Patent Application
20050045976
1. Field of the Invention
The present invention relates to a room temperature ferromagnetic semiconductor used for a spin electronic device having wide bandgap semiconductor characteristics and magnetic characteristics at a room temperature, its fabrication method, and a ferromagnetic semiconductor based device.
2. Description of the Background Art
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.
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.
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.
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.
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.
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.
Therefore, an object of the present invention is to provide a semiconductor with magnetic characteristics at a room temperature and its fabrication method.
Another object of the present invention is to provide various spin electronic devices using the room temperature ferromagnetic semiconductor.
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.
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.
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.
In the drawings:
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.
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 (LN2) supply unit 8 is positioned at a lower portion inside the chamber and LN2 covers 9 are attached inside the chamber. Reference numerals 6 and 7 denote, respectively, shutters and 3 denotes a load-lock chamber.
The plasma-enhanced molecular beam epitaxy device is an ultra high vacuum (UHV) system which has a base pressure of 1.2×10−9 torr and exhibits vacuum of about 2×10−10 when LN2 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.
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. N2 (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˜1000° C., the Mn effusion cell temperature was 600˜800° C., plasma power was 250˜350 W, N2 flow rate was 1.5˜2 sccm.
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=1016-1017/cm3, its electron mobility (μH) was about 103 cm2/Vs, and its non-resistance (ρ) was 0.2 Ω cm.
When Mg was doped in a basic experiment to grow a p-type ferromagnetic semiconductor, the electron concentration was rapidly reduced from ˜2.9×1019 cm−3 to ˜4.8×1017 cm−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.
As shown in
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.
In case that the plasma power is 350 W and the Mn cell temperature goes up to 670° C. from 630° C., the magnetization value is sharply increased. That is, as the Mn cell temperature is increased, the Mn concentration is increased.
Meanwhile, in case that the Mn cell temperature is 650° C. and the plasma power is changed in the range of 250˜350, the magnetization value is little changed.
As the greatest magnetization value, (Ga,Mn)N fabricated with the Mn cell temperature of 670° C. and plasma power of 350 W has that Ms=1.0 emu/cm3 and 0.5% Mn concentration.
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.
Therefore, the result of
R/R=10% and
R/R=20% in 4K when 20 kOe magnetic field is applied thereto.
The picture inserted at the central lower end of
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 permi energy.
As shown, GaN with a thickness of 2 μm grown on a sapphire substrate by the MOCVD method and (Ga,Mn)N grown thereon by the PEMBE method.
As noted from the electron diffraction pattern inserted to the left portion of
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.
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.
The ferromagnetic semiconductor fabricated in accordance with the present invention can be applicable to various devices.
As shown in
In addition, as shown in
Moreover, as shown in
Reference numerals 104 and 106 denote a barrier layer (insulation layer) of a quantum well structure.
Furthermore, as shown in
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0053306/2002 | Sep 2002 | KR | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10342004 | Jan 2003 | US |
| Child | 10910745 | Aug 2004 | US |
