35. Plasma Energetics in Pulsed Laser and Pulsed Electron Deposition

Surface bombardment by energetic particles strongly affects thin-film growth and allows surface processing under non-thermal-equilibrium conditions. Deposition techniques enabling energy control can effectively manipulate the microstructure of the film and tune the resulting mechanical, electrical, and optical properties. At the high power densities used for depositing stoichiometric films in the case of pulsed ablation techniques such as pulsed laser deposition (PLD) and pulsed electron deposition (PED), the initial energetics of the material flux are typically on the order of 100 eV, much higher than the optimal values (≤10  eV) required for high-quality film growth. To overcome this problem and to facilitate particle energy transformation from the original as-ablated value to the optimal value for film growth, one needs to carefully select the ablation conditions, conditions for material flux propagation through a process gas, and location of the growth surface (substrate) within this flux. In this chapter, we discuss the evolution of the material particles energetics during the flux generation and propagation in PLD and PED, and identify critical control parameters that enable optimum thin-film growth. As an example, growth optimization of epitaxial GaN films is provided.

PED is complementary to PLD and exhibits an important ability to ablate materials that are transparent to laser wavelengths typically used in PLD. Some examples include wide-bandgap materials such as SiO₂, Al₂O₃, and MgO. Both PLD and PED can be integrated within a single deposition module. PLD–PED systems enable in situ deposition of a wide range of materials required for exploring the next generation of complex structures that incorporate metals, complex dielectrics, ferroelectrics, semiconductors, and glasses.