L. K. Chu

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...

Ga2O3(Gd2O3) on Ge without interfacial layers: Energy-band parameters and metal oxide semiconductor devices

Ga2O3(Gd2O3) (GGO) directly deposited on Ge substrate in ultrahigh vacuum, without a passivation layer such as GeOxNy or Si, has demonstrated excellent electrical performances and thermodynamic stability. Energy-band parameters of GGO/Ge have been determined by in situ x-ray photoelectron spectroscopy in conjunction with reflection electron energy loss spectroscopy and current transport of Fowler–Nordheim tunneling. A conduction-band offset and a valence-band offset of ∼2.3 and ∼2.42 eV, respectively, have been obtained. Moreover, self-aligned Ge pMOSFETs of 1-μm-gate length using Al2O3/GGO as the gate dielectrics have shown a high drain current and a peak transconductance of 252 mA/mm, and 143 mS/mm, respectively.

High-resolution core-level photoemission study of CF4-treated Gd2O3(Ga2O3) gate dielectric on Ge probed by synchrotron radiation

High-resolution core-level photoemission analysis using synchrotron radiation was used to investigate the superior electrical performance of aGa 2 O 3 ( Gd 2 O 3 ) gate dielectric on Ge(001) after CF 4 treatment. Prior to the treatment, a thin germanate-like oxide layer that formed at the interface prevented Ge from diffusing to the surface. The Gesurface retained a small amount of buckled dimers from the as-grown sample. The buckled dimers were quickly removed by CF 4 plasma treatment followed by an annealing process, resulting in a more uniform interface than that of the as-grown sample. The detailed interfacial electronic structure for the untreated and treated samples are presented.

High-quality molecular-beam-epitaxy-grown Ga2O3(Gd2O3) on Ge (100): Electrical and chemical characterizations

High-κ dielectric Ga2O3(Gd2O3) (GGO) has been deposited on Ge (100) at room temperature using molecular beam epitaxy. In situ angular-resolved x-ray photoelectron spectroscopy on the GGO/Ge after gate dielectric deposition and 500°C postdeposition annealing has exhibited negligible Ge interdiffusion, thus revealing high thermal stability of the heterostructure. The CF4-plasma treatment on the passivated GGO/Ge has greatly improved the capacitance-voltage characteristics of the metal-oxide-semiconductor capacitors, besides the very low gate leakage current density of 3.2×10−9A∕cm2 at a flat-band voltage +1V. These excellent interfacial characteristics have been achieved without employing any intentional passivation layers.

Metal Oxide Semiconductor Device Studies of Molecular-Beam-Deposited Al2O3/InP Heterostructures with Various Surface Orientations (001), (110), and (111)

Passivation of InP surface was carried out in situ with molecular-beam-deposited high-κ Al2O3. InP samples with surface orientations of (001), (110), and (111) were investigated. An atomically smooth Al2O3/InP(001) interface was observed without interfacial layer formation. In-rich surfaces gave better interfacial quality as evidenced by the improved capacitance–voltage characteristics, exhibiting smaller frequency dispersions and minimized inversion response. The energy distributions of interfacial traps (Dits) were revealed by conductance measurement for the samples with In-rich surfaces. The Dits are as low as ~1011 cm-2 eV-1 near the conduction band edge, while those near the midgap region are ~1013 cm-2 eV-1.

Achieving a Low Interfacial Density of States with a Flat Distribution in High-κ Ga2O3(Gd2O3) Directly Deposited on Ge

The interfacial density of states (Dit) distribution of high-κ dielectric Ga2O3(Gd2O3) [GGO] directly deposited on n-type Ge(100) without invoking any interfacial passivation layer (IPL) was established using conductance measurements and charge pumping (CP) technique. The conductance measurements yielded Dit values in the range of (1–4)×1011 cm-2 eV-1 from the mid-gap energy to the conduction band edge within the Ge band gap, which are consistent with the mean Dit value of ~2×1011 cm-2 eV-1 near the mid-gap obtained independently by the CP method. The flat Dit distribution at the conduction band edge compares favorably with those attained using IPLs such as SiO2/Si-cap and GeO2.

Electronic structures of Ga203(Gd203) gate dielectric on n-Ge(001) as grown and after CF4 plasma treatment: A synchrotron-radiation photoemission study

The interfacial electronic structure of Ga2O3(Gd2O3) (GGO) on n-Ge(001) is determined using high-resolution synchrotron radiation photoemission. The excitation photon energy was specifically chosen to observe the interaction at the GGO/Ge interface (hv = 463 eV) as well as the possible diffusion of Ge up to the GGO surface (hν = 120 eV). The Ge 3d core-level spectra were fit to extract the contributing components. Photoemission measurements were done for four samples, as deposited, N2annealed, CF4plasmatreated, and the combined CF4plasmatreated and N2annealed. No surface passivation was employed prior to the dielectric deposition. SRPES data clearly showed that the elemental Ge in the as-deposited sample was effectively kept in the wafer. Prevention of Gediffusion was attributed to formation of a thin germanatelike oxide layer. Other than contributions from bulk Ge, an analytical fit to the Ge 3d cores gives two components that are associated with bonding to Gd2O3 (GdGe*) and to Ga2O3 (GaGe*), which had chemical shifts of 3.46 and 1.80 eV, respectively. We hereby label them as MGe*, where M stands for either Gd2O3 or Ga2O3. Area occupations of the GdGe* and GaGe* oxides are ∼87% and ∼10%, respectively. A CF4plasma treatment disturbs the film itself as well as the interfacial oxide so that the GGO surface begins to show both elemental Ge and Ga. Nevertheless, the follow-up N2annealing produces the GdGe*+GaGe* layer with characteristics similar to those at the GGO/Ge interface. Both GdGe* and GaGe* states in the CN-treated sample show simultaneously a smaller chemical shift by 0.31 ± 0.02 eV than those in the as-deposited sample. The treatments also induce upward band bending on both the high κ and the Ge sides, which causes the valence band offset at the GGO/Ge interface to be 2.95 eV.

Direct determination of flat-band voltage for metal/high κ oxide/ semiconductor heterointerfaces by electric-field-induced second-harmonic generation

We have employed electric-field-induced second-harmonic (EFISH) generation to determine the flat-band voltage (VFB) of Cr/ALD-Al2O3/MBE-HfO2/n-Si (001) MOS structure. Due to the phase sensitivity of EFISH signal to the electric field in the space charge region, the VFB of −1.20±0.07 V was determined by analyzing the relative phase change in the EFISH signal as a function of the applied gate voltage. The obtained value is in good agreement with that estimated by the capacitance-voltage measurement. This study demonstrated an all-optical technique to directly determine the flat-band voltage for the high κ oxide/Si heterointerfaces.

Achieving high-performance Ge MOS devices using high-к gate dielectrics Ga 2 O 3 (Gd 2 O 3 ) of sub-nm EOT

When channel materials other than Si are being considered to enhance the carrier mobility, Ge has always been one viable candidate since it possesses higher carrier mobility than those of Si. However, it is difficult to achieve a high-quality oxide/Ge interface comparable to SiO<inf>2</inf>/Si due to unfavorable surface properties and water-soluble native oxides of Ge. Over the past 4–5 years, two major techniques have been shown to effectively passivate the Ge surface by utilizing Si(SiO<inf>2</inf>) [1] and thermally grown stoichiometric GeO<inf>2</inf> [2,3] as the passivation layers, thus giving low D<inf>it</inf>s of ∼10¹¹ cm⁻²eV⁻¹. However, the use of the interfacial passivation layers (IPL) encountered a major hindrance primarily due to their relatively lower к values which have an adverse effect on the critical requirement of great reduction of equivalent oxide thickness (EOT) for future CMOS applications. An effective approach to achieve the ultimate EOT down-scaling is to directly deposit high-к dielectrics on Ge without IPLs, while maintaining a high к value and decent oxide/Ge interface quality.

Nano-electronics of high k dielectrics on exotic semiconductors for science and technology beyond Si CMOS

We have achieved high device performance in self-aligned inversion-channel InGaAs MOSFETs, as well as a CET of < 1 nm, a D<inf>it</inf> ≤ 10¹¹ eV⁻¹cm⁻², and high-temperature thermal stability withstanding >850°C RTA in GGO and a CET of < 1 nm in ALD-HfO<inf>2</inf> on InGaAs. Remarkable device performances in self-aligned, inversion-channel Ge MOSFET using GGO without any interfacial passivation layers (IPLs), and inversion-channel and accumulation type GaN MOSFETs with high ks as gate dielectrics have also been attained. Interfacial characteristics including energy band parameters were studied using x-ray photoelectron spectroscopy (XPS).