Y. H. Chang

Achieving a low interfacial density of states in atomic layer deposited Al2O3 on In0.53Ga0.47As

Atomic-layer-deposited Al2O3 on In0.53Ga0.47As with short air exposure between the oxide and semiconductor deposition has enabled the demonstration of nearly ideal frequency-dependent and quasistatic capacitance-voltage (C-V) characteristics. The excellent quasistatic C-V characteristics indicate a high efficiency of 63% for the Fermi-level movement near the midgap. A low mean interfacial density of states (D¯it)∼2.5×1011 cm−2 eV−1 was determined under 1 MHz using a charge pumping method, which was also employed to probe the depth profile of bulk traps (Nbt) and the energy dependence of Dit at 50 kHz: a low Nbt∼7×1018 cm−3 and a Dit of (2–4)×1011 cm−2 eV−1 in the lower half of the band gap and a higher Dit of ∼1012 cm−2 eV−1 in the upper half of the band gap. The employment of charge pumping method has given a more accurate determination of Dit, which is usually overestimated using other commonly methods such as the Terman, conductance, and high-low frequencies due to the influence of weak inversion at ro...

Energy-band parameters of atomic layer deposited Al2O3 and HfO2 on InxGa1−xAs

X-ray photoelectron spectroscopy (XPS) combined with reflection electron energy loss spectroscopy (REELS) were used to determine the energy-band parameters, valence-band offsets ΔEV, conduction-band offsets ΔEC, and energy-band gaps Eg, of the atomic layer deposited (ALD) Al2O3 and HfO2 on InxGa1−xAs (x=0, 0.15, 0.25, and 0.53). Using REELS, Eg values of the ALD-Al2O3 and –HfO2 were estimated to be 6.77 and 5.56±0.05 eV, respectively. The ΔEV’s were determined by measuring the core level to valence band maximum binding energy difference from the XPS spectra. The ΔEC’s were then extracted from ΔEV’s and the energy-band gaps of the oxides and InxGa1−xAs, and are in good agreement with those estimated from the Fowler–Nordheim tunneling. The ΔEC’s and ΔEV’s are larger than 1.5 and 2.5 eV, respectively, for all the ALD-oxide/InxGa1−xAs samples.

Realization of high-quality HfO{sub 2} on In{sub 0.53}Ga{sub 0.47}As by in-situ atomic-layer-deposition

High {kappa} dielectric of HfAlO/HfO{sub 2} was an in-situ atomic-layer-deposited directly on molecular beam epitaxy grown In{sub 0.53}Ga{sub 0.47}As surface without using pre-treatments or interfacial passivation layers, where HfAlO (HfO{sub 2}:Al{sub 2}O{sub 3} {approx} 4:1) with high re-crystallization temperature was employed as the top oxide layer. The HfAlO ({approx}4.5 nm)/HfO{sub 2} (0.8 nm)/In{sub 0.53}Ga{sub 0.47}As metal oxide semiconductor capacitors have exhibited an oxide/In{sub 0.53}Ga{sub 0.47}As interface free of arsenic-related defective bonding, thermodynamic stability at 800 deg. C, and low leakage current densities of <10{sup -7} A/cm{sup 2} at {+-}1 MV/cm. The interfacial trap density (D{sub it}) spectra in absence of mid-gap peaks were obtained by temperature-dependent capacitance and conductance with D{sub it}s of 2-3 x 10{sup 12} eV{sup -1} cm{sup -2} below and 6-12 x 10{sup 11} eV{sup -1} cm{sup -2} above the mid-gap of In{sub 0.53}Ga{sub 0.47}As, respectively. An equivalent oxide thickness of less than 1 nm has been achieved by reducing the HfAlO thickness to {approx}2.7 nm with the same initial HfO{sub 2} thickness of {approx}0.8 nm.

Effective passivation of In0.2Ga0.8As by HfO2 surpassing Al2O3 via in-situ atomic layer deposition

High κ gate dielectrics of HfO2 and Al2O3 were deposited on molecular beam epitaxy-grown In0.2Ga0.8As pristine surface using in-situ atomic-layer-deposition (ALD) without any surface treatment or passivation layer. The ALD-HfO2/p-In0.2Ga0.8As interface showed notable reduction in the interfacial density of states (Dit), deduced from quasi-static capacitance-voltage and conductance-voltage (G-V) at room temperature and 100 °C. More significantly, the midgap peak commonly observed in the Dit(E) of ALD-oxides/In0.2Ga0.8As is now greatly diminished. The midgap Dit value decreases from ≥15 × 1012 eV−1 cm−2 for ALD-Al2O3 to ∼2–4 × 1012 eV−1 cm−2 for ALD-HfO2. Further, thermal stability at 850 °C was achieved in the HfO2/In0.2Ga0.8As, whereas C-V characteristics of Al2O3/p-In0.2Ga0.8As degraded after the high temperature annealing. From in-situ x-ray photoelectron spectra, the AsOx, which is not the oxidized state from the native oxide, but is an induced state from adsorption of trimethylaluminum and H2O, was fo...

Growth mechanism of atomic layer deposited Al2O3 on GaAs(001)-4 × 6 surface with trimethylaluminum and water as precursors

A microscopic view of in situatomic layer deposition Al2O3 on clean n-GaAs (001)-4 × 6 surfaces probed by high-resolution synchrotron radiation photoemission is presented. The precursors of trimethylaluminum (TMA) and water partially and selectively bond with the surface atoms without disturbing the atoms in the subsurface layer. The first-cycle TMA acts differently on the surface As atoms; namely, TMA is dissociative on As in the As-Ga dimer but is physisorbed on As that is 3-fold Ga coordinated. Water drastically alters the TMA-covered surface to etch off the dissociated TMA with As, giving Ga–O bonding for the later deposition of Al2O3 and at the same time to transform the configuration of the physisorbed TMA to bond strongly with As. Approximately six cycles of purges (TMA + water) are required before the interaction at the interface is complete. In comparison, the e-beam deposition of Al2O3 on GaAs greatly disturbs the III-Vsurface so that a high As 4+ charge state appears and the surface Ga atoms become clustered.

Interface Chemistry and Adhesion Strength Between Porous SiOCH Low-k Film and SiCN Layers

In this study, the interface chemistry and adhesion strength between a porous SiOCH extra-low-dielectric-constant film and SiCN etch stop layers were investigated with different plasma treatments. An interlayer of ∼6 6 nm thick between the porous SiOCH film and SiCN layers was found to be composed of Si, N, C, and O. The SiOCH/SiCN interface was constructed by mixing bonds, including Si-C-N, Si-N-C, Si-O-C, Si-O 2 , etc. Under H 2 and NH 3 plasma treatments, a large amount of weak Si-CH 3 and SiO-CH 3 bonds were broken, and more Si-O related bonds of high binding energy formed at the interfaces. Moreover, under the accumulation of sufficient shear stresses around the indented regions during nanoindentation tests, interface delamination between the porous SiOCH film and SiCN layers occurred. The interface adhesion energy between untreated porous SiOCH film and SiCN layers was accordingly measured as 1.68 J/m 2 . After plasma treatments, especially NH 3 plasma, the adhesion strength was effectively improved to 2.13 J/m 2 .

Room temperature ferromagnetic behavior in cluster free, Co doped Y2O3 dilute magnetic oxide films

Extensive structural analysis and magnetic properties are reported on cluster free, dilute magnetic oxide of Co doped Y2O3 (Co:Y2O3) film by low temperature deposition and characterized by extended x-ray absorption fine structure, x-ray absorption near edge structure, magnetometer, and x-ray magnetic circular dichroism. Room temperature ferromagnetism was observed, and the saturation magnetic moment was modulated by oxygen vacancy concentration through post annealing process. Oxygen vacancies are shown to play a crucial role in ferromagnetic ordering, as defect centers in the bound magnetic polaron model to account for this dilute magnetic oxide of medium band gap with low carrier concentration.

Ferromagnetism in cluster free, transition metal doped high κ dilute magnetic oxides: Films and nanocrystals

The structural and magnetic properties of high κ dilute magnetic oxides (DMOs) have been studied in two types of samples: thin films and nanocrystals, including Co doped HfO2 films, Co doped Y2O3 films, Co doped Y2O3 nanocrystals, and Mn doped Y2O3 nanocrystals. The characterizations were conducted by extended x-ray absorption fine structure, x-ray absorption near edge structure, and superconducting quantum interference device vibrating sample magnetometer. Oxygen vacancies are shown to play a crucial role in ferromagnetic ordering, as defect centers in the bound magnetic polaron model to account for DMOs with medium band gap and low carrier concentration. The observation of room temperature ferromagnetism in tri-valence oxide of Y2O3 as well as in tetra-valence oxide of HfO2 suggests a generic feature of transition metal doped high κ oxides as good candidates for DMO. The ability to modulate the magnetic behavior of DMO via oxygen vacancy concentration by means of post anneals can be exploited for potent...

InAs MOS devices passivated with molecular beam epitaxy-grown Gd2O3 dielectrics

InAs MOS devices passivated with molecular beam epitaxy (MBE)-grown Gd2O3 2–3 monolayers thick followed by an Al2O3 cap have demonstrated excellent electrical performances and interfacial properties. Band offset energies of in situ atomic-layer-deposited (ALD)-Al2O3/MBE-Gd2O3/InAs and ALD-Al2O3/InAs were determined by in situ x-ray photoelectron spectroscopy in conjunction with Fowler–Nordheim tunneling current analysis. A conduction-band offset energy (ΔEc) and a valence-band offset energy of 2.3 and 3.92 eV for ALD-Al2O3/InAs were determined, respectively. The insertion of a Gd2O3 layer increases the value of ΔEc by nearly 0.1 eV as compared to the case for Al2O3 directly deposited on InAs. The distribution of interfacial density of states (Dit) within the InAs bandgap, deduced by the conductance method at 77 K, gives a low Dit value of 1012 cm−2 eV−1 near the conduction-band edge. Moreover, with energy band engineering in the heterostructure, gate-first depletion channel InAs MOSFETs have produced drai...