Browsing by Author "Lu, Chung-Yu"

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30-GHz Low-Noise Performance of 100-nm-Gate-Recessed n-GaN/AlGaN/GaN HEMTs
(2010-02-01)
Chang, Chia-Ta
;
Hsu, Heng-Tung
;
Chang, Edward Yi
;
Kuo, Chien-I
;
Huang, Jui-Chien
We demonstrate a 100-nm-gate-recessed n-GaN/AlGaN/GaN high-electron mobility transistor (HEMT) with low-noise properties at 30 GHz. The recessed GaN HEMT exhibits a low ohmic-contact resistance of 0.28 Omega . mm and a low gate leakage current of 0.9 mu A/mm when biased at V(GS) = -3 V and V(DS) = 10 V. At the same bias point, a minimum noise figure of 1.6 dB at 30 GHz and an associated gain of 5 dB were achieved. To the best of our knowledge, this is the best noise performance reported at 30 GHz for gate-recessed AlGaN/GaN HEMTs.
460-nm InGaN-Based LEDs Grown on Fully Inclined Hemisphere-Shape-Patterned Sapphire Substrate With Submicrometer Spacing
(2009-10-01)
Chang, Chia-Ta
;
Hsiao, Shih-Kuang
;
Chang, Edward Yi
;
Hsiao, Yu-Lin
;
Huang, Jui-Chien
This letter investigates 460-nm InGaN-based light-emitting diodes (LEDs) grown on a hemisphere-shape-patterned sapphire substrate (HPSS) with submicrometer spacing. The full-width at half-maximum of the (102) plane rocking curves for GaN layer grown on a conventional sapphire substrate (CSS) and HPSS are 480 and 262 arcsec, respectively. Such improvement is due to the reduction of the pure edge threading dislocations. At the forward current of 20 mA, the light output power of the LEDs grown on CSS and HPSS were 4.05 and 5.86 mW, respectively. This improvement of 44% light-output power can be attributed to the improved quality of the material and the increase of the light extraction by the fully inclined facets of the HPSS.
Changes of Electrical Characteristics for AlGaN/GaN HEMTs Under Uniaxial Tensile Strain
(2009-03-01)
Chang, Chia-Ta
;
Hsiao, Shih-Kuang
;
Chang, Edward Yi
;
Lu, Chung-Yu
;
Huang, Jui-Chien
This letter investigates the characteristics of unpassivated AlGaN/GaN high-electron mobility transistors (HEMTs) under uniaxial tensile strain. Mechanical stress can produce additional charges that change the HEMT channel current. is phenomenon is dependent upon gate orientation and may be the result of the piezoelectric effect and changes in electron mobility due to the applied uniaxial stress. In addition, results show that tensile strain reduces the transient current, which is, likely due to the additional donorlike surface states created through the piezoelectric effect.
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
Enhancement of the Schottky barrier height using a nitrogen-rich tungsten nitride thin film for the schottky contacts on AlGaN/GaN heterostructures
(2008-05-01)
Lu, Chung-Yu
;
Chang, Edward Yi
;
Huang, Jui-Chien
;
Chang, Chia-Ta
;
Lin, Mei-Hsuan
Tungsten, stoichiometric W2N, and nitrogen-rich W2N films were used as Schottky contacts on AlGaN/GaN heterostructures. The nitrogen content in the film was controlled by varying the nitrogen-to-argon gas flow ratio during the reactive sputter deposition. The diode with the nitrogen-rich film exhibited a higher Schottky barrier height and the leakage current was comparable to that of the Ni/Au Schottky contact. Analysis suggested that this was due to the increase of the tungsten nitride work function as the result of higher nitrogen incorporation. Furthermore, after 600 degrees C thermal annealing, the diode was stable and showed no change in the leakage current.
GaN HEMT with Nitrogen-Rich Tungsten Nitride Schottky Gate and Method of Forming the Same
(2011-03-10)
Chang, Edward Yi
;
Lu, Chung-Yu
A GaN HEMT with Schottky gate is disclosed. The GaN HEMT sequentially has a GaN layer, an AlGaN layer, and a Schottky gate on a substrate, and a source and a drain on two sides of the Schottky gate. The Schottky gate is made by a material of nitrogen-rich tungsten nitride, which has a nitrogen content of about 0.5 molar ratio.
Linearity Characteristics of Field-Plated AlGaN/GaN High Electron Mobility Transistors for Microwave Applications
(2010)
Huang, Jui-Chien
;
Hsu, Heng-Tung
;
Chang, Edward-Yi
;
Lu, Chung-Yu
;
Chang, Chia-Ta
A field-plated (FP) AlGaN/GaN high electron mobility transistor (HEMT) was fabricated. Investigations on the linearity characteristics were performed through two-tone and wide band code division multiple access (WCDMA) modulated excitations. The FP-HEMT exhibited an improved breakdown voltage of 160 V compared with that of the conventional HEMT. Additionally, a higher output power of 25.4 dBm with 43% power added efficiency at a 30 V drain bias at 2 GHz was achieved. When biased at 30 V and 15 mA/mm current density, the third-order intermodulation (IM3) level was measured to be -27.1 dBc (at P(1dB)) and the adjacent channel power rejection (ACPR) was -33.8 dBc (at P(1dB)) under WCDMA modulation at 2 GHz. Measurement results revealed that the field-plated structure improved the linearity performance over the conventional structure at high output power levels even beyond P(1dB). (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.
RF Characteristics of AlGaN/GaN HEMTs under Different Temperatures
(2012-01-01)
Chiu, Yu-Sheng
;
Huang, Jui-Chien
;
Lin, Tai-Ming
;
Chou, Yu-Ting
;
Lu, Chung-Yu
We present the Rf characteristics of 0.7-mu m gate length n-GaN/AlGaN/GaN high-electron mobility transistors (HEMTs) with different source-drain spacing tested under different temperatures.. The 7-mu m source-drain spacing device demonstrated 800 mA/mm drain current density and 257 mS/mm tranceconductance, and the 5-mu m source-drain spacing device demonstrated 700 mA/mm drain current density and 260 mS/mm tranconductance. The 7-mu m source-drain spacing device was measured at room temperatures of 25 degrees C and -40 degrees C, the current gain (f(T)) were 18 GHz and 21GHz and the maximum oscillation (f(max)(U)) frequency were 63 GHz-and 87 GHz, respectively The f(T) was nearly linearly dependent on the temperature. As operating temperature increased from -40 degrees C to 50 degrees C, the f(T) dropped more dramatically for the 5-mu m SD spacing device than for the 7-mu m device. The f(max) characteristic of 5-mu m SD spacing device decreases more dramatically above 125 degrees C than the 7-mu m SD spacing device. This phenomenon might be due to stronger phonon scattering for shorter channel device at high temperatures.
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.