J. Osvald

Influence of barrier height distribution on the parameters of Schottky diodes

I‐V curves of Schottky diodes are simulated for a Gaussian type of the Schottky barrier height (SBH) distribution using the model of noninteracting parallel diodes. The mean value and the standard deviation of the distribution are supposed to be constant, i.e., not dependent on the voltage and the temperature. The influence of the distribution parameters and the temperature on the apparent barrier height and the ideality factor is analyzed. It is shown that the ideality factor increases and the apparent barrier height decreases with increasing standard deviation and decreasing temperature. The simulation also provides a rough estimate for the standard deviation. Values of ∼0.09 V can result in ideality factors up to 1.2. The importance of the effect of series resistance in the approach of noninteracting diodes is emphasized.

Current–voltage characteristics of Schottky diode simulated using semiconductor device equations

The Poissons equation and the drift diffusion equations have been used to simulate the current–voltage characteristics of Schottky diode. The potential variation inside the bulk semiconductor near the metal–semiconductor contact was estimated first and then the current as a function of bias through the Schottky diode using silicon parameters were calculated over a wide temperature range. From the simulated current–voltage characteristics the diode parameters were extracted by fitting of current–voltage data into thermionic emission diffusion current equation. The derived barrier parameters are analysed to study the effect of various parameters, e.g. semiconductor thickness, doping concentration, temperature dependence of carrier mobility and energy band gap, on the current–voltage characteristics of Schottky diode in view of the thermionic emission diffusion current equations.

Interface Electron Traps as a Source of Anomalous Capacitance in AlGaN/GaN Heterostructures

We studied by modeling and simulation how deep traps at the AlGaN/GaN heterostructure interface influence the shape of capacitance–voltage (C–V) curves of the heterostructure. Assuming donor and acceptor type of traps, we found differences in the C–V curves for sharp energy interface states or continuously distributed states with the same total concentration for the acceptor-type interface states. The background doping concentration of GaN had only a marginal influence on the shape of the C–V curves. We observed that an anomalous capacitance peak occurred for the continuous distribution of traps in the bandgap; a similar peak had been observed in experiment. We also saw that the capacitance curves shifted slightly to the right or to the left depending on the GaN doping concentration. A remarkable difference was found between the capacitance curves for the structures with the sharp acceptor trap level and continuous distribution of traps. For donor-type interface states, we found practically no influence on C–V curves since they remain populated and charge neutral during the measurement.

Influence of Interface Deep Traps on Capacitance of AlGaN/GaN Heterojunctions

We have studied by modeling and simulation dependence of capacitance of AlGaN/GaN heterostructures by the presence of deep traps localized at the AlGaN and GaN interface. For low frequency capacitance the deep traps cause voltage shift of capacitance curves when the traps concentration is relatively low. With increasing traps concentration the voltage shift increases and above some critical traps concentration the new capacitance peak is observed in the C–V curve. We expect that in experimental structures only traps located close to the conduction band minimum can follow external signal.

Effect of Inverse Doped Surface Layer in Schottky Barrier Modification: A Numerical Study

Poisson’s equation and the drift–diffusion equations are used to simulate the current–voltage characteristics of a Schottky diode with an inverse doped surface layer. The potential inside the bulk semiconductor near the metal–semiconductor contact is estimated by simultaneously solving these equations, and then current as a function of bias through the Schottky diode is calculated. The Schottky diode parameters are extracted by fitting of simulated data to the thermionic emission diffusion equation. The simulation is carried out for various inverse layer thicknesses and doping concentrations. The obtained diode parameters are analyzed to study the effect of the inverse layer thickness and doping concentration on Schottky diode modification and its behavior at low temperatures. It is shown that an increase in the inverse layer thickness and doping concentration leads to Schottky barrier height enhancement and a change in the ideality factor. The temperature dependences of the Schottky barrier height and ideality factor are also studied.