In Situ Hall Effect Monitoring of Vacuum Annealing of In2O3:H Thin Films

Abstract

Hydrogen doped In2O3 thin films were prepared by room temperature sputter deposition with the addition of H2O to the sputter gas. By subsequent vacuum annealing, the films obtain high mobility up to 90 cm2/Vs. The films were analyzed in situ by X-ray photoelectron spectroscopy (XPS) and ex situ by X-ray diffraction (XRD), optical transmission and Hall effect measurements. Furthermore, we present results from in situ Hall effect measurements during vacuum annealing of In2O3:H films, revealing distinct dependence of carrier concentration and mobility with time at different annealing temperatures. We suggest hydrogen passivation of grain boundaries as the main reason for the high mobility obtained with 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).…”

“…AFM topography scans indicate that the root-mean-square (RMS) surface roughness of the films changes only very slightly from 0.5 nm RMS before DH to 0.7 nm RMS after DH. Consequently, this suggests that degradation in R s is not caused by a modification in the microstructure of the films (amorphization for example 27 ) but points to H 2 O or OH-species adsorption at the grain boundaries. 14 The creation or annihilation of point defects in IO:H caused by DH is equally discarded based on the unchanged N e before and after DH (N e changes by <10%).…”

“…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. Figure 1 displays the relative change (%) in sheet resistance (R s ), carrier concentration (N e ), and electron Hall mobility (µ Hall ) of annealed ITO, IO:H, IZO, and IO:H/ITO bilayers as a function of DH time.…”

“…Peak C at BE of 532 eV is attributed to chemisorbed OH groups on the surface, often shown as indium oxyhydroxide (InOOH). 22,27,29 This peak is indicative for the amount of chemisorbed OH in the layers, surface, and grain boundaries. The fourth peak at 533 eV, peak D, we assign to O in metal carbonates (C-O-M) 29 or molecularly chemisorbed H 2 O.…”

Transparent Electrodes for Efficient Optoelectronics

“…The high free electron mobilities in these polycrystalline hydrogenated In 2 O 3 -based materials are explained by the formation of large grains, together with possible grain-boundary passivation by hydrogen, as well as the fact that H atoms in the film do not contribute significantly to ionized or neutral impurity scattering. [118,119] IO:H, ICO:H, and IWO:H have been successfully applied in SHJ, [117,[120][121][122] CIGS, [123] and perovskite solar cells. [124] Amorphous indium zinc oxide (IZO) is another TCO with low FCA and good electrical properties.…”