Heteroepitaxial Thin-Film Growth of a Ternary Nitride Semiconductor CaZn2N2

Autor: Tsuji, Masatake, Hanzawa, Kota, Kinjo, Hiroyuki, Hiramatsu, Hidenori, Hosono, Hideo
Rok vydání: 2019
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Zdroj: ACS Appl. Electon. Mater., vol. 1, pp. 1433-1438 (2019)
Druh dokumentu: Working Paper
DOI: 10.1021/acsaelm.9b00248
Popis: Zinc-based nitride CaZn2N2 films grown by molecular beam epitaxy (MBE) with a plasma-assisted active nitrogen-radical source are promising candidates of next-generation semiconductors for light-emitting diodes and solar cells. This nitride compound has previously only been synthesized in a bulk form by ultrahigh-pressure synthesis at 5 GPa. Three key factors have been found to enable heteroepitaxial film growth: (i) precise tuning of the individual flux rates of Ca and Zn, (ii) the use of GaN template layers on sapphire c-plane as substrates, and (iii) the application of MBE with an active N-radical source. Because other attempts at physical vapor deposition and thermal annealing processes have not produced CaZn2N2 films of any phase, this rf-plasma-assisted MBE technique represents a promising way to stabilize CaZn2N2 epitaxial films. The estimated optical band gap is ~1.9 eV, which is consistent with the value obtained from bulk samples. By unintentional carrier doping, n- and p-type electronic conductions are attained with low carrier densities of the order of 1013 /cm3. These features represent clear advantages when compared with Zn-based oxide semiconductors, which usually have much higher carrier densities irrespective of their intentionally undoped state. The carrier mobilities at room temperature are 4.3 cm2/(Vs) for electrons and 0.3 cm2/(Vs) for hole carriers, which indicates that transport properties are limited by grain boundary scattering, mainly because of the low-temperature growth at 250 {\deg}C, which realizes a high nitrogen chemical potential.
Comment: Accepted for publication in ACS Appl. Electon. Mater
Databáze: arXiv
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