Scanning tunneling microscopy and spectroscopy at low temperatures of the (110) surface of Te doped GaAs single crystals

TL;DR

This study uses low-temperature STM to image and analyze Te dopants and defect states on GaAs (110) surfaces, revealing localized charge states and Friedel oscillations around dopants.

Contribution

It provides detailed spatial and spectroscopic characterization of Te dopants and defect states on GaAs (110) surfaces at low temperatures, including the observation of localized states within the band gap.

Findings

Te dopants are identifiable down to the fifth subsurface layer.

Friedel oscillations are observed around negatively biased dopants.

Localized conductance peaks are found inside the band gap.

Abstract

We have performed voltage dependent imaging and spatially resolved spectroscopy on the (110) surface of Te doped GaAs single crystals with a low temperature scanning tunneling microscope (STM). A large fraction of the observed defects are identified as Te dopant atoms which can be observed down to the fifth subsurface layer. For negative sample voltages, the dopant atoms are surrounded by Friedel charge density oscillations. Spatially resolved spectroscopy above the dopant atoms and above defect free areas of the GaAs (110) surface reveals the presence of conductance peaks inside the semiconductor band gap. The appearance of the peaks can be linked to charges residing on states which are localized within the tunnel junction area. We show that these localized states can be present on the doped GaAs surface as well as at the STM tip apex.