JPH0297075A - Heterojunction magnetic sensor - Google Patents

Abstract

PURPOSE:To obtain a magnetic sensor which is not saturated in sensitivity even with strong electric field driving and capable of outputting a high power by a method wherein two or more semiconductor layers of quantum well structure, whose energy level are higher than that of a two-dimensional electron gas layer, are provided. CONSTITUTION:Two or more semiconductor layers 5a-2, whose energy levels are higher than that of a two-dimensional electron gas layer 6, are provided to a heterojunction magnetic sensor that contains a heterojunction structure in which the two-dimensional electron gas layer 6 of high mobility if formed at a junction between different semiconductors, 4 and 5, whose energy gaps are different from each other. For instance, a non-doped GaAs layer 4, non- doped barrier layers 5a-1, non-doped quantum well layers 5a-2, a carrier supply layer 5b, and an Si doped GaAs layer 5c are successively formed on a semi- insulating GaAs substrate 7, where the number of the quantum well layers 5a-2 is two. And, Au-Ge ohmic electrodes 200 serving as a current terminal and a hole terminal are so formed as to have an ohmic contact with the above layers 4, 5a, 5b, and 5c.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic sensor used for various measurements and controls in the electronic and mechanical industry fields.

[Prior art] Conventionally, a heterojunction magnetic sensor uses Ga that does not contain impurities.
By bonding AsFj to an impurity-free AlGaAs layer (spacer layer), a two-dimensional electron gas layer (hereinafter referred to as 2DEC) is formed on the impurity-free GaAs layer at the heterojunction interface.
) is formed and this Al2GaAs layer contains n-type impurities! .

It was configured to bond a GaAs layer (carrier supply layer).

However, in the above sensor, when a high electric field is input, n
Surplus carriers are generated in the type AfGaAs layer and 2DEG
The problem is that sensitivity is saturated because the layer is filled with excess carriers, and furthermore, this excess carrier contributes to electrical conduction in parallel with the 2DEG layer, reducing the average mobility, making it impossible to obtain high output. There was a point.

[Problem to be solved by the invention]

In view of the above points, the present invention has been made with the object of providing a magnetic sensor that can obtain high output without saturating its sensitivity even when driven in a high electric field.

[Means to solve the problem]

Let's consider the design principle of the Hall element, which is a basic magnetic sensor. In the rectangular Hall element, the relationship between the input voltage v1 and the output voltage (Hall voltage) VH is expressed by the following equation when vi, is sufficiently small and there is no influence of high electric field effect or Joule heat.

V)l = (W#ri・μ,.・B・
■Five. ・・・・・・・・・(1) Here! and W
are the length and width of the element, μNO is the low-field hole mobility of the element, and B is the magnetic flux density.

As the input voltage increases, it is necessary to take into account Joule heat and a decrease in Hall mobility due to electric field dependence, and the maximum Hall voltage is expressed by the following equation.

■, □=B-w・μ, (E)・(2・h・ΔT・ρ/
t) I/R・・・・・・・・・(2) Here, μ
H(E), h, ρ, and t are the high field hole mobility, heat transfer coefficient, resistivity, and thickness of the device, and ΔT is the temperature difference between the device and the surroundings.

Here, ρ/l is a term representing the internal resistance of the element, and the internal resistance of the element is preferably within a certain range (several tens of ohms to several kilohms) from the viewpoint of compatibility with an external circuit.

Therefore, in order to increase the output of the Hall element, under this condition,
High electric field mobility is required.

Therefore, in the present invention, in a heterojunction magnetic sensor having a 2DEC layer, a plurality of quantum well structure semiconductor layers having an energy level higher than the free carrier energy level of the 2DEC layer are provided adjacent to the 2DEG layer, By exhibiting its characteristics in a high electric field, the sensitivity does not saturate even in a high electric field, and it is a technical means to obtain high output by improving mobility.

[Effect]

Since a semiconductor layer with a quantum well structure is provided adjacent to the 2DEG layer with a low energy state, the electrons in the 2DEG, which gain energy and increase their effective mass when a high electric field is applied, have a higher energy state than in the 2DEC. A real-space transition occurs in the high quantum well layer, and at this time, part of the energy is converted to potential energy, reducing the effective mass of electrons and increasing their mobility. In order to make real space transition more likely to occur, it is effective to increase the number of carriers that can enter the quantum well layer, but if the quantum well layer is made thicker, the energy state of the quantum well layer becomes lower. ,
Even during real space transition, the mobility does not increase much because the loss of electron energy is small.

However, by providing multiple quantum well layers, the number of electrons that can fill the quantum well layer can be increased without lowering the energy state of the quantum well layer, making it easier for real space transitions to occur. The mobility increases compared to when the number of well layers is one.

In addition, surplus carriers generated in the carrier supply layer by a high electric field not only fill the 2DEC layer but also the semiconductor layer of the quantum well structure, so the 2DEC layer is not saturated with surplus carriers, and Carriers move to the 2DEC layer or quantum well layer and their mobility improves, so it is possible to prevent the average mobility from decreasing due to contribution to electrical conduction in parallel with the 2DEG layer, but by providing multiple quantum well layers, Since the number of carriers that can fill the quantum well layer increases, the mobility further increases, and a high-output heterojunction magnetic sensor can be obtained even in high electric fields.

〔Example〕

Hereinafter, the present invention will be explained in detail based on 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 2DEC layer) 6 is formed at the heterojunction between the two types of semiconductor layers 4 and 5 having different band gaps.

The semiconductor layer 5 includes a semiconductor layer 5b doped with impurities (carrier supply layer) and an undoped semiconductor 115a (spacer layer), and the semiconductor layer 5a has a quantum well structure. In addition, in FIG. 1, 2a and 2b are current terminals for flowing current to the Hall element H, and 3a and 3b are
is a Hall terminal for taking out the Hall electromotive force (8) 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 described above and a method of manufacturing the same will be explained.

FIG. 2 shows the structure of a heterojunction semiconductor with a quantum well layer as a first embodiment. On a semi-insulating GaAs substrate 7, non-doped GaAs 4 and a non-doped barrier layer 5a
-1, a non-doped well (N-well) layer 5a-2, a carrier supply layer 5b, and a St-doped GaAs layer 5C were sequentially formed using molecular beam crystal growth (MBE). In addition, metal organic vapor phase epitaxy, liquid phase epitaxy, etc. may also be used.

5a-1 is non-doped AffiGaAs, 5a-2 is non-doped GaAs, and 5b is Si-doped A2GaAs.
A case will be described as a first example.

In addition, in Figure 2, the number of additional non-doped quantum well layers is 2.
The case of

As can be seen from FIG. 2, 20EGJi6 is formed on the heterojunction boundary surface of the non-doped GaAs layer 4 on the non-doped barrier layer 5a-i side. Non-doped barrier layer 5a
-1 and a non-doped well layer 5a-2, the carrier supply layer 5 is doped with n-type impurity Si.
This is provided not only to prevent St in b from entering the non-doped GaAs layer 4, but also to improve mobility in a high electric field.

In addition, the above-mentioned current terminals 2a, 2b and Hall terminals 3
Au-Ge ohmic electrodes 200 functioning as electrodes a and 3b are connected to each layer 4.5a-1, 5a-2, 5b, 5.
An Au-3n electrode, which has low low frequency noise, may also be used.

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

1. Ga flux: 4.8 x 10-7 Torr
2. As flux = 1. OX 10-'Torr
3. Af flux: 1.2 x 10-'Torr
4. Crystal growth temperature = 630°C 5. Crystal growth rate: 1.20 μm/hr (GaA
s) 1,65 g m/hr (AfGaAs) 0.45 am/hr (A/!As)6, 1st layer:
Non-doped GaAs (500 nm) 2nd layer: Non-doped AfGaAs (1.5 nm) 3rd layer: Non-doped G
aAs (2.5 nm) 4th layer: non-doped Aj2Ga
As (1,5 nm) 5th N: non-doped GaAs (
2.5 nm) 6th layer: non-doped Ajl! GaAs (
1.5 nm) 7th layer: Si-doped A/! GaAs (7
5 nm) 8th layer: Si-doped GaAs (10 nm) where the Si doping concentration is I x 10 lIlcm-'.

7. Ohmic electrode is AuC;e (7% to 12%
) / Ni / Au by alloying the deposited film.

The possible effects of the heterojunction Hall element obtained by the above method will be explained using the energy band diagram shown in FIG.

In addition, quantum wells 5a-2-1, 5a-2-2 and 2D
EGN6 shows the energy state at the bottom of the conduction band and also shows the base quantum level A caused by quantum effects.

First, when a positive voltage is applied to the current terminals 2a, 2b, the n-type A l Ga A s which is the carrier supply layer
2D with a lower energy state of the ground quantum level A than the layer 5b
When a current flows through the EG layer 6, the energy of electrons is low and the mobility of electrons is high.

When a high electric field is applied in this state, the energy of the electrons filled in the 2DEG layer 6 increases, the effective mass increases, and the mobility decreases. However, in the structure of the first example, 1.5 nm of non-doped AAG
ZDE via the aAs layers 5a-1-1 and 5a-1-2
Since the GaAs layers 5a-2-1 and 5a-2-2 whose energy state of the ground quantum level A is slightly higher than that of the G layer 6 are provided, electrons undergo real space transition and the non-doped AffiGaAs layer 5a- The GaAs layers 5a-2-1 and 5a-2-2 begin to be filled through the layers 1-1 and 5a-1-2. Therefore, G a A s j15 a -2-
A part of the energy of the electrons filled in 1,5a-2-2 is converted into potential energy, thereby reducing the effective itt of the electrons and increasing the mobility again.

Further, carriers in the AfGaAs layer 5b, which is a carrier supply layer, generated by applying a high electric field are 2
Since the energy state of not only the DEC layer 6 but also the quantum well layer 5a-2 can be determined, the presence of surplus carriers with low mobility can be prevented, and a decrease in average mobility can be prevented.

Here, as the width of the GaAs layer 5a-2 increases, the GaAs layer 5a-2 becomes larger.
The energy state of the fundamental quantum level of the As layer 5a-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, GaA
The number of carriers that can fill the quantum well layer can be increased without lowering the energy state of the base quantum level of the s-layer 5a-2, and the above effect becomes even more effective.

Next, the GaAs layers 5a-2-1 and 5a-2 of the first embodiment
-2 thickness, for example, 5a-2-1 is 2.5 nm,
The second embodiment is one in which 5a-2-2 is changed to 1.5nn+. In this way, by changing the width of the quantum well layer, the energy state of the quantum well layer 5a-22 on the opposite side from the quantum well layer 5a-2-1 of 20EG@ is made higher, A real space transition between the quantum well layers to -2-2Ji occurs and the mobility further increases.

Next, 5a-1 is non-doped AfAs, 5a-2 is non-doped GaAs, and 5b is non-doped AlAS/non-doped GaAs/Si doped GaAs.
A third embodiment is a superlattice whose basic structure is non-doped GaAs, and a schematic cross-sectional view thereof is shown in FIG.

In the third embodiment, the n-type AffiGaAs layer 5b of the first embodiment is replaced with a non-doped GaAs layer (1.5 nm) 50b-
1. Non-doped GaAs layer (0.5 nm) 50 b2
, St-doped GaAs layer (1,5 nm) 50 b −
3. Non-doped GaAsJi (0.5 nm) 50
The basic structure is a 4 nm layer consisting of b-4, and these 1
A superlattice Hall element with a quantum well layer is obtained by replacing the non-doped AfGaAs layer 5a-1 with a non-doped GaAs layer (1°5 nm) by replacing the superlattice structure semiconductor layer 50b with a total film thickness of 60 nm consisting of 5 repetitions. . In addition,
FIG. 4 shows a case where the number of quantum well layers 50a=2 is 2.

FIG. 5 shows the electric field dependence of the mobility during direct current driving of the device of the third example. As the number n of quantum well layers 50a-2 increases, the low electric field mobility decreases, but the rate of decrease in mobility due to an increase in electric field decreases.

The reason why the low electric field mobility is higher when n=1 than when n=o is because the thicker spacer layer improves the separation between doped impurities and carriers in the 2DEC layer.

FIG. 6 shows the electric field dependence of the magnetic field sensitivity of the element of the third example when driven with direct current. As the number n of quantum wells 7150a-2 increases, the magnetic field sensitivity becomes smaller in low electric fields, but becomes larger in high electric fields than when n=o, and a high output can be obtained.

Furthermore, if the element is miniaturized and driven with a high electric field, the effect of increasing the output of the magnetic sensor by providing a plurality of quantum well layers 50a-2 will be even greater.

In addition, the fourth embodiment has a double hetero structure in which multiple quantum well layers are provided on one side or both sides adjacent to the 2DEC layer, and a reverse hetero structure in which a carrier supply layer is provided on the substrate side. In the fifth embodiment, a structure in which multiple quantum well layers are provided adjacent to a 2DEC layer is a heterojunction structure, and a 2DEC
A sixth embodiment has a structure in which a plurality of quantum well layers are provided adjacent to the substrate on the substrate side, and schematic cross-sectional views are shown in FIGS. 7, 8, and 9, respectively. Even with such a structure, high output power of the device can be achieved.

Furthermore, high output can be achieved with magnetic sensors other than Hall elements, such as the drain-separated type magnetic sensors with the cross-sectional structures shown in the first to sixth embodiments.

〔Effect of the invention〕

As described above, according to the present invention, since the spacer layer of the heterojunction Hall element has a quantum well structure, the decrease in high electric field mobility can be reduced, a high output magnetic sensor can be obtained, and measurement and control can be improved. An excellent effect can be obtained in that it can greatly contribute to precision improvement.

...Carrier supply layer.

6...Two-dimensional electron gas layer.

Claims (1)

[Claims] In a heterojunction magnetic sensor including a heterojunction structure that forms a two-dimensional electron gas layer with high mobility at a junction of dissimilar semiconductors with different band gaps, the sensor has an energy state higher than that of the two-dimensional electron gas layer. A heterojunction magnetic sensor characterized by having multiple semiconductor layers with a quantum well structure.