Deep Silicon Amorphization Induced by Femtosecond Laser Pulses up to the Mid‐Infrared

Abstract

Direct laser writing of amorphous lines in crystalline silicon has the potential for becoming a flexible alternative to silicon‐on‐insulator technology for photonic integrated circuits. Yet, the maximum amorphous layer thickness achieved is 60 nm, which is below the requirements for waveguiding at telecom wavelengths. Here, the authors report on different strategies to push the layer thickness beyond today's limit. To this end, irradiation with femtosecond laser pulses covering an extremely broad wavelength range (515 nm–4 µm) up to the yet unexplored near‐ and mid‐infrared region of silicon transparency is investigated. The results show that much thicker amorphous layers can be obtained upon multipulse irradiation at 3‐µm wavelength. The deepest amorphization is achieved in silicon wafers covered with a thick silicon dioxide layer that strongly assists the heat extraction, yielding steep index profiles with a maximum amorphous layer thickness of 128 nm. This superior thickness is compatible with single mode waveguiding for a symmetric waveguide configuration. This study also contributes to a better understanding of the mechanisms involved in laser‐induced amorphization.

Thermodynamical Analysis of the Formation of α-Si Ring Structures on Silicon Surface

“…It is important to note that the amorphization depth found from the graph represented only the lower value of the real depth. For example, the model predicted that the amorphization depth was 23 nm for the fluence J/cm (see the line marked by the ▽ symbol), whereas the experiment showed it to be around 45 nm [ 19 ]. One reason for this discrepancy is the fact that we did not take into account the heat transport after the interaction.…”

“…In addition, laser patterning can generate features with subwavelength resolution, as demonstrated by the production of highly periodic LIPPS with alternating -Si and c -Si regions [ 14 , 15 , 16 , 17 ]. -Si surrounded by c -Si can support waveguiding [ 18 ] and the research on the DLW integration of such devices was carried out in several studies [ 19 ]; however, the successful integration has yet to be demonstrated—the laser-produced -Si layer is too thin and prevents waveguiding for practical wavelengths. Using fluences well over the ablation threshold [ 20 ] or selecting the laser wavelength inside the silicon transparency window [ 19 ] still produces an amorphous layer of tens of nanometers in thickness.…”

Ultrashort‐Pulsed‐Laser Annealing of Amorphous Atomic‐Layer‐Deposited MoS2 Films

“…The use of shorter laser pulses (pico-or femtosecond pulses) is characterized by high cooling rates (up to 10 12 Ks À1 ) [18] and hence, it is often used to disorder crystalline structures. [19,20] Nevertheless, ultrashort-pulsed (usp)-laser-induced crystallization of silicon layers and titanium oxides [21,22] are reported employing a pulse-to-pulse temperature accumulation effect. [23] For amorphous MoS 2 , a first-pulsed-laser-induced crystallization was reported, as a crystalline ring was formed during the processing with nanosecond Bessel beam pulses.…”

Transmission Electron Microscopy Characterizations of Local Amorphization of Single Crystal Silicon by Nanosecond Pulsed Laser Direct Writing

“…Methods for fabrication include chemical vapor deposition, [7][8][9] ion irradiation, [10,11] and laser irradiation. [12,13] Laser direct writing employs a pulsed laser source to modify the structure of Si resulting in the recrystallization or amorphization of c-Si, [14,15] which has attracted great attention from manufacturers and researchers due to its high precision and efficiency. [15] This technique relies on a wide variety of material changes induced by a high-intensity laser focused inside the bulk sample.…”