Geok Ing Ng

AlGaN/GaN two-dimensional-electron gas heterostructures on 200 mm diameter Si(111)

This Letter reports on the epitaxial growth, characterization, and device characteristics of crack-free AlGaN/GaN heterostructures on a 200 mm diameter Si(111) substrate. The total nitride stack thickness of the sample grown by the metal-organic chemical vapor deposition technique is about 3.3 ± 0.1 μm. The structural and optical properties of these layers are studied by cross-sectional scanning transmission electron microscopy, high-resolution x-ray diffraction, photoluminescence, and micro-Raman spectroscopy techniques. The top AlGaN/GaN heterointerfaces reveal the formation of a two-dimensional electron gas with average Hall mobility values in the range of 1800 to 1900 cm2/Vs across such 200 mm diameter GaN on Si(111) samples. The fabricated 1.5 μm-gate AlGaN/GaN high-electron-mobility transistors exhibited the drain current density of 660 mA/mm and extrinsic transconductance of 210 mS/mm. These experimental results show immense potential of 200-mm diameter GaN-on-silicon technology for electronic devi...

High Microwave-Noise Performance of AlGaN/GaN MISHEMTs on Silicon With

High microwave-noise performance is realized in AlGaN/GaN metal-insulator semiconductor high-electron mobility transistors (MISHEMTs) on high-resistivity silicon substrate using atomic-layer-deposited (ALD) Al₂O₃ as gate insulator. The ALD Al₂O₃/AlGaN/GaN MISHEMT with a 0.25- ¿m gate length shows excellent microwave small signal and noise performance. A high current-gain cutoff frequency <i>fT</i> of 40 GHz and maximum oscillation frequency <i>f</i> _max of 76 GHz were achieved. At 10 GHz, the device exhibits low minimum-noise figure (NF_min) of 1.0 dB together with high associate gain (<i>Ga</i>) of 10.5 dB and low equivalent noise resistance (<i>Rn</i>) of 29.2 ¿. This is believed to be the first report of a 0.25-¿m gate-length GaN MISHEMT on silicon with such microwave-noise performance. These results indicate that the AlGaN/GaN MISHEMT with ALD Al₂O₃ gate insulator on high-resistivity Si substrate is suitable for microwave low-noise applications.

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

We report for the first time the DC and microwave characteristics of sub-micron gate (~0.3 µm) AlGaN/GaN high-electron-mobility transistors (HEMTs) on 8-in. diameter Si(111) substrate. The fabricated sub-micron gate devices on crack-free AlGaN/GaN HEMT structures exhibited good pin.-off characteristics with a maximum drain current density of 853 mA/mm and a maximum extrinsic transconductance of 180 mS/mm. The device exhibited unit current-gain cut-off frequency of 28 GHz, maximum oscillation frequency of 64 GHz and OFF-state breakdown voltage of 60 V. This work demonstrates the feasibility of achieving good performance AlGaN/GaN HEMTs on 8-in. diameter Si(111) for low-cost high-frequency and high-power switching applications.

Gate Insulator Grown by ALD

We have demonstrated 0.15-µm-gate-length AlGaN/GaN high-electron-mobility transistors (HEMTs) with direct-current (DC) and microwave performances for the first time using a complementary metal–oxide–semiconductor (CMOS)-compatible non-gold metal stack. Si/Ta-based ohmic contact exhibited low contact resistance (Rc=0.24 Ωmm) with smooth surface morphology. The fabricated GaN HEMTs exhibited gmmax=250 mS/mm, fT/fmax=39/39 GHz, B Vgd=90 V, and drain current collapse <10%. The device Johnsons figure of merit (J-FOM = fT × B Vgd) is in the range between 3.51 to 3.83 THzV which are comparable to those of other reported GaN HEMTs on Si with a conventional III–V gold-based ohmic contact process. Our results demonstrate the feasibility of realizing high-performance submicron GaN-on-silicon HEMTs using a Si CMOS-compatible metal stack.

Direct Current and Microwave Characteristics of Sub-micron AlGaN/GaN High-Electron-Mobility Transistors on 8-Inch Si(111) Substrate

In this Letter, an optical gradient force driven Nanoelectromechanical Systems (NEMS) actuator, which is controlled by the Q-factor attenuation of micro-ring resonator, is demonstrated. The actuator consists of a tunable actuation ring resonator, a sensing ring resonator, and a mechanical actuation arc. The actuation displacement can reach up to 14 nm with a measured resolution of 0.8 nm, when the Q-factor of the ring resonator is tuned from 15 × 103 to 6 × 103. The potential applications of the NEMS actuator include single molecule manipulation, nano-manipulation, and high sensitivity sensors.

Demonstration of submicron-gate AlGaN/GaN high- electron-mobility transistors on silicon with complementary metal-oxide-semiconductor-compatible non-gold metal stack

The band alignment between Ga-face GaN and atomic-layer-deposited ZrO2 was investigated using X-ray photoelectron spectroscopy (XPS). The dependence of Ga 3d and Zr 3d core-level positions on the take-off angles indicated upward band bending at GaN surface and potential gradient in ZrO2 layer. Based on angle-resolved XPS measurements combined with numerical calculations, valence band discontinuity ΔEV of 1 ± 0.2 eV and conduction band discontinuity ΔEC of 1.2 ± 0.2 eV at ZrO2/GaN interface were determined by taking GaN surface band bending and potential gradient in ZrO2 layer into account.

A nanoelectromechanical systems actuator driven and controlled by Q-factor attenuation of ring resonator

The effect of silicon nitride passivation on the electrical characteristics of InP/InGaAs heterojunction bipolar transistors (HBTs) has been investigated comprehensively. The major degradations of I–V characteristics identified in our InP/InGaAs HBTs are: (1) the decrease of current gain due to a significant increase in the forward base leakage current and (2) large increase of base-collector (B-C) and base-emitter (B-E) reverse leakage currents. We found that different physical origins should be attributed to these two degradation behaviors.

Band alignment between GaN and ZrO2 formed by atomic layer deposition

Electrical and structural properties of strontium titanate (SrTiO3) thin films deposited on Si and GaAs substrates by a conventional radio frequency-magnetron sputtering technique at different oxygen (O2) partial pressures and substrate temperatures have been reported. Dielectric constant of the as-deposited samples increases with the substrate temperature as well as the O2 partial pressure. However, it shows a decreasing trend at higher O2 partial pressure values. When the samples were annealed for 1 h at temperatures above 500 °C the dielectric constant value of the SrTiO3 (STO) films increased by five times and a maximum value of 147 was obtained. The increase in the dielectric constant value is reflected in x-ray diffraction measurements with the development of high intensity lines corresponding to STO phase. The thickness dependence of the dielectric constant is also reported. Thin film STO capacitors fabricated with Pt as top and bottom electrodes showed low leakage current densities and a high brea...

Studies on the Degradation of InP/InGaAs/InP Double Heterojunction Bipolar Transistors Induced by Silicon Nitride Passivation

We report, for the first time, the successful fabrication of aluminum-free metamorphic (MM) InP/In/sub 0.53/ Ga/sub 0.47/ As/InP double heterojunction bipolar transistors (DHBTs) on GaAs substrates with a linearly graded In/sub x/Ga/sub 1-x/P buffer grown by solid-source molecular beam epitaxy (SSMBE). Devices with 5/spl times/5 /spl mu/m/sup 2/ emitters display a peak current gain of 40 and a common-emitter breakdown voltage (BV/sub CE0/) higher than 9 V, a current gain cut-off frequency (f/sub T/) of 48 GHz and a maximum oscillation frequency (f/sub max/) of 42 GHz. A minimum noise figure of 2.9 dB and associated gain of 19.5 dB were measured at a collector current level of 2.6 mA at 2 GHz. Detailed analysis suggests that the degradation of the base-emitter heterojunction interface and the increase of bulk recombination are the most probable causes for the poorer device performance of current metamorphic HBTs compared with lattice-matched HBTs.

Preparation and characterization of rf-sputtered SrTiO3 thin films

The electrical properties of InP/InGaAs HBTs have been comprehensively investigated between room and near liquid helium temperature. Physical mechanisms for the devices operated in different temperature ranges have been clearly identified. The low temperature measurements indicate that, in the temperature range of 240 K to 300 K, the base current is dominated by electron-hole band-to-band recombination; in the temperature range 77 K to 240 K, trap-related recombination (Shockley-Read-Hall recombination) plays an important role in determining base current; and for temperature lower than 77 K, the collector and base currents are found to be limited by electron tunneling through the barrier formed by the conduction-band discontinuity at the E-B junction. These findings provide us with better physical insight of the device operation at low temperature, which is particularly important for the optimization of InP HBT technology for low temperature applications as well as the development of a quantitative model for circuit design.