Chia-Ta Chang

Changes of Electrical Characteristics for AlGaN/GaN HEMTs Under Uniaxial Tensile Strain

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. This 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.

460-nm InGaN-Based LEDs Grown on Fully Inclined Hemisphere-Shape-Patterned Sapphire Substrate With Submicrometer Spacing

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.

30-GHz Low-Noise Performance of 100-nm-Gate-Recessed n-GaN/AlGaN/GaN HEMTs

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 ¿·mm and a low gate leakage current of 0.9 ¿A/mm when biased at VGS = -3 V and VDS = 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.

Material growth and device characterization of AlGaN/GaN single-heterostructure and AlGaN/GaN/AlGaN double-heterostructure field effect transistors on Si substrates

An Al0.2Ga0.8N/GaN/Al0.1Ga0.9N double-heterostructure field effect transistor (DH-FET) structure was grown on a 150-mm-diameter Si substrate and the crystalline quality of the epitaxial material was found to be comparable to that of an Al0.2Ga0.8N/GaN single-heterostructure field effect transistor (SH-FET) structure. The fabricated DH-FET shows a lower buffer leakage current of 9.2 × 10−5 mA/mm and an improved off-state breakdown voltage of higher than 200 V, whereas the SH-FET shows a much higher buffer leakage current of 6.0 × 10−3 mA/mm and a lower breakdown voltage of 130 V. These significant improvements show that the Al0.2Ga0.8N/GaN/Al0.1Ga0.9N DH-FET is an effective structure for high-power electronic applications.

Linearity Characteristics of Field-Plated AlGaN/GaN High Electron Mobility Transistors for Microwave Applications

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 P1dB) and the adjacent channel power rejection (ACPR) was -33.8 dBc (at P1dB) 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 P1dB.

Investigation of impact ionization from In x Ga 1-x As to InAs Channel HEMTs for high speed and low power applications

80-nm high electron mobility transistors (HEMTs) with different indium content in In_xGa_1-xAs channel from 52%, 70% to 100% have been fabricated. Device performance degradation were observed on the DC measurement and RF characteristics caused by impact ionization at different drain bias, >0.8 V (InAs/In_0.7Ga_0.3As), >1 V (In_0.7Ga_0.3As) and >1.5 V (In_0.52Ga_0.48As), respectively. The impact ionization phenomenon should be avoided for high speed, low power application because it limits the highest drain bias of the device which in turn limits the drift velocity under specific applied electric field.

An Al2O3 AlGaAs/InGaAs Metal-Oxide-Semiconductor PHEMT SPDT Switch with Low Control Currents for Wireless Communication Applications

An AlGaAs/InGaAs metal-oxide-semiconductor pseudomorphic high electron mobility transistor (MOS-PHEMT) single-pole-double-throw (SPDT) switch using Al 2 O 3 high-κ gate dielectric by atomic layer deposition is fabricated. The MOS-PHEMT exhibited a comparable dc performance and a much lower gate current compared to PHEMT. Radio-frequency (rf) test shows that the MOS-PHEMT switch has an insertion loss of less than 0.5 dB, an isolation larger than 30 dB, a return loss larger than 15 dB, and an input power for 1 dB compression of 31.4 dBm at 2.5 GHz. Overall, MOS-PHEMT monolithic microwave integrated circuits switches have comparable rf performance to PHEMT switches but with much lower dc power consumption.