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This paper distinguished hydrogen roles to improve electron mobility and carrier concentration in ZnO and Al doped ZnO sputtered films. By combining experimental evidences and theoretical results, we find out that hydrogen located at oxygen vacancy sites (HO) is the main factor gives rise to increase simultaneously mobility and carrier concentration which has not been mentioned before. Introducing appropriate hydrogen content during sputtering not only results in crystalline relaxation but also supports doping Al into ZnO, increasing carrier concentration and electron mobility in the film. First principles calculations confirmed hydrogen substitutional stability for oxygen vacancy, significantly reducing electron conductivity effective mass and hence increasing electron mobility. In particular, 0.8% hydrogen partial pressure ratio achieved 61 cm2V−1s−1 maximum electron mobility, optical transmittance above 82% in visible and near-infrared regions, and 2 × 1020 cm−3 carrier concentrations for H Al co-doped ZnO film. These values approach ideal electrical and optical properties for transparent conducting oxide films. The presence of one maximum electron mobility was attributed to competition between increasing mobility due to restoring effective electron mass and hydrogen passivation of native defects, and decreased electron mobility due to electron-phonon scattering.

Point-defect engineering is an effective way to control the mobility and transparent-conducting performance of sputtered fluorine-doped ZnO (FZO) thin films. In this study, doping with fluorine (F) is accomplished through a simple one-step deposition process and is demonstrated to enhance the crystal quality, eliminate the point defects, and boost the mobility as well as the performance of the films. Furthermore, the films’ characteristics are observed to be strongly dependent on F content. At the optimum F content of 1%, the FZO films exhibited the best crystal quality and the lowest concentration of Zn interstitial and O vacancy defects due to F passivation. Moreover, a mobility as high as 45.3 cm2/V and the greatest figure-of-merit performance are achieved for cutting-edge transparent electrode applications. However, a further increase of F content brought about an increased concentration of defects relating to Zn vacancies, especially F interstitials, which yielded the low mobility and poor performance due to the degraded structure.

Conductivity σ and thermal conductivity κ are directly related to carrier concentration while Seebeck coefficient S is inversely proportional to carrier concentration. Therefore, improving thermoelectric (TE) performance is challenging. Here, the first-time analysis of secondary phase-controlled TE performance in terms of density-of-state effective mass m d ∗ , weighted mobility μw and quality factor B is discussed in ZnO system. The results show that the secondary spinel phase Ga2O3(ZnO)9 not only impacts on κ but also on σ and S at high temperature, while the effect of carrier concentration seem to be dominant at low temperature. For the high-spinel-segregation sample, a compensation of dopant atoms from the spinel to substitutional sites in the ZnO matrix at high temperature leads to a low decreased rate of temperature-dependent m d ∗ . The compensation process also induces a band sharpening, a small μw reduction, and a large B enhancement. As a result, In and Ga co-doped ZnO bulk with the highest spinel segregation achieves the greatest PF improvement by 112.8%, owing to enhanced Seebeck coefficient by 110% as compared to the good Zn-substitution sample.

Structure modification has been found to tune significantly the transparent-conducting performance, especially mobility and conductivity of hydrogenated Ga-doped ZnO (HGZO) films. The strong correlation between film thickness and mobility of the films is revealed. The mobility increases quickly with increasing the thickness from 350 to 900 nm, and then tends to be saturated at further thicknesses. A higher mobility than 50 cm2/Vs can be achieved, which is an extra-high value for polycrystalline ZnO films deposited by using the sputtering technique. The thickness-dependent mobility originates from scatterings on grain boundaries and dislocation-induced defects controlled by thin-film growth. Based on the Volmer-Weber model, an expansion model is built up to describe the thickness-dependent crystal growth of the HGZO films, especially at the thick films. As a result, the 800 nm-thick HGZO film obtains the highest performance with high mobility of 51.5 cm2/Vs, low resistivity of 5.3 × 10−4 Ωcm, and good transmittance of 83.3 %.

In this work, several X-ray and nuclear analysis techniques were used to examine ZnO materials co-doped with In and Ga, or IGZO materials. X-ray diffraction analysis, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy revealed multi-scale defects in the materials. A nanoscale secondary Ga2Zn9O12 spinel phase, mesoscale grain boundaries, and atomic-scale lattice defects were detected. The lattice defects included oxygen vacancies, zinc vacancies, and complex defects. Positron annihilation spectroscopy and Doppler broadening spectroscopy provided evidence of interactions between charge carriers and defects sites, which explained the low thermal conductivities of the IGZO materials (κtotal ≈ 3.9 W/mK) at 773 K. This combination of X-ray and nuclear analytical techniques can be viewed as a novel approach for investigating the thermoelectric properties of materials with complex crystal structures that contain atomic-scale voids, nanoscale secondary phases, and mesoscale grain boundaries.

In this paper, thermoelectric performance of the ZnO thin films were investigated via doping (Gallium - Ga and Indium - In) and post-thermal treatment. Various kinds of defects, such as zinc (Zn) vacancies, Ga substitute for Zn, zinc interstitials, oxygen vacancies, oxygen interstitials, oxygen antisite, were induced in the ZnO thin films by doping with Ga, In and post-thermal treatment. Annealed thin films have better thermoelectric performance than unannealed thin films. The figure of merit ZT values at 300 °C were 0.114 and 0.186 for the single Ga-doped ZnO (GZO@500) and dually In, Ga doped ZnO (IGZO@500) thin films annealed at 500 °C, respectively. Higher concentration of zinc interstitial led the GZO@500 thin film to have larger power factor and larger total thermal conductivity, resulting in lower ZT than the IGZO@500 thin film. To the best of our knowledge, the ZT value of 0.186 at 300 °C obtained from our IGZO@500 thin films is the highest ever reported for n-type ZnO based thin films.

In this work, role of phase composition and interstitial oxygen on the thermoelectric properties of CuCr0.85Mg0.15O2 materials prepared at different sintering temperatures (1273–1673 K) for short time (3 h) are reported. Interestingly, the samples sintered at 1273 K and 1673 K had the same Seebeck coefficient, despite the 1273 K sample having significantly lower conductivity, which are discussed via phase composition and interstitial oxygen induced during the CuCrO2 phase formation and its related defect (VCu, VCr, …). Besides, high conductivity of the 1673 K sample originated from the low percentage of CuO phase and the appearance of Cu2O phase. Since the 1273 K and 1673 K sintered samples have almost the same percentage of delafossite and spinel phases so the 1673 K sample still remain its high Seebeck coefficient. We suggest some reaction chemical equations for elucidating the roles of interstitial oxygen on the phase composition and thermoelectric properties CuCr0.85Mg0.15O2 delafossite material.

We investigated the effect of single and multidopants on the thermoelectrical properties of host ZnO films. Incorporation of the single dopant Ga in the ZnO films improved the conductivity and mobility but lowered the Seebeck coefficient. Dual Ga- and In-doped ZnO thin films show slightly decreased electrical conductivity but improved Seebeck coefficient. The variation of thermoelectric properties is discussed in terms of film crystallinity, which is subject to the dopants' radius. Small amounts of In dopants with a large radius may introduce localized regions in the host film, affecting the thermoelectric properties. Consequently, a 1.5 times increase in power factor, three times reduction in thermal conductivity, and 5-fold enhancement in the figure of merit ZT have been achieved at 110 °C. The results also indicate that the balanced control of both electron and lattice thermal conductivities through dopant selection are necessary to attain low total thermal conductivity.

In this work, we prepare H and Ga co-doped ZnO (HGZO) films by a sputtering method with over 80% transparency in 400–1100 nm wavelength range and a sheet resistance as low as 3.9 Ω/sq. Hydrogen is recognized as a key element to enhance transmittance and conductivity. Spectroscopic evidence has indicated that hydrogen assists in substituting Ga3+ for Zn2+ (GaZn) in ZnO lattice; it produces more effective GaZn donors and increases electron concentration. We propose for the first time based on interstitial and substitutional hydrogen configurations that the interactions of Zn atom with its neighboring hydrogen atoms can weaken Zn–O bonds in ZnO lattice, and thus facilitate the substitution of Ga3+ for Zn2+. Furthermore, hydrogen can improve the quality of crystalline grains by lowering point-defect density such as Ga, Zn interstitials, Zn, and O vacancies, which strongly enhance electron mobility in HGZO films. The highest mobility of 48.6 cm2/Vs was obtained in the best-performing film.

The thermoelectric performance of CuCr1-xMgxO2 materials in terms of multi-scale defects induced at various Mg dopant concentrations (x = 0–0.3) was thoroughly studied in this paper. At 748 K and for x = 0.05, 0.15, and 0.30, we report the following power factors and thermal conductivities: 175, 213, and 2.3 μW/m K2 and 7.85, 5.60, and 3.82 W/m K, respectively. In the low doping regime (x

The transparent-conducting performance is estimated through figure-of-merit (FOM) value. To improve poor FOM value of pure ZnO thin films, boron ( B ) as a donor impurity was doped into the films. Direct-current magnetron sputtering was used to prepare B -doped ZnO (BZO) thin films from sintered ZnO targets with variable B 2 O 3 content changing from 0 to 2 wt. %. The x ray diffraction analysis confirmed the preferably c -axis-oriented structure of hexagonal wurtzite ZnO host. The results also showed variation in the film structure versus the B 2 O 3 content through calculations of crystal size and residual stress. Depending on the B 2 O 3 content, a competition of interstitial and substitutional B 3 + ions induced more stress or relaxation in lattice structure of the films. At 1% B 2 O 3 , the BZO thin film had the best crystalline characterization with the lowest stress and large crystal size. In consequence, the BZO 1% film obtained the lowest resistivity of 2.7 × 1 0 − 3 Ω c m , average transmittance of 82.1%, and the best FOM value of 18.8 × 1 0 2 Ω − 1 c m − 1 . The transparent-conducting performance of the ZnO thin films deposited by direct-current (DC) magnetron sputtering was significantly enhanced through B doping. The good-performance BZO film at 1% B 2 O 3 is believed to be of use as electrodes in thin-film solar cells.