Smaller Ge Quantum Dots Obtained by ArF Excimer Laser Annealing

Ge self-assembled quantum dots （SAQDs） are grown with a self-assembled UHV/CVD epitaxy system. Then, the as-grown Ge quantum dots are annealed by ArF excimer laser. In the ultra-shot laser pulse duration, -20ns, bulk diffusion is forbidden,and only surface diffusion occurs, resulting in a laser induced quantum dot （LIQD）. The diameter of the LIQD is 20-25nm which is much smaller than the as-grown dot and the LIQD has a higher density of about 6 ×10^10cm^-2. The surface morphology evolution is investigated by AFM.

Electric properties of Ge quantum dot embedded in Si matrix

The electric characteristics of Ge quantum dot grown by molecular beam epitaxy in Si matrix were investigated by admittance spectroscopy and deep level transient spectroscopy. The admittance spectroscopy measurements show that the activation energy of 0.341eV can be considered as the emitting energy of hole from the ground state of the quantum dot. And the capacitance variation with temperature of the sample shows a platform at various frequencies with reverse bias (0.5 V,) which indicates that the boundary of space charge region is located at the quantum dot layer where the large confined hole concentration blocks the further extension of space charge region. When the temperature increases from 120K to 200K, the holes in the dot emit out completely. The position of the platform shifting with the increase of the applied frequency shows the frequency effects of the charges in the quantum dot. The deep level transient spectroscopy results show that the charge concentration in the Ge quantum dot is a function of the pulse duration and the reverse bias voltage, the activation energy and capture cross-section of hole decrease with the increase of pulse duration due to the Coulomb charging effect. The valence-band offsets of hole in Ge dot obtained by admittance spectroscopy and deep level transient spectroscopy are 0.341 and 0.338eV, respectively.

Temperature dependence of photoluminescence from self-organized Ge quantum dots with large size and low density

Photoluminescence(PL) from self-organized Ge quantum dots(QDs) with large size and low density has been investigated over a temperature range from 10 to 300 K using continuous-wave(CW) optical excitation.The integrated PL intensity of QDs observed is negligible at about 10 K and rapidly increases with raising temperature up to 100 K.Through analyzing the PL experimental data of the QDs and wetting layer(WL),we provide direct evidence that there exists a potential barrier,arising from the greater compressive strain surrounding large QDs,which could trap carriers in WL at low temperatures and could be overcome via increasing temperature.

Ge quantum dots light-emitting devices

Si photonics becomes one of the research focuses in the field of photonics. Si-based light-emitting devices are one of the most important devices in this field. In this paper, we review the Si-based light-emitting devices fabricated by embedding Ge self-assembled quantum dots into optical microcavities. Ge self-assembled quantum dots emit light in the telecommunication wavelength range from 1.3 to 1.6 pro, for which Si is transparent. Ge self- assembled quantum dots were grown on silicon-on- insulator （SOI） by molecular beam epitaxy （MBE） in Stranski-Krastanov （S-K） mode. Then, electron beam lithography （EBL） was used to define the pattern of optical microcavities on the wafer. Finally, the pattern was transferred onto the Si/Ge slab by inductive coupled plasma （ICP） dry etching. Room-temperature photolumi- nescence （PL） was used to characterize the light-emitting properties of fabricated devices. The results showed that strong resonant light emission was observed in different optical microcavities. Significant enhancement of the intensity was obtained by the optical resonance. Based on the results of PL, we designed and fabricated current- injected light-emitting devices based on Ge self-assembled quantum dots in optical microcavities. Room-temperature resonant light emission was observed from Ge dots in a 3.8 μm microdisk resonator.