The electronic structure of tris͑8-hydroxyquinoline͒ aluminum (Alq 3 ) has been studied in the pristine molecular solid state as well as upon interaction ͑doping͒ with potassium and lithium. We discuss the results of a joint theoretical and experimental investigation, based on a combination of x-ray and ultraviolet photoelectron spectroscopies with quantum-chemical calculations at the density functional theory level. Upon doping, each electron transferred from an alkali metal atom is stored on one of the three ligands of the Alq 3 molecule, resulting in a new spectral feature ͑peak͒ in the valence band that evolves uniformly when going from a doping level of one to three metal atoms per Alq 3 molecule.

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We have demonstrated the operation of high on-off current ratio (Ion/Ioff) and low subthreshold slope planar-type InGaAs tunnel field effect transistors (TFETs) with Zn-diffused source junctions. The solid-phase Zn diffusion process has been shown to form defect-less p+/n source junctions with steep profiles because of the inherent nature of Zn diffusion into InGaAs, which has significantly improved the TFET performance. The devices presented in this paper have exhibited a record low subthreshold slope of 64 mV/dec for planar-type III-V TFETs and a large Ion/Ioff ratio of more than 106 at the same time.

The plasma dispersion effect and free-carrier absorption are widely used to change refractive index and absorption coefficient in Si-based optical modulators. However, the weak free-carrier effects in Si cause low modulation efficiency, resulting in large device footprint and power consumption. Here, we theoretically and experimentally investigate the enhancement of the free-carrier effects by strain-induced mass modulation in silicon-germanium (SiGe). The application of compressive strain to SiGe reduces the conductivity effective mass of holes, resulting in the enhanced free-carrier effects. Thus, the strained SiGe-based optical modulator exhibits more than twice modulation efficiency as large as that of the Si modulator. To the best of our knowledge, this is the first demonstration of the enhanced free-carrier effects in strained SiGe at the near-infrared telecommunication wavelength. The strain-induced enhancement technology for the free-carrier effects is expected to boost modulation efficiency of the most Si-based optical modulators thanks to high complementary metal-oxide-semiconductor (CMOS) compatibility.

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Using an atmospheric metal-organic chemical vapor deposition system, we passivated GaAs with AlN prior to atomic layer deposition of Al2O3. This AlN passivation incorporated nitrogen at the Al2O3/GaAs interface, improving the capacitance-voltage (C–V) characteristics of the resultant metal-oxide-semiconductor capacitors (MOSCAPs). The C–V curves of these devices showed a remarkable reduction in the frequency dispersion of the accumulation capacitance. Using the conductance method at various temperatures, we extracted the interfacial density of states (Dit). The Dit was reduced over the entire GaAs band gap. In particular, these devices exhibited Dit around the midgap of less than 4 × 1012 cm−2eV−1, showing that AlN passivation effectively reduced interfacial traps in the MOS structure.

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