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Narrow gap InGaAs two-dimensional electron gas (2DEG) bilayer samples are fabricated and confirmed to have good electronic qualities as well as strong Rashba-type spin-orbit interactions (SOIs). The 2DEG systems are realized by molecular beam epitaxy in the form of wide quantum wells (QWs) with thicknesses tQW∼40-120nm modulation doped in both the upper and lower InAlAs barriers. From the Hall measurements, the overall mobility values of μe ∼15 m2/V s are found for the total sheet electron density of ns ∼8 × 1011/cm2, although the ns is distributed asymmetrically as about 1:3 in the upper and lower 2DEGs, respectively. Careful low temperature magneto-resistance analysis gives large SO coupling constants of α ∼20 × 10 -12eV m as well as expected electron effective masses of m*/m0 ∼0.033-0.042 for each bilayer 2DEG spin sub-band. Moreover, the enhancement of α with decrease of tQW is found. The corresponding self-consistent calculation, which suggests the interaction between the bilayer 2DEGs, is carried out and the origin of α enhancement is discussed., QC 20130118

We investigated double-doped InGaAs/InAlAs heterostructures with high indium compositions. The heterostructures were grown by molecular beam epitaxy on GaAs(001) with metamorphic step-graded buffer layers. The magneto-transport characterization was performed by using Hall-bar devices. We observed non-monotonic magnetoresistanceoscillations, which indicate a single two-dimensional electron gas (2DEG) with multiple-subband occupationor a 2DEG bilayer. We also observed weak-antilocalization in all samples, which is an evidence of spin-orbit coupling., identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/10602

The influence of temperature on selective area (SA) InAs nanowire growth was investigated formetal-organic vapor phase epitaxy (MOVPE) using N_2 as the carrier gas and (111)B GaAs substrates.In contrast to the growth temperature range – below 600°C – reported for hydrogen ambient, theoptimal growth temperature – between 650° and 700°C was 100K higher than the optimal ones for H_2 carrier gas. At these temperatures nanowires with aspect ratios of about 80 and a symmetric hexagonal shape were obtained. The results found are attributed to the physical and chemical properties of the carrier gas., identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/10271

We investigated the transport properties of ferromagnetic/semiconductor hybrid two-terminal structures utilizing an In_<0.75>Ga_<0.25>As/In_<0.75>Al_<0.25>As 2DEG formed on a GaAs (001) substrate with In_xAl_<1-x>As step-graded buffer layers. We used NiFe as ferromagnetic electrodes for injection/detection of spin-polarized electrons, which were formed on side walls of the semiconductor mesa to contact electron channel directly. We measured spin valve properties at low temperatures, and successfully found clear spin valve signals as well as clear channel width dependence. The results with such clear dependence suggest successful spin transport in the present samples., identifier:0094243X, identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/3325

We investigated the transport properties of ferromagnetic/semiconductor hybrid structures utilizing an InAs/In_<0.75>Al_<0.25>As modulation-doped heterostructures formed on a GaAs (001) substrate with In_xAl_<1-x>As step-graded buffer layers. We used NiFe as ferromagnetic electrodes for injection/detection of spin-polarized electrons, which were formed on side walls of the semiconductor mesa to contact electron channel directly. We measured magneto-transport properties of the samples with current flow between the ferromagnetic electrodes at low temperatures. Under vertical magnetic fields, magneto-resistance oscillations were clearly observed, thus the ferromagnetic electrodes worked as ohmic contacts. In addition, we successfully found spin-valve properties under parallel magnetic fields. Furthermore, we observed the enhancement of spin-valve properties by squeezing the channel width., identifier:14686996, identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/3324