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Hot Electron Transport in AlN

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 that were transported through a thin intrinsic AlN film was directly measured as a function of the applied field. The measurements were realized by extracting the electrons into vacuum through a semitransparent Au contact and measuring their energy using an electron spectrometer. At moderate applied fields (350 kV/cm), the energy distribution followed a Maxwellian model corresponding to an electron temperature of 2700 K and a drift component below the spectrometer resolution. At higher fields, intervalley scattering was evidenced by the presence of a second peak at 0.7 eV. This coincides well with the energy position of the L-M valley in AlN. To the best of our knowledge, these are the first measurements that offer direct evidence of intervalley scattering in any solid system. INTRODUCTION There are two basic types of electron transport in solid state. Steady state transport occurs when the transport of electrons is confined to the conduction band minimum (thermalized transport). 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. Transient 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, and, as an extreme case, ballistic transport, when no energy loss occurs. Transient transport is characterized by an overshoot of the average electron velocity with respect to the steady state drift velocity. Hot electron energy transport has been observed in other materials, e.g., ZnS and GaAs.[1,2,3] The experimental procedure consists of extracting hot electrons into vacuum through a semitransparent electrode and performing direct measurements of their kinetic energy by means of an electron spectrometer. Measured energy spectra allow one to distinguish between the aforementioned types of electron transport. These are similar measurements as those obtained by using a Tunneling Hot Electron Transistor (THETA) device [4], substituting the collector with an electron spectrometer. In contrast to the

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complexity of a THETA device, the structure needed to perform the measurements presented in this paper is simple and can be readily fabricated. EXPERIMENT The nature of electron transport through materials can be de