TUNNEL-INDUCED PHOTON-EMISSION IN SEMICONDUCTORS USING AN STM

The need for higher resolution in the study of semiconductor nanometer structures has led to the development of sharper probes for imaging of the geometrical structures, all the way down to the atomic level as in scanning tunnelling microscopy (STM). Simultaneously there is a pressing need for a possibility to make spectroscopic investigations of the electronic properties of such nm-structures, especially for the excitations of individual nm-features. In this paper we describe results from investigations of spectral analysis of photons emitted as a consequence of tunnel-injection of minority carriers in semiconductor bulk or quantum-well (QW) samples. We denote this technique scanning tunnelling luminescence (STL). Two different types of STL-experiments will be described: One where electrons are injected from states having energies close to the Fermi-level of a metal STM-tip into the conduction-band of p-type InP where they recombine, partly radiatively, as minority carriers. In the other type of experiment we employ a tip of a large band-gap semiconductor, p-type GaP, to which electrons tunnel from an n-type InP/GaInAs/InP QW sample. We report the first observation of such minority carrier injection where the sharply defined carrier (hole) energy distribution of the emitting tip is employed for almost mono-energetic injection and, again for the first time, on the observation at higher bias levels of how electrons are being injected from the InP surface into the tip where they recombine radiatively with the emission spectrum having the characteristic energy distribution of the tip material.