Structural, electrical, and optical characterization of as grown and oxidized zinc nitride thin films

Abstract

Zinc Nitride (Zn3N2) films were grown by DC sputtering of a Zn target in a N2 plasma under a variety of different growth conditions, which resulted in the deposition of films with variable compositions. The as deposited films exhibited a polycrystalline Zn3N2 structure, which was converted to a ZnO-based structure after several weeks of ambient exposure. Zn3N2 films that were N-poor exhibited electrical properties indicative of a natively doped semiconductor and reached a minimum carrier concentration in the order of 1018 cm−3 at compositions, which approached the stoichiometric ratio of Zn3N2. A maximum carrier mobility of 33 cm2 V−1 s−1 was obtained in N-rich films due to an improved microstructure. The Zn3N2 films had an optical band gap of 1.31–1.48 eV and a refractive index of 2.3–2.7. Despite a wide range of Zn3N2 samples examined, little variation of its optical properties was observed, which suggests that they are closely related to the band structure of this material. In contrast to the as grown films, the oxidized film had a band gap of 3.44 eV and the refractive index was 1.6–1.8, similar to ZnO and Zn(OH)2.

Temperature dependence of the band gap of zinc nitride observed in photoluminescence measurements

“…In addition to PL measurements, the optical bandgap of the sample was identified as 1.43 eV based on the absorption coefficient calculated from reflectivity and transmission measurements at room temperature. 8 Therefore, it is evident from the PL measurements that the sample exhibited a photoluminescence band near the absorption onset at room temperature. Furthermore, the temperature dependence of band A, which is the highest energy band observed, matches the profile of band to band transitions.…”

“…For instance, in a previous paper, we showed that the range of optical properties between asgrown and fully oxidised films can explain the widely varying reports of the optical bandgap found in the literature. 8 In addition to oxidation, several other competing effects can also influence the bandgap, including Burstein-Moss shifts and composition variation.…”

“…Samples were grown at 150 C, a N 2 flow rate of 45 SCCM, and a sputter power of 85 W. The physical and optical properties of samples grown on the same system are examined in detail in a previous publication. 8 Photoluminescence (PL) measurements were performed with the sample mounted on a copper plate inside an Oxford Instruments Optistat Dry cryostat. The cryostat chamber was pumped down to 10 À4 mbar and subsequently cooled down to 3.7 K using a closed-circuit liquid He compressor.…”

Carrier-Induced Band-Gap Variation and Point Defects in Zn3N2 from First Principles

“…The most controversial but technologically important physical property of Zn 3 N 2 is the band gap. The reported band gaps of as-grown Zn 3 N 2 range from 0.85 to 3.2 eV [14][15][16]26,[28][29][30][31]33,35,36]. Indeed, experimental gaps of some other nitride semiconductors notoriously scatter as well.…”

“…Likewise, the BM effect has been considered as the most likely cause for the wide variety of reported gaps for Zn 3 N 2 , although the variation range is much larger than those of other nitrides. Another suggested possibility includes oxygen impurities leading to a larger ionicity, which may cause wider band gaps [28,36]. Besides, most Zn 3 N 2 samples have been found to be unintentionally n type with a carrier concentration of 10 18 -10 20 cm −3 .…”