U.S. patent application number 10/342004 was filed with the patent office on 2004-03-04 for room temperature ferromagnetic semiconductor grown by plasma enhanced molecular beam epitaxy and ferromagnetic semiconductor based device.
This patent application is currently assigned to Korea Institute of Science and Technology. Invention is credited to Chang, Joon Yeon, Han, Suk Hee, Kim, Hi Jung, Lee, Jung Mi, Lee, Woo Young, Myoung, Jae Min.
Application Number | 20040041217 10/342004 |
Document ID | / |
Family ID | 31713179 |
Filed Date | 2004-03-04 |
United States Patent
Application |
20040041217 |
Kind Code |
A1 |
Lee, Woo Young ; et
al. |
March 4, 2004 |
Room temperature ferromagnetic semiconductor grown by plasma
enhanced molecular beam epitaxy and ferromagnetic semiconductor
based device
Abstract
A 3 group-5 group compound ferromagnetic semiconductor,
comprising one material `A` selected from the group of Ga, Al and
In and one material `B` selected from the group consisting of N and
P, wherein one material `C` selected from the group consisting of
Mn, Mg, Co, Fe, Ni, Cr and V is doped as a material for
substituting the material `A`, the compound semiconductor has a
single phase as a whole. The ferromagnetic semiconductor can be
fabricated by a plasma-enhance molecular beam epitaxy growing
method and since it shows the ferromagnetic characteristics at a
room temperature, it can be applied as various spin electron
devices.
Inventors: |
Lee, Woo Young; (Seoul,
KR) ; Han, Suk Hee; (Seoul, KR) ; Chang, Joon
Yeon; (Seoul, KR) ; Kim, Hi Jung; (Seoul,
KR) ; Lee, Jung Mi; (Seoul, KR) ; Myoung, Jae
Min; (Koyang, KR) |
Correspondence
Address: |
DARBY & DARBY P.C.
805 Third Avenue
New York
NY
10022
US
|
Assignee: |
Korea Institute of Science and
Technology
|
Family ID: |
31713179 |
Appl. No.: |
10/342004 |
Filed: |
January 14, 2003 |
Current U.S.
Class: |
257/414 ;
257/E21.097 |
Current CPC
Class: |
H01F 41/30 20130101;
H01L 21/02631 20130101; H01L 43/10 20130101; H01L 33/40 20130101;
H01F 10/193 20130101; B82Y 40/00 20130101; H01F 10/3213 20130101;
B82Y 25/00 20130101; H01F 1/404 20130101; H01L 21/0242 20130101;
H01L 21/0262 20130101; H01L 21/02543 20130101; H01L 21/0254
20130101; H01L 21/02573 20130101; H01L 43/08 20130101; H01L
29/66984 20130101; H01L 21/02581 20130101 |
Class at
Publication: |
257/414 |
International
Class: |
H01L 027/14; H01L
029/82; H01L 029/84 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 4, 2002 |
KR |
53306/2002 |
Claims
What is claimed is:
1. A 3 group-5 group compound ferromagnetic semiconductor,
comprising one material `A` selected from the group of Ga, Al and
In and one material `B` selected from the group consisting of N and
P, wherein one material `C` selected from the group consisting of
Mn, Mg, Co, Fe, Ni, Cr and V is doped as a material for
substituting the material `A`, the compound semiconductor has a
single phase on the whole.
2. The semiconductor of claim 1, wherein the ferromagnetic
semiconductor has its Curie temperature above room temperature.
3. A method for fabricating a ferromagnetic semiconductor
comprising the steps of: forming a 3 group-5 group compound
semiconductor thin film comprising one material `A` selected from
the group consisting of Ga, Al and In and one material `B` selected
from the group consisting of N and P on a substrate; and doping one
material `C` selected from the group consisting of Mn, Mg, Co, Fe,
Ni, Cr and V as a material for substituting the material `A`, while
forming the compound semiconductor thin film by a plasma-enhanced
molecular beam epitaxy, wherein the materials `A` and `C` are
supplied from an effusion cell and the material `B` is supplied
from a plasma source.
4. The method of claim 3, wherein the temperature of the effusion
cell is 600.about.800.degree..
5. The method of claim 3, wherein the plasma power is 250.about.350
W.
6. The method of claim 3, wherein the doping concentration is in
the range of 0.06.about.3%.
7. The method of claim 3, wherein the temperature of the substrate
is in the range of 300.about.1000.degree. C.
8. A ferromagnetic semiconductor device comprising an insulation
layer, a spacer and a ferromagnetic semiconductor sequentially
formed on a substrate, the ferromagnetic semiconductor being a 3
group-5 group compound semiconductor comprising one material `A`
selected from the group of Ga, Al and In and one material `B`
selected from the group consisting of N and P, wherein one material
`C` selected from the group consisting of Mn, Mg, Co, Fe, Ni, Cr
and V is doped as a material for substituting the material `A`, the
compound semiconductor has a single phase on the whole.
9. A ferromagnetic semiconductor device comprising a gate, an
insulation layer formed at a lower side of the gate, and a
ferromagnetic semiconductor layer formed at a lower side of the
insulation layer, the ferromagnetic semiconductor being a 3 group-5
group compound semiconductor comprising one material `A` selected
from the group of Ga, Al and In and one material `B` selected from
the group consisting of N and P, wherein one material `C` selected
from the group consisting of Mn, Mg, Co, Fe, Ni, Cr and V is doped
as a material for substituting the material `A`, the compound
semiconductor has a single phase on the whole.
10. A ferromagnetic semiconductor device comprising a gate, an
insulation layer formed at a lower side of the gate, a source and
drain region formed at the left and right side of the insulation
layer and using a ferromagnetic semiconductor, and a secondary
electron gas layer formed at a lower side of the insulation layer,
p1 the ferromagnetic semiconductor being a 3 group-5 group compound
semiconductor comprising one material `A` selected from the group
of Ga, Al and In and one material `B` selected from the group
consisting of N and P, wherein one material `C` selected from the
group consisting of Mn, Mg, Co, Fe, Ni, Cr and V is doped as a
material for substituting the material `A`, the compound
semiconductor has a single phase on the whole.
11. A ferromagnetic semiconductor device comprising a seed layer,
an anti-ferromagnetic layer, a ferromagnetic semiconductor layer,
an insulation layer and a ferromagnetic semiconductor layer
sequentially formed on a substrate, the ferromagnetic semiconductor
being a 3 group-5 group compound semiconductor comprising one
material `A` selected from the group of Ga, Al and In and one
material `B` selected from the group consisting of N and P, wherein
one material `C` selected from the group consisting of Mn, Mg, Co,
Fe, Ni, Cr and V is doped as a material for substituting the
material `A`, the compound semiconductor has a single phase on the
whole.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a room temperature
ferromagnetic semiconductor used for a spin electronic device
having wide bandgap to semiconductor characteristics and magnetic
characteristics at a room temperature, its fabrication method, and
a ferromagnetic semiconductor based device.
[0003] 2. Description of the Background Art
[0004] A research on a GaN-based nitride semiconductor was started
to fabricate a blue light emitting device in the early 1990, and
currently, researches are being actively conducted on various
electronic devices in addition to light emitting and light
receiving devices.
[0005] In forming a triple element compound, an energy gap) can be
controlled from 1.9 eV to 6.2 eV, so that the nitride semiconductor
is used for fabrication of a light emitting device of a wave length
region of the entire visible light including an ultraviolet ray
region. A blue and green light emitting diode (LED) and a
ultraviolet ray detector was successfully commercialized years ago,
and a blue light emitting diode (LED0 is anticipated to be
commercialized soon.
[0006] Meanwhile, research on an electronic device using the
nitride semiconductor is actively ongoing. Since a report on a
research on a GaN MESFET (metal-semiconductor field effect
transistor), a crystal growing technique has been much developed
and an electronic device fabrication technique has been also
remarkably improved. Diverse researches are being conducted on the
electronic device on the basis of excellent physical properties
such as a large energy gap, a high thermal and chemical stability,
a high electron mobility, a high breakdown voltage and saturation
electron speed, the large discontinuation of conduction band, or
the like.
[0007] Meanwhile, in view of a novel conceptual spintronics (a
compound word of spin and electronics, a fresh paradigm intending
to develop an electron and an optical device in consideration of
freedom of a spin together with the electronic charge of the
electron, a research has been ongoing on the applicability of
spintronics in the wake of report on ferromagnetic semiconductor
characteristics at a temperature of about 110 K by substituting a
portion of Ga in GaAs with Mn, a transition metal, by using a
molecular beam epitaxy (MBE) process in the late 1990.
[0008] In this respect, however, (In,Mn)As (Tc=35K), (Ga,Mn)As
(Tc=110K) and MnGe (Tc=116 K) are representative ferromagnetic
semiconductors which have been studied up to date but owing to the
low Curie temperature there is a limitation in fabricating a spin
device that can be operated at a room temperature. Therefore,
finding a ferromagnetic semiconductor with a Curie temperature
above a room temperature is the most critical factor in this
field.
[0009] According to a theoretical computation result using a Zener
model, GaN, ZnO are anticipated to exhibit a Curie temperature
above the room temperature, on which, thus, researches are being
focussed to testify experimentally.
SUMMARY OF THE INVENTION
[0010] Therefore, an object of the present invention is to provide
a semiconductor with magnetic characteristics at a room temperature
and its fabrication method.
[0011] Another object of the present invention is to provide
various spin electronic devices using the room temperature
ferromagnetic semiconductor.
[0012] To achieve these and other advantages and in accordance with
the purpose of the present invention, as embodied and broadly
described herein, there is provided a ferromagnetic semiconductor,
a 3 group-5 group compound semiconductor comprising one material
`A` selected from the group of Ga, Al and In and one material `B`
selected from the group consisting of N and P, in which one
material `C` selected from the group consisting of Mn, Mg, Co, Fe,
Ni, Cr and V is doped as a material for substituting the material
`A`, the compound semiconductor has a single phase on the
whole.
[0013] To achieve the above objects, there is further provided a
method for fabricating a ferromagnetic semiconductor including the
steps of: forming a 3 group-5 group compound semiconductor thin
film comprising one material `A` selected from the group consisting
of Ga, Al and In and one material `B` selected from the group
consisting of N and P; and doping one material `C` selected from
the group consisting of Mn, Mg, Co, Fe, Ni, Cr and V as a material
for substituting the material `A`, whiling forming the compound
semiconductor thin film by a plasma-enhanced molecular beam
epitaxy, wherein the materials `A` and `C` are supplied by
thermally evaporating from an effusion cell and the material `B` is
supplied from a plasma source.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention.
[0015] In the drawings.
[0016] FIG. 1 is a schematic view showing a plasma enhanced
molecular beam epitaxy (PEMBE) used in the present invention;
[0017] FIG. 2 is a graph showing a result of a secondary ion mass
spectroscopy (SIMS) measured to observe a Mn distribution in a thin
film according to a Mn cell temperature of a (Ga,Mn)N thin film
fabricated by the PEMBE method in accordance with the present
invention;
[0018] FIG. 3 is a graph showing a room temperature hysteresis loop
of a (Ga,Mn)N thin film fabricated according to a change in the Mn
cell temperature and plasma power in the PEMBE method in accordance
with the present invention;
[0019] FIG. 4 is a graph showing a hysteresis loop of a (GaMn)N
thin film fabricated under the condition of 670.degree. C./350 W by
the PEMBE method in accordance with the present invention;
[0020] FIG. 5 is a graph showing a temperature dependency of
magnetization of a (Ga,Mn) N thin film with a Mn concentration of
0.16% and 0.50% fabricated by the PEMBE method;
[0021] FIG. 6 is a graph showing a change of a magnetic resistance
according to magnetic field perpendicular to the thin film for a
(Ga,Mn)N thin film fabricated when plasma power is 250 W and Mn
cell temperatures are 600.degree. C. (.smallcircle.) and
650.degree. C. (.cndot.) in the PEMBE method;
[0022] FIG. 7 is a photograph showing a sectional view of a
transmission electron microscope (TEM) and an electron diffraction
pattern for a (Ga,Mn)N thin film with a Mn concentration of 0.2%
fabricated by the PEMBE method in accordance with the present
invention;
[0023] FIG. 8 is a graph showing a lattice constant a measured by a
high-order Laue zone (HOLZ) method for a ferromagnetic
semiconductor fabricated by the PEMBE method in accordance with the
present invention;
[0024] FIG. 9 is a sectional view showing a structure of a spin LED
using a ferromagnetic semiconductor fabricated by the PEMBE method
in accordance with the present invention;
[0025] FIG. 10 is a sectional view showing a structure of a Hall
effect memory device using the ferromagnetic semiconductor
fabricated by the PEMBE method in accordance with the present
invention;
[0026] FIG. 11 is a sectional view showing a structure of a
spin-polarized field effect transistor (spin FET)) using the
ferromagnetic semiconductor fabricated by the PEMBE method in
accordance with the present invention; and
[0027] FIG. 12 is a sectional view showing a magnetic tunnelling
junction device with a structure of ferromagnetic
semiconductor/insulating material/ferromagnetic semiconductor using
the ferromagnetic semiconductor fabricated by the PEMBE method in
accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] As one embodiment of the present invention, a Mn- or
Mg-doped GaN thin film was grown by using a plasma-enhanced
molecular beam epitaxy device, for which an undoped GaN (GaN
templete) grown on a surface of sapphire (0001) by using a metal
organic chemical vapor deposition (MOCVD) device was used as a
substrate.
[0029] FIG. 1 is a schematic view showing the plasma-enhanced
molecular beam epitaxy device used in the present invention.
[0030] Turbomolecular pumps 1 and 2 are connected at the right side
and left side of a chamber 20, and a substrate 5 is positioned at
an upper portion of the chamber 20. The substrate is controlled in
its position by a substrate manipulator 10 formed at an upper
portion of the chamber. A heater 4 is positioned at an upper side
of the substrate to control a temperature of the substrate. A
liquefied nitrogen (LN.sub.2) supply unit 8 is positioned at a
lower portion inside the chamber and LN.sub.2 covers 9 are attached
inside the chamber. Reference numerals 6 and 7 denote,
respectively, shutters and 3 denotes a load-lock chamber.
[0031] The plasma-enhanced molecular beam epitaxy device is an
ultra high vacuum (UHV) system which has a base pressure of
1.2.times.10.sup.-9 torr and exhibits vacuum of about
2.times.10.sup.-10 when LN.sub.2 is supplied thereto. The
rotational substrate manipulator can handle a substrate with a
diameter of 3". There are 8 ports at the bottom flange so that
effusion cells 11, 12 and 13 for thermally evaporating a requested
chemical element can be mounted thereto. The effusion cells are
connected to a matching box together with an RF plasma source
14.
[0032] Ga with a purity of 99.99999% (7N) was used to grow the GaN
thin film, and Mn (6N) and Mg (6N) were used for doping. N.sub.2
(7N) gas was supplied through the RF plasma source. A high purity
refractory material, for example, PbN, Mo or the like, was used
inside the plasma source to prevent contamination by the high
temperature plasma, to which cooling water flew. During the growth
of Mn-doped GaN thin film, the temperature of the substrate was
750.about.1000.degree. C., the Mn effusion cell temperature was
600.about.800.degree. C., plasma power was 250.about.350 W, N.sub.2
flow rate was 1.5.about.2 sccm.
[0033] Hall-measuring of the thusly fabricated (Ga,Mn)N thin film
by Van der Pauw method showed that it has characteristics of an
n-type semiconductor, its carrier concentration was
n=10.sup.16-10.sup.17/cm.sup- .3, its electron mobility
(.mu..sub.H) was about 10.sup.3 cm.sup.2/Vs, and its non-resistance
(.rho.) was 0.2 .OMEGA.cm.
[0034] When Mg was doped in a basic experiment to grow a p-type
ferromagnetic semiconductor, the electron concentration was rapidly
reduced from .about.2.9.times.10.sup.19 cm.sup.-3 to
.about.4.8.times.10.sup.17 cm.sup.-3 as FGa/FN flux ratio was
increased. It is believed that this is because a compensation
effect is increased due to the increase in the Mg concentration
according to the increase in the flux ratio. Therefore, it is noted
that an Mg-doped GaN thin film of p-type conductance can be grown
and p-type ferromagnetic semiconductor can be grown by
simultaneously doping Mn and Mg.
[0035] FIG. 2 is a graph showing a result of secondary ion mass
spectroscopy (SIMS) measured to observe a Mn distribution in a thin
film according to a Mn cell temperature of the (Ga,Mn)N thin
film.
[0036] As shown in FIG. 2, it is noted that Mn in the thin film has
an even distribution in the range of 0.7.about.1.0 .mu.m. In
Addition, it is noted that the Mn concentration in the GaN thin
film is increased as the Mn cell temperature goes up. Without a
basic sample with an information of Mn concentration, it is not
possible to know an accurate Mn concentration for each sample. But
from the SIMS result, it can be noted that Mn is effectively doped
when GaN is grown. Mn concentration of each sample was indicated as
obtained from a magnetic moment measured for each sample. The
concentration of the doping material affects a physical property of
a magnetization value, and a suitable Mn concentration for growing
a single-phase ferromagnetic semiconductor was 0.06.about.3%.
[0037] FIG. 3 shows a hysteresis loop of the (Ga,Mn)N thin film
fabricated according to a change in a Mn cell temperature and
plasma power as measured at a room temperature with
high-sensitivity (10.sup.-8 emu) AGM (alternating gradient
magnetometer). The Mn cell and plasma power in this context are (a)
630.degree. C./350 W, (b) 650.degree. C./350 W, (c) 650.degree.
c./250 W, (d) 650.degree. C./400 W, and (e) 670.degree. C./350 W,
respectively.
[0038] It can be observed from the hysteresis loop that the
(Ga,Mn)N fabricated in accordance with the present invention have
the typical magnetic characteristics at a room temperature.
[0039] In case that the plasma power is 350 W and the Mn cell
temperature goes up to 670.degree. C. from 630.degree. C., the
magnetization value is sharply increased. That is, as the Mn cell
temperature is increased, the Mn concentration is increased.
[0040] Meanwhile, in case that the Mn cell temperature is
650.degree. C. and the plasma power is changed in the range of
250.about.350 the magnetization value is little changed.
[0041] As the greatest magnetization value, (Ga,Mn)N fabricated
with the Mn cell temperature of 670.degree. C. and plasma power of
350 W has that Ms=1.0 emu/cm.sup.3 and 0.5% Mn concentration.
[0042] That is, the magnetization value can be more increased by
increasing the concentration of Mn. The temperature of the effusion
cell has a great influence on the physical property of the
ferromagnetic semiconductor, and an optimum temperature is set
depending on a doped material.
[0043] FIG. 4 is graph showing an enlarged hysteresis loop of the
(Ga,Mn)N thin film fabricated under the condition of 670.degree.
C./350 W. As illustrated, a coercive force (H.sub.c)=69.0e. If
there exists a secondary phase such as nano-cluster showing
magnetic characteristics in the (Ga,Mn)N thin film, since it
exhibits a superparamagnetic behavior, a coercive force can not be
expected.
[0044] Therefore, the result of FIG. 4 reflects (Ga,Mn)N has a
single phase formed by substituting Ga with Mn and this single
phase has the magnetic characteristics at the room temperature.
[0045] FIG. 5 is a graph showing a temperature dependency of
magnetization of (Ga,Mn)N thin films, respectively, with Mn
concentration of 0.16% and 0.50%. The two thin films all show a
typical ferromagnetization in 4-300K. According to a computation
result by using a mean field theory in order to predict a Curie
temperature, each Curie temperature (Tc) shows about 550 K and 700
K for (Ga,Mn)N thin films respectively with the Mn concentration of
0.16% and 0.50%. This result tells that a spin device fabricated by
using the ferromagnetic (Ga,Mn)N thin film has an enough thermal
stability. The picture inserted into a right upper end of FIG. 5
shows hysteresis loop that (Ga,Mn)N thin film with an Mn
concentration of 0.50% was measured in 4K and 300K.
[0046] FIG. 6 shows a magnetoresistance change according to
magnetic fields perpendicular to (Ga,Mn)N thin film fabricated when
plasma power was 250 W and Mn cell temperatures were 660.degree. C.
(.smallcircle.) and 650.degree. C. (.cndot.). The (Ga,Mn)N thin
film fabricated under the two conditions exhibits little resistance
change according to the magnetic fields in 300K but exhibits a
negative magnetoresistance of R/R=10% and R/R=20% in 4K when 20kOe
magnetic field is applied thereto.
[0047] The picture inserted at the central lower end of FIG. 6
shows that the negative magnetoresistance changes according to a
temperature in 4.about.300 K.
[0048] The negative magnetoresistance is representative
characteristics of the ferromagnetic semiconductor, which is much
similar to the result of the known (Ga,MN)As (Tc=110K). With this
fact, (Ga,Mn)N fabricated in accordance with the present invention
is the semiconductor having the magnetic characteristics at the
room temperature. The cause of the negative magnetoresistance is
not known yet but widely believed that it is because that a
magnetic polaron is formed made up of a carrier and an electron
cloud of the Mn spin or because of a Zeeman shift of to permi
energy.
[0049] FIG. 7 is a photograph showing a section of the TEM for the
(Ga,Mn)N thin film with an Mn concentration of 0.2%.
[0050] As shown, GaN with a thickness of 2 .mu.m grown on a
sapphire substrate by the MOCVD method and (Ga,Mn)N grown thereon
by the PEMBE method.
[0051] As noted from the electron diffraction pattern inserted to
the left portion of FIG. 6, there is observed (0-110), (-1100),
(1-100), (01-10) additional diffraction spot which are not observed
in GaN grown by the MOCVD method.
[0052] This is a phenomenon occurring as Ga is substituted with Mn
in the (Ga,Mn)N thin film corresponding to a wurtzite structure
among hexagonal structures, showing that Mn shows a single (Ga,Mn)N
phase by effectively substituting Ga without forming a secondary
phase. Meanwhile, according to the observation result of the TEM,
the secondary phase such as the nano cluster was not observed.
[0053] FIG. 8 is a graph showing lattice constants (a) of several
samples measured by a high-order Laue zone (HOLZ) method. A
standard sample of them is GaN with a thickness of 200 .mu.m
fabricated by hydride vapor phase epitaxy (HVPE) method and has no
lattice mismatch by sapphire. As shown, comparison between the
lattice constants of (Ga,Mn)N and GaN grown by the PEMBE method
shows that (Ga,Mn)N is greater than Ga. With this fact, it is
confirmed that (Ga,Mn)N is a single (Ga,Mn)N phase formed by
substituting Ga with Mn.
[0054] Meanwhile, as well as Mn, a ferromagnetic semiconductor can
be grown by doping a suitable amount of Co, Fe and Ni, the typical
ferromagnetic transition element, and Cr, V or the like which has a
similar quality to Mn.
[0055] The ferromagnetic semiconductor fabricated in accordance
with the present invention can be applicable to various
devices.
[0056] FIG. 9 is a sectional view showing a structure of a spin LED
using a ferromagnetic semiconductor fabricated by the PEMBE method
in accordance with the present invention.
[0057] As shown in FIG. 9, on an n-type (or p-type) ferromagnetic
semiconductor 81, there are sequentially formed a spacer 82, an
insulation layers 83 and 84, a p-type (or n-type) buffer 85, a
p-type (or n-type) substrate 86.
[0058] In addition, as shown in FIG. 10, as for the ferromagnetic
semiconductor fabricated in accordance with the present invention a
ferromagnetic semiconductor 93 can be changed to have a
ferromagnetic property or to have a non-ferromagnetic property by
controlling a carrier concentration with a voltage of a gate 91 so
as to be-applicable as a Hall effect memory device by using the
properties that a Hall resistance is big from an extraordinary Hall
effect when the ferromagnetic semiconductor has the ferromagnetic
property, while the Hall resistance is small from an ordinary Hall
effect when the ferromagnetic semiconductor has the
non-ferromagnetic property. In FIG. 10, reference numerals 92 and
94 denote insulation layers, 95 denotes a buffer layer, 96 denotes
a spin of a material doped in the ferromagnetic semiconductor, and
97 denotes an electron (or Hole).
[0059] Moreover, as shown in FIG. 11, the ferromagnetic
semiconductor fabricated in accordance with the present invention
can be applicable as a spin-polarized field effect transistor (spin
FET) by injecting a spin-polarized carrier into a two dimensional
electron gas 105 by using a source 101 and a drain 102 of a spin
transistor and by using a change in a resistance according to an
external magnetic field or controlling a procession of the
spin-polarized carrier with a voltage of the gate 103.
[0060] Reference numerals 104 and 106 denote a barrier layer
(insulation layer) of a quantum well structure.
[0061] Furthermore, as shown in FIG. 12, the ferromagnetic
semiconductor fabricated in accordance with the present invention
can be applicable to a magnetic tunnelling junction with a
structure of ferromagnetic semiconductor/insulation
material/ferromagnetic semiconductor.
[0062] Reference numeral 111 denotes a substrate, 112 denotes a
buffer, 113 denotes a seed layer 114 denotes an anti-ferromagnetic
layer 115 and 117 denote ferromagnetic semiconductor, 116 denotes a
tunnel barrier (insulation layer), and 118 denotes a capping
layer.
[0063] As so far described, unlike the conventional art where the
ferromagnetic semiconductor shows characteristics only at a low
temperature, the ferromagnetic semiconductor of the present
invention implements the ferromagnetic characteristics even at the
room temperature. Therefore, the ferromagnetic semiconductor of the
present invention can be adopted to various spin electron devices
as a novel ferromagnetic semiconductor implementing a
spintronix.
[0064] As the present invention may be embodied in several forms
without departing from the spirit or essential characteristics
thereof, it should also be understood that the above-described
embodiments are not limited by any of the details of the foregoing
description, unless otherwise specified, but rather should be
construed broadly within its spirit and scope as defined in the
appended claims, and therefore all changes and modifications that
fall within the metes and bounds of the claims, or equivalence of
such metes and bounds are therefore intended to be embraced by the
appended claims.
* * * * *