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Study of Hot-Electron Effects, Breakdown and Reliability in FETS, HEMTS, and HBT'S

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Final rept.

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The objective of this project has been the understanding of the physical limitation of GaAs, InP and wide-bandgap semiconductors through experimental and the theoretical evaluation. In particular evaluation of scaling properties, hot electron effects, breakdown phenomena and failure mechanisms in AlGaAsInGaAs and InAlAsInGaAs High Electron Mobility Transistors HEMTs and in InAlAsInGaAs Heterojunction Bipolar Transistors HBTs has been carried out. Physical phenomena studied in this work include 1 impact ionization 2 short-channel effects 3 quantum confinement and real space transfer 4 failure mechanisms of GaAs- and InP-based devices. Devices adopting wide bandgap semiconductors SiC have also been studied. We have studied the impact ionization coefficient in In0.53Ga0.47As material by using a suitable HBT structure. A positive temperature coefficient has been found in this material. Theoretical work has included the development of ionization models for InGaAs layers, and the inclusion of non local ionization effects into drift-diffusion simulators. Hot-electron effects in pseudomorphic AlGaAsInGaAs HEMTs has also been studied. The behaviour of electroluminescence at high fields has been analyzed and the presence of a band-to-band recombination peak has been demonstrated. On the theoretical side, we have used the self consistent HEMT Monte Carlo code to study short channel effects, impact ionization and electroluminescence in pseudomorphic HEMTs GaAsInGaAsAlGaAs. The analysis also demonstrate that holes generated by impact-ionization are able to reach the source and recombine there. Accelerated tests at high VDS have been carried out both in GaAs- and InP based HEMTs. Permanent degradation resulting in the development of a remarkable kink in the output characteristics has been found. DC, pulsed, low-frequency AC and DLTS measurements demonstrate that the failure mechanism consists in the creation of deep levels.

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  • Electrical and Electronic Equipment
  • Solid State Physics

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