Studies on the quantum well heterostructure for gallium nitride based high electron mobility transistors

Abstract

In this thesis, a different high electron mobility transistor(HEMT) structures are designed using gallium nitride(GaN). Also, the electrical characteristics and conduction band engineering corresponding to each designed HEMT are investigated. Each HEMT consists of a heterojunction between the AlGaN layer(doped) and GaN layer(Undoped). The conduction band discontinuity forms a quantum well at the hetero-interface. Electrons are confined in the quantum well forming the 2DEG. HEMT is also popular as MODFET due to the modulation doping between the doped AlGaN layer (wide band-gap) and Undoped GaN layer(narrow band-gap). Due to this modulation doping, the undoped channel at the hetero-interface in GaN layer is spatially separated from the doped AlGaN layer resulting into no impurity scattering for mobile electrons in the channel of GaN layer providing high electron mobility in HEMTs. At the beginning of investigations, the designs of devices have been optimised by the studies on electrical characteristics (current-voltage characteristics) of microelectronic HEMTs and Nanoelectronic HEMTs using the SILVACO-ATLAS software tool. In the same set of studies, the optimisation of designs has been carried out with respect to singleheterojunction GaN based HEMTs and double-heterojunction GaN based HEMTs. The electrical parameters in optimisation are drain voltage and gate voltage. The structural parameters in optimisation are aluminium mole fraction, AlGaN doping concentration, AlGaN thickness, and the presence of aluminium nitride (AlN) nucleation layer. Also, the simulation studies are performed on the conduction band engineering of above mentioned HEMT structures. In the next phase, the electrical characteristics of Nanoelectronic AlGaN/GaN singleheterojunction HEMTs are investigated with the electrical parameters like drain voltage and gate voltage, and with structural parameters like aluminium mole fraction, doping concentration, gate length, and thickness of AlGaN nano-layer.