Photoconductive a-GaN prepared by reactive sputtering

Nonomura, Shuichi; Kobayashi, Satoshi; Gotoh, Tamihiro; Hirata, Shuzo; Ohmori, Takashi; Itoh, Takashi; Nitta, Shoji; Morigaki, Kazuo

doi:10.1016/0022-3093(95)00675-3

Cited by 42 publications

(32 citation statements)

References 7 publications

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“…5 Although the III-nitride based devices are key elements for the development of new highly efficient LEDs and lasers, their reliability and efficiency depends strongly on the precise knowledge of optical constants. 6 Thin films of GaN, AlN, and their alloys have been deposited by a variety of deposition processes including sputtering, 7,8 metal-organic chemical vapor deposition (MOCVD), [9][10][11] plasma enhanced-CVD, 12 molecular beam epitaxy (MBE), 13,14 and atomic layer deposition (ALD). [15][16][17] During the last decade, numerous papers have been published on the deposition of epitaxial layers of GaN, AlN, and their alloys using both the MOCVD and MBE methods.…”

Section: à4mentioning

confidence: 99%

Optical characteristics of nanocrystalline AlxGa1−xN thin films deposited by hollow cathode plasma-assisted atomic layer deposition

Goldenberg

Özgit-Akgün

Bıyıklı

et al. 2014

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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Gallium nitride (GaN), aluminum nitride (AlN), and AlxGa1−xN films have been deposited by hollow cathode plasma-assisted atomic layer deposition at 200 °C on c-plane sapphire and Si substrates. The dependence of film structure, absorption edge, and refractive index on postdeposition annealing were examined by x-ray diffraction, spectrophotometry, and spectroscopic ellipsometry measurements, respectively. Well-adhered, uniform, and polycrystalline wurtzite (hexagonal) GaN, AlN, and AlxGa1−xN films were prepared at low deposition temperature. As revealed by the x-ray diffraction analyses, crystallite sizes of the films were between 11.7 and 25.2 nm. The crystallite size of as-deposited GaN film increased from 11.7 to 12.1 and 14.4 nm when the annealing duration increased from 30 min to 2 h (800 °C). For all films, the average optical transmission was ∼85% in the visible (VIS) and near infrared spectrum. The refractive indices of AlN and AlxGa1−xN were lower compared to GaN thin films. The refractive index of as-deposited films decreased from 2.33 to 2.02 (λ = 550 nm) with the increased Al content x (0 ≤ x ≤ 1), while the extinction coefficients (k) were approximately zero in the VIS spectrum (>400 nm). Postdeposition annealing at 900 °C for 2 h considerably lowered the refractive index value of GaN films (2.33–1.92), indicating a significant phase change. The optical bandgap of as-deposited GaN film was found to be 3.95 eV, and it decreased to 3.90 eV for films annealed at 800 °C for 30 min and 2 h. On the other hand, this value increased to 4.1 eV for GaN films annealed at 900 °C for 2 h. This might be caused by Ga2O3 formation and following phase change. The optical bandgap value of as-deposited AlxGa1−xN films decreased from 5.75 to 5.25 eV when the x values decreased from 1 to 0.68. Furthermore, postdeposition annealing did not affect the bandgap of Al-rich films.

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Section: à4mentioning

confidence: 99%

Optical characteristics of nanocrystalline AlxGa1−xN thin films deposited by hollow cathode plasma-assisted atomic layer deposition

Goldenberg

Özgit-Akgün

Bıyıklı

et al. 2014

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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“…Other features of a-GaN include blue luminescence, excellent ability to serve as a matrix for rare-earth metal impurities, and clear photoconductivity with sensitivity peaking in the ultraviolet (UV), making it more suitable to be used as a material for an electron field emitter and transparent thin-film transistor (TFT). [9][10][11][12][13][14][15] Generally, a-GaN would be suspected of instability, which often occurs in any amorphous material, but it may also happen in c-GaN. Tan and Grigorescu have reported that a-GaN under thermal treatment (annealing under N 2 atmosphere) recrystallizes and preserves the initial stoichiometry while resulting in transformation to the nanocrystalline or polycrystalline phase.…”

Section: Introductionmentioning

confidence: 97%

Optical Properties of Nanocrystalline GaN Films Prepared by Annealing Amorphous GaN in Ammonia

Zhang

Pan

Wang

et al. 2008

Journal of Elec Materi

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Nanocrystalline GaN films were prepared by thermal treatment of amorphous GaN films under flowing NH 3 at a temperature of 600°C to 950°C for 1 h to 2 h. X-ray diffraction and field-emission scanning electron microscopy confirmed the formation of high-crystal-quality hexagonal GaN films with preferential (002) orientation. The photoluminescence spectrum showed a sharp peak near the band gap emission located at 368 nm and a broad blue peak centered at 430 nm. Five first-order Raman modes near $143 cm -1 , 535 cm -1 , 555 cm -1 , 568 cm -1 , and 731 cm -1 with two new additional Raman peaks at 257 cm -1 and 423 cm -1 were observed. The origin of these new Raman peaks is discussed briefly.

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“…2,3 This technique has much more often been used to grow polycrystalline and amorphous materials. [4][5][6][7][8][9][10][11] These films, using N 2 as the reactive gas and Ar or N 2 to sputter a Ga target, are usually grown at low temperatures ͑Շ450°C͒. A disordered material grown at low temperatures using remote-plasma CVD has been shown to have potential for lighting and photodiode applications.…”

Section: Introductionmentioning

confidence: 99%

The properties and deposition process of GaN films grown by reactive sputtering at low temperatures

Knox-Davies

Shannon

Silva

2006

Journal of Applied Physics

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Polycrystalline gallium nitride films, 100 nm to 1 m thick, were deposited under a range of conditions. Substrate electrode temperatures during sputtering were varied from room temperature to 450°C, the pressure from 0.15 to 6.0 Pa, the nitrogen fraction of the deposition atmosphere from 10% to 100% and the target bias from −400 to − 1800 V. The deposition rates as functions of these conditions are in the range 0.5-25 nm/ min. The growth rate is considered to be controlled respectively by the thermally activated desorption from the substrate, changes in the mean free path and concentration of gas particles, differences between the sputter yields of Ga and GaN in Ar and N 2 , and changes in the ion current and sputter yields. The films are generally columnar, with the grain size increasing with film thickness. The most crystalline films were grown at mid range temperatures, low N 2 concentrations, and low target biases, and the most disordered were grown at low pressures. The latter two cases suggest that decreasing the energy of particles incident on the film during deposition results in a more ordered film. The biaxial stress is compressive and shows an increasing trend with the target bias and N 2 concentration, reaching 4.7 GPa at 75% N 2 . Oxygen contamination of 3 -30 at. % has a major effect on the optical properties of the films, increasing the band gap values from 3.02 to Ͼ 4.0 eV and the Urbach tail energies from around 150 to 840 meV and decreasing the refractive index from 2.46 to 2.03. At a 40% N 2 deposition fraction, the N:Ga ratio is more or less constant at 1:1. Since the absolute oxygen incorporation rate changes very little, it is the relative film deposition rate which determines the final oxygen concentration. Excess Ga at low N 2 concentrations causes a decrease in the band gap and an increase in the Urbach tail energy.

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Photoconductive a-GaN prepared by reactive sputtering

Cited by 42 publications

References 7 publications

Optical characteristics of nanocrystalline AlxGa1−xN thin films deposited by hollow cathode plasma-assisted atomic layer deposition

Optical characteristics of nanocrystalline AlxGa1−xN thin films deposited by hollow cathode plasma-assisted atomic layer deposition

Optical Properties of Nanocrystalline GaN Films Prepared by Annealing Amorphous GaN in Ammonia

The properties and deposition process of GaN films grown by reactive sputtering at low temperatures

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