Study of the ZnO crystal growth by vapour transport methods

Tena‐Zaera, Ramón; Martinez-Tomas, M.C.; Hassani, Saïd; Triboulet, R.; Muñoz‐Sanjosé, V.

doi:10.1016/j.jcrysgro.2004.06.053

Cited by 27 publications

(26 citation statements)

References 39 publications

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“…As already shown [12,30], the ZnO growth in presence of graphite can be well understood as a process in which graphite reacts with the O 2 provided by the ZnO decomposition through the following reactions:…”

Section: Some Ways To Control the Zn Excess During The Growth Experimmentioning

confidence: 87%

“…1). This consumption generates an excess of Zn that will activate the ZnO decomposition process [12]. On the other hand, the formation energies of intrinsic point defects and, therefore, some physical properties of ZnO depend on the Zn partial pressure during the growth process [28,29].…”

Section: Some Ways To Control the Zn Excess During The Growth Experimmentioning

confidence: 99%

“…As regards the growth of ZnO bulk crystals, it has been carried out by different "classical" methods, as flux [4], vapour transport [5,6], hydrothermal [7,8] and solution [9,10], being hydrothermal and vapour transport the most frequently used ones. It has been well established that the growth of ZnO by vapour transport in closed ampoules at moderate temperatures (∼1000°C) and temperature gradients results in very low growth rates in absence of other species [11,12]. We refer them as "additional species" and we can find a good variety in literature: F 2 [13], Cl 2 [5,6,13,14], Br 2 [13,14], I 2 [13], HF [13], HCl [5,[13][14][15], HBr [14,15], HI [15], NH 3 [5], NH 4 Cl [14,15], NH 4 Br [14,15], ZnCl 2 [15,16], HgCl 2 [5,17,19], Zn [16,18], H 2 [5,20,21], C [6,21,23] and different mixtures: H 2 O+H 2 [2,20], H 2 +C+H ...…”

Section: Introductionmentioning

confidence: 99%

“…Recently, we have proposed a new frame to analyse the chemical role of carbon as an "additional species" in the ZnO growth process [12,30]. Carbon promotes a partial consumption of the O 2 provided by the ZnO decomposition and, consequently, produces a Zn excess.…”

Section: Introductionmentioning

confidence: 99%

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Growth of ZnO crystals by vapour transport: Some ways to act on physical properties

Tena‐Zaera

Martı́nez-Tomás

Gómez‐García

et al. 2006

Cryst. Res. Technol.

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Nowadays, the growth of ZnO by vapor transport in silica ampoules is generally made in presence of graphite. As it has been already shown, this means that the growth process is carried out in presence of a Zn excess. In order to control that and act, as a consequence, on the physical properties of crystals we have performed a systematic study of the growth process in a wide range of Zn excess compositions using well defined experimental conditions. As a preliminary characterization, optical absorption and electrical properties have been analyzed at room temperature. The results show how some physical properties of asgrown ZnO crystals can be changed in a controlled way by an adequate combination of different growth conditions such as graphite covering of inner ampoule walls, thermal difference between source material and crystallization zone and additional gas (composition and pressure). In this frame some post-growth annealing processes can be avoided reducing the time and cost of processes.

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Section: Some Ways To Control the Zn Excess During The Growth Experimmentioning

confidence: 87%

Section: Some Ways To Control the Zn Excess During The Growth Experimmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Growth of ZnO crystals by vapour transport: Some ways to act on physical properties

Tena‐Zaera

Martı́nez-Tomás

Gómez‐García

et al. 2006

Cryst. Res. Technol.

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“…Details of the growth process can be found in Ref. [13,14]. The halfwidth of the X-ray diffraction of the (0002) rocking curves are about 50 to 200 arcsec.…”

Section: Methodsmentioning

confidence: 99%

Negative U‐properties of the oxygen‐vacancy in ZnO

Pfisterer

Sann

Hofmann

et al. 2006

Phys. Status Solidi (c)

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It is shown that the intensity of the oxygen vacancy (V O ) related emission in ZnO at 2.45 eV correlates to the concentration of the donor level E4. E4 is located 530 meV below the conduction band and attributed to the V O 0/++ recharging. Deep level transient spectroscopy (DLTS) experiments with optical excitation locate the V O 2+/+ level position 140 meV below the conduction band and give evidence for the "negative-U" properties of the oxygen vacancies in ZnO. 1 Introduction Interest in ZnO has grown during the rescent years due to progress in crystal growth and its unique optical and electrical properties. ZnO has a direct bandgap of about 3.3 eV at room temperature and can be thought of as alternative to GaN opto-electronic devices for the blue spectral range. The reports on successful p-type doping have led to even higher expectations about the materials potential applications in electronics [1][2][3]. In addition, when doped with Mn, ZnO has been reported to exhibit ferromagentic behavior above room temperature [4], making it a prospective material for spintronics.Point defects have important effects on the optical and electronic properties of semiconductors. Their understanding is needed for a description of the specific properties of the material. In this paper we concentrate on the optical and electrical properties of the oxygen vacancy (V O ) in ZnO. Theoretical estimates for the level positions have been made recently by two independent groups [5,6]. In both cases neative-U ordering was predicted, implying that the (2+/+) lies above the (+/0) in the bandgap. Van de Walle [5] calculated the (0/++) transition level at ~ E v + 2.7 eV, the (2+/+) level close to the conduction band (E v + 3.3 eV) and the (+/0) level at ~ E v + 2.0 eV, while Lany [6] in his calculations obtained the respective level positions approximately 1 eV lower in energy.If the predicted negative-U behaviour is correct the V O + charge state is thermodynamically unstable. This seems to be o.k. since electron paramagnetic resonance (EPR) experiments required optical excitation for the detection of the V O + charge state [7][8][9]. Optically detected magnetic resonance (ODMR) experiments have shown that the V O is the cause of one of the "green" emissions in ZnO [10]. It originates from a spin-triplet excited state (S = 1) of the neutral vacancy V O 0 , and has its intensity maxmum at 2.45 eV (~506 nm) and a halfwidth of 450 meV at a temperature of 4 K.

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A new approach to the growth of ZnO by vapour transport

Muñoz‐Sanjosé

Tena‐Zaera

Martı́nez-Tomás

et al. 2005

phys. stat. sol. (c)

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The crystal growth of ZnO by vapour transport is classically made in presence of additional species which enhance the growth process. Usually, additional species have been considered as chemical transport agents that promote a typical CVT (Chemical Vapour Transport) process. Recently, we have proposed a new interpretation of the chemical role of some of these species. This new interpretation considers that, in some cases, the additional species promote a partial consumption of the O 2 provided by the ZnO decomposition and, consequently, a Zn excess is generated. This excess of Zn pressure activates the ZnO decomposition and the growth rate is enhanced. Among those species, carbon shows an additional beneficial role in the ZnO growth process. The deposition of a graphite layer on the inner walls of the generally used growth silica ampoules avoids the reaction between the ZnO crystals and the silica. In order to gain a further insight into the growth process, the time dependence of the transported mass in presence of graphite has been studied using an in-situ dynamic technique. A systematic study of the mass transport rate dependence on the thermal difference between the source material and the crystallisation zone (∆T) has been made. On the other hand the influence of a residual gas on the transport rate has been also systematically analysed. Two different gases have been used, argon (Ar) and carbon dioxide (CO 2 ). The experiments with Ar have allowed the analysis of the effects of an inert gas on the transport processes. Meanwhile, the experiments with CO 2 have shown its chemical role on the generation of a non-reacted Zn which is necessary to activate the ZnO decomposition. This role paves the way to control the Zn excess during the growth experiments. Thus, CO 2 can be used to act on the off-stoichiometry degree of the ZnO crystals and consequently to control, at least partially, some of the physical properties of this material.

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Study of the ZnO crystal growth by vapour transport methods

Cited by 27 publications

References 39 publications

Growth of ZnO crystals by vapour transport: Some ways to act on physical properties

Growth of ZnO crystals by vapour transport: Some ways to act on physical properties

Negative U‐properties of the oxygen‐vacancy in ZnO

A new approach to the growth of ZnO by vapour transport

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