Caroline Andersson

H plasma cleaning and a-Si passivation of GaAs for surface channel device applications

We discuss GaAs(001) cleaning and surface passivation for metal-oxide-semiconductor capacitors and field effect transistors fabricated with HfO2 as high-κ gate oxide. An amorphous-Si passivating layer is deposited by molecular beam deposition on a 2×1 reconstructed GaAs surface cleaned using a remote rf H plasma. The H plasma effectively removes C contaminants from the surface, but a progressive Ga enrichment and the presence of Ga–O bonds are observed. The capacitance-voltage measurements on capacitors under peripheral illumination show inversion, which is an indication of a passivated interface. The Dit distribution as function of energy in the band gap is extracted by using the conductance technique at high and low temperatures and is reported for HfO2/a-Si gate stacks on H-cleaned GaAs. The observed Dit distribution is asymmetric. Values as low as 7×1011 eV−1 cm−1 are found in the upper half of the band gap. One clear peak at 0.7 eV and a tail at 0.2 eV above the valence band maximum, which can be par...

Ge p-channel MOSFETS with La 2 O 3 and Al 2 O 3 gate dielectrics

We report on p-MOSFETs based on La₂O₃, Al₂O₃ and a mixture of both as high-k dielectric deposited by molecular beam epitaxy (MBE). Mobilities of about 140 cm²/Vs were achieved, which are 1.3 to 1.5 times larger than the universal hole mobility of Si/SiO₂. This demonstrates the potential advantage of La₂O₃-based Ge p-MOSFETs over Si devices. The negative threshold voltages V_T, which range between -0.2 and -1 V, make these gate stacks particularly attractive, given the fact that in several cases Ge p-MOSFETs exhibit an unwanted positive V_T shift.

Mobility and Dit distributions for p-channel MOSFETs with HfO2/LaGeOx passivating layers on germanium

Scaled layers of HfO2 on LaGeOx on Ge grown by molecular beam deposition and their electrical properties and passivation are discussed. The interfacial LaGeOx thickness as well as the deposition temperature of the HfO2 cap are varied and the effects thereof on properties like peak mobility and interface trap distributions are compared. We report on negative threshold voltages, around -0.8 V, in combination with scaled devices with a minimum EOT of 1.4 nm, which shows beneficial characteristics for the LaGeOx passivation of Ge. The effect of various post-metallization anneals in FG and O2 is shown to improve the gate stack properties of the scaled samples, yielding higher peak mobilities with maximum values of about 120 cm2/Vs for annealed samples. The impact of LaGeOx interfacial layer thickness and HfO2 deposition temperature on the density of interface traps (Dit) distributions for as-deposited and annealed samples is discussed, and Hf in-diffusion into the LaGeOx is shown to be detrimental to its passi...

Impact of La 2 O 3 Thickness on HfO 2 /La 2 O 3 /Ge capacitors and p-channel MOSFETs

In this study we report on HfO<inf>2</inf>/La<inf>2</inf>O<inf>3</inf>/Ge gate stacks grown by MBE with varying thicknesses of La<inf>2</inf>O<inf>3</inf> for MOS capacitors and pMOSFETs. Negative threshold voltages, around −0.8 V, in combination with scaled devices with an EOT of 1.4 nm shows good characteristics for the La<inf>2</inf>O<inf>3</inf> as a passivation for Ge. Also the effect of various post-metallization anneals in oxygen and forming gas is shown to improve the capacitors and MOSFETs, yielding mobility of 121 cm²/Vs.