Spin-polarized tunneling with GaAs tips in scanning tunneling microscopy

Prins, Mwj Menno; Jansen, R.; Kempen, H. van

doi:10.1103/physrevb.53.8105

Cited by 69 publications

(32 citation statements)

References 36 publications

(44 reference statements)

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“…Magnetic imaging can be achieved in two distinct ways, namely, by magneto-optical near-field imaging 8 and by spin-polarized tunneling due to optical spin-orientation. [9][10][11] In magnetooptical imaging, the semiconductor tip operates as a local photodetector that maps the polarization-dependent optical properties of a magnetic material. This implies that the main interest is directed toward a small collection volume for photocarriers and a high sensitivity to variations of the optical intensity.…”

Section: Discussionmentioning

confidence: 99%

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Photoelectrical properties of semiconductor tips in scanning tunneling microscopy

Prins¹,

Jansen²,

Groeneveld³

et al. 1996

Phys. Rev. B

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We describe a model as well as experiments on the electrical properties of a photoexcited tunnel junction between a metal and a semiconductor material, as is established in a scanning tunneling microscope. The model treats the case in which carrier transport is mediated by capture and relaxation in the semiconductor surface states. In the semiconductor, majority carrier transport is determined by thermionic emission over the Schottky barrier and subsequent surface recombination. By optical excitation an additional minority carrier current is generated. The voltage that develops on the semiconductor surface is determined by the balance between majority and minority carrier current in the semiconductor, and the current across the tunnel barrier. We present model calculations of the ͑nonplanar͒ band-bending profile in the semiconductor, which indicate that the subsurface electric field operates as an electrical lens that can focus or defocus the current. Measurements were performed with moderately doped GaAs tips or samples prepared by cleavage. Continuous as well as modulated photoexcitation was used. Relationships are determined between tunnel current, applied voltage, incident optical power, and tip-sample distance. The experimental results are well described by the model that includes carrier capture in the semiconductor surface states. It is shown that the sensitivity of the tunnel current to small variations in optical power is determined by the ratio of the tunnel barrier conductance to the Schottky barrier conductance. The implications for near-field optical imaging and spin-polarized tunneling with semiconductor tips are discussed.

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Section: Discussionmentioning

confidence: 99%

“…5 Ϫ7 These tips hold special attraction with regard to near-field optical imaging 8 and as sources of optically oriented spin-polarized electrons. [9][10][11] In this paper, we intend to develop a thorough understanding of the current transport properties of photoexcited semiconductor materials in the STM. The outline is as follows.…”

Section: Introductionmentioning

confidence: 99%

Photoelectrical properties of semiconductor tips in scanning tunneling microscopy

Prins¹,

Jansen²,

Groeneveld³

et al. 1996

Phys. Rev. B

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“…For simplicity, tunnel junctions with planar symmetry are considered, although in our experiments we are dealing with low-symmetry STM junctions. 15,22 The description is based on the nonpolarized transport model that was discussed in a previous paper, 13 in which also the influence of the STM geometry, the calculation of time-dependent signals, and a comparison with experimental results was given.…”

Section: B Semiconductor Subsurface Currentsmentioning

confidence: 99%

Theory of spin-polarized transport in photoexcited semiconductor/ferromagnet tunnel junctions

1998

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We present a theory for spin-polarized transport in tunnel junctions consisting of a ferromagnet and a semiconductor, in which spin-polarized carriers are created by optical orientation. The model includes, for both spin orientations, the current due to tunneling between the ferromagnet and the semiconductor surface as well as the photoinduced and the thermionic emission currents through the semiconductor subsurface region. Tunneling is described in terms of a spin-dependent tunnel conductance, taking account of the magnetic structure of the ferromagnet. We consider spin depolarization of photoexcited electrons in the semiconductor bulk material and in surface states that have a spin-dependent occupation. The total tunnel current is evaluated as well as current modulations due to modulated spin polarization of photoelectrons ͑CPM signal͒ or modulated optical intensity. The calculations show that the CPM signal is proportional to the tunnel conductance polarization and is relatively insensitive to spin depolarization of photoelectrons during their transport to the surface. A severe signal reduction can, however, result from spin relaxation in semiconductor surface states. In addition, it is demonstrated that a crucial role is played by the operating regime of the junction, i.e., photoamperic or photovoltaic, where the selection is determined mainly by the choice of applied bias voltage. We find that the photovoltaic mode is favored, as it yields the highest contribution from spin-polarized tunneling, combined with the smallest sensitivity for unwanted light intensity modulations. ͓S0163-1829͑98͒03207-X͔

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“…A measurement scheme that is closely related to the above presented technique is spin-polarised tunneling by optical spin-orientation in GaAs [22]. The MCD is sensitive to the bulk magnetization, whereas spin-polarised tunneling is sensitive to the spin-polarization of electronic states at the sample surface.…”

Section: Magneto-optical Near-field Microscopymentioning

confidence: 99%