Femtosecond laser doped silicon for photovoltaic applications

Femtosecond laser doped silicon forphotovoltaic applicationsMeng-Ju Sher, Mark T. Winkler, Yu-Ting Lin and Eric MazurHarvard UniversityPhotonics West, CA2011/01/27

Intermediate-band photovoltaicsEconduction bandeehhvalence band

Intermediate-band photovoltaicsEconduction bandeeintermediate bandhhvalence bandLuque and Marti, Phys. Rev. Lett. 78, 5014 (1997)

Intermediate-band photovoltaicsEconduction bandeehintermediate bandhvalence bandLuque and Marti, Phys. Rev. Lett. 78, 5014 (1997)

Intermediate-band photovoltaicsSiconduction band0 eV1.12 eVvalence band

Intermediate-band photovoltaicsSisulfur energy levelsconduction bandS0 eV0.3180.188 0.2480.371} 0.1000.6141.12 eVvalence bandJanzén et al, Phys. Rev. B 29, 1907 (1984)

Intermediate-band photovoltaicsSimetal-insulator transitionconduction bandS0 eV0.3180.188 0.2480.371} 0.1000.6141.12 eVvalence bandJanzén et al, Phys. Rev. B 29, 1907 (1984)

Intermediate-band photovoltaicsSimetal-insulator transitionconduction bandS0 eV0.3180.188 0.2480.371} 0.1000.614deep levelhigh concentration1.12 eVvalence bandJanzén et al, Phys. Rev. B 29, 1907 (1984)

Outline• fs-laser doping• non-equilibrium dopant concentrations• optical and electronic propertiesSiS

Fs-laser dopingfs laserchamberfilled with SF6Si wafermotorizedx-y stage

Fs-laser doping

Fs-laser dopingDoped Region~1% Sulfur

Fs-laser doping3 µm

Fs-laser doping

Outline• fs-laser doping• non-equilibrium dopant concentrations• optical and electronic propertiesSiS

Non-equilibrium dopant concentrationsSi substrate1 fs-laser pulse (800 nm, 80 fs, 6 kJ/m 2 )varying SF 6pressure

Non-equilibrium dopant concentrationsSi substrateSIMS10 20S conc. (1/cm 3 )10 1910 1810 17SF 6pressure (Torr)76050010010Vacuumsolubility10 16 depth (nm)0 20 40 60 80 100Carlson et al., J. Physics and Chemistry of Solids 8, 81 (1959)

Non-equilibrium dopant concentrationsSi substrateSIMS10 15sulfur dose (1/cm 2 )10 1410 1310 12 SF 6pressure (Torr)0.1 1 10 100 1000

Outline• fs-laser doping• non-equilibrium dopant concentrations• optical and electronic propertiesSiS

Optical and electronic propertiesSi:SSi substrate50 fs-laser pulsesSF 6500 Torr

Optical and electronic propertiesSi:SSi substrateA = 1 - T int- R intSF 6500 Torr1.0105wavelength (µm)210.8absorptance0.60.4fs-laser doped Si0.2crystalline Si00 0.5 1 1.5photon energy (eV)C. Pruner and A. Asenbaum, University of Salzburg, unpublished

Optical and electronic propertiesSi:SSi substrateA = 1 - T int- R intSF 6500 Torr1.0105wavelength (µm)210.8absorptance0.60.4fs-laser doped Si0.2crystalline Si3 µm00 0.5 1 1.5photon energy (eV)C. Pruner and A. Asenbaum, University of Salzburg, unpublished

Optical and electronic propertiesSi:SSi substrateA = 1 - T int- R intSF 6500 Torr1.0105wavelength (µm)210.8absorptance0.60.4fs-laser doped Si0.2crystalline Si00 0.5 1 1.5photon energy (eV)C. Pruner and A. Asenbaum, University of Salzburg, unpublished

Optical and electronic propertiesSi:SSi substrateA = 1 - T int- R intSF 6500 Torr1.0105wavelength (µm)210.8dopant energylevel ~ 0.2 eVabsorptance0.60.4fs-laser doped Si0.2crystalline Si00 0.5 1 1.5photon energy (eV)C. Pruner and A. Asenbaum, University of Salzburg, unpublished

Optical and electronic propertiesSi:SSi substrateSiO2SF 6500 TorrB → VNIBqdVIHall measurements

Optical and electronic propertiesSi:SSi substrateSiO2T-HallSF 6500 Torr10 16300100temperature (K)5020|ns| (cm -2 )10 1210 8fs-laser doped SiSi substrate10 40 10 20 30 40 501000/T -1 (K -1 )

Optical and electronic propertiesCB0 eV0.318 eV0.188 eV0.371 eV0.110 eV0.092 eV0.082 eV0.248 eV0.614 eV1.12 eVsulfur-related energy levels in siliconJanzén et al, Phys. Rev. B 29, 1907 (1984)VB

Conclusions• Fs-laser doping• light trapping microstructures• non-equilibrium concentrations of S in Si• IR absorption and T-Hall measurements• absorption to λ ≈ 8 μm• n s(T=300K) ≈ n s(T=21K)• evidence of intermediate band formation1.0105wavelength (µm)2110 16300100temperature (K)5020absorptance0.80.60.4fs-laser doped Si|ns| (cm -2 )10 1210 8fs-laser doped Si0.2crystalline SiSi substrate00 0.5 1 1.5photon energy (eV)10 40 10 20 30 40 501000/T -1 (K -1 )

Thanks!Questions?sher@physics.harvard.eduhttp://mazur-www.harvard.edu/