Electromodulation study of Fermi level pinning in semiconductors.
Item
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Title
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Electromodulation study of Fermi level pinning in semiconductors.
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Identifier
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AAI9218288
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identifier
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9218288
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Creator
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Yin, Xiaoming.
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Contributor
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Adviser: Fred H. Pollak
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Date
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1992
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter | Engineering, Materials Science
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Abstract
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In this thesis we present a photoreflectance (PR) study of the Fermi level pinning (V{dollar}\sb{lcub}\rm F{rcub}{dollar}) on (001) MBE grown GaAs with uniform electric field. Surface photovoltage (V{dollar}\sb{lcub}\rm S{rcub}{dollar}) effects were evaluated as a function of temperature (77K {dollar}<{dollar} T {dollar}<{dollar} 450K), pump beam wavelength, W-metal coverage (in-situ) and light intensity. The dependence of the measured barrier height, V{dollar}\sb{lcub}\rm B{rcub}{dollar} (= V{dollar}\sb{lcub}\rm F{rcub}{dollar} {dollar}-{dollar} V{dollar}\sb{lcub}\rm S{rcub}{dollar}) on T and light intensity P can be explained by a modified version of the theory of Hecht yielding values of V{dollar}\sb{lcub}\rm F{rcub}{dollar} = 0.77 {dollar}\pm{dollar} 0.02V for n-type GaAs and V{dollar}\sb{lcub}\rm F{rcub}{dollar} = 0.75 {dollar}\pm{dollar} 0.02V for p-type GaAs at 300K. This analysis also provides an experimental estimation of the densities of surface states on the GaAs surface. The influence of W-metal coverage (in-situ) is to increase the effective area of the surface states and hence to reduce the effect of V{dollar}\sb{lcub}\rm S{rcub}{dollar}.;The PR measurements with different pump wavelengths allowed us to accurately determine the photo-induced current.;Using photoreflectance the effects of Ar{dollar}\sp{lcub}+{rcub}{dollar} sputtering and thermal annealing on V{dollar}\sb{lcub}\rm F{rcub}{dollar} on (001) n- and p-type GaAs were studied. The measurements were performed in-situ in an ultrahigh vacuum chamber. The effect of the sputtering was to move V{dollar}\sb{lcub}\rm F{rcub}{dollar} from midgap to near the conduction band for both types of materials. Subsequent UHV annealing (350{dollar}\sp\circ{dollar}C) and air exposure restored V{dollar}\sb{lcub}\rm F{rcub}{dollar} its original midgap value. These observations have considerable implications for various models of Schottky barrier formation. This work also demonstrates the need to simultaneously measure both n- and p-type material in order to obtain unambiguous results.;The effects of environment on the determination of V{dollar}\sb{lcub}\rm F{rcub}{dollar} were investigated. The air exposure tend to passivate the surface and hence increase the surface photovoltage effects.;We report a new contactless mode of electroreflectance (CER) which employs a capacitor-like system. We have measured the CER spectra at 300K from a number of materials including SI bulk GaAs and bulk Hg{dollar}\sb{lcub}0.8{rcub}{dollar}Cd{dollar}\sb{lcub}0.2{rcub}{dollar}Te. We demonstrate that CER can conveniently be used to determine the sign of the surface band bending in semiconductors and semiconductor structures. Results will be presented on n- and p-type bulk GaAs, semi-insulating GaAs, nominally undoped In{dollar}\sb{lcub}0.15{rcub}{dollar}Ga{dollar}\sb{lcub}0.85{rcub}{dollar}As (p-type) and n- and p-type GaAs and InP structures with large, almost constant electric fields.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
