Rathnait Long

Origin and passivation of fixed charge in atomic layer deposited aluminum oxide gate insulators on chemically treated InGaAs substrates

We report experimental and theoretical studies of defects producing fixed charge within Al2O3 layers grown by atomic layer deposition (ALD) on In0.53Ga0.47As(001) substrates and the effects of hydrogen passivation of these defects. Capacitance-voltage measurements of Pt/ALD-Al2O3/n-In0.53Ga0.47As suggested the presence of positive bulk fixed charge and negative interfacial fixed charge within ALD-Al2O3. We identified oxygen and aluminum dangling bonds (DBs) as the origin of the fixed charge. First-principles calculations predicted possible passivation of both O and Al DBs, which would neutralize fixed charge, and this prediction was confirmed experimentally; postmetallization forming gas anneal removed most of the fixed charge in ALD-Al2O3.

Temperature and frequency dependent electrical characterization of HfO2/InxGa1−xAs interfaces using capacitance-voltage and conductance methods

Electrical properties of metal-oxide-semiconductor capacitors using atomic layer deposited HfO2 on n-type GaAs or InxGa1−xAs (x=0.53, 0.30, 0.15) epitaxial layers were investigated. Capacitance-voltage (CV) measurements indicated large temperature and frequency dispersion at positive gate bias in devices using n-type GaAs and low In content (x=0.30, 0.15) InxGa1−xAs layers, which is significantly reduced for devices using In0.53Ga0.47As. For In0.53Ga0.47As devices, the CV response at negative gate bias is most likely characteristic of an interface state response and may not be indicative of true inversion. The conductance technique on Pd/HfO2/In0.53Ga0.47As/InP shows reductions in interface state densities by In0.53Ga0.47As surface passivation and forming gas annealing (325 °C).

Surface Preparation and Deposited Gate Oxides for Gallium Nitride Based Metal Oxide Semiconductor Devices

The literature on polar Gallium Nitride (GaN) surfaces, surface treatments and gate dielectrics relevant to metal oxide semiconductor devices is reviewed. The significance of the GaN growth technique and growth parameters on the properties of GaN epilayers, the ability to modify GaN surface properties using in situ and ex situ processes and progress on the understanding and performance of GaN metal oxide semiconductor (MOS) devices are presented and discussed. Although a reasonably consistent picture is emerging from focused studies on issues covered in each of these topics, future research can achieve a better understanding of the critical oxide-semiconductor interface by probing the connections between these topics. The challenges in analyzing defect concentrations and energies in GaN MOS gate stacks are discussed. Promising gate dielectric deposition techniques such as atomic layer deposition, which is already accepted by the semiconductor industry for silicon CMOS device fabrication, coupled with more advanced physical and electrical characterization methods will likely accelerate the pace of learning required to develop future GaN-based MOS technology.

In situ H2S passivation of In0.53Ga0.47As∕InP metal-oxide-semiconductor capacitors with atomic-layer deposited HfO2 gate dielectric

We have studied an in situ passivation of In0.53Ga0.47As, based on H2S exposure (50–350°C) following metal organic vapor phase epitaxy growth, prior to atomic layer deposition of HfO2 using Hf[N(CH3)2]4 and H2O precursors. X-ray photoelectron spectroscopy revealed the suppression of As oxide formation in air exposed InGaAs surfaces for all H2S exposure temperatures. Transmission electron microscopy analysis demonstrates a reduction of the interface oxide between the In0.53Ga0.47As epitaxial layer and the amorphous HfO2 resulting from the in situ H2S passivation. The capacitance-voltage and current-voltage behavior of Pd∕HfO2∕In0.53Ga0.47As∕InP structures demonstrates that the electrical characteristics of samples exposed to 50°C H2S at the end of the metal-organic vapor-phase epitaxy In0.53Ga0.47As growth are comparable to those obtained using an ex situ aqueous (NH4)2S passivation.

Charged Defect Quantification in Pt/Al2O3/In0.53Ga0.47As/InP MOS Capacitors

This work focuses on the separation and quantification of fixed bulk oxide charge, fixed charge at the dielectric-semiconductor interface and interface state charge components in the Pt/Al 2 O 3 /In 0.53 Ga 0.47 As metal-oxide-semiconductor (MOS) system. The availability of atomic layer deposited Al 2 O 3 dielectrics over n- and p-type In 0.53 Ga 0.47 As with a range of well-controlled thickness values opens up an experimental route for the determination of the interface state density (D it ) independently of the total fixed oxide charge using capacitance-voltage measurements taken at 1 MHz and -50°C. Low temperature forming gas annealing (350°C) significantly reduces the amount of fixed charge. The interface fixed charge is reduced from ~ -8.5 x 10 12 cm -2 preanneal to ~-7.4 × 10 11 cm -2 postanneal and the bulk oxide charge is reduced from ~1.4 x 10 19 cm -3 preanneal to ~5 x 10 1 cm -3 postanneal. The forming gas anneal also has a significant effect on the interface state charge, reducing its density from 1.3 x 10 13 cm -2 preanneal to 4 x 10 12 cm -2 postanneal.

Interface trap evaluation of Pd/Al2O3/GaN metal oxide semiconductor capacitors and the influence of near-interface hydrogen

Three interface state density (Dit) characterization methods to evaluate the oxide-semiconductor interface on metal-oxide-semiconductor capacitors fabricated on GaN are compared and discussed. Capacitance-voltage, conductance-voltage, and constant capacitance deep level transient and optical spectroscopy measurements are used to evaluate Dit at the Al2O3/GaN interface. The effect of annealing ambient on the Pd/Al2O3/GaN capacitors is also examined. Forming gas annealing reduces Dit; nitrogen annealing increases Dit for the annealing conditions tested. The Dit variation correlates with changes in hydrogen concentration at the Al2O3/GaN interface detected by secondary ion mass spectrometry suggesting that hydrogen plays an important role passivating Al2O3/GaN interfaces.

The Characterization and Passivation of Fixed Oxide Charges and Interface States in the

In this paper, we present a review of experimental results examining charged defect components in the Al₂O₃/In_0.53Ga_0.47As metal-oxide-semiconductor (MOS) system. For the analysis of fixed oxide charge and interface state density, an approach is described where the flatband voltage for n- and p-type Al₂O₃/In_0.53Ga_0.47As MOS structures is used to separate and quantify the contributions of fixed oxide charge and interface state density. Based on an Al₂O₃ thickness series (10-20 nm) for the n- and p-type In_0.53Ga_0.47As layers, the analysis reveals a positive fixed charge density ( ~ 9 ×10¹⁸ cm^-3) distributed throughout the Al₂O₃ and a negative sheet charge density (- 8 × 10¹² cm^-2) located near the Al₂O₃/In_0.53Ga_0.47As interface. The interface state density integrated across the energy gap is ~1 ×10¹³ cm^-2 and is a donor-type (+/0) defect. The density of the fixed oxide charge components is significantly reduced by forming gas (5 % H₂/ 95% N₂ ambient at 350 °C for 30 minutes) annealing. The interface state distribution obtained from multi-frequency capacitance-voltage and conductance-voltage measurements on either MOS structures or MOSFETs indicates a peak density located around the In_0.53Ga_0.47As midgap energy, with a sharp increase in the interface state density toward the valance band and evidence of interface states aligned with the In_0.53Ga_0.47As conduction band. The integrated interface state density obtained from multi-frequency capacitance-voltage and conductance-voltage analysis is in good agreement with the approach of comparing the flatband voltages in n- and p -type Al₂O₃/In_0.53Ga_0.47As MOS structures. Finally, this paper reviews recent work based on an optimization of the In_0.53Ga_0.47As surface preparation using (NH₄)₂S, combined with minimizing the transfer time to the atomic layer deposition reactor for Al₂O₃, which indicates interface state reduction and genuine surface inversion for both n- and p -type Al₂O₃/In_0.53Ga_0.47As MOS structures.

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

In this work results are presented on the structural analysis, chemical composition, and interface state densities of HfO2 thin films deposited by atomic layer deposition (ALD) from Hf[N(CH3)2]4 and H2O on In0.53Ga0.47As/InP substrates. The structural and chemical properties are investigated using high resolution cross-sectional transmission electron microscopy and electron energy loss spectroscopy. HfO2 films (3–15 nm) deposited on In0.53Ga0.47As are studied following a range of surface treatments including in situ treatment of the In0.53Ga0.47As surface by H2S exposure at 50–350 °C immediately following the metal organic vapor phase epitaxy growth of the In0.53Ga0.47As layer, ex situ treatment with (NH4)2S, and deposition on the native oxides of In0.53Ga0.47As with no surface treatment. The structural analysis indicates that the In0.53Ga0.47As surface preparation prior to HfO2 film deposition influences the thickness of the HfO2 film and the interlayer oxide. The complete interfacial self-cleaning of th...

MOS System

Capacitance-voltage measurements of Pd/atomic layer deposited Al2O3/GaN metal oxide semiconductor capacitors performed over a temperature range of 77 K-500 K are reported. Border trap response is not detected in these measurements, consistent with the energy levels of bulk Al2O3 defects predicted in reported first principles calculations. The limitations of the conductance method for estimation of the interface state density of the wide band gap GaN semiconductor, even at a measurement temperature of 500 K, are discussed. As GaN-based devices are intended for high temperature applications, the role of the pyroelectric effect in the interpretation of higher-temperature capacitance-voltage data is described.

Structural analysis, elemental profiling, and electrical characterization of HfO2 thin films deposited on In0.53Ga0.47As surfaces by atomic layer deposition

We correlate interfacial defect state densities with the chemical composition of the Al2O3/GaN interface in metal-oxide-semiconductor (MOS) structures using synchrotron photoelectron emission spectroscopy (PES), cathodoluminescence and high-temperature capacitance-voltage measurements. The influence of the wet chemical pretreatments involving (1) HCl+HF etching or (2) NH4OH(aq) exposure prior to atomic layer deposition (ALD) of Al2O3 were investigated on n-type GaN (0001) substrates. Prior to ALD, PES analysis of the NH4OH(aq) treated surface shows a greater Ga2O3 component compared to either HCl+HF treated or as-received surfaces. The lowest surface concentration of oxygen species is detected on the acid etched surface, whereas the NH4OH treated sample reveals the lowest carbon surface concentration. Both surface pretreatments improve electrical characteristics of MOS capacitors compared to untreated samples by reducing the Al2O3/GaN interface state density. The lowest interfacial trap density at energies in the upper band gap is detected for samples pretreated with NH4OH. These results are consistent with cathodoluminescence data indicating that the NH4OH treated samples show the strongest band edge emission compared to as-received and acid etched samples. PES results indicate that the combination of reduced carbon contamination while maintaining a Ga2O3 interfacial layer by NH4OH(aq) exposure prior to ALD results in fewer interface traps after Al2O3 deposition on the GaN substrate.