We report on zinc oxide thin films grown by atomic layer deposition at a low temperature, which is compatible with a low thermal budget required for some novel electronic devices. By selecting appropriate precursors and process parameters, we were able to obtain films with controllable electrical parameters, from heavily n-type to the resistive ones. Optimization of the growth process together with the low temperature deposition led to ZnO thin films, in which no defect-related photoluminescence bands are observed. Such films show anticorrelation between mobility and free-electron concentration, which indicates that low n electron concentration is a result of lower number of defects rather than the self-compensation effect.

We have investigated photoluminescence ͑PL͒ from Sb-doped p-type ZnO films obtained by thermal oxidation of the Zn-Sb starting material. Very well resolved PL spectra were obtained from samples, with the hole concentration above 1 ϫ 10 17 cm −3 . Acceptor binding energy is determined to be 137 meV from free electron to acceptor transitions. The binding energy between the acceptor and the exciton obtained from the analysis of the acceptor bound excitonic PL transitions measured as a function of temperature is 12-15 meV.

Understanding the origin of the strong difference of electrical parameters between as grown and annealed undoped ZnO films prepared at a temperature range of 100–200 °C by thermal atomic layer deposition is essential for their future applications. In this paper, we show that the conductivity drop by up to 4 orders of magnitude as effect of post-growth annealing is accompanied by multiple simultaneous effects like a two orders of magnitude decrease of hydrogen impurity content, a strong width reduction of the luminescence peaks, and an increase of crystallite sizes influencing the carrier scattering. We show that a level of structural and optical improvement as well as the final electrical parameters of annealed films strongly depend on the previously employed growth temperature, which is related to transition from oxygen- to zinc-rich conditions influencing a type and concentration of native point defects. The growth temperature does not only influence the bandgap energy but also the binding energies of existing donors and the relative ratio between the number of donors and acceptors; hence, it determines the final electrical characteristics of the films. This means that electrical properties of undoped ZnO-atomic layer deposition films can be tuned by native defects engineering.

ZnO doped with N and/or As layers was fabricated by thermal oxidation of ZnTe films grown by MBE on different substrates. Hall effect measurements demonstrated p-type conductivity with a hole concentration of ∼5 × 10 19 cm −3 for ZnO:As and ZnO:As:N on GaAs substrates and ∼6 × 10 17 cm −3 for ZnO:N on ZnTe substrates. The concentration of N and As atoms in ZnO is estimated to be ∼10 20 cm −3 . This suggested that simple substitutional N atoms form acceptor impurities with a smaller efficiency than an As-related complex, probably As Zn -2V Zn. In particular, we were able to distinguish between nitrogen and arsenic acceptor-related luminescence. Optical studies showed meaningful differences of the PL features in samples with different acceptors, grown on different substrates.

We report the first results of the low-temperature photoluminescence study on polycrystal zinc oxide (ZnO) films obtained by atomic layer deposition at 100 • C, 130 • C and 200 • C. These ZnO films, when studied 'as-grown', show a strong excitonic emission even at room temperature. Low-temperature (T = 9 K) photoluminescence reveals lack of defect-related bands and a sharp photoluminescence peak at 3.36 eV with full width at half maximum of 6 meV which is comparable with the value reported for good quality bulk ZnO crystals. The energy position of the excitonic peak scales with temperature according to standard formulas and give the Debye temperature of 963 ± 26 K. We show that optical properties of low-temperature 'as-grown' ZnO films are correlated with structural and electrical ones and that optical study can be a valuable tool for evaluation of quality of ZnO films for novel electronic applications.

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