[PDF]  https://doi.org/10.3952/physics.v60i1.4163

Open access article / Atviros prieigos straipsnis
Lith. J. Phys. 60, 48–56 (2020)
 

ESTIMATION OF THE CHARGED DEFECT DENSITY FROM HOT-ELECTRON TRANSPORT STUDIES IN EPITAXIAL ZnO
  Linas Ardaravičius, Oleg Kiprijanovič, Mindaugas Ramonas, Emilis Šermukšnis, Artur Šimukovič, and Arvydas Matulionis
Center for Physical Sciences and Technology, Saulėtekio 3, 10257 Vilnius, Lithuania
Email: linas.ardaravicius@ftmc.lt

Received 20 May 2019; revised 11 July 2019; accepted 25 November 2019

High-field electron transport measurements by applying short (few ns) voltage pulses on nominally undoped n-type Zn-polar ZnO epilayers are reported and interpreted in terms of the Boltzmann kinetic equation. The transient measurements do not demonstrate a significant change in the electron density up to 320 kV/cm electric field. This result together with the experimental data on the current allows one to estimate the electron drift velocity from the measured current: the highest value of ~2.9 × 107 cm/s is obtained at the pre-breakdown field of 320 kV/cm for the ZnO layer with the electron density of 1.5 × 1017 cm–3. The densities of double-charged oxygen vacancies (~1.6 × 1017 cm–3) and other charged centres (~1.7 × 1017 cm–3) are assumed for the best fit of the simulated and measured hot-electron effect. A correlation with the epilayer growth conditions is demonstrated: the higher Zn cell temperature favours the formation of a higher density of the oxygen vacancies (1.9 × 1017 cm–3 at 347°C).
Keywords: ZnO epilayer, charged defects, differential mobility, electron drift velocity, high electric fields


ĮELEKTRINTŲ DEFEKTŲ TANKIO ĮVERTINIMAS NAUDOJANT KARŠTŲJŲ ELEKTRONŲ PERNAŠOS TYRIMUS EPITAKSINIAME ZnO
  Linas Ardaravičius, Oleg Kiprijanovič, Mindaugas Ramonas, Emilis Šermukšnis, Artur Šimukovič, Arvydas Matulionis

Fizinių ir technologijos mokslų centras, Vilnius, Lietuva
 
Naudojant nanosekundinių įtampos impulsų matavimo metodiką ištirta karštųjų elektronų pernaša kambario temperatūroje nominaliai nelegiruotuose ZnO epitaksiniuose sluoksniuose. Bolcmano kinetinė lygtis išspręsta sferinių harmonikų metodu siekiant atsižvelgti į karštųjų elektronų efektus. Naudojant šiuos metodus įvertintas įelektrintų taškinių defektų tankis (vakansijų 1,6–1,9 × 1017 cm–3 ir sočiųjų jungčių 1,7–2,0 × 1017 cm–3), elektronų dreifo judris silpnuose ir vidutiniuose laukuose bei elektronų tankis. Įvertintas deguonies vakansijų tankis koreliuoja su Zn celės auginimo temperatūra. Naudojant trumpus impulsus (3 ns) sumažintas savaiminio pakaitimo efektas ir tirtuose sluoksniuose pasiekiami 430 ± 50 kV/cm elektriniai laukai. Išskiriami du elektrinių laukų ruožai, kuriuose srovės priklausomybė nuo elektrinio lauko stiprio gali būti aproksimuota skirtingio polinkio tiesėmis. Matuojant srovės laiką aiškėja, kad elektronų tankis yra pastovus, kai elektrinio lauko impulsas siekia iki 320 kV/cm. Nuokrypis nuo Omo dėsnio aiškinamas karštųjų elektronų efektais ir elektronų sklaida įkrautais taškiniais defektais bei fononais. Įvertintas didžiausias elektronų dreifo greitis lygus ~2,9 × 107 cm/s, kai elektronų tankis 1,5 × 1017 cm–3 sudarant 320 kV/cm stiprio elektrinį lauką.

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