SGER: Polar-Opitcal-Phonon Enhancement of Nonlinear Effects at the Shottky Barrier Interface

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

0096519 Gelmont As high-frequency devices are extended farther into the terahertz (THz) regime, the electron physics will, for the first time, be impacted by polar optical phonon resonance (POP) that typically lies above 1 THz. In this frequency region, the dispersion of the permittivity in all heteropolar materials can not be neglected. At the POP frequency, the permittivity has a singularity that influences and perturbs all physical processes within heterostructure barrier devices. Thus, the emerging area of THz electronics requires the development of new physical theories for the analysis of the heterojunction interface in the vicinity of the POP frequencies. In the last two years, the new theory of POP effects within depletion layers of GaAs barrier heterostructures has been proposed [1-2]. This physical phenomenon is based upon dramatic change in complex permittivity of electronic material near the polar optical-phonon resonance frequency which cause highly nonlinear behavior of depleted heterostructure modified by the interaction between the lattice and the electric field. While this simplified theory to date has considered only forward bias conditions and has ignored neutral layer and external parasitic effects, it predicts a strong POP influence. Specifically, it predicts that the POPs present within the electron-depleted region influence the barrier charging dynamics near the semiconductor resonant frequency, directly modify the potential barrier, perturb the spatial dependence of the electric field within the depletion-region and strongly alter the nonlinearity associated with the heterostructure current. This strong and highly-localized frequency-space phenomenon has broad implications to all polar-semiconductor-based heterostructure devices that utilize nonlinear electron transport effects. The goals of this exploratory research project is to develop a new quantitative and physics-based model for investigating the high frequency dynamics of semiconductor interfaces. In particular, a research investigation is proposed to study the nonlinear behavior of forward and reversed bias heterostructures. The physical model will be integrated with a circuit-embedding algorithm to conduct computer simulation of dynamic behavior of heterojunction based high frequency devices operating within realistic situations. This work will also consider the physical operation of interfaces that are constructed from novel materials systems which can be used to release Schottky interfaces with good barriers heights and very low resonance frequencies (~600 GHz). These particular scientific investigations hold great promise for introducing new degrees of freedom into the functionality and performance of semiconductor-based electronic devices. For example, the possibility of enhancing the nonlinearity, and therefore the innate harmonic generation capacity, of heterojunction structures would have a profound impact on the search for high-efficiency harmonic multiplier sources operating at THz frequencies.