Direct and simultaneous observation of ultrafast electron and hole dynamics in germanium

Understanding excited carrier dynamics in semiconductors is crucial for the development of photovoltaics and efficient photonic devices. However, overlapping spectral features in optical pump-probe spectroscopy often render assignments of separate electron and hole carrier dynamics ambiguous. Here, ultrafast electron and hole dynamics in germanium nanocrystalline thin films are directly and simultaneously observed by ultrafast transient absorption spectroscopy in the extreme ultraviolet at the germanium M4,5 edge. We decompose the spectra into contributions of electronic state blocking and photo-induced band shifts at a carrier density of 8 × 1020 cm−3. Separate electron and hole relaxation times are observed as a function of hot carrier energies. A first-order electron and hole decay of ∼1 ps suggests a Shockley–Read–Hall recombination mechanism. The simultaneous observation of electrons and holes with extreme ultraviolet transient absorption spectroscopy paves the way for investigating few- to sub-femtosecond dynamics of both holes and electrons in complex semiconductor materials and across junctions.

[1]  Prashant Nagpal,et al.  Role of mid-gap states in charge transport and photoconductivity in semiconductor nanocrystal films , 2011, Nature communications.

[2]  V. Apalkov,et al.  Controlling dielectrics with the electric field of light , 2012, Nature.

[3]  A. Dutoi.  Visualising many-body electron dynamics using one-body densities and orbitals , 2014 .

[4]  Stephen R. Leone,et al.  Attosecond band-gap dynamics in silicon , 2014, Science.

[5]  D. Attwood.  X-Rays and Extreme Ultraviolet Radiation: Principles and Applications , 2017 .

[6]  Daniel M Neumark,et al.  Real-Time Probing of Electron Dynamics Using Attosecond Time-Resolved Spectroscopy. , 2016, Annual review of physical chemistry.

[7]  U. Keller,et al.  Multiphoton transitions for delay-zero calibration in attosecond spectroscopy , 2014, 1406.3137.

[8]  Liying Jiang,et al.  Direct versus indirect optical recombination in Ge films grown on Si substrates , 2011, 1106.3300.

[9]  Simultaneous generation of sub-5-femtosecond 400  nm and 800  nm pulses for attosecond extreme ultraviolet pump-probe spectroscopy. , 2016, Optics letters.

[10]  A. Smirl,et al.  Hole spin relaxation and intervalley electron scattering in germanium , 2011 .

[11]  Frequency comb generation at terahertz frequencies by coherent phonon excitation in silicon , 2012, 1211.0769.

[12]  Fausto Rossi,et al.  Theory of ultrafast phenomena in photoexcited semiconductors , 2002 .

[13]  Jürgen Hafner,et al.  Ab‐initio simulations of materials using VASP: Density‐functional theory and beyond , 2008, J. Comput. Chem..

[14]  R. Bachrach,et al.  L 2 , 3 threshold spectra of doped silicon and silicon compounds , 1977 .

[15]  Mak,et al.  Femtosecond transmission spectroscopy at the direct band edge of germanium. , 1994, Physical review. B, Condensed matter.

[16]  E. Ivchenko,et al.  Spin-dependent intravalley and intervalley electron-phonon scatterings in germanium , 2012, 1212.3661.

[17]  R. Newman,et al.  Intrinsic Optical Absorption in Single-Crystal Germanium and Silicon at 77°K and 300°K , 1955 .

[18]  Vanessa Wood,et al.  A quantitative model for charge carrier transport, trapping and recombination in nanocrystal-based solar cells , 2015, Nature Communications.

[19]  Akio Kotani,et al.  Core Level Spectroscopy of Solids , 2008 .

[20]  Zhou,et al.  Femtosecond kinetics of photoexcited carriers in germanium. , 1994, Physical review. B, Condensed matter.

[21]  M. Goto,et al.  Thermal conductivity of sputtered amorphous Ge films , 2014 .

[22]  Cao,et al.  Core-level shifts of the Ge(100)-(2 x 1) surface and their origins. , 1992, Physical review. B, Condensed matter.

[23]  C. Kittel.  Introduction to solid state physics , 1954 .

[24]  G. F. Bertsch,et al.  Time-dependent density functional theory for strong electromagnetic fields in crystalline solids , 2011, 1112.2291.

[25]  Aram Amassian,et al.  Colloidal-quantum-dot photovoltaics using atomic-ligand passivation. , 2011, Nature materials.

[26]  N. Esser,et al.  Band gap renormalization and Burstein-Moss effect in silicon- and germanium-doped wurtzite GaN up to 10 20 cm − 3 , 2014 .

[27]  Takashi Nakatsukasa,et al.  First-principles electron dynamics simulation for optical breakdown of dielectrics under an intense laser field , 2008 .

[28]  R. Kienberger,et al.  What will it take to observe processes in 'real time'? , 2014, Nature Photonics.

[29]  R. Soref.  Mid-infrared photonics in silicon and germanium , 2010 .

[30]  V. Driel.  Influence of hot phonons on energy relaxation of high-density carriers in germanium , 1979 .

[31]  F. Krausz.  Attosecond Physics , 2007, 2007 Conference on Lasers and Electro-Optics - Pacific Rim.

[32]  G. Boschloo,et al.  Ultrafast relaxation dynamics of charge carriers relaxation in ZnO nanocrystalline thin films , 2004 .

[33]  Yasushi Shinohara,et al.  Coherent phonon generation in time-dependent density functional theory , 2010 .

[34]  G. Kresse,et al.  From ultrasoft pseudopotentials to the projector augmented-wave method , 1999 .

[35]  M. Guzzi,et al.  Valley-dependent spin polarization and long-lived electron spins in germanium , 2014 .

[36]  Taisuke Boku,et al.  Electron Dynamics Simulation with Time-Dependent Density Functional Theory on Large Scale Symmetric Mode Xeon Phi Cluster , 2016, 2016 IEEE International Parallel and Distributed Processing Symposium Workshops (IPDPSW).

[37]  Giulia Galli,et al.  X-ray absorption spectra of water from first principles calculations. , 2006, Physical review letters.

[38]  H. Tahini,et al.  Diffusion of tin in germanium: A GGA+U approach , 2011 .

[39]  T. Schmidt,et al.  Ultrafast Carrier Dynamics of a Photo-Excited Germanium Nanowire–Air Metamaterial , 2015 .

[40]  C. Bostedt,et al.  Photoemission spectroscopy of germanium nanocrystal films , 2002 .

[41]  S. Leone,et al.  High-spectral-resolution attosecond absorption spectroscopy of autoionization in xenon , 2014 .

[42]  A. Fert,et al.  Emergent phenomena induced by spin–orbit coupling at surfaces and interfaces , 2016, Nature.

[43]  P. Blaha,et al.  Improving the modified Becke-Johnson exchange potential , 2012 .

[44]  Shik Shin,et al.  Core-level reflectance spectroscopy of germanium by means of synchrotron radiation , 1982 .

[45]  Richard A. Soref,et al.  Carrier-induced change in refractive index of InP, GaAs and InGaAsP , 1990 .

[46]  K. Kreher.  Ultrafast Spectroscopy of Semiconductors and Semiconductor Nanostructures , 1997 .

[47]  Burke,et al.  Generalized Gradient Approximation Made Simple. , 1996, Physical review letters.

[48]  Gernot Deinzer,et al.  Ab initio calculation of the linewidth of various phonon modes in germanium and silicon , 2003 .

[49]  Polarization-assisted amplitude gating as a route to tunable, high-contrast attosecond pulses , 2016 .

[50]  W. Read,et al.  Statistics of the Recombinations of Holes and Electrons , 1952 .

[51]  R. Madden,et al.  Resonances in the Photo-ionization Continuum of Ar i (20-150 eV) , 1969 .

[52]  V. Apalkov,et al.  Optical-field-induced current in dielectrics , 2012, Nature.

[53]  D. Law,et al.  40% efficient metamorphic GaInP∕GaInAs∕Ge multijunction solar cells , 2007 .

[54]  S. T. Picraux,et al.  Ultrafast electron and hole dynamics in germanium nanowires. , 2008, Nano letters.

[55]  Manuel Cardona,et al.  Temperature dependence of the direct gap of Si and Ge , 1983 .

[56]  Mak,et al.  Femtosecond carrier dynamics in Ge measured by a luminescence up-conversion technique and near-band-edge infrared excitation. , 1995, Physical review. B, Condensed matter.

[57]  Feng He,et al.  Attosecond time-resolved autoionization of argon. , 2010, Physical review letters.

[58]  K. Oguri,et al.  Petahertz optical drive with wide-bandgap semiconductor , 2016, Nature Physics.

[59]  Stergios Logothetidis,et al.  Temperature dependence of the dielectric function of germanium , 1984 .

[60]  B. Alonso,et al.  Simultaneous compression, characterization and phase stabilization of GW-level 1.4 cycle VIS-NIR femtosecond pulses using a single dispersion-scan setup. , 2014, Optics express.