Photoluminescence of confined excitons in MBE-grown Si1 − xGex/Si(100) single quantum wells

Wachter, M.; Thonke, Klaus; Sauer, R.; Schäffler, F.; Herzog, H.‐J.; Kasper, E.

doi:10.1016/0040-6090(92)90027-9

Cited by 46 publications

(19 citation statements)

References 18 publications

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“…Some PL studies claimed evidence for type I behavior, using line shifts [12] and hydrostatic pressure effects [13], respectively. Optically induced band-bending effects resulting in excitation intensity dependent shifts of PL energies were cited by Baier et al [14] and Wachter et al [15] as evidence for type II alignment. However, studies of the effects of compressive ͓001͔ uniaxial stresses by the same group produced results which were only consistent with type I alignment, although that conclusion was not explicitly stated [16].…”

mentioning

confidence: 96%

Type II Band Alignment inSi1−xGex/Si(001)
Thewalt
¹
,
Harrison
²
,
Reinhart
³

et al. 1997
Phys. Rev. Lett.
119
4
53
0
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We present experimental verification of type II band alignment in a coherently strained Si 0.7 Ge 0.3 ͞Si͑001͒ quantum well by studying photoluminescence energy shifts under external strains. A recent determination of type I band alignment from a similar experiment is shown to result from band-bending effects due to high excitation. In high quality samples, the type II luminescence can be observed in the absence of external stress by using extremely low excitation. The type II luminescence differs from the well known type I spectrum in a dramatic but as yet unexplained change in the relative intensities of the phonon replicas. [S0031-9007(97)03558-8] PACS numbers: 73.20.Dx, 78.66.Db The growth and properties of strained Si 12x Ge x , and more recently Si 12x2y Ge x C y heterostructures on (001) Si has attracted intense interest, not only because of the technological promise of combining band gap engineering with a materials system compatible with standard Si processing, but also due to the fact that this is the prototypical indirect band gap heterostructure system. Until recently, little was known about the optical properties of such structures, compared to the exhaustively studied direct gap heterostructures, but the discovery of well-resolved neargap photoluminescence (PL) [1,2] led to a speedy adaptation of PL as a standard assessment tool, and to a rapid increase in our understanding of the physical processes involved [2][3][4][5][6][7]. As in bulk, relaxed, Si 12x Ge x alloys [3], the PL of typical samples is dominated by impuritybound excitons (BE) at liquid He temperatures, and "free" excitons (FE) at higher temperatures [2], remembering that these FE move in a random potential due to alloy disorder whose width exceeds kT at low temperatures. Related to this, localized excitons (LE) associated with local band gap minima have been discovered and shown to have much higher PL quantum efficiency and longer lifetimes than BE (dominated by Auger recombination [4,5]). While most descriptions of the now ubiquitous PL spectra of these systems limit discussion to the BE͞FE species, the long carrier lifetimes make it easy to reach high excitation conditions in the quantum well (QW), and the importance of biexcitons and electron-hole plasmas in the PL processes under normal excitation conditions has been demonstrated [6,7].One of the remaining contentious issues regarding the physics and optical properties of these systems involves the band-edge alignments. While it was known early on that the majority of the band gap difference was taken up in the valence-band (VB) discontinuity, the only certainty regarding the conduction band (CB) edge was that the discontinuity was small. Theoretical studies have predicted both type I band alignments [8,9], with electrons ͑e͒, and holes ͑h͒ localized in the Si 12x Ge x , and type II alignments [10,11], with h localized in the Si 12x Ge x and e in the Si. Some PL studies claimed evidence for type I behavior, using line shifts [12] and hydrostatic pressure effects [13], respectiv...

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mentioning

confidence: 96%

Type II Band Alignment inSi1−xGex/Si(001)
Thewalt
¹
,
Harrison
²
,
Reinhart
³

et al. 1997
Phys. Rev. Lett.
119
4
53
0
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“…34 We also considered an additional temperature-dependent term in Eq. (1), which should account for the different dimensionalities of the bound states in the WL and the QDs, 35 but found little influence on the two activation energies extracted from the simplified equation (1). 36 The inset in Fig.…”

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confidence: 99%

Optical properties of individual site-controlled Ge quantum dots

Grydlik

Brehm

Tayagaki

et al. 2015

Applied Physics Letters

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We report photoluminescence (PL) experiments on individual SiGe quantum dots (QDs) that were epitaxially grown in a site-controlled fashion on pre-patterned Si(001) substrates. We demonstrate that the PL line-widths of single QDs decrease with excitation power to about 16 meV, a value that is much narrower than any of the previously reported PL signals in the SiGe/Si heterosystem. At low temperatures, the PL-intensity becomes limited by a 25 meV high potential-barrier between the QDs and the surrounding Ge wetting layer (WL). This barrier impedes QD filling from the WL which collects and traps most of the optically excited holes in this type-II heterosystem.

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“…Moreover, the QW-related PL energies are almost independent of excitation intensity, particularly at high pressures when sample heating is not important. Thus, power-dependent band bending effects typical for a spatial separation of electrons and holes in type-II heterostructures are not observed [29]. This picture remains valid under pressure because the energy separations between optical transitions in Si and quantum wells are only weakly dependent on pressure.…”

Section: Biaxial Strain Effects and Band Alignmentmentioning

confidence: 51%

High-Pressure Photoluminescence Studies of Pseudomorphic Si1-yCy/Si MQW Structures

Liu

Goñi

Manz

et al. 2000

phys. stat. sol. (b)

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We have performed photoluminescence (PL) investigations of pseudomorphic Si1–yCy/Si (y = 0.45, 1.05, and 1.62%) multiple quantum well (MQW) structures under hydrostatic pressure (0 to 8 GPa) and at low temperatures (10 to 70 K). The main MQW‐related emission, at energies below the Si band gap, consists of bound and free exciton no‐phonon lines and related Si transverse‐optic phonon replicas. All MQW‐related PL peaks shift to lower energy with increasing pressure at a rate characteristic for Γ–X indirect transitions in tetrahedral semiconductors. The total band offset and the activation energies for decay of the free and bound exciton emission increase slightly with pressure as a result of the larger negative band gap pressure coefficient of the strained pseudomorphic Si1–yCy layers compared to pure silicon. A separation of biaxial strain effects on the conduction and valence band near‐gap states in the pseudomorphic Si1–yCy layers (y ≤ 0.02) on Si indicates a decrease of the intrinsic Si1–yCy band gap which corresponds to that of pure silicon compressed to the lattice constant of the alloy. From this a type‐I band alignment with electrons and light holes localized in the SiC layers is inferred. This assignment is consistent with the dependence of PL‐peak intensities and energies on excitation power, temperature and pressure.

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Photoluminescence of confined excitons in MBE-grown Si1 − xGex/Si(100) single quantum wells

Cited by 46 publications

References 18 publications

Type II Band Alignment inSi1−xGex/Si(001)
Thewalt
¹
,
Harrison
²
,
Reinhart
³

et al. 1997
Phys. Rev. Lett.
119
4
53
0
View full text Add to dashboard Cite

Type II Band Alignment inSi1−xGex/Si(001)
Thewalt
¹
,
Harrison
²
,
Reinhart
³

et al. 1997
Phys. Rev. Lett.
119
4
53
0
View full text Add to dashboard Cite

Optical properties of individual site-controlled Ge quantum dots

High-Pressure Photoluminescence Studies of Pseudomorphic Si1-yCy/Si MQW Structures

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Photoluminescence of confined excitons in MBE-grown Si1 − xGex/Si(100) single quantum wells

Cited by 46 publications

References 18 publications

Type II Band Alignment inSi1−xGex/Si(001)Thewalt1, Harrison2, Reinhart3 et al. 1997Phys. Rev. Lett.1194530View full textAdd to dashboardCite

Type II Band Alignment inSi1−xGex/Si(001)Thewalt1, Harrison2, Reinhart3 et al. 1997Phys. Rev. Lett.1194530View full textAdd to dashboardCite

Optical properties of individual site-controlled Ge quantum dots

High-Pressure Photoluminescence Studies of Pseudomorphic Si1-yCy/Si MQW Structures

Contact Info

Product

Resources

About

Type II Band Alignment inSi1−xGex/Si(001)
Thewalt
¹
,
Harrison
²
,
Reinhart
³

et al. 1997
Phys. Rev. Lett.
119
4
53
0
View full text Add to dashboard Cite

Type II Band Alignment inSi1−xGex/Si(001)
Thewalt
¹
,
Harrison
²
,
Reinhart
³

et al. 1997
Phys. Rev. Lett.
119
4
53
0
View full text Add to dashboard Cite