Electron transport in AlN under high electric fields
- PDF / 238,963 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 34 Downloads / 218 Views
Electron transport in AlN under high electric fields
Ramón Collazo, Raoul Schlesser, Amy Roskowski, Robert F. Davis, and Z. Sitar Department of Materials Science and Engineering, North Carolina State University, Raleigh, N.C. 27695-7919
ABSTRACT The energy distribution of electrons transported through an intrinsic AlN film was directly measured as a function of the applied field, and AlN film thickness. Following the transport, electrons were extracted into vacuum through a semitransparent Au electrode and their energy distribution was measured using an electron spectrometer. Transport through films thicker than 95 nm and applied field between 200 kV/cm -350 kV/cm occurred as steady-state hot electron transport represented by a Maxwellian energy distribution, with a corresponding carrier temperature. At higher fields (470 kV/cm), intervalley scattering was evidenced by a multi-component energy distribution with a second peak at the energy position of the first satellite valley. Electron transport through films thinner than 95 nm demonstrated velocity overshoot under fields greater than 550 kV/cm. This was evidenced by a symmetric energy distribution centered at an energy above the conduction band minimum. This indicated that the drift component of the electron velocity was on the order of the "thermal" component. A transient length of less than 80 nm was deduced from these observations.
INTRODUCTION There are three basic types of electron transport in semiconductors. Steady state thermalized transport occurs when the transport of electrons is confined to the conduction band minimum. In this case, the kinetic energy saturates at a certain value from which the drift velocity can be calculated. This type of transport is common in the working regime of most electronic devices, where the drift velocity of electrons can be approximated as a linear function of the applied electric field. This defines the mobility at a low field condition, and it is considered a figure of merit for materials used for electronic devices. Steady state hot electron transport occurs when the energy gained by the electrons due to the acceleration in the applied electric field is not completely lost through various electron scattering mechanisms, primarily electron-phonon interactions. One distinguishes hot electron transport when there is a partial loss of energy due to these interactions, raising the carrier (electron) temperature to values higher than the host (lattice) temperature. In an extreme case (usually for very thin films), transient ballistic transport (or quasi-ballistic) occurs when there is no energy loss to the lattice. This transient transport is characterized by an overshoot of the average electron velocity with respect to the steady state drift velocity. Hot electron and ballistic transport has been observed in many materials, including AlN, ZnS and GaAs. [1,2,3] The experimental procedure consists of extracting I6.45.1
hot electrons into vacuum through a semitransparent electrode and performing direct measurements of thei
Data Loading...
