Browsing by Author "Kabi, Sanjib"

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Comparative DC Characteristic Analysis of AlGaN/GaN HEMTs Grown on Si(111) and Sapphire Substrates by MBE
(2014-04-01)
Mukhopadhyay, Partha
;
Bag, Ankush
;
Gomes, Umesh
;
Banerjee, Utsav
;
Ghosh, Saptarsi
A comparative assessment of AlGaN/GaN high-electron-mobility transistors (HEMTs) grown by molecular beam epitaxy on silicon and sapphire substrates has been carried out. Large-area power GaN HEMTs with identical device dimensions were fabricated on both substrates. A thicker AlN buffer layer was used for the GaN HEMT on silicon to achieve similar quality and uniformity of GaN epitaxy for rational comparison with that grown on sapphire. Direct-current analysis and physical characterization were carried out to understand the performance of the devices. Mathematical measurement of the instability of the current-voltage (I-V) characteristic at high applied drain bias was carried out to evaluate the performance of both devices. An improved two-dimensional (2D) analysis of the I-V characteristic was performed from a thermal perspective including appropriate scattering effects on the 2D electron gas mobility. The experimental and analytical studies were correlated to reveal the effects of temperature-sensitive scattering phenomena on the mobility as well as on the I-V characteristic at high drain bias in terms of lattice thermal heating. It is observed that the HEMT on Si has improved stability compared with sapphire due to its weaker scattering phenomena at high drain bias, associated with its thermal conductivity. Simulation of 2D thermal mapping was also carried out to distinguish the hot-spot regions of the devices. The comparable electrical performance of these devices illustrates the viability of AlGaN/GaN HEMTs on Si(111) to achieve low-cost stable devices with better thermal power handling for high-voltage applications.
Effects of threading dislocations on drain current dispersion and slow transients in unpassivated AlGaN/GaN/Si heterostructure field-effect transistors
(2014-08-18)
Ghosh, Saptarsi
;
Dinara, Syed Mukulika
;
Mukhopadhyay, Partha
;
Jana, Sanjay K.
;
Bag, Ankush
Current transient analysis combined with response to pulsed bias drives have been used to explore the possibilities of threading dislocations affecting the current dispersion characteristics of AlGaN/GaN heterostructure field-effect transistors (HFETs). A growth strategy is developed to modulate the dislocation density among the heterostructures grown on silicon by plasma-assisted molecular-beam epitaxy. Slow pulsed I-V measurements show severe compressions and appear to be significantly dependent on the threading dislocation density. By analyzing the corresponding slow detrapping process, a deep-level trap with emission time constant in the order of seconds was identified as the cause. Among the specimens, both in the epilayers and at the surface, the number of dislocations was found to have a notable influence on the spatial distribution of deep-level trap density. The observations confirm that the commonly observed degraded frequency performance among AlGaN/GaN HFETs in the form of DC-radio frequency dispersions can at least partly be correlated with threading dislocation density. (C) 2014 AIP Publishing LLC.