عنوان مقاله
نیم رسانای اسپینترونیک
فهرست مطالب
مقدمه
پیشنهادات نیمرسانا اسپینترونیک
فرومغناطیس و پدیده های وابسته به اسپین در نیمرساناها
چالش های SPINTRONICS نیمرسانا
نتیجه گیری
بخشی از مقاله
تغییر VG به -125 مغناطیس پذیری کانال را افزایش داده و هیستری به صورت جذر درمی آید. بالاخره، به محض برگشت به VG=0V ، منحنی مغناطیس پذیری مشابهی حاصل می گردد. اثبات این توضیح نشان می دهد که با استفاده از میادین الکتریکی خارجی به شیوه ای برگشت پذیر، می توان فاز فرومغناطیسی را روشن و خاموش نمود. اگرچه کنترل میدان الکتریکی فروفرومغناطیس در دماهای پائین صورت می گیرد، اما احتمالات و امکانات جدیدی برای کنترل وسایل مغناطیسی الکتریکی باز می کند.
کلمات کلیدی:
Semiconductor Spintronics Hiro Akinaga and Hideo Ohno, Member, IEEE Abstract—We review recent progress made in the field of semiconductor spintronics, a branch of semiconductor electronics where both charge and spin degrees of freedom play an important role in realizing unique functionalities. We first describe the new spin-dependent phenomena found in semiconductors including carrier-induced ferromagnetism in III–V compounds, followed by an account of our current understanding of such spin-dependent phenomena. Then we summarize the challenges the semiconductor spintronics has to meet in order for it to be a success as “electronics.” Index Terms—Ferromagnetic semiconductors, magnetooptic (MO) devices, magnetoresistive devices, quantum information, spin coherence. I. INTRODUCTION T HE SUCCESS of semiconductor electronics has been built on the charge degree of freedom of electrons in semiconductors. The spin degree of freedom, used in magnetic mass storage, has long been neglected in semiconductors because of the almost degenerate energies of the two spin states of electrons in semiconductors. However, because of the advances in semiconductor science and technology, the control and manipulation of the spin degree of freedom in semiconductors is becoming increasingly possible [1]–[3]. In addition, semiconductor technology has continuously reduced its working dimension to meet the demand for faster and denser integrated circuits. This leads us to a nanoscale dimension, where exchange interaction (a spin-dependent interaction) among carriers can no longer be ignored; like it or not, we will inevitably have to work with spin dependent interactions in semiconductors in the near future. Progress in magnetic imaging technologies has also started to reveal spin-dependent phenomena in nanoscale structures [4]. All these developments indicate that the time has come to explore, understand and utilize the spin-dependent phenomena in semiconductors. This may lead us to further increase the functionalities of existing devices and circuits like using the capability of mass storage and processing of information at the Manuscript received February 2, 2002; revised February 26, 2002. The work conducted at the National Institute of Advanced Industrial Science and Technology (AIST) was supported in part by the New Energy and Industrial Technology Development Organization [Atom-Technology Project and Synthetic Nano-Function Materials Project]. The work conducted at Tohoku University was supported in part by the “Research for the Future” program of the Japan Society for the Promotion of Science under Grant JSPS-RFTF97P00202, and in part by Grant-in-Aids 1230500 and 09244103 from the Ministry of Education, Culture, Sports, Science and Technology, Japan. H. Akinaga is with the Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Ibaraki 305-8562, Japan. H. Ohno is with the Laboratory for Electronic Intelligent Systems, Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577, Japan. Publisher Item Identifier S 1536-125X(02)04583-0. same time, and to realize quantum information technologies using spin as a qubit in solid state. This area of semiconductor electronics is called semiconductor spintronics, where both charge and spin degrees of freedom play an important and indispensable role in realizing functionalities. The latest semiconductor material technology offers a series of ferromagnetic semiconductors that are compatible with the existing nonmagnetic semiconductors (contain no magnetic element like Mn). Such compatibility allows us to integrate, in a single crystal structure, ferromagnetism with all the freedoms we are currently enjoying in semiconductors including heterostructures. These ferromagnetic semiconductor heterostructure can then be used to store information, amplify spin current, process information, and initialize and read-out spin quantum states. The combination of the advances in semiconductor material science, nanoscale physics and device technology, and integrated circuits, we should be able to polarize, inject, store, manipulate, and then detect spin information. To review current status, we summarized the new freedoms in spin manipulations in Section II. Section III describes our understanding of spin-dependent phenomena related to semiconductor spintronics. The prospect and challenges that we need to meet in the beginning of the 21st century are outlined in Section IV. II. SEMICONDUCTOR SPINTRONICS OFFERS A. Carrier-Induced Ferromagnetism Recent developments in materials science and technology of semiconductors resulted in carrier-induced ferromagnetism in semiconductors that are currently used in transistors and lasers. Nonmagnetic semiconductors (i.e., containing no magnetic ions), such as GaAs, have been made magnetic by introducing a small amount of magnetic ions (like Mn). The ferromagnetism (alignment of spins of magnetic ions) is brought about by the carrier-mediated interaction among magnetic ions; without carriers no ferromagnetism occurs. This carrier-induced ferromagnetism in magnetic ion-doped semiconductors offers a variety of new controllability of semiconducting properties by magnetism and magnetism by semiconducting properties. When one changes carrier concentration by some external means, which can be done in semiconductors but not in metals, magnetism changes. This electronic control of magnetism has remained elusive but recently demonstrated in ferromagnetic semiconductors. Fig. 1 shows the magnetic field dependence of Hall resistance (proportional to magnetization) of a field-effect transistor having a 5 nm thick p-type ferromagnetic (In Mn )As layer as a channel [5]. The measurement temperature is 22.5 K, in the vicinity of ferromagnetic transition temperature of the ferromagnetic semiconductor layer. When a gate voltage of
