Temperature and field dependent low frequency noise characterization of Ge n-FETs

We report temperature (RT-150 K) and field dependent low frequency noise measurements on Ge n-FETs. Specifically, we delineate the temperature, field, and interfacial layer (GeON vs. GeO2) dependence of the gate overdrive index (beta) on corresponding changes in volume interface trap density (N-it) and mobility (mu). For N-it 1 x 10(20) cm(-3) eV(-1) near the conduction band edge, changes in mu as well as N-it determine the noise mechanism. Finally, we show that the beta values of Ge n-FETs are significantly different from conventional Si transistors as well as Ge p-FETs at RT and 150 K due to much higher N-it and/or mu values of the Ge n-FETs. Published by AIP Publishing

Plasma-assisted low energy N-2 implant for V-fb tuning of Ge gate stacks

This work reports V-fb tuning of TiN/HfO2 gate stacks on Ge using low energy plasma-assisted doping with N-2 without significant impact on gate capacitance and gate/channel interface trap densities. As required for multi-V-T Ge p-FinFETs, controlled change in effective work function up to 180mV from the near midgap to the near valence band edge of Ge is demonstrated by varying implant dose and energy. Unlike Si gate stacks, increased gate leakage in implanted Ge gate stacks is shown to result from traps created in the HfO2 layer during the implant and exposed to channel carriers due to a low band offset GeO2 interfacial layer (IL). Recovery of gate leakage is demonstrated by substituting GeO2 with an Al2O3 IL. Further, a simple physical model is proposed to extract the work function and oxide charge components of the change in V-fb for varying implant doses and energies. Published by AIP Publishing

Demonstration of beta-(AlxGa1-x)(2)O-3/Ga2O3 double heterostructure field effect transistors

In this work, we demonstrate modulation-doped beta-(AlxGa1-x)(2)O-3/Ga2O3 double heterostructure field effect transistors. The maximum sheet carrier density for a two-dimensional electron gas (2DEG) in a beta-(AlxGa1-x)(2)O-3/Ga2O3 heterostructure is limited by the conduction band offset and parasitic channel formation in the barrier layer. We demonstrate a double heterostructure to realize a beta-(AlxGa1-x)(2)O-3/Ga2O3/(AlxGa1-x)(2)O-3 quantum well, where electrons can be transferred from below and above the beta-Ga2O3 quantum well. The confined 2DEG charge density of 3.85 x 10(12) cm(-2) was estimated from the low-temperature Hall measurement, which is higher than that achievable in a single heterostructure. Hall mobilities of 1775 cm(2)/V.s at 40 K and 123 cm(2)/V.s at room temperature were measured. Modulation-doped double heterostructure field effect transistors showed a maximum drain current of I-DS = 257mA/mm, a peak transconductance (g(m)) of 39 mS/mm, and a pinch-off voltage of -7.0 V at room temperature. The three-terminal off-state breakdown measurement on the device with a gate-drain spacing (L-GD) of 1.55 mu m showed a breakdown voltage of 428 V, corresponding to an average breakdown field of 2.8 MV/cm. The breakdown measurement on the device with a scaled gate-drain spacing of 196 nm indicated an average breakdown field of 3.2 MV/cm. The demonstrated modulation-doped beta-(AlxGa1-x)(2)O-3/Ga2O3 double heterostructure field effect transistor could act as a promising candidate for high power and high frequency device applications. Published by AIP Publishing

Understanding PBTI in Replacement Metal Gate Ge n-Channel FETs With Ultrathin Al2O3 and GeOx ILs Using Ultrafast Charge Trap-Detrap Techniques

We report positive bias temperature instability data in replacement metal gate Ge n-channel metaloxide-semiconductor field-effect transistors with an in situ gate stack employing an ultrathin (5 angstrom), stable Al2O3 interlayer (IL) using ultrafast (similar to microseconds) characterization techniques that ensure recovery artifactfree measurements. Comparison with state-of-the-art GeOx IL is also reported besides establishing correlations between band-edge interface trap density (D-it), mobility (mu), and threshold voltage (V-T) instability. Ultrafast measure-stress-measure (UF-MSM), ultrafast measure-stress-detrap-measure (UF-MSDM), stress-induced-leakage-current (SILC), direct-current current-voltage (DCIV), split capacitance-voltage (C-V), and low-temperature full conductance techniques along with a compact model demonstrate that: 1) trap generation occurs at IL/high-k interface during stress; 2) an increase in mu with reduction in D-it does not guarantee better reliability, i.e., V-T shift and mu are uncorrelated due to their dependence on separate regions of the gate stack; 3) contributions to total V-T degradation from trapping and generated traps are mutually exclusive; 4) UF-MSDM is a powerful tool to estimate trap generation; and 5) V-T degradation is directly proportional to high-k thickness, varies inversely with IL thickness, and reduces with annealing

Trapping Effects in Si delta-Doped beta-Ga2O3 MESFETs on an Fe-Doped beta-Ga2O3 Substrate

Threshold voltage instability was observed on beta-Ga2O3 transistors using double-pulsed current-voltage and constant drain current deep level transient spectroscopy (DLTS) measurements. A total instability of 0.78 V was attributed to two distinct trap levels, at E-C-0.70 and E-C-0.77 eV, which need to be mitigated for future applications. The traps are likely located near the gate-drain edge and below the delta-doped layer, which is determined through the DLTS technique and an understanding of the fill and empty biasing conditions. The trap modulation was consistent with a gate leakage-based trap filling mechanism, which was demonstrated. It is likely that Fe is playing a role in the observed dispersion due to the close proximity of the Fe substrate

Effect of buffer iron doping on delta-doped beta-Ga2O3 metal semiconductor field effect transistors

We report on the effect of iron (Fe)-doped semi-insulating buffers on the electron transport and DC-RF dispersion in Si delta (delta)-doped beta-Ga2O3 metal-semiconductor field effect transistors. The effect of the distance between the 2-dimensional electron gas and the Fe-doped region was investigated, and Fe doping in the buffer was found to have a significant effect on the transport properties. It was found that buffers thicker than 600 nm can enable better transport and dispersion properties for field effect transistors, while maintaining relatively low parasitic buffer leakage. This work can provide guidance for the use of Fe-doped insulating buffers for future Ga2O3 based electronics. Published by AIP Publishing

Delta Doped beta-Ga2O3 Field Effect Transistors With Regrown Ohmic Contacts

We report silicon delta-doped beta-Ga2O3 metal semiconductor field effect transistors (MESFETs) with source-drain ohmic contacts formed by patterned regrowth of n-type Ga2O3. We show that regrown n-type contacts can enable a lateral low-resistance contact to the two-dimensional electron gas channel, with contact resistance lower than 1.5 Omega-mm. The fabricated MESFET has a peak drain current (I-D,I-MAX) of 140 mA/mm, transconductance (g(m)) of 34 mS/mm, and 3-terminal off-state breakdown voltage of 170 V. The proposed device structure could provide a promising path towards vertically scaled beta-Ga2O3 field effect transistors

Ion irradiation-induced interface mixing and the charge trap profiles investigated by in situ electrical measurements in Pt/Al₂O₃/β-Ga₂O₃MOSCAPs

In situ I - V and C-V measurements were performed during the 120 MeV Au9+ ion irradiation on the Pt/Al2O3/β-Ga2O3, metal-oxide-semiconductor capacitors (MOSCAPs), to comprehend the swift heavy ion (SHI)-induced effects at the interface and in the device performance. At a maximum fluence of 2× 1012 ions/cm2, the I-V data showed a rise in the reverse leakage current by four orders of magnitude compared to the pristine device. The trap level (below the conduction band of Al2O3) from Poole-Frenkel emission exhibits a variation from ∼ 1.1 to 0.91 eV. The conduction band offset (φB) of Al2O3/β-Ga2O3 changes from 1.48 to 1.25 eV as estimated under the Fowler-Nordheim tunneling mechanism. In situ C-V measurements show a significant shift in the flat band voltages and increased oxide in the border and interface due to charge trapping. The X-ray photoelectron spectroscopy (XPS) measurements of Al 2p and O 1s core levels revealed the pre-existing oxygen defects in Al2O3, which increase with fluence. The deconvoluted peaks of Al 2p at 74.6 eV designated to Al-sub oxide and the O 1s peak variation in the FWHM signifies the increase in the O defects. Cross-sectional transmission electron microscopy (XTEM) measurements on the irradiated device (at 2× 1012 ions/cm2) revealed a modulated interface of Al2O3/β-Ga2O3 and the formation of an interlayer of ~4 nm AlxGayOz. The scanning transmission electron microscope (STEM)-based high-angle annular dark-field imaging (HAADF) energy-dispersive X-ray spectroscopy (EDS) mapping revelation and the depth profiles of XPS data confirm the formation of an AlxGayOz interlayer.The work of N. Manikanthababu was supported by the Department of Science and Technology (DST), India, from the Brazil, Russia, India, China and South Africa (BRICS) Project. The work of S. Lodha was supported by MeitY and DST, Government of India, through the Nanoelectronics Network for Research and Application (NNetRA) Project. The work of R. Singh was supported in part by the DST, India, under the Brazil, Russia, India, China and South Africa (BRICS) Cooperation Scheme DST/IMRCD/BRICS/Pilot Call 3/GaO-Nitrides/2019 under Grant RP04000G