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Focuses on the alloy semiconductor Hg1-x Cdx Te for the fabrication of high performance photoconductive detectors in the 3-5 and 8-14 mu m spectral ranges. Computation of subband dispersion relations as a function of the surface electron concentration in the accumulation layers of n-Hg1-x Cdx Te photoconductive detectors; Application of the quantitative mobility spectrum analysis.

Recently, the combination of spintronics and thermo-electricity has emerged as the new field of spin caloritronics. It focuses on the coupling of spin transport with heat dissipation and mechanical excitations in magnetic structures. The search to find applications for this new discipline is underway. Motivated by recently discovered Seebeck rectification (Zhang et al., 2012) in nano-structured magnetic tunnel junctions, we explore the possibility of utilizing spin caloritronics in microwave applications. New horizons emerge by using spin caloritronic microwave sensors made of magnetic tunneling junctions, which may be adapted to existing radar and tomographic microwave imaging approaches as well as the standard antenna design procedure. [ABSTRACT FROM AUTHOR]

Abstract: We study the spin–orbit interaction in diffusive InAs quantum wires ranging from 4 to in width by means of weak antilocalization (WAL) analysis. Our experimental data can be well fitted using the 2D model, the 1D model and a newly developed dimensional crossover model. However, the physics behind these models is quite different. The 1D and DC models take the wire width into account and show a width-independent spin–orbit interaction, in contrast to the 2D model which incorrectly shows an increase of the spin–orbit interaction with decreasing width. Our experimental data qualitatively agrees with the predicted decrease of the WAL peak amplitude as the wire becomes narrower than the spin–orbit length. However, this effect is not accompanied by the expected suppression of the extracted spin–orbit interaction, obtained from the 1D and the crossover model. [Copyright &y& Elsevier]

The various scattering times of two-dimensional electron gas were investigated in modulation-doped Al0.22Ga0.78N/GaN quantum wells by means of magnetotransport measurements. The ratio of transport and quantum scattering times, τt/τq∼1, shows that the dominant mobility-limiting mechanisms are short-range scattering potentials. The low-field magnetoresistance shows the weak antilocalization and localization phenomenon from which the spin–orbit scattering and inelastic scattering times are obtained. The inelastic scattering time is found to follow the T-1 law, indicating that electron–electron scattering with small energy transfer is the dominant inelastic process. [Copyright &y& Elsevier]

Magneto-transport measurements have been carried out on a modulation-doped Al0.22Ga0.78N/GaN heterostructure in a temperature range between 1.5 and 25 K with a rather high carrier density, 1.1×1013 cm−2. Striking beating patterns in magnetoresistance vs magnetic field are observed in the vicinity of a special temperature. Theoretical simulation is performed and the comparison between numerical simulations and the experimental data reveals that the beating patterns are due to the interference of the magneto-intersubband scattering and the SdH oscillator of first subband. [Copyright &y& Elsevier]

We report on Rashba spin–orbit splitting in a series of gated n-type HgTe/Hg0.3Cd0.7−xMnxTe quantum wells with an inverted band structure. By analyzing the gate-voltage-dependent beating pattern observed in the Shubnikov–de Haas oscillations, we determine the gate voltage dependence of the spin–orbit coupling parameter β, which can be tuned by a factor of about 5 in the narrow spacer sample. Our experimental data and its analysis show that the Hg0.3Cd0.7−xMnxTe layer strongly enhances the spin–orbit splitting, when close enough to the two-dimensional electron gas. [Copyright &y& Elsevier]

Current-voltage (I–V) characteristics of GaAs-based resonant tunneling diodes have been investigated in the presence of a perpendicular magnetic field. Electron resonant tunneling is strongly suppressed by the applied magnetic field, leading to peak current decreasing with increasing magnetic field. The observed plateau-like structures appear in negative differential resistance region on the I–V curves and are magnetic-field dependent. The plateau-like structures are due to the coupling between the energy levels in the emitter well and in the main quantum well. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Spin splitting of the two-dimentional electron gas (2DEG) in modulation-doped Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures has been studied by means of magnetotransport measurements at low temperatures and high magnetic fields. The spin splitting is observed in Shubnikov–de Haas oscillations at a magnetic field higher than 5.4 T and a temperature of 1.4 K. The effective g factor g[sup *] is enhanced due to the exchange interaction of the 2DEG at high densities. The ratio of the transverse effective g factor g[sub ⊥][sup *] and the longitudinal effective g factor g[sub ∥][sup *] is g[sub ⊥][sup *]/g[sub ∥][sup *]=2.6 indicating the large difference between g[sub ∥][sup *] and g[sub ⊥][sup *]. It is demonstrated that the anisotropy of the g[sup *] is due to the strong polarization-induced electric field at the heterointerface. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetointersubband scattering (MIS) oscillations of two-dimensional electron gas (2DEG) in Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures have been investigated by means of magnetotransport measurements at low temperatures and high magnetic fields. Double periodic Shubnikov–de Haas oscillations modulated by MIS oscillations have been observed due to the intersubband scattering of the 2DEG at the two lowest subbands in the triangular quantum well at the heterointerface. By using the fast Fourier transform analysis, it is found that the MIS oscillations become slightly weaker with an increase in temperature. From the MIS frequency, the energy separation between the first and the second subbands is determined to be 80 meV. The observation of the MIS effect indicates that the effective masses of the electrons in the first and second subbands are the same in Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: We have observed the weak antilocalization (WAL) and beating SdH oscillation through magnetotransport measurements performed on a heavily -doped In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As single quantum well in an applied magnetic field up to 13 T and a temperature at 1.5 K. Both effects are caused by the strong Rashba spin–orbit (SO) coupling due to high structure inversion asymmetry (SIA). The Rashba SO coupling constant and zerofield spin splitting are estimated and the obtained values are consistent from different analysis for this sample. [Copyright &y& Elsevier]

Abstract: Magneto-transport measurements have been carried out on double/single-barrier-doped In0.52Al0.48As/ In0.53Ga0.47As/ In0.52Al0.48As quantum well samples from 1.5 to 60 K in an applied magnetic field up to 13 T. Beating Shubnikov–de Haas oscillation is observed for the symmetrically double-barrier-doped sample and demonstrated due to a symmetric state and an antisymmetric state confined in two coupled self-consistent potential wells in the single quantum well. The energy separation between the symmetric and the antisymmetric states for the double-barrier-doped sample is extracted from experimental data, which is consistent with calculation. For the single-barrier-doped sample, only beating related to magneto-intersubband scattering shows up. The pesudospin property of the symmetrically double-barrier-doped single quantum well shows that it is a good candidate for fabricating quantum transistors. [Copyright &y& Elsevier]

Quantum and transport scattering times related to different subbands in modulation-doped Al0.22Ga0.78N/GaN single quantum wells (SQW) have been studied by magneto- transport measurements. The quantum scattering time related to the first and the second subbands is determined to he 0.078 ps and 0.088 ps, respectively, at 1.5 K. Results indicate that the scatterings from heterointerface and ionized donors at both side of GaN well are all important in limiting quantum scattering time. By using mobility spectrum technique the transport scattering time related to the first subband is determined to he 0.128 ps. Transport-to-quantum scattering time ratio in the first subband is 1.6. It is concluded the large angle scatterings play a very important role in limiting quantum scattering time in this SQW. [ABSTRACT FROM AUTHOR]

The band structure of HgTe quantum wells (QWs) has been determined from absorption experiments on superlattices in conjunction with calculations based on an 8×8 k·p model. The band structure combined with self-consistent Hartree calculations has enabled transport results to be quantitatively explained.Rashba spin–orbit, (SO) splitting has been investigated in n-type modulation doped HgTe QWs by means of Shubnikov–de Haas oscillations (SdH) in gated Hall bars. The heavy hole nature of the H1 conduction subband in QWs with an inverted band structure greatly enhances the Rashba SO splitting, with values up to 17 meV.By analyzing the SdH oscillations of a magnetic two-dimensional electron gas (2DEG) in modulation-doped n-type Hg1−xMnxTe QWs, we have been able to separate the gate voltage-dependent Rashba SO splitting from the temperature-dependent giant Zeeman splitting, which are of comparable magnitudes. In addition, hot electrons and Mn ions in a magnetic 2DEG have been investigated as a function of current.Nano-scale structures of lower dimensions are planned and experiments on sub-micrometer magneto-transport structures have resulted in the first evidence for ballistic transport in quasi-1D HgTe QW structures. [Copyright &y& Elsevier]

The MBE growth of Hg1−xCdxTe alloys and type III HgTe/Hg1−xCdxTe heterostructures has been discussed, including similarities and differences between the (0 0 1) and (1 1 2)B orientations. Furthermore the MBE growth of HgTe based quantum wells (QWs) with the incorporation of Mn are additional topics. An investigation of the optical properties of type III superlattices with a normal band structure has lead to information about band structure of these heterostructures as well as information about the interface and the semimetallic QW. For example, by means of the full 8×8 Kane Hamiltonian in the envelope function approximation, it has been demonstrated that the energy separation between the H1–E1 and L1–E1 intersubband transition energies is primarily determined by the valence band offset, Λ, between HgTe and CdTe. This has led to unambiguous values for the offset and its temperature dependence, i.e. Λ(T)=570±60 meV and dΛ/dT=−0.40±0.04T meV/K. Furthermore the energy gap of HgTe at room temperature has also been determined. Magneto-transport measurements of n-type QWs show very pronounced Shubnikov-de Haas (SdH) oscillations and well developed quantum Hall plateaus for temperatures up to approximately 60 K. A large Rashba spin–orbit splitting of the first conduction subband, H1, has been observed in HgTe/Hg1−xCdxTe QWs with an inverted band structure. Self-consistent Hartree calculations of the band structure based on the above model allows us to quantitatively describe the experimental results and demonstrates that the heavy hole nature of the H1 subband greatly influences the spatial distribution of electrons in the QW and thus enhances the Rashba spin splitting, i.e. ΔEH1=βk∥3. Furthermore, the presence of two periodic SdH oscillations in p-type QWs with an inverted band structure has been observed and is the first direct evidence that these heterostructures are indirect semiconductors. The influence of Mn in the upper barrier on the 2D electrons in the well has been investigated as a function of their separation. With spacer thicknesses of 10 and 15 nm, no appreciable change is observed, however, a reduction of the spacer thickness to 5 nm results in an increase in the maximum population difference between the two Rashba spin split H1 subbands by a factor of approximately two. [Copyright &y& Elsevier]

Transport properties of the two-dimensional electron gas (2DEG) in AlxGa1−xN/GaN heterostructures were investigated by means of magnetotransport measurements. The mobilities corresponding to the 2DEG in the first and the second subbands in the trianglar quantum well at the heterointerface were obtained. When the AlxGa1−xN barrier is partially relaxed, the mobility of the 2DEG in the first subband decreases significantly, but there is an increase of mobility in the second subband. We suggest that the scattering from the piezoelectric polarization field modulated by the misfit dislocations at the heterointerface is responsible for the decrease of the 2DEG mobility. Meanwhile, the 2DEG in the second subband leaves farther from the heterointerface than that in the first subband, and thus suffers weaker scattering from the heterointerface roughness and the modulated polarization field. Therefore, the mobility of the 2DEG in the second subband is much higher than that in the first subband. [Copyright &y& Elsevier]