Spectrally resolved luminescence of InP at low temperatures using minority carrier injection from a scanning tunneling microscope tip

The need for higher resolution in the study of materials has led to the development of sharper probes for imaging of the geometrical and surface structures. This development has led to the Scanning Tunnelling Microscope (STM), and variations thereof such as the atomic force microscope. Simultaneously there is a strong need for the possibility of making spectroscopic investigations of nm-structures. In this paper we describe results from 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 techtiique Scanning Tunneling Luminescence (STL), which is yet a new type of tunneling microscopy. Two different types of STL-experiments will be described, differing in the type of tip being used. In the first experiment we use a metallic tip to inject electrons into p-type JnP, where the charge carriers recombine, partly radiatve1y. In the second experiment we employ a tip of a large band-gap semiconductor, p-type GaP, from which electrons tunnel into an n-type InP/GaInAs/InP QW sample. We report on the first observation of such minority carrier injection where the sharply defined carrier (hole) energy distribution of the emitting tip is employed for almost monoenergetic injection and on the observation at higher bias levels of how electrons are also being injected from the InP surface into the tip where they recombine radiatively.