Analysis of synchronous phase, pump power, and pump wavelength dependent complex PR spectra from GaAs MBE structures

Hildebrandt, Stefan; Murtagh, M.; Kuz’menko, R. V.; Kircher, W.; Schreiber, J.

doi:10.1002/pssa.2211520115

Cited by 31 publications

(10 citation statements)

References 26 publications

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“…We have also analyzed the results within the framework of a more sophisticated model 3,8 and find the correct bandgap of 1.424 eV for bare GaAs, but no difference in eV S .…”

Section: Rapid Communicationsmentioning

confidence: 97%

Modification of the Fermi-level pinning of GaAs surfaces through InAs quantum dots

et al. 1999

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Room-temperature photoreflectance in van Hoof structures together with atomic force microscopy has been used to determine the influence of InAs quantum dots on the Fermi-level pinning of ͕100͖ GaAs surfaces. We show that quantum dots with base lengths of 10 and 25 nm lead to the Fermi level being pinned approximately 250 meV deeper in the band gap, an effect which is reversible by either overgrowing the dots with GaAs or by selectively etching away the dots. These results are discussed within the framework of recent theoretical investigations of surface states due to polar facets associated with quantum dots. ͓S0163-1829͑99͒51944-9͔There has been a great interest in the preparation, characterization, and potential application of self-assembled quantum dots ͑QD's͒ over the past few years. Most often, the quantum dots which are electrically or optically characterized have been overgrown with the matrix semiconductor and are not directly on the surface. Less well understood is the effect of quantum dots on the electronic properties of the surface. The surface is altered in several important ways: part of the surface is composed of the dot material rather than the matrix, new crystallographic orientations are present due to the dots, a thin wetting layer may be present, and a strain field is added. The resulting change in the surface states will be reflected in a modification of the Fermi-level pinning at the surface.The present work describes an investigation of the effect of InAs quantum dots on the Fermi-level pinning at a (001) GaAs surface. Photoreflectance measurements have been combined with atomic force microscopy ͑AFM͒ to characterize the surface with InAs QD's directly on the surface, partially and fully overgrown with GaAs, and surfaces with the dots chemically removed. Our data show that the presence of the QD's causes the surface Fermi level to be pinned deeper into the band gap than in the case of bare GaAs. This behavior is in marked contrast to what one observes for a twodimensional InAs coverage which can be used for improving ohmic contacts by pinning the band gap less deeply. 1 We discuss this quantum-dot-induced Fermi-level pinning behavior within the framework of a recent theoretical investigation of surface states on the facets of uncovered dots. 2 The normal GaAs pinning behavior is recovered by capping the dots with sufficient GaAs so that they are no longer detectable on the surface using AFM or by selectively etching the dots chemically.The structures were grown in a Riber gas-source molecular beam epitaxy system with hydrides as group V source on (001)-oriented Si-doped GaAs substrates. After the growth of a degenerately n-doped buffer, a 500-Å undoped layer was grown, followed by the deposition of 2 monolayers ͑ML͒ of InAs. The InAs was deposited at two different substrate temperatures, T G ϭ420°C ͑with growth interruptions during the InAs deposition͒ and 500°C. The self-assembly of the QD's through the Stranski-Krastanov mechanism takes place during the deposition, which is confirmed by ...

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“…We have also analyzed the results within the framework of a more sophisticated model 3,8 and find the correct bandgap of 1.424 eV for bare GaAs, but no difference in eV S .…”

Section: Rapid Communicationsmentioning

confidence: 97%

Modification of the Fermi-level pinning of GaAs surfaces through InAs quantum dots

et al. 1999

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“…1 -12 For sufficiently high electric fields in bulk material the EM spectra may exhibit amplitude, 22 PR modulation wavelength, 22 etc., in addition to the sharp derivative-like spectral features. The phase of the CER signal can be used to determine the nature of bandbending (n-or p-type) at surfaces and interfaces.…”

Section: Introductionmentioning

confidence: 99%

Study of semiconductor surfaces and interfaces using electromodulation

Pollak

2001

Surface & Interface Analysis

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The modulation spectroscopy technique of electromodulation (EM) is a major tool for the study and characterization of a number of semiconductor surfaces/interfaces and also for the evaluation of processinduced damage at surfaces. The most useful forms of EM are photoreflectance (PR) and contactless electroreflectance (CER) because they are sensitive to surface/interface electric fields and often yield the sharpest structure (third-derivative lineshape of the unmodulated spectrum in the case of bulk/thin-film material). For sufficiently high electric fields the PR/CER spectra may exhibit Franz-Keldysh oscillations, which are a direct measure of the relevant electric field. Furthermore, PR and CER require no special mounting of the sample and hence can be employed in situ (PR) or non-destructively on wafer-sized material. This article will discuss some recent applications of PR/CER for the investigation of a number of surfaces/interfaces, such as: process-induced effects on the surface of Si; Fermi-level pinning on a number of III-V materials, including low-temperature-grown GaAs (with excess As) and wurtzite GaN; Schottky barrier formation; process-induced damage (sputtering, reactive ion etching, chemically assisted ion beam etching) on III-V materials; homojunctions (GaAs/GaAs); heterojunctions (GaAlAs/GaAs, ZnSe/GaAs, CdTe/GaAs, AlInAs/InP, InGaAs/InP, InGaAs/InAlAs and wurtzite InGaN/GaN); and device structures such as heterojunction bipolar transistors and pseudomorphic high-electron-mobility transistors. A number of these studies have been performed in situ with an ultrahigh vacuum environment.

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“…Due to the refractive index change, a signal modulated inside the layer or at the interface is back-reflected from the interface and interferes with the light reflected directly at the epilayer surface. These lowenergetic interference oscillations (LEIO) have been investigated earlier on GaAs [8,21]. Here, they were detected on n-InP layers on SI substrate as n-or p-type substrate did not produce this kind of spectral structure.…”

Section: Application Examplesmentioning

confidence: 90%

“…The theoretical fundamentals of the numerical PR simulation have been given elsewhere [8]. There, the MF model starts from the broadened electrooptic functions G and F [17].…”

Section: Fundamentals Of the Model And Spectra Analysismentioning

confidence: 99%

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Quantitative Photoreflectance Experiments on Indium Phosphide Surfaces and Structures

et al. 1995

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Photoreflectance (PR) modulation spectroscopy is a widely used optical technique on GaAs but it has been applied much more rarely on InP being an equally important optoelectronic compound semiconductor. Typical PR spectral lineshapes in the fundamental gap region of various InP materials are investigated. Spectral components such as Franz-Keldysh oscillations, lowfield features, and epilayer interference phenomena are analyzed. Current applications concern the determination of the surface electric field, investigations of ion etching and hydrogenation processing, and the characterization of homo-and strained heteroepitaxial layers by means of synchronous phase and complex fitting analysis.

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Analysis of synchronous phase, pump power, and pump wavelength dependent complex PR spectra from GaAs MBE structures

Cited by 31 publications

References 26 publications

Modification of the Fermi-level pinning of GaAs surfaces through InAs quantum dots

Modification of the Fermi-level pinning of GaAs surfaces through InAs quantum dots

Study of semiconductor surfaces and interfaces using electromodulation

Quantitative Photoreflectance Experiments on Indium Phosphide Surfaces and Structures

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