Yuhua Zuo

GeSn p-i-n photodetector for all telecommunication bands detection

Using a 820 nm-thick high-quality Ge0.97Sn0.03 alloy film grown on Si(001) by molecular beam epitaxy, GeSn p-i-n photodectectors have been fabricated. The detectors have relatively high responsivities, such as 0.52 A/W, 0.23 A/W, and 0.12 A/W at 1310 nm, 1540 nm, and 1640 nm, respectively, under a 1 V reverse bias. With a broad detection spectrum (800-1800 nm) covering the whole telecommunication windows and compatibility with conventional complementary metal-oxide-semiconductors (CMOS) technology, the GeSn devices are attractive for applications in both optical communications and optical interconnects.

Enhanced photoluminescence from porous silicon nanowire arrays

The enhanced room-temperature photoluminescence of porous Si nanowire arrays and its mechanism are investigated. Over 4 orders of magnitude enhancement of light intensity is observed by tuning their nanostructures and surface modification. It is concluded that the localized states related to Si-O bonds and self-trapped excitations in the nanoporous structures are attributed to the strong light emission.

SiGe/Si resonant-cavity-enhanced photodetectors for 1.3 μm operation fabricated using wafer bonding techniques

A SiGe/Si multiple-quantum-well resonant-cavity-enhanced (RCE) photodetector for 1.3 μm operation was fabricated using bonding reflector process. A full width at half maximum (FWHM) of 6 nm and a quantum efficiency of 4.2% at 1314 nm were obtained. Compared to our previously reported SiGe RCE photodetectors fabricated on separation-by-implanted-oxygen wafer, the mirrors in the device can be more easily fabricated and the device can be further optimized. The FWHM is expected to be less than 1 nm and the detector is fit for density wavelength division multiplexing applications.

Room temperature direct-bandgap electroluminescence from n-type strain-compensated Ge/SiGe multiple quantum wells

N-type strain-compensated Ge/Si0.15Ge0.85 multiple quantum wells (MQWs) were grown on a Si0.1Ge0.9 virtual substrate using ultrahigh vacuum chemical vapor deposition on a n+-Si(001) substrate. Under low forward bias voltage ranging from 0.6 to 1.2 V, narrow direct-bandgap electroluminescence (EL) peak from MQWs light emitting diode was observed at room temperature. The quantum confinement effect of the direct-bandgap transitions and the temperature dependent EL peak redshift are in good agreement with the calculated results.

Ge-Si quantum dots thin film solar cells

Thin film p-i-n solar cells (SCs) with 30 bilayers undoped or p-type self-assembled Ge/Si quantum dots (QDs) were fabricated on n+-Si(001) substrates by ultrahigh vacuum chemical vapor deposition. Compared with the SCs without Ge QDs, the external quantum efficiency in infrared region and the short-circuit current densities of the SCs with Ge QDs increased. However, their open-circuit voltages and efficiencies decreased. The open circuit voltages of p-type Ge/Si QDs SCs recovered significantly at low temperature, which was due to the suppression of recombination centers and longer carrier lifetime.

Wavelength-Tunable Si-Based InGaAs Resonant Cavity Enhanced Photodetectors Using Sol-Gel Wafer Bonding Technology

We report resonant cavity enhanced (RCE) InGaAs/Si photodetectors fabricated by sol-gel wafer bonding technology. The bonding temperature was 300°C. A 60-μm-diameter photodetector demonstrated dark current density of 0.59 pA/μm2 at 0-V bias and 24.7 pA/μm2 at 2-V reverse bias, peak responsivity of 0.7 A/W, and full-width at half-maximum (FWHM) of 6 nm around 1.55 μm. The 3-dB bandwidth of a 20-μm-diameter photodetector was 17.05 GHz under 1-V reverse bias voltage. Red shift of the resonant wavelength caused by thermo-optic effect was observed. The thermal tuning range achieved 15 nm.

High hole mobility GeSn on insulator formed by self-organized seeding lateral growth

Tensile strained single-crystal GeSn on insulator (GSOI) was obtained using self-organized seeding lateral growth. Segregation of Sn atoms and Sn distribution occurred during the lateral growth of the GeSn stripe. At both edges of the GSOI, Sn concentration distribution was found in good agreement with calculation based on the Scheil equation. P-channel metal–oxide–semiconductor field effect transistors were fabricated using the GSOI materials. Good transistor performance with the low field peak hole mobility of 383 cm2 V−1 s−1 was obtained, which indicated the high quality of this GSOI structure.

Strong Eu2+ light emission in Eu silicate through Eu3+ reduction in Eu2O3-Si multilayer deposited on Si substrates

Eu2O3/Si multilayer nanostructured films are deposited on Si substrates by magnetron sputtering. Transmission electron microscopy and X-ray diffraction measurements demonstrate that multicrystalline Eu silicate is homogeneously distributed in the film after high-temperature treatment in N2. The Eu2+ silicate is formed by the reaction of Eu2O3 and Si layers, showing an intense and broad room-temperature photoluminescence peak centered at 610 nm. It is found that the Si layer thickness in nanostructures has great influence on Eu ion optical behavior by forming different Eu silicate crystalline phases. These findings open a promising way to prepare efficient Eu2+ materials for photonic application.

Room temperature photoluminescence of Ge-on-insulator structures formed by rapid melt growth

Room temperature photoluminescence (PL) was observed along 50 μm long Ge strips on insulator on bulk Si substrates fabricated by rapid melt growth. The PL peaks evidently exhibited a redshift from the origin to the end of the Ge strip because of the shrinkage of the direct bandgap of Ge. Moreover, PL intensities increased along the direction of lateral epitaxial growth primarily because of the decrease in the energy difference between the direct and indirect gaps of Ge. The change in the Ge band structure, which facilitated changes in PL peaks and intensities, was found to have resulted from the variation of tensile strain ratios and Si fractions along Ge strips. Furthermore, the PL intensity at the end of the strip was one magnitude higher than that of bulk Ge, which indicates the high quality of Ge-on-insulator structures.

Detailed balance limit efficiency of silicon intermediate band solar cells

The detailed balance method is used to study the potential of the intermediate band solar cell (IBSC), which can improve the efficiency of the Si-based solar cell with a bandgap between 1.1 eV to 1.7 eV. It shows that a crystalline silicon solar cell with an intermediate band located at 0.36 eV below the conduction band or above the valence band can reach a limiting efficiency of 54% at the maximum light concentration, improving greatly than 40.7% of the Shockley—Queisser limit for the single junction Si solar cell. The simulation also shows that the limiting efficiency of the silicon-based solar cell increases as the bandgap increases from 1.1 eV to 1.7 eV, and the amorphous Si solar cell with a bandgap of 1.7 eV exhibits a radiative limiting efficiency of 62.47%, having a better potential.