Bistable Charge Configuration of Donor Systems near the GaAs(110) Surfaces

Abstract

In gated semiconductor devices, the space charge layer that is located under the gate electrode acts as the functional element. With increasing gate voltage, the microscopic process forming this space charge layer involves the subsequent ionization or electron capture of individual dopants within the semiconductor. In this Letter, a scanning tunneling microscope tip is used as a movable gate above the (110) surface of n-doped GaAs. We study the build-up process of the space charge region considering donors and visualize the charge states of individual and multi donor systems. The charge configuration of single donors is determined by the position of the tip and the applied gate voltage. In contrast, a two donor system with interdonor distances smaller than 10 nm shows a more complex behavior. The electrostatic interaction between the donors in combination with the modification of their electronic properties close to the surface results in ionization gaps and bistable charge switching behavior.

From time-resolved atomic-scale imaging of individual donors to their cooperative dynamics

“…2A. Additionally, we chose a sample voltage ( U B = 1.3 V) where lateral interaction between donors can be neglected ( 17 ). Single, time-resolved spectra, taken directly at the marked dots, show significantly different decay constants for each donor (for logarithmic scale analysis of Fig.…”

“…1D). Charge fluctuations of donors and thereby field fluctuations take place ( 17 , 20 ), triggering further field-driven ionizations. We model an electrostatic potential in a cross section at the GaAs surface (Fig.…”

“…Bistabilities in the charge state of coupled donors have already been observed in the millisecond time regime ( 17 ). The map for the relaxation time of individual donors in Fig.…”

Time-resolved single dopant charge dynamics in silicon

“…Scanning tunnelling microscopy (STM) has enabled significant progress in this field, including observation of the influence of single dopants on the local density of states [3][4][5][6] and local magnetic properties 7,8 of the host semiconductor. Measurements on GaAs have shown slow dopant dynamics can be observed locally with millisecond timescale STM 9 . Dopant dynamics must exist on much faster time scales as well, but have not yet been observed using STM.…”

Fixing the Energy Scale in Scanning Tunneling Microscopy on Semiconductor Surfaces

“…From the parabolic fit to ∆f (V ) [cf. Fig 1(a)], we extract a flat-band voltage of +0.64 V for tip apex #1 [23]. The assignment of V CPD to the flat-band condition relies on the GaAs(110) surface not being subject to Fermi-level pinning, our cleaved surface being atomically flat, and our sample being homogeneous and well conducting at 5 K. As this assignment is the key to our experiments, its uncertainty was quantified as follows.…”