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 sc anning tunneling microscopy (STM) and spectroscopy (STS) at temperatures fr om 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 (dI/dU) curves are seen. Both vanish with increa sing temperature. The experimental results are described consistently in th e framework of quantized subbands of a low-dimensional electron gas within the band-bending region which is induced by the STM tip. The quantization o ccurs at unpinned semiconductors surfaces and is also relevant for a quanti tative understanding of STM data at room temperature.