Chung-Yu Lu

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.

Electrical Characterization of

Ex situ sulfide and HCl wet chemical treatments in conjunction with in situ trimethyl aluminum (TMA) pretreatment were performed before the deposition of Al2O3 on n-InAs surfaces. X-ray photoelectron spectroscopy analyses show a significant reduction of InAs native oxides after different treatments. The capacitance-voltage C- V characterization of Al2O3/n-InAs structures shows that the frequency dispersion in the accumulation regime is small (<; 0.75%/dec) and does not seem to be significantly affected by the different surface treatments, whereas the latter improves depletion and inversion behaviors of the n-channel metal-oxide-semiconductor capacitors. The interface trap density profiles extracted from the simulation mainly show donorlike interface states inside the InAs band gap and in the lower part of the conduction band. The donorlike traps inside the InAs band gap and in the lower part of the conduction band were significantly reduced by using wet-chemical-plus-TMA treatments, in agreement with C-V characteristics.

\hbox{Al}_{2} \hbox{O}_{3}

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.

/n-InAs Metal–Oxide–Semiconductor Capacitors With Various Surface Treatments

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.

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

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 30A 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.

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

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.

Transmission electron microscopy assessment of the si enhancement of Ti/Al/Ni/Au ohmic contacts to undoped AlGaN/GaN heterostructures

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.