Casey Kirkpatrick

Energy-band alignment of Al2O3 and HfAlO gate dielectrics deposited by atomic layer deposition on 4H–SiC

Energy band alignment and band gap of Al2O3 and HfAlO films grown by atomic layer deposition on 4H–SiC were determined using x-ray photoelectron spectroscopy. Al2O3 exhibited a symmetric band profile with a conduction band offset (ΔEC) of 1.88 eV and a valence band offset (ΔEV) of 1.87 eV. HfAlO yielded a smaller ΔEC of 1.16 eV and ΔEV of 1.59 eV. The higher dielectric constant and higher effective breakdown field of HfAlO compared to Al2O3, coupled with sufficient electron and hole barrier heights, makes it a potential dielectric for use on 4H–SiC, and provokes interest in further investigation of HfAlO/4H–SiC properties.

Atomic Layer Deposition of

This letter investigates the electrical properties of SiO₂ gate dielectric on GaN heterostructures deposited by atomic layer deposition (ALD). ALD SiO₂ has a dielectric constant of 3.9 and a bandgap of 8.8 eV. ALD SiO₂ provides a good interface to GaN and minimizes the interfacial layer growth. The threshold voltage of metal-oxide-semiconductor heterojunction field-effect transistors with ALD SiO₂ dielectric is -1.5 V, owing to a fixed charge concentration of -1.6 × 10¹² cm^-2. It was also found that devices with ALD SiO₂ dielectric exhibit three orders of magnitude reduction in gate leakage current compared to conventional Schottky gate HFETs.

\hbox{SiO}_{2}

In order to minimize ac–dc dispersion, reduce gate leakage and maximize ac transconductance, there is a critical need to identify optimal interfaces, low-k passivation dielectrics and high-k gate dielectrics. In this paper, an investigation of different atomic layer deposited (ALD) passivation dielectrics on AlGaN/GaN-based hetero-junction field effect transistors (HFETs) was performed. Angle-resolved x-ray photoelectron spectroscopy revealed that HCl/HF and NH4OH cleans resulted in a reduction of native oxide and carbon levels at the GaN surface. The role of high temperature anneals, following the ALD, on the effectiveness of passivation was also explored. Gate-lag measurements on HFETs passivated with a thin ALD high-k Al2O3 or HfAlO layer capped with a thick plasma enhanced chemical vapor deposited (PECVD) low-k SiO2 layer, annealed at 600–700 °C, were found to be as good as or even better than those with conventional PECVD silicon nitride passivation. Further, it was observed that different passivation dielectric stacks required different anneal temperatures for improved gate-lag behavior compared to the as-deposited case.

for AlGaN/GaN MOS-HFETs

In this work, we have demonstrated a normally-off AlGaN/GaN metal-oxide semiconductor heterojunction field effect transistor (MOSHFET) wherein the enhancement mode operation is enabled by charge storage within a metal floating gate embedded in a dielectric stack and negative charges in the tunnel oxide. By combining ALD SiO2 and TaN floating gate (FG), up to 6V of VT shift after pulse programming (corresponding ∼ 1.2×1013 charges/cm2 stored within the FG) is obtained which results in a normally-off device with low gate leakage and good transconductance.

Properties of atomic layer deposited dielectrics for AlGaN/GaN device passivation

Contact resistivity is a key contributor to the parasitic series resistance of nanoscale MOSFETs. Since the contact resistivity is an exponential function of the Schottky barrier height, new contact materials that can provide smaller barrier heights to source-drain junctions are needed. Platinum germanosilicide (PtSi_1-xGe_x) is of interest as a contact material to the recessed Si_1-xGe_x junctions of p-channel MOSFETs due to the large work function of platinum silicide (PtSi). In this paper, we explore the impact of in-plane biaxial compressive strain in Si_1-xGe_x layers on PtSi_1-xGe_x formation and the impact of the PtSi_1-xGe_x on the strain in Si_1-xGe_x. The parameters considered in this paper include the Ge content, the thickness of the Si_1-xGe_x epitaxial layer, and the PtSi_1-xGe_x thickness. The results show that the resistance, surface morphology, and the crystalline structure of the PtSi_1-xGe_x films are independent of the strain in the original Si_1-xGe_x layer. The results also indicate that PtSi_1-xGe_x does not influence the strain in the Si_1-xGe_x layer. The barrier-height measurements suggest the presence of Fermi-level pinning, and the pinning position is independent of the strain in the alloy, and it is primarily determined by the Ge concentration. As a result of Fermi-level pinning, hole Schottky barrier height of PtSi_1-xGe_x-Si_1-xGe_x contacts is 0.1-0.2 eV higher than that of the PtSi-Si contacts.

Normally-off AlGaN/GaN-on-Si MOSHFETs with TaN floating gates and ALD SiO 2 tunnel dielectrics

The effect of the atomic layer deposition (ALD) HfAlO high-k dielectric on device transport properties and breakdown characteristics of an AlGaN/GaN metal?oxide?semiconductor hetero-junction field-effect transistor (MOS-HFET) was evaluated based on temperature-dependent measurements. It was found that the MOS-HFET device with a HfAlO gate dielectric shows high-channel mobility greater than the Schottky HFET device for the measured temperature range (25?150??C). In the case of off-state breakdown characteristics, the MOS-HFET device greatly suppressed gate leakage currents for measured temperatures (25?200??C) resulting in improvements in off-state breakdown characteristics. In contrast, large gate/drain leakage currents were observed for the Schottky HFET device at high temperature (>100??C) resulting in about 200?V of breakdown voltage reduction. It was also found that the ALD HfAlO layer reduced surface leakage current by passivating the GaN surface effectively. Therefore, the MOS-HFET structure with the HfAlO gate dielectric is very attractive for GaN-based high-power and high-temperature device applications.

Platinum Germanosilicide Contacts Formed on Strained and Relaxed

AlGaN/GaN heterojunction field effect transistors (HFET) are promising candidates for both power and RF applications due to their superior material properties [1]. High-speed switching and reduction in power losses can be achieved by the use of the two-dimensional electron gas (2DEG) that forms between AlGaN barrier and GaN layer. However, a conventional HFET device with a Schottky gate suffers from high gate leakage current which in turn limits device performance [2]. The incorporation of a gate dielectric layer between the Schottky gate and AlGaN barrier can suppress the gate leakage current but the electrical characteristics are subjected to dielectric quality caused by various deposition method. ALD deposition can provide several advantages such as low temperature processing, conformal deposition, and precise thickness control. By using ALD it is possible to deposit damage free dielectrics on AlGaN/GaN layer with low defect density resulting in the performance enhancement of the device [3]. In this work, we investigate the electrical properties of a MOSHFET with ALD HfAlO gate dielectric and compare to the conventional HFET device.