Band-gap energy and electron effective mass of polycrystalline Zn3N2

Zinc oxynitride (ZnOxNy) has attracted much attention as an amorphous semiconductor with high electron mobility. Recent studies reported that ZnOxNy thin films grown by sputtering contained nanocrystals, which might reduce their electron mobility through grain boundary scattering. In this study, we fabricated amorphous ZnOxNy thin films on a glass substrate by a less-energetic nitrogen-plasma-assisted pulsed laser deposition (PLD) to suppress the formation of the nanocrystals. Grown by PLD under optimized conditions, these ZnOxNy thin films exhibited extremely flat surfaces with a root-mean-squared roughness (Rrms) of less than 0.3 nm. The Hall mobility of these films exceeded 200 cm2 V−1 s−1 at a critical carrier concentration of ∼1 × 1019 cm−3, which was twice as high as the reported values for sputter-deposited films. Meanwhile, the mobility of films with larger Rrms was limited to ∼160 cm2 V−1 s−1 even at the critical carrier concentration and comparable with that of the sputter-deposited ZnOxNy films. The substantial enhancement in mobility in extremely flat ZnOxNy films demonstrated that suppressing the formation of nanocrystals is the key to fabricating amorphous ZnOxNy thin films with very high mobility.

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confidence: 99%

Amorphous ZnOxNy thin films with high electron Hall mobility exceeding 200 cm2 V−1 s−1

Yamazaki

Shigematsu

Hirose

et al. 2016

“…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.…”

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confidence: 99%

“…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.…”

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confidence: 99%

On the true optical properties of zinc nitride

García-Núñez

Pau

Hernández

et al. 2011

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...

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confidence: 99%

“…One of them is zinc nitride (Zn 3 N 2 ), which is potential candidate due to its high mobility (156 cm 2 /Vs) and conductivity as well as its low-cost processing. 4 Zn 3 N 2 thin films have been tested as channel layers in thin film transistors after an annealing process, which made the Zn 3 N 2 layer transparent to the visible light. 5 In this work, TFTs with different geometric configurations, bottom-and top-gate, were fabricated by lithography and etching processes using Zn 3 N 2 as active channel layer.…”

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confidence: 99%

Thin film transistors based on zinc nitride as a channel layer for optoelectronic devices

García-Núñez

Pau

Ruiz

et al. 2012

Zinc nitride films were used as an active layer in thin film transistors to assess its performance in optoelectronic applications. Those nitride layers were grown by radio-frequency magnetron sputtering in Ar/N 2 ambient using a Zn target. Bottom-and top-gate thin film transistors were fabricated by photolithography processes. Transmission measurements for these particular layers showed an absorption edge around 1.3 eV. Normally off transistor characteristics with a threshold voltage of 6 V were obtained in the bottom-gate configuration without post-growth annealing. In the saturation region, those transistors produced enhanced output characteristics under illumination with infrared/visible light. Thin film transistors (TFTs) are essential devices in active-matrix liquid crystal and organic light-emitting diode displays. Although hydrogenated amorphous silicon is usually the material of choice for the TFT channel, this technology presents some issues such as the low mobility or the poor levels of stability.1,2 TFTs are also based on polycrystalline silicon with an important enhancement of the field effect mobility in comparison with those based in a-Si; however, the randomly distributed grain boundaries in a high area can hinder the fabrication process.3 Therefore, different organic and inorganic materials are being investigated as potential substitutes of Si. One of them is zinc nitride (Zn 3 N 2 ), which is potential candidate due to its high mobility (156 cm 2 /Vs) and conductivity as well as its low-cost processing. 4 Zn 3 N 2 thin films have been tested as channel layers in thin film transistors after an annealing process, which made the Zn 3 N 2 layer transparent to the visible light. 5In this work, TFTs with different geometric configurations, bottom-and top-gate, were fabricated by lithography and etching processes using Zn 3 N 2 as active channel layer. Their output characteristics were studied as-fabricated (without thermal treatment) in dark and under infrared/visible illumination. Zn 3 N 2 layers were synthesized by radio-frequency (rf) magnetron sputtering from a Zn target. Deposited on glass substrates, those layers presented excellent electrical properties with n-type characteristics, Hall mobility values around 100 cm 2 /Vs for an electron concentration of 3.2 Â 10 18 cm À3 , and resistivities in the 10 À3 X cm range. 6 Since Zn 3 N 2 tends to transform into zinc oxide (ZnO) at room temperature and atmospheric pressure, 7 the channel layers were capped with a ZnO thin layer which inhibits the reaction with the ambient oxygen and increases the stability of the devices overtime. Optical properties of those nitride layers were analyzed here by means of transmission spectroscopy in the photon energy range from 1 to 3 eV. The morphology of the Zn 3 N 2 sample surfaces was examined by scanning electron microscopy (SEM, Philips XL30) at 20-kV operation voltage.Bottom-gate TFT was first fabricated using mechanical masking and photolithography processes. A cross-sectional schematic of the fabricated trans...