JPH07283478A - Manufacture of distorted quantum well laser - Google Patents

Abstract

PURPOSE:To obtain a distorted quantum well laser of a structure, wherein the interface between a well layer and a barrier layer is formed into a steep interface in the order of atomic layer scale, by a method wherein prior to the growth of the well layer and the barrier layer of a distorted quantum well structure, the growth surfaces of the well and barrier layers are exposed to a sulfur-containing gas plasma. CONSTITUTION:A buffer layer 11 is grown on the surface of a substrate 10, subsequently, a first light guide layer 12 is grown and after this, a plasma treatment using sulfur-containing gas, such as S2F2 gas, is performed on the growth surfaces of the layers 11 and 12. After the plasma treatment, the growth surfaces are heated to remove a sulfur film. Then, after a well layer 13 is grown, a second plasma treatment using a sulfur-containing gas is again performed. After this, a barrier layer 14 is grown and a plasma treatment in the formation of the layers 14 and 13 and the formation of each layer is repeatedly performed to form an active layer 20, which is formed into a distorted quantum well structure having 4 layers of wells. After that, a second light guide layer 15, a clad layer 16 and a contact layer 17 are grown and moreover, an electrode is formed to obtain a distorted quantum well laser.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for manufacturing a strained quantum well laser.

[0002]

2. Description of the Related Art Quantum effect devices, especially quantum well lasers, which have recently been attracting attention, have a light emitting region, that is, an active layer, having a quantum well structure formed by stacking a well layer and a barrier layer, and the well layer is a lattice. Research on strained quantum well lasers, in which biaxial strain is introduced into the well by intentionally shifting from the matching condition, has been actively conducted.

This strained quantum well laser can produce new physical properties because the band structure changes due to the effect of strain in addition to the quantum size effect. Therefore, the device characteristics of the conventional quantum well laser are improved. It is attracting attention as a means.

As a first conventional example of a method of manufacturing such a strained quantum well laser, a 1.55 μm band InGaAs / I
An example in which an nGaAsP strained quantum well laser is manufactured by using the low pressure metal organic vapor phase epitaxy (MOVPE) method is reported in the proceedings of the spring compound-related lectures in the 1990 fiscal year, 30a-SA-9. In this reported example, the effective mass of holes is reduced by the effect of strain, and the density of states function of the valence band is reduced, so that the threshold carrier density is reduced and the InAs composition X = 0.62.
The threshold current density J _th +398 A / cm ² is as low as that of the broad contact strained quantum well laser.

However, in the strained quantum well laser, if the composition of the well layer is changed to deviate from the lattice matching condition, the forbidden band width also changes, so that the oscillation wavelength also changes accordingly.

Therefore, it is necessary to change the thickness of the well layer in order to obtain a desired oscillation wavelength, for example, a long wavelength band semiconductor laser of 1.3 μm or 1.55 μm. As an example, a long-wavelength strained quantum well laser is theoretically expected to improve various laser characteristics.
Considering an m-band InGaAs / InGaAsP quantum well laser, if the InAs composition X is increased to introduce biaxial compressive strain in the well layer, the well width is reduced to obtain an oscillation wavelength of 1.55 μm. Must be,
When X = 0.6 and 0.7, the well width is
It becomes 4.5 nm and 2.8 nm. In such a thin well layer, at the interface between the well layer and the barrier layer, 1
Even if there is a fluctuation in the thickness of about 2 atomic layers, the change in the layer thickness is as large as about 10%. As a result, there is a problem that theoretically predicted laser characteristics cannot be obtained.

In view of this point, Japanese Unexamined Patent Publication (Kokai) No. 5-7053 discloses a method for producing a strained quantum well laser in which the interface between a well layer and a barrier layer is a steep interface on the atomic layer order, A method for manufacturing a strained quantum well laser has been proposed which includes a step of irradiating a growth layer with a hydrogen plasma beam having an angle of 45 ° or less with respect to the surface of the growth layer when switching the growth of the well layer and the barrier layer.

However, even in this technique, hydrogen ions are irradiated onto the surface of the semiconductor layer. Therefore, even if the energy is reduced and the irradiation is performed obliquely, damage due to ion bombardment can be avoided. Absent. Further, there is a concern that hydrogen has a small atomic radius and may be implanted into the semiconductor layer.

[0009]

SUMMARY OF THE INVENTION According to the present invention, the interface between the well layer and the barrier layer is steep on the atomic layer order without damaging the semiconductor layer and leaving no impurities on the surface of the processed semiconductor layer. An object of the present invention is to provide a method for manufacturing a strained quantum well laser that serves as an interface.

That is, as a result of earnest studies by the present inventor, even if the same dry process is performed, a gas that does not damage the surface of the semiconductor layer and hardly causes impurities to remain on the surface of the semiconductor layer after the processing is obtained. The inventors have come to think that treatment by chemistry is sufficient, and have provided an invention that solves the above-mentioned problems.

[0011]

The first aspect of the present invention provides a method for manufacturing a semiconductor laser, which comprises at least a crystal growth step of laminating a semiconductor layer including at least an active layer forming a strained quantum well structure in the step. In the growth of the well layer and the barrier layer, which are the layers, a step of exposing the growth surface to a gas plasma containing sulfur is included.

A second aspect of the present invention is a gas containing sulfur.
As S₂F₂, SF₂, SF _Four, S₂F_Ten, S₃
Cl₂, SCl₂, S₂Br₂, SBr₂, S₃Br₂
At least one gas selected from is used.

A third aspect of the present invention provides the sulfur-containing gas.
S₂F₂, SF₂, SF_Four, S ₂F_Ten, S₃C
l₂, SCl₂, S₂Br₂, SBr₂, S₃Br₂Or
At least one first gas selected from₂, H₂
At least one second selected from S and silane compounds
A gas mixed with the above gas is used.

A fourth aspect of the present invention provides a gas containing sulfur.
S₂F₂, SF₂, SF_Four, S ₂F_Ten, S₃C
l₂, SCl₂, S₂Br₂, SBr₂, S₃Br₂Or
At least one first gas selected from the
At least a gas mixed with a kind of second gas is used.

[0015]

According to the method of the present invention, the surface of the semiconductor layer can be treated without using hydrogen. Therefore, unintended atoms such as hydrogen atoms are not implanted in the lattice of the semiconductor layer. Further, in addition to the effect of lowering the irradiation energy, the effect of buffering the ion bombardment by the formation of a deposited film of sulfur described later is exhibited, so that the semiconductor layer is not damaged by the ion bombardment.

Before describing this action in detail, first, the function of the gas containing sulfur will be described. In the process according to the method of the present invention described above, as disclosed in JP-A-4-84277, a gas containing a large amount of sulfur in the molecule is easily dissociated in plasma, and a halogen radical as an etchant and a deposition property It produces sulfur. Since this etching and deposition occur at the same time, the sulfur that is the deposited film is removed by the energy of the ions on the ion irradiation surface,
Etching proceeds. On the other hand, the side wall protection effect occurs due to the deposition of sulfur on the side wall of the object to be etched that is not irradiated with ions, and side etching by halogen radicals can be prevented. Anisotropic processing is possible due to the above etching and deposition effects. Further, if the ion energy is set close to 0, for example, by applying no RF (radio frequency) bias, only the deposition can be performed without causing the etching mode.

In order to make the deposition stronger, H ₂ , H
₂ Adds S and silane compounds to release hydrogen radicals (hereinafter abbreviated as H ^* ) during plasma discharge, and has the function of trapping halogen, which is an etchant, by the reaction of H ^* + X ^* → HX. . This balances the etching and the side wall protection effect of sulfur, and anisotropic etching can be stably performed with good reproducibility.

Similarly, by adding a gas containing nitrogen such as N ₂ , NF ₃ and NH ₃ , nitrogen radicals (hereinafter abbreviated as N ^* ) generated during plasma discharge react with sulfur radicals. By forming a polythiazyl polymer (SN) _x having a more stable bond, a stronger side wall protective film can be formed. This is already disclosed by the present applicant in Japanese Patent Laid-Open No. 4-
It is proposed in No. 354331.

By applying this technique, halogen radicals can be mainly etched while causing sulfur to be deposited, so that damage and damage of sulfur or halogen having a large atomic radius to the semiconductor layer are reduced. .

By applying the above-mentioned method, deposition occurs in the concave portions and etching progresses in the convex portions, so that the surface of the semiconductor layer can be flattened at the atomic layer level. Further, the deposited sulfur can be easily removed by sublimation by heating it to 90 ° C. or higher.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings.

[Embodiment 1] FIG. 1 is a process explanatory view of a method of manufacturing a strained quantum well laser for explaining an embodiment of the present invention. First, as shown in FIG. 1A, a substrate 10 having a (001) plane of n-type InP as a main surface is prepared, an oxide film on the surface is removed, and then a substrate temperature is measured by an MBE (molecular beam epitaxy) method. Si at 1 x 10 at 550 ° C
^The buffer layer 11 made of InP doped with ¹⁸ cm ⁻³ was grown to a thickness of 200 nm, and then the first optical guide layer 12 made of InGaAsP was grown to a thickness of 70 nm. After that, the growth surface was subjected to plasma treatment with a gas containing sulfur under the following conditions. Gas flow rate: 30 sccm of S ₂ F ₂ Pressure: 1.33 Pa Temperature: 10 ° C. Microwave: 850 w (2.45 GH)
z) RF (radio frequency) bias: 5 W After the plasma treatment, heating was performed at 100 ° C. or higher to remove the sulfur film.

Next, as shown in FIG. 1B, In _0.71 Ga
_{After the 0.29} As well layer 13 was grown to a thickness of 3 nm, the second plasma treatment with a gas containing sulfur was performed again. The plasma treatment conditions in this case were the same as the above conditions.

Thereafter, as shown in FIG. 1C, InGaAs
The barrier layer 14 was grown to a thickness of 15 nm. The barrier layer and the well layer were formed, and the same plasma treatment as described above before forming each layer was repeated to form an active layer 20 having a strained quantum well structure having four well layers. After that, the second optical guide layer 15 made of InGaAsP is made to have a thickness of 70 nm, the Be is 2 × 10 ¹⁸ cm ^{−3, the} cladding layer 16 made of InP is made to have a thickness of 1.5 μm, and Be is made to be 1 × 1.
A contact layer 17 made of 0 ¹⁹ cm ⁻³ doped InGaAs was grown to a thickness of 100 nm, and an electrode (not shown) was further formed to fabricate a strained quantum well laser emitting light at a wavelength of 1.3 μm. As in Example 1, in the process of manufacturing the strained quantum well structure, as a result of taking the step of exposing to the gas plasma containing sulfur, the interface between the well layer 13 and the barrier layer 14 is flattened on the atomic layer order, and the strain effect is exerted. Is now fully reflected in the laser characteristics.

[Embodiment 2] Although the same method as in Embodiment 1 was adopted, in Embodiment 2, the conditions of the plasma treatment containing sulfur in Embodiment 1 were changed, and the plasma treatment was carried out under the following conditions. Gas flow rate: S ₂ F ₂ / H ₂ of 30/5 sccm Pressure: 1.33 Pa Temperature: 30 ° C. Microwave: 850 w (2.45 GHz) RF bias: 10 W At this time, as described above, excess fluorine due to hydrogen radicals The incorporation of radicals makes it easier to form a sulfur film,
It was possible to raise the temperature of plasma processing and contribute to energy saving.

Also in this case, when the next step is carried out after each plasma treatment, it is sufficient to heat at 100 ° C. or higher to remove the sulfur deposition film as described above. Thus, a semiconductor laser having a strained quantum well structure was manufactured.

[Embodiment 3] The conditions of the pretreatment, that is, the plasma treatment containing sulfur are changed as follows, although the same steps as those of the embodiment 1 are performed. Gas flow rate: S ₂ F ₂ / N ₂ of 30/5 sccm Pressure: 1.33 Pa Temperature: 50 ° C. Microwave: 850 w (2.45 GHz) RF bias: 30 W In Example 3, as described above, nitrogen was added. In addition, more stable deposition of polythiazyl film was caused by polymerization of nitrogen radicals with sulfur radicals dissociated from sulfur halide. Therefore, since the etching of the fluorine radicals is small, the temperature of the pretreatment can be increased, which contributes to energy saving.

In this case, in the next step after each plasma treatment, the film containing sulfur may be removed by heating at 200 ° C. or higher. After that, a semiconductor laser having a strained quantum well structure was manufactured through the steps described above.

In each of the above-mentioned embodiments, the InGaAs / InGaAsP-based material is used as the strained quantum well structure.
Other materials such as GaAs / AlGaAsP-based materials can be used as long as they are strain-based materials.

Also, in the above embodiment, solid source MBE is used.
Although the method was used, other growth methods such as the gas source MBE method can also be used.

[0031]

According to the method of manufacturing a strained quantum well laser according to the present invention, the interface between the well layer and the barrier layer can be made flat on the order of atomic layers, and the well layer has a very thin strained quantum well structure. It can be realized without fluctuation,
The effect of strain is sufficiently reflected in the device characteristics, and the threshold current is 2.5 mA, the internal quantum efficiency is 80%, the internal loss is 6 cm ^-1 ,
Good characteristics with a characteristic temperature of about 75 K can be obtained.

[Brief description of drawings]

FIG. 1 is a process explanatory view of an embodiment of the manufacturing method of the present invention. A is the one process drawing B is the one process drawing C is the one process drawing

[Explanation of symbols]

 10 substrate 11 buffer layer 12 optical guide layer 13 well layer 14 barrier layer 15 optical guide layer 16 clad layer 17 contact layer

Claims (4)

[Claims] 1. A method for manufacturing a semiconductor laser, which comprises at least a crystal growth step of laminating a semiconductor layer including at least an active layer constituting a strained quantum well structure in the step, wherein the well layer and the barrier layer having the strained quantum well structure are formed. A method for manufacturing a strained quantum well laser, which comprises a step of exposing the growth surface to a gas plasma containing sulfur prior to growth. 2. The gas containing sulfur includes S ₂ F ₂ , SF ₂ , SF ₄ , S ₂ F ₁₀ , S ₃ Cl ₂ and S.
The method for producing a strained quantum well laser according to claim 1, wherein at least one gas selected from Cl ₂ , S ₂ Br ₂ , SBr ₂ , and S ₃ Br ₂ is used. 3. The gas containing sulfur includes S ₂ F ₂ , SF ₂ , SF ₄ , S ₂ F ₁₀ , S ₃ Cl ₂ and S.
Mixing at least one first gas selected from Cl ₂ , S ₂ Br ₂ , SBr ₂ and S ₃ Br _{2 with} at least one _second gas selected from H ₂ , H ₂ S and a silane compound. 3. The method for manufacturing a strained quantum well laser according to claim 1, wherein the gas is used. 4. The gas containing sulfur is S ₂ F ₂ , SF ₂ , SF ₄ , S ₂ F ₁₀ , S ₃ Cl ₂ , S.
A gas obtained by mixing at least one first gas selected from Cl ₂ , S ₂ Br ₂ , SBr ₂ , and S ₃ Br ₂ with at least one second gas containing nitrogen is used. Item 4. A method of manufacturing a strained quantum well laser according to item 1, 2 or 3.