Hydrogen-related Donors Research Articles

High-throughput and cost-effective method for production of high-quality semi-insulating InP substrates

A novel technique for preparation of high-resistivity indium phosphide (InP) via post-growth treatment of undoped n-type wafers is presented. The method includes the deposition of a controlled quantity of iron on both faces of as-cut wafers by a simple chemical bath, and the subsequent Fe diffusion by thermal annealing. The reproducible low - to – high resistivity conversion is explained considering two simultaneous phenomena: the annealing-controlled in-diffusion of Fe deep acceptors and the out-diffusion of hydrogen-related shallow donors. Differently from standard Fe-doped melt-grown InP single crystals, this process does not suffer from segregation, thus the Fe-concentration is constant from wafer to wafer, with no striations and radial gradients deriving from the convex solid–liquid interface during growth. Main advantages of the developed process are: i) an entire undoped InP boule may be sliced and converted to semi-insulating, which makes the process cost-effective; ii) reproducible and uniform semi-insulating properties from batch to batch of wafers; iii) the Fe incorporation is precisely controlled, and minimized, so that electrical characteristics of Fe-diffused wafers are superior to those of traditional semi-insulating melt-grown InP crystals doped via addition of elemental Fe to the melt.

Effect of hydrogen-related shallow donor on the physical and chemical properties of Ag-doped ZnO nanostructures

Silver-doped zinc oxide nanostructures (Ag/ZnO NSs) with Ag content of 0 wt%, 5 wt%, 10 wt%, and 20 wt% were synthesized using a hydrothermal technique. The prepared nanostructures were annealed at 500 °C for 2 h. The samples were characterized by using scanning electron microscopy, FTIR, X-ray diffraction (XRD), and electrical conductivity. FTIR spectra confirms the presence of hydrogen-related shallow donor defects in the Ag/ZnO NSs, which bind to the oxygen vacancy ({text{H}}_{text{O}}) and consequently plays a significant role in the physicochemical properties of the metal oxide nanostructures. The {text{H}}_{text{O}} defects are blended to O- and Zn-polar Ag-doped ZnO NSs, depending on their polarity. XRD results verified that Ag/ZnO NSs have a polycrystalline hexagonal structure. Williamson–Hall methods were used to estimate the microstructural properties of polycrystalline nanostructures. The electrical conductivity increased from 0.60 to 1.10 µS/cm, and the bandgap energy decreased from 3.36 to 3.10 eV by increasing the Ag from 0 wt% up to 20 wt%.

Annealing-temperature-dependent evolution of hydrogen-related donor and its strong correlation with X-photoluminescence center in proton-irradiated silicon

We have investigated the formation and decay of hydrogen-related donors (HDs) and irradiation-induced intrinsic defects. N-type m:Cz and FZ silicon wafers, which were irradiated with 2 MeV protons and subsequently annealed at 100–600 °C, were analyzed using spreading resistance profiling and photoluminescence (PL). HDs formed at 260 °C and then disappeared in two stages at 400–440 and 500–540 °C. This decay behavior indicates the existence of two types of HDs with different thermal stabilities. PL measurements showed interstitial silicon clusters (W and X center), a carbon–oxygen complex (C center), and exciton lines bound to unknown shallow centers. The origin of the HDs was investigated based on the correlation of the formation and decay temperatures between HDs and irradiation-induced defects. The predominant defects at the early stage of annealing, such as the C and W centers, are ruled out as candidates for the core defects of HDs because annealing above 260 °C is indispensable for the HD formation. In contrast, the X center was found to be thermally generated above 200 °C and disappeared at 580 °C. The similarity of the formation and decay temperatures between the X and HD centers suggests that HDs are associated with the formation of the interstitial silicon-related defects attached to hydrogen. Our results suggest that controlling the formation of interstitial silicon-related defects is important for realizing desirable doping profiles with high accuracy and reproducibility for power devices. Annealing above 400 °C exclusively provides thermally more stable HDs, leading to the realization of more rugged power devices.

Effect of carbon, oxygen, and intrinsic defects on hydrogen-related donor concentration in proton irradiated n-type silicon

We investigated the effect of the concentration of carbon, oxygen, and irradiation-induced intrinsic defects on hydrogen-related donor (HD) concentration. Several n-type silicon wafers having different carbon and oxygen concentrations were irradiated with 2 MeV protons, subsequently annealed at 300–400 °C, and analyzed by spreading resistance profiling. The HD concentration had no correlation with carbon and oxygen concentration. Additionally, the HD concentration showed a strong increasing linear dependence with proton-irradiation dose at 350 and 400 °C and a square root dependence at 300 °C. In the decay process of HD concentration at 400 °C, fast- and slow-decay components were observed regardless of wafer type. Our results show that the HD formation is based on the interactive process of irradiation-induced intrinsic defects and hydrogen, rather than hydrogen-catalyzed thermal double donor formation. Magnetic-field-applied Czochralski (m:Cz) wafers with 300 mm diameter, which are critical for the production scaling of power devices, have a relatively higher oxygen concentration than conventional floating-zone wafers. Our results further suggest that controlling the intrinsic defect formation, rather than oxygen impurity concentration, is more important in realizing designed doping profiles with high accuracy and reproducibility for next-generation power devices using large-diameter m:Cz wafers as a standard starting material.

Influence of oxygen on trap-limited diffusion of hydrogen in proton-irradiated n-type silicon for power devices

The growing demand for power devices has led to the use of magnetic field-applied Czochralski (m:Cz) wafers owing to the limited production capacity and available diameters of the traditionally used floating zone (FZ) wafers. Consequently, the influence of oxygen impurities in the wafers on the electrical properties of devices, regardless of the growth method, needs to be investigated to achieve a stable fabrication process for power devices. Using the proton irradiation doping process and spreading resistance profiling technique, we evaluated the effective diffusion coefficient (Deff) related to trap-limited diffusion of hydrogen and the effects of impurities on diffusivity. We irradiated n-type silicon wafers, which have different carbon, oxygen, and phosphorus concentrations, with 2 MeV protons and annealed them at 300–400 °C. By analyzing the width of the n-type region, where hydrogen-related shallow donors (HDs) are induced, we estimated Deff to be five to six orders of magnitude lower than the intrinsic diffusion coefficient, indicating that hydrogen motion is highly trap-limited. Deff was significantly dependent on the oxygen concentration, and the activation energy of hydrogen diffusion varied from 0.57 ± 0.15 eV (pure epitaxial wafer) to 2.19 ± 0.15 eV (m:Cz wafer). This trend suggests that oxygen-related defects preferentially trap the mobile hydrogen released from thermally dissociated HDs. This study also reveals that the diffusion coefficients of different materials when annealed at 400 °C are comparable. This information is essential to realize the cost-effective production of power devices because we can treat m:Cz and FZ wafers equivalently during the doping process.

Photoconductive detection of a hydrogen-related donor in SnO2

Hydrogen defects in single-crystalline SnO2 are studied by combined photoconductivity and IR absorption spectroscopy. Our results indicate that a defect with an O–H local vibrational mode at 3272 cm−1 (10 K) is a donor with a level less than 300 meV below the conduction band. Annealing experiments demonstrate that the defect is stable up to approximately 450 °C and therefore may contribute to persistent n-type conductivity of SnO2.

Parametric study on photoluminescence enhancement of high-quality zinc oxide single-crystal capping with dielectric microsphere array.

A dielectric microsphere is a multifunctional platform to manipulate light in microscale by nanofocusing, optical whispering gallery resonance, and unidirectional antenna. Dielectric microsphere arrays (MSAs) have demonstrated the capability for photoluminescence (PL) and Raman enhancement without plasmonics. In this work, we investigate the effects of excitation power, tilting angle, and temperature on PL enhancement of high-quality zinc oxide (ZnO) single-crystal capping with fused silica MSAs. The microsphere diameter is optimized to 3.5-5.5μm, achieving the maximum UV-PL enhancement ratio of intensity (ERI) up to tenfold by strong focusing and unidirectional antenna effects. Under the excitation power <0.2 mW, the incident light focused by the MSA increases the localized exciton state density for a higher ERI of ∼15-fold. The angle-sensitive PL intensity from the MSA enhancer provides a simple approach achieving unidirectional UV emission from planar ZnO. The 16-fold enhancement for UV-PL near 130°C is also demonstrated, for the first time, owing to thermal ionization of hydrogen-related donor that increases free-exciton concentration. The high temperature stability and reproducibility of PL enhancement up to 400°C promote the nonplasmonic MSAs superior to surface plasmon-related metal nanostructures for ZnO-based highly efficient luminescence and highly sensitive photon detection above room temperature.

Effect of proton irradiation on the breakdown voltage of a high-voltage p–n junction

The effect of hydrogen-related shallow thermal donors and acceptor-like defects arising under proton irradiation of silicon on the breakdown voltage of a high-voltage p–n junction is considered. The relations making it possible to compute the breakdown voltage of the irradiated p–n junction taking into account the increase in critical field intensity during the ingress of hydrogen-related shallow thermal donors into the region of collisional ionization of the p–n junction are obtained. A technique for determination of the layer position and the minimum dose of hydrogen-related shallow thermal donors making it possible to decrease the breakdown voltage by a specified amount is proposed.

Hydrogen-related excitons and their excited-state transitions in ZnO

The role of hydrogen in the photoluminescence (PL) of ZnO was investigated using four different types of bulk ZnO single crystal, with varying concentrations of unintentional hydrogen donor and Group I acceptor impurities. Photoluminescence spectra were measured at 3 K, with emission energies determined to \ifmmode\pm\else\textpm\fi{}50 \ensuremath{\mu}eV, before and after separate annealing in ${\mathrm{O}}_{2}$, ${\mathrm{N}}_{2}$, and ${\mathrm{H}}_{2}$ atmospheres. Using this approach, several new hydrogen-related neutral-donor-bound excitons, and their corresponding B exciton, ionized donor, and two electron satellite (TES) excited state transitions were identified and their properties further investigated using hydrogen and deuterium ion implantation. The commonly observed ${I}_{4}$ (3.36272 eV) emission due to excitons bound to multicoordinated hydrogen inside an oxygen vacancy (${\mathrm{H}}_{\mathrm{O}}$), that is present in most ZnO material, was noticeably absent in hydrothermally grown (HT) ZnO and instead was replaced by a doublet of two closely lying recombination lines ${I}_{4b,c}$ (3.36219, 3.36237 eV) due to a hydrogen-related donor with a binding energy (${E}_{D}$) of 47.7 meV. A new and usually dominant recombination line ${I}_{6\text{\ensuremath{-}}H}$ (3.36085 eV) due to a different hydrogen-related defect complex with an ${E}_{D}$ of 49.5 meV was also identified in HT ZnO. Here, ${I}_{4b,c}$ and ${I}_{6\text{\ensuremath{-}}H}$ were stable up to approximately 400 and 600 \ifmmode^\circ\else\textdegree\fi{}C, respectively, indicating that they are likely to contribute to the unintentional $n$-type conductivity of ZnO. Another doublet ${I}_{5}$ (3.36137, 3.36148 eV) was identified in hydrogenated HT ZnO single crystals with low Li concentrations, and this was associated with a defect complex with an ${E}_{D}$ of 49.1 meV. A broad near band edge (NBE) emission centered at 3.366 eV was associated with excitons bound to subsurface hydrogen. We further demonstrate that hydrogen incorporates on different lattice sites for different annealing conditions and show that the new features ${I}_{4b,c}$, ${I}_{6\text{\ensuremath{-}}H}$, and ${I}_{5}$ most likely originate from the lithium-hydrogen defect complexes $\mathrm{L}{\mathrm{i}}_{\mathrm{Zn}}\text{\ensuremath{-}}{\mathrm{H}}_{\mathrm{O}}$, $\mathrm{A}{\mathrm{l}}_{\mathrm{Zn}}\text{\ensuremath{-}}{\mathrm{H}}_{\mathrm{O}}\text{\ensuremath{-}}\mathrm{L}{\mathrm{i}}_{\mathrm{Zn}}$, and ${\mathrm{V}}_{\mathrm{Zn}}\text{\ensuremath{-}}{\mathrm{H}}_{3,4}$, respectively.

The Efficiency of Hydrogen-Doping as a Function of Implantation Temperature

– For a conventional proton implantation doping process applied to crystalline silicon comprising proton implantation and subsequent furnace annealing the effect of the substrate temperature set during implantation is examined for temperatures between 50 °C and 200 °C. The formation efficiency of the hydrogen related donors in the maximum of the related doping profiles is shown to linearly increase with the implantation temperature. Regarding the dose rate, a reverted effect is found. The appearing effects are explained by considering the evolution of the initial implantation damage towards a vacancy related precursor species of the hydrogen related donor. Additional information about the implantation temperature dependent defect distribution is gained from Fourier-DLTS results.

Mechanism of formation of ultrashallow thermal donors in carbon-doped oxygen-rich monocrystalline silicon preannealed to introduce hydrogen

We previously reported on ultrashallow thermal donors (USTDs) in carbon-doped oxygen-containing monocrystalline silicon (Czochralski-grown, CZ-Si) crystals that were preannealed to introduce hydrogen at 1300 °C, and then annealed at 480 °C. In this study, the formation mechanism of the USTDs was evaluated. It was observed that an increase in the intensity of UTSDs leads to a reduction in that of hydrogen-related shallow thermal donors [STD(H)s], and the sum of the area intensities of the lines in the transmission spectra of USTDs and STD(H)s is nearly constant when the silicon crystals are annealed for longer than 10 h at 480 °C. We also found some thermally activated processes linked to the formation of USTDs. We thus conclude that the mechanism is composed of the high-speed formation of STD(H)s in the first stage and carbon modulation of the electronic structure of STD(H)s in the second stage.

A DLTS study of hydrogen doped czochralski-grown silicon

In this study we examine proton implanted and subsequently annealed commercially available CZ wafers with the DLTS method. Depth-resolved spreading resistance measurements are shown, indicating an additional peak in the induced doping profile, not seen in the impurity-lean FZ reference samples. The additional peak lies about 10–15μm deeper than the main peak near the projected range of the protons. A DLTS characterization in the depth of the additional peak indicates that it is most likely not caused by classical hydrogen-related donors known also from FZ silicon but by an additional donor complex whose formation is assisted by the presence of silicon self-interstitials.

Degradation of the charge collection efficiency of an n-type Fz silicon diode subjected to MeV proton irradiation

We present the analysis of the charge collection efficiency (CCE) degradation of float zone grown n-type silicon detectors irradiated with 1.3, 2.0 and 3.0MeV protons. The analysis was carried out by irradiating small regions (50×50μm2) with a proton microbeam at fluences ranging from 1011 to 4·1012ions/cm2 and probing the effect of irradiation by measuring the 4.5MeV Li ion induced charge in full depletion conditions. The CCE degradation as function of the proton fluence shows an unexpected deviation from the linear behavior predicted by the Shockley–Read–Hall model of carrier recombination. The build-up of excess hydrogen related donors due to proton irradiations is suggested to be the cause of a significant perturbation of the electrostatic properties of the diode, which drastically change the electron trajectories and hence the induced charge mechanism.

The formation of shallow-donor distribution profiles in proton irradiation of silicon

A study of the formation of shallow hydrogen-containing donors (hydrogen-related shallow thermal donors, STD(H)) in silicon under proton irradiation followed by annealing in a temperature range of 300–500°C is reported. The effect of postimplantation annealing regimes on the concentration distribution of shallow donors at various proton energies and fluences is examined. It is shown that the shape of the concentration profiles strongly varies with temperature and annealing duration when a fixed concentration of radiation defects is introduced and equally with energy and dose at a given annealing temperature. It is also shown that the process in which hydrogen-containing shallow donors are formed is accompanied by the appearance in n-type silicon of H-induced buried n′-layers, the formation of which near the pn junction in the high-resistivity n-base of diode structures allows the breakdown voltage of high-voltage pn junctions to be controlled. In the general case, this makes it possible to improve the characteristics of power silicon devices of various purposes.

High dose proton implantations into silicon: a combined EBIC, SRP and TEM study

AbstractProton (H+) implantations are used in power semiconductor devices to introduce recombination centers (Hazdra et al., Microelectron. J. 32(5), 449–456 (2001)) or to form hydrogen related donor complexes (Zohta et al., Jpn. J. Appl. Phys. 10, 532–533 (1991)). Proton implantations are also used in the 'smart cut' process to generate defects that can be used to cleave thin wafers (Romani and Evans, Nucl. Instrum. Methods Phys. Res. B 44, 313–317 (1990)). However, the implantation damage resulting from H+implantations is not completely understood. In this study, protons with energies from 400 keV up to 4 MeV and doses up to 1016 H+/cm² were implanted into highly ohmic boron doped m:Cz silicon (100). Electron Beam Induced Current (EBIC) measurements were performed to locally determine the minority charge carrier diffusion length. The diffusion length decreases with increasing implantation dose and incorporated damage. Spreading Resistance Profiling (SRP) measurements were performed to analyze the charge carrier concentration profiles for different annealing procedures. The electrical activation and growth of the defect complexes varies strongly with the annealing parameters. Transmission Electron Microscopy measurements were made to investigate the microscopic structures formed by the high dose implantation processes. Due to the high local damage density resulting from low energy and high dose H+ implants, platelet structures are formed. During high‐energy high‐dose H+implantations, the implanted hydrogen generates strain in the crystal lattice resulting in changes in the distances between atomic planes. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A New Method to Increase the Doping Efficiency of Proton Implantation in a High-Dose Regime

Besides the application of local lifetime control, proton implantations can be used to create deep donor profiles in crystalline silicon. At a certain annealing temperature, the maximum hydrogen-related donor (HD) concentration is limited to a few 1015 cm-3 in the end-of-range depth of the radiation damage profile. This behavior is explained with a passivation of the shallow donors due to an excess supply of hydrogen at high proton doses. The impact of hydrogen remaining in the substrate from prior processing steps is investigated. As a countermeasure to the over-decoration effect, a pre-annealing step at elevated temperatures is investigated. This procedure is fully applicable in a commercial manufacturing environment. Experimental results from spreading resistance measurements are shown that clearly show the beneficial effect of the pre-conditioning. DLTS results of pre-conditioned samples are reported, that show a dominant deep defect level that was previously assigned to be vacancy related.

A New Method to Increase the Doping Efficiency of Proton Implantation in a High-Dose Regime

Proton-implantation doping offers a feasible method to modify the doping profile in semiconductor grade silicon in depths ranging up to several hundred micrometers at comparatively low thermal budgets. The hydrogen-related donors are radiation-induced defect complexes decorated by hydrogen. During the proton implantation, typically in the energy range of several 100 keV to several MeV and with fluences in the range between about 1013 cm-2 and 1015 cm-2, intrinsic radiation defects are induced. During a successive anneal in the temperature range between about 300—500 °C the implanted hydrogen diffuses from its projected range through the radiation damage profile and decorates the radiation-induced defects or defect complexes, thus activating, the hydrogen-related donors. Due to this basic mechanism, the profile shape of the hydrogen-related donor profiles is closely correlated to the initial damage profile of the radiation-induced lattice defects. The profiles, hence, exhibit an extended penetrated range with an approximately constant concentration followed by an expressed peak near the end-of-range of the protons.The achievable doping concentration of the hydrogen-related donors induced by the proton implantation and successive annealing is, however, typically limited to a few 1015 cm-3. Earlier studies, based mainly on co-implantations of helium and hydrogen, have led us to propose this to be due to an over-decoration effect of the hydrogen-related donors by excess hydrogen. Based on this assumption, we present a pre-conditioning method based on vacancy-related gettering sites in order to reduce the concentration of excess hydrogen. The procedure comprises a pre-implant with protons and an annealing step at elevated temperatures above the range typically used for proton-implantation doping and is thus fully applicable to a commercial manufacturing environment. During this pre-conditioning, thermally stable higher-order defect complexes are created that are for the most part electrically inactive. These defect complexes act as gettering centers and may in effect reduce the concentration of free hydrogen after a second implant. Experimental results based on spreading resistance measurements are presented in this report that clearly show the beneficial effect of the pre-conditioning and its ability to help overcome several limitations of proton-implantation doping of high-purity silicon.The figure illustrates the effect of the new pre-conditioning method on two magnetic Czochralski-grown silicon wafers. The dashed line represents the carrier concentration profile after a 3-MeV implantation with a proton dose of 4×1014 cm-2 and subsequent annealing at 490 °C for 5 h. The solid line depicts a profile resulting from the same main process steps where the wafer has been pre-conditioned before. It appears that the peak concentration could be increased by a factor of 3 to approximately 2×1015 cm-3. For consecutive studies it may also be of interest that the pre-conditioning results in a steadily increasing carrier concentration up to a depth of 80 µm from the surface.

Deep-Level Defects in High-Dose Proton Implanted and High-Temperature Annealed Silicon

Proton-implantations are valued for their ability to modify the properties of semiconductor grade silicon over a wide spatial range spanning four orders of magnitude between a depth of about 100 nm and 1 mm at comparatively low thermal budgets. At moderate proton doses up to about 1×1013 cm-2 and low annealing temperatures at about 300 °C, proton implantations are used to tailor the carrier life-times in bipolar power semiconductor devices. A large number of deep-level defects are known to form in this parameter regime. At higher doses and higher temperatures proton implantations may be used for modifying the doping profile of the silicon substrate by the creation of hydrogen-related thermal donors. While a large number of studies have investigated deep-level defects induced in the parameter regime typical to life-time tailoring, only few are concerned with the deep-level defects remaining in the samples.In this report we give a brief review of the principal mechanisms of deep-level defect formation after proton irradiation and subsequent annealing of float zone-grown crystalline silicon. Various reaction paths commonly related to vacancy-complexes, interstitial oxygen and hydrogen are discussed. In the experimental part of the study, new DLTS measurements of proton-irradiated pn-diode structures are presented. The study focusses on the regime of elevated doses and annealing temperatures, typically used for proton-implantation doping. The results suggest that for the increased doses used, some of the detected defects show a thermal stability differing from that reported in literature. At least for some of these defects, this may be due to their higher initial concentration. In addition, other defects may appear at higher temperatures as decay products of other, thermally more stable, defects induced by the high-dose implantations.For the first time, we also report on two defect levels at 300 meV and 418 meV below the conduction band with a metastable behavior. The observed levels and their behavior show a high similarity to a negative-U defect known from samples implanted at 88 K without any further thermal budget above room temperature. To our knowledge, these levels have not been detected in a sample annealed above room temperature before.The figure depicts possible reaction paths of vacancies in crystalline silicon under the presence of extrinsic hydrogen and oxygen. Many of these defects lead to localized levels in the silicon bandgap and can therefore impact the electrical properties of a device. The actual appearance of a defect is however determined by the activation energy for its formation together with the applied process temperatures. If known from literature, the activation energy for each reaction path is indicated.

Donor characterization in ZnO by thermally stimulated luminescence

Low temperature thermo-luminescence (TL) has been applied to measurements of the ionization energy of donors in ZnO. Three hydrogen-related donors were characterized with ionization energies of 36, 47, and 55 meV—values that are in complete agreement with previous reports. The donor types can be “switched” by relevant thermal treatments. This work shows that TL can be used to measure the donor energies in luminescent semiconductors in general. This approach can be particularly useful for thin-film investigations when the results of Hall-effect measurements are obscured by contributions from conductive interfaces or substrates.

Morphological, electrical and optical properties of highly oriented undoped and doped zinc oxide and cadmium oxide films grown by atmospheric-pressure chemical vapor deposition

Morphological, electrical and optical properties of undoped and Ga-doped ZnO and undoped CdO films grown on sapphire (Al2O3) substrates by the atmospheric-pressure CVD method using Zn, Cd, H2O and GaCl3 as source materials were investigated. The influences of the deviation from the stoichiometric composition were clearly observed on photoluminescence (PL), photoluminescence excitation (PLE) and photoacoustic (PA) spectra of the undoped ZnO films. The carrier concentration n in the undoped ZnO film was found to be dominated by the hydrogen related donors rather than native defects. The Ga doping in ZnO film led to the degradation of surface flatness, the increase in carrier concentration n and the decrease in Hall mobility μ. With increasing carrier concentration n, the Ga-related neutral donor bound exciton line of the Ga-doped ZnO film shifted towards shorter wavelengths, accompanied by asymmetric broadening. This is probably due to the screening of the Coulomb potential by heavily introduced donors and free-electrons. Highly oriented CdO films with smooth surfaces were successfully grown on r-Al2O3 substrates. Transmittance values for the CdO/r-Al2O3 films were higher than 70% in the range of 700–2500nm. Under the assumption that the reflectance is neglected, the direct and indirect optical gap energies of the CdO films determined from the transmittance spectra were 2.34–2.38eV and 1.98–2.06eV, respectively. PA measurements for the CdO films revealed that the tail states associated with the residual impurities and/or the structural defects reduce the direct optical gap energy. A maximum Hall mobility μ of 178cm2/Vs was achieved on the CdO/r-Al2O3 film with the carrier concentration n of 4.2×1019cm−3.