Electrical characterization of RuOx/n-GaN Schottky diodes formed by oxidizing ruthenium thin-films in normal laboratory air

Noah Allen,Louis Guido,Eric Carlson,Amrita Chakraborty,Timothy Ciarkowski

doi:10.1063/1.5125784

Abstract

Schottky diodes were formed by oxidizing Ru thin films deposited on n-type GaN at 400, 500, and 600 °C in normal laboratory air, and their electrical behavior was compared to that of a Ru/n-GaN reference device. The GaN epitaxial layers were grown via metalorganic chemical vapor deposition. The ruthenium films were deposited by electron beam evaporation. The Schottky barriers were characterized via current vs voltage (IV) and deep-level transient spectroscopy (DLTS) measurements between 70 and 400 K. The temperature dependent forward bias IV characteristics were fit, and the extracted temperature dependence of the effective barrier height for each device was shown to be caused by inhomogeneity at the metal/semiconductor interface. It was found that barrier inhomogeneity could be well described by a modified log-normal distribution. In reverse bias, it was shown that the low-energy tail of the barrier distribution is an important factor in determining leakage current. Favorable results occur for diodes oxidized at 400 and 500 °C, but raising the oxidation temperature to 600 °C results in a drastic increase in leakage current. DLTS measurements reveal one electron trap at EC − 0.57 eV in each of the samples. It was found that the concentration of this 0.57 eV trap increases substantially at 600 °C and that trap-assisted tunneling likely contributes an additional pathway for reverse leakage current.

Highlights

Gallium nitride (GaN) has been examined with great interest for its implementation in both optical and high power semiconductor devices
Favorable results occur for diodes oxidized at 400 and 500 ○C, but raising the oxidation temperature to 600 ○C results in a substantial increase in leakage current
Schottky diodes were formed by oxidizing Ru thin films deposited on n-type GaN at 400, 500, and 600 ○C in normal laboratory air, and their electrical behavior was compared to that of a Ru/n-GaN reference device

Summary

Introduction

Gallium nitride (GaN) has been examined with great interest for its implementation in both optical and high power semiconductor devices. Ruthenium oxide has been considered for making Schottky and ohmic contacts to various semiconductor devices because of its large work-function (>5.0 eV), low sheet resistance, high optical transparency, and good thermal stability. In the case of p-type GaN, ohmic contacts with specific contact resistivity in the range 10−5 to 10−6 Ω-cm have been realized by depositing Ru/Pt5 or Ru/Ni6 metal bilayers and annealing in nitrogen or oxygen, respectively. For n-type GaN, RuO2 formed by reactive sputtering of a RuO2 target has been employed to make Schottky diodes with large barrier height and low leakage current and to form Schottky gate electrodes on AlGaN/GaN heterojunction fieldeffect transistors.. Thin ruthenium layers deposited on n-GaN were annealed in oxygen to make transparent Schottky electrodes for use in metal-semiconductor-metal ultraviolet photodetectors. For n-type GaN, RuO2 formed by reactive sputtering of a RuO2 target has been employed to make Schottky diodes with large barrier height and low leakage current and to form Schottky gate electrodes on AlGaN/GaN heterojunction fieldeffect transistors. Alternatively, thin ruthenium layers deposited on n-GaN were annealed in oxygen to make transparent Schottky electrodes for use in metal-semiconductor-metal ultraviolet photodetectors.

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