Physical study of the dissipated power area in high electron mobility transistors for thermal modelling
The hot area in power transistors due to the power dissipation is determined from a 2D-hydrodynamic model. The power is calculated everywhere in the device from the knowledge of the physical quantities (current density, electric field). The hot area is determined accurately to be coupled to a thermal modelling giving the temperature everywhere in the device [J. Park, M.-W Shin, C.-C. Lee, Thermal modeling and measurement of GaN-based HFET devices, IEEE Electron Device Lett. 24(7) (2003) 424-426 [1]; J.-C Jacquet, R. Aubry, H. Gerard, E. Delos, N. Rolland, Y. Cordier, A. Bussutil, M. Rousseau, S.L. Delage, Analytical transport model of AlGaN/GaN HEMT based on electrical and thermal measurement, 12th GAAS Symposium, Amsterdam, 2004, pp. 235-238 [2].]. The method is applied to HEMTs (high electron mobility transistors) based on GaAs or GaN. It is shown that the hot area depends on the bias conditions and on the transistor gate recess topology.
Comparison of wurtzite and zinc blende III–V nitrides field effect transistors: a 2D Monte Carlo device simulation
Abstract An ensemble Monte Carlo method is used to compare the potentialities of zinc blende and wurtzite GaN for field effect transistor applications. First, bulk material electron transport properties are compared and we find that mobility, steady state velocity and velocity overshoot are at the advantage of zinc blende GaN. Then, zinc blende GaN and wurtzite GaN MESFET with very short gate length (Lg=0.12 μm) are investigated using a 2D Monte Carlo device simulation. A 50% gain in performance is obtained for the zinc blende GaN MESFET as compared with the wurtzite one. A zinc blende AlGaN/GaN HEMT is also simulated and exhibits a current density of 900 mA mm−1, a transconductance of 480 mS mm−1 and a cut-off frequency of 180 GHz.
Taphonomy of Isisfordia duncani specimens from the Lower Cretaceous (upper Albian) portion of the Winton Formation, Isisford, central-west Queensland
Taphonomic analysis of fossil material can benefit from including the results of actualistic decay experiments. This is crucial in determining the autochthony or allochthony of fossils of juvenile and adult Isisfordia duncani, a basal eusuchian from the Lower Cretaceous (upper Albian) distal-fluvial-deltaic lower Winton Formation near Isisford. The taphonomic characteristics of the I. duncani fossils were documented using a combination of traditional taphonomic analysis alongside already published actualistic decay data from juvenile Crocodylus porosus carcasses. We found that the I. duncani holotype, paratypes and referred specimens show little signs of weathering and no signs of abrasion. Disarticulated skeletal elements are often found in close proximity to the rest of the otherwise articulated skeleton. The isolated and disarticulated skeletal elements identified, commonly cranial, maxillary and mandibular elements, are typical of lag deposits. The holotype QM F36211 and paratype QM F34642 were classified as autochthonous, and the remaining I. duncani paratypes and referred specimens are parautochthonous. We propose that I. duncani inhabited upper and lower delta plains near the Eromanga Sea in life. Their carcasses were buried in sediment-laden floodwaters in delta plain overbank and distributary channel deposits. Future studies should refer to I. duncani as a brackish water tolerant species.