Quantum dots applied in solar cells will be of great importance to enhance the quantum tunneling efficiency and improve the photogenerated current transport. In this study, a new easy-to-operate technology was developed to fabricate germanium-silicon quantum dots in a SiOx matrix. The quantum dots were formed by first deposited germanium-rich SiO on quartz substrate using pulsed laser deposition technique and then annealed under a comparatively high temperature. We have demonstrated a stable and low-cost fabrication process which is much cheaper than the epitaxy method to provide for the fabrication of high density germanium-silicon quantum dots. Quantum dots with diameters of 3~4 nm embedded in the amorphous SiOx layer were clearly observed. The morphological features of the thin film were characterized. The optical properties were performed by Raman spectroscopy, photoluminescence spectrum and XRD test respectively to verify the crystallization of quantum dots in the SiOx matrix. Reflectance spectrum displayed a high light absorption rate in a spectra region from 300 nm to 1200 nm, evidencing that germanium-silicon quantum dots have promising features to be used as absorber for photovoltaic application.

Light trapping in the absorber layer of thin-film solar cells is of great importance for obtaining a high photocurrent. A novel light-trapping technique is based on light scattering by metal nanoparticles through excitation of localized surface plasmons. By evaporation of thin silver layers of different thicknesses followed by thermal annealing, silver nanoparticles with different sizes were formed. We show that the plasmon resonance wavelength can be tuned by changing the embedding medium and the particle size. Furthermore, amorphous silicon solar cells with silver nanoparticles embedded between the absorber layer and the back reflector were fabricated. The effect of different sizes of the particles on the solar cell performance was studied. The performance of the solar cells was characterized by quantum efficiency and current-voltage measurements. Both the external quantum efficiency in the wavelength region of 600 to 800 nm and the current density increase as particle size increases, but remain lower than those of the reference device without particles. These results demonstrate that nanoparticles can enhance light trapping, provided that parasitic absorption in the nanoparticles is minimized. This can be achieved by better control of particle shape and size using improved fabrication techniques.

We fabricated high performance junctionless nanowire transistors (JNTs) directly on ultrathin-body Ge-on-insulator (GOI) substrates using a simple Si-compatible process. We reported the detailed fabrication process employing both optical lithography (OL) and electron beam lithography (EBL) to reduce costs and improve efficiency. These JNTs have gate lengths and channel widths that are both less than 100 nm and exhibit good electrical properties. The JNT with W/L=40 nm/70 nm, Na=1018 cm-3, and Ge-thickness dGe= 10 nm has Ion/Ioff ratio of approximately 105 at Vd=-1 V. The subthreshold slope and the drain-induced- barrier lowering (DIBL) are estimated to be 110 mV/dec at Vd=-0.1 V and 140 mV/V, respectively. The influence of Ge film thickness and temperature on electrical properties of these JLTs were investigated. Finally, we extracted the mobility of these JNTs and a peak mobility larger than 200 cm2V-1s-1 was observed.

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