We have grown compositionally graded GexSi1−x layers on Si at 900 °C with both molecular beam epitaxy and rapid thermal chemical vapor deposition techniques. Triple‐crystal x‐ray diffraction reveals that for 0.10<x<0.53, the layers are totally relaxed. GexSi1−x cap layers grown on these graded layers are threading‐dislocation‐free when examined with conventional plan‐view and cross‐sectional transmission electron microscopy. Electron beam induced current images were used to count the low threading dislocation densities, which were 4×105±5×104 cm−2 and 3×106±2×106 cm−2 Eq. 2×106 cm−2 for x=0.23 and x=0.50, respectively. Photoluminescence spectra from the cap layers are identical to photoluminescence from bulk GexSi1−x.

Totally relaxed GexSi1−x layers with low threading dislocation densities grown on Si substrates

Global transition path search for dislocation formation in Ge on Si(001)

Nanometre-scale semiconductor devices have been envisioned as next-generation technologies with high integration and functionality. Quantum dots, or the so-called ‘artificial atoms’, exhibit unique properties due to their quantum confinement in all 3D. These unique properties have brought to light the great potential of quantum dots in optoelectronic applications. Numerous efforts worldwide have been devoted to these promising nanomaterials for next-generation optoelectronic devices, such as lasers, photodetectors, amplifiers, and solar cells, with the emphasis on improving performance and functionality. Through the development in optoelectronic devices based on quantum dots over the last two decades, quantum dot devices with exceptional performance surpassing previous devices are evidenced. This review describes recent developments in quantum dot optoelectronic devices over the last few years. The paper will highlight the major progress made in 1.3 μm quantum dot lasers, quantum dot infrared photodetectors, and quantum dot solar cells.

https://iopscience.iop.org/article/10.1088/0022-3727/48/36/363001/pdf

Quantum dot optoelectronic devices: lasers, photodetectors and solar cells

Thin epitaxial Ge-Si(111) films: Study and control of morphology

Two approaches to the growth of high‐quality epitaxial Ge epilayers on (100) Si have been investigated. The first consisted of compositional‐grading Si1−xGex layers and the use of strained‐layer superlattices as dislocation filters. In general, this method produced unsatisfactory results, due to the difficulty in achieving good epitaxial growth in the Ge concentration interval 30%−70%. The second approach consisted of simply depositing pure Ge directly on (100) Si. Excellent epitaxial films with dislocation densities of less than 107 cm−2 and smooth morphology were obtained after optimization of the growth parameters. The initial growth temperature and post‐growth annealing were found to be critical in obtaining good epitaxial material.

Growth and characterization of Si1−xGex and Ge epilayers on (100) Si

Epitaxial GaAs/Ge films are grown by molecular beam epitaxy (MBE) on Si substrates. The effect of various MBE growth conditions on the sample morphology, the defect density, and the optical properties of GaAs and Ge epilayers is examined. Scanning electron microscopy, plan‐view and cross‐sectional transmission electron microscopy, reflection high‐energy electron diffraction, and photoluminescence are used to characterize epitaxial layers. It is found that the defect density decreases with increasing epilayer thickness. This is due to an annihilation process that affects both threading dislocations and stacking faults. The substrate temperature during Ge growth is found to affect the properties of both the Ge and GaAs films. GaAs surface morphology degrades and the stacking fault density increases at high Ge buffer‐layer substrate temperatures; however, the threading dislocation density remains unchanged. Variations in growth conditions are correlated with defect densities and luminescence efficiencies to determine material quality and optimize growth conditions.

D. J. Dunlavy

Papers

Growth and characterization of GaAs/Ge epilayers grown on Si substrates by molecular beam epitaxy