Electrical characterization, modeling and reliability of microwaves devices with particular attention to the “hot electrons” related phenomena (impact ionization, breakdown, light emission, hot carriers degradation)
A systematic characterization and reliability study of MESFETs and HEMTs and HBT devices grown on GaAs and/or InP semiconductor have been carried out. Particularly, the followings matters have been considered:
(a) Characterization of the on-state and off-state breakdown (in open and closed channel conditions) and of the impact ionization coefficient;
(b) Improvement of the breakdown in devices with InP substrate through the use of a compound (InGaAs/InP) and channel quantization (channel thickness below 100 Å);
(c) Breakdown mechanisms study in devices under accelerated life tests (high electric fields and high temperatures regimes);
(d) Study of the passivation effects in InP HEMT devices in order to improve their reliability.
The results produced within this research activity have allowed to get important indications in order, to obtain best performances and greater reliability in devices development.
- Impact ionization characterization: Through heterostructure bipolar devices (HBT) the ionization coefficient has been investigated both for electrons and holes in the In0.53Ga0.47As materials and an anomalous behavior in temperature have been found (an increases with the temperature increasing).
- Breakdown characterization: The fundamental role of the holes generated by the impact ionization phenomena in the breakdown trigger through the parasitic bipolar transistor activation has been investigated in HEMTs and MESFET devices. Furthermore, an innovative technological solutions for HEMT with InP substrate, that allows to reduce the impact ionization phenomena (compound and quantization channel) and therefore to improve the performances in breakdown regime, has been individualized;
- Microwaves devices reliability: Several degradation mechanisms have been identified on GaAs and InP HEMT in “hot electrons” bias conditions. Particularly, the more frequently observed degradation mechanism was the traps generation and/or the charge trapped modulation. Moreover the sensitivity of the surface access regions has been investigated in order to determine the devices stability and, in the InP HEMTs, a technological solution has been individualized that allow to improve its reliability (InP etch stopper layer);
- Effects induced by radiations effects in MESFETs: The radiations induced effects by means of static and dynamics electrical characterization of GaAs MESFETs devices have been analyzed. Particularly, the traps induced by neutrons on MESFET devices have been characterized through frequency variation related transconductance (gm) and output conductance (gD) measurements.