Pulsed Laser Doping Research Articles

Enhanced performance in perovskites films by defect engineering and charge carrier transportation via pulsed laser doping of 2D MoS2

High-performance perovskite-based optoelectronic devices require low defect density and efficient charge carrier extraction. In this paper, pulsed laser annealing was combined with two-dimensional MoS2 doping to develop an efficient strategy for the extraction of charge carriers from perovskite films with low defect density. In pulse laser annealing of perovskite films with 2D MoS2 dopant, due to their localized temperature gradients caused by fast laser annealing, the grains are much larger, and the film quality is much better than that of traditional thermal annealing perovskite films. As a result, the films absorb light better. After doping of 2D MoS2, the carrier transport in perovskite films can be increased significantly by passivating Pb-related defects through PbS coordination bonds. Additionally, the shift of the conduction band minimum (CBM) from the perovskite layer to the Au layer provides a well-matched alignment in energy levels between the perovskite and Au layers, which encourages charge carrier extraction. Moreover, the interfacial perovskite lattice moves freely during the annealing and chilling processes due to laser-induced thermomechanical momentum and weak interactions between 2D MoS2 and, thereby reducing the tensile strain in perovskite films. In addition, by improving surface hydrophobicity and relieving residual stresses, perovskite films are more humidity and thermal stable.

Laser-based ion doping is a suitable alternative to dope biologically active ions into colloidal bioglass nanoparticles

We show that pulsed laser doping is a promising technique to dope multiple ions in nBGs without negatively impacting their structure or size and that laser doping of FeSr into nBGs can improve the angiogenic properties of nBGs.

Исследование механизма фото-активированного выделения водорода на кремниевом фотокатоде с тонкопленочным катализатором a-MoSx

Silicon cathodes for the efficient production of hydrogen in the photoelectrochemical process of water splitting have been created and studied. A photoactive layer on p-Si wafer was obtained by pulsed laser doping of the wafer with phosphorus from a solution of orthophosphoric acid. A film of amorphous molybdenum sulfide (a-MoSx) up to 4 nm thick was deposited on the surface of the modified n+p-Si wafer. This caused a significant increase in photocurrents in the acid solution as compared to the bare n+p-Si. The composition of the catalytic film was modified during the photoelectrochemical process of hydrogen evolution. The study of the energy bands at the interface of the a-MoSx heterojunction with the n+-Si layer showed that the reaction of hydrogen evolution proceeded, probably, because of electron tunneling through the a-MoSx film. Using the density functional theory, a thermodynamic analysis of the possible effect of chemical changes on the silicon surface and in the a-MoSx film itself on the efficiency of hydrogen catalysis was carried out.

Imaging and quantifying carrier collection in silicon solar cells: A submicron study using electron beam induced current

In this work electron-beam-induced current (EBIC) is used to study the collection efficiency of emitters in industrial silicon solar cells. Laser-doped local emitters have been deployed industrially, yet in mas production they are designed wider than the screen-printed silver fingers to allow alignment tolerances. EBIC has allowed to image and quantify the laser-induced damage that occurs in these local emitter regions. A model is developed to account for such damage, so that losses in EQE could be quantified from the observed EBIC collection characteristics. The damaged regions present ~12% lower collection efficiency at short wavelength (300–500 nm) than the homogenous emitter. Sentaurus TCAD simulations reveal that eliminating such damage would improve cell efficiency by ~0.12%. Additional degradation is found in a region 1–2 µm wide adjacent to the silver fingers, which has not been detected before. It is also found that pulsed laser doping leads to ~15 µm long un-doped gaps, along the direction of laser movement. As laser doping becomes a key part of industrial cell fabrication, it is crucial to develop a better understanding of the potential pitfalls, and future improvements to the process. The versatility of EBIC imaging is also demonstrated using FIB milling to improve lateral resolution and study the depth profile of boron emitters in newly developed industrial i-TOPCon cells. EBIC imaging, in combination with advanced device simulations, have proven powerful tools to elucidate carrier collection characteristics and drawbacks, thus helping to understand and improve fabrication processes at industrial level.

Influence of precursor layer ablation on laser doping of silicon

AbstractThis paper presents a numerical model, which quantitatively demonstrates that ablation and partial recondensation of the dopant precursor layer are some of the dominating physical processes in laser doping (LD) of crystalline silicon. Our pulsed LD process uses a line focused laser beam, enabling the creation of solar cell emitters without the generation of dislocations, if the width w of the short axis of the line focus is w < 10 μm. The concentration profiles of the dopant atoms strongly depend on the pulse energy density Ep, the pulse to pulse separation Δx and the number of laser scans Ns. By comparing measured with modeled concentration profiles, we are able to evaluate the ablation width as well as the amount of the ablated precursor layer. In case of a sputtered phosphorus precursor layer, the ablation width wa is wa = 6 μm, whereas the width of the molten silicon layer wm is wm = 5 μm. The model also explains the dependence of experimental dopant concentration profiles on the number of subsequent laser scans Ns and pulse to pulse separation Δx. Copyright © 2010 John Wiley & Sons, Ltd.

Reducing the effective barrier height of a PtSi Schottky diode by a p+ doping spike using pulsed laser doping

The structure of PtSi/p+/p-Si fabricated by chemical vapour doping has been investigated for reduction of the Schottky barrier height. The interface structure and photoelectric properties of PtSi/p+/p-Si thin film structure have been studied. The results from AES profile analysis show that doped boron moves with the PtSi/Si interface during silicide growth. Concomitantly, the boron at the PtSi/Si interface out-diffuses to the Pt–PtSi interface. Finally, the boron piles up at the surface. It has been considered that the redistribution of the dopant boron is due to the solubility of the dopant in the silicide. The Schottky barrier height of PtSi/p+/p-Si is 0.13 eV (for cutoff wavelength 9.5 µm). That is lower than the 0.19 eV value of PtSi/p-Si (for cutoff wavelength 6.5 µm). Since the Schottky barrier height is lowered, the cutoff wavelength can be extended. Due to the Fowler dependence, the detector's quantum efficiency can be improved.

Formation of an ohmic electrode in SiC using a pulsed laser irradiation method

We have succeeded in the formation of a Ni electrode on n-type silicon carbide (6HSiC) at room temperature using the pulsed laser doping (PLD) method. Characteristics of the PLD method for the formation of an ohmic electrode in SiC are shown to be as follows; (1) The formation of an ohmic electrode in SiC at room temperature was achieved. (2) Metal dopants are doped to a depth of about 150 nm from the surface. (3) The interface between the laser doped region and the SiC substrate was found to be an abrupt junction. Furthermore, we have attempted to form the ohmic contact by metal atoms doping with laser irradiation into a bulk SiC through a mask during thermal evaporation of the metal. This technique is successful for the formation of dot electrodes 0.8 mm in diameter on the SiC substrate.

Ultra-shallow p+-junction formation in silicon by excimer laser doping: a heat and mass transfer perspective

Heat and mass transfer at the nanosecond time scale and the nanometer length scale in pulsed laser fabrication of ultra-shallow p +-junctions is studied in this work. A new technique is developed to fabricate the ultra-shallow p +-junctions with pulsed laser doping of crystalline silicon with a solid spin-on-glass (SOG) dopant, through the nanosecond pulsed laser heating, melting, and boron mass diffusion in the 100 nm thin silicon layer close to the surface. High boron concentration of 10 20 atoms cc −1 and the ‘box-like’ junction profile are achieved. The key mechanism determining the ‘box-like’ junction shape is found to be the melt-solid interface limited diffusion. The ultra-shallow p +-junctions with the depth from 30 to 400 nm are successfully made by the excimer laser. The optimal laser fluence condition for SOG doping is found about 0.6–0.8 J cm −2 by studying the ultra-shallow p +-junction boron profiles measured by the secondary ion mass spectroscopy (SIMS) vs the laser fluence and the pulse number. The one-dimensional numerical analysis agrees reasonably with the experiment, within the available physical picture. Possible mechanisms such as boron diffusivity dependence on the dopant concentration in the molten silicon are proposed.

Formation of a p-n junction in silicon carbide by aluminum doping at room temperature using a pulsed laser doping method

A p-n junction has been formed in n-type silicon carbide (6H–SiC) by aluminum (Al) doping at room temperature using a pulsed laser doping method. A 6H–SiC substrate in [H2+(CH3)3Al] atmosphere was irradiated by an KrF excimer laser of 20 ns full width at half-maximum. The depth profile of Al determined by secondary ion mass spectroscopy showed a rectangularlike shape with a maximum concentration of 1×1022 Al/cm3. Furthermore, Al atoms were doped to a depth of about 0.05 μm from the surface. The current–voltage characteristics of the p-n junction clearly showed the rectifying property with low leakage current.

Excimer-laser doping of spin-on dopant in silicon

Solid films containing phosphorus impurities were formed on p-type silicon wafer surface by traditional spin-on of commercially available dopants. The doping process is accomplished by irradiating the sample with a 308 nm XeCl pulsed excimer laser. Shallow junctions with a high concentration of doped impurities were obtained. The measured impurity profile was “box-like”, and is very suitable for use in VLSI devices. The characteristics of the doping profile against laser fluence (energy density) and number of laser pulses were studied. From these results, it is found that the sheet resistance decreases with the laser fluence above a certain threshold, but it saturates as the energy density is further increased. The junction depth increases with the number of pulses and the laser energy density. The results suggest that this simple spin-on dopant pre-deposition technique can be used to obtain a well controlled doping profile similar to the technique using chemical vapor in pulsed laser doping process.

Laser doping of silicon role of the surface status in the incorporation mechanism

Abstract Pulsed laser doping of silicon has been investigated in order to evaluate the role of the surface status on the dopant incorporation rate as well as the influence of the irradiation parameters on the process. A XeCl excimer laser was used to irradiate silicon samples at different dopant PCl 3 vapour pressures, number of pulses per frame, fluence and surface preparation. The results indicate that the incorporation rate is heavily affected by the surface status and suggest that the adsorbed layer which forms on the surface is the most important source of dopant material.