Changes in volume in (GST) films due to the density change during phase transformations between amorphous and crystallized states and consequent void formations were examined. Transmission electron microscopy (TEM) was used to measure changes in volume during laser-induced crystallization for both as-deposited and melt-quenched GST amorphous films, and changes in density were estimated. We found the formation of voids and their coalescence during repeated heat cycling by laser. A variation in chemical composition around the voids was confirmed using energy-dispersive spectroscopy analysis. The void formation and compositional changes can lead to degradation of reliability in phase-change random access memory devices.

Thermal stability of ${\text{HfO}}_2$ high-k gate dielectric on GaAs is investigated. Compared to ${\text{HfO}}_2$ gate dielectric, significant improvements in interfacial properties as well as electrical characteristics were found by constructing a ${\text{Al}}_2{\text{O}}_3/{\text{HfO}}_2/{\text{Al}}_2{\text{O}}_3$ dielectric stack. At elevated temperatures, the amorphous ${\text{Al}}_2{\text{O}}_3$ layers were effective in inhibiting crystallization of ${\text{HfO}}_2$ . Since the passivating ${\text{Al}}_2{\text{O}}_3$ layers prevent interfacial oxide and trap charge formation, it aids in reducing the increasing rate of equivalent oxide thickness as well as capacitance-voltage hysteresis. Transmission electron microscopy and x-ray photoelectron spectroscopy data supported the improved electrical characteristic of GaAs metal-oxide-semiconductor capacitors with ${\text{Al}}_2{\text{O}}_3/{\text{HfO}}_2/{\text{Al}}_2{\text{O}}_3$ gate dielectric stack.

Energy band alignment of a nitrided HfO2 film and dependence of the band gap (Eg) on annealing treatments with nitrogen plasma and ambient gases (N2 and O2) were studied by reflection electron energy loss spectra and x-ray photoelectron spectroscopy. We also investigated the nitrogen content in the film and its influence on the band alignment using medium energy ion scattering. The nitrogen incorporated into the HfO2 film by directed nitrogen plasma treatment significantly decreased the band gap and band offsets, i.e., the incorporated N in the film decreased both conduction and valance band offsets. The nitrogen content in depth direction was dependent on the postannealing conditions using O2 or N2.