JPH0687509B2 - Heterojunction magnetic sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic sensor used for various measurements and controls in the fields of electronic and mechanical industries.

[Conventional technology]

Conventionally, the heterojunction magnetic sensor is made of GaAs containing no impurities.
Two-dimensional electron gas layer (hereinafter referred to as 2DEG layer) by bonding the layer to the AlGaAs layer (supervisor layer) that does not contain impurities
And AlGa containing n-type impurities in the AlGaAs layer.
It was configured to join the As layer (carrier supply layer).

However, in the above sensor, when a high electric field is input, n
Type surplus carriers are generated in the AlGaAs layer and the 2DEG layer is excessively filled with carriers, resulting in saturation of sensitivity, and this extra carrier contributes to electrical conduction in parallel with the 2DEG layer, reducing the average mobility. However, there was a problem that high output could not be obtained.

[Problems to be Solved by the Invention]

The present invention has been made in view of the above points, and an object thereof is to provide a magnetic sensor that can obtain a high output without saturating the sensitivity even when driven by a high electric field.

[Means for Solving the Problems]

Consider the design principle of a Hall element, which is a basic magnetic sensor. In rectangular Hall element, the input voltage V _in and the output voltage (Hall voltage) relationship V _H, if V _in is sufficiently small,
It is expressed by the following equation.

V _H = (W / l) · μ _HO · B / V _in (1) where l and W are the length and width of the device, μ _HO is the Hall mobility of the device in the low electric field, and B is , The magnetic flux density.

When the input voltage increases, it is necessary to consider the decrease in hole mobility due to the generated heat and electric field, and the maximum hole mobility is expressed by the following equation.

V _Hmax = B ・ w ・ μ _H・ (2 ・ h ・ ΔT ・ ρ / t) ^1/2 ……
(2) Here, μ _H , h, ρ, and t are high electric field hole mobility, heat transfer coefficient, specific resistance, and thickness of the element, and ΔT is a temperature difference between the element and the surroundings.

Here, ρ / t is a term representing the internal resistance of the element, but the internal resistance of the element is within a certain range (number +
Ω to several kilo Ω) is preferable. Therefore, in order to increase the output of the Hall element, it is necessary that the mobility of the high electric field is large under this condition.

Therefore, the present invention provides a heterojunction magnetic sensor having a two-dimensional electron gas layer, which is provided adjacent to the two-dimensional electron gas and has a quantum well structure having an energy state larger than that of the two-dimensional electron gas layer. Further, the present invention provides a technical means in which the sensitivity is not saturated even in a high electric field by providing the element and a high output is obtained by improving the mobility. In a heterojunction magnetic sensor including a heterojunction structure forming a two-dimensional electron gas layer,
A heterojunction magnetic sensor is provided, which is provided adjacent to a carrier supply layer that supplies electrons to the two-dimensional electron gas layer and has a quantum well structure semiconductor layer having an energy state higher than that of the two-dimensional electron gas layer.

[Action]

In addition to the 2DEG layer having a low energy state, a semiconductor layer having a quantum well structure is provided, so that the excess carriers generated by a high electric field are not only filled in the 2DEG layer but also in the semiconductor layer having a quantum well structure. , The 2DEG layer is not saturated by the excess carriers, and the excess carriers move to the 2DEG layer or the quantum well layer to improve the mobility, so that the average mobility by contributing to the electric conduction in parallel with the 2DEG layer A heterojunction magnetic sensor can be obtained that can prevent deterioration and that can output high power even in a high electric field.

〔Example〕

Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings.

FIG. 1 shows a schematic configuration diagram when the present invention is applied particularly to a Hall element. In this case, a high mobility two-dimensional electron gas layer (hereinafter referred to as a 2DEG layer) is formed at the heterojunction portion between the two types of semiconductor layers 4 and 5 having different band gaps.
6 is formed. The semiconductor layer 5 is composed of an impurity-doped semiconductor layer 5b (carrier supply layer) and an undoped semiconductor layer 5a (supervisor layer), and the semiconductor layer 5a has a quantum well structure. In addition, in FIG. 1, 2a and 2b are
Current terminals 3a and 3b for supplying current to the Hall element H
Is a Hall terminal for taking out the Hall electromotive force V _H generated when a magnetic field of magnetic flux density B is applied to the Hall element H.

Next, a specific structure of the Hall element H and a manufacturing method thereof will be described.

FIG. 2 shows, as a first embodiment, the structure of a heterojunction semiconductor with a quantum well layer, on a semi-insulating GaAs substrate 7,
Non-doped CaAs 4, non-doped barrier layer 5 that is a barrier layer
a-1, non-doped well (quantum well) layer 5a-2, non-doped barrier layer 5a-3 that is a barrier layer, carrier supply layer
5b, Si-doped CaAs layer 5c are sequentially grown by molecular beam crystal growth (MBE)
Was formed using. In addition to the above, metal organic vapor phase epitaxy,
A liquid phase growth method or the like may be used. Here, the case where 5a-1 is non-doped AlAs, 5a-2 is non-doped GaAs, 5a-3 is non-doped AlGaAs, and 5b is Si-doped AlGaAs will be described as a first embodiment.

As can be seen from FIG. 2, the 2DEG layer 6 is made of undoped GaAs.
It is formed on the boundary surface of the layer 4 on the non-doped barrier layer 5a-1 side. The quantum well structure consisting of the non-doped barrier layers 5a-1 and 5a-3 and the non-doped well layer 5a-2 prevents Si in the n-type Si-doped carrier supply layer 5b from entering the non-doped GaAs4. In addition to the above, it is provided to improve the mobility in a high electric field.

Further, the above-mentioned current terminals 2a, 2b, and the Au-Ge ohmic electrode 200 functioning as an electrode of the hole terminals 3a, 3b, the layers 4,5a-1, 5a-2, 5a-3, 5b, and 5c. Formed to have ohmic contact.

The semi-insulating GaAs substrate for crystal growth is cleaned by a mixed solution of concentrated sulfuric acid, hydrogen peroxide solution, and pure water (volume ratio of 4:
Etching was performed for about 1 minute in a 1: 1, liquid temperature 60 ° C.), and thermal etching was performed in a vacuum chamber for crystal growth while applying arsenic vapor. Typical examples of the crystal growth conditions in the first embodiment are as follows.

1.Ga flux: 4.8 × 10 ^-7 Torr 2.As flux: 1.0 × 10 ^-5 Torr 3.Al flux: 1.2 × 10 ^-7 Torr 4.Crystal growth temperature: 630 ° C 5.Crystal growth rate: 1.20 μm / hr (GaAs) 1.65 μm / hr (AlGaAs) 0.45 μm / hr (AlAs) 6. First layer: non-doped GaAs (500 nm) Second layer: non-doped AlAs (1.5 nm) Third layer: non-doped GaAs (2.0 nm) 4th layer: non-doped AlGaAs (5.0 nm) 5th layer: Si-doped AlGaAs layer (75 nm) 6th layer: Si-doped GaAs (10 nm) Here, Si doping concentration is 1 × 10 ¹⁸ cm ⁻³ .

7. Ohmic electrode is due to alloying of AuGe (7% to 12%) / Ni / Au evaporated film.

A possible action of the heterojunction Hall element obtained by the above method will be described with reference to the energy band diagram of FIG.

First, when a positive voltage is applied to the current terminals 2a and 2b, when a current flows through the 2DEG layer 6 having a lower energy state than the n-type AlGaAs layer 5b which is a carrier supply layer, the energy possessed by the electrons is lowered and the electrons move. The degree increases.

In that state, when a high electric field is applied, the energy of the electrons filled in the 2DEG layer 6 increases and the effective mass increases, so that the mobility decreases. However, in the structure of the first embodiment, Ga having a slightly higher energy state than the 2DEG layer 6 is provided through the 1.5 nm non-doped AlAs layer 5a-1.
Since the As layer 5a-2 is provided, the electrons cause a real space transition, and the GaAs layer 5a-2 passes through the non-doped AlAs layer 5-1.
Begin to meet. Therefore, a part of the energy of the electrons filled in the GaAs layer 5a-2 is converted into potentian energy, which reduces the effective mass of the electrons and increases the mobility again.

In addition, the excess carriers in the AlGaAs layer 5b, which is a carrier layer generated by applying a high electric field, can take the energy state of not only the 2DEG layer 6 but also the quantum well layers 5a-b, so that the mobility is high. It is possible to prevent the existence of surplus carriers having a low mobility, and to prevent a decrease in average mobility.

Here, when the width of the GaAs layer 5a-2 becomes large, the GaAs layer 5a-
The energy state of 2 becomes low, and Ga
The number of electrons remaining in the As layer 5a-2 increases, and it becomes difficult to obtain the above effect.

Therefore, FIG. 4 shows the relationship between the low electric field mobility and the quantum well width (thickness of 5a-1) of the device of the first embodiment. In this structure, the mobility drops sharply when the quantum well width is 2.5 mm or more.

Next, 5a-1 is non-doped AlAs and 5a-2 is non-doped Ga.
As and 5a-3 are undoped AlAs, 5b is undoped AlAs
A second embodiment is a superlattice having a basic structure of / non-doped GaAs / Si-doped GaAs / non-doped GaAs, and FIG. 5 shows a schematic sectional view thereof.

In the second embodiment, the n-type AlGaAs layer 5b of the first embodiment is replaced by a non-doped AlAs layer (1.5 nm) 50b-1 and a non-doped GaAs layer (0.
5 nm) 50b-2, Si-doped GaAs layer (1.5 nm) 50b-3, and non-doped GaAs layer (0.5 nm) 50b-4 with a basic structure of 4 nm.
Replaced by a semiconductor layer 50b with a superlattice structure of m
The GaAs layer 5a-3 is replaced with a non-doped AlAs layer (1.5 nm) 50a-3 to form a superlattice Hall element with a quantum well layer. Second
FIG. 6 shows the quantum well width dependence of the low electric field mobility of the example. In this structure, the mobility drops sharply when the quantum well width is 5.0 nm or more. It should be noted that the fact that the quantum well width with reduced mobility is thicker than that in the case of FIG. 4 corresponds to the fact that the non-doped AlAs layer 5a-3 is thin in the second embodiment.

Next, the characteristics of the magnetic sensors of the first and second embodiments when driven in a high electric field will be described based on the measurement values measured by the present invention. FIG. 7 shows the electric field dependence of the mobility of the heterojunction Hall element with a quantum well layer of the first embodiment. In the element having a quantum well width of 2.0 nm or less, which does not cause the decrease in low electric field mobility described above, the decrease in high electric field mobility decreases as the quantum well width increases. FIG. 8 shows the electric field dependence of the magnetic field sensitivity of the second embodiment. The magnetic field sensitivity becomes maximum when the quantum well width is 2.0 nm.

FIG. 9 shows the quantum well width dependence of the mobility of the superlattice Hall element with a quantum well layer of the second embodiment. As in the case of the first embodiment, the maximum mobility is obtained when the quantum well width is 2.0 to 2.5 nm. The measurement was carried out at a low temperature in order to prevent the measured value from changing due to a deep level donor.

Table 1 shows the maximum magnetic field sensitivities of the first comparative example and the second comparative example, which do not have the quantum well layers of the first and second embodiments and have the same structure as the others.

As shown in Table 1, in the first embodiment, the quantum well width is 2.0 nm.
The maximum magnetic field sensitivity is 7 V / T at that time, which is 20% higher than that of the conventional heterojunction Hall element. In the second embodiment, the maximum magnetic field sensitivity is 18 V / T when the quantum well width is 2.5 nm. The output power is 60% higher than that of the superlattice Hall element.

Further, a structure in which the positional relationship among the semiconductor layer having the quantum well structure, the two-dimensional electron gas layer, and the carrier supply layer is changed is referred to as a third embodiment to a sixth embodiment, and is shown in FIGS. 10 to 13. Even with such a structure, high output of the device can be realized.

Further, the magnetic sensor other than the Hall element, such as the drain-separated magnetic sensor having the cross-sectional structure shown in the first to sixth embodiments, can achieve high output.

As described above, according to the present invention, by providing a semiconductor layer having a quantum well structure having an energy state higher than that of the two-dimensional electron gas layer, the sensitivity is saturated even in a high electric field. In addition, a magnetic sensor can be obtained with high output due to improved mobility, and an excellent effect that it can greatly contribute to high accuracy of measurement and control can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a heterojunction Hall element that is the first embodiment of the present invention, FIG. 2 is a schematic cross-sectional view of the heterojunction Hall element of the first embodiment, and FIG. 3 is energy of the first embodiment. FIG. 4 is a band diagram, FIG. 4 is a characteristic diagram showing the relationship between the low electric field mobility and the quantum well width of the first embodiment, FIG. 5 is a schematic sectional view showing the second embodiment of the present invention, and FIG. FIG. 7 is a characteristic diagram showing the relationship between the low electric field mobility and the quantum well width of the second embodiment.
A characteristic diagram showing the relationship between the relative mobility of the example and the input electric field,
FIG. 8 is a characteristic diagram showing the relationship between the magnetic field sensitivity and the input electric field in the first embodiment, FIG. 9 is a characteristic diagram showing the relationship between the relative mobility and the input electric field in the second embodiment, and FIGS. 13 figures,
It is a schematic sectional drawing of the Hall element of a 3rd example-6th example. 5a ... semiconductor layer, 5a-2 ... quantum well width layer, 5b ... carrier supply layer, 6 ... two-dimensional electron gas layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page Examiner Shigehiro Toyonaga

Claims (6)

[Claims] 1. A heterojunction magnetic sensor including a heterojunction structure in which a high-mobility two-dimensional electron gas layer is formed at a junction of different semiconductors having different band gaps, the heterojunction magnetic sensor being adjacent to the two-dimensional electron gas layer. A heterojunction magnetic sensor provided with a semiconductor layer having a quantum well structure having an energy state higher than that of the two-dimensional electron gas layer. 2. The heterojunction magnetic sensor according to claim 1, wherein the semiconductor layer forms the quantum well structure by being provided between two barrier layers serving as energy barriers. 3. The semiconductor layer having the quantum well structure is located between the two-dimensional electron gas layer and a carrier supply layer that supplies electrons to the two-dimensional electron gas layer. The heterojunction magnetic sensor according to the item. 4. The hetero according to claim 1, wherein the semiconductor layer having the quantum well structure is provided between the two-dimensional electron gas layer and the substrate of the heterojunction magnetic sensor. Junction magnetic sensor. 5. A heterojunction magnetic sensor including a heterojunction structure in which a high mobility two-dimensional electron gas layer is formed at a junction of different semiconductors having different band gaps, and electrons are supplied to the two-dimensional electron gas layer. A heterojunction magnetic sensor provided adjacent to the carrier supply layer having a quantum well structure having an energy state higher than that of the two-dimensional electron gas layer. 6. The heterojunction magnetic sensor according to claim 5, wherein the semiconductor layer forms the quantum well structure by being provided between two barrier layers serving as energy barriers.