On the Connection of Anisotropic Conductivity to Tip Induced Space Charge Layers in Scanning Tunneling Spectroscopy of p-doped GaAs

TL;DR

This study explores how anisotropic conductivity in p-doped GaAs affects tip-induced space charge layers observed in STM, revealing the importance of depletion layers and tunneling processes in imaging shallow acceptors.

Contribution

It provides a detailed analysis of the relationship between anisotropic conductivity and space charge layers in STM of p-GaAs, including experimental validation and theoretical insights.

Findings

Triangular contrasts are linked to depletion layers under the STM tip.

The tip's work function significantly influences the observed contrasts.

Tunneling involves electrons passing through vacuum and a finite semiconductor region.

Abstract

The electronic properties of shallow acceptors in p-doped GaAs{110} are investigated with scanning tunneling microscopy at low temperature. Shallow acceptors are known to exhibit distinct triangular contrasts in STM images for certain bias voltages. Spatially resolved I(V)-spectroscopy is performed to identify their energetic origin and behavior. A crucial parameter - the STM tip's work function - is determined experimentally. The voltage dependent potential configuration and band bending situation is derived. Ways to validate the calculations with the experiment are discussed. Differential conductivity maps reveal that the triangular contrasts are only observed with a depletion layer present under the STM tip. The tunnel process leading to the anisotropic contrasts calls for electrons to tunnel through vacuum gap and a finite region in the semiconductor.