On the true optical properties of zinc nitride

Abstract

Refractive index (n) and extinction coefficient (k) of Zn 3 N 2 layers deposited by radio-frequency magnetron sputtering at temperatures (T s ) between 298 and 523 K were determined by spectroscopic ellipsometry. Results showed strong variations of the apparent optical constants with T s and time attributed to surface effects. Resonant Rutherford backscattering and spectroscopic ellipsometry confirmed the formation of a ZnO surface layer provoked by the ambient exposure. Samples grown at low T s presented the lowest surface roughness and exhibited 2.0 < n < 2.8 and 0.6 < k < 1.0 in the 1.5-4.5 eV energy range. The extracted n and k values accurately reproduced the reflectance properties. Zinc nitride (Zn 3 N 2 ) is a promising material for application in electronics and optoelectronics due to its high electron mobility and conductivity. Electrical studies in Zn 3 N 2 showed similar mobility and resistivity values to those obtained in poly-Si (at the same carrier concentration) and even better than in a-Si.1 Moreover, the low cost of its elements and synthesis procedure makes Zn 3 N 2 an excellent choice for mass production in electronic systems. Thus, Zn 3 N 2 is recognized as a potential substitute of Si for the fabrication of thin film transistors along with other materials such as graphene or ZnO. Furthermore, it has been demonstrated the possibility of transforming Zn 3 N 2 into p-type ZnO by thermal treatment in oxidizing ambient, which enables the fabrication of ZnO p-n homojunctions for the development of ultraviolet light emitters. 5 The oxygen content varied depending on the surface properties, as found by means of surface analysis techniques such as Auger electron spectroscopy and x-ray photoelectron spectroscopy. Although optical constants have been determined in the past, 1,6 the impact of surface effects such as surface roughness or the formation of native oxide on the calculated parameters has not been discussed yet. Therefore, it is important to analyze the changes introduced by those on the apparent optical characteristics of the Zn 3 N 2 films. Ellipsometry is an effective tool to rapidly detect morphology and chemical modification of materials over time. 7This work provides insight on the relationship between surface effects and the optical properties of Zn 3 N 2 layers using resonant Rutherford backscattering (RBS), scanning electron microscopy (SEM), spectroscopic ellipsometry (SE), and reflectance spectroscopy (RS). SE was used to determine the optical constants, i.e., refractive index (n) and extinction coefficient (k), of zinc nitride layers and RS helped to confirm their values.Zn 3 N 2 layers were prepared from a pure Zn (99.995%) plasma sputtered target using N 2 (99.999% purity) as working gas. N 2 gas was introduced through a mass flow controller. To study the effect of growth temperature (T s ), five samples were synthesized at T s between 298 and 523 K on Si(100) and glass substrates keeping a constant chamber pressure of 1 Pa by adjusting the pumping rate with a throttle valve. The...

Epitaxial Zn3N2 thin films by molecular beam epitaxy: Structural, electrical, and optical properties

“…All measured samples show optical band-gap energies between 1.05 and 1.37 eV, being in agreement with most of the previous literature. 10,15,[25][26][27][28][29][30][31][32][33][34][35][36][37][38] Burstein and Moss 43,44 described the influence of the carrier concentration in semiconductors on their optical band-gap. The displacement of the Fermi level into a parabolic conduction band leads to a band-gap shift according to (8) where denotes the electron concentration.…”

“…[14][15][16][17][18][19][20][21][22] Although some band-gap studies on Zn 3 N 2 estimated values of 2.9-3.4 eV, 14,16,23,24 most of the recent studies and theoretical calculations, including photoluminescence measurements, find values in the 0.8-1.5 eV range. 10,15,[25][26][27][28][29][30][31][32][33][34][35][36][37][38] The reason for this large discrepancy lies probably in the tendency of Zn 3 N 2 to oxidize in ambient conditions, 34,39 which could lead to a strong overestimation of the band-gap energy, as masked by the presence of ZnO (with a band-gap in the order of 3.3 eV 40 ). However, even in recent literature, the reported values display a large spread.…”

Confinement Effects and Charge Dynamics in Zn3N2 Colloidal Quantum Dots: Implications for QD-LED Displays

“…5−7 Zinc nitride (Zn 3 N 2 ) is a nontoxic, low-cost, and earthabundant semiconductor 8 that has not yet been exploited as much as group III nitrides because of the difficulties in the preparation of high-quality Zn 3 N 2 crystals. 9 Studies of the structural, electrical, and optical properties of this material have been largely limited to thin film geometries, which have been prepared by a variety of methods including metal−organic chemical vapor deposition, 9 RF−molecular beam epitaxy, 9 direct reaction by annealing metallic zinc in an ammonia atmosphere, 10 pulsed laser ablation, 11 molten salt potentiostatic electrolysis of zinc, 12 as well as DC 13,14 and RF 15,16 magnetron sputtering. A wide range of optical bandgap values have been reported in these studies (varying from ∼1.0 to 3.2 eV), generating some controversy about the origin and true nature of the electronic transitions.…”

Atomic layer deposition of Zn3N2 thin films: growth mechanism and application in thin film transistor

“…3 Additionally, it has a wide direct bandgap and high refractive index (2.2-2.4). 4,5 These unique combinations of electrical and optical properties render zinc nitride as a prospective transparent conductor. Though not studied extensively, lately its applications in sensors 6 and thin lm transistors (TFT) 2,7 have drawn considerable attention.…”