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A study was conducted on the electrical properties of subbands in the accumulation layers of the alloy semiconductor Hg1-xCdxTe. Quantitative mobility spectrum analysis (QMSA) and Shubnikov-de Haas oscillation measurements were employed to identify the concentration and mobility all types of subband carriers. Results demonstrate the capability of QMSA to generate accurate electric parameters without using complex semiconductor energy bands.

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]

The magnetotransport measurements before and after illumination are employed to explore the weak antilocalization (WAL) effects of the two-dimensional electron gas (2DEG) in high mobility [Al.sub.x][Ga.sub.1-x]N/GaN heterostructure as well as beating patterns in the Shubnikov-de Haas (SdH) oscillatory magnetoresistance. The results showed that the zero-field spin splitting energy associated with the Rashba effect has decreased after illumination.

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]

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]

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]

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]

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]