Electronic Transport in Highly Mismatched InAs Films on GaAs

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dc.contributor.authorZhang, Yaoen
dc.contributor.committeechairGuido, Louis J.en
dc.contributor.committeecochairHeremans, Jean J.en
dc.contributor.committeememberOrlowski, Mariusz K.en
dc.contributor.departmentElectrical and Computer Engineeringen
dc.date.accessioned2017-06-13T19:43:41Zen
dc.date.adate2014-02-07en
dc.date.available2017-06-13T19:43:41Zen
dc.date.issued2013-12-09en
dc.date.rdate2014-02-07en
dc.date.sdate2013-12-17en
dc.description.abstractElectrical properties of Si- and Mg-doped InAs epitaxial layers grown by MOCVD were studied by performing magneto-transport measurements at different temperatures, from 300 K down to 1.2 K. The longitudinal magnetoresistance and Hall effect indicate a three-band system existing in n-type (p-type) InAs, which consists of the surface accumulation (inversion) layer, the bulk electron (hole) layer, and the nucleation layer. Therefore, a classical parabolic background in magnetoresistance due to multi-carrier occurs at low fields. With the magnetic field being further applied, a linear magnetoresistance caused by inhomogeneities is revealed. At liquid helium temperature, the Shubnikov-de Haas magneto-oscillations are also observed. These transport characterizations provide a means of analyzing the band structure at the InAs surface. In a set of n-type InAs epilayers with Si doped at different levels, the bulk electron density increases as the doping level increases. The increased ionized impurities lead to lower electron mobilities due to more Coulomb scatterings. For all the n-type InAs films, except the two active layers (surface and the bulk), the nucleation layer contributes to the film conductivity as well with an electron density of ~ 5 x 10¹⁷ cm⁻³ and a mobility of ~ 2000 cm²}/Vs. In a cooldown process, the electron density of each layer slightly and monotonically decreases whereas the mobility experiences a maximum from the competition between phonon scatterings and Coulomb scatterings. The phonon scattering overwhelms the Coulomb scatting at high temperatures, but declines as temperature decreases, thus the mobility increases. Around 100 K, the temperature-independent ionized impurity scattering becomes comparable with and starts exceeding the phonon scattering, as temperature further lowered, the screening effect of the Coulomb scattering is weakened because of the decreased carrier densities. As a result, the mobility starts dropping. The maximum mobility corresponds to a minimum resistance, which explains the non-trivial temperature dependence of the resistance in the cooldown history. For the p-type InAs film, the doping with Mg in the course of MOCVD growth allows us to obtain a large hole density and a low mobility at 300 K. At low temperatures, holes are frozen out, and a strong negative magnetoresistance with a dip at 0 field are observed, which is the antilocalization signal from accumulation electrons. This is a strong technique to probe the surface quantum states and derive the phase coherence length and the spin flip length of surface electrons.en
dc.description.degreeMaster of Scienceen
dc.identifier.otheretd-12172013-155644en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-12172013-155644/en
dc.identifier.urihttp://hdl.handle.net/10919/78064en
dc.language.isoen_USen
dc.publisherVirginia Techen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectnucleation layeren
dc.subjectband structureen
dc.subjectthree-banden
dc.subjectsurface accumulation layeren
dc.subjectInAsen
dc.titleElectronic Transport in Highly Mismatched InAs Films on GaAsen
dc.typeThesisen
dc.type.dcmitypeTexten
thesis.degree.disciplineElectrical and Computer Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.levelmastersen
thesis.degree.nameMaster of Scienceen

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