S. Fukatsu

Island formation during growth of Ge on Si(100): A study using photoluminescence spectroscopy

We present a photoluminescence (PL) study on the growth mode changeover during growth of Ge on Si(100) substrates. Intense PL signals originating from both the flat Ge layer and the three‐dimensional (3D) Ge islands are observed from Si/Ge/Si quantum wells with various Ge coverage. The onset of the 3D island formation is determined to be 3.7 monolayers (ML). It is also found that the 3D islands grow with only 3.0 ML of the flat Ge layer retained. This implies that only the 3.0 ML Ge is thermodynamically stable on Si(100) and hence corresponds to the ‘‘equilibrium’’ critical thickness.

Optical anisotropy in wire‐geometry SiGe layers grown by gas‐source selective epitaxial growth technique

We report on the successful fabrication of SiGe quantum wire structures on a V‐groove patterned substrate by gas‐source selective epitaxial growth technique, and their optical properties. Optical anisotropy, showing the realization of luminescent SiGe layers with wire geometry, was clearly observed in electroluminescence from the SiGe layers grown inside the groove.

Realization of crescent‐shaped SiGe quantum wire structures on a V‐groove patterned Si substrate by gas‐source Si molecular beam epitaxy

SiGe/Si quantum wire structures were successfully fabricated on a V‐groove patterned Si substrate by using gas‐source Si molecular beam epitaxy (GS‐SiMBE). A cross sectional image of transmission electron microscope clarified a crescent‐shaped SiGe layer at the bottom of the V‐groove owing to anisotropy of the growth rate on the different crystal orientations in GS‐SiMBE.

ABRUPT SI/GE INTERFACE FORMATION USING ATOMIC HYDROGEN IN SI MOLECULAR BEAM EPITAXY

Compositional abruptness of strained Si/Ge heterointerfaces grown by solid source Si molecular beam epitaxy under supply of atomic hydrogen (AH) was investigated using secondary ion mass spectrometry and reflection high‐energy electron diffraction. Systematic variation of growth temperature and AH exposure pressure revealed that Ge segregation length is a steadily decreasing function of AH coverage on the growth surface.

Gas-source molecular beam epitaxy and luminescence characterization of strained Si1−xGex/Si quantum wells

Abstract We describe gas-source molecular beam epitaxy (MBE) and luminescence characterization of strain Si 1− x Ge x /Si quantum wells (QWs). Successful and reproducible growth of strained QWs is demonstrated, addressing the significance of selecting a higher growth temperature to establish a high degree of structural integrity and to maintain the crystallinity in terms of “optical” quality. Excellent heterointerface transcience was evidenced by an almost perfect match between the spectral shift due to exciton confinement and the theoretical calculation. A good spatial uniformity in terms of well width and composition was obtained when QWs are grown in the adsorption/dissociation-limited growth regime.

Luminescence study on interdiffusion in strained Si1-xGex/Si single quantum wells grown by molecular beam epitaxy

Optical investigation of interdiffusion at Si1−xGex/Si heterointerfaces has been performed for the first time in strained Si1−xGex/Si single quantum wells (SQWs). Photoluminescence (PL) peak energy blue shift of up to 22 meV due to interdiffusion‐induced potential profile modulation was observed after annealing in vacuum. The diffusion coefficients obtained were found to closely follow an Arrhenius behavior with an activation energy of 2.47±0.4 eV. Dramatic increase in the integrated PL intensity was observed in the annealed samples, as a result of the elimination of effective nonradiative centers. Strain relaxation was hardly observed even after 900u2009°C annealing, indicating the unprecedented structural stability of SQWs in contrast to rather vulnerable thick alloy layers. Anomalous peak red shift, probably due to surface oxidation, was observed by annealing in N2 ambient.

Observation of deep‐level‐free band edge luminescence and quantum confinement in strained Si1−xGex/Si single quantum well structures grown by solid source Si molecular beam epitaxy

Well‐resolved band edge luminescence with no deep level emissions is reported for Si0.8Ge0.2/Si single quantum well (SQW) structures grown at high substrate temperatures (Ts≊620u2009°C) by solid source Si molecular beam epitaxy (MBE). No‐phonon (NP) transitions due to symmetry‐breaking alloy disordering in SiGe layers and transverse optical (TO) phonon replicas were clearly identified. With decreasing well width, NP and TO emissions were found to show systematic blue shift due to quantum confinement effect. Excellent crystal quality was evidenced by total absence of defect‐related deep level emissions characteristic of photoluminescence spectra of samples grown at lower temperatures, Ts<600u2009°C. This result indicates that high growth temperature environment is essential to efficient radiative recombination in SiGe/Si QW structures.

ENHANCEMENT OF RADIATIVE RECOMBINATION IN SI-BASED QUANTUM WELLS WITH NEIGHBORING CONFINEMENT STRUCTURE

Intense photoluminescence (PL) was observed from a new class of Si‐based quantum well structures (QWs), that is, neighboring confinement structure (NCS). NCS consists of a single pair of tensile‐strained‐Si layer and a compressive‐strained Si1−yGey layer sandwiched by completely relaxed Si1−xGex ( layers. In spite of the indirect band structure in real and k spaces, radiative recombination was enhanced compared with not only type‐II strained‐Si/relaxed‐Si1−xGex QWs but also type‐I strained‐Si1−yGey/relaxed‐Si1−xGex QWs. PL without phonon participation was found to dominate the spectrum possibly due to the effective carrier confinement for both electrons and holes. Quantum confinement effect was clearly observed by varying the well width, showing that the expected band alignment is realized.

Photoluminescence investigation on growth mode changeover of Ge on Si(100)

Abstract Growth mode changeover during gas source molecular beam epitaxy of Ge on Si(100) is explored by photoluminescence (PL) spectroscopy with a subatomic layer resolution. By observing confinement effect and development of island-related emissions with increasing Ge coverage in Si/pure-Ge/Si quantum wells, the onset of the island formation is determined to be 3.7 monolayers (ML). Furthermore, the equilibrium critical thickness for island formation is found to be lower, i.e. 3.0 ML, by adopting growth interruption after the Ge growth. Intense quantum-confined PL is clearly observed at room temperature from the islanded Ge of quantum dot character, demonstrating the potential of the Ge islands as efficient light emitters.

Dislocation glide motion in heteroepitaxial thin films of Si1−xGex/Si(100)

Abstract Measurements of dislocation glide velocity in heteroepitaxial Si1−xGex thin films grown on Si(100) substrates revealed that the velocity of threading dislocations penetrating the epitaxial layers depends almost linearly on the film thickness (dislocation length) in very thin films and shows saturation as the film thickness exceeds about 1 μm, in agreement with results of a similar experiment performed by Tuppen and Gibbings in 1990. The activation energy of dislocation motion is unaltered over this transition, which is incompatible with the view that such saturation is brought about by commencement of kink collision in long dislocations. This fact, together with other findings in the present study, supports an interpretation that the dislocation glide in bulk crystals of Si, even though the segment of straight dislocation is of a macroscopic dimension, proceeds without kink collision and is controlled solely by the formation rate of double kinks.