A low-temperature scanning near-field optical microscope for photoluminescence at semiconductor structures

Abstract

We report on the design of a scanning near-field optical microscope (SNOM) for spatially resolved photoluminescence experiments at temperatures down to 90 K. First results on In 0.4 Ga 0.6 As quantum dots are presented.Scanning near-field optical microscopy (SNOM) [1], with its spatial resolution much better than the diffraction limit, is ideally suited to the optical investigation of inhomogeneous semiconductor structures on a lateral scale of about 100 nm. In such systems, the different sizes of the structures result in different optical transition energies, which lead to inhomogeneous broadening in conventional photoluminescence spectroscopy. Spatially resolved photoluminescence experiments, in contrast, allow detailed investigation of individual structures.In this work, we describe a SNOM setup for spatially resolved photoluminescence experiments at temperatures down to 90 K. In our first experiments on self-organized In 0.4 Ga 0.6 As quantum dots embedded in a GaAs matrix using uncoated fiber tips, we can resolve the photoluminescence emission of a few dots or even of single dots.

Photoluminescence Scanning Near-Field Optical Microscopy on III–V Quantum Dots

“…In a recent paper we have shown that the line width at T 300 K of a single InGaAs/GaAs quantum dot is 15 meV measured with 2 meV resolution [11]. This line width is of course temperature dependent, decreasing with decreasing temperatures [19]. In a more recent theoretical work describing the InAs/ GaAs quantum dot system as a multiple state system [20], a line width in good agreement with our experimental data has been obtained [11,19].…”

Finite linewidth observed in photoluminescence spectra of individual In0.4Ga0.6As quantum dots

“…Most peaks are characterized by an almost circular shape and similar emission intensities, representing the signal from individual dots. 14,17 This result clearly demonstrates that etched, metal-coated fiber tips, operated in internal-reflection geometry, allow to resolve the pure PL signal of individual quantum dots with sufficient intensity. A lateral resolution of about 300 nm is obtained, as revealed from the cross section displayed in Fig.…”

“…14 used for coarse approach. One design is mounted inside of a glass dewar and can be used for measurements down to liquidnitrogen temperature.…”