Recent Advances in Understanding the Structure and Properties of Amorphous Oxide Semiconductors

Abstract

conductivity. [1] Following the discovery of SnO 2 with a similar unique combination of properties, [2] several patents were filed in the 1940s to employ TCOs as antistatic coatings and transparent heaters-long before the discovery of the now well-known Sn-doped In 2 O 3 (ITO) and Al-doped ZnO, [3] widely employed as flat panel display electrodes in the past decades. Despite great technological demand for TCOs [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and extensive experimental efforts to improve the conductivity via impurity doping, [21,22] to tune the work function and carrier concentration via cation composition, [23][24][25][26][27][28] to achieve two-dimensional transport via heterointerfaces, [29] and to p-dope the oxides toward active layers of transparent electronics, [30][31][32] theoretical understanding of these fascinating materials has lagged behind significantly. The first electronic band structure of ITO was calculated in 2001; [33] the role of native defects in prototype TCOs was understood after 2002; [34][35][36][37] the properties of multi-cation TCOs were first considered in 2004 [37][38][39][40][41][42] followed by modeling of novel TCO hosts [43,44] and spin-dependent transport in transition-metal-doped TCOs; [45] the nature of the band gap in In 2 O 3 was clarified in 2008; [46] and a first highthroughput search for p-type TCOs was performed in 2013. [47] Complex oxides that consist of multiple post-transition metals, such as InGaZnO 4 , have recently become competitive with silicon as the active transistor layer to drive arrays of pixels in large area displays. [9,[13][14][15][16][17][18][19]24] As the billion-dollar display industry moves forward, the amorphous phase of the complex oxides is favored both for flexible and high-resolution display applications. [13][14][15][16][48][49][50][51][52][53][54][55][56][57][58][59] The unique properties of AOSs were first demonstrated in 1990, [60] and the research area has been growing exponentially since then. Unlike Si-based semiconductors, AOSs were shown to exhibit optical, electrical, thermal, and mechanical properties that are comparable or even superior to those possessed by their crystalline counterparts. [48][49][50][51][52][53][54][55][56][57][58] Table 1 summarizes the key physical properties of best-performing crystalline TCOs and AOSs; the differences (or the lack thereof) between the two will be discussed in detail in the respective sections below.

In2O3‐Based Transparent Conducting Oxide Films with High Electron Mobility Fabricated at Low Process Temperatures

“…As shown in Figure , all of the as‐deposited films exhibited higher N values when deposited at high P H2O . In general, the N of a ‐In 2 O 3 ‐based TCOs, including a ‐IZO, a ‐ITO, and a ‐In 2 O 3 :H, can be controlled by the oxygen deficiency in the film . Herein, only P H2O was varied; the O 2 and Ar flow rates were constant.…”

“…In general, the N of a-In 2 O 3 -based TCOs, including a-IZO, a-ITO, and a-In 2 O 3 :H, can be controlled by the oxygen deficiency in the film. [59,61] Herein, only P H2O was varied; the O 2 and Ar flow rates were constant. Therefore, the oxygen deficiency in the film increased with increasing P H2O because of the presence of H radicals and ions produced in the plasma during deposition.…”

Infinite-randomness fixed point of the quantum superconductor-metal transitions in amorphous thin films

“…To preserve neutrality, some In atoms have a valence of +1 instead of +3. This results in a random distribution of valence and charge fluctuations-a distribution which is thought to give rise to a stochiometric disorder [38] and may give rise to extended defect states [39]. In addition to structural and chemical disorder, there is longer-scale disorder stemming from the films' characteristic undulating morphology.…”

Energetic, structural and electronic features of Sn-, Ga-, O-based defect complexes in cubic In2O3

“…Therefore, the sum of chemical potential values (left side of Eqs. (2)(3)(4)(5)) determines the transition boundary between the formation/decomposition of secondary phases only. The appearance of reverse reactions results in decomposition onset of secondary phases to their elementary phases.…”