Ian M. Povey

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).

Broadband cavity ringdown spectroscopy of the NO3 radical.

Abstract Cavity ringdown spectroscopy (CRDS) has been demonstrated using a broadband (20 nm) laser source and a two-dimensional clocked detector array. Absorption spectra of dilute samples (50–500 parts per trillion) of the nitrate radical, NO 3 , have been obtained between 650 and 670 nm by monitoring simultaneously the time and wavelength resolved output of a ringdown cavity. The potential of broadband CRDS for making measurements on samples containing multiple absorbers (e.g., atmospheric samples) is shown by applying analysis methods from differential optical absorption spectroscopy to quantify the NO 3 concentration in the presence of nitrogen dioxide impurities.

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.

Impact of Forming Gas Annealing on the Performance of Surface-Channel

We investigated the effect of forming gas (5% H₂/95% N₂) annealing on surface-channel In_0.53 Ga_0.47As MOSFETs with atomic-layer-deposited Al₂O₃ as the gate dielectric. We found that a forming gas anneal (FGA) at 300°C for 30 min was efficient at removing or passivating positive fixed charges in Al₂O₃ , resulting in a shift of the threshold voltage from -0.63 to 0.43 V and in an increase in the <i>I</i>_on/<i>I</i>_off ratio of three orders of magnitude. Following FGA, the MOSFETs exhibited a subthreshold swing of 150 mV/dec, and the peak transconductance, drive current, and peak effective mobility increased by 29%, 25%, and 15%, respectively. FGA significantly improved the source- or drain-to-substrate junction isolation, with a reduction of two orders of magnitude in the reverse bias leakage exhibited by the Si-implanted In_0.53Ga_0.47As n⁺/p junctions, which is consistent with passivation of midgap defects in In_0.53Ga_0.47As by the FGA process.

\hbox{In}_{0.53}\hbox{Ga}_{0.47}\hbox{As}

In this work, we present the results of an investigation into charge trapping in metal/high-k/In0.53Ga0.47As metal-oxide-semiconductor capacitors (MOS capacitors), which is analysed using the hysteresis exhibited in the capacitance-voltage (C-V) response. The availability of both n and p doped In0.53Ga0.47As epitaxial layers allows the investigation of both hole and electron trapping in the bulk of HfO2 and Al2O3 films formed using atomic layer deposition (ALD). The HfO2/In0.53Ga0.47As and Al2O3/In0.53Ga0.47As MOS capacitors exhibit an almost reversible trapping behaviour, where the density of trapped charge is of a similar level to high-k/In0.53Ga0.47As interface state density, for both electrons and holes in the HfO2 and Al2O3 films. The experimental results demonstrate that the magnitude of the C-V hysteresis increases significantly for samples which have a native oxide layer present between the In0.53Ga0.47As surface and the high-k oxide, suggesting that the charge trapping responsible for the C-V hys...

MOSFETs With an ALD

The optical transmission of photonic crystals self-assembled from colloidal nanospheres in opals and assembled from two-dimensional colloidal crystals in a periodic stack by the Langmuir-Blodgett technique has been compared. Elimination of all related zero order diffraction resonances other than that from growth planes and broadening and deepening of the remaining one-dimensional diffraction resonance have been observed for samples prepared by the Langmuir-Blodgett approach, which are explained in terms of the partial disorder of a crystal lattice.The optical transmission of photonic crystals self-assembled from colloidal nanospheres in opals and assembled from two-dimensional colloidal crystals in a periodic stack by the Langmuir-Blodgett technique has been compared. Elimination of all related zero order diffraction resonances other than that from growth planes and broadening and deepening of the remaining one-dimensional diffraction resonance have been observed for samples prepared by the Langmuir-Blodgett approach, which are explained in terms of the partial disorder of a crystal lattice.

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

The electrical properties of metal-oxide-semiconductor capacitors incorporating atomic layer deposited Al2O3 on n-type and p-type In0.53Ga0.47As were investigated. A clear minority carrier response was observed for both n-type and p-type Au/Ni/Al2O3/In0.53Ga0.47As devices following an optimized ammonium sulfide (NH4)2S treatment. Capacitance-voltage and conductance-voltage measurements performed at varying temperatures allowed an Arrhenius extraction of activation energies for the minority carrier response, indicating a transition from a generation-recombination regime to a diffusion controlled response.

Gate Dielectric

High mobility III-V substrates with high-k oxides are required for device scaling without loss of channel mobility. Interest has focused on the self-cleaning effect on selected III-V substrates during atomic layer deposition of Al2O3. A thin (∼1 nm) Al2O3 interface control layer is deposited on In0.53Ga0.47As prior to HfO2 growth, providing the benefit of self-cleaning and improving the interface quality by reducing interface state defect densities by ∼50% while maintaining scaling trends. Significant reductions in leakage current density and increased breakdown voltage are found, indicative of a band structure improvement due to the reduction/removal of the In0.53Ga0.47As native oxides.

An investigation of capacitance-voltage hysteresis in metal/high-k/In0.53Ga0.47As metal-oxide-semiconductor capacitors

Band alignment at the interfaces of (100)GaAs with Al2O3 and HfO2 grown using atomic layer deposition is determined using internal photoemission and photoconductivity measurements. Though the inferred conduction and valence band offsets for both insulators were found to be close to or larger than 2 eV, the interlayer grown by concomitant oxidation of GaAs reduces the barrier for electrons by approximately 1 eV. The latter may pose significant problems associated with electron injection from GaAs into the oxide.

Erasing diffraction orders: Opal versus Langmuir-Blodgett colloidal crystals

Abstract Ex-situ Fourier transform infrared spectroscopy has been used to study the decomposition of tertiarybutylphosphine (TBP), trimethylindium (TMIn) and mixtures of TBP and TMIn under MOCVD conditions using dihydrogen as a carrier gas. IR bands due to TBP, TMIn, phosphine, isobutene, isobutane, ethene and methane have been monitored as a function of susceptor temperature. The decomposition of TBP alone in dihydrogen is observed to commence at temperatures above 773 K and is accompanied by the formation of isobutene, phosphine and isobutane. The pyrolysis of TBP is observed to be complete at temperatures in excess of 973 K. For TMIn in dihydrogen, the only observable product at temperatures greater than 573 K is methane. For TBP in the presence of TMIn a room temperature reaction is observed, the only detachable product of which is methane. The implication is that TMIn reacts in some way with TBP, possibly forming an “adduct” or polymer; however, decomposition products from TBP are not observed until temperatures are in excess of 573 K, while decomposition is observed to be complete at temperatures of 873 K. Once again isobutene, isobutane and phospine formation accompanies the TBP decomposition at 573K. At temperatures in excess of 900 K, both methane and ethene were observed during both of these experiments and are assumed to arise via the decomposition of isobutene. The deposited product on the reactor wall was found to be InP and phosphorus (rhombohedral) by X-ray diffraction. Some mechanistic steps for these reactions are proposed. In addition, preliminary data for the decomposition of cyclohexylphosphine are presented.