Growth of single crystal, metastable Ge1-xSnx alloys and Ge1-xSnx/ge strained-layer superlattices on Ge(001)2x1 by molecular beam epitaxy
Başlık çevirisi mevcut değil.
- Tez No: 400020
- Danışmanlar: PROF. JOE GREENE
- Tez Türü: Doktora
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1997
- Dil: İngilizce
- Üniversite: University of Illinois at Urbana-Champaign
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Malzeme Bilimi ve Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 87
Özet
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Özet (Çeviri)
Epitaxial metastable Ge1-xSnx single crystal alloys with x up to 0.26 (the equilibrium solidsolubility of Sn in Ge is < 0.01) were grown on Ge(001)2x1 by low-temperature molecularbeam epitaxy. Film growth temperatures Ts in these experiments were limited to a relativelynarrow range around 100 °C by the combination of increased kinetic surface roughening at lowtemperatures and Sn surface segregation at high temperatures. All Ge1-xSnx films consisted ofthree distinct sublayers: the first was a highly perfect epitaxial region followed by a sublayer,with an increasingly rough surface, containing 111 stacking faults and microtwins, while theterminal sublayer was amorphous. Based upon reflection high energy electron diffraction andcross-sectional transmission electron microscopy (XTEM) analyses, critical epitaxialthicknesses tepi, defined as the onset of amorphous growth, were found to decrease from 1080 Åfor pure Ge to ? 35 Å for alloys with x = 0.26. TEM and XTEM analyses revealed no indicationof misfit dislocations (except in Ge0.74Sn0.26 samples) and high-resolution x-ray reciprocallattice mapping showed that epitaxial Ge1-xSnx layers were essentially fully strained. From ananalysis of tepi(x) results, surface morphological evolution leading to epitaxial breakdown iscontrolled by kinetic roughening for alloys with x ? 0.09 and by strain-induced roughening athigher Sn concentrations. We propose that the thermal activation required for the cross-over,reported for the first time, from kinetic to strain-induced roughening is partially overcome bythe fact that kinetic roughening provides local surface chemical potential gradients over laterallength scales which are sufficiently small to initiate strain-induced roughening even at these lowtemperatures.Single-crystal metastable diamond-structure Ge1-xSnx/Ge strained-layer superlattices(SLS) with x up to 0.24 (the equilibrium solid solubility of Sn in Ge is < 0.01) were also grownon Ge(001)2x1 substrates using temperature-modulated molecular-beam epitaxy with maximumgrowth temperatures Ts ? 140 °C. In-situ reflection high energy electron diffraction combinedwith post-deposition high-resolution x-ray diffraction (HR-XRD) and XTEM results showedthat the Ge1-xSnx(001)2x1 alloy and Ge(001)2x1 spacer layers were commensurate. In fact, thealloy layers were essentially fully strained with an average in-plane lattice constant mismatch of(1±2)x10-5 and an average tetragonal strain in the growth direction of (1.39±0.03)x10-2 asdetermined from HR-XRD reciprocal-space lattice maps obtained using asymmetric (113)reflections. ? broadening of the zero-order SLS peak was only 30.1 arc-s full width at halfmaximum (FWHM), indicating that the degree of mosaicity in these structures was negligible.The intensities and positions of the satellite reflections and finite-thickness interference fringesin HR-XRD 004 rocking curve ?-2? scans were in good agreement with simulated curvesobtained using a dynamical scattering model.
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