Optical studies of ballistic currents in semiconductors [Invited]

Abstract

We present a summary of recent studies of ballistic currents using nonlinear optical techniques. Quantum interference between one-and two-photon absorption pathways is used to inject and control ballistic currents in GaAs samples. With this, a pure charge current, pure spin current, or spin-polarized charge current can be injected by changing the polarization configuration of the two pump pulses. Such currents are temporally and spatially resolved using high-resolution pump-probe techniques, including a derivative-detection scheme, which allows detection of the motion of carriers as small as 0.1 nm. Observation of the intrinsic inverse spin Hall effect in the ballistic regime, a study of time-resolved ballistic spin-polarized charge currents, and a study of the efficiency of spin current injection by quantum interference were all achieved using these techniques. Additionally, we discuss demonstrations of second-order nonlinear optical effects induced by charge and spin currents, which allow for the nondestructive, noninvasive, and real-time imaging of currents.

Proposed measurement of spin currents in a GaAs crystal using the electro-optical Pockels effect

“…By this pump configuration of quantum interference and control technique, a pure transverse spin current along the x direction with spin orientations along z direction will be achieved. 5,21 In Fig. 1, the red upward arrows indicate the electrons with spin along the direction, the black arrows to the right are the flow of electrons along the direction, and the red downward arrows represent the electrons with spin along the -z direction, the violet arrows to the left are the flow of electrons along the -x direction.…”

Invited Review Article: Pump-probe microscopy

“…97,101,102 In addition, counter-propagating pump and probe beams have been used. 103 To achieve focal scanning in the microscope, several options exist, ranging from home-built systems and microscope kits to complete, commercial microscope system (for example, the authors have successfully equipped a Zeiss LSM510 for pump-probe contrast). For home-built systems, care must be taken to avoid excessive chromatic aberrations, which would degrade focal overlap when scanning a wide field of view.…”

“…Because transient absorption provides details not only on electronic energy levels but also on the population dynamics within them, it has been used extensively for characterization of a wide range of nanomaterials such as the following: nanostructures such as quantum wells, 130 silver nanocubes, 131 and nanowires of various materials; [100][101][102][132][133][134] bulk and patterned semiconductors, 84,92,103,106 polymer blends, and organic semiconductor films; 80,82,83,135,136 topological insulators; 137 graphene, 98,[138][139][140][141][142][143] and carbon nanotubes; 76,144,145 and most recently, perovskites. 81,97 For excellent review papers on transient absorption microscopy in materials sciences, we refer the reader to Refs.…”

Ultrafast Excited-State Transport and Decay Dynamics in Cesium Lead Mixed Halide Perovskites

“…Carrier trapping can impact transport as well. If either electrons or holes are trapped in the lattice (and thus exhibit lower mobility than free carriers), space charge effects will reduce the overall ambipolar transport of the photogenerated carrier cloud depending on the depth of the trap sites and the intrinsic mobility of the carriers. , While we have recently shown that trapping plays a minimal role in MAPbI 3 transport because of the high static dielectric and the short intrinsic carrier scattering time, there may be significant differences in material properties, e.g., the static dielectric constant, that enhance the impact of trap sites in Cs-based perovskite carrier transport (and recombination) relative to the organic–inorganic analogues. Temperature-dependent transport measurements should provide further insight into the role of trap sites and their impact on carrier mobility in these materials.…”