JPH0824194B2 - Switchable coupled quantum well conductor - Google Patents

Description

Description: FIELD OF THE INVENTION This invention relates to electronic semiconductor devices, and more particularly to switching quantum well devices.

Conventional Technology and Problems Quantum well devices are known in various forms, and a heterostructure laser is a good example. Quantum well heterostructure lasers achieve high efficiency depending on the discrete energy levels in the quantum well and are typically composed of a small number of coupled quantum wells. See, for example, Suze's "Physics of Semiconductor Devices" (second edition, 1981, published by Wiley InterScience), pages 729 to 730. High electron mobility transistors (HEMTs) are another form of quantum well device that typically uses only half the quantum well (one heterojunction), but includes a stack of few quantum wells. You can go out. The HEMT property arises from the conduction in the quantum well or the conduction within the valence subband, parallel to the heterojunction.
Conductive carriers (electrons or holes) are isolated from their donors or acceptors, which isolation limits carrier impurity scattering. For example, T. Drummond et al., Journal of Applied Physics 1023 (1982), “Doped by Single and Multiple Periodic Modulation (Al, G
See a) Electron mobility in As / GaAs heterostructures. A superlattice is composed of many quantum wells that are so tightly coupled that the individual wells are indistinguishable, but the wells resemble atoms in the lattice. Because of this, superlattices behave like new types of materials rather than as a group of coupled quantum wells. For example, CRC Critical Reviews
See L. Esaki et al., "Ultrafine Structure of Semiconductors Grown by Molecular Beam Epitaxial Method," in In Solid State Sciences 195 (April 1976 issue). Incorporation of two-dimensional and three-dimensional quantum well superlattices in the diode shows differential negative resistance.
See U.S. Pat. No. 4,503,447.

Quantum wells are typically about 100 thick and can be easily made to occupy an area of a few square microns,
Therefore, a very compact device having a high packing density and a small propagation delay can be obtained. However, known quantum wells cannot act as standard electronic components such as flip-flops, shift registers, multiplexers, operational amplifiers, random access memories, etc.

Means and Actions for Solving the Problems The present invention provides a crossed conductive line of a coupled quantum well having a common switchable well at the crossing. The switchable wells make it possible to choose which crossing line is conducting. Providing a common switchable well at the intersection of lines to allow an array of parallel conductive lines that intersect with other parallel conductive lines to select which set of parallel lines conducts. . Since the conductive lines can clock the information, the array can act as a shift register and the data can be transferred as the heart contracts along two orthogonal directions, thus creating a vector -Matrix multiplication can be performed. The conductive lines may all lie in a single plane, so in one plane,
Multiple crossings of lines without crosstalk can be used. Various multi-crossing devices allow the electronic well conductors to perform the functions of standard electronic components. For example, a common switchable well, each with n intersections with other lines.
^** Demultiplexer a set of n (2 to the nth power) lines
It can be configured into a tree, thus acting as a demultiplexer for the n-bit switch signal. One switch bit is applied to each group of 2 ^** (n-1) (2 to the power of (n-1)) intersections. Thus, such a switchable common well solves the problem of using standard quantum well conductors to perform standard signal transport and logic functions.

Practical Example FIG. 1 is a plan view of the switching device of the first preferred embodiment for two crossed conductive lines 12, 14 of a coupled quantum well. Lines 12 and 14 are formed of GaAs potential wells in the Al0.3Ga0.7As substrate 15. Wells within line 12 have reference numerals 121, 122, 123
Etc. and the wells in line 14 are labeled with reference numerals 141, 142, 143, etc. The dimensions of the wells in line 12 are 100Å × 100Å × 1 micron depth, with 100Å spacing between adjacent wells. The well in line 14 is 80 Å × 80 Å × 1 micron deep, with 100 Å between adjacent wells. Well 16 is 1
It is 00Å × 100Å × 1 micron deep and extends in a direction perpendicular to the plane of the drawing of FIG. 1 and forms the control electrode 18 and the Schottky barrier. In FIG. 1, the vertical dimension is greatly reduced to make the drawing easier to see, but FIG. 2 is a side sectional view taken along line 2-2 of FIG. Note that well 16 is 100Å away from the closest well of line 12 and the closest well of line 14, and electrode 18 is insulated from substrate 15 by insulator 20.

The substrate 15, the well 16 and the wells of the lines 12 and 14 are lightly n-doped with Si. This results in a diagram of the electron energy bands occurring along lines 12 and 14, including the discrete energy levels (bottoms of subbands) due to spatial quantization in the direction of lines 12 and 14, respectively. This is shown in Figures 3A and 3B. By using the approximation of effective mass for conducting electrons, it is possible to calculate discrete energy levels approximately, the wells are close enough, and the wavefunctions overlap (resonant tunneling And at 300K, the discrete energy levels are
Note that they are far enough apart to avoid the Honon-assisted mixing. Furthermore, the conduction electrons provided by the dopants in the substrate 15 diffuse rapidly into and are trapped by the GaAs well due to the conduction band discontinuity. The separation between the donor in the substrate 15 and the electrons in the well creates an electrostatic field. However, to make it easier to see,
The resulting bending of the strip is omitted in the drawing.

4A and 4B show the energy bands seen along line 4-4 of FIG. 2 when no voltage is applied and when -0.5 volts is applied to the electrode 18 relative to the substrate 15, respectively. Show.
The connection 19 from the electrode 18 to the substrate 15 is also shown in FIGS. 4A and 4B.
It is shown in the right part of the figure. Electrodes of Figures 3A and 3B
Including the effect of this applied voltage on 18, the results are as shown in FIGS. 5A and 5B, respectively.

From the above description, it is clear that for lines 12 and 14 well 16 operates as a switch. When no voltage is applied to electrode 18, wire 12 conducts. (Resonant tunneling occurs when the well energy levels are aligned.) In contrast, line 14 presents a high impedance because resonant tunneling is interrupted in well 16. Conversely, on the electrode 18 −
When 0.5 volts is applied, wire 12 loses conductivity,
The resonant tunneling of line 14 is set. Collectively, biasing well 16 turns line 12 on and
It is possible to switch from the state where 14 is off to the state where line 12 is off and line 14 is on. Of course, in this example, applying a voltage substantially different from the voltage leveling the well energy levels, such as -0.25 volts, eliminates the resonant tunneling of both lines 12,14. This feature lends itself to a signal bus in which attached but unselected equipment must be tri-stated.

The switching device of the first preferred embodiment can be made by electron beam patterning a 1 micron thick GaAs epitaxial layer on a substrate of Al0.3Ga0.7As in the pattern of FIG. The GaAs is then removed by reactive ion etching, except for the 1 micron tall pillars that underlie this pattern. After that, Al0.3Ga0.7As is grown to fill the space between the GaAs pillars, and this GaAs forms wells 121 and 12
It will be 2 mag.

Second preferred for conductive lines 12 and 14 of coupled quantum well
The switching device of the preferred embodiment is similar to that of the preferred first embodiment, except that the well 16 of the preferred first embodiment is replaced by a well 216, as shown in FIG. FIG. 6 is similar to FIG. 2 and includes wells 122, 123, 124, 125 of line 12, substrate 15,
An insulator 220 and a metal electrode 218 are shown. Preferred second
Embodiment has a ground plane 228, which is n
+ Layer. The electrode 218 causes the well 216 to switch (relative to the electrons) by raising the potential of the well 216 and its surroundings, similar to a MOS capacitor, thus eliminating the need for a direct electrical connection to the well 216. . Switching of well 216 is similar to switching of well 16, with line 12 conducting and line 14 open circuit when no voltage is applied to electrode 218. In contrast, when about 0.5 volts is applied to electrode 218, wire 12 is open and wire 14 is conductive. Please refer to FIGS. 3A, 3B and 5A, 5B which are established in the same manner as the first preferred embodiment.

The switching device of the third preferred embodiment includes a well 16 and a seventh
Same as the first preferred embodiment except that the well 316 shown in the figure is replaced. FIG. 7 is similar to FIG. 2 and shows wells 122, 123, 124, 125 of line 12, substrate 15 and electrode 318. The electrodes are p + type GaAs and form a reverse bias junction with well 316. When a negative voltage is applied to the electrode 318 with respect to the substrate 15, the potential of the well 316 also rises, as shown in FIG.
Figure B and Figures 5A and 5B hold.

A variation of the preferred first, second and third embodiments is to simply allow more wells to be affected by the electrodes 18,218,318. For example, along with well 16, wells 123,124,14
3,144 can be switched. Switching three wells in both line 12 and line 14 in this way is much easier than the open line because the non-resonant tunneling across the three wells is much smaller than if only one well were crossed. It should reduce the leakage current.

The apparatus of the preferred fourth embodiment is the first, second preferred embodiment.
And a similar fourth embodiment, but instead of changing the energy level in the well limited by the compositional difference from the surroundings (GaAs well in AlGaAs), the preferred fourth embodiment is The control electrode is used to create or eliminate a limited potential well as an inversion layer. Specifically, FIG. 8 is a plan view of a preferred fourth embodiment, which is AlxGa (1
-X) GaAs well 4 in As substrate 415 forming line 42
21,422,423,424,425,426, GaAs wells 442,443,444 in substrate 415 and region 416 of substrate 415, the latter wells and regions forming line 44. These wells are about 100
They are Å separated and have a diameter of about 100 Å in the plane of Fig. 8. The depth of the well is also not critical as the energy level is determined by the area and a depth of 1 micron is sufficient. FIG. 9 is a side cross-sectional view taken along line 9-9 of FIG. 8 showing electrode 418 with insulator 420 above region 416. Note that the vertical magnification is significantly reduced in FIG. 9 to make the drawing easier to see.

The operation of the preferred fourth embodiment is shown in FIG. 10A, FIG. 10B,
It is shown in Figures 11A and 11B and is similar to the other preferred embodiments. In this embodiment, the control potential sets or eliminates the periodicity of the tunnel structure, thus effecting the switching operation. In particular, when no voltage is applied to electrode 418, FIG. 10A shows the edges of the conduction band along conductive line 42 and FIG. 10B shows the edges of the conduction band along conductive line 44. . The edges of both conduction bands correspond to the portion of the conductive line passing through the region 416 immediately below the electrode 418 (broken line 10-10 in FIG. 9). When 3V is applied to the electrode 418,
FIG. 11A shows the edge of the conduction band along line 42 and FIG.
The figure shows the edges of the conduction band along line 44. In Figures 10 and 11 the corresponding well reference numbers are entered,
Resonant tunneling along line 42 when no voltage is applied is shown in FIG. 10, but not along line 44. In contrast, when a voltage is applied to electrode 418, a potential well is formed in region 416, which eliminates the resonant state of line 42 (FIG. 11A), but sets the resonant state of line 44, thus Set its conductivity (11B
Figure). Like the first, second and third embodiments, the intersection line 4
The energy of the 2,44 resonant tunneling does not have to be the same. Therefore, a high electrical isolation between the intersecting lines can be achieved regardless of the state of the control element.

FIG. 12 shows in plan view a preferred embodiment of an array of crossed conductive lines, with switchable wells at the crossings, where the conductive lines are interconnected with the nodes of the processor. In particular, the processor section is indicated by the square with the reference numeral 501, the quantum well conductive line in the x direction (horizontal direction in FIG. 12) is indicated by reference numeral 503, and the quantum well conductive line in the y direction is referred to. Reference numeral 505 denotes a switchable well and reference numeral 5
It is shown as a small circle with 07. Many or all switchable wells using one large electrode if desired
Note that you can control the 507. In operation, when setting the electrode switchable well 507 such that line 503 conducts and line 505 opens, parallel data is read from left to right along the x direction, line 505 conducts, and line 505 conducts. When setting the well 507 with switchable electrodes so that 503 opens,
Parallel data is read from top to bottom along the y direction. The processor 501 can be unidirectional, with inputs from the left or bottom and outputs from the right or top. This array has a systolic structure. Spreading this structure into a hexagonal array with three signal directions is straightforward.
Of course, data flow along the processor and conductive lines in both directions is also possible.

FIG. 13 shows that the quantum well conductors are simply connected to a switchable common well to form a logic function. In particular, FIG. 13 shows common switchable wells 605 and 607.
Conductive wires 601 and 603 having connection portions are shown in FIG. This configuration enables logical operations such as AND and inverter, as described below. Sections 609 and 611 (see Figure 13
With the control electrode for the switchable well 605 (shown as a dashed line extending from 615), node 613
Is considered to be the output. In this configuration, the low (logic 0) voltage on node 615 causes line 601 to conduct and line 603 to open.
Assume that switchable well 605 is set such that the high (logic 1) voltage on node 615 opens line 601 and causes line 603 to conduct. At this time, if you connect Section 609 to ground, Section 613
The output at is the AND of the inputs of clauses 611 and 615.
(If the input at 615 is low, then wire 601 conducts and the output at 613 is equal to the input at 609 grounded.
If the input of is high, line 603 will conduct and the output of 613 will be 611.
Equal to the input of. ) Similarly, the input in clause 609 is high,
If the input of clause 611 is low, the output of clause 613 will be the inverse of the input of 615.

The dimensions and materials of the preferred embodiment can vary significantly while preserving the switching action. In fact, the gallium arsenide / aluminum system can be replaced with another system such as indium arsenide phosphide, mercury cadmium telluride, etc., but still maintain the single crystal structure. Further, the device can be made of glass, insulators, metals, etc., having and operating a quantum well structure as in the preferred embodiment. Holes may be carriers instead of electrons, or both holes and electrons may be carriers at the same time. Resonant tunneling may be through energy levels other than the ground level shown in the preferred embodiment. In fact, using multiple levels in multiple wells under a common electrode can be the basis for a multipole switch. Of course, conductive lines can be of different types of wells (different depths, energy level spectra, materials, etc.) as long as resonant tunneling is available.
Can be done for a mixture of

The switching of intersecting coupling area well conductors in one plane results in both small devices (logic circuits, multiplexers, contracted arrays, etc.) and arrays of planar devices.

 The following items will be further disclosed in connection with the above description.

(1) having a plurality of coupled quantum wells in a substrate and electrodes in the substrate, the electrodes affecting one or more of the wells by applying a voltage to the electrodes And a switchable coupled quantum well conductor positioned to set or eliminate resonant tunneling between the affected well and another well.

(2) A switchable coupled quantum well conductor as set forth in paragraph (1), wherein the electrode comprises a conductive material that forms a Schottky barrier with the affected well.

(3) In the switchable coupled quantum well conductor according to paragraph (1), the electrode comprises a conductive material forming a reverse biased junction with the affected well. Well conductor.

(4) The switchable coupled quantum well conductor of paragraph (1), wherein the electrode comprises a conductive material capacitively coupled to the affected well.

(5) The switchable coupled quantum well conductor according to the item (1), wherein the electrode induces a well by applying a voltage.

(6) A switchable coupled quantum well conductor as set forth in paragraph (1), wherein the electrode induces an extension of at least one well.

(7) A first plurality of coupled quantum wells in a substrate, a second plurality of coupled quantum wells in the substrate, and an electrode in the substrate, wherein the electrode has a voltage applied to the electrodes. To set or eliminate resonant tunneling between the affected well and another well in the first plurality and another well in the second plurality. Switched cross-coupled quantum well conductors positioned.

(8) A switchable cross-coupled quantum well conductor as set forth in paragraph (7), wherein the electrode comprises a conductive material that forms a Schottky barrier with the affected well. Well conductor.

(9) In the switchable cross-coupled quantum well conductor of paragraph (7), the electrode comprises a conductive material that forms a reverse biased junction with the affected well. Coupled quantum well conductor.

(10) A switchable cross-coupled quantum well conductor as set forth in paragraph (7), wherein the electrode comprises a conductive material capacitively coupled to the affected well. .

(11) The switchable cross-coupled quantum well conductor according to item (7), wherein the electrode induces a well by applying a voltage.

(12) A switchable cross-coupled quantum well conductor as set forth in paragraph (7), wherein the electrode induces an extension of at least one well.

(13) Having a first plurality of coupled quantum well conductors in a substrate, wherein the first plurality of conductors do not intersect each other, and each of the first plurality of conductors is in the substrate. A plurality of coupled quantum well conductors, and further comprising a second plurality of coupled quantum well conductors in the substrate, the second plurality of conductors not intersecting each other, but the first plurality of Of the second plurality of conductors, each of the second plurality of conductors has a plurality of coupled quantum wells in the substrate, and a plurality of electrodes are provided in the substrate, each electrode being Applying a voltage to the electrodes is positioned to affect one or more wells at one or more intersections to form the affected wells and intersections. A connection adapted to set or eliminate resonant tunneling between different wells of the plurality of conductors. Array of quantum wells conductors.

(14) The array described in paragraph (13) has a plurality of processors, each processor being one of the intersections not having one of the affected wells. Array located in.

[Brief description of drawings]

FIG. 1 is a simplified plan view of the switch of the first preferred embodiment for two cross-coupled quantum well conductive lines, and FIG.
Simplified side cross-sectional view taken along line 2-2 of the figure, FIGS. 3A and 3B
The figure shows the conduction band and the valence band along the conduction line of FIG. 1, and FIGS. 4A and 4B show the bends of the conduction band and the valence band for biasing the switch of the first preferred embodiment. Figures 5A and 5B show 3A when bias is applied.
3 and FIG. 3B showing the states of the conduction band and valence band, FIG. 6 is a schematic side sectional view showing the switch of the second preferred embodiment, like FIG. 2, and FIG. Similar to the figure, a simplified side sectional view showing a switch of a preferred third example,
Figure is a simplified plan view of the switch of the preferred fourth embodiment for two cross-coupled quantum well conductive lines, Figure 9 is a simplified side sectional view taken along line 9-9 of Figure 8, Figures 10A and 10A. FIG. 10B is a diagram showing the conduction band along the conduction line in FIG. 9, and FIGS. 11A and 11B are diagrams showing the state of the conduction band in FIGS. 10A and 10B when a bias is applied. The figure shows the preferred embodiment,
A simplified plan view of a processor array of cross-coupled quantum well lines, and FIG. 13 is a simplified plan view of the preferred embodiment logic connections consisting of two cross-coupled quantum well conductive lines. Explanation of main symbols 12,14: Conductive wire 15: Substrate 16,121,122,123,141,142,143: Well 18: Control electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 29/812

Claims (8)

[Claims] 1. A switchable cross-coupled quantum well conductor comprising a plurality of quantum wells arranged on a first conductor, said first well comprising:
Has a first energy that maximizes tunneling between the adjacent quantum wells of the first conductor, and the quantum well in the second conductor crosses the first conductor A plurality of quantum wells disposed in the second conductor, wherein the quantum well in the second conductor has a second energy that maximizes tunneling between adjacent quantum wells in the second conductor. , The second energy is different from the first energy, and is an electrode coupled to the quantum well at an intersection of the first conductor and a second conductor, and applying a voltage to the electrode,
A switchable cross-coupled quantum well conductor that acts to conduct along one of the first and second conductors and to discontinue along the other. 2. The switchable cross-coupled quantum well conductor of claim 1, wherein the electrode has a conductive material that forms a Schottky barrier with the affected well. 3. The switchable cross-coupled quantum well conductor of claim 1, wherein the electrode has a conductive material that forms a reverse biased junction with the affected well. 4. The switchable cross-coupled quantum well conductor of claim 1 wherein said electrodes have a capacitively coupled conductive material affected. 5. The switchable cross-coupled quantum well conductor of claim 1, wherein the electrode induces a well by applying a voltage. 6. The switchable cross-coupled quantum well conductor of claim 1, wherein the electrode induces an extension of at least one well. 7. An array of coupled quantum well conductors, the first plurality of coupled quantum well conductors, wherein the first plurality of coupled quantum well conductors do not intersect each other and the first plurality of coupled quantum well conductors. Each of the quantum well conductors has a plurality of coupled quantum well conductors and is a second plurality of coupled quantum well conductors, the second plurality of coupled quantum well conductors not intersecting each other, but the first plurality of coupled quantum well conductors. Intersecting a coupled quantum well conductor, each of the second plurality of coupled quantum well conductors has a plurality of coupled quantum wells, and a plurality of electrodes, each of which is configured to have a voltage applied thereto. One of the first plurality of coupled quantum well conductors
And at one or more of the second plurality of coupled quantum well conductors and at one or more of the intersections.
One or more of the wells are affected, and coupled quantum wells are provided to establish or eliminate resonant tunneling between the affected well and another well of the coupled quantum well conductors. An array of conductors. 8. The array of coupled quantum well conductors of claim 7, wherein the intersection without the affected well has a processor that directs signals.