|
ertain wide band gap semiconductors are emerging as viable candidate materials
for electronic devices that can operate in environments and under bias conditions
for which the standard semiconductor material, silicon, is not suitable. Among
the new materials are the III-nitrogen compounds, GaN, AlN, and their alloys.
The principal advantage of these materials over silicon can be traced to their
electronic structure that has (filled) valence bands separated from (empty)
conduction bands by an energy gap that is&emdash;depending on the group III element‹between three and five times as large as that of silicon. The wide band gap implies that large electric fields are sustainable in the materials and the principal electrical characteristics are relatively insensitive to temperature. In addition, conduction electrons can be very mobile, allowing for large current densities and rapid changes in currents. This combination of properties makes III-nitride semiconductors excellent candidates for the fabrication of high-power, high-frequency, high-temperature electronic devices with applications ranging from satellite communication systems to engine control electronics.
 |
| Figure 1: Average drift velocity of electrons in wurtzite structure GaN as a function of the applied field strength for three different temperatures as obtained from Monte Carlo simulations.
|
III-nitride materials preparation technology is currently in a state of very rapid development, and exploratory devices are already being made. However, device design is still rather rudimentary. One of the main reasons for this relatively low level of sophistication is the lack of predictive models needed for successful optimization. The standard device models are not immediately useful because they rely on a large number of materials parameters that, although well known for conventional materials such as silicon, are not yet available for the III-nitride compounds.
Supercomputing Institute Associate Fellow Professor Paul Ruden and his Modeling
and Simulation group in the Electrical and Computer Engineering Department,
together with Professor Kevin Brennan and students at the Georgia Institute
of Technology, have developed a materials-theory based device modeling technique
that is particularly suitable for the current state of III-nitride technology
development. Briefly summarized, the technique starts from very fundamental
materials properties that are known from parameter-free, first-principles calculations
of the electronic structure. It then proceeds to microscopic electron transport
simulations using the Monte Carlo method. In these simulations, electrons are
 |
| Figure 1: Average drift velocity of electrons in wurtzite structure GaN as a function of the applied field strength for three different temperatures as obtained from Monte Carlo simulations.
|
accelerated by an applied electric field and scattered through interactions with lattice vibrations and impurities. From the resulting trajectories, which may involve 107 scattering events, the average drift velocity for a given field strength is computed. Representative results are displayed in figure 1. Finally, based on the microscopic simulation results, macroscopic materials characteristics of suitable forms are defined and incorporated into device models.
The materials-theory based device models have yielded predictions of breakdown voltages for simple GaN diodes as well as output performance results for relatively complex AlGaN/GaN Heterostructure Field Effect Transistors (HFETs). Temperature effects have been found to be very important in these high-power devices due to inevitable self-heating. As an example, figure 2 shows model results for the output characteristics of an HFET, together with experimental data recently obtained at the Naval Research Laboratory. Further modeling results indicate that even higher currents can be obtained with simple changes in device design. These new designs are presently being explored.
|
|
This information is available in alternative formats upon request by
individuals with disabilities. Please send email to
alt-format@msi.umn.edu
or call 612-624-0528.
|
|
URL: http://
|
|
|
This page last modified on
|
|
Website related questions or problems should be directed to
webmaster@msi.umn.edu
The Supercomputing Institute does not collect personal information on
visitors to our website. For the University of Minnesota policy, see
www.privacy.umn.edu.
|
|
| |
