Instrumentation for dual-probe scanning near-field optical microscopy

Abstract

To investigate local carrier motions, we developed a dual-probe scanning near-field optical microscope (SNOM) with two fiber probes where one is for photoexcitation and the other is for light collection. This instrumentation is based on two important techniques: the design of probe structures and distance control between the sample surface and the two probes. A finite-difference time-domain method numerically analyzed and optimized the design for high efficiency photoexcitation and light collection, while a dual band modulation realized distance control. Real time detection of the oscillations of the probe tips using different frequencies independently controls the distance between the probe tip and the sample surface as well as the distance between the two probes. Thus, the collection probe can be scanned around an illumination probe without destroying the probe tips. To demonstrate our SNOM, we performed photoluminescence spectroscopy under the dual-probe configuration and observed carrier motions in an InGaN quantum well.

Wide-bandgap semiconductor materials: For their full bloom

“…They showed that (i) in the violet-emitting quantum well (QW), shallow localized states enhance carrier diffusion and photoluminescence (PL) intensity mapping is well correlated with threading dislocation (TD) distribution [Fig. 3 Later they developed a dual-probe SNOM, 64) and visualized the more detailed processes of carrier motion in space. 65) Photodynamics research on such ultrasmall regions will greatly contribute to improving the efficiency of LEDs and LDs in the future.…”

Multimode scanning near-field photoluminescence spectroscopy and its application for studies of InGaN epitaxial layers and quantum wells

“…Compared to the mentioned techniques, SNOM stands out because it allows a small excitation spot far beyond the diffraction limit. A twoprobe experiment, in which one stationary fibre probe is used for an optical carrier injection and another one scans the sample collecting PL emitted by the diffused carriers, is the most straightforward approach [9]. However, for small, sub-µm diffusion lengths, this technique becomes very complicated because of the mechanical difficulties in positioning the probes close to each other and the near-field interaction between them.…”

“…In most cases, a single probe is used. Dual probe technique has been developed and applied for studies of ambipolar carrier diffusion [9]; however, for ternary nitrides, in which diffusion lengths are of the order of 100 nm, such experiments are complicated due to mechanical difficulties and the near-field crosstalk between the closely located probes. As will be shown below, the transport parameters can be assessed from single probe measurements as well.…”

Determination of critical diameters for intrinsic carrier diffusion-length of GaN nanorods with cryo-scanning near-field optical microscopy

“…Reports using SNOM to detect thin films or single quantum wells 17 18 for the distribution of carrier densities can be found. Carrier/exciton diffusion with different crystalline planes and different modes of SNOM operations with single/dual probe-setups has been investigated in the room temperature 19 .…”