Browsing by Author "Rorsman, Niklas"

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A versatile low-resistance ohmic contact process with ohmic recess and low-temperature annealing for GaN HEMTs
(2018-09-01)
Lin, Yen-Ku
;
Bergsten, Johan
;
Leong, Hector
;
Malmros, Anna
;
Chen, Jr-Tai
Deeply recessed ohmic contacts for GaN-based high electron mobility transistors (HEMTs) are demonstrated. It is shown that low-resistance ohmic contacts can be achieved with recessing beyond the AlGaN Schottky barrier where the ohmic contacts are formed on the sidewall of the recess. This makes the process versatile and relatively insensitive to the exact recess depth. The ohmic contact is based on a gold-free metallization scheme consisting of a Ta/Al/Ta metal stack requiring a low-temperature annealing. Important parameters for this type of ohmic contact process include the metal coverage, slope of the etched sidewall, bottom Ta-layer thickness, as well as annealing temperature and duration. The optimized contact resistance is as low as 0.24 Omega mm after annealing at 575 degrees C. Moreover, this sidewall contact approach was successfully implemented on different epitaxial heterostructures with different AlGaN barrier thickness as well as with and without AlN exclusion layer. All the samples exhibited excellent contact resistances in a wide range of recess depths. The Ta-based, sidewall ohmic contact process is a promising method for forming an ohmic contact on a wide range of GaN HEMT epitaxial designs.
Electrical Characterization and Transmission Electron Microscopy Assessment of Isolation of AlGaN/GaN High Electron Mobility Transistors with Oxygen Ion Implantation
(2010)
Shiu, Jin-Yu
;
Lu, Chung-Yu
;
Su, Ting-Yi
;
Huang, Rong-Tan
;
Zirath, Herbert
A multienergy oxygen ion implantation process was demonstrated to be compatible with the processing of high-power microwave AlGaN/GaN high electron mobility transistors (HEMTs). A high sheet resistivity and thermally stable isolation were demonstrated. The microstructures of implanted and postannealed specimens were investigated by transmission electron microscopy (TEM). The dependences of the sheet resistivity and different postannealing temperatures were correlated with the defect clusters and microstructure of lattice stacking faults. After 300 degrees C annealing, the sheet resistivity was higher than 10(12) Omega/square, which was attributed to the severe defect interaction eliminating the trapping centers and reducing the leakage current. A maximum output power density of 5.3 W/mm at V(gs) = -4 V and V(ds) = 50 V at 3 GHz was demonstrated on lag-free HEMTs without field plates on sapphire substrate. (C) 2010 The Japan Society of Applied Physics
Oxygen ion implantation isolation planar process for AlGaN/GaN HEMTs
(2007-06-01)
Shiu, Jin-Yu
;
Huang, Jui-Chien
;
Desmaris, Vincent
;
Chang, Chia-Ta
;
Lu, Chung-Yu
A multienergy oxygen ion implantation process was demonstrated to be compatible With the processing of high-power microwave AlGaN/GaN high electron mobility transistors (HEMTs). HEMTs that are isolated by this process exhibited gate-lag- and drain-lag-free operation; A maximum output power density of 5.3 W/mm at V-gs = -4 V and V-ds = 50 V and a maximum power added efficiency of 51.5% at V-gs = -4 V and V-ds = 30 V at 3 GHz were demonstrated on HEMTs without field plates on sapphire substrate. This isolation process results in planar HEMTs, circumventing potential problems with enhanced gate leakage due to the gate contacting the 2-D electron gas at the mesa sidewall.
Transmission electron microscopy assessment of the Si enhancement of Ti/Al/Ni/Au Ohmic contacts to undoped AIGaN/GaN heterostructures
(2006-08-01)
Desmaris, Vincent
;
Shiu, Jin-Yu
;
Lu, Chung-Yu
;
Rorsman, Niklas
;
Zirath, Herbert
The microstructure of Si/Ti/Al/Ni/Au was investigated using transmission electron microscopy and energy dispersive x-ray spectroscopy. The dependence of the contact resistance on the silicon layer thickness and the temperature was correlated to the microstructure of the alloyed contacts. The enhancement of the contact resistance by inserting a 30 angstrom thick Si layer under the Ti/Al/Ni/Au metallization was attributed to diffusion of the contact into the AlGaN layer. Increasing the Si thickness and or the temperature resulted in the formation of Gold (Au)-based silicides, which prevent the formation of low interfacial TiN or AlN layers. (c) 2006 American Institute of Physics.