JPH0691287B2 - 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.
By joining the layers to the AlGaAs layer (spacer layer) containing no impurities, the GaAs containing no impurities at the heterojunction interface
A two-dimensional electron gas layer (hereinafter referred to as a 2DEG layer) is formed in the layer, and the AlGaAs layer (carrier supply layer) containing n-type impurities is bonded to this AlGaAs layer.

However, in the above sensor, when a high electric field is input, n
-Type AlGaAs layers generate excess carriers and the 2DEG layer is overfilled with carriers, which saturates the sensitivity, and the excess carriers contribute 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 Problem] Consider the design principle of a Hall element, which is a basic magnetic sensor. In rectangular Hall element, the relationship between the input voltage V _in and the output voltage (Hall voltage) V _H, if V _in is no influence of sufficiently small high field effect and Joule heat 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 Magnetic flux density.

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

V _Hmax = B ・ w ・ μ _H (E) ・ (2 ・ h ・ ΔT ・ ρ / t)
^1/2 (2) where μ _H (E), h, ρ, and t are the high electric field Hall mobility, heat transfer coefficient, specific resistance, and thickness of the device, and ΔT is the device and its surroundings. Is the temperature difference.

Here, ρ / t is a term representing the internal resistance of the element, but the internal resistance of the element is preferably within a certain range (several tens of Ω to several kilo Ω) from the compatibility with the external circuit. 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, in the present invention, in a heterojunction magnetic sensor having a 2DEG layer, a plurality of quantum well structure semiconductor layers having energy levels higher than the energy levels of free carriers of the 2DEG layer and different from each other are adjacent to the 2DEG layer. By providing a layer and exhibiting its characteristics in a high electric field,
The technical means is that sensitivity is not saturated even in a high electric field and high output is obtained by improving mobility.

[Action]

Since a quantum well structure semiconductor layer is provided adjacent to the 2DEG layer having a low energy state, the electrons in the 2DEG layer whose energy gained and the effective mass increased when a high electric field was applied
A real-space transition occurs in the quantum well layer, which has a higher energy state than the EG layer, and at this time part of the energy is converted to potential energy, which reduces the effective mass of the electron and increases the mobility. It is effective to increase the number of carriers that can enter the quantum well layer in order to facilitate real space transition, but if the quantum well layer is made thicker,
The mobility of the quantum well layer does not increase much because the energy state of the quantum well layer becomes low and the electron energy loss is small even if the transition occurs in real space. However, by providing multiple quantum well layers, it is possible to increase the number of electrons that can fill the quantum well layer without lowering the energy state of the quantum well layer, and to facilitate real-space transitions. The mobility is higher than that when the number of well layers is one.

In addition, the excess carriers generated in the carrier supply layer in a high electric field are not only filled in the 2DEG layer but also in the semiconductor layer of the quantum well structure, so that the 2DEG layer is not saturated by the excess carriers, and the excess carriers are not generated. The carriers move to the 2DEG layer or the quantum well layer, and the mobility is improved.
Although it is possible to prevent the average mobility from decreasing by contributing to electric conduction in parallel with the layers, the mobility is further increased because the number of carriers that can fill the quantum well layer is increased by providing multiple quantum well layers. Is increased, and a heterojunction magnetic sensor having a high output even in a high electric field can be obtained.

Furthermore, the present invention is characterized in that not only a plurality of quantum well layers having an energy state higher than that of the two-dimensional electron gas layer are provided, but also quantum well layers having different energy levels are provided. To do.

Then, by making the energy levels of the quantum well layers different from each other in this way, it is easy to cause a real space transition from a high energy level to an appropriate quantum well layer for all electrons having a higher energy level. It is possible.

That is, when an ordinary high electric field is applied, the energy of the electron given according to the applied electric field is converted into the potential energy of the quantum well layer, and the quantum energy of the quantum well layer having the lower energy level is converted. A real space transition can be made to the well layer. Then, when an even higher electric field is applied, the electrons have very high energy, so this energy is converted into high potential energy in the quantum well layer, and the higher energy level in the quantum well layer is converted. It is possible to make a real-space transition to the quantum well layer that it has.

〔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 of 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 (spacer 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 GaAs4, non-doped barrier layer 5a-1, non-doped well (quantum well) layer 5a-2, carrier supply layer 5b,
The Si-doped GaAs layer 5c was sequentially formed by the molecular beam crystal growth method (MBE). Alternatively, a metal organic vapor phase epitaxy method, a liquid phase epitaxy method, or the like may be used. 5a-1 is undoped AlGaAs,
A case where 5a-2 is non-doped GaAs and 5b is Si-doped AlGaAs will be described as a first embodiment. Note that FIG. 2 shows the case where the number of non-doped quantum well layers added is two.

As can be seen from FIG. 2, the 2DEG layer 6 is made of undoped GaAs.
It is formed on the heterojunction boundary surface of the layer 4 on the non-doped barrier layer 5a-1 side. The quantum well layer composed of the non-doped barrier layer 5a-1 and the non-doped well layer 5a-2 contains n-type impurities.
Si in the carrier supply layer 5b doped with Si is undoped
It is provided not only to prevent invasion into the GaAs layer 4 but also to improve 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 make ohmic contact with the layers 4,5a-1, 5a-2, 5b, 5c. Although it is formed so as to have an Au—Sn electrode with low low-frequency noise, it may be used.

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 ℃ 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 AlGaAs (1.5 nm) Third layer: non-doped GaAs (2.5 nm) 4th layer: Non-doped AlGaAs (1.5nm) 5th layer: Non-doped GaAs (2.5nm) 6th layer: Non-doped AlGaAs (1.5nm) 7th layer: Si-doped AlGaAs (75nm) 8th layer: Si-doped GaAs (10nm) Therefore, the Si doping concentration is 1 × 10 ¹⁸ cm ⁻³ .

7. Ohmic electrodes are formed by alloying 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.

In the quantum wells 5a-2-1 and 5a-2-2 and the 2DEG layer 6, the energy state at the bottom of the conduction band is shown and the ground quantum level A generated by the quantum effect is also shown.

First, when a positive voltage is applied to the current terminals 2a and 2b, the ground quantum level A from the n-type AlGaAs layer 5b, which is the carrier supply layer, is increased.
When a current flows through the 2DEG layer 6 having a low energy state, the energy of electrons is low and the mobility of electrons is high.

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, the 1.5 nm non-doped AlGaAs layer 5a-1-
GaAs layers 5a-2-1 and 5a whose energy state of the ground quantum level A is slightly higher than that of the 2DEG layer 6 via 1, 5a-1-2.
-2-2 is provided, the electrons cause a real space transition, and the GaAs layers 5a-2-1 and 5a-2-2 are passed through the non-doped AlGaAs layers 5a-1-1 and 5a-1-2. Begin to meet. Therefore, a part of the energy of the electrons filled in the GaAs layers 5a-2-1 and 5a-2-2 is converted into potential energy, which reduces the effective mass of the electrons and increases the mobility again.

Also, the carriers in the AlGaAs layer 5b, which is a carrier supply 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 layer 5a-2. 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 the ground quantum level of 2 becomes low, and the number of electrons remaining in the GaAs layer 5a-2 increases even in a low electric field, making it difficult to obtain the above effect.

However, by providing multiple quantum well layers, the GaAs layer
The number of carriers that can fill the quantum well layer can be increased without lowering the energy state of the ground quantum level of 5a-2, and the above effect becomes more effective.

Further, in the first embodiment, the quantum well layer 5a-2-2
The energy level of 2 is set higher than that of the quantum well layer 5a-2-1 to obtain quantum well layers having different energy levels. Therefore, it is possible to make a real-space transition to the quantum well layer corresponding to the energy of the electrons in the 2DEG layer corresponding to the strength of the electric field, so that it is appropriate for all the electrons having higher to higher energy levels. A real space transition to the quantum well layer can be easily generated.

Next, the thicknesses of the GaAs layers 5a-2-1 and 5a-2-2 of the first embodiment are, for example, 2.5 nm for 5a-2-1 and 1.5 nm for 5a-2-2.
The second embodiment is changed as described above. In this way, by changing the width of the quantum well layer to increase the energy state of the quantum well layer 5a-2-2 on the opposite side to the quantum well layer 5a-2-1 on the 2DEG side, 5a-2-1 From 5a-2-2
A real space transition between the quantum well layers to the layers occurs and the mobility is further increased.

Next, 5a-1 is non-doped AlAs and 5a-2 is non-doped Ga.
As, 5b is non-doped AlAs / non-doped GaAs / Si-doped
A case of a superlattice having a basic structure of GaAs / non-doped GaAs is taken as a third embodiment, and its schematic sectional view is shown in FIG.

In the third 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.
5nm) 50b-2, Si-doped GaAs layer (1.5nm) 50b-3, non-doped GaAs layer (0.5nm) 50b-4 with a basic structure of 4nm.
Replaced with the semiconductor layer 50b of the superlattice structure of
The aAs layer 50a-1 is replaced with a non-doped AlAs layer (1.5 nm) to form a quantum well layered superlattice Hall element. The fourth
The figure shows the case where the number of quantum well layers 50a-2 is two.

FIG. 5 shows the electric field dependence of the mobility of the device of the third embodiment when driven by direct current. When the number n of the quantum well layers 50a-2 increases,
Although the low electric field mobility decreases, the rate of decrease in mobility with increasing electric field decreases. It should be noted that n =
In the case of 1, the low electric field mobility is high because the spacer layer becomes thicker to improve the separation between the doped impurities and the carriers in the 2DEG layer.

FIG. 6 shows the electric field dependence of the magnetic field sensitivity of the device of the third embodiment when driven by direct current. When the number n of the quantum well layers 50a-2 increases, the magnetic field sensitivity in a low electric field decreases, but the magnetic field sensitivity in a high electric field becomes larger than that in the case of n = 0, and a high output can be obtained.

Furthermore, if the element is downsized and driven by a high electric field, the effect of increasing the output of the magnetic sensor by providing a plurality of quantum well layers 50a-2 is further enhanced.

In addition, a double hetero structure in which a plurality of quantum well layers are provided on one side or both sides adjacent to the 2DEG layer is the fourth embodiment. In the hetero structure of the reverse structure in which the carrier supply layer is provided on the substrate side, the 2DEG layer is formed. In the fifth embodiment, a structure having a plurality of quantum well layers adjacent to, is a heterojunction structure, and a sixth embodiment has a structure having a plurality of quantum well layers adjacent to 2DEG on the substrate side.
Schematic sectional views are shown in FIG. 7, FIG. 8 and FIG. 9, respectively. 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 separation type magnetic sensor having the sectional structure shown in the first to sixth embodiments can achieve high output.

〔The invention's effect〕

As described above, according to the present invention, since the spacer layer of the heterojunction Hall element has the quantum well structure, the decrease in high electric field mobility can be reduced, a high output magnetic sensor can be obtained, and high measurement and control can be achieved. An excellent effect that it can greatly contribute to the improvement of accuracy is obtained. Furthermore, a real space transition from a high energy level to a suitable quantum well layer for all electrons with a higher energy level can easily occur.

[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 schematic sectional view showing a third embodiment of the present invention, FIG. 5 is a characteristic diagram showing the relationship between the mobility and the input electric field of the third embodiment, and FIG. 6 is a third embodiment. Is a characteristic diagram showing the relationship between the magnetic field sensitivity and the input electric field of FIG. 7, FIG. 8, FIG.
It is a schematic sectional drawing of the Hall element of an Example, a 5th Example, and a 6th Example. 5a ... semiconductor layer, 5a-2 ... quantum well layer, 5b ... carrier supply layer, 6 ... two-dimensional electron gas layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page Examiner Shigehiro Toyonaga (56) References The Institute of Electronics, Information and Communication Engineers, "Technical Research Report of The Institute of Electronics, Information and Communication Engineers" ED87 "369" (Sho 63-2-15) p. 7-14

Claims (1)

[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 hand gaps. A heterojunction magnetic sensor comprising a plurality of quantum well structure semiconductor layers having high energy states different from each other.