High temperature (500 °C) operating limits of oxidized platinum group metal (PtOx, IrOx, PdOx, RuOx) Schottky contacts on β -Ga2O3

Abstract

Very high temperature operation β-Ga2O3 Schottky contacts were fabricated on moderately doped 2¯01 β-Ga2O3 single crystal substrates using four different types of intentionally oxidized platinum group metal (PGM) Schottky contacts (SCs), i.e., PtOx, IrOx, PdOx, and RuOx (x ∼ 2.0, 2.2, 1.1, and 2.4, respectively) formed by reactive rf sputtering of plain-metal targets in an oxidizing plasma. All four types of oxidized PGM SCs showed rectification ratios (at ± 3 V) of more than 10 orders of magnitude up to 300 °C, with almost no measurable increase in reverse leakage current density (Jrev) from that at room temperature. From 350 to 500 °C, a measurable increase in Jrev was observed, which was consistent with the thermionic emission of charge carriers over the respective image force (IF) lowered Schottky barriers. Despite this increase, PtOx(IrOx)[PdOx]{RuOx} SCs showed large rectification ratios (at ± 3 V) of 6 × 106(8 × 106)[5 × 105]{2 × 104} and IF-corrected barrier heights of 2.10(2.10)[1.90]{1.60} ± 0.05 eV, respectively, while operating at 500 °C. The significantly lower 500 °C barrier height of the RuOx SCs was due to the thermal reduction of RuOx to Ru that occurred above 400 °C. In contrast, the Schottky barriers of IrOx, PtOx, and PdOx SCs were thermally stable while operating at 500 °C, indicating significant potential for their use in very high temperature rectifying devices.

Bidirectional Control of the Band Bending at the (2̅01) and (010) Surfaces of β-Ga2O3 Using Aryldiazonium Ion and Phosphonic Acid Grafting

“…Beta gallium oxide (β-Ga 2 O 3 ) is an ultrawide-bandgap ( E g = 4.6–4.9 eV) transparent semiconducting oxide (TSO) that is attracting strong interest for applications such as high-efficiency power electronics, deep-ultraviolet photodetectors, electrocatalysis, gas and biological sensors, and transparent electronic devices. − It has one of the highest-known semiconductor breakdown strengths (∼8 MV/cm) and the availability of the bulk growth of high-quality single-crystal wafers . This should provide gains in speed and efficiency through the scaling of devices to small dimensions and by allowing the homoepitaxial growth of high-quality thin films. , However, β-Ga 2 O 3 technologies are still at an early stage of their development and a better understanding and a more-precise control of the electronic nature of the surfaces of β-Ga 2 O 3 are required to optimize the performance of real-world devices.…”

Superior high temperature performance of 8 kV NiO/Ga2O3vertical heterojunction rectifiers

“…While the heterojunction devices show no significant change in V B up to 600 K, the Schottky rectifiers show the commonly reported negative temperature coefficient. The temperature dependence of V B follows an approximate relationship of the form: 4,37–42 V B = V B0 [1 + β ( T − T 0 )]where β = −2 ± 0.6 V K −1 . The negative temperature coefficient precludes impact ionization as the breakdown mechanism in the Schottky rectifiers.…”

“…A less studied aspect has been the elevated temperature performance of such devices. 37–42 In this paper we report an investigation of the temperature dependence of the performance of NiO/Ga 2 O 3 and also co-fabricated Au/Ni/Ga 2 O 3 vertical rectifiers on the same wafers. While the breakdown voltage of the latter fall-off quickly with increasing temperature, the heterojunction rectifiers exhibit nearly temperature-independent V B to 600 K. While we focused on small area devices (100μ), we also fabricated a large area device (1 mm 2 ) to examine the scaling properties.…”

Exploiting the Nanostructural Anisotropy of β-Ga2O3 to Demonstrate Giant Improvement in Titanium/Gold Ohmic Contacts

“…For degenerate semiconductors, , u F can be approximated as , where γ = ( N D – N A )/ N C and N C = 2­(2π m * kT / h 2 ) 3/2 is the conduction band density of states. Since the extracted effective barrier height values are temperature-dependent (see Table S1 and Figure S7) and it has been reported previously that Schottky barriers to Ga 2 O 3 are spatially inhomogeneous, ,− we use an inhomogeneous barrier height (IB) to explain the temperature dependence of φ b,eff . From IB theory, the barrier height has a Gaussian distribution, leading to a temperature-dependence of φ b , eff that is expressed as where φ b0 is the mean barrier height and σ 0 is its standard deviation.…”