JP2793875B2 - Composite quantum structure type semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite quantum structure type semiconductor device used for a photodetector or the like.

[Problems to be Solved by the Related Art and the Invention] As devices of a new concept utilizing a structure growth technique such as a molecular beam epitaxy method and an organic metal CVD method, for example, a quantum well laser, a quantum well thin wire transistor, and a quantum well light detection Devices using a quantum structure such as a vessel have been proposed.

In a quantum well laser, the active layer has a quantum structure with a thickness about the same as the de Broglie wavelength λ of the electrons (about 100 °), so that the electrons are quantum-confined in the thickness direction and the electrons become thinner. It can behave as free particles only in the two-dimensional directions along it. The feature of this quantum well laser is that the oscillation wavelength can be controlled by controlling the structure such as the film thickness, and excellent oscillation threshold current characteristics can be obtained.

As described above, with respect to the quantum well structure in which electrons are quantum-confined in the thickness direction (z) of the structure, 2
In the dimension (x, y), the quantum box structure has a quantum confinement of electrons, and the quantum wire structure has a quantum confinement of electrons in one of them.

In a multiple quantum well structure in which GaAs and (AlGa) As ultrathin films are stacked, electrons supplied from donor impurities are
It is confined inside the ultra thin GaAs film. At this time, the electrons
Mountain one of the standing wave, i.e. at the lowest energy level states E _1, it can not contribute to electrical conduction of the z direction perpendicular to the film surface. When infrared light of a predetermined wavelength is irradiated along the film surface of this structure, electrons absorb light energy and are raised to a high energy level. When the composition and dimensions of the multiple quantum well are properly selected, the confinement effect does not effectively act on electrons at this high energy level, and conduction in the z direction becomes possible. Therefore, in such a structure, the electric conductivity changes depending on the presence or absence of light irradiation, so that the structure can be used for an infrared light detector (L.
Esaki and H. Sakaki "NEW PHOTOCONDUCTOR" IBM Tec
hnical Disclosure Bulltein Vol.20 No.6 November
1977 P2456-2457). However, with such a structure,
Since the electrons lifted to a high energy level return to the lowest energy level in a very short time, there is a disadvantage that the change in conductivity is extremely small and the sensitivity as a detector is reduced. Furthermore, the energy level E ₁ in the quantum thin film
To optically excite the E ₂ from the need to incident light along a thin film surface, there has been inconvenience of use.

An object of the present invention is to provide a semiconductor device having a function as a photodetector by using a composite quantum structure including the quantum well, the quantum wire, and the quantum box, and overcoming one or both of the above disadvantages. Is what you do.

[Means for solving the problem]

First, in order to increase the sensitivity to irradiation light, when electrons are excited by light and transferred to a new state, the process of returning electrons to the original state is suppressed, and the time for electrons to stay in the excited state is set relatively long. It is necessary to increase the change in the mobility of electrons before and after. Therefore, the composite quantum structure type semiconductor device of the present invention is characterized in that two types of quantum structures A and B having different first energy levels and the same second or higher energy level are arranged with a thin tunnel barrier interposed therebetween. This creates a situation in which electrons move efficiently from the quantum structures A to B, but the reverse process requires a longer time. Furthermore, a quantum structure having high conductivity is used as one quantum structure A or B, and the other quantum structure B or A is added with impurities or non-uniformity in composition, or is processed into a fine line or island structure. The feature is that the change in mobility accompanying the movement of electrons is increased by embedding a grid of different materials.

Further, the composite quantum structure type semiconductor device of the present invention is characterized in that quantum wells having different first energy levels from the quantum well and having the same second energy level are arranged with a thin tunnel barrier interposed therebetween, The present invention is also characterized in that quantum wires and quantum boxes having different first energy levels and the same second energy level are alternately arranged with a thin tunnel barrier interposed therebetween.

[Action]

In the composite quantum structure type semiconductor device of the present invention, two quantum structures (A, B) having different first energy levels and having the same second or higher energy level are arranged with a thin tunnel barrier interposed therebetween. When light of a predetermined energy enters in a state in which electrons are confined in the quantum structure A having a low energy level (E ₁ (A)), these electrons become the second energy level (E
₂ (A)) and the second quantum structure B
Energy level (E ₂ (B)). Thereafter, about half of the electrons at the second energy level in a short time release excess energy to release the first energy of the quantum structure A.
Return to the energy level (E ₁ (A)), but the other half is the first energy level (E ₁ (B)) of quantum structure B.
And remain in that state for a relatively long time. With this movement, the first energy levels (E ₁₎ of the quantum structures A and B
(A)) and (E ₁ (B)) electron conductivities μ _A , μ
_{If B} can be set to sufficiently different values, the conductivity for the entire composite structure will change. Therefore, this property can be used as a photodetector and other light control devices.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 shows a composite quantum structure type semiconductor device 1 according to the present invention.
FIG. 2 is a diagram showing the configuration of an embodiment, FIG. 2 is a diagram for explaining the energy level of each quantum well, and FIG. 3 is a diagram for explaining a use mode of the composite quantum structure type semiconductor device. In the figure,
QWA and QWB are quantum wells, 1 and 2 are barrier crystals, 3 is a tunnel barrier, and 4 and 5 are electrodes.

In the composite quantum structure type semiconductor device of the present invention, as shown in FIG. 1, for example, a thin tunnel barrier 3 made of AlGaAs is sandwiched between GaAs quantum wells QWA and QWB, and AlGaAs barrier crystals 1 and 2 are formed on the outside.
The basic structure of the quantum well
QWA and QWB differ in the first energy level as shown in FIG. 2, but have the same second or higher energy level, confine electrons inside, and stand by the standing wave of electrons at each energy level. To form Quantum well QWA
Between QWB and the second energy level,
Since the levels are the same and in a resonance state, the mutual transfer of electron energy is smooth and the state can freely move back and forth through the thin tunnel barrier 3. However, the electrons at this level move to the lower first energy level. It gradually moves over time. Also, the first energy level is different and has a poorer coupling state than the second energy level, but here too, it gradually seeps through the thin tunnel barrier 3 and moves to the lower level. Therefore, in the steady state, electrons are confined in the lower quantum well, for example, QWA at the first energy level.

Thus, in the above configuration, when light having a predetermined energy hν is incident on the quantum well QWA in parallel with the surface, the electrons at the first energy level are excited and shift to the second energy level. Then, as described above, the electrons that have moved to the second energy level are
And a half thereof moves to the quantum well QWB through the tunnel barrier 3. Then, over time, the quantum wells QWA and QWB each fall to the lower first energy level, and
As time elapses, the electrons that have moved to the first energy level of the QWB also move to the first energy level of the quantum well QWA and settle in the initial state. That is, from this, it can be understood that when electrodes are connected to both ends, a change in the surface conductivity G can be measured by the incidence of light, and light can be detected. FIG. 3 shows an example of the configuration.

In FIG. 3, electrodes 4 and 5 are arranged so that quantum wells QWA and QWB are connected in parallel, and conductance G (1 / R; R is resistance) between electrodes 4 and 5 is measured. can do. Assuming that the mobility of electrons in the quantum well QWA is μ _A , the areal density of electrons is N ₁ , the mobility of electrons in the quantum well QWB is μ _B , and the areal density of electrons is N ₂ , the conductivity G is The number of electrons in the layer and the ease of flow are combined. That is, Becomes Here, since N = N _A + N _B is a constant value, μ _A
>> When mu _B or _μ B >> _{μ A,} N _A due to the incidence of light
/ N, changes in N _B / N can be measured with high sensitivity as changes in conductivity G (resistance R).
Light detection can be performed as a result of no longer contributing to electrical conduction due to the incidence of light or vice versa. Furthermore, for example, mu _{A =} 0, when the mu _B ≠ 0 may conductivity G is measured with high sensitivity due to a change in N _B.

4 to 7 show another embodiment of the present invention, in which 11 is a tunnel barrier, and 12 and 13 are electrodes.

In the example shown in FIG. 4, the quantum well QWB is arranged between the electrodes 12 and 13, and the quantum well QWA is shorter than the quantum well QWB and the electrode 1
It is configured to be separated from 2 and 13. In this way, mu _{A =} 0 between the electrodes 12 and 13 may be a mu _B ≠ 0. Further, to lower the mu _A by adding impurities into the quantum well QWA, the higher the mu _B by the quantum QWB high purity, it is possible to increase the high detection sensitivity as well.

Example shown in Fig. 5, one of the quantum wells 21 and 24 disposed to sandwich a tunnel barrier 23, to lower the electron mobility by cutting a quantum well 21 in a thin line, and a μ _B >> μ _A Things.

The example shown in FIG. 6 is a combination of the quantum wire 26 and the quantum box 27. If a tunnel barrier 28 is provided between the quantum wire 26 and the quantum box 27, the same as above, μ _B >> μ Become _A. In this case, unlike the example described above, the high irradiation direction can be set in the vertical direction in the figure.

In the example shown in FIG. 7, a grid mesh 33 using a material different from the material GaAs of the quantum well, for example, AlGaAs or InGaAs is embedded in one quantum well QWB.
The grid meshes 33 or the island-like structures are arranged at intervals close to the extent that quantum mechanical effects occur.

FIG. 8 is a view for explaining an example of specific means for forming a quantum structure according to the present invention.

As described above, the composite quantum structure type semiconductor device of the present invention basically has two types of quantum structures having different first energy levels and the same second energy level with a thin tunnel barrier interposed therebetween. Configuration.
As a method of forming the quantum structure, for example, FIG.
As shown in the figure, a wide quantum well of AlGaAs is obtained by adding a little Al to a high-purity GaAs quantum well, so that a composite quantum structure type semiconductor device having a first set of quantum wells having different first energy levels can be obtained. Can be configured.

As another method, only one layer of AlAs is put in one of the quantum wells as in the grid as shown in FIG.
Alternatively, a composite quantum structure type semiconductor device can be similarly formed by adding InAs as shown in FIG.

In the composite quantum structure type semiconductor device according to the present invention, 10
Conventionally, it can be used as an optical sensor in a long infrared region without a very good sensor of about 100 μm to 100 μm.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above embodiment, light is read out as a change in resistance or the like, but a device that reads out light using a change in optical characteristics may be used.

〔The invention's effect〕

As is clear from the above description, according to the present invention, only by arranging quantum structures having different properties with a thin tunnel barrier interposed therebetween, when light of a predetermined energy enters, the spatial distribution of electrons in the quantum structure is improved. Is changed, and consequently the conductivity and the like are changed. Therefore, this property can be used as a photodetector and other light control devices. In addition, it can be used as an optical sensor in a long infrared region where there is no conventional good sensor.

[Brief description of the drawings]

FIG. 1 is a diagram showing the configuration of one embodiment of a composite quantum structure type semiconductor device according to the present invention, FIG. 2 is a diagram for explaining the energy level of each quantum well, and FIG. FIG. 4 to FIG. 7 are diagrams showing another embodiment of the present invention, and FIG. 8 is an example of a specific means for forming a quantum well according to the present invention. It is a figure for explaining. QWA and QWB ... quantum well, 1 and 2 ... barrier crystal, 3 ... tunnel barrier, 4 and 5 ... electrodes.

Claims (6)

(57) [Claims] 1. A composite quantum structure type semiconductor device comprising two types of quantum structures having different first energy levels and having the same second or higher energy level with a thin tunnel barrier interposed therebetween. 2. The composite quantum structure according to claim 1, wherein a quantum well is used as the quantum structure, and electron mobility is reduced by adding an impurity or a non-uniform alloy composition to one of the quantum wells. Type semiconductor element. 3. The composite according to claim 1, wherein a quantum well is used as the quantum structure, and the other quantum well is cut into a thin line with respect to one of the quantum wells to reduce electron mobility. Quantum structure type semiconductor device. 4. The method according to claim 1, wherein a quantum well is used as the quantum structure, and the mobility of electrons is reduced by embedding a grid of a different material in one quantum well with respect to the other quantum well. Composite quantum structure type semiconductor device. 5. A quantum well and a first well sandwiching a thin tunnel barrier.
Wherein the quantum boxes having different energy levels and the same second energy level are arranged. 6. A composite quantum structure type semiconductor device wherein quantum wires and quantum boxes having different first energy levels and having the same second energy level are alternately arranged with a thin tunnel barrier interposed therebetween.