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

Abstract

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 NH 4 OH 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 Al 2 O 3 or HfAlO layer capped with a thick plasma enhanced chemical vapor deposited (PECVD) low-k SiO 2 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.

Preparation of gallium nitride surfaces for atomic layer deposition of aluminum oxide

“…4 Silicon nitride (Si 3 N 4 ) is currently the standard for passivation of GaN surfaces because it readily forms an interface to GaN with good electrical properties. 5,6 Unfortunately, the band offset of silicon nitride on GaN is relatively small due to its modest band gap (5 eV), so the barrier to tunneling between the gate and channel is insufficient to significantly reduce leakage current when silicon nitride is used as a gate dielectric.…”

Equations for the Electron Density of the Two-Dimensional Electron Gas in Realistic AlGaN/GaN Heterostructures

“…Both capabilities are the results of high electron mobility and high electron density of the two-dimensional electron gas (2DEG), which is formed at the AlGaN/GaN heterojunction even in the absence of intentional doping [6]. The formation of 2DEG is considered to be due to the spontaneous and piezoelectric polarizations in the AlGaN/GaN heterostructure [7,8], however, the existing equations for the electron density in the 2DEG, N 2DEG , are inconsistent and confusing [6,9]. For example, the prevalent equations for N 2DEG do not include its dependence on the polarization charges [10,11].…”

Incorporation of Al or Hf in atomic layer deposition TiO2 for ternary dielectric gate insulation of InAlN/GaN and AlGaN/GaN metal-insulator-semiconductor-heterojunction structure

“…A few desired properties of insulators include high dielectric constants, 3 large conduction and valence band offsets to the semiconductor, 4 high crystallization temperature, low interface trap densities at the insulator/semiconductor interface and others. A high dielectric constant insulator is desired to maintain maximum channel control, increase AC transconductance, 5 and minimize threshold voltage shift. 3 TiO 2 is attractive due to its high reported dielectric constant in the range of 60-120; [6][7][8] however, it suffers from high leakage current and low crystallization temperature of 370 C. 9 A method to improve these values while maintaining a high dielectric constant is by forming a ternary compound such as Ti-Al-O or Ti-Hf-O.…”