C.R. Becker

Voltage-controlled spin selection in a magnetic resonant tunneling diode.

We have fabricated all II-VI semiconductor resonant tunneling diodes based on the (Zn,Mn,Be)Se material system, containing dilute magnetic material in the quantum well, and studied their current-voltage characteristics. When subjected to an external magnetic field the resulting spin splitting of the levels in the quantum well leads to a splitting of the transmission resonance into two separate peaks. This is interpreted as evidence of tunneling transport through spin polarized levels, and could be the first step towards a voltage controlled spin filter.

Temperature dependent investigation of the HgTe/CdTe valence band offset

We report here on a temperature dependent magneto-optical investigation of the valence band offset between HgTe and CdTe. The HI-E1 gap and the conduction band edge mass of various HgTe-(HgCd)Te superlattices were studied in a wide regime from liquid helium to nearly room temperature. With an offset of 550 meV which was determined previously at liquid helium temperatures and the temperature dependence of the F6-F s gap of bulk Hg]_xCdxTe, a nearly perfect description of the experimental data was obtained. Our experiment provides strong evidence that a temperature dependence of the band offset can essentially be neglected. A reliable prediction of the band structure of heterostructures based on Hgt_xCdxTe has not been possible until recently. Due to the uncertainty in the size of the valence band offset between the semimetal HgTe and the wide gap semiconductor CdTe, a quantitative comparison with experimental data was limited. The offsets determined at liquid helium temperatures from magneto-optical experiments scatter considerably between about 40 and 800 meV, and do not agree with the offset of 350 meV determined from X-ray (XPS) and ultraviolet photoelectron spectroscopy (UPS), as reviewed in Ref. [1]. The discrepancy between magneto-optical investigations and XPS and UPS experiments has not yet been resolved

Growth of the half-Heusler alloy NiMnSb on (In,Ga)As/InP by molecular beam epitaxy

Electrical spin injection into nonmagnetic semiconductors has attracted much attention recently. While effective spin injection has been achieved using all-semiconductor structures, these devices only work at temperatures below 100 K. For device applications at room temperature however ferromagnetic materials with 100% spin polarization at room temperature are needed.

Intra- and inter-band transitions in HgSe in megagauss fields

Abstract IR-megagauss spectroscopy on HgSe provides information on both intra- and inter-band transitions resulting in a new set of k*p-parameters for high magnetic field application. Transient effects in the resonance intensities are due to hysteresis effects in the spin dependent population and provide a novel tool for the determination of the spin-lattice relaxation.

Landau-split and spin-split cyclotron resonance of two-dimensional electron systems in HgTe quantum wells

Cyclotron resonances of high-mobility electrons in inverted semiconducting type HgTe quantum wells were investigated at liquid helium temperatures by far-infrared Fourier transform spectroscopy. Due to the energy dependence of the electron effective mass and the high electron mobilities in excess of 70000 cm 2 V -1 s -1 , the spin-splitting and the Landau-splitting of the cyclotron resonance could be resolved. At the conduction subband edge an effective mass m 0 * 0.016 m c and a Lande g-factor |g 0 | 20 was obtained. The experiment is in good agreement with predictions based on the single-particle approximation.

Spin dynamics in megagauss fields

Transient magnetic fields in the megagauss regime prove as a new tool to investigate detailed information on spin-lattice relaxation using the delayed population change of the spin levels in the presence of rapidly varying magnetic fields. The method is applied to HgSe and HgTe epitaxial layers in magnetic fields up to 150 T.

Molecular beam epitaxial growth of CdMnSe on InAs and AlGaSb

Abstract In this contribution we describe the growth of hybrid II–VI/III–V heterostructures, CdMnSe on either InAs or AlGaSb, using molecular beam epitaxy. These material combinations are promising candidates for research on spin-dependent transport phenomena. The grown layers are characterized by X-ray diffraction (XRD). We find that the incorporation of a ZnTe buffer layer between the II–VI and the III–V materials strongly improves the quality of the CdMnSe layers. We have compared different techniques for the growth of this ZnTe buffer. Preliminary transport measurements to deduce the magnetoresistance of the grown CdMnSe layers are presented.

Growth and optical properties of (1 1 2)B HgTe/Hg1-xCdxTe superlattices

The molecular beam epitaxial growth and the optical properties of (1 1 2)B oriented HgTe/Hg 1-x Cd x Te superlattices (SLs) are compared with those of (0 0 1) orientated SLs. First of all, the Hg 1-x Cd x Te barriers have a much higher Cd concentration than those in (0 0 1) grown under similar conditions, i.e. x = 0.95 ± 0.02 as opposed to x = 0.68 ± 0.02 at a growth temperature of 180 C. In addition the optical absorption edges are appreciably sharper than those in (0 0 1) oriented SLs grown under similar conditions, by a factor of at least two. Analogously, the full-width at half-maximum of the photoluminescence (PL) peaky e.g. 8 meV for a band gap of 100 meV at 4 K. is at least a factor of two narrower than that in our best (0 0 1) oriented SLs. This can be explained by a more homogeneous growth laterally, i.e. in the plane perpendicular to the growth direction: either more homogeneous quantum well and barrier thicknesses or a more homogeneous interface width.

Spectroscopy of interface states in HgTe/Hg1-xCdxTe superlattices

Information on interface states in HgTe/Hg 1-x Cd x Te superlattices has been obtained via studies of interband transitions in an external magnetic field. Interband transitions can exhibit novel characteristic features if interface states are involved. For example, the magnetic field dispersion can be negative at sufficiently small magnetic field strengths if the initial state is an interface state. We discuss in detail the influences of the magnetic field strength, the well and barrier thicknesses, and the temperature on the properties of interband transitions involving interface states.

High-field magneto-spectroscopy in HgSe and HgTe up to 225 Tesla

We report on high-field magneto-spectroscopy in HgSe and HgTe using 10.6 /spl mu/m and 5.4 /spl mu/m wavelength radiation in magnetic fields up to 225 T using the single-turn-coil generator. The experimental data agree excellently with the theoretical prediction of suitable energy-band models.