We present evidence, from theory and experiment, that ZnSnN 2 and MgSnN 2 can be used to match the band gap of InGaN without alloying-by exploiting cation disorder in a controlled fashion. We base this on the determination of S, the long-range order parameter of the cation sublattice, for a series of epitaxial thin films of ZnSnN 2 and MgSnN 2 using three different techniques: x-ray diffraction, Raman spectroscopy, and in situ electron diffraction. We observe a linear relationship between S 2 and the optical band gap of both ZnSnN 2 (1.12-1.98 eV) and MgSnN 2 (1.87-3.43 eV). The results clearly demonstrate the correlation between controlled heterovalent cation ordering and the optical band gap, which applies to a broad group of emerging ternary heterovalent compounds and has implications for similar trends in other material properties besides the band gap.
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.
Oxidized iridium (IrOx) Schottky contacts (SCs) with excellent high temperature stability were fabricated on 2¯01 β-Ga2O3 single crystal substrates. These IrOx:β-Ga2O3 SCs were operated at temperatures from 24 to 350 °C with only a very small increase in reverse leakage current, while maintaining extremely high rectification ratios (at ±3 V) of more than 10 orders of magnitude at all temperatures, including 350 °C. This remarkable high temperature performance was due to their very high and thermally stable rectifying barriers that, after an initial heat-related improvement, were characterized by zero-bias effective barrier heights of 2.05 ± 0.02 eV and ideality factors of 1.05–1.10, which were almost unchanged by further repeated operation at 350 °C. The reverse leakage current density at 350 °C was only ∼2.3 × 10−9 A cm−2 (∼3.0 pA) at −3 V and ∼7.5 × 10−8 A cm−2 (∼100 pA) at −100 V. These IrOx:β-Ga2O3 SCs represent a significant improvement in high-temperature β-Ga2O3 SC performance, with considerable potential for the fabrication of high temperature β-Ga2O3 rectifying diodes, deep UV photodetectors, and metal-semiconductor field effect transistors.
MgSnN 2 thin films have been grown on yttria-stabilized zirconia substrates via plasma-assisted molecular beam epitaxy and analyzed using reflection high-energy electron diffraction, X-ray diffraction, optical transmission, and cathodoluminescence. By systematically varying the growth parameters, particularly the substrate temperature, Mg:Sn flux ratio, substrate, and nitrogen flow rate, we were able to achieve high quality films and control disorder in the cation sublattice. This control of disorder allows for the ability to adjust the band gap continuously over a wide range of values.
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