The microstructure and electrical properties of directly deposited TiN ohmic contacts to Gallium Nitride.
- PDF / 1,753,560 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 43 Downloads / 210 Views
STRACT When the stoichiometric TiN was deposited directly on GaN, we obtained columnar TiN grains of 5-20 nm section which cross the whole film thickness and are rotated mostly around the [111] axis. The conventional epitaxial relationship is obtained and no amorphous patches are observed at the interface. The deposition of TiN on Si doped GaN layers lead to the formation of an ohmic contact, whereas we obtain a rectifying contact on p type layers. INTRODUCTION The performance of optoelectronic devices and transistors depends critically on the contact resistance. Hence, a successful development of reliable ohmic contacts on GaN is of great practical importance. Until now, the best results include Ti as the first layer deposited on the GaN surface (1,2). In the case of Ti/Al, a thin layer of titanium (20 nm) is first deposited and covered by aluminium to a total thickness of 100-200nm. The ohmic contact forms during a subsequent anneal at temperatures which can be as high as 900°C, and it has been shown to be due to a thin TiN film from the reaction of Ti with GaN (3). In this process, resistivity in the range of 10-5 ohm.cm2 is obtained upon 1018 cm-3 silicon doped GaN layers. During the annealing steps many reactive phases form between Al, Ga, Ti and N which may be a problem for the quality of the contact. Moreover, the formation of TiN may lead to a loss of N from the GaN surface layer, as well as to an excess of Ga in the reactive area. One of the ways to avoid these drawbacks would be to deposit TiN directly on the GaN surface. In this work, a
F99W11.75 Downloaded from https://www.cambridge.org/core. University of Birmingham, on 14 Apr 2020 at 08:37:55, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300005226
comparative TEM investigation has been carried out on annealed Al/Ti/GaN and directly deposited TiN films on GaN. EXPERIMENTAL Two types of specimens were investigated. In one case, a 20 nm Ti film was deposited on GaN and covered by a 80nm Al layer in order to avoid mostly the interaction of titanium with air. They were then submitted to a rapid thermal annealing for 10 seconds at 500°C. In the other case, TiN contacts were deposited at room temperature on the GaN films by dc reactive magnetron sputtering using an Alcatel SCM 600 deposition system equipped with an in situ ultrafast spectroscopic ellipsometer. Details of the deposition system are presented elsewhere (4). First, the samples were cleaned in air with a HCl:H2O (1:1) solution and loaded into the deposition chamber. Then, a very low energy (~ 5 eV) Ar+ ion dry etching was used to remove the native surface oxide just before the deposition. The working and reactive gases were respectively Ar (99.999%) and N2 (99.999%). The deposition conditions of the substrate bias voltage Vb was -40 or -120 V and the N2 flow rate was about 2 sccm. The Ar flow was kept constant at 15 sccm with a partial pressure of 7.5x10-3 mbar. In-situ spectroscopic ellipsometry investigations hav
Data Loading...
