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A graded composition superlattice structure is proposed by combining simulation with experimentation. The structural factors affecting graded symmetric superlattices and graded asymmetric superlattices and their action modes are simulated and analyzed. A Mg-doped graded symmetric superlattice structure with high Al content, excellent structural quality, good surface morphology and excellent electrical properties was grown by MOCVD equipment. The AlxGa1−xN superlattice with Al composition of 0.7 in the barrier exhibits a hole concentration of approximately 5 × 1015 cm−3 and a resistivity of 66 Ω·cm.

In this paper, we present the dependence of source resistance sensibility on the gate bias effect in a High Electron Mobility Transistor (HEMT) using the Drift-Diffus (D-D) model with the SILVACO Technology Computer-Aided Design (TCAD) tool. The obtained results show that the increases of gate bias effect on substrate lead to decreasing the source resistance of the simulated device. The reported increase in the effect of gate induces the increases of transferred holes concentration towards the source region and which induce the decreases of source resistance. The decrease of source resistance can also be made by reducing the buffer thickness which leads to an increase in the gate effect on the substrate. The source resistance value is influenced by the Drain-Induced Barrier Lowering (DIBL) effect where the rate of decreasing the source resistance will be decreasing consequently to increase the drain bias. The reduction of the source resistance induces the increase of device sensibility for lows values of current.

In this letter, novel heterostructure p-i-n GaN avalanche photodiodes (APDs) with p-type In0.05Ga0.95N layer are proposed and analyzed through Silvaco Atlas simulations. The introduction of the In0.05Ga0.95N layer generates a negative polarization charge at the p-In0.05Ga0.95N/i-GaN heterojunction interface via the piezoelectric polarization effect. Three times higher hole concentration in the p-In0.05Ga0.95N layer is obtained due to the smaller activation energy of the Mg dopant. Induced polarization charge and increased hole concentration work together to reduce the voltage drop in the p-In0.05Ga0.95N layer and enhance the electric field intensity in the i-GaN layer. The calculated results show that the heterostructure APD demonstrates a reduced operating voltage of more than 26 V and an improved multiplication gain by an order of magnitude in comparison to the conventional one.

Polycrystalline samples of Nd1-xPrxBa2Cu3O7-δ with 0≤x≤0.30 were made by standard solid state methods. The transport and superconducting properties were studied by the resistivity and the thermoelectric power measurements as a function of temperature and doping concentration. The resistance and the thermoelectric power were increased by increasing doping concentration. The pseudogap temperature was measured from downturn deviation in a linear dependence of resistance as a function of temperature. The resitivity, the thermoelectric power, the critical temperature, and the pseudogap temperature results suggested that the hole concentration in CuO2 planes was decreased by increasing Pr doping concentration. The resistivity and the thermoelectric power results were analyzed by the bipolaron and the phenomenological narrow band model, respectively. A good agreement between models and data was obtained. On the basis of these models, it was inferred that the localization tendency is one of the main reasons for decreasing the hole concentration in the CuO2 plane, which results in the strong depression of the superconductivity.