Laboratoire Charles Coulomb UMR 5221 CNRS/UM2 (L2C)


Accueil > La Recherche > Axes & Equipes > Physique Appliquée > Semi-conducteurs : Graphène, grand gap & Photovoltaïques > Thème : Composants et Capteurs

Nitride devices

par Sébastien LAYSSAC - publié le

High temperature devices. At elevated temperature, the semiconductor materials like Si or “classical” III-V compounds reach their natural limit and the use of a wide band gap material like diamond, silicon carbide (SiC) or gallium nitride (GaN) appears a most natural issue. In the case of Hall sensors the use of a 2DEG confined in a quantum well has then long been recognized as an optimum solution to achieve metrological performances and from this reason the high temperature Hall sensor based on nitride HEMT-type heterostructures are strongly requested for applications. The basic material system is robust and can sustain up to 900°C. Unfortunately, up to now, most of the AlGaN/GaN investigated structures could hardly work with a low thermal drift at temperatures higher than 300°C. The origin of the high temperature device degradation is not known, but commonly attributed to uncontrolled leakage currents in the underlying buffer or top capping layers. To suppress, or at least, lower these leakage currents, it is necessary to act at the same time on the (deep) buffer layers and (top) capping structure. For this reason the study of the problem has to be developed in close collaboration and complementary expertise of growth and characterization methods.

p-type doping. p-type (Al,Ga)N alloys are of critical importance for a host of nitride-based devices including light emitting diodes, lasers, photodetectors, and bipolar transistors. While there is no doubt that the Mg is the only acceptor dopant which generates sufficient p-type conductivity in a reproducible manner, the procedure of Mg activation remains still an actual issue. In the case of the MOVPE growth process, the Mg acceptor is electrically inactive in as-grown material and an additional annealing procedure is required. Despite its technological importance, the detailed characteristics of this process and the optimal annealing conditions are still not well defined and the annealing temperatures between 500 and 950°C are reported.

In the case of GaN material we have demonstrated that the lowest resistivity is obtained after some minutes annealing at temperature T 500°C. Annealing at temperatures higher than 550°C corresponds to a more complex process which leads to the deterioration of the p-type conductivity of the sample. In the case of AlGaN or InGaN structures the fundamental study of Mg-dopant activation are still necessary. Our expertise in high temperature electrical transport measurements allow to study the annealing process by in-situ measurements of electrical properties of the material as a function of temperature up to 1000°C.

Collaboration/Contract : Associated European Laboratory - L.E.A.« NODLab », Foreign Office “Polonium” Project, CRHEA CNRS Laboratory