Pulsed modification of germanium films on silicon, sapphire, and quartz substrates: Structure and optical properties

Abstract

The structural and optical properties of thin Ge films deposited onto semiconducting and insulat ing substrates and modified by pulsed laser radiation are studied. The films are deposited by the sputtering of a Ge target with a low energy Xe + ion beam. Crystallization of the films is conducted by their exposure to nanosecond ruby laser radiation pulses (λ = 0.694 μm) with the energy density W = 0.2-1.4 J cm -2 . During pulsed laser treatment, the irradiated area is probed with quasi cw (quasi continuous wave) laser radiation (λ = 0.532 and 1.064 μm), with the reflectance recorded R(t). Experimental data on the lifetime of the Ge melt are compared with the results of calculation, and good agreement between them is demonstrated. Through the use of a number of techniques, the dependences of the composition of the films, their crystal structure, the level of strains, and the reflectance and transmittance on the conditions of deposition and annealing are established.

Experimental Study and Simulation of the Structure-Phase Transitions in Deposited Ge Layers during Pulsed Laser Annealing

“…Instead, the results of calculations depend highly on the heat conductivity coefficients for film and substrates. According to [8] in present calculations K = 0.02 W/cm K for amorphous Ge that is significantly lower than for liquid (K = 0.3 W/cm K) and for crystalline (K(T) = 180/T W/cm K).…”

“…It is also assumed that the melting and crystallization from the overcooled melt take place at the melting temperature of a-Ge (T m = 965 K) lower than the equilibrium melting point of the crystal Ge (T m = 1210 K). The characteristic feature compared to earlier performed calculations [8] is the reduction of the heat conductivity at the film/substrate interface after complete melting of the film. This reduction is connected with poor thermal contact due to low wetting of the melt and substrate.…”

“…Where W -pulse energy density, τ -pulse duration at half maximum (FWHM). The equation was solved by finite difference method taking into account the temperature dependences of optical and thermophysical parameters of the film and substrates [7,8] as well as phase transition energies of amorphous-melt-crystal states. The reflection coefficient values for solid and liquid Ge phases (R = 0.45 and 0.7, respectively) were obtained from the experiment at the wavelength of ruby laser radiation (λ = 0.69 µm).…”

Structural and magnetic studies of thin Fe57 films formed by ion beam assisted deposition

“…It is possible to produce films and coatings with a wide range of structural characteristics, different phase structures and physical and performance properties by varying such parameters as the deposition rate, substrate temperature, composition of the reaction gas, composition of the sputtering target, etc. Earlier we used these techniques to synthesize and modify diamond-like carbon films [4,5], to form silver nanoparticles in the silica glass matrix [6,7], to prepare nanocomposite films of barium titanatebased multiferroics with magnetic cobalt nanoparticles [8], to fabricate thin germanium layers on silicon [9,10] and nanostructured ZnO and Al 2 O 3 films [11]. The characteristic feature of abovelisted single-elemental or composite films and layers is the nanocrystalline structure (when the dimensions of the crystallites of different phases are in the nanometer range), which determines their optical, magnetic and electro-physical properties.…”