For semiconductor manufacturing, a mature industry, a number of laser techniques are employed in production. Diodepumped
solid-state (DPSS) lasers are used in applications that cannot be performed by mechanical, chemical, or other
laser fabrication methods as well as where they add value through increased throughput and/or improved process quality.
Applications such as edge isolation, wafer scribing/dicing, via formation, laser doping and annealing for Semicon are
being applied to crystalline silicon PV manufacture as well as research and development for the next generation of high
efficiency cells. Similarly, selective material removal for exposing underlying layers without thermal damage is vital in
the production of thin film PV panels. In this paper, some of the most important applications of lasers along with
experimental results will be reviewed to illustrate how laser methods can have a significant impact on the development
and productivity of the photovoltaic industry.
Lasers are becoming increasingly important in today's LED revolution and are essential for increasing the efficiency and
reducing manufacturing cost of LEDs. Excimer lasers provide unique homogeneous illumination of large areas, and are
ideally suited for laser lift off (LLO) of the LED film from the sapphire substrate used for epitaxial growth. In this paper
we will discuss the excimer laser lift off technique for manufacturing vertical type LEDs, and how it can be applied to
GaN and AlN based LEDs. On the other hand, diode pumped solid state lasers excel in scribing and cutting of a number
of materials relevant to the LED industry: sapphire, silicon, silicon carbide, III-nitrides (gallium nitride and aluminum
nitride), as well as III-V semiconductors (gallium arsenide, gallium phosphide). In this paper we will discuss some of the
recent laser scribing techniques and how adequate selection of laser parameters and beam delivery optics allows for a
high quality high throughput process.
We present degenerate and nondegenerate two-photon absorption spectra in a series of CdSe and CdTe quantum dots. The measurements show that the two-photon absorption (2PA) spectrum is strongly dependent on the quantum dot size and that the 2PA coefficient decreases as the quantum dot size decreases, and it is larger for the frequency nondegenerate process. Previously we had shown a theoretical analysis of these results based on a simple model using the effective mass approximation. Although this model works well for larger quantum dots, it fails for the smaller ones. Here we use the more (formula available in manuscript) model for the band structure and consider the hole band mixing in quantum dots to describe our data. This theory better describes the spectral structures for smaller quantum dots and also predicts the decrease of the 2PA coefficient with the decrease of quantum dot size. This is due to the reduction of the number of possible transitions and the blue shift of the optical bandgap from quantum confinement. This theory predicts the reduction of the 2PA coefficient with size, although our experimental results show an even stronger reduction.
The nonlinear optical performance of several Fluorene-based molecules was studied using different measurement methods and pulse durations. We used picosecond pulses at 532 nm and, femtosecond pulses tunable from 532-810 nm for performing open and closed aperture Z-scans, and we used femtosecond 570-930 nm pulses for two-photon induced fluorescence (2PF) spectroscopy. The observed nonlinear losses were compared using the three methods. The results exhibit much stronger nonlinear absorption with picosecond pulses due to the additional excited-state absorption processes involved. Also the nonlinear refractive index was found to be higher for the picosecond measurements. In addition using a femtosecond white-light continuum (WLC) pump-probe method we showed that by proper tuning of pump and probe wavelengths an intermediate state resonance enhancement (ISRE) of the 2PA can be observed yielding the same overall nonlinear absorption observed using picosecond pulses.
Both degenerate and nondegenerate two-photon absorption (2PA) spectra are studied in two different samples of CdTe quantum-dots in borosilicate glass hosts. One sample (CdTe-600) contains quantum-dots of radius 3.2 ± 0.2 nm and has its absorption edge at 600nm. The other sample (CdTe-750) contains quantum-dots of radius 6.6 ± 0.9 nm and absorption edge at 750nm. CdTe-600 contains quantum-dots with a narrower size distribution than CdTe-750. Consequently, the peaks corresponding to discrete transitions are more clearly visible in CdTe-600 than in CdTe-750. Both nondegenerate and degenerate spectra for these samples show a marked difference from bulk CdTe. In CdTe-750 the two-photon absorption spectrum has a shape similar to that for bulk solids but for CdTe-600 the 2PA spectrum is somewhat different from that expected for the bulk. In the Z-scan measurements we also observed a photo-darkening effect, which is accompanied by an increase in the measured effective 2PA coefficient. All results suggest that 2PA cannot be predicted by the bulk theory especially near to the 2PA edge, that the 2PA in quantum dots is generally smaller than would be expected for the same volume of bulk semiconductor with the same band edge, and that the quantum-dot size and size distribution play important roles in the 2PA spectral behavior and magnitude.