PROCEEDINGS ARTICLE | March 28, 2000
Proc. SPIE. 3940, Ultrafast Phenomena in Semiconductors IV
KEYWORDS: Scattering, Luminescence, Electrons, Zinc, Gallium nitride, Monte Carlo methods, Ionization, Phonons, Strontium, Thin film devices
High field transport in wide bandgap materials such as ZnS and SrS is of current importance for thin film electroluminescent devices currently used in flat panel display applications. Typically, carriers injected into the phosphor layer of such structures undergo acceleration in fields ranging from 1 - 2 MV/cm, with average carrier energies of 1 - 2 eV, and therefore high field transport is critical to the device operation. A major problem in the understanding of transport in such wide bandgap materials is the relative lack of experimental data for the electron- phonon coupling constants and impact ionization coefficients, particularly under high electric fields, where details of the full bandstructure are important. Hence, first-principles modeling of the electronic and transport properties is required for assessing the technological potential of these materials. In the present work, a review is given on the electronic and transport properties of three wide bandgap materials, ZnS, SrS, and GaN, simulated using full-band ensemble Monte Carlo (EMC) simulations. The impact ionization rates for both electrons and holes were derived directly from bandstructure calculated using the empirical pseudopotential method (EPM). To avoid arbitrary fitting parameters for the electron-phonon coupling, a microscopic rigid-ion model calculation is performed of the electron- phonon scattering rate directly from the EPM bandstructure, and a valence-shell model for the lattice dynamics. The momentum averaged scattering rate is input directly into the full-band EMC simulation. Results for the high field distribution functions for all three materials are calculated and compared. Further, the process of impact excitation of luminescent centers by hot carriers is included, and compared to experimental photo-induced- luminescence versus field data, where good agreement is obtained.
