Low-temperature scanning tunneling spectroscopy as a probe for a confined electron gas

In situ cleaved (110) surfaces of n -doped GaAs have been investigated by scanning tunneling microscopy (STM) and spectroscopy (STS) at temperatures from 8 K to 300 K. At low temperatures oscillatory features in the topography around individual donor atoms embedded in the GaAs matrix and peaks in the differential conductivity (d I /d U ) curves are seen. Both vanish with increasing temperature. The experimental results are described consistently in the framework of quantized subbands of a low-dimensional electron gas within the band-bending region which is induced by the STM tip. The quantization occurs at unpinned semiconductors surfaces and is also relevant for a quantitative understanding of STM data at room temperature.