Probing nanoscale potential modulation by defect-induced gap states on GaAs(110) with light-modulated scanning tunneling spectroscopy

Abstract

We investigated charged defects on an n-GaAs͑110͒ surface using light-modulated scanning tunneling spectroscopy. Tunneling via a single defect-induced gap state under photoillumination was observed for the isolated atomic defects. Screened Coulomb potentials induced around a charged Ga vacancy and a step edge were visualized, for the first time, with a nanometer spatial resolution. Furthermore, the charge states of the individual defects were determined on the atomic level.

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

“…First, the I-V s curve in the dark for GaAs (blue line in Figure 3(b)) reveals that the tunneling current does not flow unless a bias voltage much larger than the bandgap energy is applied. This is because large TIBB occurs at both positive and negative bias voltages [20,[22][23][24][25]. This tendency is also present for AlGaAs and LT-GaAs (Figures 3(c) and 3(d)).…”

“…This indicates that no photocarriers are generated and the AlGaAs layer works well as a barrier against the flow of photocarriers from the adjacent LT-GaAs and GaAs layers, as expected. If photocarriers had flowed from GaAs or LT-GaAs into AlGaAs, TIBB in AlGaAs would have been reduced, as observed at the pn junction of GaAs in previous studies [23][24][25]. The slight changes seen in the red and blue curves in Figure 3(c) are due to the effect of photovoltage at the LT-GaAs/AlGaAs/GaAs interfaces, which will be discussed in Section 3.4.…”

“…Light-modulated scanning tunneling spectroscopy (LM-STS) was used for analyzing the band structure of the sample [19,[21][22][23][24][25]. In LM-STM measurement, the sample under STM is intermittently illuminated by an electrically chopped laser source and the sample bias voltage is swept to obtain tunneling current versus sample bias voltage (I-V s ) curves underilluminated and dark conditions simultaneously, which provides information for analyzing the band structure of the sample.…”

Laser-Combined STM and Related Techniques for the Analysis of Nanoparticles/Clusters

“…The addition of optical technologies to STM provides new approaches to the study of nanoscale-material physics and chemistry. Nearfield optical microscopy (NSOM) and other techniques [78][79][80][81][82][83][84][85][86], which have not been discussed in this chapter, are expected to play complementary roles in understanding and developing the physics and chemistry of new nanoparticles/clusters for realizing novel functional devices.…”

Quantitative determination of local potential values in inhomogeneously doped semiconductors by scanning tunneling microscopy

“…Quantitative potential measurements rely on a statistical analysis of interacting charged defects, 19,20,26 the band edge determination in tunneling spectra, 4,14 a work function measurement, or surface photo voltage measurements. 27 However, in the latter two cases, the tip-induced band bending severely affects the results by shifting the band edges. [28][29][30][31] This band edge shift is not homogeneous across the surface, because the screening ability varies spatially, e.g., with the fluctuations in the dopant distribution or the material across heterointerfaces.…”