Comparative analysis of the effects of tantalum doping and annealing on atomic layer deposited (Ta2O5)x(Al2O3)1­x dielectrics for GaN/AlxGa1­xN/GaN high electron mobility.transistors applications .

Potter, Richard, Partida, Teresa and Roberts, Joseph (2015) Comparative analysis of the effects of tantalum doping and annealing on atomic layer deposited (Ta2O5)x(Al2O3)1­x dielectrics for GaN/AlxGa1­xN/GaN high electron mobility.transistors applications . [Data Collection]

Collection description

This paper describes a method to optimally combine wide band gap Al2O3 with high dielectric constant (high­κ) Ta2O5 for gate dielectric applications. (Ta2O5)x(Al2O3)1­x thin films deposited by thermal atomic layer deposition (ALD) on GaN­capped AlxGa1­xN/GaN high electron mobility transistor (HEMT) structures have been studied as a function of the Ta modulation doping. X­ray photoelectron spectroscopy shows that the bandgap of the oxide films linearly decreases from 6.5 eV for pure Al2O3 to 4.6 eV for pure Ta2O5. The dielectric constant calculated from capacitance­voltage measurements also increases linearly from 7.8 for Al2O3 up to 25.6 for Ta2O5. The effect of post­deposition annealing in N2 at 600 ºC on the interfacial properties of undoped Al2O3 and Ta­doped (Ta2O5)0.12(Al2O3)0.88 films grown on GaN­HEMTs has been investigated. These conditions are analogous to the conditions used for source/drain contact formation in gate­first HEMT technology. A reduction of the Ga­O to Ga­N bond ratios at the oxide/HEMT interfaces is observed after annealing, which is attributed to a reduction of interstitial oxygen­related defects. As a result, the conduction band offsets (CBOs) of the Al2O3/GaN­HEMT and (Ta2O5)0.16(Al2O3)0.84/GaN­HEMT samples increased by 1.1 eV to 2.8 eV and 2.6 eV respectively, which is advantageous for n­type HEMTs. The results demonstrate that ALD of Ta­doped Al2O3 can be used to control the properties of the gate dielectric, allowing the κ­value to be increased, while still maintaining a sufficient CBO to the GaN­HEMT structure for low leakage currents.

Keywords: Ta-doped Al2O3, GaN, HEMT
Divisions: Faculty of Science and Engineering > School of Engineering
Depositing User: Richard Potter
Date Deposited: 10 Dec 2015 10:58
Last Modified: 14 Dec 2015 15:33
URI: http://datacat.liverpool.ac.uk/id/eprint/77

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