Photoluminescene, Electroluminesence and Photoreflectance
Multiple spectroscopic setups are used to characterize the material band structure, absorption characteristics and other optical metrics. Both a free space and mapping photoluminescence (PL) system are available. A Horiba iHR320 and MicOS PL mapping tool can be used for rapid and accurate characterization of photo-emission from layers and devices. Excitation is provided though a 523 nm diode pumped solid state (DPSS) laser. Detectors include a cooled Si CCD and InGaAs liner array, allowing rapid PL characterization from the deep UV to up to 1.6 microns. Wafer mapping gives information on spatial variation in intensity and wavelength across 50-100 mm wafers, essential to minimize variation and achieve consistent growth of both nanostructures and synthesized semiconductor thin films.
A Princeton Instruments SpectraPro monochromator allows for single point PL measurements with free-space optics with vertical sample mounting, enabling photoluminescence measurements from a Cryo Industries He recirculating cryostat (10-500K). The monochromator is fitted with a detector cradle enabling rapid swapping between detector modules, allowing for spectroscopic characterization of emission from UV wavelengths to up 4.5 µm. Excitation is provided by a 532 nm DPSS or a Spectra Physics G41 Ar-ion laser at 514.5nm.
The setup can also be modified for electroluminescence with the addition of an external bias. Both relative and absolute EL can be collected, for extraction of sub-cell Voc in multijunction devices as well as luminescent efficiency. As well, a DC light source is available for photoreflectance measurements (laser modulated reflectance), used to measure bandgap and transition energies in semiconductor thin films and nanostructures.