Hydrogen-doped In2O3 transparent conducting oxide films prepared by solid-phase crystallization method

Abstract

We have characterized amorphous to crystalline transformation of hydrogen (H)-doped In2O3 (In2O3:H) films by transmission electron microscopy, thermal desorption spectroscopy, spectroscopic ellipsometry, and Hall measurements. The In2O3:H films that show a mixed-phase structure embedded with small density of crystalline grains in a large volume fraction of amorphous phase have been fabricated at room temperature by the sputtering of an In2O3 ceramic target with introduction of H2O vapor, and the films have been postannealed in vacuum to crystallize the amorphous phase. With increasing annealing temperature up to 200 °C, the film shows a large increase in Hall mobility (μHall) from 42 to 110 cm2/V s and a decrease in carrier density (NHall) from 4.6×1020 to 2.1×1020 cm−3 with slight decrease in resistivity. The change in μHall and NHall with annealing temperature is strongly correlated with the volume fractions of the amorphous and crystalline phases in the films. Analyses of dielectric functions of the films using the Drude model revealed that the high electron mobility in the crystallized films is attributed mainly to longer relaxation time rather than smaller effective mass, as compared with as-deposited films. Temperature-dependent Hall analysis, relationship between NHall and μHall, and comparison between μHall and optical mobility showed that (i) scattering processes inside amorphous and/or crystalline matrices limit the mobility, (ii) doubly charged ionized impurity scattering is reduced by crystallization, and (iii) phonon scattering becomes dominant after crystallization in the In2O3:H films. The above results suggest that H-doping reduces carrier scattering in the crystallized In2O3:H and structural rearrangements during crystallization eliminate oxygen deficiency and generate H+ that acts as a singly charged donor. In this article, we discuss the transport properties with the variation in microscopic and chemical structures in the In2O3:H films.

Environmental stability of high-mobility indium-oxide based transparent electrodes

“…32 The formation of H 2 O molecules, and their possible desorption from the films, results in the loss of passivation at grain boundaries provided by the H-doping, i.e., higher trap density or potential barriers for electron transport, decreasing µ Hall . [24][25][26][27]33 The H 2 O desorption from the IO:H films at low temperatures is confirmed by TDS measurements (Fig. 6).…”

“…23 The results in Table I show that 24 as well as a possible oxidation of the films. 25 The crystallization, decrease in N e , and possible H passivation at grain boundaries result in a strong increase in µ Hall . 26,27 For the amorphous IZO layer, the µ Hall and N e slightly increase after annealing.…”

On the solid phase crystallization of In2O3:H transparent conductive oxide films prepared by atomic layer deposition

“…7 This material was originally developed by Koida et al, using reactive magnetron sputtering at room temperature from an In2O3 target with the addition of H2O vapour, which resulted in mostly amorphous In2O3:H films. The crucial step for achieving high μ values >100 cm 2 /Vs is a solid phase crystallization (SPC) step by thermal annealing at 160-400 o C. 5 Recently we have demonstrated a similar approach to prepare highmobility In2O3:H using an atomic layer deposition (ALD) process instead of sputtering. After deposition at 100 o C, the ALD film is almost entirely amorphous.…”

“…Due to a lower required Ne, optical losses in the infrared (IR) due to free carrier effects are reduced. In recent years, new In2O3-based TCOs with a higher carrier mobility of >50 cm 2 /Vs have gained significant interest, examples include Zn-doped indium oxide (IZO) 2 , W-doped indium oxide (IWO) 3 , Modoped indium oxide (IMO) 4 and H-doped indium oxide (In2O3:H, also referred to as IO:H or IOH) [5][6][7] . Due to the greatly-reduced IR-losses in such TCOs, they have found direct application in various solar cell devices, mainly leading to increased short-circuit current densities Jsc when compared to conventional ITO.…”

Advanced nanostructured materials for pushing light trapping towards the Yablonovitch limit

“…s) at low carrier densities (in the low 10 20 cm -3 range) resulting in excellent nearinfrared transparency [13]. Such high mobilities are obtained after a solid-phase crystallization process at 200° C, which transforms the as-deposited amorphous indium oxide film into a film with small indium oxide nanocrystals, a few hundred nanometers in size, embedded in an amorphous indium oxide matrix [14]. It is possibly this amorphous tissue around the grains, which minimizes grain boundary scattering resulting in Hall mobilities almost as high as the optical mobility.…”