JPH0516677B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION The present invention relates to improvements in semiconductor structures, and more particularly to quantum well structures that undergo interdiffusion disordering after crystal growth. It is related to.

Interest in forming different heterostructure types in AlAs-Ga _1-x Al _x As-GaAs alloy systems has been further developed by interdiffusion methods. Especially in Ga _1-x Al _x As alloys, GaAs and
Day-ordering by interdiffusion of AlAs, or
Diordering by interdiffusion of Ga and Al has been used. The interdiffused disordering method is of interest because it can be applied selectively to alloy systems after crystal growth to fabricate semiconductor lasers, optical waveguides, optical detectors, and -group opto-electronic integrated circuits. This is because it makes it possible. The interdiffusion disordering method can selectively control the region in an as-grown quantum well structure, and can shift up the energy band by mixing or misaligning the alloy composition. The active region or waveguide region can be formed in an aligned crystal structure that results in a reduction in the refractive index and has already been grown using conventional epitaxial methods.

Regarding interdiffusion disordering between Ga and Al in a Ga _1-x Al _x As alloy system or interdiffusion disordering in a GaAs-AlAs superlattice,
This is described in the following three groups of papers.

(1) “GaAs and
Interdiffusion between AlAs
between GaAs and AlAs)”Applied
Physics Letters Vol. 29 No. 3 (August 1, 1976)
The paper on pages 138 to 141 describes interdiffusion ordering by annealing.

(2) U.S. Patent No. 4378255, Applied Physics
Letters Vol. 38, No. 10 (May 15, 1981) No. 776
``Disorder of an AlAs-GaAs superlattice due to impurity diffusion'' by W. D. Laidig et al. on page 778.
"AlAs-GaAs
Diffusion and misalignment of Zn along the layers in the superlattice (Zn
Diffusion & Disordering of an AlAs−
"GaAs Superlattice Along Its Layers", which describe interdiffusion disordering caused by the diffusion of zinc (Zn) at temperatures of e.g. 600 DEG C.-650 DEG C.

(3) Albuquerque, New Mexico, USA in 1982
The International Symposium on GaAs and Related Compounds was held at
Shmposiumu on GaAs and Related
Compounds)” report collection, pages 233-239
“Disorder of AlAs/GaAs Superlattices by Impurity Implantation and Diffusion” by MD Camras et al.
the implantation and diffusion of
"Impurities" include ion implantation, i.e. Si or Zn at a temperature of approximately 675°C.
Disordered interdiffusion by ion implantation is described.

Recently, the interdiffusion disordering method has been applied to single and multiple quantum well laser structures to improve their output power by interdiffusion of Ga and Al at high temperatures, e.g. 850°C-1000°C, in the active layer heterojunction. It is becoming increasingly used for wavelength modulation. By controlling the annealing temperature and time, the wavelength of this laser structure can be shifted by as much as 1000 Å, for example from 8200 Å to 7200 Å. This method is described in U.S. patent application Ser.
Quantum Well Lasers by Thermal
Annealing)”.

Element implantation, element diffusion,
Alternatively, when interdiffusion disordering is performed by heat treatment at high temperature, the shape of the energy band of the well changes according to the degree of interdiffusion disordering treatment applied.

In the case of an AlAs-GaAs interface, a GaAs-GaAlAs interface, or a Ga _1-x Al _x As- Ga _1-y Al _y As (y>x) interface, the concentration gradient of Al across this structure is:
It is not as steep as in the epitaxial as-grown structure before the interdiffusion disordering process.

1A-1C illustrate various GaAs/GaAlAs based quantum well structures known in the art. In FIG. 1A, the quantum well structure with energy band structure 10 is Ga _1-x
It includes a well layer 12 of Al _x As. Here x is approximately between 0 and 0.35, so layer 12 is
May be a GaAs layer, GaAlAs with low Al concentration
It can also be a layer. To show the quantum size effect, layer 1
The thickness of 2 ranges from 15 Å to 500 Å. Cladding layers 15 and 16 have x′ of approximately 0.15 to 1.00.
It includes Ga _1-x ′Al _x ′As with the value of . That is, layers 15 and 16 are made of GaAlAs or AlAs containing a high concentration of Al.
It is.

Due to the disordered interdiffusion, interdiffusion of Ga and Al occurs at the interface between the quantum well region 12 and the cladding layers 15 and 16. As shown in FIG. 1A, the energy band distribution 10 forming a single quantum well region 12 has a finite rectangular well. Due to interdiffusion, the well, which was initially a finite rectangle, changes to a more parabolic shape, and the depth of the well also changes to become shallower.
Due to mutual diffusion of Ga-Al, the edges of Ga _1-x Al _x As become rounded. The shape after this change is indicated by a dotted line 13. Due to this shallowing of the well 12, the states of the electrons and holes trapped in the well are shifted to different energy levels.
A more detailed discussion of these conditions may be found in the aforementioned US Patent Application No. 528,766.

The energy band distribution 20 shown in FIG. 1B includes a similar quantum well structure, but additional outer layers 17,18. They are Ga _1-x ″Al _x ″As layers with x″ values between approximately 0.30 and 1.00, i.e. layers 17 and 18 contain a high concentration of Al.
GaAlAs or AlAs. On the other hand, in the intermediate cladding layers 15 and 16, the Al composition ratio is approximately 0.15.
and 0.85, i.e. layers 15 and 16
is a layer of GaAlAs with moderate Al concentration. When sufficient interdiffusion randomization is performed, the well 12, which initially has a finite rectangular shape, changes to a more curved or parabolic shape. The shape after the change is indicated by a dotted line 14. It should be noted that the interdiffusion randomization in shape 20 is more substantial than that in shape 10, and as shown, the filling of well 12 occurs more markedly. .

The energy band distribution 30 in FIG. 1C is the first
It represents a superlattice using a single well _in diagram B, and _four quantum wells 12A, 12B,
Contains 12C and 12D. These wells
Three barrier layers 1 of Ga _1-x ′Al _x ′As (x′ = 0.15 to 0.85)
It is separated by 5A, 15B, and 15C. layer 15
Note that A, 15B, 15C may be AlAs. Due to interdiffusion ordering, the wells 12A, 1, which were initially rectangular in shape,
2B, 12C, and 12D change in a curved manner as shown by the dotted line 19 in FIG. 1C.

During epitaxial growth to form quantum well structures, it may be necessary to control the well width at the top of the well or to ensure that it does not become too wide. Also, from the standpoint of equipment yield,
It is undesirable to apply the method of interdiffusion desordering for longer periods of time.

[Summary of the invention]

According to the invention, means are used for modifying the energy band distribution of a semiconductor structure having at least one quantum well layer and capable of exhibiting quantum size effects. Such means include at least one thin diordered component layer adjacent to the surface of the quantum well layer, which contains a higher concentration of diordered components, if any, in the layer adjacent thereto. Contains ingredients. This day-order component is
In the GaAs/GaAlAs system, they are Al and Ga. In the present invention, the diorder component Al supplies an Al accumulation region for interdiffusion, whereas the diorder component Ga is contained at a high concentration in intermediate adjacent layers such as the active region and waveguide. This is very important. The diordered component layer functions as a component accumulation portion for interdiffusion and diorderization of the quantum well layer.
The higher concentration of the disordered component in the thin layer of the disordered component adjacent to the well layer provides a readily available source for the disordered component. In other words, Al reduces the application time of the interdiffusion ordering process, and also reduces the time between the interdiffusion processes.
Avoid early depletion of Al. This reduces the exposure of the as-grown structure to the higher temperatures required for such processes. This thin component layer also serves to raise the carrier barrier at the quantum well interface and enhance the optical confinement effect. This is particularly desirable in areas where carrier and optical confinement are important, such as in the formation of semiconductor laser structures.

This amount of the disordered component is provided adjacent to one or both sides of the quantum well layer. Furthermore, a disordered component layer is also provided for multiple quantum well structures.

Other objects and features, together with a more complete understanding of the invention, will become apparent from the following detailed description taken in conjunction with the drawings.

[Description of preferred embodiment]

Referring to FIG. 2A, a "general" energy band distribution 40 for the present invention is shown. The distribution 40 represents a single quantum well layer 42 of Ga _1-x Al _x As for x, for example, with values between approximately 0 and 0.35. at least one thin di-order component layer 44 adjacent the surface of the well 42;
is attached. This layer is Ga _{1-y ly} As, in which Al is a disordered component and y is considerably larger than Al _x in the quantum well layer 42, that is, y>x. Next to the disordered component layer 44 is a cladding layer 45. it is
For example, let x′ be a value between approximately 0.15 and 0.85.
It is a layer of Ga _1-x ′Al _x ′As. However, in layer 44
The Al _y component is at least more than the Al _x ′ in the layer 45.
15% is preferably greater. quantum well layer 4
Adjacent to the other surface of 2 is a layer 46 of Ga _1-x ′Al _x ′As. Here, x′ is a value between approximately 0.15 and 0.85, for example.

A thin disordered component layer 44A may be adjacent to the other surface of the quantum well layer 42. layer 44
A is shown in dotted outline in FIG. 2A. Although it is generally desirable to provide a pair of thin, disordered component layers 44 and 44A adjacent to well layer 42, it is within the scope of the present invention to provide a single layer 44 to obtain the effects and advantages of the present invention.

As mentioned above, the thin daily order component layer 4
4, or layers 44 and 44A contain a disordered component, ie Al, layer 42 and cladding layers 45, 46.
Contains a higher concentration than in the. It is desirable that the concentration of Al differs by at least 15% between the quantum well layer 42 and the cladding layers 45 and 46, and furthermore, it should differ by at least 15% between the layer 44 and the cladding layers 45 and 46. is desirable. With respect to layer 44 in FIG. 2A, an example of the level of an energy band representing the range of amounts of Al contained in layer 44 is shown in dotted outline 47, and between layer 44 and layer 45. Assuming that there is a difference in the amount of Al, the range is shown to be 100%, that is, completely AlAs. Thus, for example, if x' in layer 45 is 0.40, then y in layer 44 is
0.55 or higher. As another example, if x′
If it is 0.85, y in layer 44 will be 1.00, or AlAs.

The purpose of the diordered component layer is not only to increase the barrier to carriers, which is useful when designing semiconductor devices, but also to increase the barrier to carriers, which is useful when designing semiconductor devices.
This is also to provide a storage section for These additional thin layers with high concentrations of Al can be used to improve the control of quantum well energy band distribution, carrier concentration, and Al delivery to the well layer interface during interdiffusion ordering for improved control over the modeling of junction properties. Provide proactive methods. Moreover, the adoption of a diordered component layer provides the advantage of increased well width at the top of the well, which provides carrier trapping and confinement benefits as well as early Al depletion avoidance during the interdiffusion diordering process.

The thickness of quantum well layer 42 typically ranges from 15 Å to 500 Å. In many applications, the thickness is at the lower end of this range, ie, in heterostructure quantum well lasers, the thickness of the quantum well layer is between 60 Å and 80 Å. The thickness of the disordered component layers 44 and 44A ranges from one atomic layer, or approximately 3 Å, to as thick as 300 Å.

FIGS. 2B to 2H show various energy band distributions of the quantum well structure using the disordered layer of the present invention. However, other examples than those shown here are believed to be possible, and those shown here are intended to be representative.

The energy band distribution 50 in FIG. 2B is given when x is, for example, a value between approximately 0 and 0.35.
A quantum well layer 52 of Ga _1-x Al _x As, where y is, for example, a value between approximately _0.15 and 0.85 _.
The adjacent diorder component layers 53 and 54,
4. When the value is approximately between 0.15 and 0.85 depending on the concentration of Al in the outer layers 57 and 58.
It includes intermediate cladding layers 55 and 56 of Ga _1-x 'Al _x 'As. Outer layers 57 and 58 are Ga _1-x ″Al _x ″As, where x″ is approximately between 0.35 and 1.00.

FIG. 2C shows a multi-well structure using the well structure of FIG. 2B. The energy band distribution 60 has four well layers 52A, 52B, 52C, 5
2D and adjacent ordered component layers 53A, 53
B, 53C, 53D and 54A, 54B, 54C,
54D is shown. These disordered layers have the same components as the cladding layers 55 and 56 and the intermediate layer 5.
9.

The energy band distribution 70 in FIG.
That is, the second B except that it contains a high concentration of Al such as Ga _1-y Al _y As up to AlAs.
When used in a heterostructure laser similar to distribution 50 in the figure, those structures provide excellent carrier confinement while allowing beam expansion into intermediate layers 55 and 56 for optical confinement and waveguiding. can give an effect.

FIG. 2E shows a multiple quantum well configuration using the well structure of FIG. 2D. The energy band distribution 80 has four quantum well layers 52A, 52B, 52
C, 52D adjacent to the ordered component layer 53
A, 53B, 53C, 53D and 54A, 54
It is shown together with B, 54C, and 54D. These disordered layers are successively separated by an intermediate layer 79 having the same or similar composition to cladding layers 55 and 56.

As already mentioned with respect to the general energy band distribution of FIG. 2A, the diorder component layer 53
and Al _y day-order components in 54 are y
When ＞x′＞x0, Ga _1-x Al _x As and Ga _1-x
Depending on the concentration of Al in the adjacent layers 52 and 55, 56, which are Al _x 'As, it takes a value, for example, between 0.15 and 1.00.

Figures 2F, 2G and 2H show three examples of energy band distributions for single quantum well structures with spatially varying energy band distributions in the region of the intermediate cladding layer. FIG. 2F shows that the intermediate cladding layers 95 and 96 have an alloy composition of Ga _1-x ′ _Al The energy band distribution 90 is shown for the same quantum well structure as shown in the distribution 50 of FIG. 2B, except that the energy band distribution 90 now changes to .

FIG. 2G shows a Ga _{1-x ′} Al
distribution 50, except that, for example, x′ gradually changes parabolically between about 0.15 and 1.00 during the growth process.
shows an energy band distribution 100 for a quantum well structure with the same distribution as .

FIG. 2H shows that the intermediate cladding layers 115 and 116 spatially change in an inverse parabolic or convex shape.
With an alloy composition of Ga _1-x ′Al _x ′As, i.e.
An energy band distribution 110 is shown for a quantum well structure having the same distribution as the distribution 50, except that x' gradually changes parabolically between about 0.15 and 1.00 during the growth process.

The advantage of using the quantum well structure represented by the energy band distributions in FIGS. By virtue of the existence of , for example, the beam intensity cross-sectional distribution of the beam output in a semiconductor laser can be designed as desired. In other words, it becomes possible to design the intensity distribution of the beam generated by the laser. For example, by using the parabolic distribution of FIG. 2G, the intensity distribution in the output beam can be shaped like a Gaussian distribution.

With the benefit of beam intensity distribution shaping, the use of di-ordered component layers 53, 54 in the semiconductor laser structure allows for interdiffusion di-ordering applications such as those described in the above-mentioned U.S. Patent Application No. 528,766. Therefore, wavelength tuning of the laser becomes possible. As a result, semiconductor lasers can be easily fabricated using current technology with a pre-designed beam intensity distribution and selected wavelength characteristics.

Figures 3A to 3C show how the original energy band distribution changes by applying the selected interdiffusion disordering method to the selected quantum well structure. This is shown according to the following. The selected quantum well structure is the second
It is based on the distribution 50 in Figure B. This distribution is the third
This is reproduced in the figure, and the dotted line represents the energy band distribution that changes due to interdiffusion disordering. Of course, the day-order components are preserved in each drawing.

FIG. 3A shows an initial stage when mutual diffusion between the quantum well layer 52, the disordered component layers 53 and 54, and the intermediate layers 55 and 56 has started, and interdiffusion of Ga and Al has started between these layers. It represents the stage of The disordered component Al interdiffuses from layers 53 and 54, which are present in relatively large amounts in an available form to enable effectively controlled interdiffusion.

As is evident from FIG. 3A, the original distribution of layers 53 and 54 begins to attenuate due to the interdiffusion of Al into the region of well layer 52, and the wells of layer 52 begin to fill. Dotted line 51A shows this initial change in energy band distribution.

As interdiffusion progresses, the layer 53
As the distribution of and 54 attenuates, the wells in layer 52 become more filled. This is shown in FIG. 3B by the dotted line distribution 51B, and a more advanced form is shown in FIG. 3C by the dotted line distribution 51C. Distribution 5
1C, the wells in layer 52 are effectively
It is filled with mutually diffused Al to almost the same extent as in 5 and 56.

The above discussion regarding energy band distribution does not take into account the type and concentration of doping required in the current injection device. Depending on the doping type and concentration used, slight changes in the refractive index and equivalent energy band distribution may occur. Furthermore, for example, the composition ratio of the ternary compound GaAlAs in the layers 45, 46 or 55, 56, or 57, 58
The ranges of x′ and x″ will not be exactly the same to accommodate differences in doping type and concentration. These factors are known to those skilled in the art and will not be used in the discussion of the invention. Not handled.

A further consideration with respect to the present invention is that in order to relieve the strain generated due to large changes in the amount of Al present between two or more layers or in several successively deposited layers or superlattices, It is about the application of this technique. for example,
Instead of growing AlAs/GaAs superlattice, Z
When it is 0.04, a superlattice of AlAs _1-z P _z /GaAs is grown. This provides optimal lattice matching in these structures. ternary compound
In order to match the GaAlAs lattice to GaAs,
It is necessary to add an appropriate amount of P depending on the amount of Al in the ternary compound. Other elements used for lattice matching purposes include Sb and In.

Although the invention has been described with respect to specific embodiments thereof, many modifications and changes will be apparent to those skilled in the art from the foregoing description. Therefore, those changes and modifications should be construed as falling within the scope of the present invention.

[Brief explanation of drawings]

FIGS. 1A, 1B, and 1C show energy band distributions before and after interdiffusion disordering is applied to a known single or multiple quantum well structure. Figures 2A-2H illustrate various energy band distributions for single or multiple quantum well structures containing thin, disordered component layers of the present invention. FIG. 2A shows the energy band distribution for a single thin diagonal component layer in a single quantum well structure. FIG. 2B shows the energy band distribution for a single quantum well structure fitted with a pair of adjacent thin diagonal component layers. FIG. 2C shows the energy band distribution of the multiple quantum well structure. 2nd D
The figure shows the energy band distribution of a quantum well structure having a multi-stage energy band distribution similar to that of FIG. 2B, except for a thinner disordered component layer containing a higher concentration of the disordered component. Second
The E diagram is similar to the second C, except that it is a thinner diordered component layer containing a higher concentration of diordered components.
The energy band distribution of a multiple quantum well structure having an energy band distribution similar to that shown in the figure is shown. Second
Figures F, 2G, and 2H show the energy band distributions of a quantum well structure with adjacent thin, diagonal component layers in which the intermediate cladding layer has an energy band distribution with a gradient of component amounts. It shows. Figures 3A to 3C are 2B
The various stages of the effect of interdiffusion disordering on the energy band distribution of the single quantum well structure in the figure are shown. (Reference code), 10...Energy band distribution,
12... Quantum well layer, 13, 14... Energy band distribution after change, 15, 16... Cladding layer, 17, 18... Outer layer, 19... Quantum well shape, 20... Energy band distribution, 30 ... Energy band distribution, 40 ... Energy band distribution, 42 ... Quantum well layer, 44 ... Disorder layer, 45 ... Clad layer, 46 ... Clad layer, 47 ... Energy band distribution, 50 ... Energy band Distribution, 52...Quantum well layer, 53
...Dais order component layer, 54...Dais order component layer, 55, 56...Clad layer, 57, 58...
...Outer layer, 59...Middle layer, 60...Energy band distribution, 70...Energy band distribution, 7
9...Middle layer, 80...Energy band distribution,
90...Energy band distribution, 95,96...
Cladding layer, 100...Energy band distribution,
105, 106... Cladding layer, 110... Energy band distribution, 115, 116... Cladding layer.

Claims (1)

[Claims] 1 A semiconductor structure including at least one quantum well layer capable of exhibiting a quantum size effect, the means used to change the energy band distribution of the quantum well layer, wherein one of the quantum well layers at least one thin layer adjacent to one surface, said thin layer containing at least a 15% higher concentration of a disordered component than in an adjacent layer, said thin layer serving as an accumulation area for said component and A semiconductor structure comprising means operative for interdiffusion disordering of quantum well layers.