Raman Spectroscopy
Raman-PL Applications
HORIBA Scientific’s Raman-PL spectrometers are used for wide-ranging evaluations, including compositional analysis of the epitaxial layer of compound semiconductors, defect evaluation of light-emitting materials, evaluation of surfaces, non-destructive evaluation of integrated optical circuits, quantitative analysis of impurities, and evaluation of various laser diodes and LEDs using materials ranging from GaN to InP.
These products are also making a major contribution to the development of ultra-high-speed devices, quantum small-gauge nano-wires, quantum dots, and new materials such as SWCNTs.
Carbon Nanotubes (CNT)
Combined Raman-PL allows fast and easy analysis for probing CNT diameter and chirality, and characterising PL emission out into the near infra-red (1.6 µm and above). Single nanotubes and bundles can be specifically targetted using the high spatial resolution capabilities of the LabRAM Raman-PL systems.
- Raman spectra of the radial breathing and D/G bands using multiple excitation wavelengths ranging from 532 nm through to 1064 nm.
- Raman image of isolated single walled carbon nanotubes (SWCNT).
- NIR photoluminescence spectrum, in the range 1100-1600 nm.
Characterisation of GaN Materials
Gallium Nitride (GaN) is one of a generation of promising light-emitting materials. High quality GaN is relatively difficult to produce, and in particular grown films may contain a large number of extended defects which can strongly perturb the performance of the final device.
Combined Raman-PL analysis allows the numbers and types of defects occuring during film growth to be characterised. Confocal mapping allows defects and discontinuities on a 1 µm scale to be visualised, whilst the high spectral resolution Raman data enables detailed investigations of stresses in the film, crystallographic orientation, and of free carrier concentration. The broader band PL characterization of emission bands, particularly at low temperature, reveals the effect of defects in the material and other such electronic and optical details.
- Combined Raman-PL spectrum of GaN acquired with 325nm laser excitation
Quantum Dots
A quantum dot is a semiconductor material have properties that are between those of bulk semiconductors and those of discrete molecules. They are currently being investigated for a wide range of applications, include for quantum computers, transistors, solar cells, LEDs, diode lasers and medical imaging.
Generally, the smaller the size of the crystal, the larger the band gap, and the higher energy (lower wavelength) the photoluminescence emission. The main advantages in using quantum dots is that because of the high level of control possible over the size of the crystals produced, it is possible to have very precise control over the conductive properties of the material.
In this example, twin quantum dots have been analysed at 4.5K, revealing discrete PL bands above 940 nm. HORIBA Scientific’s combined Raman-PL systems have been used to understand the structure and properties of the twin quantum dots, allowing researchers to move towards the implementation of twin quantum dots as “qubits” for quantum computing.
- PL image of twin quantum dots, emitting in the range 940-970 nm. Analysis was made at 4.5K using 532 nm excitation.
[Data courtesy of Dr Greg Salamo, University of Arkansas, USA]
- LabRAM HR with free space microscope, and liquid helium cryostat.
