ZnSe/GaAs heterojunctions were investigated by contactless electroreflectance and photoreflectance techniques. Negative surface charge densities on the order of 1012 cm-2 were observed for films grown on n-type GaAs indicating a large contribution to the conduction band barrier between the materials due to band bending. The conduction band offset was also measured using a new photoreflectance technique involving a tunable pump laser.

With the development of the short pulse laser source, it has been demonstrated that molecular [1–4] and lattice dynamics [5–7] can be studied in the time domain. Pulses of light that are short compared to the optical phonon period have been found to initiate coherent lattice vibrations through various mechanisms which depend on the material type. The purpose of this paper is to describe the observation of the coherent phonon phenomenon in semimetals and narrow-gap semiconductors, and to propose a potential application of this phenomenon as a terahertz light modulator.

Femtosecond time-resolved optical techniques have been shown to generate coherent phonons in some semimetals and narrow gap semiconductors. A previously-reported model describes the mechanism for generation of coherent lattice vibrations via the optically excited carriers. One of the most interesting consequences of such coherent lattice motion is the modulation of the electronic bands - and possibly of the transport properties of the material — at a THz timescale. Preliminary results are given for a band structure calculation, performed to evaluate the magnitude of these laser-induced band shifts.

We present experimental data which show that large amplitude coherent lattice vibrations can be impulsively excited using short optical pulses of light. Furthermore, using a quasi-equilibrium model, we show how the these coherent lattice vibrations suggest a ~ 7 THz modulation of the semiconductor-to-metal transition in Ti2O3.