JP2996715B2 - How to make a quantum well box - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a quantum well box expected to contribute to high performance of an optical device and an electronic device using a compound semiconductor.

(Prior Art) In order to fabricate a quantum well box, a semiconductor having a small band gap is formed on a first layer composed of a semiconductor having a large band gap among two kinds of semiconductors having different band gaps. It is necessary to form a well portion by processing and leaving the same size as the de Broglie wavelength of the above, and to cover this with a second layer made of a semiconductor having a large band gap. At this time, the technology for forming the well becomes important.

As one of the conventional methods of forming the well portion of the quantum well box,
For example, as disclosed in the literature (Applied Physics Letters (Appl. Phys. Lett.), 50 (1987) p. 413), a semiconductor having a small band gap is formed by a lithography technique using electron beam exposure and an ion beam etching technique. There has been a method of processing to a fine size and leaving it. However, this method has the drawbacks that it requires a long time for lithography and that the sample is damaged by etching.

Other methods are described in, for example, the literature (the 9th Mixed Crystal Electronics Symposium Proceedings, July 1990,
P. 117). In this method, first,
InSb on InSb substrate by molecular beam epitaxy
A buffer layer is formed, and then InSb
A first layer of CdTe lattice-matched with the first layer is formed. Next, the CdTe layer is irradiated with an In (indium) beam at a low temperature (substrate heating temperature of about 200 ° C. in the literature). Thereby, an In droplet is formed on the CdTe layer. Next, the first layer on which the In droplet is formed is irradiated with an Sb beam. In droplets become InSb microcrystals by Sb beam irradiation. As a result, a well portion made of InSb microcrystal is formed on the CdTe layer.

(Problems to be Solved by the Invention) However, in the method of the literature, a CdTe layer is used as a first layer to form InSb microcrystals.
For example, the following problems arise.

… Since each of Cd and Te is a dopant for InSb, it is diffused into InSb by a heat treatment during the fabrication of the quantum well box or a heat treatment during the process of separately fabricating the functional element using the quantum well box. The problem of forming a barrier layer in InSb.

When Sb beam irradiation is performed, InSb is formed on the portion of the CdTe layer where the In droplets exist, and Sb is deposited on the other portions. Since Sb is a dopant for CdTe as described above, it needs to be removed. However, if Sb is removed by heating, there is a risk of damaging the CdTe layer since Te is easily re-evaporated by heating. In order to avoid this, it is necessary to remove Sb by chemical etching, and thus it is necessary to take out the sample from the growth chamber of the molecular beam epitaxial growth apparatus. In this case, the CdTe layer and the InSb crystallites are exposed to the air, and the second layer (upper barrier layer) for covering the InSb crystallites is formed on the surface exposed to the air. Therefore, deterioration at the growth interface of the second layer becomes a problem.

… Moreover, when actually manufacturing a functional device using a quantum well box, it is necessary to stack several layers of electron well boxes.
It is necessary to repeat the chemical etching of Sb and the growth of the second layer many times. Therefore, there is a problem that a large amount of time is required for removing the sample from the growth chamber and repeatedly setting the sample in the growth chamber.

The present invention has been made in view of such a point, and therefore, an object of the present invention is to prepare a quantum well box by forming a layer containing an element which serves as a microcrystalline dopant constituting a well portion. It is an object of the present invention to provide a method for manufacturing a quantum well box without using a sample and removing the sample from a growth chamber during the manufacturing.

(Means for Solving the Problems) In order to achieve this object, according to the present invention, on a substrate made of a compound semiconductor, a first compound semiconductor made of a first compound semiconductor lattice-matched with a compound semiconductor constituting the substrate is provided. And forming droplets of some of the constituent elements of the second compound semiconductor having a band gap smaller than the band gap of the first compound semiconductor on the first layer; The first compound semiconductor layer on which the droplets are formed is irradiated with a beam of the remaining element among the elements constituting the second compound semiconductor, and the second compound semiconductor layer is formed on the first layer. Forming a microcrystal of the compound semiconductor, and forming a second crystal of the first compound semiconductor on the first layer on which the microcrystal has been formed.
Forming a layer of the first compound semiconductor and forming a quantum well box, wherein the second compound semiconductor is not lattice-matched with the first compound semiconductor and is any one of the elements constituting the first compound semiconductor. And the elements used to form the liquid droplets, and the elements used to form the droplets are the same as those in the second compound semiconductor described above. Elements other than the elements constituting the first compound semiconductor described above, and the elements used for beam irradiation for forming microcrystals are the same as the first elements in the elements constituting the second compound semiconductor.
And the same elements as those constituting the compound semiconductor.

In carrying out the present invention, the substrate is a III-V compound semiconductor substrate, the first compound semiconductor is a III-V compound semiconductor, and the second compound semiconductor is the first compound semiconductor. III-V
It is preferable to use a group III element other than the group III element constituting the group III compound semiconductor and the same group V element as the group V element constituting the first group III-V compound semiconductor described above.

Further, it is preferable that the second compound semiconductor has a band structure in which the valence band edge and the conduction band edge are both included in the band gap of the first compound semiconductor. .

Note that each of the compound semiconductor substrate, the first compound semiconductor, and the second compound semiconductor in the present invention is not limited to a binary compound semiconductor but may be a ternary or more.

(Operation) According to the configuration of the present invention, the second material that does not lattice match the material of the microcrystal to be formed on the first layer with the first layer
Therefore, even if a droplet is formed on the first layer and then a beam is irradiated for microcrystal formation, the elements constituting the droplet move (migrate) on the surface of the first layer. Nothing. For this reason, microcrystals of the second compound semiconductor are selectively formed only in the portion of the first layer where the droplet is present.

Further, a beam irradiated on the first layer on which droplets have been formed in order to form the microcrystal is a beam of an element included in a constituent element of a compound semiconductor included in the first layer.
Therefore, even if the element is deposited by this beam irradiation on a portion other than the portion where the droplet is present on the first layer, it is not necessary to remove the element, so that the second layer is formed on the microcrystal-formed substrate. It can be formed continuously.

In the case where the quantum well box is manufactured by using the second compound semiconductor as a material having a band structure in which the end of the valence band and the end of the conduction band are both included in the band gap of the first compound semiconductor, A semiconductor laser using a quantum well box as an active layer, and an element exhibiting a large optical nonlinearity utilizing a large exciton effect in the quantum well box can be realized.

(Example) Hereinafter, a compound semiconductor substrate is used as a GaAs (001) substrate.
The first compound semiconductor lattice-matched to the substrate is a GaAs layer, and any one of the elements that are not lattice-matched to the first compound semiconductor and constitute the first compound semiconductor and the first compound semiconductor. An example of a method for manufacturing a quantum well box according to the present invention will be described by using an example in which a second compound semiconductor made of an element other than the elements constituting the compound semiconductor is InAs. Note that this description will be made with reference to FIGS.
This is performed with reference to (D). These drawings are process diagrams schematically showing perspective views of the sample in the main steps in the manufacturing process of the embodiment.

First, as shown in FIG.
1) On the image, a GaAs buffer layer 13 is grown as a first layer by a molecular beam epitaxy method. The substrate temperature when growing the GaAs buffer layer 13 is a temperature normally set when growing GaAs in the molecular beam epitaxy method, for example, about 600 ° C.

Next, the As (arsenic) beam and the Ga (gallium) beam are cut off.

Next, on the GaAs buffer layer 13, a droplet of an element that is not a constituent element of the first compound semiconductor, GaAs, of the constituent elements of the second compound semiconductor, InAs, is formed.
The substrate temperature is lowered to form (indium) droplets. The substrate temperature here can be, for example, a temperature in the range of 100 to 400 ° C., and more preferably a temperature of 150 to 300 ° C. In this embodiment, the temperature is set to about 200 ° C.

Next, the GaAs buffer layer 13 is irradiated with an In beam of about one atomic layer to locally form an In droplet 15 having a diameter of about several nm on this layer 13 (FIG. 1B). Of course, the size of the In liquid 15 is not limited to this, and can be changed according to the application purpose of the quantum well box. Control of the size of the In droplet 15 depends on the substrate temperature and
This can be achieved by changing the irradiation amount of the In beam.

Next, with the substrate temperature kept at about 200 ° C.,
A beam of the same element as the element constituting GaAs as the first compound semiconductor among the constituent elements of InAs as the second compound semiconductor is applied to the GaAs buffer layer 13 on which the droplet 15 has been formed. An (arsenic) beam 17 is irradiated. On this occasion,
Since InAs is a lattice-mismatched system with respect to GaAs,
It is crystallized into InAs without moving on the As layer 13. As a result, on the GaAs buffer layer 13, In
As microcrystals 19 are locally formed (FIG. 1 (C)).

Next, with the substrate temperature kept at about 200 ° C, the InA
With respect to the GaAs buffer layer 19 on which the s microcrystals 19 have been formed, the amount required for growing the monolayer of the GaAs cap layer as the second layer is reduced.
Ga and As are supplied alternately. Thereby, InAs microcrystal 19
A GaAs cap layer 21 is formed on the formed GaAs buffer layer 19, and a quantum well box having a structure in which a well portion made of InAs microcrystal 19 is surrounded by GaAs layers 13 and 21 is obtained (FIG. 1 (D)). ). In this embodiment, since the example in which one layer of the quantum well box is formed has been described, the layer 21 is referred to as a cap layer. However, quantum well boxes may be further stacked,
In that case, the layer 21 serves as a barrier layer. Therefore, the film thickness of the layer 21 is set to an appropriate value depending on whether this layer is used as a cap layer or a barrier layer. When the layer 21 is used as a barrier layer, its thickness may be, for example, about 10 nm.

As is clear from the above description of the embodiment, in the method for manufacturing a quantum well box of the present invention, a sample is grown without using a CdTe layer containing Cd or Te which is a dopant for a well portion and during manufacturing the quantum well box. It can be seen that a desired quantum well box can be formed without taking it out of the chamber.

In the above, the embodiment of the method for manufacturing a quantum well box according to the present invention has been described. However, the present invention is not limited to the above-described embodiment, and various modifications as described below can be added.

For example, in the present invention, a first layer is formed on a substrate without using the substrate itself as a lower barrier layer, and this is used as a lower barrier layer. This is to improve the surface condition of the substrate, which is not always good. Therefore, for example, when the surface condition of the substrate can be improved, the first layer may not be formed.

Further, in the above-described embodiment, an example in which a well portion made of InAs is formed on a GaAs substrate has been described. However, the present invention can be applied to a case where another material is used. For example, In on a GaSb substrate
The present invention can be widely applied to a case where a well portion made of Sb is formed, a case where a well portion made of InP is formed on a GaP substrate, and a case where a ternary or more compound semiconductor is used.

(Effects of the Invention) As is clear from the above description, according to the method for manufacturing a quantum well box of the present invention, a sample can be placed in the air without using a CdTe layer containing Cd or Te as a dopant for the well portion. The quantum well box can be formed continuously in the growth chamber without taking out the sample. Therefore, the effects of the dopant, generation of defects at the interface of the growth layer, and prolongation of the formation time do not occur in the present invention.

Further, in the method of the present invention, a quantum well box is manufactured by assuming that the second compound semiconductor has a band structure in which the valence band edge and the conduction band edge are both included in the band gap of the first compound semiconductor. In this case, the quantum well box can be used as an active layer of a semiconductor laser. In this semiconductor laser, reduction in oscillation threshold current, reduction in temperature dependence of oscillation characteristics, reduction in emission line width, and increase in modulation frequency are realized. Further, this quantum well box makes it possible to realize an element exhibiting large optical non-linearity using a large exciton effect in the quantum well box. As described above, the method for manufacturing a quantum well box of the present invention can be applied to the field of ultra-high-speed optical information processing and optical communication.

[Brief description of the drawings]

1 (A) to 1 (D) are process diagrams for explaining an embodiment. 11 ... Compound semiconductor substrate (for example, GaAs substrate) 13 ... First layer (for example, Ga) composed of the first compound semiconductor
As layer) 15 Droplets of an element of the second compound semiconductor constituent element that is not regarded as the first compound semiconductor constituent element (for example,
(In droplet) 17: a beam (for example, an As beam) of the same element as the first compound semiconductor among the second compound semiconductor constituent elements 19: microcrystals of the second compound semiconductor (For example, InAs) 21... A second layer (for example, Ga
As layer).

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Ken Kamijo 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (56) References JP-A-3-116822 (JP, A) JP Hei 1-39895 (JP, A) JP-A-63-315600 (JP, A) JP-A-3-110827 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21 / 203,21 / 208 H01S 3/18

Claims (3)

(57) [Claims] 1. A first layer comprising a first compound semiconductor lattice-matched to a compound semiconductor constituting the substrate is formed on a substrate comprising the compound semiconductor, and the first compound is formed on the first layer. Forming a droplet of one of the constituent elements of the second compound semiconductor having a band gap smaller than that of the semiconductor; and forming the second compound semiconductor layer on the first compound semiconductor layer where the droplet is formed. Forming a microcrystal of the second compound semiconductor on the first layer by irradiating a beam of the remaining element among the elements constituting the compound semiconductor, and forming the microcrystal on the first layer on which the microcrystal is formed. Forming a second layer made of the first compound semiconductor to form a quantum well box, wherein the second compound semiconductor is not lattice-matched with the first compound semiconductor and the first compound semiconductor is Of each of the constituent elements It is assumed that the second compound semiconductor is composed of any element and an element other than the respective elements constituting the first compound semiconductor, and the element used for forming the droplet is selected from the elements constituting the second compound semiconductor. An element other than an element constituting the first compound semiconductor, and an element used for beam irradiation for forming microcrystals, wherein the first compound semiconductor in the element constituting the second compound semiconductor is used. A method for manufacturing a quantum well box, wherein the same element is used as the element constituting the quantum well box. 2. The method for manufacturing a quantum well box according to claim 1, wherein the substrate is a III-V compound semiconductor substrate, the first compound semiconductor is a III-V compound semiconductor, and the second compound semiconductor is a III-V compound semiconductor. The compound semiconductor includes a group III element other than the group III element constituting the first group III-V compound semiconductor and the first group III-V compound semiconductor.
A method for manufacturing a quantum well box, comprising a group V element that is the same as the group V element of the group III-V compound semiconductor. 3. The method for fabricating a quantum well box according to claim 1, wherein the second compound semiconductor has a valence band edge and a conduction band edge of the first compound semiconductor. A method for manufacturing a quantum well box, characterized by having a band structure included in both.