An ultrahigh-vacuum low-temperature scanning tunnelling microscope with a near-field optical detection system using conductive and optically transparent probes was used to study tunnelling-electron-induced photon emission from a cleaved p-type GaAs(110) surface. Photons generated in a nanometre-scale area just under the probe were collected within the optical near-field region into the core of the optical fibre tip. We observed a strong photon emission at positive sample biases by injecting electrons into the surface, where radiative recombination of electron–hole pairs is a reasonable explanation for the STM-induced photon emission. A drop in photon intensity at the Zn dopant regions was observed, which can be explained by the local band potential change around the Zn acceptor atoms located at sub-surface layers.

We have developed an ultrahigh-vacuum low-temperature scanning tunneling microscope (STM) equipped with a near-field optical detection system using novel conductive and optically transparent probes. Tunneling-electron induced photons generated in a nanometer-scale area just under the STM probe can be collected directly into the core of the optical fiber probe within the optical near-field region. Firstly, optical fiber probes coated with indium-tin-oxide thin film are applied to quantitative analysis of p-type GaAs(110) surface, where a decrease of light emission in photon mapping clearly extracts the existence of Zn accepter atoms located at the sub-surface layers. Secondly, in order to enhance the efficiency for inelastic tunneling excitation of a tip-induced plasmon mode, a STM probe coated with an Ag/ITO dual-layer film has been developed and applied to an Ag(111) surface, where photon mapping with a step resolution has been achieved by near-field detection.

Nanoscale electroluminescence (EL) was induced from n-type GaAs(110) in tunnel junctions using an indium tin oxide (ITO)-coated optical fibre probe at both polarities, room temperature (RT), and 80 K. The quantum efficiency of photon emission at negative bias is much higher than at positive bias at both RT and 80 K. A high quantum efficiency of about ∼10−4(photons/electron) was achieved at 80 K. The well-defined optical spectra exhibit two-peak features at 1.49 and 1.39 eV which are generated by the radiative recombination of hole–electron pairs over the direct band gap and surface states, respectively.

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