Optical, electrical, and structural properties of Ta-doped SnO2 films against substrate temperature using direct current magnetron sputtering

Surfaces and Interfaces 23 (2021) 100943

Available online 16 January 2021

2468-0230/© 2021 Elsevier B.V. All rights reserved.

Optical, electrical, and structural properties of Ta-doped SnO2 films against

substrate temperature using direct current magnetron sputtering

Ha Thanh Tung a

, Thanh Phuong Nguyen b

, Phuc Dang Huu c

, Tran Le d,e,*

a Institute of Research and Development, Duy Tan University, Da Nang, 700000, Viet Nam b Printing Material Lab, Faculty of Graphic Arts and Media, HCMC University of Technology and Education, No. 1 Vo Van Ngan Street, Linh Chieu Ward, Thu Duc

District, Ho Chi Minh City, 700000, Viet Nam c Faculty of Fundamental Science, Industrial University of Ho Chi Minh City, No. 12 Nguyen Van Bao, Ward 4, Go Vap District, Ho Chi Minh City, 700000, Viet Nam d Faculty of Physics & Engineering Physics, HCMC University of Science, 227 Nguyen Van Cu Street, Ward 4, District 5, Ho Chi Minh City, 700000, Viet Nam e VietNam National University − Ho Chi Minh City, Linh Trung Ward, Thu Duc District, Ho Chi Minh City, 700000, Viet Nam

ARTICLE INFO

Keywords:

Transparent conducting oxide

Ta-doped SnO2 film

direct current magnetron sputtering

X-ray diffraction

photoluminescence

X-ray photoelectron spectroscopy

ABSTRACT

Ta-doped SnO2 (TTO) films were deposited at 3 × 10− 3 Torr pressure from the 6 wt. % Ta2O5-doped SnO2 target

at temperatures of 30–500 ◦C in Ar sputtering gas. The Ta dopants in the SnO2 host lattice were detected via X￾ray photoemission, EDX mapping, and photoluminescence spectra. The Ta5+–Sn4+ substitution formed the Ox

O at

Vx

O sites in the host lattice and the substitution occurred at deposition temperatures greater than 200 ◦C. The

substitution leads to a decrease in the amount of Vx

O in the SnO2 lattice corresponding to the preferred rutile

SnO2 (110) lattice reflection in the X-ray diffraction patterns. The ultraviolet-visible transmittance in visible light

was approximately 80%. The lowest resistivity achieved was 2.0 × 10− 3 Ω.cm, with a carrier concentration of

1.28 × 1020 cm− 3 and carrier mobility of 24.5 cm2

V− 1

s

− 1

. The integration of the TTO-400 film with (n- and p-) Si

exhibited an excellent photoelectric effect.

1. Introduction

Transparent conductive oxides (TCOs) serve as low-resistance win￾dows in optoelectronic devices such as solar cells [1–7], touch screens [8],

flat panel displays (LCDs) [9,10], light-emitting diodes (LEDs) [11–14],

chromatic windows [15], and photodetectors [16,17] owing to their high

optical transmittance in visible light and excellent electrical conductivity.

Also, TCOs are used as catalytic materials, applying for photocatalytic

[18,19], electrocatalytic [20–23], and photo-electrocatalytic properties

[24,25]. Besides, TCOs are also applied for transparent electronics such as

transparent diodes [26–28] and transparent transistors [29–31].

Amongst TCOs, indium tin oxide (ITO) is the most extensively used

n-type TCO for optoelectronic devices, but indium is expensive and rare

in nature. Therefore, alternatives such as doped tin oxides (SnO2)

including F-doped SnO2 (FTO) [32–35] and Sb-doped SnO2 (STO)

[36–38] or doped zinc oxide (ZnO) including In-doped ZnO [39–41],

Ga-doped ZnO [42–44], P-doped ZnO [45], and Al-doped ZnO [46–48]

has been concerned to apply for optoelectronic devices.

Compared to doped ZnO, doped SnO2 has garnered significant

attention owing to its heat-resistant and chemically durable properties.

Therefore, doped SnO2 is more widely used in perovskite solar cells

[49–52] fabricated using chemical deposition techniques.

However, Sb and F, which are doped in SnO2, can be volatilised

during the film deposition process, as mentioned in [53]. Therefore, to

further diversify dopants for SnO2, Ta is selected as a potential candidate

because its ionic radius (0.064 nm) is nearly equal to that of Sn (0.069

nm), compared to that of Sb (0.060 nm). In addition, the ionic radius

difference between F and O is more significant as compared to that

between Ta and Sn.

In recent years, Ta-doped SnO2 (TTO) has been successfully fabri￾cated using pulsed laser deposition technique (PLD) with an expectation

for achieving the low resistivity owing to high carrier mobility, and thus,

to increase the amount of light in the near-infrared region, as mentioned

in [54–56]. To achieve this, TTO films are epitaxially grown on the TiO2

or NbO2 seed-layer at a very high substrate temperature (greater than

500 ◦C). As a result, a (200) reflection was the preferred one as TTO films

grew on the TiO2 seed layer compared to random grown lattice re￾flections without the seed layer [54], while a (110) lattice reflection was

preferentially grown on the TiO2 seed layer instead of the preferred

(101) reflection without the seed layer [55,56]. Interestingly, the works

* Corresponding author.

E-mail address: [email protected] (T. Le).

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Surfaces and Interfaces

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https://doi.org/10.1016/j.surfin.2021.100943

Received 21 July 2020; Received in revised form 4 January 2021; Accepted 8 January 2021