Search

The electronic structures of semimetal‐semiconductor (Sb2)m/(GaSb)n (111) and (Sb2)m/(AlSb)n (111) (m,n≤10) superlattices are calculated by using a tight‐binding theory including spin‐orbit interaction. It is found that a narrow gap forms in these materials due to the quantum confinement effect. This may allow strong optical nonlinearity in the infrared region. With increasing the thickness of the Sb layer, a possible semiconductor‐semimetal transition is suggested at a certain thickness. The influence of interface states on the formation of the band gap is investigated by adjusting the interface relaxation and band offsets. Our study shows that semimetal‐semiconductor Sb/Ga(Al)Sb superlattices could potentially open a new possibility in electro‐optical device manufactures.

The effect of disorder on the optical absorption of the realistic random superlattice has been investigated based on a three‐dimensional tight‐binding Hamiltonian. It is found that the absorption intensity close to the band edge of the random superlattice is considerably enhanced, which can be explained by optical matrix elements of the relevant eigenfunctions localized strongly over 2–4 monolayers. An energy‐level crossing behavior at the conduction‐band bottom is also obtained.

The electronic structure of a realistic three‐dimensional periodic random superlattice (SL) [(GaAs)m/(AlAs)n]l are calculated for the first time using the large‐cluster recursion method within the tight‐binding framework. It is found that the localized valance band‐tail states of the random SL, which are almost independent of the AlAs concentration, extend to the band‐gap region of the corresponding ordered SL. The central peaks in the Al s and Ga s states which vary with the Al concentration are studied, and comparison with the alloy AlxGa1−xAs is made. Our results provide a guide to the band‐gap engineering of the random superlattices.

The quantum size effect in thin antimony films grown along (111) direction on a GaSb substrate is studied based on a simple model. The critical film thickness, at which the semimetal‐semiconductor transition takes place, is determined. It is proposed that the optical experiments can be used to measure the critical thickness since the dependence of optical transition on thickness in the semimetal region is very different from that in semiconductor region.

In this paper, the thermal stability of TiN metal gate with various composition prepared by different preparation technology [(e.g., atomic layer deposition (ALD) or physical vapor deposition (PVD)] on HfO2 high-K dielectric is investigated and compared by physical and electrical analysis. After annealing of the TiN/HfO2 stack at 1000 °C for 30 s, it is observed that: (1) Nitrogen tends to out-diffuse from TiN for all the samples; (2) Oxygen from the interfacial layer (IL) between HfO2 and Si tends to diffuse toward TiN. PVD Ti-rich TiN shows a wider oxygen distribution in the gate stack, and a thinner IL than the N-rich sample. Ti penetration into HfO2 is also observed in the Ti-rich sample, which can potentially lead to the dielectric break-down. Besides, the oxygen out-diffusion can be significantly suppressed for ALD TiN compared to the PVD TiN samples.