Probing Electronic Strain Generation by Separated Electron-Hole Pairs Using Time-Resolved X-ray Scattering

Abstract

Photogeneration of excess charge carriers in semiconductors produces electronic strain. Under transient conditions, electron-hole pairs may be separated across a potential barrier. Using time-resolved X-ray diffraction measurements across an intrinsic AlGaAs/n-doped GaAs interface, we find that the electronic strain is only produced by holes, and that electrons are not directly observable by strain measurements. The presence of photoinduced charge carriers in the n-doped GaAs is indirectly confirmed by delayed heat generation via recombination.

Reduced Thermal Conductivity in Ultrafast Laser Heated Silicon Measured by Time-Resolved X-ray Diffraction

“…A direct means to measure lattice displacement due to electron and heat propagation would remove considerable ambiguity in explaining the relevant physical phenomena. During the past decade, synchrotron based time-resolved X-ray diffraction (TRXD) has become a versatile probe for characterizing various non-equilibrium phenomena, including the transmission of heat across an interface [14], charge carrier propagation across thin-film interfaces [15] and grain boundaries [16], and the production of anisotropic strain in bulk crystal [17] and multiferroic thin film [18][19][20]. Additionally, laser-based table-top X-ray diffraction methods have enabled probing dynamics at ultrafast time-scales, such as unexpected anisotropic strain development from nanograin film on substrate [21] and a nanoscale transport mechanism in metallic multilayer systems [22].…”

Subpicosecond Optical Stress Generation in Multiferroic BiFeO3

“…With above-bandgap radiation, the transient population of excited states begins with transitions to electron and hole states that are widely separated in energy from the band-edges and continues in a cascade of intraband transitions to the band edge. − Even when the optical excitation involves only a single photon energy, an optical pulse with a large number of photons can induce transitions between many possible pairs of ground and excited states and multiple excited states . The redistribution of the population from the initially populated states occurs on time scales ranging from picoseconds, corresponding to electron–electron or electron–phonon scattering, to much longer time scales associated with electronic traps. , The nonequilibrium electron population produces elastic stress with a magnitude depending on the precise nature of populated states and the dynamics of their population, which can vary dramatically in thin-film heterostructures in which the populated states are precisely selected . The stress contributions are often summarized by local phenomena including the deformation potential or photostriction.…”

“…4,5 The nonequilibrium electron population produces elastic stress with a magnitude depending on the precise nature of populated states and the dynamics of their population, which can vary dramatically in thin-film heterostructures in which the populated states are precisely selected. 6 The stress contributions are often summarized by local phenomena including the deformation potential or photostriction. The stress depends in detail on the electron population and on the coupling between the electron configuration and the structure.…”

Time-Resolved Structural Measurement of Thermal Resistance across a Buried Semiconductor Heterostructure Interface

“…The diffracted Xrays were collected using a high-speed Avalanche Photodiode (APD) in proportional detection mode, paired with a digital oscilloscope. As the sample cooled due to heat transfer across the epitaxial interface, the time-dependent strain provided a direct measurement of temperature variations in both layers on a nanosecond timescale [57].…”