Barry Brennan

Detection of Ga suboxides and their impact on III-V passivation and Fermi-level pinning

The passivation of interface states remains an important problem for III-V based semiconductor devices. The role of the most stable bound native oxides GaOx (0.5≤x≤1.5) is of particular interest. Using monochromatic x-ray photoelectron spectroscopy in conjunction with controlled GaAs(100) and InGaAs(100) surfaces, a stable suboxide (Ga2O) bond is detected at the interface but does not appear to be detrimental to device characteristics. In contrast, the removal of the Ga 3+ oxidation state (Ga2O3) is shown to result in the reduction of frequency dispersion in capacitors and greatly improved performance in III-V based devices.

HfO2 on MoS2 by Atomic Layer Deposition: Adsorption Mechanisms and Thickness Scalability

We report our investigation of the atomic layer deposition (ALD) of HfO2 on the MoS2 surface. In contrast to previous reports of conformal growth on MoS2 flakes, we find that ALD on MoS2 bulk material is not uniform. No covalent bonding between the HfO2 and MoS2 is detected. We highlight that individual precursors do not permanently adsorb on the clean MoS2 surface but that organic and solvent residues can dramatically change ALD nucleation behavior. We then posit that prior reports of conformal ALD deposition on MoS2 flakes that had been exposed to such organics and solvents likely rely on contamination-mediated nucleation. These results highlight that surface functionalization will be required before controllable and low defect density high-κ/MoS2 interfaces will be realized. The band structure of the HfO2/MoS2 system is experimentally derived with valence and conduction band offsets found to be 2.67 and 2.09 eV, respectively.

A systematic study of (NH4)2S passivation (22%, 10%, 5%, or 1%) on the interface properties of the Al2O3/In0.53Ga0.47As/InP system for n-type and p-type In0.53Ga0.47As epitaxial layers

In this work, we present the results of an investigation into the effectiveness of varying ammonium sulphide (NH4)2S concentrations in the passivation of n-type and p-type In0.53Ga0.47As. Samples were degreased and immersed in aqueous (NH4)2S solutions of concentrations 22%, 10%, 5%, or 1% for 20 min at 295 K, immediately prior to atomic layer deposition of Al2O3. Multi-frequency capacitance-voltage (C-V) results on capacitor structures indicate that the lowest frequency dispersion over the bias range examined occurs for n-type and p-type devices treated with the 10%(NH4)2S solution. The deleterious effect on device behavior of increased ambient exposure time after removal from 10%(NH4)2S solution is also presented. Estimations of the interface state defect density (Dit) for the optimum 10%(NH4)2S passivated In0.53Ga0.47As devices extracted using an approximation to the conductance method, and also extracted using the temperature-modified high-low frequency C-V method, indicate that the same defect is pre...

Identification and thermal stability of the native oxides on InGaAs using synchrotron radiation based photoemission

A high resolution synchrotron radiation core level photoemission study of the native oxides on In0.53Ga0.47As was carried out in order to determine the various oxidation states present on the surface. The thermal stability of the oxidation states was also investigated by annealing the samples in vacuum at temperatures ranging from 150 to 450 °C. As well as the widely reported oxidation states, various arsenic, gallium, and indium oxides, along with mixed phase gallium arsenic and indium gallium oxides are identified. Elemental binary oxides have been identified as residing at the oxide substrate interface and could play an important role in understanding the growth of metal oxide dielectric layers on the InGaAs surface, due to their apparent chemical stability.

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.

Accumulation capacitance frequency dispersion of III-V metal-insulator-semiconductor devices due to disorder induced gap states

The origin of the anomalous frequency dispersion in accumulation capacitance of metal-insulator-semiconductor devices on InGaAs and InP substrates is investigated using modeling, electrical characterization, and chemical characterization. A comparison of the border trap model and the disorder induced gap state model for frequency dispersion is performed. The fitting of both models to experimental data indicate that the defects responsible for the measured dispersion are within approximately 0.8 nm of the surface of the crystalline semiconductor. The correlation between the spectroscopically detected bonding states at the dielectric/III-V interface, the interfacial defect density determined using capacitance-voltage, and modeled capacitance-voltage response strongly suggests that these defects are associated with the disruption of the III-V atomic bonding and not border traps associated with bonding defects within the high-k dielectric.

Effect of post deposition anneal on the characteristics of HfO2/InP metal-oxide-semiconductor capacitors

The interface trap density (Dit) and bonding of the HfO2/InP interface is investigated. The energy distribution of interface states extracted using capacitance-voltage measurements show a peak near midgap in InP and a tail, which extends into the InP conduction band. Both the Dit peak and the conduction band Dit increase with increasing post-deposition annealing temperature. A substantial increase in the native oxides with annealing temperature is observed with x-ray photoelectron spectroscopy. The possible bonding states responsible for the defects are presented.

Interfacial oxide re-growth in thin film metal oxide III-V semiconductor systems

The Al2O3/GaAs and HfO2/GaAs interfaces after atomic layer deposition are studied using in situ monochromatic x-ray photoelectron spectroscopy. Samples are deliberately exposed to atmospheric conditions and interfacial oxide re-growth is observed. The extent of this re-growth is found to depend on the dielectric material and the exposure temperature. Comparisons with previous studies show that ex situ characterization can result in misleading conclusions about the interface reactions occurring during the metal oxide deposition process.

Synchrotron radiation photoemission study of in situ manganese silicate formation on SiO2 for barrier layer applications

Synchrotron radiation photoelectron spectroscopy (SRPES) is used to investigate the in situ formation of ultra thin Mn silicate layers on SiO2, which has relevance for copper diffusion barrier layers in microelectronic devices. High temperature vacuum annealing of metallic Mn (∼1.5 nm) deposited on a 4 nm thermally grown SiO2 film results in the self limiting formation of a magnesium silicate layer, the stoichiometry of which is consistent with the formation of MnSiO3. Curve fitted Mn 3p SRPES spectra show no evidence for the presence of a manganese oxide phase at the Mn/SiO2 interface, in contrast to previous reports.

In situ atomic layer deposition half cycle study of Al2O3 growth on AlGaN

The atomic layer deposition (ALD) of Al2O3 on the native oxide and hydrofluoric acid treated Al0.25Ga0.75 N surface was studied using in situ X-ray photoelectron spectroscopy (XPS), after each individual “half cycle” of the ALD process. Initially, Al2O3, Ga2O3, and N-O states were detected on both surfaces at differing concentrations. During the course of the deposition process, the N-O bonds are seen to decrease to within XPS detection limits, as well as a small decrease in the Ga2O3 concentration. The Al2O3 growth rate initially is seen to be very low, indication of low reactivity between the trimethyl-aluminum molecule and the AlGaN surface.