JPH03177085A - Multiple quantum hall element - Google Patents

Abstract

PURPOSE:To make it possible to improve measurement accuracy for various kinds of measuring instruments by carrying out mesa etching to a semiconductor multiple heterojunction crystal substrate to form a strip-shaped mesa and forming an ohmic electrode on both ends of the longer axis of a mesa and both ends of the central part respectively. CONSTITUTION:An ultraviolet light UV is radiated to the surface of a semiconductor multiple heterojunction crystal substrate 30 coated with photoresist 40 by way of a photomask 50 which draws a mesa-shaped pattern for quantum holes, and then developed. After the development, mesa etching is carried out on the surface of the semiconductor multiple heterojunction crystal substrate 30. Again a photoresist 41 is coated on the surface of the semiconductor multiple hetero crystal substrate which has been mesa-etched where ultraviolet light is exposed and developed by way of a photomask 51 which draws a portion of electrode so that it becomes a hole. Then, a thin film 60 made of an ohmic electrode material is deposited gradually on the entire surface of the semiconductor multiple hetero crystal substrate 30 to remove a metal thin film in an area not associated with the electrode and to form ohmic electrodes 31 and 32 through heat treatment.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to electrical resistance standards, particularly DC electrical quantities (resistance, The present invention relates to multiple quantum Hall devices used in ultra-precision measurement devices for voltage and current.

[Conventional technology 1] The quantum Hall effect is a phenomenon in which a current I is passed through a rectangular group of two-dimensionally distributed electrons (two-dimensional electron gas) placed at an extremely low temperature, and the current is perpendicular to the plane of the two-dimensional electron gas. When a strong magnetic field B is applied to , a Hall voltage V is generated in a direction perpendicular to both the electric current and the magnetic field B.

However, as shown in Fig. 5, this is a phenomenon in which it changes stepwise in response to changes in the magnetic field B, and at each step, the ratio of the Hall voltage 8 to the current, V, / I (Hall resistance) becomes h/ie2. However, h is a blank constant and e is an elementary charge.

i is a natural number.

This quantized Hall resistance is the quantized Hall resistance (R'H
), which is expressed only by the universal physical constants ri and e and natural numbers, and thus becomes the absolute standard for resistance.

Conventionally, as this type of element, one having a structure as shown in FIG. 6(a) is known. In addition, FIG. 6(b) shows
It is an enlarged view of the part surrounded by the dotted line in FIG. 6(a). That is, an additive-free gallium arsenide layer 2. is formed on a semiconductor substrate 1 made of semi-insulating gallium arsenide (GaAs). Additive-free aluminum gallium arsenide (AJ2GaAs) layer 3. Silicon doped aluminum gallium arsenide (S 1-AI2G
aAs) layer 4 and silicon-doped gallium arsenide (S 1
-GaAs) layers 5 are sequentially grown to form a so-called modulation doped heterojunction, and this heterojunction crystal substrate 10
is made into a rectangular shape by mesa etching, and an ohmic electrode 11 is placed in the shaded area in FIG. 6(a).
, 12, 13° 14 to form a quantum Hall element HE. In this heterojunction structure, a two-dimensional electron gas layer 6 is generated at the interface between the additive-free GaA 3 layer 2 and the additive-free AcGaA 3 layer 3.

The value of the quantized Hall resistance R is measured by configuring a circuit as shown in FIG. 7 at -8. In the figure, Rs is a certain reference resistance, and reference voltage 3 is the voltage generated at its voltage terminal. Note that ■ indicates constant current. Here, the quantities actually measured are the values of the Hall voltage VH and the reference voltage vs, and from the ratio of these values, Vs /Vo '' (Vs /I) / (VH /I)
=Rs/R.

Then, the value of the quantized Hall resistance RH and the voltage ratio v3/V,
, the value of the reference resistance R, can be determined from . Therefore, the larger the values of the Hall voltage V)I and the reference voltage V3, in other words, the larger the constant current I, the better the measurement accuracy becomes. For example, if the current measurement limit is 1 pA, the measurement accuracy is O,ippm for a current value of 10 uA, but since it is the most stable for 100 uA, the conventional quantum Hall element HE
In this case, it is important as an element for a standard resistance generator of 12.9Ω.

[Problems to be Solved by the Invention] However, in the conventional quantum Hall element HE described above, there is a limit to the amount of current that can be flowed into one quantum Hall element HE. That is, when the amount of current increases, the current concentrates at the point where the current flows into the quantum Hall element HE, which causes an important problem in that the temperature of the electrons increases and the quantum Hall effect no longer occurs. Therefore, there is a limit to the amount of current that can be flowed into the quantum Hall element HE (the limit was about 10 to 20 LLA in the case of the conventional quantum Hall element HE), and there is also a limit to the accuracy of measuring the resistance value.

Also, from the perspective of a standard resistor, the value of the quantized Hall resistance RH is 1-OKΩ, which is closest to 12.9Ω.
Since the IKΩ standard resistor is the most stable and reliable than the standard resistor, it is necessary that the value of the quantized Hall resistance R, can be measured with the highest accuracy around 1Ω.

Furthermore, with regard to voltage dividers, in conventional devices that utilize the turns ratio of the coil, the capacitance ratio of the capacitor, etc., it is impossible to avoid the effects of the resistance, inductance, etc. of the coil itself.

The present invention was made in order to solve the above-mentioned problems of the conventional quantum Hall device, and it is an object of the present invention to provide a multiple quantum Hall device that can increase the amount of current that can be injected.

[Means for Solving the Problems] The multiplexed quantum Hall device according to the present invention is a semiconductor multiplexed heterojunction by forming multiple heterojunctions that generate a two-dimensional electron gas layer on a high-purity semi-insulating gallium arsenide substrate. This semiconductor multiple heterojunction crystal plate is used as a bonded crystal plate, and this semiconductor multiple heterojunction crystal plate is etched into a plateau shape to form a rectangular plateau, and ohmic electrodes are formed at both ends of the long axis of the plateau and at both ends of the central portion.

[Effect]

According to this invention, since the two-dimensional electron gas layer is multiplexed, the amount of current that can be passed into the multiplex quantum Hall element increases by the amount of multiplex, and the measurement accuracy of quantized Hall resistance is dramatically improved. will be improved. For example, if the number of stacked layers of two-dimensional electron gas is 13, the value of the quantized Hall resistance obtained is R,412,9Ω/132O,992Ω, which is the most stable existing standard resistance. This allows for one-to-one comparative measurements with the IKΩ standard resistor, which is a standard resistor, making it possible to value the resistor with even higher accuracy.

Furthermore, by using the combination type resistance standard device according to the present invention, reference values for many types of resistance can be generated simultaneously.
At the same time, it becomes possible to value many resistors with high precision. Furthermore, by using a precision voltage divider, many types of voltage ratios can be measured with high precision without being affected by inductance or capacitance.

[Example] As an example, FIG. 1 shows an example of the structure of a semiconductor multiple heterojunction crystal plate 30 having multiple two-dimensional electron gas layers, among examples of the method for manufacturing a multiple quantum Hall device for Ω. Figure 2 (a
) to (h), as shown in FIG. 1, additive-free gallium arsenide is applied to a high purity semi-insulating gallium arsenide substrate 21 in an ultra-high vacuum. Here, the amount of silicon atoms added is lXl
The number should be around 0"pieces/cm". And each layer 23, 24
25 is repeated and grown 12 more times to form a multilayer 26, and finally, a silicon-doped gallium arsenide layer 27 is grown to a thickness of about 200 angstroms to prevent surface oxidation. Through the above steps, the semiconductor multiple heterojunction crystal plate 30 is formed. By manufacturing this structure (Fig. 1), the additive-free gallium arsenide layer 23 and the additive-free aluminum layer 23 are formed.
A two-dimensional electron gas layer is generated at each interface with the gallium arsenide layer 24. Therefore, a total of 13 two-dimensional electron gas layers are formed. A second semiconductor multi-heterojunction crystal plate 30 having 13 two-dimensional electron gas layers prepared in this way is
Processing is performed according to the process shown in the figure to produce a quantum Hall device having a structure similar to that shown in FIG. 6(a). This procedure is described below with reference to FIGS. 2(a) to (h).

In order to form a rectangular plateau containing multiple two-dimensional electron gas layers where the quantum Hall effect occurs, as shown in FIG. 2(a), the surface is Ultraviolet light U is applied to the surface of the semiconductor multiple heterojunction crystal plate 30 coated with photoresist 40 over the entire area.
Irradiate (expose) V.

Next, after developing as shown in Fig. 2(b), Fig. 2(c)
Using a mixture of sulfuric acid, hydrogen peroxide, and water, plateau-type etching (
Mesa etching).

Next, after removing the remaining photoresist 40 as shown in FIG. 2(d), photoresist 41 is again applied to the surface of the mesa-etched semiconductor multiple heterojunction crystal plate 30 as shown in FIG. 2(e). Then, it is exposed to ultraviolet light through a photomask 51 drawn so that the portions that will become electrodes are holes.

Next, after development as shown in FIG. 2(f), gold and germanium, which are ohmic electrode materials, are deposited on the entire surface of the semiconductor multiple heterojunction crystal plate 30 using a vacuum evaporation method as shown in FIG. 2(g). alloy (A u G e ).

Thin films 60 of nickel (Ni) and gold (Au) are sequentially deposited for electrodes 31 to 34 (electrodes 33 and 34 are not shown).

Next, as shown in Figure 2 (h), the excess metal thin film in areas unrelated to the electrodes is removed by a lift-off method, and finally heat treatment is performed to remove mainly germanium from the deposited metal into a two-dimensional electron gas layer. The ohmic electrode 31.3 diffuses towards
form 2.

The multiple quantum Hall device thus fabricated as shown in FIG. 6(a) was heated at a liquid helium temperature (4.2
), apply an appropriate magnetic field (about 6 to 8 Tesla) perpendicular to the surface of the multiplexed quantum Hall device according to the electron concentration of the two-dimensional electron gas layer, preferably in an atmosphere at an even lower temperature (about 1.5 Tesla). do. Under such an environment, Figure 6 (
a) If a current flows from the ohmic electrode 11 to the ohmic electrode 12 in the middle, a quantized Hall voltage ■ will be generated between the ohmic electrode 13 and the ohmic electrode 14. occurs.

By dividing this electromotive force by the inflow current, a precise value of the quantized Hall resistance R0 can be obtained.

FIG. 3 shows a configuration example of a combination type resistance standard device as an example of the use of the present invention. Here, as an example, four types of multiplexed quantum Hall elements HEI, HE2. HE13. H
A device is shown in which E129 is connected in series to a constant current source. n=1.2, 13, 129 are each RH=12.9
It corresponds to Ω, 6.45Ω, IKΩ and 100Ω, and when measuring the value of an unknown resistance R, when Rx is connected in series to this device, the voltage generated at the Rx terminal is measured. Voltage ■8 and 4 types of quantized Hall voltage (V□, V
82. The exact value of the unknown resistance Rx can be determined by finding the ratio of V Hps + V 14129) to the nearest voltage.

FIG. 4 shows an example of the configuration of a precision voltage divider as another example of the use of the present invention. In this device, a certain voltage ■. The number n of two-dimensional electron gas layers stacked in series is β, , I22, 12, respectively.
m multiple quantum hole elements HEfll, HEj22. H
Eε3 is connected and is generated as a quantized Hall voltage of each element. Therefore, by configuring this device with many multiple quantum Hall devices in which the number n of two-dimensional electron gas layers stacked is the same or different, a precision voltage divider with a very high degree of freedom in partial pressure can be obtained.

[Effects of the Invention 1] As explained in detail above, the present invention provides a semiconductor multiple heterojunction crystal plate by forming multiple Peter junctions that generate a two-dimensional electron gas layer on a high-purity semi-insulating gallium arsenide substrate. This semiconductor multiple Peter junction crystal plate was etched into a plateau shape to form a rectangular plateau, and ohmic electrodes were formed at both ends of the long axis and at both ends of the plateau. A current several steps higher than the element can be passed through the element, and the measurement accuracy of the quantized Hall resistance is improved accordingly. In addition, since a quantized Hall resistance of almost 1Ω is obtained at the same time, it becomes easier to assign a value to the existing extremely stable 1Ω standard resistor, and further accuracy can be achieved. Further, by applying the present invention to a combination type resistance standard device, it becomes possible to price many types of resistors with high accuracy. Furthermore, if used in a precision voltage divider, voltage can be divided accurately without being affected by inductance or capacitance components such as lead wires. Therefore, the measurement accuracy of various measuring instruments can be improved by using the multiple quantum Hall device according to the present invention.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of multiple two-dimensional electron gas layers in an embodiment of the multiple quantum Hall device according to the present invention, and FIG.
) to (h) are process diagrams of the method for manufacturing a multiplexed quantum Hall device according to the present invention, FIG. 3 is a diagram showing an example of a combination type resistance standard device, FIG. 4 is a diagram showing an example of a precision voltage divider, and FIG. Figure 5 is a diagram briefly explaining the quantum Hall effect, Figure 6 (a) is a perspective view showing the structure of a conventional quantum Hall element, and Figure 6 (
b) is a partially enlarged view of FIG. 6(a), and FIG. 7 is a circuit diagram for measuring quantized Hall resistance. In the figure, 21 is a semi-insulating gallium arsenide substrate, 22 is a gallium arsenide buffer layer, 23 is an undoped gallium crystal plate, 31 -
34 is an electrode, 40.41 is a photoresist, 50.51
is a photomask, and UV is ultraviolet light. Figure 1 Figure x Figure V. Figure Figure

Claims (1)

[Claims] A semiconductor multiple heterojunction crystal plate is obtained by forming multiple heterojunctions that generate a two-dimensional electron gas layer on a high-purity semi-insulating gallium arsenide substrate, and plateau-shaped etching is applied to this semiconductor multiple heterojunction crystal plate. 1. A multiplex quantum Hall device characterized by forming a rectangular plateau and forming ohmic electrodes at both ends of the longitudinal axis of the plateau and at both ends of the central part.