Hydrogen donors inSnO2studied by infrared spectroscopy and first-principles calculations

Abstract

Hydrogen is a potentially important source of n-type conductivity in oxide materials. We have investigated hydrogen in tin oxide ͑SnO 2 ͒, a wide-band-gap semiconductor with applications as a transparent conductor and in gas sensors. Infrared ͑IR͒ spectroscopy and electrical measurements indicate that hydrogen binds to a host oxygen atom and increases the conductivity. First-principles calculations confirm that interstitial hydrogen acts as a shallow donor ͑H i + ͒. Our calculations also indicate that H i + diffuses easily and combines with Sn vacancies into stable ͑V Sn-H͒ −3 complexes, with the calculated O-H frequencies in agreement with the experimental values. These results suggest that interstitial hydrogen acts as a shallow, mobile donor in a range of oxide materials.

Hydrogen impurities and shallow donors in SnO2studied by infrared spectroscopy

“…Results from the previous study by Hlaing Oo et al 27 differ from the above, and O-H absorption was reported only for E⊥c. Furthermore, the lines at 3334.2 and 3343.2, while present, were weak in the spectra reported by Hlaing Oo et al and were not discussed in their paper.…”

“…1 and 4 show that annealing SnO 2 in an H 2 ambient at 700 °C produces strong free-carrier absorption in addition to a 10 number of O-H vibrational lines, in agreement with other recent work. 27 SnO 2 and ZnO have similar electron masses and mobilities 19,38,39 suggesting that calibrations of the free-carrier absorption determined previously for ZnO, 32, 36, 37 also annealed in an H 2 ambient, can be applied approximately to the freecarrier absorption spectra measured for SnO 2 at room temperature. 40 With this approximate calibration, the free-carrier absorption shown in the "as-treated" spectrum in Fig.…”

“…[22][23][24][25][26] A recent study confirms that annealing SnO 2 single crystals in hydrogen increases their conductivity and also gives rise to several O-H vibrational lines with a complicated reaction chemistry upon annealing. 27 These lines have been assigned to H i and two different complexes of H with a Sn 3 vacancy. It was also found that H can be present in SnO 2 samples that is not seen by infrared (IR) spectroscopy.…”

“…It was suggested that this "hidden" H is present in the form of H O centers whose vibrational absorption would occur in a spectral region where the sample is opaque. 27 Our experimental results for H in SnO 2 and their interpretation will be compared and contrasted with the properties of H in ZnO. 28 Both H i and H O give rise to shallow donors in ZnO.…”

“…Furthermore, the lines at 3334.2 and 3343.2, while present, were weak in the spectra reported by Hlaing Oo et al and were not discussed in their paper. 27 C. Annealing behavior A series of annealing experiments has been performed to investigate the thermal stabilities of the freecarrier absorption and also the various O-H and O-D centers. Figure 4(a) shows free-carrier absorption spectra that were measured at room temperature for a sample treated in H 2 gas following a series of subsequent heat treatments in a He ambient at the temperatures shown.…”