Tunneling-Electron Luminescence Microscopy for Multifunctional and Real-Space Characterization of Semiconductor Nanostructures

Abstract

Mesoscopic optical and electronic properties that result from quantum effects appear in semiconductor nanometer-sized structures, or nanostructures, and these properties are very different from those in macroscopic structures. [1] Progress in crystal growth and micro-process technology has enabled the atomically controlled fabrication of artificial semiconductor nanostructures and devices. These have been actively studied for the purpose of achieving lower power consumption, faster operation, and advanced functions through mesoscopic effects. To improve the performance of the nanostructures and devices, their individual optical and electronic properties in local regions must be characterized, even where many nanostructures with a high density are integrated. Furthermore, it is important to characterize both buried structures and semiconductor surfaces with single-digit nanometer-level (<10 nm) spatial resolution. The intensities and emission spectra of luminescence due to the radiative recombination of electron-hole pairs confined in the nanostructures sensitively reflect atomic-scale variations in structures as well as the quality of materials in nanometer-sized regions. Therefore, luminescence measurements in local regions, or luminescence microscopy, are effective for characterizing nanostructures and have been widely used for this purpose. In luminescence microscopy, photon-induced luminescence (photoluminescence: PL) [2] and high-energy electron induced luminescence (cathodoluminescence: CL) [3] have been widely used. However, these conventional methods cannot easily produce nanometer-level lateral spatial resolution. Thus, experimental results include statistical fluctuations that result from the convolution of the number of nanostructures, so individual nanostructures are difficult to evaluate. If the nanostructure density is low enough for there to be only one structure in an excitation region, this nanostructure can be characterized. This method, however, is not generally applied. A new concept is therefore needed for luminescence microscopy with nanometer-level spatial resolution that will enable the characterization of the optical and electronic properties of individual nanostructures even if they are fabricated with a high density in local regions.