4 research outputs found
Comparative Study of Atomic-Layer-Deposited Stacked (HfO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub>) and Nanolaminated (HfAlO<sub><i>x</i></sub>) Dielectrics on In<sub>0.53</sub>Ga<sub>0.47</sub>As
The
high-k gate dielectric structures in stacked (HfO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub>) and nanolaminated (HfAlO<sub><i>x</i></sub>) forms with a similar apparent accumulation capacitance were
atomic-layer-deposited on n-type In<sub>0.53</sub>Ga<sub>0.47</sub>As substrates, and their electrical properties were investigated
in comparison with a single-layered HfO<sub>2</sub> film. Al-oxide
interface passivation in both forms proved to be effective in preventing
a significant In incorporation in the high-<i>k</i> 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 In<sub>0.53</sub>Ga<sub>0.47</sub>As. 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
Tailoring the Interface Quality between HfO<sub>2</sub> and GaAs via <i>in Situ</i> ZnO Passivation Using Atomic Layer Deposition
We investigated ZnO surface passivation
of a GaAs (100) substrate
using an atomic layer deposition (ALD) process to prepare an ultrathin
ZnO layer prior to ALD–HfO<sub>2</sub> gate dielectric deposition.
Significant suppression of both Ga–O bond formation near the
interface and As segregation at the interface was achieved. In addition,
this method effectively suppressed the trapping of carriers in oxide
defects with energies near the valence band edge of GaAs. According
to electrical analyses of the interface state response on p- and n-type
GaAs substrates, the interface states in the bottom half of the GaAs
band gap were largely removed. However, the interface trap response
in the top half of the band gap increased somewhat for the ZnO-passivated
surface
Al<sub>2</sub>O<sub>3</sub> Passivation Effect in HfO<sub>2</sub>·Al<sub>2</sub>O<sub>3</sub> Laminate Structures Grown on InP Substrates
The
passivation effect of an Al<sub>2</sub>O<sub>3</sub> layer on the
electrical properties was investigated in HfO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub> laminate structures grown on indium phosphide
(InP) substrate by atomic-layer deposition. The chemical state obtained
using high-resolution X-ray photoelectron spectroscopy showed that
interfacial reactions were dependent on the presence of the Al<sub>2</sub>O<sub>3</sub> passivation layer and its sequence in the HfO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub> laminate structures. Because
of the interfacial reaction, the Al<sub>2</sub>O<sub>3</sub>/HfO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> structure showed the best electrical
characteristics. The top Al<sub>2</sub>O<sub>3</sub> layer suppressed
the interdiffusion of oxidizing species into the HfO<sub>2</sub> films,
whereas the bottom Al<sub>2</sub>O<sub>3</sub> layer blocked the outdiffusion
of In and P atoms. As a result, the formation of In–O bonds
was more effectively suppressed in the Al<sub>2</sub>O<sub>3</sub>/HfO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub>/InP structure than that
in the HfO<sub>2</sub>-on-InP system. Moreover, conductance data revealed
that the Al<sub>2</sub>O<sub>3</sub> layer on InP reduces the midgap
traps to 2.6 × 10<sup>12</sup> eV<sup>–1</sup> cm<sup>–2</sup> (compared to that of HfO<sub>2</sub>/InP, that is,
5.4 × 10<sup>12</sup> eV<sup>–1</sup> cm<sup>–2</sup>). The suppression of gap states caused by the outdiffusion of In
atoms significantly controls the degradation of capacitors caused
by leakage current through the stacked oxide layers
Structural and Electrical Properties of EOT HfO<sub>2</sub> (<1 nm) Grown on InAs by Atomic Layer Deposition and Its Thermal Stability
We report on changes in the structural,
interfacial, and electrical characteristics of sub-1 nm equivalent
oxide thickness (EOT) HfO<sub>2</sub> grown on InAs by atomic layer
deposition. When the HfO<sub>2</sub> film was deposited on an InAs
substrate at a temperature of 300 °C, the HfO<sub>2</sub> was
in an amorphous phase with an sharp interface, an EOT of 0.9 nm, and
low preexisting interfacial defect states. During post deposition
annealing (PDA) at 600 °C, the HfO<sub>2</sub> was transformed
from an amorphous to a single crystalline orthorhombic phase, which
minimizes the interfacial lattice mismatch below 0.8%. Accordingly,
the HfO<sub>2</sub> dielectric after the PDA had a dielectric constant
of ∼24 because of the permittivity of the well-ordered orthorhombic
HfO<sub>2</sub> structure. Moreover, border traps were reduced by
half than the as-grown sample due to a reduction in bulk defects in
HfO<sub>2</sub> dielectric during the PDA. However, in terms of other
electrical properties, the characteristics of the PDA-treated sample
were degraded compared to the as-grown sample, with EOT values of
1.0 nm and larger interfacial defect states (D<sub>it</sub>) above
1 × 10<sup>14</sup> cm<sup>–2</sup> eV<sup>–1</sup>. X-ray photoelectron spectroscopy data indicated that the diffusion
of In atoms from the InAs substrate into the HfO<sub>2</sub> dielectric
during the PDA at 600 °C resulted in the development of substantial
midgap states