Ge quantum dots

In this paper the potential to address some of this obstacles and challenges by using Ge quantum dots and Si/SiGe quantum well structures are discussed with respect to applications in micro- and opto-electronics. 

Growing of the epitaxial Er doped Si layers was performed by sublimation molecular-beam epitaxy method. Layers with Ge quantum dots were also grown by sublimation molecular-beam epitaxy method in GeH4. 

Si L XANES of multilayer nanostructures, grown on c-Si <100> substrates are presented in Fig. 2. In this series we have investigate multilayer nanostructures of two groups. The first group samples contain Er doped epitaxial layers of Si obtained by sublimation molecular-beam epitaxy. The second group samples contain layers with Ge quantum dots which were produced by sublimation epitaxy in GeH4. All the investigated structures with quantum dots were capped by thin silicon layers of about 50 nm. 

Figure 2. Si L2,i XANES of Si nanostructure with Er doped layers (left) and Si nanostructure with Ge quantum dots (right).

A study of formation and modification of Ge quantum dots (QD) in Si is the actual problem due to perspectives to apply Ge/Si nanostructures in optoelectronic devices [1], To obtain nanoclusters with specified properties it is important to control sizes and density of Ge QDs. The modification of Ge nanocluster sizes is reached [2,3] by variation of temperature and growth rate, change of interfacial mechanical stresses, creation of buffer layers, insertion of impurities as nucleation centres, and stimulation of island growth by ion beams. In this paper, modification of Ge QDs by pulsed laser radiation was studied by Raman spectroscopy. 

PHOTOCONDUCTIVITY AND PHOTOFIELD ELECTRON EMISSION IN THE SYSTEMS OF VERTICALLY INTEGRATED Ge QUANTUM DOTS ON Si(100)... 

Lateral photoconductivity spectra and photofield electron emission of multilayer Ge/Si heterostructures with Ge quantum dots were studied at 77 and 300 K. Measurements of lateral photoconductivity spectra at 77 K showed the presence of localized states in the potential well. The photocurrent with limiting energies of 0.3 eV and 0.33 eV can be attributed to electron transitions from localized to delocalized states. A correlation between the regularities of the photoconductivity and photofield emission from such systems was revealed. 

Figure 1. Photoconductivity of Ge/Si heterostructure with eight layers of Ge quantum dots (solid line) and Si without the quantum dots (dot line) at 300 K.

Laser annealing of Ge/Si heterostructures with Ge quantum dots (QDs) embedded in the depth of 0.15 and 0.3 pm has been studied. The samples were irradiated by 80-nanosecond ruby laser pulses. The irradiation energy density was near the melting threshold of Si surface. The nanocluster structure was analyzed by Raman spectroscopy. Changes in the composition of QDs are observed for both types of samples. The decrease in dispersion of nanocluster sizes after laser irradiation is obtained for samples with QDs embedded in 0.3 pm depth. The numerical simulation shows that the maximum temperature in the depth of QDs bedding differs by -100 K. This difference is likely to lead to different effects of laser annealing of heterostructures with QDs. 

As well as compound semiconductors elemental semiconductors can be obtained from ionic liquids. Si and Ge are widely used as wafer material for different electronic applications furthermore junctions of n- and p-doped Si are still interesting for photovoltaic applications. A controlled electrodeposition of both elements and their mixtures would surely also be interesting for nanotechnology as Ge quantum dots made under UHV conditions show interesting photoluminescence. 

Ross, F. M., J. Tersoff, and R. M. Tromp. 1998. Coarsening of self-assembled Ge quantum dots on Si(001). Physical Review Letters 80(5) 984-987. 

We previously described some methods used to obtain an array of unstrained Ge quantum dots (QD) on heteroepitaxial ZnSe layers. The examined ZnSe/Ge heterosystem is characterized by similar type of the lattice and small mismatch value for their constants, w 0.2%, which excludes occurrence of the mechanical stress in the substrate-nanoobject system When studying the islets formation in this system, we observed a low-temperature recrystallization of Ge - the transition from the amorphous state to the polycrystalline one, and then into the continuous epitaxial layer (Suprun Fedosenko, 2007). The temperature was significantly below the melting temperature of the bulk material. Later we conducted experiments in situ for direct observation of this process using RHEED and XPS methods, and the results were analyzed in terms of BOLS model. 

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