- [Show abstract] [Hide abstract] ABSTRACT: Shubnikov-de Haas (SdH) oscillation measurements at 1.5 K were carried out for In0.52Al0.48As/In0.65Ga0.35As heterostructures with different Si delta-doping concentration and spacer thickness. The dominant zero-magnetic field spin splitting mechanism is attributed to the contribution by the Rashba term due to the structure inversion asymmetry (SIA) in the In0.65Ga0.35As quantum well. The origin of the beating pattern in the SdH oscillations is investigated through the calculation of the transverse magnetoresistance versus magnetic field B by considering the Zeeman splitting and zero-magnetic field spin splitting in Si delta-doped In0.65Ga0.35As quantum wells. The good agreement between the theoretical and experimental curves suggest that the origin of beating patterns of the SdH oscillations is due to interplay of Rashba spin splitting, Zeeman splitting and Landau splitting.
- [Show abstract] [Hide abstract] ABSTRACT: We study the effects of GaN interlayer on the transport properties of two-dimensional electron gases confined in lattice-matched AlInN/AlN/GaN heterostructures. It is found that the Hall mobility is evidently enhanced when an additional ultrathin GaN interlayer is introduced between AlInN and AlN layers. The enhancement of the Hall mobility is especially remarkable at low temperature. The high Hall mobility results in a low sheet resistance of 23 Ω / ◻ at 2 K. Meanwhile, Shubnikov-de Haas oscillations (SdH) are also remarkably enhanced due to the existence of GaN interlayer. The enhancement of the SdH oscillations is related to the larger quantum mobility μ q owing to the suppression of the interface roughness, alloy disorder, and ionized impurity scatterings by the GaN interlayer.
- [Show abstract] [Hide abstract] ABSTRACT: The silicon/poly(3, 4-ethylenedioxythiophene) core/shell organic/inorganic nanowire array (SiNWs/PEDOT) hybrid heterojunction solar cells are successfully fabricated by silver-assisted chemical etching method and vapor phase polymerization processes. The SiNWs/PEDOT hybrid solar cell shows that the performance is improved greatly and an excellent power conversion efficiency of 3.23% is achieved, which is as seven times as large as that of the planar cell without the nanowire structure. In addition, the studies of the reflectance, the I-V curve and the external quantum efficiency show that the great enhancement of performance for the SiNWs/PEDOT cell is due to the fact that the Si/PEDOT core/shell nanowire structure is successfully fabricated by vapor phase polymerization method, resulting in a high light trapping effect, a large junction area and an enhancement of the carrier collection efficiency.
- [Show abstract] [Hide abstract] ABSTRACT: The magneotransport properties of a high carrier concentration and high mobility 20-nm thick In0.53Ga0.47As/In0.52Al0.48As quantum well (QW) are investigated by tilt angle dependent Shubnikov-de Haas oscillations and by weak antilocalization (WAL) in an in-plane magnetic field. The effective g-factor g* and zero field spin splitting Δ0 are extracted from tilt angle dependent beating pattern. We found that g* shows a dramatic reduction with increasing carrier density due to the increased effective band gap. Furthermore, an anomalously rapid suppression of the WAL effect with increasing in-plane magnetic field B|| is observed. This reveals that the total dephasing rate is not solely contributed by Zeeman splitting. The microroughness scattering in the QW is proposed to be another factor to cause the dephasing and thus responsible for this effect.
- [Show abstract] [Hide abstract] ABSTRACT: The magnetotransport measurement is performed on a GaN/AlxGa1-xN heterostructure sample in a low temperature range of 1.4-25 K and at magnetic fields ranging from 0 T up to 13 T. Magnetoresistance of a two-dimensional electron gas confined in the heterostructure is investigated. The negative magnetoresistivity in the whole magnetic field range originates from the electron-electron interactions (EEIs), while the positive magnetoresistivity in the high field range results from the parallel conductance. The EEI correction terms, as well as the concentration and mobility of the parallel channel are obtained by fitting the experimental data. Furthermore, another method of calculation is used to check their accuracy.
- [Show abstract] [Hide abstract] ABSTRACT: A series of AlGaN/GaN/InGaN/GaN double-heterojunction high-electron-mobility-transistors (DH-HEMT) is fabricated with GaN channel layer thicknesses from 6 nm to 20 nm by two-dimensional (2D) numerical simulations. A new idea for optimizating of DH-HEMT structure is proposed. The hot electron effect and self-heating effect are investigated by using hydrodynamic model. Current collapse and negative differential conductance are observed to be directly relevant to GaN channel layer thickness. DH-HEMT with thicker GaN channel layer can confine electrons better in channel, which significantly diminishes the penetration ability of hot electrons from channel layer to buffer layer under high voltage. Increasing the thickness of GaN channel layer appropriately can effectively restrict current collapse and negative differential conductance, and consequently improve device performance under high voltage condition.
- [Show abstract] [Hide abstract] ABSTRACT: The effects of different scattering on two-dimensional electron gases (2DEGs) in lattice matched In0.53Ga0.47As/In0.52Al0.48As quantum wells with silicon δ-doped in one barrier layer have been investigated by means of magneto-transport measurements. For the studied samples, the 2DEGs have occupied two subbands. It is found that the dominant scattering mechanism is ionized impurities scattering for the two subbands’ electrons. Besides the dominant scattering mechanism of ionized impurities scattering, Coulomb scattering also plays a role in scattering mechanism for both subbands. Both the transport scattering time and the quantum scattering time of the second subband are larger than those of the first subband. It is because that the electrons of the first subband are, on average, closer to the ionized impurities in the doped layer, they will be scattered more strongly than those in the second subband. Due to the electron wave functions for the second subband spread more widely in the quantum wells, the alloy disorder scattering is more important for the carriers in the second subband than that in the first subband.
- [Show abstract] [Hide abstract] ABSTRACT: The effective masses for spin-up and spin-down electrons of a partially spin-polarized Fermi liquid are theoretically expected to be different. We extract the spin-up and spin-down effective masses from magnetotransport measurements at different temperatures for a two-dimensional electron gas in an In0.65Ga0.35As/In0.52Al0.48As quantum well exhibiting zero-field spin splitting. We apply two analytical methods, one involving the simultaneous fitting of fast Fourier transform (FFT) spectra and the other involving inverse FFT analysis. Both methods confirm that the effective masses for spin-up and spin-down are different, consistent with theoretical expectations.
- [Show abstract] [Hide abstract] ABSTRACT: We have investigated spin-related oscillatory magnetoresistances of the two-dimensional electron gas in the inversion layer on bulk p-Hg1−xCdxTe at low temperatures. The oscillatory magnetoresistances are found to display beating pattern at low magnetic fields and to exhibit spin-splitting structure at high magnetic fields. We attribute the beating pattern to zero-field spin splitting due to spin-orbit coupling by analyzing fast-Fourier-transform results and Hall resistance. By modulating the oscillatory magnetoresistances we investigate the influence of spin-orbit coupling, Zeeman splitting, and the second populated subband on the appearance of beating patterns and the spin-splitting structure in oscillatory magnetoresistances. The strong spin-orbit coupling and the large effective g factor are demonstrated to be the significant parameters in controlling the appearance of spin-related oscillatory magnetoresistance in the inversion layer on bulk p-Hg1−xCdxTe. A good agreement between magnetoresistance data and theory suggests a spin-orbit coupling parameter α = 2.8 × 10−11 eV•m and the effective g factor g* = −44.0. The spin-orbit coupling effect presented in the inversion layer on bulk p-Hg1−xCdxTe provides a potential candidate for spintronic devices.
- [Show abstract] [Hide abstract] ABSTRACT: The results of an experimental study of quantum correction of electron–electron interaction (EEI) to the conductivity of two-dimensional electron gas (2DEG) in an undoped heterostructure are reported. A small but significant decrease of the Hall slope with the increase of temperature was discovered. This is not due to the increase of electron concentration as temperature increases but to the EEI effect. Both diffusion and ballistic contributions of EEI to the conductivity of 2DEG were observed. As the temperature increases, the negative diffusion EEI correction to the conductivity increases in an absolute value while the ballistic EEI correction reduces to a renormalization of the transport mobility.Highlights► The electron–electron interactions are studied by magneto-transport measurements. ► The Hall slope decreases with the increase of temperature. ► The ballistic EEI correction reduces to a renormalization of the mobility. ► The diffusion EEI correction increases in absolute value with the temperature.
- [Show abstract] [Hide abstract] ABSTRACT: The surface transport properties of naturally oxidized p-type Hg0.776Cd0.224Te thin film were investigated in the magnetic-field region 0–14 T and in the temperature region 8–300 K. The Hall electron concentration increases with temperature, while the surface concentration of the two-dimensional electrons in the naturally oxidized surface, calculated by Shubnikov–de Haas oscillations, decreases as temperature increases at temperatures below 20 K. The contradiction and the extraordinary quantum Hall filling factors are accounted for by assuming extra bulk-like electrons in the surface region, which dominate the surface transport properties at temperatures over 8 K.
- [Show abstract] [Hide abstract] ABSTRACT: We study the insulator-quantum Hall conductor transition in two high-density gated InGaAs/InAlAs quantum well samples. We observe a well-defined critical magnetic field and verify this marks a genuine phase transition by investigating the scaling behavior of the longitudinal resistivity with field and temperature at fixed electron density. Consistent with prevailing experimental results the critical field decreases with increasing electron density in one sample (QW0710). In the other sample (QW0715), with higher delta doping density, however, we unexpectedly find that the critical field increases with increasing electron density. This unexpected behavior may be the result of the system entering the classical percolation regime.
- [Show abstract] [Hide abstract] ABSTRACT: The beating patterns in the Shubnikov-de Haas oscillatory magnetoresistance originating from zero-field spin splitting of two-dimensional electron gases (2DEGs) in In0.52Al0.48As/InxGa1-xAs/In0.52Al0.48As quantum wells with silicon δ doped on the upper barrier layer have been investigated by means of magnetotransport measurements before and after illumination. Contrary to the expectation, after each illumination, the beating nodes induced by the zero-field spin-splitting effect shift to lower and lower magnetic field due to the decrease in the zero-field spin-splitting energy of the 2DEGs. The anomalous phenomenon of the shift of the beating nodes and the decrease in spin-orbit coupling constants after illumination cannot be explained by utilizing the previous linear Rashba model. It is suggested that the decrease in the zero-field spin-splitting energy and the spin-orbit coupling constant arise from the nonlinear Rashba spin splitting.
- [Show abstract] [Hide abstract] ABSTRACT: We report on the strong spin-orbit (SO) interaction in a gated high-mobility In <sub>0.53</sub> Ga <sub>0.47</sub> As / InP quantum well two-dimensional electron gas. We establish that the SO interaction is dominated by the Rashba mechanism. The Rashba coupling parameters determined from analysis of both weak antilocalization and the beating pattern in the Shubnikov–de Haas oscillations are in reasonable agreement, and the small difference between them was explained by a magnetic-field-dependent effective g factor. The zero-field spin splitting shows nonmonotonic behavior with a maximum as the electron density is varied with the applied gate voltage. This is related to strong Rashba SO coupling in our sample.
- [Show abstract] [Hide abstract] ABSTRACT: We study the parabolic negative magnetoresistivity in a gated In0.53Ga0.47As/InP quantum well structure where the scattering potential is predominantly long range. This magnetoresistivity is caused by the electron–electron interactions and is fitted to estimate the interaction corrections to the Drude conductivity. These corrections are smaller than the prediction of a recent theory [I.V. Gornyi, A.D. Mirlin, Phys. Rev. Lett. 90 (2003) 076801], and can be quantitatively described by Altshuler’s theory.
- [Show abstract] [Hide abstract] ABSTRACT: We study the magnetotransport properties of a gated In <sub>0.53</sub> Ga <sub>0.47</sub> As / In P quantum well structure in the presence of spin splitting when only one electronic subband is occupied. We develop an analytical method to extract the quantum mobilities for the two spin subbands. Ionized impurity scattering and alloy disorder scattering are determined to be important in this system. Larger quantum mobility is found for the higher-energy spin subband. We also demonstrate that the difference between the quantum mobilities for the two spin subbands can be altered with the gate.
- [Show abstract] [Hide abstract] ABSTRACT: (La0.5Sr0.5)CoO3 (LSCO) thin films have been fabricated on silicon substrate by the pulsed laser deposition method. The effects of substrate temperature and post-annealing condition on the structural and electrical properties are investigated. The samples grown above 650°C are fully crystalline with perovskite structure. The film deposited at 700°C has columnar growth with electrical resistivity of about 1.99×10−3Ω cm. The amorphous films grown at 500°C were post-annealed at different conditions. The sample post-annealed at 700°C and 10−4Pa has similar microstructure with the sample in situ grown at 700°C and 25Pa. However, the electrical resistivity of the post-annealed sample is one magnitude higher than that of the in situ grown sample because of the effect of oxygen vacancy. The temperature dependence of resistivity exhibits semiconductor-like character. It was found that post-annealing by rapid thermal process will result in film cracks due to the thermal stress. The results are referential for the applications of LSCO in microelectronic devices.
- [Show abstract] [Hide abstract] ABSTRACT: We study the magnetoresistance of a high-density two-dimensional electron gas confined in an InAlAs/InGaAs quantum well and observe a parabolic negative magnetoresistivity at moderate field. This negative magnetoresistivity is induced by electron-electron interactions. The interaction correction to the Drude conductance is extracted from the negative magnetoresistivity. However, due to inhomogeneity in the electron density, there is a contribution of positive magnetoresistivity, which induces the larger extracted correction than anticipated.
- [Show abstract] [Hide abstract] ABSTRACT: We report on the magnetotransport properties of 100 nm wide parabolic quantum wells and observe an enhancement of the Hall resistance in one sample but not the other. This phenomenon is likely related to the effective thickness of the electronic slab. We also observe a parabolic negative magnetoresistance originating from electron-electron interactions when only one subband is occupied in one of the samples. The interaction correction to the Drude conductivity is extracted using two methods. We find that the extracted interaction correction increases with increasing tilted angle, for which two possible explanations are given.
Guangxi UniversityYung-ning, Guangxi Zhuangzu Zizhiqu, China
East China Normal University
Shanghai, Shanghai Shi, China
- Department of Electronic Engineering
Chinese Academy of Sciences
Peping, Beijing, China
- National Laboratory for Infrared Physics