Effects of free carriers on the optical properties of high mobility transition metal dopedIn2O3transparent conductors,Physical Review Materials

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Effects of free carriers on the optical properties of high mobility transition metal dopedIn2O3transparent conductors
Physical Review Materials ( IF 3.1 ) Pub Date : 2021-09-17 , DOI: 10.1103/physrevmaterials.5.094603
Kingsley O. Egbo ₁ , Ayotunde E. Adesina ₂ , Chioma V. Ezeh ₁ , Chao Ping Liu ₃ , Kin Man Yu _{1,

2}

Affiliation

Transition metal doped

{In}_{2} O_{3}

with high mobility can be used as a transparent conductor with enhanced transparency spectral window. In this work, we carried out a comprehensive study on the electrical and optical properties of

{In}_{2} O_{3}

doped with several transition metal (TM) species (

{In}_{2} O_{3} : TM

) including W, Zr, Mo, and Ti. Detailed optical properties obtained by spectroscopic ellipsometry (SE) are correlated with electrical properties obtained by Hall effect measurements. We find that the mobility of

{In}_{2} O_{3} : TM

thin films lies in the range of

50 – 75 c m^{2} V^{− 1} s^{− 1}

, much higher than the typical mobility of

30 – 40 c m^{2} V^{− 1} s^{− 1}

for conventional ITO. The complex dielectric functions of the thin films reveal remarkable carrier density dependent changes in the optical properties. SE analyses show that the electron effective mass of

{In}_{2} O_{3} : TM

at the bottom of the conduction band

m_{o}^{*}

(

0.11 – 0.14 m_{o}

) is much smaller than the reported

m_{o}^{*} \sim 0.18 - 0.30 m_{o}

for ITO, which directly results in their higher mobility. This low

m_{o}^{*}

is consistent with recent theoretical studies which proposed that

4 d

donor states of the TMs are resonance in the CB. For films with comparably low resistivity of

1 – 2 \times 10^{− 4} Ω cm

, we find that

{In}_{2} O_{3} : TM

films have ∼4–10 times lower absorption coefficient at

λ = 1300 nm

due to free carrier absorption and have their plasma reflection edge extended to ∼1.7 μm compared to ∼1.2–1.4 μm for ITO. Hence, using TM doping we have achieved transparent conductors with conductivity comparable to ITO but with transmission extended to >1600 nm. These materials will be potentially important as transparent conductors for optoelectronic devices utilizing NIR photons.

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