Abstract
We theoretically and experimentally analyzed the non-obvious intersections of Schottky diode
I
–
V
curves measured at different temperatures caused by increasing the series resistance of the ...diode with increasing temperature. We considered a homogeneous diode and an inhomogeneous diode with two ways of influencing the
I
–
V
curve by the series resistance. In each case we developed a numerical method that enabled anticipation of the
I
–
V
intersection point. We studied the Ni/Au/4H-SiC diode for which such an intersection was measured. For homogeneous diodes and temperature interval 300–400 K we found a voltage dispersion of intersection points of only ∼0.002 V, which is in accordance with experimental observations and suppositions in the literature that the curves intersect at almost the same
I
–
V
point. Even for an inhomogeneous diode with a common series resistance we obtained a dispersion of the intersection voltage of only ∼0.02 V which is hardly discernible by the common visualization of the
I
–
V
curves. The largest dispersion of intersection points was obtained for an inhomogeneous diode composed of non-interacting diode patches.
We have studied numerically the capacitance properties of insulator/AlGaN/GaN MIS heterostructures and the influence of interface traps on the capacitance curves shape. By using the basic ...semiconductor equations we simulated the capacitance–voltage (C–V) curves of these structures for high‐frequency signals. We obtained two steps in the C–V curves. The curves with the interface traps are shifted in voltage at both steps depending on whether the trap is of an acceptor or a donor type. The new knowledge found is that the shift caused by the change of the population of interface states is overlapped in almost the whole semiconductor energy gap by a charge change in a two‐dimensional electron gas (2DEG). Finally, the presence of deep levels causes widening of the capacitance plateau instead of stretching of the C–V curves. So, the assessment of interface states density for MIS heterostructures is not expected to be so straightforward like in Si metal oxide semiconductor structures.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We have shown by numerical simulations of
I–
V–
T curves that the ideality factor of inhomogeneous Schottky diodes does not increase for decreasing temperature to such extent as is commonly observed ...for Schottky diodes in experiment. The main consequence of such a result is that in spite of the fact that the barrier height inhomogeneities fullfil the conditions for barrier height lowering for decreasing temperature they might not be a general or the only reason for occuring of this effect in experimental structures. We found out much slower ideality factor temperature dependence than reported in the literature and the dependence was even not monotonous for simulation conditions used. We conclude that some other reason as barrier inhomogeneity is responsible for ideality factor temperature dependence.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•High temperature stable Schottky MOS diodes on AlGaN/GaN with Ir-Al oxide gate were prepared.•Temperature dependent electrical parameters up to 500 °C were analyzed.•Temperature and voltage ...dependence of the barrier height has been ascribed to interface states.
We have prepared high temperature stable Schottky MOS diodes on AlGaN/GaN heterostructure with Ir-Al oxide based gate oxide layer and analyzed current transport mechanism in these diodes up to very high temperatures. The thermionic emission analysis of I-V curves gave high ideality factor in between 2 and 3 decreasing with increasing temperature. Simulation of the thermionic transport with the barrier height extracted from the measured curves and ideality factor unity gave the simulated current densities many orders of magnitude higher than experimentally measured. We explained experimental data by a bias dependent barrier height as a result of thin dielectric layer and a bias dependent charge localized in interface traps between the semiconductor and this dielectric layer. The measured data are then explained by the thin dielectric layer at the interface between (GaN)AlGaN and the metal electrode. Increasing forward voltage and moving Fermi level towards conduction band the charge in the traps becomes negative and increases the effective barrier height for electrons moving from the semiconductor into the metal. By this mechanism also a linear increase of reverse current with bias can be explained. The opposite is true for the reverse voltage.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We have studied intersecting behaviour of
I–
V curves measured at different temperatures for inhomogeneous Schottky diodes with a common series resistance. Analytical expression for the voltage where
...I–
T curves have their minima and the existence of which is a necessary condition for the intersection of
I–
V curves was derived. It is shown that this voltage remains in the low voltage region where
I–
V curves of Schottky diodes are commonly measured.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We describe a new feature connected with Schottky barriers with nanosize dimensions. We found out by theoretical analysis that the
I–
V curves of such small diodes measured at different temperatures ...should intersect and consecutively at higher voltages larger current flows through the diode at lower temperatures. This effect which is at first glance in contradiction with the thermionic theory is caused by the series resistance influence. We show that the presence of the series resistance is a necessary condition of its observation. However, the intersection voltage—minimum voltage at which the intersection may occur—increases with the value of the series resistance and the diode dimensions for which the effect could be observable in Si diodes and the common series resistance values must be in submicrometer range. Diodes with several hundreds nanometers dimension have the intersection voltage ∼1
V. Analytical expression for the intersection voltage values was also derived.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Interface traps between dielectric and barrier layers influence the electrical properties of MISHEMT (metal–insulator–semiconductor heterojunction field effect transistor) structures. We demonstrate ...an approximate method for extraction of the density of interface traps from experimental MISH structures. First, the capacitance curve of an ideal structure without interface traps was generated by fitting the experimental curve in the capacitance plateau and depletion region. Then, the fit in the forward part of the curve was found by a trial and error method using several interface trap distributions. Special U‐shape interface trap distributions were used with different ratio between the magnitudes of the trap densities at the conduction‐band and valence‐band extremes and the middle of the energy gap. A very good fit between the experimental and the theoretical curve has been obtained for the interface trap density 1.3 × 1013 eV−1 cm−2 at the band edges and 1.3 × 1011 eV−1 cm−2 in the middle of the gap.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We studied theoretically the influence of the tunneling current on the leakage current in AlGaN Schottky diodes. It is shown that the most important conductance mechanism in these structures is the ...tunneling. The thermionic emission has lower influence on the total current practically throughout the whole reverse bias range and doping concentrations studied. For high doping concentrations we found very slow temperature dependence of the diode current.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We report on a classical approach used to calculate energy band diagrams of AlGaN/GaN heterostructures. We were able to calculate the band diagram and carrier concentrations by this method also when ...the external bias was applied on the structure. The potential on the Schottky barrier side of the structure is defined more exactly than in a self-consistent solution of Poisson and Schrödinger equations. Dependence of the band profile and the carrier concentration of the two-dimensional gas on the piezoelectric charge can also be calculated by this approach.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
