Asymmetric strain-symmetrized Ge-Si interminiband laser

Friedman, L.; Soref, Richard A.; Sun, Greg; Lu, Yanwu

doi:10.1109/68.730479

Cited by 5 publications

(2 citation statements)

References 7 publications

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“…The shortest emission wavelength of about 8 µm reached so far is limited by the valence band offsets accessible in high-quality strained Si/SiGe structures. Strain-engineered Si/Ge multilayers on relaxed SiGe buffers may enable quantum cascade waveguide laser structures for MIR light of about 4 µm wavelength (Friedman et al 1998). Inversion of the subband population in such cascade structures can be reached by a large current through the structure with a carrier relaxation that should be slow out of the upper laser level (hh2) and fast for other levels.…”

Section: Optical Intra-valence-band Transitionsmentioning

confidence: 99%

Si/Ge nanostructures

2001

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A review is given on the formation mechanisms and the properties of Si/Ge nanostructures that have been synthesized by self-assembling and self-ordering during heteroepitaxy of silicon-germanium alloys on single-crystal silicon substrates. The properties of electronic subbands in smooth strained Si/SiGe quantum well structures are presented as a basis for characterizing coherent Si/Ge nanostructures with free motion of carriers in a reduced number of dimensions. The low-dimensional band structure of valence band states confined in strained Si/Ge and Si/SiGe nanostructures is analysed by optical and electrical spectroscopy.The nanostructures presented were fabricated by self-assembly induced by elastic strain relaxation without applying any patterning technique. Misfit lattice strain of SiGe material deposited on Si substrates can relax by bunching of atomic surface steps with SiGe agglomeration at the step edges or by nucleation of Ge-rich islands in the Stranski-Krastanow growth mode. The size, density and composition of such Si/Ge nanostructures representing quantum wires and dots, respectively, can be tuned in a wide range by the growth parameters. Local strain fields extending into the Si host influence the nucleation and the lateral arrangement of nanostructures in subsequent layers and can be applied for self-ordering of nanostructures in the vertical as well as the lateral direction.Interband and intra-valence-band photocurrent, absorption and photoluminescence spectroscopy as well as C-V and admittance measurements reveal a consistent view of the band structure in Si/Ge quantum dot structures. This is in good agreement with model calculations based on band offsets, deformation potentials and effective electron masses known from earlier studies of Si/SiGe quantum well structures. The effective valence band offsets of hole states within Si/Ge nanostructures reach about 400 meV. Typical quantization energies of about 40 meV due to lateral confinement and Coulomb charging energies up to about 15 meV were observed for holes confined in 20 nm sized Si/Ge dots. Future applications of Si/Ge nanostructures such as photodetectors with improved performance or novel functionality are discussed.

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Section: Optical Intra-valence-band Transitionsmentioning

confidence: 99%

Si/Ge nanostructures

2001

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“…Layers of Si 1-x Ge x alloys deposited on Si substrates induce strain which can be rather significant in QCLs because a working structure typically consists of at least hundreds of layers with a total thickness that easily exceeds the critical thickness above which the built-in strain simply relaxes to develop defects in the structure. In dealing with the issue of strain in SiGe/Si QC structures, one popular approach is to use strain balanced growth where the compressively strained Si 1-x Ge x and tensile strained Si are alternately stacked on a relaxed Si 1-y Ge y buffer deposited on a Si substrate where the buffer composition ( ) is chosen to produce strains in Si 1-x Ge x and Si that compensate each other, so that the entire structure maintains a neutral strain profile [46,47]. Strain balanced structures have effectively eliminated the limitations of critical thickness and produced high quality SiGe/Si structures consisting of nearly 5000 layers (15 m) by chemical vapor deposition [48].…”

Section: Valence Band Sige Qclsmentioning

confidence: 99%