JP3536978B2 - Method of forming quantum wire or quantum well layer, and distributed feedback semiconductor laser using quantum wire or quantum well layer formed by the method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a quantum wire or a quantum well layer which is most suitable for use, for example, embedded in an active layer of a distributed feedback semiconductor laser (DFB laser). On a grating substrate having a plurality of parallel V-grooves at a predetermined pitch in parallel, for example, through a base layer that can be a lower cladding layer in a semiconductor laser, quantum wires parallel to each other are aligned with respective positions of the V-grooves. Forming a quantum well layer on the V-groove.

[0002]

2. Description of the Related Art In a semiconductor laser, a distributed feedback semiconductor laser having a periodic structure of a refractive index and a gain in a traveling direction of a waveguide is capable of strictly controlling an oscillation wavelength.
Further, unlike a Fabry-Perot laser, there is no need for a cleavage step, which facilitates integration, and plays an extremely important role as an element used in future wavelength division multiplexing communication.

[0003] The first problem with such distributed feedback semiconductor lasers is the simplification of the manufacturing process. In old times, the lower cladding layer, lower guide layer, active layer and upper guide layer were formed from the substrate in the first crystal growth step,
After forming a grating corresponding to the wavelength in the waveguide on the guide layer, a second crystal growth was performed as a separate process group to form an upper clad layer on the guide layer having a periodic structure (for example, 1 (P.K. York, J.M.
C. Connolly et al., “MOCVD regrow
th over GaAs / AlGaAs grati
ngs forhigh power long-li
ved InGaAs / AlGaAs lasers ",
Journal of Crystal Growth
h 124 (1992) 709-715).

[0004] In addition to these basic steps,
In order to obtain the lateral confinement effect, stripes along the optical waveguide are formed by etching or the like using SiO ₂ or the like as a mask, the side surfaces are buried by a third growth, and a current block layer is formed. Then, by removing the SiO ₂ mask used for the selective growth and performing the fourth growth, an ohmic contact was formed and the substrate was smoothed.

[0005] Such a large number of times of lithography and crystal growth causes an increase in manufacturing cost and hinders the spread to industry. Further, since the regrowth interface is near the active layer, the recombination current and the like increase, which also causes an increase in the threshold current. Therefore, these methods are limited in principle,
It cannot be a technique that can be applied in the future.

Therefore, the present inventors have sought a separate method step by step. First, from a slightly characteristic point of view, a material having a narrow band gap, such as a quantum wire, is used as an active layer with a band gap of several nm corresponding to the de Broglie wavelength of electrons. The quantum nanostructure embedded in a wide material is suitable for realizing a high-performance optical device because the density of states of an electronic system is concentrated at a specific energy level. Therefore, even if the problem of the manufacturing process is cleared, it is more reasonable to aim at realizing such a structure.

That is, when quantum wires are uniformly and densely integrated in a positional relationship having a specific rule, if this can be realized by a single crystal growth, there is no difference.
This makes it possible to rationally realize a saturable absorber required for self-pulsation of a wavelength-controlled semiconductor laser or an ultrafast solid-state laser.

Generally, in order to confine light in a semiconductor waveguide, the upper and lower cladding layers must be at least 0.5 to 1 μm.
It must be formed to a thickness of the order of magnitude. Therefore, even after forming a grating on a substrate and growing a lower cladding layer of such a thickness, if the grating can be maintained in a satisfactory shape on the surface of the lower cladding layer, a single crystal growth can be performed. An active layer close to the grating of the cladding layer can be formed, and the manufacturing process of the distributed feedback semiconductor laser can be significantly simplified.

[0009] From such a viewpoint, the present inventors firstly refer to Document 2 (Xue-Lun Wang et al., "Fabrica").
Tion of highly uniform Al
GaAs / GaAs quantum wire su
perlatices by flow rate
modulation epitaxy on V-g
roofed substrate ", Journal
of Crystal Growth 171 (199
7) In 341-348), a stripe pattern is formed in the (1-10) direction on the (100) compound semiconductor substrate, and a V-groove is formed by wet etching. Containing Al in the composition
After growing a cladding layer holding a V-groove profile by growing As and InAlAs, GaAs and In containing Ga or In having a large surface atom movement are formed.
A method of forming crescent-shaped quantum wires by supplying GaAs was proposed. At this time, if the slopes can be (111) A planes intersecting with each other, by setting an appropriate crystal growth temperature according to the mixed crystal ratio of the compound semiconductor, the V-groove shape can be 1 μm or more in the growth thickness direction. Can be grown while maintaining good conditions.

This is because when the (111) A plane, which has a relatively low crystal growth rate with respect to the (100) plane, which has a high growth rate, has a growth rate of sin θ with respect to the inclination angle θ of the crystal plane, the steady state occurs. This is because it is possible to maintain a typical profile. In general, the growth rate of a particular surface depends on the chemical activity of that surface and the diffusion of source elements from the surroundings,
As the temperature increases, the anisotropy due to the crystal plane orientation disappears, and the growth rate tends to be uniform. On the other hand, when the temperature becomes low, (1
11) Since the growth rate is reduced in an inactive crystal orientation such as the A-plane, it is possible to form a repetitive structure at a constant period by adjusting the substrate temperature.

[0011]

However, in this proposal, the repetition period, that is, the interval (pitch) of juxtaposed V-grooves, was on the order of microns. In order to obtain a distributed feedback semiconductor laser with satisfactory characteristics, the interval is too coarse and needs to be on the order of submicrons. However, in the case of a submicron grating having a shorter period than the diffusion distance of Ga atoms attached to the substrate surface, it is generally difficult to grow while maintaining a specific crystal growth profile. Met.

Thereafter, as a result of experiments and research conducted by the present inventor, if the thickness of the V-groove is maintained at a certain level, the cross-sectional shape of the V-groove can be maintained well even on the surface of the AlGaAs layer grown on the substrate. Success was done. This is described in Reference 3 (Cha
ng-Sik Son et al., "V-groove AlG
aAs / GaAs multilayers grow
non-patterned GaAs subst
rates withsubmicron grati
ngs ", IEICE Technical Report, TECHNICAL REPORT
OF IECIE, ED99-318, SDM99-
211 (2000-02)) and produced the results shown in FIG. 9 attached to this document.

The profile of the grating formed on the surface of the GaAs substrate 10 corresponds to the profile of A formed thereon.
To see how thick the lGaAs layer can be held, the AlGaAs layer 11 of about 100 nm and the 10 nm
It is easy to judge if about GaAs layers 12 are alternately stacked. Also in the above document 3, a relatively thick AlGaAs layer 11 having a thickness of about 100 nm and a GaAs layer 12 having a relatively thin thickness of about 10 nm are alternately formed on a GaAs substrate 10 having V grooves formed on the surface at a pitch of 0.38 μm. A case in which a plurality of layers are stacked is shown. As a result, it was confirmed that the V-groove shape of the substrate was substantially maintained up to a thickness of about 1 μm from the substrate surface. But, conversely,
Beyond that, the V-groove shape was significantly impaired. Note that G
The aAs quantum wire 13 is formed in a crescent shape in cross section parallel to the bottom of the V-groove.

Of course, when actually producing a distributed feedback semiconductor laser or the like, AlGaAs as a cladding layer is used.
The layer 11 may be one layer, and the GaAs quantum wires 13 may be one or several in the vertical direction. However, according to the lamination experiment shown in FIG. It can be said that the lower the V-groove shape is, the better the cross-sectional shape of the quantum wire 13 formed therein is. This proves that a good grating shape can be maintained even on the upper surface of the AlGaAs cladding layer, which means that a good quantum wire formed thereon can be obtained. Furthermore, even if it is not a quantum wire but a planar quantum well layer, if the underlying grating structure is accurately reproduced, the periodic structure such as the refractive index distribution in the quantum well layer can be accurately determined. It can be constructed as desired and can also be used very effectively as an active layer of a distributed feedback semiconductor laser. Here, for simplicity,
First, only quantum wires will be described.

According to the proposal of the present inventor, as described above, the shape of the V-groove formed in the GaAs substrate 10 can be maintained well up to the vertical distance (lamination thickness) of about 1 μm. It has been found that such a structure is insufficient when used in a distributed feedback semiconductor laser having a grating shape of a submicron pitch.
The shape of the quantum thin wire 13 formed at a position close to the GaAs substrate 10 and located relatively below was not yet at a satisfactory level. Naturally, it was recognized that there is still room for improvement in characteristics. For example, V of a GaAs substrate
Even with one groove shape, the peak is almost flat. This was initially (111)
That's what happened, despite trying to be A-side.

From various experiments and considerations based on these proposals, it is considered that the thickness exceeds at least 1 μm, preferably 1.5 μm.
Even if the thickness of the cladding layer approaches or exceeds m, it is only when the condition that the V-groove shape is well maintained on the surface is presented, and the V-groove shape formed in the lower portion, and It has been found that the goodness of the formed quantum wires 13 is ensured, and that the V-groove shape itself formed in the GaAs substrate 10 must be improved in the first place.

In view of the above circumstances, the present invention is indispensable for obtaining a quantum wire in the form of a high-density quantum wire array or a quantum well layer that is sufficient for application to a distributed feedback semiconductor laser or the like. The conditions and configuration are not presented.

[0018]

According to the present invention, in order to achieve the above object, a plurality of V-grooves extending in the [01-1] direction on a (100) GaAs substrate are formed on a surface of a GaAs substrate at a pitch of a submicron order. After etching so that each side surface becomes the (111) A surface, and after the surface oxide film is removed, the angle of the V-groove is made to be 80 degrees or less; 68
Thermal cleaning is performed in the range of 0 ° C. to 720 ° C., and thereafter, a GaAs buffer layer of the same material is formed on the surface of the GaAs substrate, so that the V that has become dull due to the thermal cleaning.
Restores the dullness of the top between the grooves;
Within the range of 0 ° C. to 685 ° C., an AlGaAs layer having an Al composition ratio of 0.3 to 0.6, or an In composition ratio of 0.05.
GaAs or InGaAs is supplied after growing a 0.3 InAlAs layer as a cladding layer from GaAs quantum wires or GaAs quantum wires having a crescent cross section in the V-groove.
Whether a plurality of nGaAs quantum wires are formed in an array,
Forming a quantum well layer on the V-groove; a method for forming a quantum wire is proposed.

Here, the above-mentioned pitch is desirably from 0.3 μm to 0.5 μm, and the thickness of the GaAs buffer layer can find an optimum value within a range from 0.1 to 0.3 μm. Is common. Further, on the cladding layer, an AlGaAs guide layer having an Al composition ratio smaller than the Al composition ratio of the AlGaAs layer forming the cladding layer, or an InAlAs guide layer having an In composition ratio smaller than the In composition ratio of the InAlAs layer forming the cladding layer. Form
On this guide layer, GaAs quantum wires or InGaAs
Quantum wire, or GaAs quantum well layer or InGa
It is more preferable to form an As quantum well layer. In particular, when such a guide layer is provided with respect to the formation of a quantum well layer, planarization is promoted by increasing the growth temperature at the guide layer, and a method of forming this quantum well layer thereon, It is also possible to propose a method of extending the growth time of the layer portion and forming a folded quantum well layer having a modulated thickness.

The AlGaAs guide layer having an Al composition ratio smaller than the Al composition ratio of the AlGaAs layer forming the cladding layer or the InAlAs layer forming the cladding layer is also formed on the portions where the quantum wires or quantum well layers are formed. I
An InAlAs guide layer having an In composition ratio smaller than the n composition ratio is formed, and an upper clad layer is further formed thereon as an Al cladding layer.
An AlGaAs layer having a composition ratio of 0.3 to 0.6, or I
It is desirable to grow an InAlAs layer having an n composition ratio of 0.05 to 0.3 in manufacturing a device using the present invention.

In addition, according to the present invention, as the most effective application of the quantum wires or quantum well layers thus formed, a plurality of arrays of quantum wires formed by the method of the present invention emit light. In the active layer for guiding, it is used in a positional relationship where each extends in a direction orthogonal to the light guiding direction,
A distributed feedback semiconductor laser using the quantum well layer formed according to the present invention in the active layer is also proposed.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below. First, FIG. 2 shows that a grating (based on a continuous structure of V grooves) of a GaAs substrate 10 is formed by an interference exposure method, (16H ₃ PO ₄ , 9H ₂ O ₂ , 75H ₂ O) used at room temperature for 15 seconds. FIG. 3A is a cross section immediately after the etching, and the slope of the V-groove is a very desirable straight line, and a substantially (111) A plane is formed. In principle, the angle of the V-groove is ideally 700.053
Slightly, but etching may be more. FIG. 1B shows the oxide film removed by, for example, hydrochloric acid before crystal growth described later, but the apex angle of the apex between adjacent V-grooves is slightly rounded. Here,
Even after etching with sufficient consideration and removing the oxide film, unless the angle of the V-groove is at least 80 degrees or less, the AlGaAs layer or the InAl
When the As layer is laminated as a cladding layer, the height exceeds a sufficient height (lamination thickness), for example, 1 μm, preferably 1.5 μm.
It has been found that it is no longer possible to maintain a good grating structure up to m. The V groove period, that is, the pitch is 0.38 μm in this experimental example.

FIG. 3 shows that the GaAs substrate 10 shown in FIG. 2 is thermally cleaned in a MOCVD reactor at a temperature in the range of 680 ° C. to 730 ° C., here 700 ° C. for 5 minutes.
The aAs layer 12 and the AlGaAs layer 11 are alternately heated at 670 ° C.
To 685 ° C., where the desired temperature is 68
It shows a cross-sectional view when grown at 0 ° C. to form a stacked experiment buffer layer 16A. This lamination experiment example is for observing the state of formation of the buffer layer made of the same material as the substrate, so that the GaAs layer 12 is thicker and about 100 nm.
In the figure, the layer that appears white is a thin AlG
The aAs layer 11. The first thing that can be said from this lamination experiment is that the GaAs substrate 10
The upper grating is such that even if the top is dull due to mass transport, this can be recovered by forming a GaAs buffer layer of the same material as the substrate. As can be seen from the illustration, the GaAs layer in contact with the substrate 10 is used as a buffer layer, and the buffer layer alone is 0.1 to 0.3 μm, preferably 0.1 to 0.3 μm.
It can be said that if the growth is performed by about 2 μm, the vertex angle portion of the grating becomes sharp again, and a steady growth profile can be developed. This is because the sharpest state can be recognized at such a height dimension. In actual device fabrication, it is necessary to form a GaAs buffer layer of such a thickness because it is necessary to form a single layer as a matter of course. After that, the desired grating shape is maintained substantially after that. In addition, the growth of the AlGaAs layer 11 for forming the quantum wires 13 becomes possible.

FIG. 1 shows the structure formed according to the method of the present invention.
This shows an example of a desirable experimental result. Even after the thermal cleaning, the aspect ratio of the substrate grating is kept good by inserting the GaAs buffer layer 16 having a thickness of, for example, about 0.2 μm. 3 to 0.6
AlGaAs layer, in this case, the Al composition ratio is 0.38
A to form a cladding layer having a thickness of 0.1 μm
The GaAs layer 11 and the GaAs layer 12 having a thickness of about 10 nm are alternately grown at a growth temperature of 670 ° C. to 685 ° C., particularly at 680 ° C.
In the portion of the s-layer 12, the quantum wire 1 having a crescent-shaped cross section
3 could be formed in an array, and the shape could be maintained well up to about 1 μm and up to 1.5 μm in the height direction of the entire laminated structure 100. Of course, the fact that the V-groove shape can be maintained at such a height proves that the shape of the lower quantum wire 13 and the V-groove shape in the first place are also extremely good. Using this as, for example, a buried quantum wire in the active layer of a distributed feedback semiconductor laser, sufficient characteristics were obtained. In other words, from the construction experiment of such a laminated structure 100, even if the AlGaAs layer 11 is grown as the single clad layer to the above-mentioned thickness range, the grating shape on the surface matches the substrate grating and is sufficiently satisfactory. It was proved that it could be kept. Naturally, the shape and characteristics of the quantum wires 13 formed thereon are improved, and even when a quantum well layer is formed, a periodic structure such as a refractive index distribution inside the quantum well layer is accurately constructed as desired. be able to.
Of course, better results can be expected with an AlGaAs cladding layer having a thickness less than the upper limit thickness.

Incidentally, the growth temperature is out of the above range,
For example, if the temperature is lowered to 610 ° C., flattening proceeds rapidly at the top of the grating. Conversely, if the temperature is increased to 720 ° C., diffusion of the group III element is promoted, so that flattening also proceeds. As a result, the grating shape cannot be maintained. In such a case, even if a GaAs buffer layer was formed thereon, recovery was impossible. The same is true at the bottom of the groove. At 720 ° C., the formation angle of the V-groove becomes shallower than the optimum value at 680 ° C., and the tendency increases as the number of stacked layers increases. Was.

The result equivalent to the above mentioned as a favorable condition is:
It was also obtained when an InAlAs layer having an In composition ratio of 0.05 to 0.3 was used as the cladding layer. The growth temperature conditions are the same as above. However, when such a steady growth condition according to the present invention is used, a highly desirable structure as a distributed feedback semiconductor laser structure as shown in FIG. 4 can be obtained. Here, as described above, the GaAs buffer layer 16 of the same material is formed on the GaAs substrate 10 to such a thickness that the V-groove shape can be recovered.
AlGaAs lower cladding layer 11C having a composition ratio of 0.38
L, and an AlGaAs lower guide layer 1 having an Al composition ratio of preferably about 0.2 is formed on the cladding layer 11CL.
By supplying InGaAs having an In composition ratio of 0.2 through 5GL, the corresponding InGaAs layer 12 and the InGaAs quantum wire 13 formed in the V-groove are laminated. In the figure, the part that looks white like a crescent has a width of 30.
The quantum wires 13 having a thickness of 10 nm and a thickness of 10 nm are arranged at a period (430 nm) that is 3/2 times the wavelength in the waveguide. On top of that, an AlGaAs upper guide layer 15GU having an Al composition ratio of preferably 0.2 as described above,
AlGaAs upper cladding layer 1 having an Al composition ratio of 0.38
1 CU is formed.

In this embodiment, InGaAs having a composition ratio of 0.2 is used in place of GaAs. Of course, satisfactory results can be obtained with GaAs. However, since the surface diffusion speed of In is higher than that of Ga, the V diffusion from the (111) slope or the (100) terrace of the V-groove.
By rapidly diffusing to the bottom of the groove, the (111) slope or (10) formed parasitically in such a stepped substrate growth.
0) It is a more desirable feature that the quantum well on the terrace surface is thinned and sufficiently separated in energy. In addition, even when InGaAs is used as described above,
The formation angle condition of the above-described V-groove on the substrate surface and the subsequent crystal growth temperature condition for the underlying structure are essential, and by observing these conditions, the grating on the cladding layer at a submicron order pitch, and hence the formation, The resulting quantum wire array can be improved. Regarding the clad layer, more specifically, considering the third-order waveguide mode induced on the grating waveguide analyzed by the finite element method, when the clad layer having an Al composition ratio of 0.3 is used, the thickness is 0.1 mm. When the thickness is 5 μm or more, there is also obtained a result that the influence of radiation on the substrate side can be reduced.

FIG. 5 is a schematic view showing various periodic structures which can be formed on the AlGaAs cladding layer 11 in which the grating of the GaAs substrate 10 is well maintained. The symbol “CL,
CU, GL, GU, etc. are omitted. Since the surface diffusion distance of the adsorbed atoms increases in the order of Al, Ga, and In, the gain is modulated mainly by adjusting the composition, film thickness, and crystal growth conditions, as shown in FIG. A gain coupling mode can be obtained. Further, as described above, the guide layer is formed on the clad layer, and as shown in FIG. 3B, the growth temperature is increased at the guide layer to promote flattening. Even if the quantum well layer 12 is formed, if the underlying grating shape is formed as desired according to the present invention, a desired refractive index distribution can be accurately realized in the quantum well layer. It is also possible to obtain a refractive index coupling mode in which the refractive index is modulated. Further, a configuration in which the gain and the refractive index are simultaneously changed as shown in FIG. Based on the configuration shown in FIG. 3A, the active layer (quantum fine wire) 13 may be formed after the planarization is completed by the GaAs guide layer 15, and a periodic structure of the refractive index may be formed. In addition, by extending the growth time of the quantum well layer portion and forming a bent quantum well layer having a modulated thickness, a combined mode in which the gain and the refractive index are simultaneously changed can be obtained. be able to. It is known that in the refraction guided mode, two modes have the same oscillation threshold, which causes a problem in wavelength stability.However, in the gain mode or the composite mode, only one mode is selected and the As well as reducing the number of times, it greatly contributes to the production yield of the distributed feedback semiconductor laser.

FIGS. 6A and 6B show V according to the present invention.
An example is shown in which a gain-coupled distributed feedback laser 20 is manufactured by one-time crystal growth using a constant profile crystal growth condition on a groove. Usually, the fabrication of the distributed feedback laser 20 involves forming a grating after the growth of the cladding layer,
A guide layer having a higher refractive index than the cladding layer is formed by regrowth, and a periodic structure having a refractive index is formed near the active layer. However, according to the present invention described above, in the illustrated example, the period formed on the n-type GaAs substrate 10 is 0.38.
holding a 0.8 μm grating in the height direction,
For example, after forming the n-type AlGaAs cladding layer 11 having an Al composition ratio of 0.5, a low Al composition, for example, A
AlGaAs guide layer 15 having a composition ratio of 0.2, GaAs
Quantum wire 13, similarly p-type A having Al composition ratio of 0.5
An lGaAs cladding layer 11 is sequentially formed, and a p-type GaAs cap layer 19 used in this type of laser is formed thereon.
Can be continuously grown in a single growth. In addition to the fact that the number of times of crystal growth is not only one, there is no regrowth surface containing crystal defects near the active layer, and the active layer itself has a very good grating structure, which results in a frequency stabilizing effect. It is an excellent gain coupling type. In the illustrated case, the GaAs quantum wires 13 are used in a three-layer structure also in the height direction, but this is an arbitrary problem as required. On the advantage of the GaAs substrate 10, a suitable electrode, for example an Au-Ge-Ni electrode
8 are formed, and a Cr / Au electrode 17 is formed on the upper surface side. By injecting current from these electrodes, an oscillated optical output is obtained in the direction indicated by the thick arrow. Since the light radiation direction and the quantum wires 13 are orthogonal to each other, they can be coupled with strong TE polarized light. In terms of oscillation characteristics, desirable results have been obtained compared to a distributed feedback semiconductor laser of approximately the same specifications made in accordance with the manufacturing method of the conventional example, and the regrown surface containing crystal defects is located near the active layer. Since it does not exist, low threshold current oscillation has become possible. Further, since the active layer itself has a preferable grating structure, a gain coupling type excellent in frequency stabilizing effect is obtained. Needless to say, a quantum well layer formed according to the present invention and having a predetermined refractive index distribution with a high precision with respect to the design specification distribution provided in the active layer instead of the quantum wire 13 can also be provided.

FIGS. 7 and 8 are sectional views (A) of an InGaAs / AlGaAs high-density quantum wire array 31 and a GaAs / AlGaAs high-density quantum wire array 32 formed on a GaAs grating substrate 10, respectively, as further applied examples of the present invention. Figure) and emission spectrum (Figure B)
Is shown. Each of them is manufactured according to the manufacturing method of the present invention, and the Al composition ratio is set to 0.1 on the GaAs buffer layer 16.
38 AlGaAs cladding layers 11 are formed.
In the case of the high-density quantum wire array 31 of InGaAs shown in FIG. 7, the width of the parasitic quantum well is narrow due to the surface diffusion of In, and the energy level of the quantum wire 13 is sufficiently low. Light emission is dominant. Further, even at room temperature, the luminescence half width is narrow, which indicates that excitons in the quantum wires are stably present even at room temperature.

On the other hand, in the case of the GaAs / AlGaAs high-density quantum wire array 32 shown in FIG. 7, the emission of the parasitic quantum well and that of the quantum wire 13 at 200 K are almost the same. Light emission from the well 13A is dominant. In this figure, since the quantum wire is not clearly shown, its position is surrounded by a white circle. In each case, the quantum wire array has only one layer in the vertical direction. However, a plurality of layers may be stacked in the vertical direction.

In any case, as described above, the quantum wire arrays 31 and
By stacking 32, it is expected to be used for new optical materials such as stable use of exciton emission caused by the quantum wires 13. For example, when this thin film is used as a saturable absorber of a femtosecond solid-state laser, it has a small active layer volume and strong absorption characteristics for a specific polarization plane, and can be used as a functional optical thin film.

[0033]

As described above, the present invention has been described with reference to the preferred embodiments, but any application conforming to the gist of the present invention is possible. According to the present invention, by a single selective growth, a high-density multiple quantum wire or a quantum well layer having a predetermined refractive index distribution or the like is formed at a desired position in a device structure with a good shape and characteristics. Through the fabrication process, advanced semiconductor lasers and new optically functional materials can be realized.

[Brief description of the drawings]

FIG. 1 shows experimentally AlGa on a grating GaAs substrate in accordance with the present invention to demonstrate the effectiveness of the method of the present invention.
It is explanatory drawing using the scanning electron micrograph of the cross section at the time of laminating | stacking several layers of As layer and GaAs layer.

FIG. 2 is an explanatory sectional view using a scanning electron micrograph immediately after forming a grating on a GaAs substrate by etching and after removing an oxide film.

FIG. 3 is an explanatory view using a scanning electron microscope photograph of an experimental example for knowing how the dullness of the top of the grating can be recovered by forming a GaAs buffer layer on the grating GaAs substrate.

FIG. 4 is an explanatory view using a scanning electron micrograph of a cross-sectional example when the method of the present invention is applied to the formation of a distributed feedback semiconductor laser structure.

FIG. 5 is an explanatory diagram showing various periodic structures that can be formed on an AlGaAs cladding layer in which a grating of a GaAs substrate is well held, and a case where a quantum well layer can be used instead of a quantum wire.

FIG. 6 is a schematic configuration diagram of an example of a gain-coupled distributed feedback laser formed by one-time crystal growth using a constant-profile crystal growth condition on a V-groove according to the present invention.

FIG. 7: InGaAs / Al made according to the present invention.
FIG. 2 is a cross-sectional view of a GaAs high-density quantum wire array using a scanning electron micrograph and an explanatory diagram of an emission spectrum.

FIG. 8 shows a GaAs / AlGa fabricated according to the present invention.
It is a sectional view using a scanning electron micrograph of an As high-density quantum wire array, and an explanatory diagram of an emission spectrum.

FIG. 9 shows an experimentally proposed method in which an AlGaAs layer and a GaAs layer are experimentally formed on a grating GaAs substrate.
It is explanatory drawing using the scanning electron micrograph of the cross section at the time of laminating several layers.

[Explanation of symbols]

Reference Signs List 10 Grating GaAs substrate 11 AlGaAs cladding layer 12 GaAs or InGaAs layer (active layer or quantum well layer) 13 GaAs or InGaAs quantum wire 15 AlGaAs guide layer 16 GaAs buffer layer 17 Cr / Au electrode 18 Au-Ge-Ni electrode 19 GaAs cap Layer 20 Distributed feedback semiconductor laser 31 InGaAs quantum wire array 32 GaAs quantum wire array

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kim Taine 1-1-4 Umezono, Tsukuba, Ibaraki Pref. Within the Institute of Electronics and Technology, (72) Inventor Masafumi Son 1-1-1 Umezono, Tsukuba, Ibaraki 4 Inside the Research Institute of Electronics, National Institute of Advanced Industrial Science and Technology (56) References JP-A-7-86685 (JP, A) JP-A-7-245446 (JP, A) JP-A-9-214047 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 29/06 601

Claims (14)

(57) [Claims] 1. The method according to claim 1, wherein [01-
A plurality of V-grooves extending in the [1] direction are formed on the surface of the GaAs substrate, and the side surfaces of each of the V-grooves are arranged at submicron pitches (11).
1) Etching so as to make the surface A, and after the surface oxide film is removed, the angle of the V-groove is made to be 80 degrees or less; thermal cleaning is performed in the range of 680 ° C. to 730 ° C., and then Forming a GaAs buffer layer on the substrate surface to recover the dullness at the top between the V-grooves dulled by the thermal cleaning;
AlGaAs layer having an Al composition ratio of 0.3 to 0.6 or In composition ratio of 0.05 to 685 ° C.
Growing GaAs or InGaAs after growing an InAlAs layer as a cladding layer from 0.3 to 0.3 mm; thereby forming a plurality of GaAs quantum wires or InGaAs quantum wires having a crescent cross section in the V groove in an array. A method for forming a quantum wire. 2. The method of claim 1 wherein said Ga
A method for forming a quantum wire, wherein the thickness of the As buffer layer is in the range of 0.1 to 0.3 μm. 3. The method according to claim 1, wherein an AlGaAs guide layer having an Al composition ratio smaller than an Al composition ratio of an AlGaAs layer forming the clad layer, or the clad layer is formed on the clad layer. Forming an InAlAs guide layer having an In composition ratio smaller than that of the InAlAs layer to be formed, and forming the GaAs quantum wire or the InGaAs quantum wire on the guide layer. 4. The method according to claim 1, wherein an AlGaAs guide layer having an Al composition ratio smaller than the Al composition ratio of the AlGaAs layer forming the cladding layer also on a portion on which the quantum wire is formed, or I having an In composition ratio smaller than the In composition ratio of the InAlAs layer forming the cladding layer
An nAlAs guide layer is formed, and an AlGa layer having an Al composition ratio of 0.3 to 0.6 is further formed thereon as an upper cladding layer.
As layer or In with In composition ratio of 0.05 to 0.3
Growing a AlAs layer; a method for forming a quantum wire. 5. The method according to claim 1, wherein the pitch is 0.3 μm to 0.5 μm. 6. An array of quantum wires formed by the method according to claim 1 in an active layer for oscillating and guiding light. A distributed feedback semiconductor laser used in a positional relationship in which each extends in a direction orthogonal to. 7. The method according to claim 7, wherein [01-
A plurality of V-grooves extending in the [1] direction are formed on the surface of the GaAs substrate, and the side surfaces of each of the V-grooves are arranged at submicron pitches (11).
1) Etching so as to make the surface A, and after the surface oxide film is removed, the angle of the V-groove is made to be 80 degrees or less; thermal cleaning is performed in the range of 680 ° C. to 730 ° C., and then Forming a GaAs buffer layer on the substrate surface to recover the dullness at the top between the V-grooves dulled by the thermal cleaning;
AlGaAs layer having an Al composition ratio of 0.3 to 0.6 or In composition ratio of 0.05 to 685 ° C.
Forming a GaAs quantum well layer or an InGaAs quantum well layer on the V-groove by growing an InAlAs layer from 0.3 to 0.3 as a cladding layer; and then forming a GaAs quantum well layer or an InGaAs quantum well layer on the V-groove. Method. 8. The method of claim 7, wherein said Ga
The method of forming a quantum well layer, wherein the thickness of the As buffer layer is in a range of 0.1 to 0.3 μm. 9. The method according to claim 7, wherein an AlGaAs guide layer having an Al composition ratio smaller than an Al composition ratio of an AlGaAs layer forming the clad layer or the clad layer is formed on the clad layer. Forming an InAlAs guide layer having an In composition ratio smaller than that of the InAlAs layer to be formed, and forming the GaAs quantum well layer or the InGaAs quantum well layer on the guide layer. Method. 10. The method according to claim 9, wherein a planarization is promoted by increasing a growth temperature in a portion of the guide layer, and the quantum well layer is formed thereon. A method for forming a quantum well layer. 11. The method of claim 10, wherein the growth time of the portion of the quantum well layer is extended to form a folded quantum well layer having a modulated thickness. A method for forming a quantum well layer. 12. The method according to claim 7, wherein an AlGaAs guide layer having an Al composition ratio smaller than an Al composition ratio of the AlGaAs layer forming the cladding layer is also provided on the portion where the quantum well layer is formed. Alternatively, an InAlAs guide layer having an In composition ratio smaller than the In composition ratio of the InAlAs layer forming the cladding layer is formed, and an Al cladding layer having an Al composition ratio of 0.3 to 0.6 is further formed thereon as an upper cladding layer.
Growing a GaAs layer or an InAlAs layer having an In composition ratio of 0.05 to 0.3; a method of forming a quantum well layer. 13. The method according to claim 7, wherein the pitch is 0.3 μm to 0.5 μm. 14. A distributed feedback semiconductor laser using the quantum well layer formed by the method according to claim 7 in an active layer for oscillating and guiding light.