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TCAD analysis of GaN FinFET structures and their parametric sensitivity

Eva Catoggio

TCAD analysis of GaN FinFET structures and their parametric sensitivity.

Rel. Simona Donati Guerrieri, Fabrizio Bonani. Politecnico di Torino, Corso di laurea magistrale in Ingegneria Elettronica (Electronic Engineering), 2019

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Gallium Nitride is a promising material for different applications due to its superior characteristics with respect to conventional semiconductors: wide band gap, low intrinsic carrier density, high electron mobility, high critical field, high thermal stability and high saturation velocity. Despite of these advantages, GaN materials also show negative aspects, such as the very high cost and the less effective growing methods. In fact, the different techniques used for the GaN epitaxial growth does not seem very simple due to the risk of obtaining undesired effects in the final structure. Valid examples can be the presence of non-intentional doping inside the material or the formation of dislocation layers, which produce worse electrical and optical properties that compromise the resulting structure. The III-V Nitride materials, such as GaN, AlN, InN and compounds, have a wurzite structure characterized by a strong polarization in the <0001> direction, known as the C-direction, whose effect is very important to understand the electronic properties of these materials. The total polarization field has two different components, the piezoelectric and the spontaneous one. The piezoelectric field is associated to an electrostatic charge produced in a strained material and the spontaneous field corresponds to the same charge density in relaxed conditions. These polarization charges exist in the whole crystal, but the sum of the internal components is zero, therefore the remaining charge density is distributed along the two opposite faces of the material forming a dipole. In this work, the electronic properties of Gallium Nitride and the polarization effect of the wurzite crystals are exploited in an AlGaN/GaN heterostructure to form the two-dimensional electron gas (2DEG) at the interface between the two materials without the use of dopants. The 2DEG channel is not considered into a conventional planar device, but in a three-dimensional structure like the FinFET, that can be called more precisely Fin-HEMT. A simulation on the TCAD Synopsys Sentaurus is performed in order to understand how the device works and what are the physical mechanisms responsible of a certain behaviour. Moreover, the purpose of this kind of analysis is to highlight advantages and disadvantages of using, in the same structure, an interesting material like Gallium Nitride and a Fin-shaped channel instead of the conventional planar one. With this aim, the simulation is carried on by modulating precise quantities that characterize the device. As regards the Gallium Nitride, the parameters under analysis can be the thickness, the spontaneous and piezoelectric charges and the presence of traps. On the other hand, the quantities to be modified in the Fin-shaped structure are the geometrical ones, for example the gate length, the fin width and the fin height. The simulation results are evaluated in order to understand the possible advantages that the device shows with respect to a conventional planar structure and if each positive feature can be exploited for a specific application. For example, digital applications require the shift of the threshold voltage towards positive values, while analogue applications need an improvement in the cut-off frequency, gains and output power density.

Relators: Simona Donati Guerrieri, Fabrizio Bonani
Academic year: 2018/19
Publication type: Electronic
Number of Pages: 107
Corso di laurea: Corso di laurea magistrale in Ingegneria Elettronica (Electronic Engineering)
Classe di laurea: New organization > Master science > LM-29 - ELECTRONIC ENGINEERING
Ente in cotutela: Universidad Carlos III de Madrid (SPAGNA)
Aziende collaboratrici: UNSPECIFIED
URI: http://webthesis.biblio.polito.it/id/eprint/11681
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