Chee-Hong An

Thickness dependence on crystalline structure and interfacial reactions in HfO2 films on InP (001) grown by atomic layer deposition

The crystalline structure and interfacial reactions in HfO2 films grown on InP (001) substrates was investigated as a function of film thickness. High resolution transmission electron microscopy and x-ray diffraction measurements were used to investigate changes in the crystalline structure of the HfO2 films. As the thickness of the HfO2 increased, the crystal structure was transformed from monoclinic to tetragonal, and the interfacial layer between the HfO2 film and the InP substrate disappeared. High resolution x-ray photoelectron spectroscopy was also applied to confirm the existence of an interfacial chemical reaction in HfO2/InP. An interfacial self-cleaning effect occurred during the atomic layer deposition process, resulting in a clear interface with no indication of an interfacial layer between the HfO2 film and the InP surface. Finally, the crystallization process in the HfO2 films was found to be significantly affected by the interfacial energy.

Resistive switching characteristics of solution-deposited Gd, Dy, and Ce-doped ZrO2 films

Several rare earth elements (Gd, Dy, and Ce) having different valence numbers were doped into a solution-synthesized ZrO2 film, and the corresponding resistive memory characteristics were discussed in relation to the oxygen vacancies and film microstructure. Pure and trivalent ion-doped ZrO2 films showed forming-free behavior, probably because of the large amount of inherent and additional dopant-incurred oxygen vacancies, respectively. In contrast, tetravalent Ce ion doping caused the forming process to be required and afforded stable long-term switching characteristics with a relatively large memory window, which is attributed to the dopant-enhanced crystallization/densification effect without excessive oxygen vacancy generation.

The effects of the microstructure of ZnO films on the electrical performance of their thin film transistors

This study examined a fundamental aspect of ZnO-based thin film transistors (TFTs): the connection between the deposition conditions and the microstructure of ZnO films, and the electrical performance of the TFTs. We characterized the microstructure of ZnO films deposited under various rf powers by using high resolution transmission electron microscopy and x-ray diffraction. In further investigating the effects of the microstructure on the device performance, we experimentally demonstrated that the electrical mobility of the devices was coupled to the grain size of the ZnO films in an exponential function.

Change of the trap energy levels of the atomic layer deposited HfLaOx films with different La concentration

Ultrathin HfO2 and HfLaOx films with La/(Hf+La) ratios of 42%, 57%, and 64% were synthesized with an atomic layer deposition process. By measuring the leakage current at different temperatures, the conduction mechanism of HfO2 and HfLaOx films was shown to follow the Poole–Frenkel emission model under a gate injection condition. Based on the temperature and field-dependence measurements, the intrinsic trap energy levels were found to be 1.42, 1.34, 1.03, and 0.98 eV for the HfLaOx samples with La/(Hf+La) ratios of 0%, 42%, 57%, and 64%, respectively, showing a decreasing behavior as the La content increased.

Interfacial reaction of atomic-layer-deposited HfO2 film as a function of the surface state of an n-GaAs (100) substrate

The characteristics of interfacial reactions and the valence band offset of HfO2 films grown on GaAs by atomic layer deposition were investigated by combining high-resolution x-ray photoelectron spectroscopy and high-resolution electron transmission microscopy. The interfacial characteristics are significantly dependent on the surface state of the GaAs substrate. Polycrystalline HfO2 film on a clean GaAs surface was changed to a well-ordered crystalline film as the annealing temperature increased, and a clean interface with no interfacial layer formed at temperatures above 600°C. The valence band offset of the film grown on the oxidized GaAs surface gradually increased with the stoichiometric change in the interfacial layer.

Comparative Study of Atomic-Layer-Deposited Stacked (HfO2/Al2O3) and Nanolaminated (HfAlOx) Dielectrics on In0.53Ga0.47As

The high-k gate dielectric structures in stacked (HfO2/Al2O3) and nanolaminated (HfAlOx) forms with a similar apparent accumulation capacitance were atomic-layer-deposited on n-type In0.53Ga0.47As substrates, and their electrical properties were investigated in comparison with a single-layered HfO2 film. Al-oxide interface passivation in both forms proved to be effective in preventing a significant In incorporation in the high-k film and reducing the interface state density. The measured valence band spectra in combination with the reflection electron energy loss spectra were used to extract the energy band parameters of various dielectric structures on In0.53Ga0.47As. A further decrease in the interface state density was achieved in the stacked structure than in the nanolaminated structure. However, in terms of the other electrical properties, the nanolaminated sample exhibited better characteristics than the stacked sample, with a smaller border trap density and lower leakage current under substrate injection conditions with and without voltage stressing.

Microstructural Evolution and Electrical Characteristics of Co-Germanide Contacts on Ge

The microstructural evolution and corresponding electrical contact properties of Co-germanide systems were investigated. The Co-germanide formation process underwent several intermediate, high-resistive phases (CoGe and Co 5 Ge 7 ), while low-resistive CoGe 2 was formed over 650°C in a narrow process window of < 100°C. Because of the strong Fermi level pinning effect, Co, CoGe, and Co 5 Ge 7 phases exhibited Schottky contact behaviors with similar Schottky barrier heights on n-type Ge and ohmic contact behavior on p-type Ge, respectively. However, for the CoGe 2 /n-type Ge contact formed at 700°C, a nearly ohmic contact behavior started to appear, which was attributed to the possible diffusion of Co atoms into the Ge substrate due to the high-temperature germanidation process.

Changes in the structure of an atomic-layer-deposited HfO2 film on a GaAs (100) substrate as a function of postannealing temperature

The effects of postannealing temperature on the crystal structure and energy band gap (Eg) values of atomic-layer-deposited HfO2 films grown on a GaAs (100) substrate were investigated. In postannealed HfO2 films prepared using a rapid thermal annealing (RTA) process in a N2 ambient at temperatures over 600 °C, the initially produced, partially crystallized HfO2 film changed into a well-ordered crystalline structure with no detectable interfacial layer between the film and the GaAs substrate. In the case of a RTA prepared at 700 °C, the thickness of the film was relatively increased compared to that of an as-grown film. Changes in the depth profile data related to stoichiometry and electronic structure after the annealing treatment indicated that Ga oxide is formed within the HfO2 film during the RTA. The formation of Ga oxide in the film significantly affected the Eg values, i.e., the Eg changed from 5.5 for an as-grown film to 4.7 eV for a film annealed at 700 °C.

Atomic-layer-deposited (HfO2)1−x(Al2O3)x nanolaminate films on InP with different Al2O3 contents

The effect of Al2O3 mixing in HfO2 on the electrical properties was studied on InP substrates using nanolaminate films grown by atomic layer deposition. The In out-diffusion and the subsequent In-related oxide phase generation were effectively suppressed by introducing more Al2O3 to the HfO2 film. Although the decrease in the maximum capacitance was taken into consideration, more Al2O3 introduction significantly improved the dielectric properties. The magnitude of the capacitance–voltage frequency dispersion was decreased with the reduced border trap and interface state densities. Additionally, the leakage current characteristics were improved, including the voltage-stress-dependent reliability.

Characteristics of Ce-Doped ZrO2 Dielectric Films Prepared by a Solution Deposition Process

The microstructural and electrical properties of sol-gel deposited ultrathin Zr 1―x Ce x O 2 films with different Ce contents (x = 0, 0.1, 0.3, and 0.5) were studied using various characterization tools. Ce doping reduced the crystallization (densification) temperature and increased the dielectric constant of the Zr 1―x Ce x O 2 film. There was no degradation of the hysteresis characteristics, and a systematic negative shift in the flatband voltage was observed by incorporating Ce atoms. Leakage current measurements showed no detrimental effects of Ce doping up to x = 0.5, and the conduction mechanism analyses revealed that the Zr 1―x Ce x O 2 films follow a Poole-Frenkel (PF) conduction, exhibiting a systematic increase in the linear slope of the PF plot possibly due to the decrease in dielectric trap sites with increasing Ce content.