In situ comprehensive characterization of optoelectronic nanomaterials for device purposes

Optically and electrically invariant multi-color single InGaN/GaN nanowire light-emitting diodes on a silicon substrate under mechanical compression

Recent years have seen immense advances in electroluminescent InGaN-based light-emitting diodes (LEDs) that may revolutionize lighting and display technologies. Driven by the need for the development of submicrometer-sized, multicolor light sources monolithically integrated on a single chip, it is necessary to accurately characterize the size-dependent electroluminescence (EL) properties of selective-area grown single InGaN-based nanowire (NW) LEDs. Moreover, InGaN-based planar LEDs generally undergo; external mechanical compression induced by the packaging process which could potentially degrade the emission efficiency this further motivates us to investigate the size-dependent EL properties of single InGaN-based NW LEDs on a Si substrate under external mechanical compression. In this work, we perform opto-electro-mechanical characterization of single InGaN/GaN NWs using a scanning electron microscopy (SEM)-based multi-physical characterization technique. We first tested the size-dependent EL properties of selective-area grown single InGaN/GaN NWs on a Si substrate with a high injection current density up to 12.99 kA cm^-2. In addition, the effect of external mechanical compression on the EL properties of the single NWs was investigated. Stable EL properties (no degradation of EL peak intensity and no peak wavelength shift) and electrical characteristics have been observed by applying a 5 μN compressive force to single NWs with different diameters. The results confirm no degradation of the NW light output with the applied stress (up to 62.2 MPa) and demonstrate the superior optical and electrical robustness of single InGaN/GaN NW LEDs under mechanical compression.

In situ fabrication and investigation of nanostructures and nanodevices with a microscope

The widespread availability of nanostructures and nanodevices has placed strict requirements on their comprehensive characterization.

An integrated photoluminescence sensing platform using a single-multi-mode fiber coupler-based probe

We demonstrate an integrated fiber optic photoluminescence sensing platform using a novel single-multi-mode fiber coupler (SMFC)-based probe with high collection efficiency for fluorescence signals. The SMFC, prepared using fused biconical taper technology, not only transmits excitation light, but also collects and transmits fluorescence. The entire system does not use complex optical components and rarely requires optical alignment. The simple structure of the SMFC considerably improves the light transmission efficiency, signal-to-noise ratio, and sensitivity of the system. Theoretical and experimental results show that the proposed probe increases the collection efficiency by more than eight-fold compared with a bifurcated fiber probe. The performance of the proposed probe was experimentally evaluated by measuring the fluorescence spectra of well-known targets and a fresh Tall Fescue leaf.

A hybrid fiber-optic photoluminescence measurement system and its application in InGaN/GaN light emitting diode epi-wafer morphology studies

We report a fiber optic photoluminescence (PL) measurement system using a novel hybrid probe composed of a series of single mode fiber (SMF) and double-clad fiber (DCF) terminated with a coreless silica fiber (CSF) segment and glass micro-lens formed on its cleaved-facet. The fiber probe provided a good guidance and focusing capability for the excitation photon with a focal length of 125 μm and a beam diameter of 13.6 μm. Utilizing a special DCF-to-DCF coupling scheme, the photoluminescence signals were efficiently collected and delivered to a photodetector with a low loss. Utilizing the proposed system, PL morphology was investigated over a 200 × 200 μm(2) area for two types of InGaN/GaN blue light emitting diode (LED) epi-wafers grown on 1) an un-patterned sapphire substrate (UPSS), and 2) a patterned sapphire substrate (PSS). The uniformity in the relative PL intensity and the spectral uniformity in terms of the peak PL wavelength were experimentally compared and analyzed.