Atomic Layer Deposited Al2O3 Films Research Articles

Novel and low reflective silicon surface fabricated by Ni-assisted electroless etching and coated with atomic layer deposited Al2O3 film

In this paper, nickel nanoparticles (Ni NPs) were deposited on planar silicon and pyramidal silicon wafers by the magnetron sputtering method, and then these Ni NP-covered samples were etched in a hydrofluoric acid, hydrogen peroxide, and deionized water mixed solution at room temperature to fabricate a low reflective silicon surface. An alumina (Al2O3) film was then deposited on the surface of the as-etched pyramidal sample by atomic layer deposition to further reduce the reflectance. The morphologies and compositions of these samples were studied by using a field emission scanning electron microscope attached to an energy-dispersive X-ray spectrometer. The surface reflectance measurements were carried out with a UV-Vis-NIR spectrophotometer in a wavelength range of 200–1100 nm. The SEM images show that the as-etched planar and pyramidal silicon samples were covered with many rhombic nanostructures and that some nanostructures on the planar silicon surface were ready to exhibit a flower-like burst. The reflectances of the as-etched planar and pyramidal silicon samples were 5.22 % and 3.21 % in the wavelength range of 400–800 nm, respectively. After being coated with a 75-nm-thick Al2O3 film, the etched pyramidal silicon sample showed an even lower reflectance of 2.37 % from 400 nm to 800 nm.

Passivation mechanism of thermal atomic layer-deposited Al2O3 films on silicon at different annealing temperatures

Thermal atomic layer-deposited (ALD) aluminum oxide (Al2O3) acquires high negative fixed charge density (Qf) and sufficiently low interface trap density after annealing, which enables excellent surface passivation for crystalline silicon. Qf can be controlled by varying the annealing temperatures. In this study, the effect of the annealing temperature of thermal ALD Al2O3 films on p-type Czochralski silicon wafers was investigated. Corona charging measurements revealed that the Qf obtained at 300°C did not significantly affect passivation. The interface-trapping density markedly increased at high annealing temperature (>600°C) and degraded the surface passivation even at a high Qf. Negatively charged or neutral vacancies were found in the samples annealed at 300°C, 500°C, and 750°C using positron annihilation techniques. The Al defect density in the bulk film and the vacancy density near the SiOx/Si interface region decreased with increased temperature. Measurement results of Qf proved that the Al vacancy of the bulk film may not be related to Qf. The defect density in the SiOx region affected the chemical passivation, but other factors may dominantly influence chemical passivation at 750°C.

Role of Annealing Conditions on Surface Passivation Properties of ALD Al2O3 Films

The surface passivation performance of Al2O3 films attracted attention in the field of solar cells and semiconductor devices and depends on the conditions of the applied post-deposition annealing step. The effect of annealing temperature and different annealing atmospheres on the surface passivation quality of atomic layer deposited Al2O3 films was investigated on n-type float-zone Si wafers. Photoconductance decay measurements were carried out to characterize recombination velocities and carrier lifetimes. The chemical and field-effect passivation mechanism, i.e. the interface trap density and the fixed charge density, respectively, were studied by capacitance-voltage experiments. Low surface recombination velocities of Seff,max ∼1cm/s corresponding to a carrier lifetime of 9.0ms were achieved for samples annealed in O2 atmosphere whereas annealing in H2 and N2 led to slightly higher Seff,max-values ∼2cm/s. The annealing temperature was found to affect both the fixed charge density and the interface trap density whereas in contrast the annealing atmosphere affected only the interface trap density, i.e. the chemical passivation. According to the expectations the highest surface passivation quality is based on a high fixed charge density and a low interface trap density.

Characterization of atomic layer deposition HfO2, Al2O3, and plasma-enhanced chemical vapor deposition Si3N4 as metal–insulator–metal capacitor dielectric for GaAs HBT technology

Characterization was performed on the application of atomic layer deposition (ALD) of hafnium dioxide (HfO2) and aluminum oxide (Al2O3), and plasma-enhanced chemical vapor deposition (PECVD) of silicon nitride (Si3N4) as metal–insulator–metal (MIM) capacitor dielectric for GaAs heterojunction bipolar transistor (HBT) technology. The results show that the MIM capacitor with 62 nm of ALD HfO2 resulted in the highest capacitance density (2.67 fF/μm2), followed by capacitor with 59 nm of ALD Al2O3 (1.55 fF/μm2) and 63 nm of PECVD Si3N4 (0.92 fF/μm2). The breakdown voltage of the PECVD Si3N4 was measured to be 73 V, as compared to 34 V for ALD HfO2 and 41 V for Al2O3. The capacitor with Si3N4 dielectric was observed to have lower leakage current than both with Al2O3 and HfO2. As the temperature was increased from 25 to 150 °C, the breakdown voltage decreased and the leakage current increased for all three films, while the capacitance increased for the Al2O3 and HfO2. Additionally, the capacitance of the ALD Al2O3 and HfO2 films was observed to change, when the applied voltage was varied from −5 to +5 V, while no significant change was observed on the capacitance of the PECVD Si3N4. Furhermore, no significant change in capacitance was seen for these silicon nitride, aluminum oxide, and hafnium dioxide films, as the frequency was increased from 1 kHz to 1 MHz. These results show that the ALD films of Al2O3 and HfO2 have good electrical characteristics and can be used to fabricate high density capacitor. As a result, these ALD Al2O3 and HfO2 films, in addition to PECVD Si3N4, are suitable as MIM capacitor dielectric for GaAs HBT technology, depending on the specific electrical characteristics requirements and application of the GaAs devices.

Evaluating Al2O3 gas diffusion barriers grown directly on Ca films using atomic layer deposition techniques

Al2O3 gas diffusion barriers grown directly on Ca films using atomic layer deposition (ALD) techniques were evaluated using several methods based on Ca oxidation. The Al2O3 ALD films were grown on Ca films at 120 °C using trimethylaluminum and H2O as the reactants. The oxidation of the Ca films was then monitored versus time at 70 °C and ∼28% relative humidity either by measuring the electrical conductance of the Ca film or by recording the photographic image of the Ca film. In the photographic images, the Ca films revealed that the Al2O3 ALD films have a small number of pinhole defects that lead to Ca film oxidation areas that grow radially around the pinhole defect versus time. A burst of new oxidation areas also appeared suddenly at later times and grew radially versus time. This rapid “blooming” may be related to another type of defect caused by water corrosion of the Al2O3 ALD films. In the electrical conductance measurements, the conductance of the Ca film initially showed little change versus time. The conductance then dropped rapidly when the oxidation area in the photographic image was a noticeable fraction of the Ca film area. The conductance measurements yielded a water vapor transmission rate (WVTR) value of ∼2 × 10−2 g/(m2 day) prior to the rapid reduction of the conductance. The photographic images of the Ca film were also analyzed to obtain a WVTR value assuming radial oxidation of the Ca film around defects. The WVTR values obtained from the electrical conductance and the photographic images were in approximate agreement and increased versus Ca film oxidation until the rapid blooming of new circular oxidation areas. The WVTR values are larger than previous measurements and may indicate that Al2O3 ALD films grown directly on Ca are less stable and degraded by Ca film oxidation. This study reveals that a range of WVTR values can be obtained from different variations of the Ca test depending on the extent of Ca film oxidation.

Atomic layer deposition α-Al2O3 diffusion barriers to eliminate the memory effect in beta-gamma radioxenon detectors

Well designed scintillator detectors, including such examples as ARSA, SAUNA, and XIA’s “PhosWatch”, can readily achieve the state of the art radioxenon detection limits required for nuclear explosion monitoring. They are also reliable, robust detectors that do not require cryogenic cooling for operation. All three employ the principle of beta-gamma coincidence detection to reduce background counting rates, using a BC-404 plastic scintillator to detect the betas and a CsI or NaI scintillator to detect the gamma-rays. As a consequence of this commonality of design, all three also display a “memory effect” arising from the diffusion of Xe into BC-404. Thus, when one sample is pumped out of the detector, a fraction remains behind, embedded in the BC-404, where it artificially raises the signal counting rate for the next sample. While this is not a fatal flaw in scintillator detectors, developing a method to eliminate the memory effect would significantly enhance their utility. This paper reports efforts to develop thin, amorphous Al2O3 films, deposited by atomic layer deposition (ALD) to act as diffusion barriers on the BC-404 surfaces exposed to radioxenon. Using radon as a convenient substitute for Xe, film thicknesses between 2 and 10 nm were originally investigated and found to show a memory effect to varying degrees. A second set of 20 and 30 nm films was then produced, which appeared to completely eliminate the radon memory effect, but, when consequentially tested with radioxenon, were found to exhibit xenon memory effects that were approximately half of the effect found on uncoated BC-404. We draw two conclusions from this result. The first is that it will be necessary to develop an improved method for depositing thicker ALD Al2O3 films at lower temperatures while still retaining high film quality. The second is that, since xenon is required to test for the xenon memory effect, we need a test method that does not require xenon radio-isotopes in order to facilitate screening large numbers of samples.

Permeability and corrosion in ZrO2/Al2O3 nanolaminate and Al2O3 thin films grown by atomic layer deposition on polymers

The authors studied moisture permeation and corrosion in Al2O3 and Al2O3/ZrO2 nanolaminate (NL) thin films grown by atomic layer deposition (ALD) at 100 °C on polyester substrates. A percolation model accurately described the dependence of permeation on the volume fraction of ZrO2 in the nanolaminates. As the fraction of ZrO2 was reduced to ∼0.5, moisture permeation in the NLs approached the measurement limit ∼1 × 10−4 g-H2O/m2-day, equivalent to Al2O3 with the same total thickness. However, resistance to corrosion by water was modestly better for Al2O3 than for the NL, and we proposed that corrosion in ALD Al2O3 films was associated with hydrogen incorporation and a consequent film chemical composition that is an oxy-hydroxide, AlOx(OH)3−2x. The authors present x-ray diffraction evidence for conversion of ALD Al2O3 to hydroxide corrosion products, AlO(OH) and Al(OH)3, after aging films in damp heat (85 °C/85% relative humidity) for two weeks.

Porous Alumina Protective Coatings on Palladium Nanoparticles by Self-Poisoned Atomic Layer Deposition

Atomic layer deposition (ALD) of Al2O3 using trimethylaluminum (TMA) and water on Pd nanoparticles (NPs) was studied by combining in situ quartz crystal microbalance (QCM) measurements, in situ quadrupole mass spectrometry (QMS), and transmission electron microscopy (TEM) with density functional theory (DFT) calculations. TEM images of the ALD Al2O3 overcoated Pd showed conformal Al2O3 films on the Pd NPs as expected for ALD. However, hydrogen detected by in situ QMS during the water pulses suggested that the ALD Al2O3 films on the Pd NPs were porous rather than being continuous coatings. Additional in situ QCM and QMS measurements indicated that Al2O3 ALD on Pd NPs proceeds by a self-poisoning, self-cleaning process. To evaluate this possibility, DFT calculations were performed on Pd(111) and Pd(211) as idealized Pd NP surfaces. These calculations determined that the TMA and water reactions are thermodynamically favored on the stepped Pd(211) surface, consistent with previous observations. Furthermore, the DFT studies identified methylaluminum (AlCH3*, where the asterisk designates a surface species) as the most stable intermediate on Pd surfaces following the TMA exposures, and that AlCH3* transforms into Al(OH)3* species during the subsequent water pulse. The gas phase products observed using in situ QMS support this TMA dissociation/hydration mechanism. Taken together, the DFT and experimental results suggest a process in which the Pd surface becomes poisoned by adsorbed CH3* species during the TMA exposures that prevent the formation of a complete monolayer of adsorbed Al species. During the subsequent H2O exposures, the Pd surface is cleaned of CH3* species, and the net result is a porous Al2O3 film. This porous structure can retain the catalytic activity of the Pd NPs by providing reagent gases with access to the Pd surface sites, suggesting a promising route to stabilize active Pd catalysts.

Impact of the Deposition and Annealing Temperature on the Silicon Surface Passivation of ALD Al2O3 Films

The effect of the deposition and annealing temperature on the surface passivation of atomic layer deposited Al2O3 films was investigated on n-type Cz silicon wafers. The deposition temperature was varied between 200 and 500̊C and the annealing temperature between 300 and 450̊C, respectively. Films prepared at 200 and 300̊C showed an improvement of surface passivation with increasing anneal temperature. The Al2O3 films grown at 400 and 500̊C did not improve by annealing. By corona charging experiments it was revealed that the improvement in surface passivation with increasing anneal temperature of films grown at 300̊C can be attributed to a significant increase in chemical passivation with a minor increase in field-effect passivation. For Cz and FZ wafers an identical surface passivation was achieved with the chemical passivation being lower for Cz wafers due to the surface morphology and the field-effect passivation being quite similar. Consequently the field-effect passivation was found to be the more important passivation mechanism.

Quantitative in situ infrared analysis of reactions between trimethylaluminum and polymers during Al2O3 atomic layer deposition

The reactions of trimethylaluminum (TMA) toward substrates during the Al2O3 atomic layer deposition (ALD) on a variety of polymers were studied by in situ Fourier transform infrared spectroscopy (FTIR). The experiments demonstrate that TMA reacts with certain nucleophilic functional groups on the polymer surface during the first several ALD cycles. For some polymer substrates, TMA vapor penetrates into the polymer and reacts in the polymer bulk. In both cases, the initial reaction plays an important role in the nucleation and growth of Al2O3. For chemically inert polymers, such as polypropylene, nucleation of Al2O3 ALD is relative slow at the initial stage due to the lack of reactive groups on the substrate. However, polyester, polyamide and polyether are more reactive, and in situ FTIR spectra showed a larger extent of reaction with TMA, facilitating the nucleation of ALD film on these polymers. By comparing FTIR spectra, we quantitatively estimate the extent of TMA reaction towards different polymers, and confirmed the results using X-ray photoelectron spectroscopy and scanning electron microscopy. Results give insight into the importance of the polymer structure in determining the nature and extent of the reaction during ALD film processing on polymer substrates.

Nucleation and Growth of Platinum Films on High-k/Metal Gate Materials by Remote Plasma and Thermal ALD

Platinum films were grown on Si wafers, SiO2, Al2O3 and high-k dielectric HfO2 ALD films on Si substrates by both remote plasma and thermal atomic layer deposition (ALD) at 300°C, using methylcyclopentadienyl_trimethyl platinum (MeCpPtMe3) and O2 as precursors. The ALD Pt-films deposited were homogeneous and resulted in a low resistivity of 12.8 μΩ-cm. AES studies revealed high quality Pt films deposited by both thermal and plasma ALD with carbon impurity less than 1.5% and oxygen found only in the interface. SEM and EDX were used to investigate Pt nucleation and growth in ALD processes. It is remarkable that the nucleation delay of between thermal and plasma ALD Pt was different though they are a similar growth rate of 0.45 Å/cycle. In this work, the Pt ALD nucleation and growth behaviours with precursor dose times, O2 or O2 plasma exposures and substrates are also investigated.

Simple model for atomic layer deposition precursor reaction and transport in a viscous-flow tubular reactor

Precursor reaction and transport are both critical in determining the thickness uniformity and conformality of atomic layer deposition (ALD) thin films. However, it is sometimes difficult to predict how changes in conditions, such as mass flow rate or precursor reactivity, will affect the outcome of an ALD experiment. To provide some insight and guidance, we have developed a simple 1D model to describe precursor transport and reaction in a tubular viscous flow ALD reactor. After making some simplifying assumptions, we show that the transport problem depends only on three independent parameters, the Peclet number, the Damkoeler number, and the excess number, which can be easily calculated for most ALD processes. Despite its simplicity, we obtain very good agreement with experimental results for the thickness profiles of ALD Al2O3 films deposited using trimethyl aluminum and H2O. The authors have applied the model to study the impact of precursor properties and experimental conditions on the growth profiles and saturation curves obtained during ALD, including the presence of nonself-limited wall recombination.

Cathode encapsulation of organic light emitting diodes by atomic layer deposited Al2O3 films and Al2O3/a-SiNx:H stacks

Al2O3 thin films synthesized by plasma-enhanced atomic layer deposition (ALD) at room temperature (25 °C) have been tested as water vapor permeation barriers for organic light emitting diode devices. Silicon nitride films (a-SiNx:H) deposited by plasma-enhanced chemical vapor deposition served as reference and were used to develop Al2O3/a-SiNx:H stacks. On the basis of Ca test measurements, a very low intrinsic water vapor transmission rate of ≤ 2 × 10−6 g m−2 day−1 and 4 × 10−6 g m−2 day−1 (20 oC/50% relative humidity) were found for 20–40 nm Al2O3 and 300 nm a-SiNx:H films, respectively. The cathode particle coverage was a factor of 4 better for the Al2O3 films compared to the a-SiNx:H films and an average of 0.12 defects per cm2 was obtained for a stack consisting of three barrier layers (Al2O3/a-SiNx:H/Al2O3).

Electrical properties of atomic layer deposited aluminum oxide on gallium nitride

We report on our investigation of the electrical properties of metal/Al2O3/GaN metal-insulator-semiconductor capacitors. We determined the conduction band offset and interface charge density of the alumina/GaN interface by analyzing the capacitance-voltage characteristics of atomic layer deposited Al2O3 films on GaN substrates. The conduction band offset at the Al2O3/GaN interface was calculated to be 2.13 eV, in agreement with theoretical predications. A non-zero field of 0.93 MV/cm in the oxide under flat-band conditions in the GaN was inferred, which we attribute to a fixed net positive charge density of magnitude 4.60 × 1012 cm−2 at the Al2O3/GaN interface. We provide hypotheses to explain the origin of this charge by analyzing the energy band line-up.

Charge trapping characteristics of Au nanocrystals embedded in remote plasma atomic layer-deposited Al2O3 film as the tunnel and blocking oxides for nonvolatile memory applications

Remote plasma atomic layer deposited (RPALD) Al2O3 films were investigated to apply as tunnel and blocking layers in the metal-oxide-semiconductor capacitor memory utilizing Au nanocrystals (NCs) for nonvolatile memory applications. The interface stability of an Al2O3 film deposited by RPALD was studied to observe the effects of remote plasma on the interface. The interface formed during RPALD process has high oxidation states such as Si+3 and Si+4, indicating that RPALD process can grow more stable interface which has a small amount of fixed oxide trap charge. The significant memory characteristics were also observed in this memory device through the electrical measurement. The memory device exhibited a relatively large memory window of 5.6 V under a 10/−10 V program/erase voltage and also showed the relatively fast programming/erasing speed and a competitive retention characteristic after 104 s. These results indicate that Al2O3 films deposited via RPALD can be applied as the tunnel and blocking oxides for next-generation flash memory devices.

Atomic Layer Deposition Ultra-Barriers for Electronic Applications—Strategies and Implementation

We show that Al2O3 thin films, grown by atomic layer deposition (ALD) on polyester, are ultrabarriers with moisture permeation <10(-5) g-H2O/m2-day, as determined after aging for more than three years. We present evidence that the mechanism for gas permeation in ALD Al2O3 films is not due to pinholes, but that the onset of permeation occurs abruptly, analogous to electrical breakdown in oxide thin films. We show that the permeation onset time increases for thicker Al2O3 films and higher ALD process temperature, for which the hydrogen defect concentration in Al2O3 films is less. Further, we show that mild plasma treatment of the polyester, prior to ALD deposition of Al2O3, makes the surface more hydrophilic and reduces moisture permeation compared to an untreated surface. Similarly, ALD deposition on the bare or non-slip side of the polyester film is preferred for low permeation.

The Role of Nucleation Surfaces in the Texture Development of Magnesium Oxide During Ion Beam Assisted Deposition

Both the structure and the type of the nucleation surface play a key role in texture development of IBAD MgO films. We have examined these features in Al2O3 and Y2O3 thin films using two different types of deposition methods, atomic layer deposition (ALD) and electron beam evaporation (EBE). Examination of EBE Al2O3 with in situ reflected high-energy electron diffraction (RHEED) films reveals the presence of a nanocrystalline structure that remains unchanged after and is insensitive to ion irradiation with 750 eV argon ions. In contrast, ALD Al2O3 examined with the same method reveals a featureless image that appears amorphous. Use of the ALD Al2O3 film can result in well-textured films with reasonable in-plane mosaic spread values (~ 14°) without process optimization. Similar results were obtained on ALD and EBE Y2O3 films, although, the EBE Y2O3 appeared amorphous in the RHEED even before exposure to the ion beam. The ALD Y2O3 film resulted in an in-plane texture of ~ 10°. Finally, bare silicon substrates were examined. It was found that even with the native oxide remaining on its surface, the silicon underneath was amorphized by the ion beam and provided a suitable surface for the deposition of biaxial textured MgO with an in-plane texture of ~ 7° FWHM.

Critical tensile and compressive strains for cracking of Al2O3 films grown by atomic layer deposition

Al2O3 atomic layer deposition (ALD) is a model ALD system and Al2O3 ALD films are excellent gas diffusion barrier on polymers. However, little is known about the response of Al2O3 ALD films to strain and the potential film cracking that would restrict the utility of gas diffusion barrier films. To understand the mechanical limitations of Al2O3 ALD films, the critical strains at which the Al2O3 ALD films will crack were determined for both tensile and compressive strains. The tensile strain measurements were obtained using a fluorescent tagging technique to image the cracks. The results showed that the critical tensile strain is higher for thinner thicknesses of the Al2O3 ALD film on heat-stabilized polyethylene naphthalate (HSPEN) substrates. A low critical tensile strain of 0.52% was measured for a film thickness of 80 nm. The critical tensile strain increased to 2.4% at a film thickness of 5 nm. In accordance with fracture mechanics modeling, the critical tensile strains and the saturation crack densities scaled as (1/h)1/2 where h is the Al2O3 ALD film thickness. The fracture toughness for cracking, KIC, of the Al2O3 ALD film was also determined to be KIC = 2.30 MPa m1/2. Thinner Al2O3 ALD film thicknesses also had higher critical strains for cracking from compressive strains. Field-emission scanning electron microscopy (FE-SEM) images revealed that Al2O3 ALD films with thicknesses of 30–50 nm on Teflon fluorinated ethylene propylene (FEP) substrates cracked at a critical compressive strain of ∼1.0%. The critical compressive strain increased to ∼2.0% at a film thickness of ∼20 nm. A comparison of the critical tensile strains on HSPEN substrates and critical compressive strains on Teflon FEP substrates revealed some similarities. The critical strain was ∼1.0% for film thicknesses of 30–50 nm for both tensile and compressive strains. The critical compressive strain then increased more rapidly than the critical tensile strain for thinner films with thicknesses &amp;lt; 30 nm. The high critical tensile and compressive strains for thin Al2O3 ALD films should be very useful for flexible gas diffusion barriers on polymers.

Deposition Temperature and Thermal Annealing Effects on the Electrical Characteristics of Atomic Layer Deposited Al2O3 Films on Silicon

Atomic layer deposition (ALD) of Al2O3 is of interest for a wide range of micro-nanoelectronic applications, where the electrical properties of the deposited layers can be strongly affected by deposition conditions and post-deposition treatments. In this work, a mercury-probe capacitance-voltage characterization is carried out on Al2O3 films deposited on silicon by ALD at different temperatures and subjected to various thermal treatments in N2 ambient. Effective positive charges located at the semiconductor/dielectric interface are encountered for the films deposited at the lowest temperature (100°C). Positive Vfb shifts are always registered after the different thermal annealing conditions studied; however, the impact of the thermal treatments is found to be different depending on the deposition temperature. A significant negative charges build-up is observed after a 30 min anneal at 450°C, where improved surface passivation properties are achieved. Interestingly, the hysteresis, as well as the Vfb shifts, clearly diminish for higher deposition temperatures or after a thermal anneal. However, the highest temperature treatments (≥800°C) result in significant interface states generation. Finally, exploratory experiments about the stability of the Al2O3 layers under UV-light irradiation (in the 200–300 nm wavelengths range) show that this can be responsible for a significant degradation of their electrical characteristics.

Effect of surface treatments on interfacial characteristics and band alignments of atomic‐layer‐deposited Al2O3 films on GaAs substrates

AbstractThe GaAs surfaces were passivated by two kinds of chemical pretreatments (using NH4OH and (NH4)2S as passivation agents) for atomic layer deposited (ALD) Al2O3 dielectric film growth. The chemical information at Al2O3/GaAs interfaces was carefully characterized. The impact of surface treatments on the band alignments of ALD Al2O3 films on nGaAs (100) substrates was also investigated. After postdeposition annealing, the NH4OH passivated samples not only have a slight increase of the AsAs peaks with an appearance of As suboxide (AsOx) feature at Al2O3/GaAs interfaces but also exhibit a serious interfacial interdiffusion between Al2O3 and GaAs. However, the (NH4)2S passivated samples produce the GaS and AsS overlayers on GaAs, effectively preventing from the intermixed diffusion between Al2O3 films and GaAs substrates with a sharper interface. Both NH4OH and (NH4)2S passivated Al2O3 samples show the same band gap of 6.67 eV. The conduction band offset at Al2O3/GaAs interface for the (NH4)2S passivated samples have a slight enhancement of 0.14 eV in comparison to NH4OH passivated ones. Copyright © 2010 John Wiley &amp; Sons, Ltd.