Glen Wilk

GaN metal-oxide-semiconductor high-electron-mobility-transistor with atomic layer deposited Al2O3 as gate dielectric

We report on a GaN metal-oxide-semiconductor high-electron-mobility-transistor (MOS-HEMT) using atomic-layer-deposited (ALD) Al2O3 as the gate dielectric. Compared to a conventional GaN high-electron-mobility-transistor (HEMT) of similar design, the MOS-HEMT exhibits several orders of magnitude lower gate leakage and several times higher breakdown voltage and channel current. This implies that the ALD Al2O3∕AlGaN interface is of high quality and the ALD Al2O3∕AlGaN∕GaN MOS-HEMT is of high potential for high-power rf applications. In addition, the high-quality ALD Al2O3 gate dielectric allows the effective two-dimensional (2D) electron mobility at the AlGaN∕GaN heterojunction to be measured under a high transverse field. The resulting effective 2D electron mobility is much higher than that typical of Si, GaAs or InGaAs metal-oxide-semiconductor field-effect-transistors (MOSFETs).

HfO2 and Al2O3 gate dielectrics on GaAs grown by atomic layer deposition

High-performance metal-oxide-semiconductor field effect transistors (MOSFETs) on III–V semiconductors have long proven elusive. High-permittivity (high-κ) gate dielectrics may enable their fabrication. We have studied hafnium oxide and aluminum oxide grown on gallium arsenide by atomic layer deposition. As-deposited films are continuous and predominantly amorphous. A native oxide remains intact underneath HfO2 during growth, while thinning occurs during Al2O3 deposition. Hydrofluoric acid etching prior to growth minimizes the final interlayer thickness. Thermal treatments at ∼600°C decompose arsenic oxides and remove interfacial oxygen. These observations explain the improved electrical quality and increased gate stack capacitance after thermal treatments.

Leakage current and breakdown electric-field studies on ultrathin atomic-layer-deposited Al2O3 on GaAs

Atomic-layer deposition (ALD) provides a unique opportunity to integrate high-quality gate dielectrics on III-V compound semiconductors. We report detailed leakage current and breakdown electric-field characteristics of ultrathin Al2O3 dielectrics on GaAs grown by ALD. The leakage current in ultrathin Al2O3 on GaAs is comparable to or even lower than that of state-of-the-art SiO2 on Si, not counting the high-k dielectric properties for Al2O3. A Fowler-Nordheim tunneling analysis on the GaAs∕Al2O3 barrier height is also presented. The breakdown electric field of Al2O3 is measured as high as 10MV∕cm as a bulk property. A significant enhancement on breakdown electric field up to 30MV∕cm is observed as the film thickness approaches to 1nm.

Capacitance-voltage studies on enhancement-mode InGaAs metal-oxide-semiconductor field-effect transistor using atomic-layer-deposited Al2O3 gate dielectric

Atomic layer deposition (ALD) Al2O3 is a high-quality gate dielectric on III-V compound semiconductor with low defect density, low gate leakage, and high thermal stability. The high-quality of Al2O3∕InGaAs interface surviving from high temperature annealing is verified by excellent capacitance-voltage (CV) curves showing sharp transition from depletion to accumulation with “zero” hysteresis, 1% frequency dispersion per decade at accumulation capacitance, and strong inversion at split CV measurement. An enhancement-mode n-channel InGaAs metal-oxide-semiconductor field-effect-transistor is also demonstrated by forming true inversion channel at Al2O3∕InGaAs interface.

High-κ Dielectric Materials for Microelectronics

This article reviews the current status of high-κ dielectric materials for microelectronics. In particular, recent work impacting the integration of these high-κ materials for gate dielectric and capacitor applications in advanced scaled microelectronic devices is reviewed.

Nucleation and interface formation mechanisms in atomic layer deposition of gate oxides

We present an in situ infrared spectroscopic study of the interface formation during atomic layer deposition of alternative high-permittivity (high-κ) gate dielectrics. Layer-by-layer oxide growth may be achieved by alternating pulses of a molecular metal precursor (e.g., trimethylaluminum for aluminum oxide growth) and water vapor. Contrary to common belief, we find that the metal precursor, not the oxidizing agent, is the key factor to control Al2O3 nucleation on hydrogen-terminated silicon. Metal surface species catalyze subsurface Si oxidation. These findings have direct implications on growth conditions to optimize semiconductor-dielectric interfaces.

Correlation of annealing effects on local electronic structure and macroscopic electrical properties for HfO2 deposited by atomic layer deposition

Atomic-scale electron spectroscopy is used to determine the local electronic structure of atomic-layer-deposited HfO2 gate dielectrics as a function of annealing conditions. Oxygen core-loss spectra from monoclinic crystallites exhibit a more strongly pronounced crystal-field splitting with increasing anneal temperature up to 1000 °C, consistent with a decrease in point defects. Concomitantly, electrical measurements of the same structures show a correlated reduction of fixed charge. An unintentional ∼5 A SiO2 layer is observed at the top interface, between the HfO2 and poly-Si electrode. No Hf–silicate intermixing is detected at either interface on a scale down to 2 A.

Photo-assisted capacitance-voltage characterization of high-quality atomic-layer-deposited Al2O3∕GaN metal-oxide-semiconductor structures

The authors report on an Al2O3 gate oxide deposited on n-type GaN by atomic layer deposition technique. The high-frequency C‐V characteristic shows deep-depletion behavior at room temperature due to the wide band gap semiconductor nature of GaN. Systematic photoassisted C‐V measurements demonstrate the importance of postdeposition-annealing process which could improve the average interface trap density Dit of (1–2)×1012∕cm2eV on the as-grown films to 7×1010∕cm2eV on the same films after 800°C rapid thermal annealing in a N2 ambient. The high-frequency C‐V technique or Terman technique is also applied to estimate the mid-gap Dit and compare to the results from photoassisted C‐V technique.

Minority-carrier characteristics of InGaAs metal-oxide-semiconductor structures using atomic-layer-deposited Al2O3 gate dielectric

Atomic layer deposition (ALD) provides a unique opportunity to integrate high-quality gate dielectrics on III-V compound semiconductors. ALD Al2O3 is a high-quality gate dielectric on III-V compound semiconductor with low interface trap density, low gate leakage, and high thermal stability. The authors study the minority-carrier response of Al2O3∕InGaAs metal-oxide-semiconductor (MOS) structures, which sheds light on the device physics for realizing high-performance inversion-type metal-oxide-semiconductor field-effect-transistor. The minority carriers in InGaAs do not respond to a small ac signal down to 100Hz at 300K, while they respond to up to 100kHz at 500K. Temperature dependent capacitance-voltage (C-V) measurement on the InGaAs MOS structure reveals the activation energy (Ea) of the minority-carrier recombination to be about 0.62eV.

Formation and characterization of nanometer scale metal-oxide-semiconductor structures on GaAs using low-temperature atomic layer deposition

Atomic layer deposition (ALD) grown Al2O3 has excellent bulk and interface properties on III-V compound semiconductors and is used as gate dielectric for GaAs and GaN metal-oxide-semiconductor field-effect transistors (MOSFETs). The low-temperature (LT) ALD technology enables us to fabricate 100nm MOS structures on GaAs, defined by nanoimprint lithography. The electrical characterization of these nanostructured dielectrics demonstrates that the bulk oxide films and the oxide-GaAs interfaces are of high quality even in nanometer scale. The submicron gate length GaAs MOSFET formed by LT-ALD and lift-off process shows well-behaved transistor characteristics. This GaAs MOSFET process is ready to scale the gate length below 100nm for ultra-high-speed or THz transistor applications.