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

Tena‐Zaera, Ramón; Martı́nez-Tomás, C.; Gómez‐García, Carlos J.; Muñoz‐Sanjosé, V.

doi:10.1002/crat.200510662

Cited by 12 publications

(6 citation statements)

References 34 publications

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“…As regards the decrease of the mass transport rate in the second step several hypotheses can be invoked, being one of them the change in the inner total pressure. Nevertheless it is worth noticing that the same effect was observed in our group during growth experiments with non-graphitised ampoules in which an additional Zn was directly added [30]. In the experiences using an additional Zn pressure, the total pressure is constant and the change in slope can not be mainly associated to pressure effects.…”

Section: Resultssupporting

confidence: 68%

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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Section: Resultssupporting

confidence: 68%

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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“…8 The samples were annealed at 900°C for 20 h in atmosphere composed of oxygen ͑O 2 ͒ vapor 2 atm overpressured, in atmosphere composed of Zn vapor 2 atm overpressured, and in vacuum. A couple of identical samples are necessary to measure the positron annihilation lifetime.…”

Section: Methodsmentioning

confidence: 99%

Positron annihilation lifetime spectroscopy of ZnO bulk samples

et al. 2007

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In order to gain a further insight into the knowledge of point defects of ZnO, positron annihilation lifetime spectroscopy was performed on bulk samples annealed under different atmospheres. The samples were characterized at temperatures ranging from 10 to 500 K. Due to difficulties in the conventional fitting of the lifetime spectra caused by the low intensity of the defect signals, we have used an alternative method as a solution to overcome these difficulties and resolve all the lifetime components present in the spectra. Two different vacancy-type defects are identified in the samples: Zn vacancy complexes ͑V Zn -X͒ and vacancy clusters consisting of up to five missing Zn-O pairs. In addition to the vacancies, we observe negative-ion-type defects, which are tentatively attributed to intrinsic defects in the Zn sublattice. The effect of the annealing on the observed defects is discussed. The concentrations of the V Zn -X complexes and negative-ion-type defects are in the 0.2-2 ppm range, while the cluster concentrations are 1-2 orders of magnitude lower.

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“…The advantageous feature of this method has purification effect like sublimation refining during the growth by difference in reactivity and vapor pressure [7]. Recently, available mass transport at growth temperature of lower than 1000 1C, which is usable for silica tube, has been reported using carbon or carbon-oxygen compounds [8][9][10][11][12]. Almost CVT experiments for ZnO crystal growth are carried out using closed tube as shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

“…Almost CVT experiments for ZnO crystal growth are carried out using closed tube as shown in Fig. 1(a) and spontaneous nucleation [9,[11][12][13]. The crystal orientations of grown crystals rely on the spontaneous nucleation and thus are uncontrollable.…”

Section: Introductionmentioning

confidence: 99%