Ga-doped ZnO films grown on GaN templates by plasma-assisted molecular-beam epitaxy

Ko, Hang-Ju; Chen, Yanfang F.; Hong, Soon–Ku; Wenisch, H.; Yao, Takafumi; Look, David C.

doi:10.1063/1.1331089

Cited by 375 publications

(192 citation statements)

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“…The monotonic increase in luminescence efficiency with an increase in doping concentration also shows that luminescence killers (deep levels) do not increase with increase in doping concentration, which is indicative of high quality of the epitaxial films. In the case of ZnO epitaxy, it has been difficult to achieve such a situation, i.e., impurity doping has so far induced a sizable increase in the trap center concentration [2,4,12]. On the other hand, the luminescence efficiency decreases at the highest doping concentrations.…”

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confidence: 99%

“…Impurity-doping, defect, and surface profile both have influence to its broadening, Stokes shift, and radiative efficiency. Room-temperature (RT) near-bandedge (NBE) luminescence has not been observed in donor-doped ZnO except for lightlydoped ones despite the long research history of this material as a transparent conductive window [1,2,3,4]. Indeed when ZnO:Al films were grown on lattice matched substrates, detectable NBE PL could be observed only at 5 K. As pointed out by Ko et al, oxidation of the Al during the growth owing to its high reactivity may be responsible for that.…”

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confidence: 99%

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Gallium concentration dependence of room-temperature near-band-edge luminescence in n-type ZnO:Ga

Makino

Segawa

Yoshida

et al. 2004

Applied Physics Letters

176

107

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We investigated the optical properties of epitaxial n-type ZnO films grown on lattice-matched ScAlMgO4 substrates. As the Ga doping concentration increased up to 6×10 20 cm −3 , the absorption edge showed a systematic blueshift, consistent with the Burstein-Moss effect. A bright near-bandedge photoluminescence (PL) could be observed even at room temperature, the intensity of which increased monotonically as the doping concentration was increased except for the highest doping level. It indicates that nonradiative transitions dominate at a low doping density. Both a Stokes shift and broadening in the PL band are monotonically increasing functions of donor concentration, which was explained in terms of potential fluctuations caused by the random distribution of donor impurities.PACS numbers: 78.55. Et, 81.15.Fg, 71.35.Cc, Optical properties of ZnO are currently subject of tremendous investigations, in response to the industrial demand for shortwavelength optoelectronics devices. Production of high-quality doped ZnO films is indispensable for the device application. Photoluminescence (PL) is a sensitive and non-destructive method, the results of which provide a good indicator of material quality. Impurity-doping, defect, and surface profile both have influence to its broadening, Stokes shift, and radiative efficiency. Room-temperature (RT) near-bandedge (NBE) luminescence has not been observed in donor-doped ZnO except for lightlydoped ones despite the long research history of this material as a transparent conductive window [1,2,3,4]. Indeed when ZnO:Al films were grown on lattice matched substrates, detectable NBE PL could be observed only at 5 K. As pointed out by Ko et al., oxidation of the Al during the growth owing to its high reactivity may be responsible for that. On the other hand, Ga is less reactive and more resistive to oxidation. The covalent bond lengths of Ga-O is slightly smaller than that of Zn-O, which will make the deformation of the ZnO lattice small even in the case of high Ga concentration [2]. In this publication, we report observation of the RT NBE luminescence from ZnO:Ga epitaxial layers. The radiative efficiency, threshold energy and the linewidth of the near-band-gap optical transition are investigated as a function of doping density of Ga.Ga-doped ZnO samples were grown by laser molecular-beam epitaxy on the (0001)-plane of a ScAlMgO 4 substrate. The samples were grown at temperatures of 650 to 680 • C. The Ga doping was varied to achieve doping densities in the range of 8 × 10 18 to 6 × 10 20 cm −3 [5]. We used Fig. 2 of Ref. 6 for the conversion from prescribed Ga concentration. The photoluminescence measurements were performed using an He-Cd laser, with emission at 325 nm. The luminescence from samples was dispersed in a 0.3 m spectrometer and detected by a charge-coupled device. Absorption was measured by using a UV/visible spectrometer (Shimadzu, UV2450) [4].Figure 1(a) shows room-temperature near-bandedge photoluminescence spectra (left-hand side) in n-type Ga-doped ZnO samples wit...

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Gallium concentration dependence of room-temperature near-band-edge luminescence in n-type ZnO:Ga

Makino

Segawa

Yoshida

et al. 2004

Applied Physics Letters

176

107

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“…Al-and Ga-ZnO films grown by PLD, molecular beam epitaxay and chemical vapor deposition methods have shown carrier concentrations on the order of 10 20 cm -3 . 4,5 Various wet chemistry coating techniques [6][7][8][9][10] have also been applied to synthesize ZnO thin films, but high levels of intrinsic defects make it difficult to control the film a Corresponding author: faselim@bgsu.edu properties. Despite considerable research on sol-gel ZnO films, no detailed structural information on film layering, thickness uniformity, and defect nature are available.…”

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confidence: 99%

Induced conductivity in sol-gel ZnO films by passivation or elimination of Zn vacancies

et al. 2016

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Undoped and Ga-and Al-doped ZnO films were synthesized using sol-gel and spin coating methods and characterized by X-ray diffraction, high-resolution scanning electron microscopy (SEM), optical spectroscopy and Hall-effect measurements. SEM measurements reveal an average grain size of 20 nm and distinct individual layer structure. Measurable conductivity was not detected in the unprocessed films; however, annealing in hydrogen or zinc environment induced significant conductivity (∼10 −2 Ω.cm) in most films. Positron annihilation spectroscopy measurements provided strong evidence that the significant enhancement in conductivity was due to hydrogen passivation of Zn vacancy related defects or elimination of Zn vacancies by Zn interstitials which suppress their role as deep acceptors. Hydrogen passivation of cation vacancies is shown to play an important role in tuning the electrical conductivity of ZnO, similar to its role in passivation of defects at the Si/SiO2 interface that has been essential for the successful development of complementary metal-oxide-semiconductor (CMOS) devices. By comparison with hydrogen effect on other oxides, we suggest that hydrogen may play a universal role in oxides passivating cation vacancies and modifying their electronic properties. © 2016 Author(s)

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“…13 ZnO has the potential to be a more favorable candidate than ITO in this regard, because the a-axis lattice constant of ZnO is closely matched to that of GaN, and so high-quality ZnO films can be grown epitaxially on GaN. 17,18 There is also great economical motivation for implementing ZnO as a contact over ITO, as the price of In has been rising and is significantly higher than the price of Zn.…”

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Properties of In-Doped ZnO Films Grown by Metalorganic Chemical Vapor Deposition on GaN(0001) Templates

Ben-Yaacov

Ive

Walle

et al. 2009

Journal of Elec Materi

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We investigated the properties of indium-doped zinc oxide layers grown by metalorganic chemical vapor deposition on semi-insulating GaN(0001) templates. Specular and transparent films were grown with n-type carrier concentrations up to 1.82 9 10 19 cm À3 as determined by Hall measurements, and all In-doped films had carrier concentrations significantly higher than that of a comparable undoped film. For low In flows, the carrier concentration increased accordingly with trimethyl-indium (TMIn) flow until a maximum carrier concentration of 1.82 9 10 19 cm À3 was realized. For higher In flows, the carrier concentration decreased with increasing TMIn flow rate. Sheet resistance as low as 185 X/sq was achieved for the In-doped films, which is a significant decrease from that of a comparable undoped ZnO film. Our n-type doping studies show that In is an effective dopant for controlling the n-type conductivity of ZnO.

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Ga-doped ZnO films grown on GaN templates by plasma-assisted molecular-beam epitaxy

Cited by 375 publications

References 15 publications

Gallium concentration dependence of room-temperature near-band-edge luminescence in n-type ZnO:Ga

Gallium concentration dependence of room-temperature near-band-edge luminescence in n-type ZnO:Ga

Induced conductivity in sol-gel ZnO films by passivation or elimination of Zn vacancies

Properties of In-Doped ZnO Films Grown by Metalorganic Chemical Vapor Deposition on GaN(0001) Templates

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