Micro-Raman spectroscopy and micro-probe photoluminescence

The research aims to study the thermal and electronic properties of MID-IR and THz quantum cascade laser.

Raman and photoluminescence (PL) spectroscopies offer several advantages for microscopic analysis. Since they are scattering techniques, specimens do not need to be fixed or sectioned. Spectra can be collected from a very small volume (down to 1 µm in diameter); these spectra allow the identification of species present in that volume. Thus, Raman and PL spectroscopies are suitable for the microscopic examination of minerals, materials such as semiconductors, polymers and ceramics, cells, proteins and forensic trace evidence. Expanding applications for Raman and photoluminescence microscopy and analysis into low dimensional semiconductors heterostructures and devices requires advanced performances in spectral resolution, laser rejection and sampling capabilities. Our high performance micro-probe laboratory give unique access to devices and measurements not easily achieved on a routine spectroscopic instrument.

In the last eight years we dedicated our activities to the experimental study of important issues for the development of both GaInAs/AlInAs/InP and GaAs/AlGaAs Quantum Cascade Lasers (QCLS).

The QCL is a ground-breaking design based on the engineering of electronic wavefunctions on a nanometre scale. In as far as the macroscopic properties of materials are defined by their electronic structure, the QCL is based an artificial, man-made nano-material. The QCL is a pure product of nano-technology. Added functionalities, over and above the materials natural properties, are created through dimensional control on the nanometer scale. These artificial structures are produced by the epitaxial growth of semiconductors materials. In the QCL this technique is pushed to its limits with typically several hundreds of layers.

The lab instrumentations include a micro-probe Raman and photoluminescence set-up , a Kr-ion laser, a triple/single spectrometer with notch filters, a microscope stage, a piezo-controlled XY table, a He-flow micro-cryostat and three different detector systems: a standard Si-CCD, an intensified Si-CCD for fast photoluminescence (PL) measurements and an InGaAs array for long-wavelength (λ > 1 µm) detection.