Impact of strain relaxation of AlmGa1?mN layer on 2-DEG sheet charge density and current voltage characteristics of lattice mismatched AlmGa1?mN/GaN HEMTs
An accurate charge control model to investigate the effect of aluminum composition, strain relaxation, thickness and doping of the AlmGa1?mN barrier layer on the piezoelectric and spontaneous polarization induced 2-DEG sheet charge density, threshold voltage and output characteristics of partially relaxed AlmGa1?mN/GaN HEMTs is proposed. The strain relaxation of the barrier imposes an upper limit on the maximum 2-DEG density achievable in high Al content structures and is critical in determining the performance of lattice mismatched AlmGa1?mN/GaN HEMTs. The model incorporates the effects of field dependent mobility, parasitic source/drain resistance and velocity saturation to evaluate the output characteristics of AlmGa1?mN/GaN HEMTs. Close proximity with published results confirms the validity of the proposed model.
strain relaxation 2-deg sheet charge density almga1?mn/gan hemts aluminum composition piezoelectric and spontaneous polarization currentvoltage characteristics output conductance