Y. Guhel

High linearity performances of GaN HEMT devices on silicon substrate at 4 GHz

In this letter, we demonstrate that, for high linearity application, GaN devices benefit from their high drain-source bias voltages. An improvement up to 20 dB in intermodulation ratio can be observed at high power levels compared to usual GaAs PHEMT devices. This study demonstrates that the high bandgap GaN devices are ideal candidates for the applications requiring high power and linearity simultaneously.

Characterization of the self-heating of AlGaN/GaN HEMTs during an electrical stress by using Raman spectroscopy

Abstract We report on the non-invasive measurements of the temperature in active AlGaN/GaN HEMTs grown on sapphire substrate during an electrical stress. The original study permits to highlight the drop of the self-heating in operando during the electrical stress by using Raman spectroscopy. Moreover, a correlation between the decrease of the self-heating and the fall of the drain current during the stress has been demonstrated. This study also highlights that the self-heating of the components and the influence of the ageing test on the self-heating are clearly linked to the position where temperature measurements are carried out.

Load impedance influence on the I/sub D/(Y/sub DS/) characteristics of AlGaN/GaN HEMTs in large signal regime at 4 GHz

A measurement system allowing one to put in evidence the trap effects on the power performance of Al/sub 0.1/Ga/sub 0.9/N/GaN high electron mobility transistors (HEMTs) made on sapphire substrate is presented in this paper. This setup permits simultaneous measurements of the output power supplied by the device under test (DUT) and the I/sub D/(V/sub DS/) characteristic in large signal regime at 4 GHz for different load impedances. It shows the traps influence on the maximum drain-current at 4 GHz for different load impedances under large signal operating conditions. The measurements carried out on a device (2/spl times/50/spl times/1 /spl mu/m/sup 2/) have shown a linear decrease of the maximum drain-current when the load impedance increases. These observations make it possible to determine the origin of the power performances difference obtained at microwave frequencies opposite to the static regime.

Annihilation of electrical trap effects by irradiating AlGaN/GaN HEMTs with low thermal neutrons radiation fluence

In this paper, we report on an original method, which permits to change the trap effects on the dc electrical performances of AlGaN/GaN HEMTs. In fact, electrical traps induced by an OFF-stress state on AlGaN/GaN transistors can be strongly reduced by using low thermalized neutrons radiation fluence. We also highlight that a neutron irradiation induces the creation of electrical traps, which act as acceptor. As a result, the electrical behaviour of devices under OFF-state stress is totally different if the component is irradiated or not before the ageing test because electrical traps induced by OFF-state stress can compensate the electrical traps involved by neutron irradiation. To our knowledge, it is the first time that such observation was made.

Influence of Thermal and Fast Neutron Irradiation on dc Electrical Performances of AlGaN/GaN Transistors

The influence of thermal neutron irradiation and fast neutron irradiation on the electrical properties of AlGaN/GaN HEMTs is investigated. An increase in the drain current and a decrease in the access resistances are observed when devices are irradiated with a thermalized neutrons fluence of 4.3 × 1010 neutrons.cm-2 while no evolution is observed with the same fluence of fast neutrons. However, the same phenomenon is observed when the fast neutron fluence is higher (1.8 × 1012 neutrons.cm-2). AlGaN/GaN heterojunctions are analyzed by gamma spectroscopy after thermalized or fast neutron irradiations to understand the physical mechanisms induced by irradiations. In fact, we have shown that the improvement of electrical properties of devices after thermal neutrons irradiation is linked to a Ga-Ge transmutation effect. Moreover, the evolution of the drain current and access resistance when the AlGaN/GaN heterojunctions are irradiated by fast neutrons can be induced by N vacancies creation and/or a change of the strain state of the layers and/or Ga-Ge transmutation effect.

Determination of AlGaN/GaN power transistor junction temperature for radar applications

AlGaN/GaN technology provides a lot of power density, which causes a thermal effect and degrades the whole electronic characteristics of the component. The local heating source appears when the component is biased. Moreover, radar applications work in pulsed rate and emphasize the impact of this source. So it is important to measure the temperature in transient mode, close to this local source as reliable as possible In this paper we present a review of the more reliable methods for time-resolving the thermal characterization of semiconductor devices for radar applications.