| About this Abstract |
| Meeting |
2010 Electronic Materials Conference
|
| Symposium
|
TMS 2010 Electronic Materials Conference
|
| Presentation Title |
BB5, Nearly Ideal Current-Voltage Characteristics of Schottky Barrier Diodes Directly Formed on GaN Free-Standing Substrates |
| Author(s) |
Jun Suda, Kazuki Yamaji, Yuichirou Hayashi, Tsunenobu Kimoto, Kenji Shimoyama, Hideo Namita, Satoru Nagao |
| On-Site Speaker (Planned) |
Jun Suda |
| Abstract Scope |
GaN-based electronic devices have attracted much attention due to its potential for low on-resistance and high operation temperature. At present, these devices are fabricated by using epitaxial layers. On the other hand, most of Si electronic devices are directly formed on Si substrate without epitaxial growth process. Recently, high-quality GaN free-standing substrates are available by various methods. It is important to assess the possibility of GaN-based electronic devices directly formed on GaN substrates. In this study, we fabricated Schottky barrier diodes directly on hydride vapor phase epitaxy (HVPE)-grown GaN free-standing substrates.
Substrates with different donor concentrations ranging from 1x10<SUP>16</SUP> to 2x10<SUP>17</SUP> cm<SUP>-3</SUP> were prepared. The threading-dislocation densities (TDD) of these substrates were estimated to be 3x10<SUP>6</SUP> cm<SUP>-2</SUP> by cathodoluminescence mapping. After formation of backside Ohmic contacts by Ti/Al, Ni Schottky contacts were formed by physical evaporation directly on chemical mechanical polished (CMP) GaN surfaces. The diameter of electrode is 100-300 μm.
Current-voltage (I-V) characteristics and capacitance-voltage (C-V) characteristics were measured at room temperature. We have measured 10-50 diodes for each substrate. A small number of diodes exhibited leaky characteristics. We excluded these diodes from the following analysis, since these diodes may contain macroscopic defects originating from substrate itself or device processing. The diodes showed ideal forward I-V characteristics. The I-V curves were well fitted by the formula (I=I<SUB>0</SUB>{exp(eV/nkT)-1}) with series resistance. Ideality factors (n) of the diodes were 1.02-1.03 for all substrate. Barrier heights of these diodes were estimated to be 0.93 eV from I<SUB>0</SUB>. Almost identical barrier heights were obtained from built-in potential of 1/C<SUP>2</SUP>-V plots. The doping range investigated is rather high. In the case, thermionic field emission (TFE) instead of simple thermionic emission (TE) should be considered. We calculated reverse I-V characteristics by TFE theory with values of barrier height and accurate doping concentration obtained from forward I-V and C-V characteristics. Measured reverse I-V characteristics showed excellent agreement with the calculations. The agreement was observed for all diodes with the doping range investigated.
As a reference, we also fabricated Schottky diodes on GaN heteroepitaxial layers grown on sapphire substrates by metalorganic vapor phase epitaxy (MOVPE). The TDD of layers was 10<SUP>9</SUP> cm<SUP>-2</SUP>. The diodes exhibited good forward characteristics. However, for reverse bias, measured currents were four orders of magnitude larger than that predicted from TFE theory. Reverse leakage is severely affected by high-density threading dislocations in the MOVPE-grown GaN diodes.
These results indicate that surface damaged layer due to CMP process and leakage current due to threading dislocations (3x10<SUP>6</SUP> cm<SUP>-2</SUP>) are negligible for Schottky diodes directly fabricated on HVPE-grown GaN substrates with doping range of 1x10<SUP>16</SUP> to 2x10<SUP>17</SUP> cm<SUP>-3</SUP>. Our results show that CMP-processed HVPE-grown GaN substrates have a potential for electronic device fabrication. |
| Proceedings Inclusion? |
Undecided |