M. Milojevic

GaAs interfacial self-cleaning by atomic layer deposition

The reduction and removal of surface oxides from GaAs substrates by atomic layer deposition (ALD) of Al2O3 and HfO2 are studied using in situ monochromatic x-ray photoelectron spectroscopy. Using the combination of in situ deposition and analysis techniques, the interfacial “self-cleaning” is shown to be oxidation state dependent as well as metal organic precursor dependent. Thermodynamics, charge balance, and oxygen coordination drive the removal of certain species of surface oxides while allowing others to remain. These factors suggest proper selection of surface treatments and ALD precursors can result in selective interfacial bonding arrangements.

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.

Half-cycle atomic layer deposition reaction studies of Al2O3 on In0.2Ga0.8As (100) surfaces

The reduction in III–V interfacial oxides by atomic layer deposition of Al2O3 on InGaAs is studied by interrupting the deposition following individual trimethyl aluminum (TMA) and water steps (half cycles) and interrogation of the resultant surface reactions using in situ monochromatic x-ray photoelectron spectroscopy (XPS). TMA is found to reduce the interfacial oxides during the initial exposure. Concentrations of Ga oxide on the surface processed at 300 °C are reduced to a concentration on the order of a monolayer, while AsOx species are below the level of detection of XPS.

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...

Frequency dispersion reduction and bond conversion on n-type GaAs by in situ surface oxide removal and passivation

The method of surface preparation on n-type GaAs, even with the presence of an amorphous-Si interfacial passivation layer, is shown to be a critical step in the removal of accumulation capacitance frequency dispersion. In situ deposition and analysis techniques were used to study different surface preparations, including NH4OH, Si-flux, and atomic hydrogen exposures, as well as Si passivation depositions prior to in situ atomic layer deposition of Al2O3. As–O bonding was removed and a bond conversion process with Si deposition is observed. The accumulation capacitance frequency dispersion was removed only when a Si interlayer and a specific surface clean were combined.

Half-cycle atomic layer deposition reaction studies of Al2O3 on (NH4)2S passivated GaAs(100) surfaces

“Half-cycle” atomic layer deposition reactions of trimethyl aluminum (TMA) and water on GaAs exposed to wet chemical sulfur treatments are studied for the formation of Al2O3. Trivalent oxides of gallium and arsenic are completely reduced following the first TMA pulse. The same processing step also removes As–S bonding below the level of detection, while the relative concentration of gallium suboxides as well as Ga–S bonds is not affected. A concomitant decrease in the S 2p peak intensity is observed, indicating that sulfur is lost through a volatile reaction product. Further precursor exposures do not measurably affect substrate surface chemistry.

Interface studies of GaAs metal-oxide-semiconductor structures using atomic-layer-deposited HfO2∕Al2O3 nanolaminate gate dielectric

A systematic capacitance-voltage study has been performed on GaAs metal-oxide-semiconductor (MOS) structures with atomic-layer-deposited HfO2∕Al2O3 nanolaminates as gate dielectrics. A HfO2∕Al2O3 nanolaminate gate dielectric improves the GaAs MOS characteristics such as dielectric constant, breakdown voltage, and frequency dispersion. A possible origin for the widely observed larger frequency dispersion on n-type GaAs than p-type GaAs is discussed. Further experiments show that the observed hysteresis is mainly from the mobile changes and traps induced by HfO2 in bulk oxide instead of those at oxide/GaAs interface.

Indium stability on InGaAs during atomic H surface cleaning

Atomic H exposure of a GaAs surface at 390°C is a relatively simple method for removing the native oxides without altering the surface stoichiometry. In-situ reflection high energy electron diffraction and angle-resolved x-ray photoelectron spectroscopy have been used to show that this procedure applied to In0.2Ga0.8As effectively removes the native oxides resulting in an atomically clean surface. However, the bulk InGaAs stoichiometry is not preserved from this treatment. The In:Ga ratio from the substrate is found to decrease by 33%. The implications for high-mobility channel applications are discussed as the carrier mobility increases nearly linearly with the In content.

Comparison of n-type and p-type GaAs oxide growth and its effects on frequency dispersion characteristics

The electrical characteristics of n- and p-type gallium arsenide (GaAs) capacitors show a striking difference in the “accumulation” capacitance frequency dispersion. This difference has been attributed by some to a variation in the oxide growth, possibly due to photoelectrochemical properties of the two substrates. We show that the oxide growth on n- and p-type GaAs substrates is identical when exposed to identical environmental and chemical conditions while still maintaining the diverse electrical characteristics. The difference in electron and hole trap time constants is suggested as the source of the disparity of the frequency dispersion for n-type versus p-type GaAs devices.

The significance of core-level electron binding energies on the proper analysis of InGaAs interfacial bonding

The detection and removal of interfacial oxides on InGaAs semiconductors is of critical importance for their implementation as high-mobility channels for improved complementary metal oxide semiconductor device performance. X-ray photoelectron spectroscopy is a powerful tool to determine the chemical bonding at these interfaces. To correctly analyze these spectra, one must consider the binding energies and escape depths of the core-level electrons being detected, as monolayer level interfacial oxides (As–O and Ga–O) are detectable only in certain surface sensitive spectral regions. Also, inherent asymmetries associated with the In spectra must be taken into account for analysis of In-oxide bonding.