness 0.'In, carrier density 2XIO"cm-" 7: P-type 1nP current sandwich Insertion layer, thickness': 1.511111
Zn-doped, carrier density I Xl01'cm bow 8:
N-type InP current interlayer, thickness! 1.5n+Sn doped,
The device with carrier density I After forming 11, the optical output characteristics were measured. In continuous operation at 25°C, the optical output increased as current was injected.
It oscillated at 11A, and the oscillation wavelength was 1.31J110
There was no kink or mode skipping up to 5 times the oscillation threshold, and the side mode suppression ratio was over 30 dB, and the optical output was 30 mW at 125 A.

FIG. 2 shows the selective growth characteristics of InP by light irradiation with respect to the relationship between growth temperature and growth rate. Selective growth of InP was performed at around 400°C, and other growths were performed at around 500°C.

[Example 2] FIG. 3 shows a lateral cross-sectional view of a semiconductor laser of Example 2. As in Example 1, the structure shown in FIG. 3(a) was grown by gas source MBE. Initially, an n-type 1nP buffer layer 12. Thickness 1n, carrier density I XIO”ca
t-", then undoped Ga1nAsP active layer 4. thickness 0.In, carrier density I XIO"c+s-" then p
Ga1n^3P light guide layer 13. Thickness 1.5n+ Carrier density 5 Xl01? cm-”, wavelength 1.1n&I
A P-type 1nP selective growth layer 14 was grown by performing I-formation and then light irradiation.

The pitch, thickness, etc. are exactly the same as in Example 1. The zero-order growth is interrupted and taken out, and the p-type 1nP selectively grown layer 14 is used as a mask and a sulfuric acid-based selective etching solution (38% SO
The optical guide layer 13 was selectively etched to a depth of 0.1n using (n+H*Ot+HtO), and the diffraction grating was transferred.

This is used as a substrate and two
As the second growth, p-type 1nP cladding layer 5. Carrier concentration 5 Xl0I? cs+-”, thickness 1.5n, then p
Ga1nAsP electrode layer 6. Carrier concentration 2XIO”c
At-' was grown. The wafer thus obtained was processed in the same manner as in Example 1 to perform buried growth,
The electrode process, mounting, etc. were carried out in the same manner, and when the 1-L characteristics and spectral characteristics were measured, the same characteristics as in Example 1 were obtained.

In Example 2, the crystal growth process was performed using the metal organic molecular beam epitaxy (MOMBB) method, and only the buried growth was performed using the liquid phase epitaxy (LPE) method.
Crystal growth layers other than the P selective growth layer are grown using other crystal growth methods (L
It is clear that PE, VPE, MOVPE) etc. can be used.

(Example 3) FIG. 4 is an example of a semiconductor laser according to the method of the present invention using GaAs/AlGaAs-based materials. The growth method was the same as in Example 1, using the gas source MBE method.

As a raw material source, trimethyl aluminum (TMA) was added as an aluminum raw material, and was also supplied using a mass flow controller. The light source was the same as in Example 1, and the oscillation wavelength was 485 nw. The selective growth of the GaAs layer was adjusted so that a third-order GaAs diffraction grating with a period of 370 rv could be formed.

51st! The selective growth characteristics of GaAs by light irradiation are shown in Figure I with respect to the relationship between growth temperature and growth rate. Selective growth of GaAa was performed at ~400°C, and other growths were performed at ~650°C.
It was carried out at ℃. (The growth rate is approximately 1.8 n/hr, which has little to do with the rate of light irradiation.) To obtain this growth layer, first deposit an n-type GaAs substrate 16 on an n-type GaAs substrate 16 at a growth temperature of 650°C. GaAs bacifer layer 17. Next, light irradiation was performed at 400°C to form an n-type GaAs selectively grown layer 1 with a thickness of 1n1.
8. Thickness 0.5n, then stop light irradiation and heat at 650℃
Form Al @T x * Gaa, @oAs Hikari Gaitoga 41
Layer 19. Thickness - I n s then non-doped Ale, as
Ga*, *sAs active layer 20, thickness 0.15n, then p-type Ale, 1sGao, *sAs cladding layer 21
Layer thickness 1. thickness, then p-type GaAs electrode layer 22. Thickness ~0.
5n was grown using the same method as in Example 1 to form an inverted mesa stack for buried growth.As buried growth for zero-order transverse mode control, the LPE method was used.
P-type A1m, 5s on the part removed by etching
Ga*, 1sAS layer 23, and n-type ALm, ■G
a*, □As layer 24 was grown for electrode insertion and optical confinement.

The structure of each layer of the element thus obtained in the state shown in FIG. 4 is as follows, and each crystal layer matches the lattice constant of GaAs.

16, +Sl-doped n-type GaAs substrate, thickness 80fl,
Carrier density 5 XIO”cm-co+EPD50
0csi-"17: S1-doped n-type GaAs buffer layer, carrier density 1 XIO"cm-co18: St-doped n-type GaAs selectively grown layer, carrier density 5 @, 5eda's, *
oAs optical guide layer, carrier density 5 XIO"cs+-
” 20: n-type Ale, *5Gao, *@As active layer,
Non-doped 21: Zn-doped p-type Ale, 5sG
ao, =5As cladding layer, carrier density 5XIO
"cm-' 22: Zn-doped p-type GaAs electrode layer, carrier density 5 x 10"cm-' 23: Zn-doped p-type Al@, 5sGa*, &
Jl buried layer, carrier density I Xl0I? cm-” 24: St-doped n-type Ale, 5sGae, h
sAs buried layer, carrier density I XIOIfam
-” The wafer thus obtained was subjected to the formation of p-type ohmic electrodes, substrate polishing, and formation of n-type ohmic electrodes in the same manner as in Example 1, and then mounted on an St heat sink, and the current-light output characteristics were and the emission spectrum was measured.The light extraction surface of the element was coated with 1% AR coating.

Oscillation starts with an injection current of f5mA, and the oscillation wavelength is 875nm.
.

There was no kinking in the oscillation mode up to 5 times the oscillation threshold (the side mode suppression ratio was over 30 dB).

At this time, the optical output was 75-A, and 8 proverbs were obtained.

In this example, in order to grow a multilayer crystal layer including a diffraction grating in one growth, the growth method was changed to MOMBE.
The LPE method was used only for buried growth, but other growth methods (VPE) were used except for the selective growth of the diffraction grating.
, MO-CVD, LPE, etc.), it is clear that multiple growth layers including an active layer can be grown. In addition, in the example, I
Diffraction gratings were grown using a selective growth function by light irradiation of nP and GaAa.Although the DFB laser was described above, selective growth of GaInAsP and AlGaAs by light irradiation is also possible, and in this case, these Ga1nA
By selectively growing sP and GaAlAs light guide layers and forming a diffraction grating in the light guide layer, DFB and DB
It is possible to manufacture a laser with R function.

In addition, in the present invention, an example using n-type 1nP and n-type GaAs substrates has been described, but p-type InP and p-type GaA
The effect is the same even if an s substrate is used; in that case, the n shadow region and the p shadow region may be replaced in each structure.
Furthermore, although the embodiments have been described using a BH type and a buried DFB laser, similar effects can be obtained using a DCPBH or other types.

In addition, in the example, InP-GaInAs with a wavelength of 1.31
Although P-based and 0.85n GaAs-AlGaAs-based semiconductors have been described, the present invention can also be applied to DFB and DBR lasers in other wavelength ranges and using semiconductors different from this example.

Furthermore, when the n-type 1nP selectively grown layer of Example 1 was made into p-type, current injection into the active layer became non-uniform, and an optical bistability effect could be imparted to the current-light output characteristics.

Further, in the second embodiment, the optical guide layer 13 can be formed by etching by sputtering during continuous growth without using a sulfuric acid-based selective etching solution.

(Effects of the Invention) As described above, according to the present invention, the formation of a diffraction grating can be
By performing crystal growth, it is possible to prevent contamination from entering the process.

This simplifies the pretreatment of the diffraction grating forming substrate during crystal growth on the diffraction grating, improves the quality of the crystal growth layer on the diffraction grating, and improves reproducibility for each wafer.

In addition, since the diffraction grating can be formed during crystal growth, D
The manufacturing process of FB and DBR lasers is simplified and device productivity is improved. In particular, since photowork is no longer required to form the diffraction grating, the number of manufacturing steps is reduced, and contamination from photoresist is eliminated, which eliminates variations in devices within the wafer and improves device productivity. be.

[Brief explanation of the drawing]

FIG. 1 shows a first embodiment of a semiconductor laser according to the method of the present invention, in which (a) is a plan view, (b) is a cross-sectional view, and (c) is a cross-sectional view of the light extraction surface. Fig. 3 shows the selective growth characteristics of [nP] by irradiation. Fig. 3 shows the second embodiment of the semiconductor laser, (a) and (b) show cross-sectional views, and Fig. 4 shows the third embodiment of the semiconductor laser. (a) is a cross-sectional view, (b)
5 shows the selective growth characteristics of GaAs by light irradiation, and FIG. 6 shows a semiconductor thin film forming apparatus. 1... N-type 1nP substrate 2... N-type 1nP selectively grown diffraction grating layer 3... Non-doped GaInAsP optical guide layer 4... Non-doped Ga
1nAaP active layer 5...p-type 1nP cladding layer 6...p-type Ga1nAsP electrode layer 7...p-type InP current intercalating layer 8...n-type 1nP current intercalating layer 9...n-type ohmic Electrode 10...p-type ohmic electrode 11...AR film 12...n-type 1aP buffer layer 13...p-type Ga1nAsP light guide layer 14...p
InP selective growth layer 15...groove 1 etched by selective etching
6... N-type GaAs substrate 17, 18, 19, 20, 21, 22, 23, 24, n-type GaAs buffer layer, n-type GaAs selectively grown diffraction grating layer, n-type^IGaAa optical guide layer, non-doped AlGaAs active layer, p-type AIGaAa crat layer P-type GaAs electrode layer p-type AlGaAs current sandwich layer , 1m/h) Figure 4 (a) (b)

Claims (1)

[Claims] A buried distributed feedback type and distributed reflection type semiconductor laser having a double heterostructure of InP and GaAs layers, characterized in that a diffraction grating in the laser is selectively grown as a crystal by light irradiation. Fabrication method.