-Wei Cheng

Growth of highly tensile-strained Ge on relaxed InxGa1−xAs by metal-organic chemical vapor deposition

Highly tensile-strained Ge thin films and quantum dots have the potential to be implemented for high mobility metal-oxide-semiconductor field-effect transistor channels and long-wavelength optoelectronic devices. To obtain large tensile strain, Ge has to be epitaxially grown on a material with a larger lattice constant. We report on the growth of tensile-strained Ge on relaxed InxGa1−xAs epitaxial templates by metal-organic chemical vapor deposition. To investigate the methods to achieve high quality Ge epitaxy on III–V semiconductor surfaces, we studied Ge growth on GaAs with variable surface stoichiometry by employing different surface preparation processes. Surfaces with high Ga-to-As ratio are found to be necessary to initiate defect-free Ge epitaxy on GaAs. With proper surface preparation, tensile-strained Ge was grown on relaxed InxGa1−xAs with a range of In content. Low growth temperatures between 350 and 500 °C suppress misfit dislocation formation and strain relaxation. Planar Ge thin films with ...

The effect of interface processing on the distribution of interfacial defect states and the C-V characteristics of III-V metal-oxide-semiconductor field effect transistors

We have investigated the effect of interface formation and processing conditions of Al2O3 on GaAs on the density and distribution of interface state charge in the band gap. We have formed the insulator/semiconductor interface using both atomic layer deposition (ALD) and chemical vapor deposition (CVD). In situ ALD, ex situ ALD, and in situ CVD of aluminum oxide (Al2O3) on GaAs were employed using metal-organic CVD. Isopropanol (IPA) was chosen as the oxygen source for Al2O3 deposition. No arsenic or gallium oxide was detected at the in situ ALD Al2O3/GaAs interface, while gallium oxide was observed at the in situ CVD Al2O3/GaAs interface. The entire distributions of interfacial defects from different processes were determined by conductance frequency method with temperature-variation capacitance-voltage (C-V) measurements. The existence of Ga2O3 at the interface was found to be a possible method to lower the density of midgap defect states. From the C-V simulation, the midgap defect states are acceptorlik...

In situ metal-organic chemical vapor deposition atomic-layer deposition of aluminum oxide on GaAs using trimethyaluminum and isopropanol precursors

In situ atomic-layer deposition (ALD) of Al2O3 on p-GaAs in metal-organic chemical vapor deposition system is demonstrated in this article. Isopropanol was chosen as the oxygen source for Al2O3 ALD, instead of common H2O. The ALD mechanism is discussed and it is proposed that water does not form in the process. The saturation growth rate of Al2O3 is about 0.8A∕cycle. X-ray photoetectron spectroscopy depth profiles were performed and no arsenic oxide is observed at the interface. The capacitance-voltage measurements show a small accumulation capacitance dispersion and voltage shift in the depletion region. The interfacial defect density near the midgap of the GaAs bandgap has been determined with the conductance-frequency method. The interfacial defect density is determined as 2.5×1011eV−1cm−2 at the midgap of the GaAs.

Self-cleaning and surface recovery with arsine pretreatment in ex situ atomic-layer-deposition of Al2O3 on GaAs

Annealing native oxide covered GaAs samples in Arsine(AsH3) prior to atomic-layer-deposition of Al2O3 with trimethyaluminum (TMA) and isopropanol (IPA) results in capacitance-voltage (C-V) characteristics of the treated samples that resemble the superior C-V characteristics of p-type GaAs grown by an in situ metal-organic chemical vapor deposition process. Both TMA and IPA show self-cleaning effect on removing the native oxide in ex situ process, little evidence of a native oxide was observed with high resolution transmission electron microscopy at the Al2O3/GaAs interface. The discrepancy in the C-V characteristics was observed in in situ p- and n-type GaAs samples.

High mobility In0.53Ga0.47As quantum-well metal oxide semiconductor field effect transistor structures

In this paper, we demonstrate high electron mobility In0.53Ga0.47As quantum-well metal oxide semiconductor field effect transistor (MOSFET) structures. The Al2O3 (gate dielectric)/ In0.53Ga0.47As-In0.52Al0.48As (barrier)/In0.53Ga0.47As (channel) structures were fabricated, and the mobility was obtained by Hall measurements. The structures with in-situ chemical vapor deposition (CVD) Al2O3 displayed higher mobility than identical structures fabricated with in situ atomic layer deposition Al2O3, which indicates that CVD process resulted in a lower Al2O3/In0.53Ga0.47As interfacial defect density. A gate bias was applied to the structure with CVD Al2O3, and a peak mobility of 9243 cm2/V s at a carrier density of 2.7 × 1012 cm−2 was demonstrated for the structure with a 4 nm In0.53Ga0.47As-In0.52Al0.48As barrier. A model based on internal phonon scattering and interfacial defect coulomb scattering was developed to explain the experimental data and predict the mobility of In0.53Ga0.47As MOSFET structures.

Improved interfacial state density in Al2O3/GaAs interfaces using metal-organic chemical vapor deposition

In situ deposition of Al2O3 on GaAs was performed by chemical-vapor-deposition (CVD) with trimethyaluminum and isopropanol as precursors. A gallium-rich region in the Al2O3 thin film above the interface was spontaneously formed via the in situ CVD process. Ga-enrichment of the interface was observed using secondary ion mass spectrometry (SIMS) depth profile measurement. X-ray photoelectron spectroscopy (XPS) results show that the gallium-rich region consists of Al2O3 and Ga2O3, but no As2O3 was observed. The Ga2O3–Al2O3 layer above the oxide/GaAs interface reduces the frequency dispersion as measured with capacitance-voltage (C-V) characteristics and lowers the interfacial state density as compared to atomic-layer-deposition *(ALD) deposited films which do not display this gallium enrichment above the interface.

Field enhancement effect of nanocrystals in bandgap engineering of tunnel oxide for nonvolatile memory application

Charge storage characteristics of metal-oxide-semiconductor (MOS) structures containing Au nanocrystals on tunnel oxide composed of Al2O3/HfO2/Al2O3 stacks in different thickness piling up sequences were investigated. A significant enhancement of charge injection efficiency for both electrons and holes without sacrificing charge retention performance was found in the sample with a relatively thicker (∼3 nm) Al2O3 sublayer adjacent to Au nanocrystals and a thinner (∼1 nm) Al2O3 sublayer in front of the Si substrate. It is attributed to the local enhancement of electric field induced by the embedded Au nanocrystals, which greatly modifies the effective barrier of tunnel oxide.

Monolithic III-V/Si integration

We summarize our work on creating substrate platforms, processes, and devices for the monolithic integration of silicon CMOS circuits with III-V optical and electronic devices. Visible LEDs and InP HBTs have been integrated on silicon materials platforms that lend themselves to process integration within silicon fabrication facilities. We also summarize research on tensile Ge, which could be a high mobility material for III-V MOS, and research on an in-situ MOCVD Al2O3/GaAs process for III-V MOS.