Laser-Combined Scanning Tunneling Microscopy on the Carrier Dynamics in Low-Temperature-Grown GaAs/AlGaAs/GaAs

Abstract

We investigated carrier recombination dynamics in a low-temperature-grown GaAs (LT-GaAs)/AlGaAs/GaAs heterostructure by laser-combined scanning tunneling microscopy, shaken-pulse-pair-excited STM (SPPX-STM). With the AlGaAs interlayer as a barrier against the flow of photocarriers, recombination lifetimes in LT-GaAs of 4.0 ps and GaAs of 4.8 ns were successfully observed separately. We directly demonstrated the high temporal resolution of SPPX-STM by showing the recombination lifetime of carriers in LT-GaAs (4.0 ps) in the range of subpicosecond temporal resolution. In the carrier-lifetime-mapping measurement, a blurring of recombination lifetime up to 50 nm was observed at the LT-GaAs/AlGaAs boundary, which was discussed in consideration of the screening length of the electric field from the STM probe. The effect of the built-in potential on the signal, caused by the existence of LT-GaAs/AlGaAs/GaAs boundaries, was discussed in detail.

Bases for time-resolved probing of transient carrier dynamics by optical pump–probe scanning tunneling microscopy

“…[23][24][25][26] By applying the microscopy technique, fundamental carrier dynamics in semiconductors were successfully probed and visualized, using the two-type decay modes depending on purpose. For a semiconductor sample, two components, i.e., bulk-side decay and surface-side decay, which respectively reect the decay of photocarriers on the bulk side and the decay of minority carriers tentatively trapped at the surface, are observed.…”

“…1(b)). [23][24][25][26][27][28][29] Therefore, bulk-side decay and surface-side decay can be probed by measuring the tunneling current as a function of delay time. The excited state subsequently relaxes to the original state via two processes: the decay of photocarriers on the bulk side via recombination, diffusion and dri (bulk-side decay with decay constant s b , Fig.…”

Single-Atomic-Level Probe of Transient Carrier Dynamics by Laser-Combined Scanning Tunneling Microscopy

“…Moreover, STM combined with ultrashortpulse laser technology, such as the optical pump-probe method, has enabled us to study ultrafast dynamics with pulse-width time resolution, in principle, in the femtosecond range simultaneously with the atomic resolution of STM. [10][11][12][13][14][15][16] Subnanoscale analyses on semiconductors by this microscopy technique have been reported with high time resolution provided by the ultrashort-pulse laser: however, single-atomic-level analysis taking advantage of STM has not yet been directly demonstrated until now.…”

Direct Probing of Transient Photocurrent Dynamics in p-WSe2by Time-Resolved Scanning Tunneling Microscopy

“…By applying the method to GaAs-based structures, fundamental carrier dynamics in semiconductors, such as photocarrier recombination and the effect of the inner potential on carrier dynamics, were successfully probed and visualized. [9][10][11] To increase the generality of this method of microscopy and its applicability to various types of materials and structures, additional techniques are desired. For example, as an application of TR-STM based on a similar method to the analysis of a molecular electronic structure, two-photon absorption measurement was used together with TR-STM.…”