Wojciech Macherzynski

Mode-locking in Er-doped fiber laser based on mechanically exfoliated Sb 2 Te 3 saturable absorber

We demonstrate the usage of a new saturable absorber material – antimony telluride (Sb2Te3) for efficient mode-locking of an Erbium-doped fiber laser. The Sb2Te3 layers were obtained by mechanical exfoliation and transferred onto the fiber connector tip. The all-fiber laser was capable of generating optical solitons with the full width at half maximum of 1.8 nm centered at 1558.6 nm, with 4.75 MHz repetition rate. The pulse energy of the generated 1.8 ps pulses was at the level of 105 pJ.

Black phosphorus saturable absorber for ultrashort pulse generation

Low-dimensional materials, due to their unique and versatile properties, are very interesting for numerous applications in electronics and optoelectronics. Recently rediscovered black phosphorus, with a graphite-like layered structure, can be effectively exfoliated up to the single atomic layer called phosphorene. Contrary to graphene, it possesses a direct band gap controllable by the number of stacked atomic layers. For those reasons, black phosphorus is now intensively investigated and can complement or replace graphene in various photonics and electronics applications. Here, we demonstrate that black phosphorus can serve as a broadband saturable absorber and can be used for ultrashort optical pulse generation. The mechanically exfoliated ∼300 nm thick layers of black phosphorus were transferred onto the fiber core, and under pulsed excitation at 1560 nm wavelength, its transmission increases by 4.6%. We have demonstrated that the saturable absorption of black phosphorus is polarization sensitive. The fabricated device was used to mode-lock an Er-doped fiber laser. The generated optical solitons with the 10.2 nm bandwidth and 272 fs duration were centered at 1550 nm. The obtained results unambiguously show that black phosphorus can be effectively used for ultrashort pulse generation with performances similar or even better than currently used graphene or carbon nanotubes. This application of black phosphorus proves its great potential to future practical use in photonics.

Harmonically mode-locked Er-doped fiber laser based on a Sb2Te3 topological insulator saturable absorber

In this letter we present for the first time, to the best of our knowledge, a harmonically mode-locked Er-doped fiber laser with antimony telluride (Sb2Te3) topological insulator material used as a saturable absorber (SA). The SA was prepared via mechanical exfoliation of the bulk material. The 80 nm thick Sb2Te3 layers transferred onto fiber ferrule entirely cover the fiber core. The Er-doped fiber mode-locked laser based on such SA generated optical pulses was centered at 1558 nm with 1.9 ps duration and a fundamental repetition rate of 3.75 MHz. Increasing the pump power results in stable harmonic mode-locked operation up to the 81st harmonic at 304 MHz repetition frequency. The laser was capable of generating optical solitons with 2.2 ps duration. The number of generated harmonics could be tuned only by changing the pump power injected into the laser cavity.

Fabrication of ohmic contact based on platinum to p-type compositionally graded AlGaAs layers

Novel metallization scheme was proposed for ohmic contact formation to compositionally graded p-type AlGaAs. A metal multilayers of Ti/Pt/Au, Pt/Ti/Pt/Au and Pt/Ti/Ni/Au were deposited by thermal evaporation using electron gun and resistance heater. The contacts were sequentially annealed by rapid thermall annealing system in N2 atmosphere at various temperatures (in the range from 350°C to 550°C). The duration of annealing step was 2 minutes. The as-deposited Pt/Ti/Pt/Au and Pt/Ti/Ni/Au multilayer metallizations had resistivities of 1.4·10-5 Ω·cm2 which have been gradually deteriorated after each subsequent annealing. The current-voltage characteristics of the ohmic contacts to compositionally graded p-type AlGaAs epitaxial layers were studied and discussed.

Thermal joints based on sintered silver micro- and nano- sized particles

Downsizing and increase of working speed of the electronic circuits bring out generating of large amount of heat during operating. The thermal interface materials (TIMs) are one of the best choice to increase the efficiency of heat transfer from the heat source to the heat spreader. Moreover, micro- and nano-sized metallic compounds of thermal interface materials which aim is to increase the thermal conductivity combined with low temperature sintering process allows to create highly conductive (both, thermal and electrical), reliable mechanical joints. Within the paper the results of developing the thermal interface materials will be presented. The thermal resistance, electric parameters and mechanical strength measuring methods, the same as the structures analysis methods will be shown.

Ruthenium based Schottky contacts on n-type GaN

The paper presents the investigation of ruthenium based Schottky contact to n-GaN:Si layers with different Si concentration grown by metalorganic vapour phase epitaxy (MOVPE) technique. Metallizations of ruthenium/gold were evaporated by an electron gun (Ru) and resistance heater (Au). The contacts were sequentially annealed at rapid thermal annealing (RTA) system under nitrogen ambient at various temperatures from 200degC to 650degC. The time of annealing process was 2 minutes. The barrier height of ruthenium based Schottky contacts to n-GaN MOVPE epitaxial layers were studied in a function of annealing temperature by current-voltage (I-V) method on dedicated test structures. The barrier heights of as-deposited Au/Ru/n-GaN Schottky contacts were evaluated and found to be 0.61 eV (n_d=9.9times10¹⁶ cm³) and 0.19 eV (n_d=8times10¹⁷ cm^-3). It was established that the temperature of 500degC was the most suitable for obtaining the highest values of Schottky barrier height (SBH) like 1.1 eV (n_d=9.9times10¹⁶ cm^-3) and 0.51 eV (n_d=8times10¹⁷ cm^-3) of Schottky contact based on ruthenium.

Functionally Graded Structures of AIII-BV(N) Materials for Detectors

Functionally graded materials are widely applied for mechanical applications. Nowadays they become more and more attractive for electronic and optoelectronic devices fabrication. This is caused by their unique properties. FGM are potential candidates for high sensitive photonic devices which could operate in a wide spectral range (also for voltage tunable photodetectors). In this paper the analysis of several photodetectors constructions fabricated in FGM were presented. The influence of AIII-BV (N) grading layers composition and configuration of the detector on its optical and electrical properties was discussed. Also the comparison between conventional non-graded and graded devices was shown. All simulations presented in the work were performed by the specialized software designed for modeling of AIII-BV (N) graded structures. The software allows us to calculate both the parameters of FMG structure and device characteristics

Fabrication of Si3N4 Layers by Pulse Magnetron Sputtering Method

Amorphous silicon nitride thin layers are the most widely applied dielectric layers in modern semiconductor devices. It is caused by their excellent properties such as high chemical inertness, high thermal stability and corrosion resistance. Si3N4 also has remarkable mechanical, optical and dielectric properties. Silicon nitride thin layer can be fabricated by low-pressure chemical vapour deposition (LPCVD), plasma enhanced chemical vapour deposition (PECVD), reactive evaporation and ion beam deposition. More recently reactive sputtering techniques were proposed for Si3N4 fabrication. We have applied the pulsed reactive magnetron sputtering of a Si target in nitrogen atmosphere for preparation of Si3N 4 layers. Parameters of the deposition process were examined. Their influence on layer properties was studied and discussed

Study of interface of ohmic contacts to AlGaN/GaN heterostructure

The paper embraces studies of the interface of ohmic contacts and AIIIBV-N heterostructure. The TiAl based metallization stack was investigated. The Ti/Al/Ni/Au contact to AlGaN/GaN heterostructures fabricated by metal-organic vapour phase epitaxy was examined using three methods i.e. etching of annealed contact metallization, fractures (prepared at room temperature and after a bath in liquid nitrogen) and microsections imaging. The main focus was on the estimation of reaction range on the metal-semiconductor interface of samples. In the first method, the surface of AlGaN/GaN heterostructure after etching of metallization was studied by an optical microscope, scanning electron microscope and atomic force microscope. The changes of surface morphology of heterostructure directly reflect solid state reactions range between metallization and semiconductor. The range of reactions was also observed using the small-angle microsections method while the fractures analysis did not bring valuable information.

Hydrogen permeation properties of Pd-coated Pd33Ni52Si15 amorphous alloy membrane

Abstract The vast majority of experimental techniques used for the measurements of hydrogen permeability through metallic membranes whose one or both surfaces are covered with a thin Pd film is based on the assumption that a ratio of film-to-membrane thickness is small enough to cause hydrogen flow to be independent of the Pd film thickness. In an attempt to verify this assumption, we have measured the hydrogen flow through the Pd33Ni52Si15 amorphous membrane covered with Pd film of 10, 20, and 30 nm in thickness. Contrary to our expectations, we have found a dramatic decrease in hydrogen flow with the increase in Pd film thickness. Our findings are discussed in terms of potential barrier between the two different phases.