G. I. Ng

Improved two-dimensional electron gas transport characteristics in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor with atomic layer-deposited Al2O3 as gate insulator

The effects of Al2O3 gate insulator grown by atomic layer deposition (ALD) system on the two-dimensional electron gas (2DEG) transport characteristics in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MISHEMT) were investigated. The shape of the electron lateral distribution in the quantum well at AlGaN/GaN interface was found to be slightly influenced by the Al2O3 thin layer. The drift mobility (μd) of the electrons in ALD-Al2O3/AlGaN/GaN MISHEMT is increased due to the surface passivation effects of the included dielectric layer. The higher dynamic channel current of the MISHEMT indicates that the electron saturation velocity (vsat) is also increased. These results show the improvement of the transport characteristics of 2DEG in Al2O3/AlGaN/GaN MISHEMT by the excellent properties of the Al2O3 grown by ALD.

Reduced surface leakage current and trapping effects in AlGaN/GaN high electron mobility transistors on silicon with SiN/Al2O3 passivation

The surface leakage currents and the surface trapping effects of the AlGaN/GaN high electron mobility transistors (HEMTs) on silicon with different passivation schemes, namely, a 120 nm plasma enhanced chemical vapor deposited SiN, a 10 nm atomic layer deposited (ALD) Al2O3 and a bilayer of SiN/Al2O3 (120/10 nm) have been investigated. After SiN passivation, the surface leakage current of the GaN HEMT was found to increase by about six orders; while it only increased by three orders after the insertion of Al2O3 between SiN and AlGaN/GaN. The surface conduction mechanism is believed to be the two-dimensional variable range hopping for all the samples. The leakage current in the etched GaN buffer layer with SiN/Al2O3 bilayer passivation was also much smaller than that with only SiN passivation. The pulse measurement shows that the bilayer of SiN/Al2O3 passivation scheme can effectively reduce the surface states and suppress the trapping effects.

Metamorphic InP/InGaAs double-heterojunction bipolar transistors on GaAs grown by molecular-beam epitaxy

InP/InGaAs double-heterojunction bipolar transistor (HBT) structures were grown metamorphically on GaAs substrates by solid-source molecular-beam epitaxy. A linearly graded InxGa1−xP (x varying from 0.48 to 1) buffer layer was used to accommodate the strain relaxation. The crystallinity of the buffer layer and the HBT structure was examined by x-ray diffractometry. Devices with 5×5 μm2 emitter area showed a typical peak current gain of 40, a common-emitter breakdown voltage (BVCEO) higher than 9 V, a current gain cut-off frequency (fT) of 46 GHz, and a maximum oscillation frequency (fmax) of 40 GHz.

Temperature dependence of Ohmic contact characteristics in AlGaN/GaN high electron mobility transistors from −50 to 200 °C

The temperature dependent characteristics of Ti/Al/Ni/Au Ohmic contact for AlGaN/GaN high electron mobility transistors (HEMTs) on high-resistivity Si and sapphire substrates were investigated over the temperature range from −50 to 200 °C. The sheet resistances (Rsh) of AlGaN/GaN HEMTs on Si and sapphire substrates were found to increase with the temperature according to the power-law equation with power indices of −2.7 and −2.3, respectively. The specific contact resistivity (ρC) decreased with the temperature, and it was observed to be determined by the electron thermionic field emission (TFE) from the lowered conduction band edge in the modified AlGaN region with high-density N-vacancies to the quantum well at the AlGaN/GaN heterojunction with two dimensional electron gas (2DEG). Three important parameters in the TFE are extracted, that is, the barrier height (ϕB) of around 0.5 eV, the energy difference between the effective conductive-band edge and the Fermi level in 2DEG (En) of around 0.1 eV, and th...

Atomic layer deposition of ZrO2 as gate dielectrics for AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors on silicon

In this Letter, the device performance of AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MISHEMTs) on silicon substrate using 10-nm-thick atomic-layer-deposited ZrO2 as gate dielectrics is reported. The ZrO2 AlGaN/GaN MISHEMTs showed improved maximum drain current density (Idmax) with high peak transconductance (gmmax) as comparison to Schottky-barrier-gate HEMTs (SB-HEMTs). Also compared to SB-HEMTs, reverse gate leakage current was four orders of magnitude lower and forward gate bias extended to +7.4 V. At energy from −0.29 eV to −0.36 eV, low interface trap state density evaluated by AC conductance and “Hi-Lo frequency” methods indicates good quality of atomic-layer-deposited ZrO2 dielectric layer.

Effect of gate-source and gate-drain Si3N4 passivation on current collapse in AlGaN∕GaN high-electron-mobility transistors on silicon

The effects of gate-source (GS) and gate-drain (GD) region passivation on the drain current (ID) collapse in AlGaN∕GaN high-electron-mobility transistors (HEMTs) were studied. Electrical stresses were applied to the GS and GD regions of HEMTs, (1) unpassivated (device A), (2) fully passivated (device B), (3) GD passivated only (device C), and (4) device C with additional full passivation (device D). An increase of ID density and the extrinsic transconductance was observed in devices with full Si3N4 passivation. Due to the increase of gate leakage current by Si3N4 passivation, breakdown voltage decreases. Device A exhibited severe (96%) ID collapse when it was electrically stressed in both the GS and GD regions. Devices C and D have suppressed only 14% of ID collapse after passivation. However, HEMTs with full Si3N4 passivation (device B) have suppressed more than 80% of the ID collapse. Full passivation is required to suppress the ID collapse effectively for AlGaN∕GaN HEMTs. The remaining ID collapse (19%...

Electrothermal Large-Signal Model of III–V FETs Including Frequency Dispersion and Charge Conservation

An empirical large-signal III-V field-effect transistor (FET) model has been developed. Three improved drain-source current (I-V) modeling equations capable of representing arbitrarily shaped transconductance (Gm) curves are proposed from level-1 to level-3. These models are characterized by the static dc and the multibias pulsed I-V measurements along with their dependences on temperature, so as to account for the frequency dispersion and the self-heating effects. By partitioning the Gm plots into five regions, specific parameters of the various model levels can be directly associated with the regions. Besides, the fitting parameters have inherent consistent definitions among different model levels, where some of the key model parameters can be extracted directly from measurements. For the gate-charge formulation (Q-V), a novel charge-conservative gate charge model is presented to accurately trace the nonlinear gate-source (C gs) and gate-drain (C gd) capacitance values. The comprehensive large-signal model is then validated by comparing the predicted I-V, C-V, S-parameters as well as power characteristics with the measured results of III-V FETs.

Temperature-dependent forward gate current transport in atomic-layer-deposited Al2O3/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor

The mechanisms of the temperature-dependent forward gate current transport in the atomic-layer-deposited Al2O3/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MISHEMT) were investigated. In contrast to the conventional Schottky-gate AlGaN/GaN HEMT, thermionic field emission was found not to be the dominant transport mechanism for the Al2O3/AlGaN/GaN MISHEMT. Fowler–Nordheim tunneling was found to be dominant at low temperature (T 0 °C).

Improved Linearity for Low-Noise Applications in 0.25-

Improved device linearity for low-noise applications has been demonstrated in 0.25-μm AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) using atomic-layer-deposited (ALD) Al2O3 as gate dielectric. The measured dc transconductance, microwave small signal, and noise performance feature less dependence on drain current as compared to conventional Schottky-gate AlGaN/GaN HEMTs. Two-tone intermodulation measurement shows that the MISHEMT has a higher value of third-order intercept (IP3). The improved device linearity suggests that the ALD Al2O3/AlGaN/GaN MISHEMT on high-resistivity silicon substrate is promising for high-linearity low-noise amplifier applications.

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The experimental and theoretical studies of electron multiplication in InP/InGaAs double heterojunction bipolar transistors (DHBTs) with an InGaAs/InP composite collector are carried out. Both local electric field model and energy model are used to investigate the electron impact ionization in the composite collector. The analysis reveals that the nonlocal effect of the electron impact ionization in the composite collector is responsible for the suppression of the contribution of electron multiplication in the InGaAs layer. Experimental results for the fabricated devices were compared with the theoretical calculations, indicating that the conventional impact ionization models based on the local electric field significantly overestimate the electron multiplication for the composite collector. The energy model which takes into account the nonlocal effect is found to provide a more accurate prediction of electron multiplication for the DHBTs.