| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
Q9, Tunneling Current via Dislocations in AlGaN/GaN Schottky Contacts |
| Author(s) |
Peter Kordos, Jaroslav Kovac, Roman Sramaty, Jaroslava Skriniarova, Alexander Satka, Ales Chvala, Daniel Donoval |
| On-Site Speaker (Planned) |
Peter Kordos |
| Abstract Scope |
We present a study of the gate current in the Ni/AlGaN/GaN Schottky contacts by temperature dependent measurement of I-V characteristics and their analysis considering various transport mechanisms. Commercial AlGaN/GaN/SiC structure and conventional device processing with Ti/Al/Ni/Au ohmic and Ni/Au Schottky contacts were used. The gate characteristics were measured at temperatures between 150 and 550 K. The main results obtained can be summarized as follows: (i) The forward gate current vs voltage characteristics measured at different temperatures were successfully fitted considering thermionic emission, generation-recombination, and tunneling and leakage currents (fitting error <20%). These can be divided, in general, into three distinguish regions concerning the current transport mechanism. (ii) It is found that the thermionic emission dominates only at higher biases and thus it is not coincident with the measured I-V characteristic as commonly supposed. This is the reason of incorrectly evaluated low barrier heights and their increase with temperature (e.g. 0.16 eV at 80 K and 0.86 eV at 410 K [1], or 0.81 eV at 300 K and 1.27 eV at 475 K [2]). From our analysis it follows that the barrier height at room temperature is 1.36-1.39 eV with slightly negative temperature coefficient. (iii) Tunneling current dominates in the main part of I-V characteristics at all used temperatures. This can be explained by consideration that the current is caused by tunneling through dislocations in the space charge region. The saturation tunneling current can be described as I<SUB>TU,s(0K)</SUB> = q.v<SUB>D</SUB>.N<SUB>dis</SUB>.exp(φ<SUB>B</SUB>/E<SUB>TU</SUB>) [3]. The dislocation density N<SUB>dis</SUB> = (3-5)x10<SUP>8</SUP> cm2 was evaluated using experimental I<SUB>TU,s</SUB> = f(T) dependence. This reliable N<SUB>dis</SUB> value confirms our assumption that high number of dislocations affects significantly the current flow through the gate contact in AlGaN/GaN structures.
(iv) At low biases the leakage current dominates, as expected. However, this current depends on the structure used. It is shown that the gate current of the mesa-type device is higher than that of the planar devices and this additional current shows ohmic behavior. Mapping by EBIC yielded enhanced current located on the mesa-sidewall where the gate contact is placed. Two-dimensional simulation of the device structure confirms this observation and shows that the additional gate leakage current is originated by a current path through the mesa sidewall. |
| Proceedings Inclusion? |
Undecided |