Optical / Devices / Systems Characterization Facility

Extensive material characterization facilities are available to support such operations as Hall measurements, optical reflectance, photoluminescence mapping, x-ray diffractometering, atomic force microscopy, confocal and scanning near-field optical microscopy, as follows:

Optical Materials and Nanostructure Characterizations

The laboratory consists of numerous equipment for enabling characterizations of optical materials, semiconductor materials, and nanostructures. Several key analysis enabled within this laboratory include: plasmonic characterizations, terahertz optical material spectroscopy, nonlinear optical materials, and low temperature analysis of laser diodes for mid up to terahertz spectral range. The development of sensors, emitters, and detectors based on nanostructures and metamaterials have resulted in cutting edge technological advances in the field.

Prof. Rotkin and the group of 13 other faculty across different Science and Engineering disciplines acquired a new shared facility: Witec alpha300RA, combined confocal Raman and Fluorescence Zeiss microscope setup with in situ Scanning Probe microscope. Customized configuration allows hyper‐spectral imaging of submicrometer features in nanomaterials and nanofabricated samples in visible and/or near‐IR spectral range – that is, to perform “multi-color” Raman, or photoluminescence (PL) mapping of the samples, revealing chemical content and electronic properties at the single pixel level (down to the focal spot size). Using a scanning probe, AFM image can be superimposed on the hyper-spectral map.

Condensed-Matter Spectroscopy

The Condensed Matter Spectroscopy Laboratory focuses on the laboratory for understanding the role of defects and impurities in semiconductors and semiconductor oxides. The laboratory is a fully equipped facility for making highly sensitive, polarized, infrared absorption measurements of solid-state materials at low temperature. This lab includes a Bomem DA3.16 Fourier Transform Spectrometer that is outfitted with several InSb and MCT detectors for the range 550 to 8500 cm-1; a custom, liquid-He-cooled, Si bolometer with a cooled filter wheel for the range 200 to 2000 cm-1; and a Si bolometer for the range 10 to 370 cm-1 to provide outstanding sensitivity from the far-IR to near-IR. A vacuum interface has been constructed so that an Oxford Instruments CF1204 cryostat can be introduced into the evacuated sample compartment of the Bomem spectrometer. Several continuous-flow, cold-finger cryostats are also available. Absorption measurements can be made from liquid He to room temperature.

While the primary focus of this laboratory has been on impurity vibrations, the broad frequency range of our instrumentation permits far IR studies of the electronic absorption of shallow donor and acceptor impurities and well as the ability to measure accurate free-carrier-absorption spectra providing a contact-free method to measure the conductivity of samples.

Optical Laser Spectroscopy

The laboratory provides various laser sources and optical characterization systems dedicated to spectroscopy and imaging using time- and frequency-resolved laser-based techniques. Available pulsed laser sources range in pulse length from 100 fs to 1 ps and in repetition rate from 80 MHz to 1 kHz, and several continuous wave lasers are also available. In particular, our 1 ps laser source at a repetition rate of 1 kHz can be wavelength-tuned from ~300 nm in the UV to 3 micrometers in the infrared and can also provide pulses in the far infrared up to a 20 micrometers wavelength. Various laser systems are used for pump & probe and four-wave mixing experiments, for studying nonlinear optical effects in fibers, for imaging, and for the investigation of photoluminescence transients on the sub-nanosecond time-scale. The laboratory has a scanning near-field optical microscope with the possibility of providing localized excitation also at UV wavelengths, and a flexible Olympus microscope with several input and output ports that can be used for laser-based nonlinear optical and multiphoton microscopy, optical tweezing, and luminescence or Raman spectroscopy.

In addition, this lab contains a tunable laser sources providing 20 ps duration laser pulses at a repetition rate of 10 Hz for enabling nanoseconds carrier dynamics analysis. The wavelength of this pulsed source can be tuned over the visible and near infrared spectral range. It is used for transient grating pump and probe experiments over a time scale of up to 10 ns after excitation, and for the investigation of photoluminescence dynamics on time scales from 10 ns to 100 ms. The transient grating experiments use a flexible degenerate four-wave mixing setup with the possibility of delaying one optical pulse by up to 10 ns.

Semiconductor Material Characterizations

Philips PLM-100 Photoluminescence mapper

The PLM-100 is a versatile screening tool, producing high resolution maps of compound semiconductor epitaxial wafters that make variations in layer composition, quality or thinkness available. It provides the PI and their group with reliable feedback needed to optimize the growth processes. It also give valuable information on a wafer's projected device yield. Screening wafers helps to ensure a supply of high quality and high uniformity epilayers required in efficient processing.

Bede Scientific QC2a X-Ray Diffractometer

The QC2a has five motorized axes on the sample stage and extended angular range, allowing access to asymmetrical reflections for the measurement of relaxed systems and samples with highly misoriented substrates. The QC2a uses double crystal X-ray diffraction to remove the divergence characteristics of the X-ray beam from a 60W air-cooled X-ray source. Reference crystals are mounted in interchangeable, pre-aligned beam conditioner blocks, which are selected to mathc the substrate material of the specimen being analyzed. The instrument can perform high-resolution X-ray diffraction on a variety of compound semiconductor materials.

Bio-Rad HL 5200 Hall Measurement System

BioRad HL 5200 Hall Measurement System: The HL 5200 provides for the measurement of net carrier concentration and carrier mobilitiy via the Van der Pauq Hall analysis. The HL 5200 is fully computer controlled and is equpped with software to verify contact ohmicity over the measurement current range and to calculate van der Pauw statistics for the measurement. This system can be used on a variety of semiconductor materials.

Confocal Luminescence Microscope

The confocal luminescence microscope is a specially developed in-house system capable of conducting the optical luminescence measurement from low temperatures (T=~10K) up to room temperature. It is a completely fiber-based set up. The output and the input of single mode fibers replace the usually required pinholes, and allow a light, compact design of the instrument. For this reason, the whole microscope can operate accurately without sacrificing speed.While most commercial instruments record only the emission intensity, the in-house system is capable of acquiring a whole spectrum for each spacial position.

WiTec AlphaSNOM Scanning Near-field Optical Microscope

The design of the Alpha-SNOM features a Confocal Microscope (CM), a Scanning Near-Field Optical Microscope (SNOM) and an Atomic Force Microscope (AFM) in a single instrument. SNOM allows optical microscopy with highest spatial resolution beyond the diffraction limit. The AlphaSNOM uses an extremely precise capacitively-controlled piezo platform to scan the sample in three dimensions. The stage is used not only in SNOM and AFM, but also in Confocal mode. As a result, it is possible to analyze the same sample area with different techniques and combine the benefits of all three modes.

Semiconductor Device Characterizations

Semiconductor Optoelectronics Characterizations

Lehigh laser diode testing facility allows measurements of DC and AC characteristics of laser devices and LEDs. The facilities here allow measurements of the pulsed laser P-I, continuous-wave laser P-I, device I-V characteristics, absorption loss measurements, optical gain and alpha-parameters measurements, and high-speed measurements. Complete photodetector characterization can also be conducted at Lehigh. A new Keithley 2520 pulsed laser diode set up and Labsphere integrating sphere (with Ge and strained Si detectors) also allow accurate pulsed laser / LEDs testing (with temperature range from 5 oC up to 100 oC) from wavelengths of 200nm to 1800nm. This testing facility allows measurements of basic characteristics of optoelectronics devices, as well as extractions of physical parameters essential for further understanding and optimization of devices.

New testing set up for solar cells is also available. The new solar cell measurement set up allows measurements of open voltage and short-circuit current, and efficiency of solar cells fabricated. The solar cell measurement set up include I-V testing equiptment (Agilent U2722A), solar simulator (ABET 150 Watt Xenon Arc Lamp with AM 1.5G Filter), and reference cell. The thermoelectric test measurement allows simultaneous measurements of electrical conductivity, thermal conductivity, and Seebeck coefficients. The measurement of thermal conductivity of material is conducted by using 3- method.

Solar Cell Quantum Efficiency Measurement System (QE-PV SI)

The new equipment is a light measurement system with free-space design made purposely for solar cell measurement. The system is capable of measuring the spectral response, internal quantum efficiency of a solar cell as a function of wavelength.

Fluorescence Spectrometer (F-2700)

The F-2700 set up is available for carrying out the measurements of the emission spectrum and excitation of phosphor used in white LEDs devices. The wavelength of the measurements can be tuned from UV to infrared (200-800 nm), and this set up is also available for measurements of photoluminescence of visible active materials for light-emitting diodes.

MEMS and High Speed Semiconductor Characterizations

The MEMS laboratory consists of numerous RF and bio MEMS characterization set up, which is built for addressing research on sensors and transducers with a focus on biomedical, biometric, communications, and other applications. In addition, numerous facilities for characterizing high speed devices and microwave integrated circuits are available. The laboratory is also equipped for characterizing microwave and RF photonics and electronics. The facility for characterizing high speed optoelectronics devices including quantum dots and quantum dash lasers is also available.

Biophotonics and Bioelectronics Laboratory

The biophotonics laboratory is interested in developing novel optical imaging technologies for biomedical applications, especially in developing optical coherence tomography (OCT) and microscopy (OCM) technologies to perform “optical biopsy” and generate 3D in situ images of tissue morphology, function and pathological status in real-time without the need to remove and process specimens. The laboratory is also interested in applying these technologies to a variety of biological and clinical applications, including cancer research, neuroscience, developmental biology and tissue engineering.

In the area of bioelectronics, the laboratory is focused at the intersection of microtechnology/nanotechnology and neuroscience. We combine living neural tissues with microchannels and electrodes to create hybrid systems (brain-on-a-chip). Current projects focus on analysis of biological neural circuit function and formation, development of a high-throughput system for antiepileptic drug discovery, and assessment of the complex role of growth factor receptors in epilepsy. The integration of micro and nanoelectronics for understanding and advancing the biology and health medicine is also pursued.