J Dekoster

Effective reduction of interfacial traps in Al2O3/GaAs (001) gate stacks using surface engineering and thermal annealing

To effectively passivate the technologically important GaAs (001) surfaces, in situ deposition of Al2O3 was carried out with molecular beam epitaxy. The impacts of initial GaAs surface reconstruction and post-deposition annealing have been systematically investigated. The corresponding interfacial state density (Dit) were derived by applying the conductance method at 25 and 150 °C on both p-type and n-type GaAs metal-oxide-semiconductor capacitors to establish the Dit spectra in proximity of the critical midgap region. We show that significant reduction of Dit near the midgap is achieved by applying an optimized thermal annealing on samples grown on a Ga-rich (4×6) reconstructed surface.

AlGaN/GaN/AlGaN Double Heterostructures Grown on 200 mm Silicon (111) Substrates with High Electron Mobility

In this work, we demonstrate, for the first time, Al0.35GaN/GaN/Al0.25GaN double heterostructure field effect transistors on 200 mm Si(111) substrates. Thick crack-free Al0.25GaN buffer layers are achieved by optimizing Al0.75GaN/Al0.5GaN intermediate layers and AlN nucleation layers. The highest buffer breakdown voltage reaches 1380 V on a sample with a total buffer thickness of 4.6 µm. According to Van der Pauw Hall measurements, the electron mobility is 1766 cm2 V-1 s-1 and the electron density is 1.16×1013 cm-2, which results in a very low sheet resistance of 306±8 Ω/square.

Concentration-controlled phase selection of silicide formation during reactive deposition

Slow (low-rate) reactive deposition of a metal onto a Si substrate can result in direct formation of a metal disilicide, thereby skipping the metal-rich phases in the formation sequence. These observations have been explained thermodynamically by using the effective heat of formation model. As a result of this concentration-controlled phase selection, it is possible to form disilicides, such as CoSi2, NiSi2, or β-FeSi2 at much lower growth temperatures than possible in conventional solid-phase reaction of a metal layer deposited onto Si at room temperature (i.e., lower than the nucleation temperature). Moreover, epitaxial growth of CoSi2/Si(100), which is not possible by solid-phase reaction, becomes achievable when depositing Co atoms sufficiently slowly onto a heated Si substrate.

Low interfacial trap density and sub-nm equivalent oxide thickness in In0.53Ga0.47As (001) metal-oxide-semiconductor devices using molecular beam deposited HfO2/Al2O3 as gate dielectrics

We investigated the passivation of In0.53Ga0.47As (001) surface by molecular beam epitaxy techniques. After growth of strained In0.53Ga0.47As on InP (001) substrate, HfO2/Al2O3 high-κ oxide stacks have been deposited in-situ after surface reconstruction engineering. Excellent capacitance-voltage characteristics have been demonstrated along with low gate leakage currents. The interfacial density of states (Dit) of the Al2O3/In0.53Ga0.47As interface have been revealed by conductance measurement, indicating a downward Dit profile from the energy close to the valence band (medium 1012 cm−2eV−1) towards that close to the conduction band (1011 cm−2eV−1). The low Dit’s are in good agreement with the high Fermi-level movement efficiency of greater than 80%. Moreover, excellent scalability of the HfO2 has been demonstrated as evidenced by the good dependence of capacitance oxide thickness on the HfO2 thickness (dielectric constant of HfO2 ∼20) and the remained low Dit’s due to the thin Al2O3 passivation layer. The...

Selective area growth of high quality InP on Si (001) substrates

In this work, we demonstrate the selective area growth of high quality InP layers in submicron trenches on exactly (001) oriented Si substrates by using a thin Ge buffer layer. Antiphase domain boundaries were avoided by annealing at the Ge surface roughening temperature to create additional atomic steps on the Ge buffer layer. The mechanism of Ge surface atomic step formation and the corresponding step density control method are illustrated. The elimination of antiphase boundaries from the optimized Ge buffer layer, together with the defect necking effect, yield defect-free top InP layers inside the trenches.

Polytypic InP Nanolaser Monolithically Integrated on (001) Silicon

On-chip optical interconnects still miss a high-performance laser monolithically integrated on silicon. Here, we demonstrate a silicon-integrated InP nanolaser that operates at room temperature with a low threshold of 1.69 pJ and a large spontaneous emission factor of 0.04. An epitaxial scheme to grow relatively thick InP nanowires on (001) silicon is developed. The zincblende/wurtzite crystal phase polytypism and the formed type II heterostructures are found to promote lasing over a wide wavelength range.

GaSb molecular beam epitaxial growth on p-InP(001) and passivation with in situ deposited Al2O3 gate oxide

The integration of high carrier mobility materials into future CMOS generations is presently being studied in order to increase drive current capability and to decrease power consumption in future generation CMOS devices. If III–V materials are the candidates of choice for n-type channel devices, antimonide-based semiconductors present high hole mobility and could be used for p-type channel devices. In this work we first demonstrate the heteroepitaxy of fully relaxed GaSb epilayers on InP(001) substrates. In a second part, the properties of the Al2O3/GaSb interface have been studied by in situ deposition of an Al2O3 high-κ gate dielectric. The interface is abrupt without any substantial interfacial layer, and is characterized by high conduction and valence band offsets. Finally, MOS capacitors show well-behaved C–V with relatively low Dit along the bandgap, these results point out an efficient electrical passivation of the Al2O3/GaSb interface.

Epilayer-Induced Structural Transition to b.c.c. Co during Epitaxial Growth of Co/Fe Superlattices

Molecular Beam Epitaxy was used to grow single-crystal b.c.c. Co/Fe multilayers on GaAs(10). The epitaxial relation between Co, Fe and GaAs has been determined during growth with Reflection High-Energy Electron Diffraction (RHEED). The presence of metastable b.c.c. Co was confirmed by 59Co NMR experiments. The thickness limit for the stability of the b.c.c phase established from the ex situ NMR study in a sandwiched structure is found to be twice the value determined from the in situ RHEED observed on an open surface. This shows that the Fe epilayer causes recrystallisation of the top atomic layers of Co to the b.c.c. structure.

Selective Area Growth of InP in Shallow-Trench-Isolated Structures on Off-Axis Si(001) Substrates

In this paper, we report a comprehensive investigation of InP selective growth in shallow trench isolation (STI) structures on Si(001) substrates 6° off-cut toward (111). Extended defect-free InP layers were obtained in the top region of 100 nm wide trenches. A thin Ge epitaxial layer was used as an intermediate buffer layer between the Si substrate and the InP layer. A Ge buffer was used to reduce the thermal budget for surface clean and to promote double-step formation on the surfaces. Baking the Ge surface in an As ambient improved the InP surface morphology and crystalline quality. InP showed highly selective growth in trenches without nucleation on SiO 2 . However, strong loading effects were observed at all growth pressures, which induced variation in local growth rates. We found trench orientation dependence of facet and stacking fault formation. More stacking faults and nanotwins originated from the STI sidewalls in [110] trenches. High quality InP layers were obtained in the top of the trenches along [110]. The stacking faults generated by the dissociation of threading dislocations are trapped at the bottom of the trenches with an aspect ratio greater than 2.

Epitaxial growth of bcc Co/Fe superlattices

Abstract Molecular beam epitaxy has been used to grow single-crystal bcc Co/Fe multilayers on GaAs[(110¯)] and MgO(001). The influence of the substrate and its temperature on the formation of bcc Co has been examined. The crystal quality and thickness stability limits for this metastable phase are significantly improved with respect to samples grown by rf sputtering. The presence of Fe epilayer and its thickness are found to be critical in the stabilization of bcc Co.