In this paper, InP barrier was used instead of InAlAs barrier due to its better interface quality with gate oxides. The effects of different InP barrier thicknesses on device performance were investigated. We have also deposited different ALD gate oxides (single Al2O3, HfO2 and Al2O3/HfO2 bilayer) and studied the influence of various oxides on oxide/barrier interface and device characteristics.

We present a first-principles study of the structure and dynamics of small As-interstitial complexes (AsI2, As2I2, AsI3, and As2I3) in crystalline Si. These complexes can be important components of stable As-interstitial clusters or play a key role in interstitial-mediated formation of As-vacancy clusters. Neutral AsI2 and As2I2 are identified as fast-diffusing species that contribute to As transient enhanced diffusion. We demonstrate that the extended defect configuration As2I3ext is a stable configuration with a binding energy of 2.64 eV. As2I3ext can serve as a nucleation site and facilitate the formation of larger As-interstitial clusters in presence of excess Si interstitials and high As concentration. We also discuss the implications of our findings on As transient enhanced diffusion and clustering and highlight the role of small As-interstitial complexes in ultrashallow junction formation.

The behavior of arsenic defect complexes at amorphous SiO2/Si(110) interfaces has been studied using density-functional theory calculation. We find that arsenic defect complexes that are stable in bulk Si show moderate energy gain in SiO2/Si interface region due to the interface-induced strain effect. We have identified three arsenic defect complex configurations, As-it, As2I2I, and As2I2II, which exist only at SiO2/Si interface. These interface arsenic defect complexes are highly stabilized due to their unique bonding configurations at SiO2/Si interface. Therefore, they could contribute to arsenic segregation as both initial stage precursor and dopant trapping sites. Our calculation indicates that arsenic atoms trapped in such interface complexes are electrically inactive. Finally, the formation and evolution dynamics of interface arsenic defect complexes are discussed.

A kinetic arsenic-interstitial interaction model has been developed to study and predict arsenic transient enhanced diffusion (TED) and deactivation behavior during ultrashallow junction (USJ) formation. This model is based on density functional theory and has been verified by previous experiments in which the significant role of interstitial mechanism in arsenic TED was revealed. The mechanism of enhanced and retarded arsenic diffusion in different point defect environments is investigated by utilizing this model in kinetic Monte Carlo simulation. The arsenic-interstitial pair, with low binding energy and low migration energy, is shown to be the major contributor to arsenic TED in silicon interstitial-rich situations. In addition, by using this model, we demonstrate the transient existence of arsenic-interstitial clusters (AsnIm) during postimplant annealing and propose their possible role in deactivation for short time annealings such as laser annealing and spike annealing. Moreover, we have developed a novel surface-trap based kinetic Monte Carlo model to simulate arsenic uphill diffusion in proximity of the Si∕SiO2 interface. The simulation results show that the activation behavior of the uphill portion of arsenic has considerable impact on the junction sheet resistance. The activation behavior of this arsenic is expected to become more important when USJ depth is scaled down further.

Using density-functional theory calculations we identified an interstitial-based fast boron diffusion mechanism in amorphous silicon. We found that interstitial-like point defects, omnipresent in as-implanted silicon, to be very stable in an amorphous network and can form highly mobile pair with Boron atoms. The transient existence of such point defects in amorphous silicon is suggested to play an important role in boron diffusion. We found the activation energy for this pathway to be 2.73 eV, in good agreement with experimental results. In addition, this mechanism is consistent with the experimentally reported transient and concentration-dependent features of boron diffusion in amorphous silicon.

We propose new structural configurations and novel diffusion mechanisms for neutral di-arsenic interstitial (As2I2) in silicon with a first-principle density functional theory simulation within the generalized gradient approximation. With an assumption of excess silicon interstitials and high arsenic concentrations, neutral As2I2 is expected to be favorable and mobile with low-migration barrier. Moreover, because the diffusion barrier of arsenic interstitial pairs (AsI) is very low (< 0.2eV) under the same conditions, As2I2 can be easily formed and likely intermediate stage of larger arsenic interstitial clusters.

We report that arsenic diffusion can be enhanced and retarded by surrounding interstitial rich and vacancy rich environments created by Si point defect engineering implant. The enhancement and retardation can be attributed to the dominant arsenic interstitial diffusion mechanism during post-implant anneal. Kinetic Monte Carlo simulations with newly implemented models show good match with experiments. Our study suggests the importance of arsenic interstitial mechanism and a possible approach for n-type ultra shallow junction fabrication.

Arsenic enhanced or retarded diffusion is observed by overlapping the dopant region with, respectively, interstitial-rich and vacancy-rich regions produced by Si implants. Enhanced diffusion can be attributed to interstitial-mediated diffusion during postimplant annealing. Two possible mechanisms for diffusion retardation, interstitial-vacancy recombination and dopant clustering, are analyzed in additional experiments. The point defect engineering approach demonstrated in this letter could be applied to fabrication of n-type ultrashallow junctions.

Backside-illuminated germanium photodiodes fabricated on silicon substrate with two Si xGe1-x buffer layers are reported. At 1.3 mum, the responsivity was 0.62 A/W for reverse bias greater than 0.1 V. The 3-dB bandwidth was 21.5 GHz at 10-V reverse bias, achieving a bandwidth-efficiency product of 12.6 GHz

We report photodiodes fabricated on Ge grown on Si substrate. At 2V bias these photodiodes exhibited 28mA/cM(2) dark current, 0.57A/W responsivity, and 4GHz bandwidth. Monolithic fabrication of Ge PIN photodiodes with Si MOSFETs is also described.