| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
Q3, MBE Regrown Ohmic Contacts with Rc of 0.15 ohm-mm in InAlN/GaN High Electron Mobility Transistor |
| Author(s) |
Jia Guo, Jai Verma, Yu Cao, Xiang Gao, Shiping Guo, Ed Beam, Andrew Ketterson, Michael Schuette, Paul Saunier, Mark Wistey, Debdeep Jena, Huili (Grace) Xing |
| On-Site Speaker (Planned) |
Jia Guo |
| Abstract Scope |
GaN-based high electron mobility transistors (HEMTs) have been adopted as power amplifiers in the wireless communication base stations and switches in power conditioning applications. To further improve the device performance and reliability, e.g. operating at higher frequencies and higher efficiency, it is highly desirable to minimize parasitics. Among all parasitics ohmic contact resistance is an important one to minimize since that in GaN-based HEMTs, due to its large bandgap, is generally 3-5 X higher than that in InGaAs-based HEMTs. Numerous approaches, including ion implantation, ohmic regrowth, recessed ohmics and plasma pre-treatment, have been studied with various degrees of success on GaN based HEMTs. In this work, we report our results on ohmic regrowth on metal face lattice matched InAlN/GaN HEMTs heterostructures. A total contact resistance of 0.15 ohm-mm was obtained, which is the lowest reported to date on InAlN/AlN/GaN HEMTs. Temperature dependent measurements indicate that there is a minimal barrier (< 74 ueV) existing between the regrown n++GaN and the 2-dimensional electron gas (2DEG) channel. The InAlN/GaN sample used in this work was grown by metal-organic chemical vapour deposition (MOCVD) on SiC substrate at IQE RF LLC. It consists of 5.2 nm InAlN barrier with 1 nm AlN on top of semi-insulating GaN. SiN mask was first deposited using plasma-enhanced chemical vapour deposition (PECVD) and then patterned by reactive ion etching (RIE). With the patterned SiN as mask InAlN/AlN/GaN was etched down for 50 nm in the ohmic region. Heavily doped GaN:Si of 100 nm was then grown on top of the patterned sample by molecular beam epitaxy (MBE) using the conditions described by Yu Cao . Polycrystalline GaN deposited on top of SiN mask during regrowth was lifted off by HF. Ohmic contacts were formed by deposition of Ti/Al based metallization stack and annealed at 800 oC. Rc ~ 0.15 ohm.mm was obtained at room temperature from transmission line method (TLM) measurement and TLM gaps were measured by a scanning electron microscope (SEM). It was found that Rc remained almost constant to 77 K and then increased to ~ 0.24 ohm.mm at 4 K, accompanied by monotonic decrease of sheet resistance from 474 ohm/sq. at room temperature to 243 ohm/sq. at 4 K. This small contact resistance observed over a large temperature window, particularly at cryogenic temperatures, indicates that a minimal barrier for electron flow was introduced at the regrowth interface. High resolution transmission electron microscope (TEM) images also confirmed that the regrown GaN is in an intimate contact with the HEMT channel. This study coupled with variations of process and regrowth conditions thus allows us to further optimize these regrown contacts. |
| Proceedings Inclusion? |
Undecided |