Yoontae Hwang

Comparison of methods to quantify interface trap densities at dielectric/III-V semiconductor interfaces

Methods to extract trap densities at high-permittivity (k) dielectric/III-V semiconductor interfaces and their distribution in the semiconductor band gap are compared. The conductance method, the Berglund intergral, the Castagne–Vapaille (high-low frequency), and Terman methods are applied to admittance measurements from metal oxide semiconductor capacitors (MOSCAPs) with high-k/In0.53Ga0.47As interfaces with different interface trap densities. The results are discussed in the context of the specifics of the In0.53Ga0.47As band structure. The influence of different conduction band approximations for determining the ideal capacitance-voltage (CV) characteristics and those of the MOSCAP parameters on the extracted interface trap density are investigated. The origins of discrepancies in the interface trap densities determined from the different methods are discussed. Commonly observed features in the CV characteristics of high-k/In0.53Ga0.47As interfaces are interpreted and guidelines are developed to obtain...

Analysis of trap state densities at HfO2/In0.53Ga0.47As interfaces

HfO2 was deposited on n- and p-type In0.53Ga0.47As by chemical beam deposition. Interface trap densities (Dit) and their energy level distribution were quantified using the conductance method in a wide temperature range (77 to 300 K). A trap level close to the intrinsic energy level caused the Dit to rise above 1013 cm−2 eV−1. The trap level at midgap gives rise to false inversion behavior in the capacitance-voltage curves for n-type channels at room temperature. The apparent decrease of the Dit close to the band edges is discussed.

Metal-oxide-semiconductor capacitors with ZrO2 dielectrics grown on In0.53Ga0.47As by chemical beam deposition

Zirconium oxide films were grown by chemical beam deposition with zirconium tert-butoxide as the source on (2×4) reconstructed, n-type In0.53Ga0.47As surfaces obtained after As decapping. Optimized growth conditions yielded ZrO2/In0.53Ga0.47As interfaces that were free of second phases. Capacitance-voltage (CV) measurements with different top electrodes showed a frequency dispersion of less than 2% per decade in accumulation. The accumulation capacitance and horizontal position of the CV curve were independent of temperature, while the inversion capacitance was strongly temperature dependent. Flat band voltages correlated with the work function of the metal electrode.

Quantification of trap densities at dielectric/III-V semiconductor interfaces

High-frequency capacitance-voltage curves for capacitors with high-k gate dielectrics and III–V semiconductor channels are modeled. The model takes into account the low conduction band density of states, the nonparabolicity of the Γ valley, and the population of higher lying conduction band valleys. The model is used to determine interface trap densities (Dit) and band bending of HfO2/In0.53Ga0.47As interfaces with different Dit and with pinned and unpinned Fermi levels, respectively. Potential sources of errors in extracting Dit are discussed and criteria that establish unpinned interfaces are developed.

Effect of postdeposition anneals on the Fermi level response of HfO2/In0.53Ga0.47As gate stacks

The electrical characteristics, in particular interface trap densities, oxide capacitance, and Fermi level movement, of metal oxide semiconductor capacitors with HfO2 gate dielectrics and In0.53Ga0.47As channels are investigated as a function of postdeposition annealing atmosphere. It is shown, using both conductance and Terman methods, that the Fermi level of nitrogen annealed stacks is effectively pinned at midgap. In contrast, samples annealed in forming gas show a large band bending in response to an applied gate voltage and a reduced midgap interface trap density compared to those annealed in nitrogen.

Influence of trimethylaluminum on the growth and properties of HfO2/In0.53Ga0.47As interfaces

The growth and the electrical properties of HfO2/In0.53Ga0.47As interfaces are characterized as a function of exposure to trimethylaluminum (TMA) prior to chemical beam deposition of HfO2 from an alkoxide precursor. It is shown that TMA can act as a surfactant for HfO2 growth for (2×4) but not for the group-III-rich (4×2) reconstructed surfaces. The Fermi-level can be unpinned by postdeposition forming gas anneals only for interfaces that were exposed to low doses of TMA at low temperatures. The results are discussed in the context of the interaction between TMA and III-V surfaces.

Influence of gate metallization processes on the electrical characteristics of high-k/In0.53Ga0.47As interfaces

The influence of different gate metal deposition processes on the electrical characteristics of dielectric/III-V interfaces is investigated. Al2O3 and HfO2 dielectrics are grown on In0.53Ga0.47As channels and top metal electrodes are deposited by either thermal evaporation or electron beam deposition. It is shown that metal-oxide-semiconductor capacitors with electron beam evaporated electrodes exhibit substantially larger midgap interface trap densities than those with thermally evaporated electrodes. The damage caused by electron beam metallization can be mitigated by subsequent, long anneals in forming gas.

Al-doped HfO2/In0.53Ga0.47As metal-oxide-semiconductor capacitors

Hafnium oxide gate dielectrics doped with a one to two percent of aluminum are grown on In0.53Ga0.47As channels by codeposition of trimethylaluminum TMA and hafnium tertbutoxide HTB. It is shown that the addition of TMA during growth allows for smooth, amorphous films that can be scaled to 5 nm physical thickness. Metal-oxide-semiconductor capacitors MOSCAPs with this dielectric have an equivalent oxide thickness of 1 nm, show an unpinned, efficient Fermi level movement and lower interface trap densities than MOSCAPs with HfO2 dielectrics grown by sequential TMA/HTB deposition.

High Density Individually Addressable Nanowire Arrays Record Intracellular Activity from Primary Rodent and Human Stem Cell Derived Neurons

We report a new hybrid integration scheme that offers for the first time a nanowire-on-lead approach, which enables independent electrical addressability, is scalable, and has superior spatial resolution in vertical nanowire arrays. The fabrication of these nanowire arrays is demonstrated to be scalable down to submicrometer site-to-site spacing and can be combined with standard integrated circuit fabrication technologies. We utilize these arrays to perform electrophysiological recordings from mouse and rat primary neurons and human induced pluripotent stem cell (hiPSC)-derived neurons, which revealed high signal-to-noise ratios and sensitivity to subthreshold postsynaptic potentials (PSPs). We measured electrical activity from rodent neurons from 8 days in vitro (DIV) to 14 DIV and from hiPSC-derived neurons at 6 weeks in vitro post culture with signal amplitudes up to 99 mV. Overall, our platform paves the way for longitudinal electrophysiological experiments on synaptic activity in human iPSC based disease models of neuronal networks, critical for understanding the mechanisms of neurological diseases and for developing drugs to treat them.

Metal-oxide-semiconductor capacitors with erbium oxide dielectrics on In0.53Ga0.47As channels

Erbium oxide dielectrics with a thickness of ∼6 nm were fabricated in situ on In0.53Ga0.47As channels. Leakage current and capacitance densities were characterized as a function of applied voltage using metal-oxide-semiconductor capacitors with two different top electrode materials, Pt and Al. Leakage current densities were less than 10−3 A/cm2 at gate voltages up to ±2 V. The capacitance densities were lower with the Al electrode, which was attributed to a low-permittivity aluminum oxide layer at the electrode interface. The capacitors with the Pt electrode showed a pronounced increase in the capacitance in the depletion region at frequencies as high as 1 MHz, which was not observed for the Al electrode. Possible origins of the differences in the capacitance-voltage characteristics with Pt and Al electrodes are discussed.