Correlating electron trapping and structural defects in Al2O3 thin films deposited by plasma enhanced atomic layer deposition

Emanuela Schilirò,Fabrizio Roccaforte,Giuseppe Greco,Raffaella Lo Nigro,Salvatore Di Franco,Corrado Spinella,Patrick Fiorenza,Corrado Bongiorno

doi:10.1063/5.0023735

Emanuela Schilirò, Fabrizio Roccaforte + Show 6 more

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https://doi.org/10.1063/5.0023735

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Abstract

In this article, electron trapping in aluminum oxide (Al2O3) thin films grown by plasma enhanced atomic layer deposition on AlGaN/GaN heterostructures has been studied and a correlation with the presence of oxygen defects in the film has been provided. Capacitance–voltage measurements revealed the occurrence of a negative charge trapping effect upon bias stress, able to fill an amount of charge traps in the bulk Al2O3 in the order of 5 × 1012 cm−2. A structural analysis based on electron energy-loss spectroscopy demonstrated the presence of low-coordinated Al cations in the Al2O3 film, which is an indication of oxygen vacancies, and can explain the electrical behavior of the film. These charge trapping effects were used for achieving thermally stable (up to 100 °C) enhancement mode operation in AlGaN/GaN transistors, by controlling the two-dimensional electron gas depletion.

Highlights

Thin Al2O3 layers can be used as a gate insulator to reduce the leakage current in gallium nitride (GaN) high electron mobility transistors (HEMTs) or as a passivation layer to reduce the current collapse phenomena in these devices
Perevalov et al estimated an oxygen vacancy content for amorphous Al2O3 thin films grown by atomic layer deposition (ALD) in the order of 7 × 1020 cm−3.7 Based on the above considerations, since the experimental trapped charge density is lower than the expected oxygen vacancy density, it is plausible to argue that not all these intrinsic defects are electrically active in our system
Electron trapping occurring in Al2O3 films grown by plasma enhanced atomic layer deposition on AlGaN/GaN heterostructures has been monitored and correlated with the structural properties of the films

Summary

Introduction

Aluminum oxide (Al2O3) is an attractive material for a variety of applications in electronic devices.1 As an example, thin Al2O3 layers can be used as a gate insulator to reduce the leakage current in gallium nitride (GaN) high electron mobility transistors (HEMTs) or as a passivation layer to reduce the current collapse phenomena in these devices.2,3 The great interest toward Al2O3 in the GaN technology arises from the excellent physical properties of this insulator, i.e., high dielectric constant κ (∼9), high critical electric field (10 MV/cm), large bandgap (∼8.9), and favorable band alignment with GaN.4In this context, atomic layer deposition (ALD) is the most widely used technique today to deposit Al2O3 thin films on GaN. The electron trapping phenomena in Al2O3 thin films deposited by plasma enhanced atomic layer deposition on AlGaN/GaN heterostructures have been investigated and correlated with the interface and bulk structural quality of the film.

Results

Conclusion