Scanning Tunneling Microscopy Barrier Height Imaging of Subsurface Dopant Atoms on Hydrogen-Terminated Si(111)

Abstract

Dopant atoms beneath a hydrogen-terminated Si(111) 1×1 surface are investigated by scanning tunneling microscopy (STM) and barrier height (BH) imaging. Because of the weak screening effect of the hydrogen-terminated Si(111) surface, subsurface donors and acceptors can be imaged by STM. From BH images, we can deduce a local change in BH at subsurface dopant sites. Both the sign and magnitude of the observed BH change are in good agreement with calculations assuming a screened Coulomb potential for a dopant potential.

Two Dimensional Dopant Profiling by Scanning Tunneling Microscopy

“…Consequently, the measured (dI/dZ) signal depends not only on the vacuum barrier height〈F〉but also on charge concentration Q S beneath the STM probe. The correlation of the (dI/dZ) signal to the surface charge density was conˆrmed by bias-dependent measurements on hydrogen-terminated Si(111) surfaces, 55,56) oxidized Si(110) surfaces 53) and cross sectional (001) surfaces of MOSFET devices. 41) Figure 6(a) shows line proles of the diŠerential conductance (dI/dZ) as a function of position across a drain extension for a cross section of a MOSFET device in Fig.…”

“…One promising STM-based spectroscopy to investigate nanometer-scale roughness of electric interfaces in actual devices is vacuum-gap modulation (VGM) spectroscopy, also called barrier-height spectroscopy. 21,23,41,52,55,56) In this method, while the STM probe was scanning the sample, small modulation of the STM probe-sample gap was introduced at a frequency of 10-20 kHz with a small amplitude dZ of 20 pm by applying a sinusoidal voltage to the STM piezo-scanner. Current response dI was measured with a lock-in ampliˆer at each point of the topographical image.…”

“…Current response dI was measured with a lock-in ampliˆer at each point of the topographical image. 41,53,56) On metal surfaces, the eŠective local work function (LWF) value is deˆned as…”

“…In this technique the sensitivity to variation in the tunneling current is greatly enhanced owing to the lock-in technique. Accordingly, detection of individual dopant charges has been demonstrated on well-prepared Si surfaces passivated by hydrogenation 55,56) and an ultra-thin oxide layer. 53) The authors analyzed ‰uctuations in LWF maps for oxidized (110) surfaces of boron-doped p-p ＋ multi-layers (1×10 17 -5×10 19 cm -3 ) grown on a (001) substrate.…”

Three- to two-dimensional transition in electrostatic screening of point charges at semiconductor surfaces studied by scanning tunneling microscopy

“…[9][10][11][12][13][14] Second, the close proximity of the STM tip near the surface induces localized band bendings, [15][16][17][18] which modify the potential around charged defects significantly and thus the screening cannot be probed quantitatively. Third, the limited signal to noise ratio of barrier height or surface photovoltage measurements [19][20][21] restrict a quantitative data analysis. These problems drastically limit the availability of reliable experimental data on screening at semiconductor surfaces.…”