Exciton luminescence in Si1−<i>x</i>Ge<i>x</i>/Si heterostructures grown by molecular beam epitaxy

Rowell, N. L.; Noël, J.‐P.; Houghton, D. C.; Wang, A.; Lenchyshyn, L. C.; Thewalt, M. L. W.; Perović, D. D.

doi:10.1063/1.354628

Cited by 54 publications

(28 citation statements)

References 40 publications

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“…Initially, Ge atoms form small 2D platelets that evolve into pre-pyramids 22 as the Ge coverage is increased. Further deposition leads to the formation of well-defined square pyramids or elongated pyramids, or so called hut-clusters, 2 with side-walls oriented along [105] crystallographic directions [Figs. 2(a) and 2(b)].…”

Section: A Growth and Shape Evolutionmentioning

confidence: 99%

Advances in the growth and characterization of Ge quantum dots and islands

2005

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We review recent advances in the growth of Si1−xGex islands and Ge dots on (001) Si. We first discuss the evolution of the island morphology with Si1−xGex coverage and the effect of growth parameters or post-growth annealing on the shape of the islands and dots. We outline some of the structural and optical properties of Si1−xGex islands and assess progress in the determination of their composition and strain distribution. Finally, we discuss various approaches currently being investigated to engineer Si1−xGex quantum dots and in particular to control their size, density, and spatial distribution. For example, we show how C pre-deposition on Si (001) can influence the nucleation and growth of Ge islands.

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Section: A Growth and Shape Evolutionmentioning

confidence: 99%

Advances in the growth and characterization of Ge quantum dots and islands

2005

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“…Photoluminescence (PL) provides accurate measurement of the SiGe band gap in unstrained (cubic) alloys [1] and strained SiGe [2] epitaxially deposited on (001) Si. Quantum confinement effects [3] and SiGe/Si interface integrity [4] have also been studied by PL. However, evidence of the band lineup at the SiGe/Si heterointerface has remained elusive.…”

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confidence: 99%

Type I Band Alignment inSi1−xGex/Si(001<

et al. 1995

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We present experimental verification of a type I conduction band alignment for coherently strained Si~,Ge, layers in (001) silicon, with 0.15~x~0.38. A novel substrate bending scheme is used to apply in-plane uniaxial compressive and tensile stress along the [100] and [110] directions. Band edge photoluminescence from SiGe and Si is shifted with stress in accordance with deformation potential theory. Tensile stress along [110]allows clear distinction between types I and II band alignment where the predicted shifts are in opposite directions. PACS numbers: 62.20.Dc, 68.55. -a, 71.35.+z, 73.20.Dx Si& Ge alloys deposited epitaxially and coherently on Si(001) substrates have been extensively investigated in recent years [1 -14] and are rapidly gaining technological importance. Photoluminescence (PL) provides accurate measurement of the SiGe band gap in unstrained (cubic) alloys [1] and strained SiGe [2] epitaxially deposited on (001) Si. Quantum confinement effects [3] and SiGe/Si interface integrity [4] have also been studied by PL. However, evidence of the band lineup at the SiGe/Si heterointerface has remained elusive. Although it is accepted that the valence band (VB) offset AE is much larger than AE, for the conduction band (CB), more precise knowledge of band alignments is essential to optimize SiGe heterostructures for advanced devices. Previous attempts at estimating band alignments in this system have met with only modest success [5 -13]. Controversy even remains as to the sign of AE"and thus the extent of the VB discontinuity is in dispute. Early theoretical studies [5] suggested type I (electron confinement in SiGe) alignment (maximum AE, = 20 meV at x -0.2). More recent theory [7] supports type II (electron confinement in Si) behavior with AE,~x. Recent PL measurements of SiGe quantum wells (QW's) show both type I [8,9] and type II [10] behavior, whereas earlier luminescence studies [2,11] were interpreted to support either band alignment. Northrup et al. [12], using PL under hydrostatic pressure, claimed "circumstantial" evidence for type I band alignment for x -0.25. Mantz et al. [13], using uniaxial [001] stress, present PL data implicitly supportive of type I behavior at zero stress, in contradiction with their recent publication [10] in which type II behavior is claimed. Much of this confusion is due to the absence of a technique to uniquely identify the electron and hole states responsible for the observed optical transitions. Here we describe a novel technique providing in-plane uniaxial tension and compression along [110]and [100]. This reduces the SiGe QW lattice symmetry from tetragonal to orthorhombic while simultaneously distorting intermediate Si layers into tetragonal symmetry. The degeneracy at the band edges can be lifted systematically, unambiguously revealing the CB's and VB's contributing to the observed PL transition. External [100] and [110]uniaxial stresses were applied during PL by bending a Si wafer to create an elastic half space on either side of its center plane. This results ...

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“…The alloy layer luminescence energy exhibits the same dependence on x as the bulk energy gap, but it is at an overall lower energy Rowell et al, 1990;Sturm et al, 1991;Lenchyshyn et al, 1992). The recombination mechanism can vary depending on the alloy layer thickness, its crystalline quality, and the heterointerface sharpness and can give rise to near band-edge light emission and/or excitonic luminescence (Noël et al, 1992;Lenchyshyn et al, 1993;Rowell et al, 1993). In early work, it was found that the EL from Si1−xGex/Si p-i-n diodes was quenched when the temperature was increased above 80 K , but EL was later reported at higher temperatures (up to 220 K) in p-i-n diode structures (Robbins et al, 1991).…”

Section: Band Structure Engineering Via Alloyingmentioning

confidence: 98%

Si/SiGe Heterointerfaces in One-, Two-, and Three-Dimensional Nanostructures: Their Impact on SiGe Light Emission

Lockwood

Baribeau

et al. 2016

Front. Mater.

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Fast optical interconnects together with an associated light emitter that are both compatible with conventional Si-based complementary metal-oxide-semiconductor (CMOS) integrated circuit technology is an unavoidable requirement for the next-generation microprocessors and computers. Self-assembled Si/Si1−xGex nanostructures (NSs), which can emit light at wavelengths within the important optical communication wavelength range of 1.3-1.55 μm, are already compatible with standard CMOS practices. However, the expected long carrier radiative lifetimes observed to date in Si and Si/Si1−xGex NSs have prevented the attainment of efficient light-emitting devices, including the desired lasers. Thus, the engineering of Si/ Si1−xGex heterostructures having a controlled composition and sharp interfaces is crucial for producing the requisite fast and efficient photoluminescence (PL) at energies in the range of 0.8-0.9 eV. In this paper, we assess how the nature of the interfaces between SiGe NSs and Si in heterostructures strongly affects carrier mobility and recombination for physical confinement in three dimensions (corresponding to the case of quantum dots), two dimensions (corresponding to quantum wires), and one dimension (corresponding to quantum wells). The interface sharpness is influenced by many factors, such as growth conditions, strain, and thermal processing, which in practice can make it difficult to attain the ideal structures required. This is certainly the case for NS confinement in one dimension. However, we demonstrate that axial Si/Ge nanowire (NW) heterojunctions (HJs) with a Si/ Ge NW diameter in the range 50-120 nm produce a clear PL signal associated with bandto-band electron-hole recombination at the NW HJ that is attributed to a specific interfacial SiGe alloy composition. For three-dimensional confinement, the experiments outlined here show that two quite different Si1−xGex NSs incorporated into a Si0.6Ge0.4 wavy superlattice structure display PL of high intensity while exhibiting a characteristic decay time that is up to 1000 times shorter than that found in conventional Si/SiGe NSs. The non-exponential PL decay found experimentally in Si/SiGe NSs can be interpreted as resulting from variations in the separation distance between electrons and holes at the Si/SiGe heterointerface. The results demonstrate that a sharp Si/SiGe heterointerface acts to reduce the carrier radiative recombination lifetime and increase the PL quantum efficiency, which makes these SiGe NSs favorable candidates for future light-emitting device applications in CMOS technology.

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Exciton luminescence in Si1−xGex/Si heterostructures grown by molecular beam epitaxy

Cited by 54 publications

References 40 publications

Advances in the growth and characterization of Ge quantum dots and islands

Advances in the growth and characterization of Ge quantum dots and islands

Type I Band Alignment inSi1−xGex/Si(001<

Si/SiGe Heterointerfaces in One-, Two-, and Three-Dimensional Nanostructures: Their Impact on SiGe Light Emission

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