S. Ishida

Magnetic freeze-out and impurity band conduction in n-InSb

Abstract Non-ohmic conduction of n-InSb with different donor concentrations ( N d =2×10 14 – 1×10 15 cm −3 ) in perpendicular magnetic fields has been measured at low temperatures, in order to infer the impurity band mobility μ i with the aid of the two-band analysis. The decrease of μ i with increasing magnetic fields has been found to reflect exactly the shrinkage of donor wave functions due to magnetic field and the magnetic-field induced metal–insulator transition is an event in the impurity band. The temperature dependence of μ i in moderate magnetic fields above the transition field B c appears to obey the Mott variable-range hopping law as μ i =μ 0 exp [−(T 0 /T) x ] with x =1/4.

Interfacial trap states and improvement of low-temperature mobility by doping in InSb/AlInSb quantum wells

The effect of doping on InSb/Al0.1In0.9Sb quantum wells (QWs) was investigated, and it was found that doping improves the electron mobility at low temperatures and leads to a weaker dependence of the resistivity with temperature. The dependence of the carrier density on the well width revealed trap states at the interfaces of the QW whose sheet density per interface was estimated to be about 4u2009×u20091010u2009cm−2. The low mobility of undoped InSb QWs, in particular, at low temperature seems to have been caused by positively ionized impurity scattering at the interfacial trap states. Doping compensates for the trap states and enhances mobility by suppressing ionized impurity scattering. Thus, intentional doping is necessary for developing high-mobility InSb QW devices. The origin of the trap states is qualitatively discussed.

Transport properties and observation of quantum Hall effects of InAs 0.1 Sb 0.9 thin layers sandwiched between Al 0.1 In 0.9 Sb layers

InAs0.1Sb0.9 active layers sandwiched between Al0.1In0.9Sb insulating buffer layers were grown on GaAs (100) substrates by molecular beam epitaxy. The basic transport properties at room temperature and quantum Hall effects at low temperature of the InAs0.1Sb0.9 were studied as a function of InAs0.1Sb0.9 thickness. The electron mobility of the InAs0.1Sb0.9 active layers had a very high value and very small thickness dependence at less than 500nm. The quantum Hall effects of the InAs0.1Sb0.9 were observed at thicknesses 15, 20, 30, 50, 70, and 100nm. The observation of the quantum Hall effect at thickness more than 50nm strongly suggests the existence of two-dimensional electron gas in the InAs0.1Sb0.9 layer sandwiched between Al0.1In0.9Sb layers.

Negative and Positive Magnetoresistance in Variable-Range Hopping Regime of Undoped AlxIn1−xSb/InSb Quantum Wells

Low-temperature magnetoresistance (MR) in the variable-range hopping (VRH) regime of undoped AlxIn1−xSb/InSb quantum wells was studied. The low-T resistance shows that the two dimensional (2D) Mott VRH crossovers to Efros-Shklovskii (ES) VRH due to the Coulomb interaction with lowering T. The anisotropic negative MR in weak magnetic fields was explained by the quantum interference in the VRH. The in-plane positive MR in higher fields found in ES VRH regime was attributed to the spin-Zeeman effect that suppresses the hops between singly occupied states in the presence of intra-state correlation. As for the orbital MR subtracted from perpendicular MR, in deeply insulating regime the negative MR saturates above a characteristic field followed by an exponential increase of the positive MR in agreement with the quantum interference and the subsequent shrinkage of wave functions with increasing field, while in barely insulating regime of the 2D metal-insulator (MI) transition a large negative MR inexplicable survives even in the extremely high magnetic-fields.

Low-temperature transport properties of InSb films on GaAs(1 0 0) substrates

Abstract Low-temperature magnetoresistance (MR) has been studied for undoped and Sn-doped InSb thin films grown on GaAs(1xa00xa00) substrates by MBE. Sn-doped films show the Shubnikov–de Haas oscillations which reflect a large g -factor ( g ∗ ∼−40 depending on the carrier concentration) of electrons in InSb films. In undoped films, on the other hand, almost whole carriers fall into the accumulation layer at the InSb/GaAs interface at low temperatures, resulting in the advent of positive MR arising from the two-dimensional weak anti-localization due to spin–orbit interaction.

Relationship between transport properties and band diagrams in InAsxSb1−x/Al0.1In0.9Sb quantum wells

The resistivity of InAs0.1Sb0.9/Al0.1In0.9Sb quantum wells (QWs) is much lower than that of InSb/Al0.1In0.9Sb QWs, staying low resistivity even at low temperature. Fundamental difference in low temperature transport properties between InSb/Al0.1In0.9Sb and InAs0.1Sb0.9/Al0.1In0.9Sb QWs was revealed, based on the band diagram calculations of these QWs. Band diagrams of InAsxSb1−x/Al0.1In0.9Sb QWs showed that the energy band of the InAsxSb1−x layer moves downward with increasing As content x. The QW is type I at x equal to 0, becomes type II at x equal to 0.1. The Fermi level (EF) of the InSb QWs lies in the band gap and below apart from the bottom of the conduction band, while EF of the InAs0.1Sb0.9 QWs is above the bottom of the conduction band of the well. The calculated sheet carrier densities are in good agreement with the experimental results. It well explains that the sheet carrier density difference between InSb and InAs0.1Sb0.9 QWs mainly originates from this band diagram difference and the positio...

Study of Spin‐Orbit Interaction in AlxGa1−xAsySb1−y/InAs Quantum Well by Means of Persistent Photoconductivity Effect on Weak Localization

Weak localization has been studied in an AlxGa1−xAsySb1−y/InAs quantum well (QW) by means of tuning the carrier density n via the persistent photoconductivity effect in order to explore the origin of spin‐orbit interaction (SOI) in this system. The magnetoconductance in extremely weak B‐fields has been fitted by taking account of the spin‐Zeeman effect on the SOI arising from the spin splitting in asymmetric systems. The SO field (Bso) deduced has been found to be independent of n, thereby confirming the dominant role of the Rashba field as the cause of the SOI.

Negative Persistent Photoconductivity Effect on Weak Anti‐Localization in Hetero‐Interface of InSb/GaAs(100)

Spin‐orbit interaction (SOI) in the weak anti‐localization has been investigated for the accumulation layer at InSb/GaAs(100) hetero‐interface, tuning carrier concentration and mobility by means of negative persistent photoconductivity effect. The SO field deduced from the fits of magnetoconductance taking account of the spin‐Zeeman effect on SOI has been found to be independent of the carrier concentration, indicating that the Rashba effect due to the asymmetric electric field at the interface is the dominant mechanism of SOI in our system.

Spin‐Orbit Interaction in InSb Thin Films Grown on GaAs (100) Substrates by MBE: Effect of Hetero‐Interface

Magnetoresistance (MR) effects caused by quantum interference have been investigated in order to search into the spin‐orbit interaction (SOI) in the InSb films grown on GaAs(100) substrates by MBE. The positive MR in the accumulation layer at the InSb/GaAs interface arises from the two‐dimensional (2D) weak anti‐localization (WAL) and is explained by taking account of the spin‐Zeeman effect on the SOI caused by the asymmetric potential at the hetero interface (Rashba term with SO scattering rate τSO−1u2009∼u20091.7u2009×u20091012u2009s−1). The negative MR in extremely weak magnetic fields found for Sn‐doped films dramatically crossovers to the positive MR with decreasing the film thickness. The results have been analyzed using a two‐layer model for the films; the SO scattering rate in the intrinsic InSb film due to the bulk inversion asymmetry (Dresselhaus term) has been found to be as small as τSO−1u2009⩽u20092u2009×u2009109u2009s−1 and when the interface is approached in the film the WL crossovers to the WAL with the increase of SOI in the la...