Shaoxu Hu

Improved photoresponse characteristics in Se-doped Si photodiodes fabricated using picosecond pulsed laser mixing

Silicon doped with selenium beyond the solid solubility limit was prepared by picosecond pulsed laser mixing of an evaporation-deposited Se film with the underlying p-Si wafer. Photodiodes fabricated from this material exhibit enhanced spectral response over the range from 400 to 1600 nm. The responsivity strongly depends on reverse bias voltage and pulsed laser fluence. At 5 V bias, a room-temperature responsivity of 16 A W−1 at 1000 nm is obtained. At below-bandgap wavelengths, measurable responsivities of 15 mA W−1 at 1330 nm and 12 mA W−1 at 1550 nm are also observed. Extended Se impurity states might form within Si bandgap and contribute to the prominent photoresponse in these photodiodes.

Selenium-Doped Silicon-on-Insulator Waveguide Photodetector With Enhanced Sensitivity at 1550 nm

This letter describes the fabrication and characterization of a silicon-on-insulator all silicon rib waveguide photodetector with sensitivity at 1550 nm. Response at the subbandgap wavelength is provided through the introduction of deep levels via Se ion implantation. Se ions were implanted into the waveguide using an ion beam energy of 240 keV at a dose of 3×1015 cm-2. The most efficient device has a responsivity of 25 mA/W at 3 V reverse bias. The fabrication is fully compatible with standard complementary metal-oxide-semiconductor processes.

Deep Energy Levels Formed by Se Implantation in Si

To transfer a photon with a 1.55μm wavelength into an electron in an integrated optoelectronic silicon waveguide detector, selenium-doped silicon with deep energy levels is used. The deep levels in the silicon with implanted selenium are studied. Three levels are observed and their captured cross sections, concentrations and in-depth profiles are measured.

The Effects of Femtosecond Laser Irradiation and Thermal Annealing on the Optoelectronic Properties of Silicon Supersaturated with Sulfur

Electrochemical capacitance-voltage profiling, Raman and absorption spectroscopy measurements are employed to characterize the electronic and optical properties of silicon supersaturated with sulfur above the equilibrium solubility limit. Silicon wafers are ion implanted with 50keV32S+ to a dose of 1 × 1016 ions/cm2 and subsequently irradiated by femtosecond pulses at a fluence of 0.2 J/cm2, followed by thermal annealing at 825 K for 30 min. The spectral response of the photodiode fabricated from the laser-irradiated sample is also investigated. It is found that femtosecond laser irradiation and subsequent thermal annealing can electrically and optically activate the supersaturated sulfur dopant in silicon, as well as reduce the implantation-induced damage in the silicon lattice.

Optical and Electrical Properties of Single-Crystal Si Supersaturated with Se by Ion Implantation

Optical and electrical properties of single-crystal Si supersaturated with Se by ion implantation and followed by different thermal annealing conditions are reported. Si is implanted with 1 × 1016 cm−2 Se ions at 100 keV. The total substitutional fraction of Se atoms in Si is 45% under the annealing at 800°C for 30 min and the peak concentration of substitutional Se atoms is exceeded 1 × 1020 cm−3. A temperature-independent carrier concentration of 3 × 1019 cm−3 is measured and the near-infrared absorption is closed to 30%. These results indicate the insulator-to-metal transition of the doped layer and the formation of impurity bands in the Si band gap.

Investigation of diffusion length distribution on polycrystalline silicon wafers via photoluminescence methods.

Characterization of the diffusion length of solar cells in space has been widely studied using various methods, but few studies have focused on a fast, simple way to obtain the quantified diffusion length distribution on a silicon wafer. In this work, we present two different facile methods of doing this by fitting photoluminescence images taken in two different wavelength ranges or from different sides. These methods, which are based on measuring the ratio of two photoluminescence images, yield absolute values of the diffusion length and are less sensitive to the inhomogeneity of the incident laser beam. A theoretical simulation and experimental demonstration of this method are presented. The diffusion length distributions on a polycrystalline silicon wafer obtained by the two methods show good agreement.

Investigation of the forming process and characteristics of Al-BSF in silicon solar cells

This paper is intended to give insights into the forming process and characteristics of aluminum back surface field (Al-BSF) made by thermal evaporation and conventional thermal processing. It is indicated that Al-BSF formation is the result of the recrystallization of silicon and the dissolved silicon is responsible for the BSF thickness. A sufficient oxygen supply at the early stage of firing process is essential to thicken and strengthen oxide layer to protect the liquid aluminum and silicon during firing. It will be formed Al-BSF/Al-Si eutectic/Al2O3 multilayer structure at the back side of Si solar cells and the X-ray measurement demonstrates that the eutectic layer mainly contains Al3.21Si0.47. The Al-BSF has good electrical properties compared with boron-doped p+-Si by Hall tests. Solar cell with Al-BSF significantly increases long-wavelength response compared with the cells with diffused or ion implanted boron-BSF, and the back surface recombination velocity can be reduced as low as to 200 cm/s for Al-BSF passivation.