Semiconductor point contacts can be a useful tool for producing spin-polarized currents in the presence of spin-orbit (SO) interaction. Neither magnetic fields nor magnetic materials are required. By numerical studies, we show that (i) the conductance is quantized in units of 2e 2 /h unless the SO interaction is too strong, (ii) the current is spin-polarized in the transverse direction, and (iii) a spin polarization of more than 50% can be realized with experimentally accessible values of the SO interaction strength. The spin-polarization ratio is determined by the adiabaticity of the transition between subbands of different spins during the transport through the point contacts.

We propose a spin-injection method utilizing quantum point contacts (QPCs) fabricated on narrow-gap semiconductors with strong Rashba spin-orbit (SO) interaction. When the conductance through a QPC is quantized in units of 2e2 /h, the current is spin-polarized in the transverse direction to the current even in the absence of magnetic field. The spin polarization, which would be larger than 50% in InGaAs heterostructures, can be detected by connecting the QPC to a ferromagnetic lead. Then the conductance is maximal (minimal) when the magnetization in the lead is parallel or antiparallel (perpendicular) to the spin polarization of the current. The same conductance in the parallel and antiparallel alignments is explained by the Onsager relation, reflecting the fact that the SO interaction does not break the time reversal symmetry.1 Introduction Injection of spin-polarized current into semiconductors is an important issue for the development of spin-based electronics, "spintronics." To manipulate electron spins, the Rashba spin-orbit (SO) interaction is useful since its strength is controllable by applying an electric field [1-3].In our previous paper [4], we have theoretically studied the ballistic transport through a quantum point contact (QPC) in the presence of Rashba SO interaction and shown that the QPC can be a useful tool for the spin injection. No magnetic field is required. We have found that the conductance is quantized in units of 2e2 /h and that the current is spin-polarized in the transverse direction. The spin polarization of more than 50% can be realized in InGaAs heterostructures. The QPC structure is easy to fabricate compared with other devices which have been proposed for the spin injection [5][6][7][8][9].In this paper, we discuss the detection of the spin-polarized current when the QPC is connected to a ferromagnetic lead. The conductance depends on the spin polarization of the current from QPC and magnetization direction in the lead. The conductance is maximal (minimal) when the magnetization is parallel or antiparallel (perpendicular) to the spin polarization of the current. The same conductance in the parallel and antiparallel alignments can be explained by the Onsager relation.

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JapanFor monolithic integration of an analog/digital compatible circuit, a high-voltage shallow junction process with a complementary dielectric isolation technique has been developed. Both high-voltage and high-frequency requirements can be simultaneously, and easily met with this technique.In this process, complementary high-voltage transistors (BVbco>350V) are fabricated by employing shallow junctions (X <2pm) which are used in common with high-frequency low-voltage devices. To realize a high breakdown voltage with shallow junctions, a combination of a field-plate structure, optimized by computer simulation, and semi-insulating film passivation is adopted. PNP as well as NPN transistors are formed in a vertical structure using a newly developed self-aligning complementary dielectric isolation technique. The transistors made by this 350V process have highfrequency characteristics {fT(NPN)=450MHz; f (PNP)=2OOMHZ}, and an excellent hFE complementarity between NPN and PNP transistors. One of the most important applications of this process is the integration of subscriber line interface circuits for a digital local switching system. An L S I with battery feed, supervision and 2wire-4wire hybrid functions has been successfully fabricated with this process. jb T Fig. 1Table 1 Fig. 2Fig. 3Fig. 4 SUPPLEMENT A schematic cross-sectional view of the high voltage transistor. Shallow junctions of less than 2pm are used in common with low-voltage high-frequency devices. High-voltage devices have a specially designed field-plate structure and semi-insulating passivation film. Shallow junction high-voltage structure obtained by computer simulation. Definition of NC, LF, Ls, T and T are shown in Fig. 1. (a)Base-collector junction breakdown characteristics of complementary transistors with the structure shown in Table I. Breakdown voltage of 370V for the NPN transistor and 360V for the PNP transistor are obtained by using collectors doped with a 3~1 0~~c m -~ impurity concentration. (a) Complementary characteristics of NPN and PNP transistors. Excellent complementarity with hFE of more than 50 and low series resistance are obtained, spite of the use of a high-voltage process. (b)fT versus IC characteristics of the PNP and NPN transistors fabricated with the 350V process. (a)Block diagram of the Subscriber Line I-nterface sircuit(SL1C) LSI including battery feed, supervision and 2wire-4wire hybrid functions. (b) Photomicrograph of the SLIC-LSI chip fabricated with the 350V complementary dielectric isolation technique. 1 2 18.8 IEDM 82 -193

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