Er2O3 Thin Films Research Articles

Staggered band alignment of n-Er2O3/p-Si heterostructure for the fabrication of a high-performance broadband photodetector

The low responsivity of conventional Silicon photodiodes in ultraviolet and near-infrared regimes restricts their utility as broadband photodetectors (BBPDs). Despite ongoing investigations into various p-n heterostructures for Silicon-based BBPDs, challenges such as high dark current (Idark), low collection efficiency, low detectivity, and compatibility issues with large-scale Silicon-based devices persist. In this context, we have fabricated relatively unexplored n-Er2O3/p-Si heterojunction-based BBPDs. Polycrystalline Er2O3 thin films (∼110 nm) were deposited on p-Si 〈100〉 substrates by radio frequency magnetron sputtering. Although this process induces a microstrain of approximately 0.022 and a dislocation density of about 0.00303/nm2, the presence of optically active defects is minimal, indicated by a low Urbach energy (∼0.35 eV). X-ray photoelectron spectroscopy (XPS) analysis confirms staggered band alignment at the heterointerface, facilitating efficient charge carrier separation and transport. Consequently, the In/p-Si/n-Er2O3/In device demonstrated significant BBPD properties– low Idark ∼0.15 μA (at +5 V), photo-to-dark current ratio (PDCR) ∼6.5 (at +5 V, 700 nm) with a maximum photoresponsivity ∼22.3 A W−1, and impressive detectivity (∼1013 Jones) even in UV-C region where traditional silicon-based photodetectors respond feebly. The device also demonstrates transient photo-response across an ultrawide spectrum (254 nm–1200 nm) with a fast rise time/fall time ∼79 ms/∼86 ms (at −5 V for 600 nm illumination). This work establishes a straightforward and reliable method for proper material engineering, surface texturing, staggered heterojunction formation, and high-performance BBPD fabrication with prominent broad-spectrum responsivity, sizeable detectivity, and fast response. The integration of these BBPDs with Silicon opens possibilities for their use in electronic devices containing optical switches for communications and broadband image sensors, enhancing their utility in various applications.

Phonon-mediated temperature dependence of Er3+ optical transitions in Er2O3

Characterization of the atomic level processes that determine optical transitions in emerging materials is critical to the development of new platforms for classical and quantum networking. Such understanding often emerges from studies of the temperature dependence of the transitions. We report measurements of the temperature dependent Er3+ photoluminescence in single crystal Er2O3 thin films epitaxially grown on Si(111) focused on transitions that involve the closely spaced Stark-split levels. Radiative intensities are compared to a model that includes relevant Stark-split states, single phonon-assisted excitations, and the well-established level population redistribution due to thermalization. This approach, applied to the individual Stark-split states and employing Er2O3 specific single-phonon-assisted excitations, gives good agreement with experiment. This model allows us to demonstrate the difference in the electron-phonon coupling of the 4S3/2 and 2H11/2 states of Er3+ in E2O3 and suggests that the temperature dependence of Er3+ emission intensity may vary significantly with small shifts in the wavelength (~0.1 nm) of the excitation source.

Exploration of microstructural, chemical states and electrical features of the Au/Er2O3/n-GaN MIS diode with a Er2O3 interlayer

The study involved the formation of high-k erbium oxide (Er2O3) films on the n-GaN surface and evaluated their microstructural and chemical states by XRD, TEM and XPS approaches. By employing Er2O3 as an interlayer between the Au and n-GaN substrate, the metal/insulator/ semiconductor (MIS) diode is developed and explored its electrical features by I–V and C–V procedures. The electrical properties of the MIS diode demonstrate a better rectification nature with a lower leakage current compared with the Au/n-GaN Schottky diode (SD). The MIS diode's derived barrier height (BH) is higher than the SD, suggesting that Er2O3 plays a momentous role in altering the BH. The BH was determined using Cheung’s and Norde techniques, and the measurements showed a high degree of consistency, indicating the methods used are valid. The derived density of states (NSS) value for the MIS diode is beneath the SD, suggesting that the Er2O3 layer significantly contributes to the reduction of NSS. Under reverse bias, the PFE is a dominant current mechanism in the lower-bias, whereas the SE is the leading current mechanism in the higher-bias region of the SD. However, the PFE is the prevailing conduction mechanism in the lower-bias and higher-bias regions of the MIS diode. Outcomes of the investigation reveal that the Er2O3 thin films are favorable interfacial layers for fabricating MIS/MOS diodes.

Relationship between oxidation, stresses, morphology, local resistivity, and optical properties of TiO2, Gd2O3, Er2O3, SiO2 thin films on SiC

The relationship between internal mechanical stresses, surface morphology, nanoscale electrical properties, and optical characteristics in TiO2, Gd2O3, Er2O3, and SiO2 thin films on SiC substrates was investigated. The oxide films were synthesized using the rapid thermal annealing and analyzed through scanning spreading resistance microscopy, photoluminescence, and absorption spectroscopy. Tensile stresses were found in the films, they are attributed to thermal and lattice mismatch, oxidation, and grain boundaries. These stresses influence on surface morphology, resistivity variations, and photoluminescence intensity. Surface roughness and grain structure were found to correlate with variations in resistivity, which were attributed to conductive pathways along grain boundaries and possible metallic phases. Photoluminescence intensity was also observed to correlate with estimated lattice mismatch strain. Gd2O3/SiC exhibited the fewest defects, while Er2O3 and TiO2 showed more, with Er2O3 being the most mismatched and roughest. The results indicate that internal strains in oxide thin films on SiC substrates can influence on surface morphology, leading to formation of defects and spatial inhomogeneity. These fluctuations in local conductivity and luminescence center density have significant implications for dielectric and optical applications. The study provides insights for future processing refinements to mitigate internal strains and enhance the performance of oxide thin films in semiconductor and optical technologies.

Effects of processing parameters on the morphologies of complex sesquioxide thin films

Controlling and predicting the morphology of lanthanide sesquioxides in thin film form is vital to their use in current applications. In the present study, single and codeposited Sm2O3, Er2O3, and Lu2O3 thin films were grown on yttria-stabilized zirconia (8%) substrates by radio frequency magnetron sputtering at room temperature and 500 °C. The effect of two different substrate temperatures and altering the oxide cation on the structural and morphological properties of the films was analyzed. The thin films were characterized by profilometry, scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The single-component Lu2O3 and Sm2O3 films obtained were of the cubic phase, and the Er2O3 was a mix of cubic and monoclinic phases. It was observed for both the Er2O3 and Lu2O3 films that increasing the substrate temperature to 500 °C resulted in larger grained polycrystalline films. In contrast, large grained polycrystalline films were obtained at both room temperature and 500 °C for Sm2O3 and uneven granularity increased as temperature increased. Codeposition of Lu2O3 and Sm2O3, and Lu2O3 and Er2O3 resulted in a cubic bixbyite phase (the C phase of the lanthanide sesquioxide) solid solution. It was observed that the structure and morphology of the films can be controlled by manipulating deposition parameters. Both substrate temperature and altering the oxide cation contributed to changes in crystallinity and grain structure, which can modify the chemical and physical properties of the films for their applications.

Effects of Helium on the creep resistance of Er2O3 films

The nanostructured Er2O3 thin films implanted by Helium (He) were prepared by magnetron sputtering under different He partial pressure. The creep properties of the Er2O3 films under different temperatures ranging from ambient temperature to 450 °C were investigated systematically by nanoindentation measurements. The morphology and microstructure of the films were determined by a scanning electron microscope (SEM) and an X-ray diffractometer (XRD), respectively. The effects of He on the creep properties of the Er2O3 film were discussed by using a slope (dε˙/dσ) of the creep rate stress curve at the steady-state creep stage. The results show that the crystallinity of the films became weak with the He partial pressure. Furthermore, the implanting He has a strong impact on the creep resistance of the Er2O3 thin films.

Comprehensive investigation of Er2O3 thin films grown with different ALD approaches

The effect of Er precursor nature (Er(CpMe)3 or Er(tmhd)3) and annealing treatment at 500–1100 °C on the structural and optical properties of Er2O3 films grown on Si substrates by thermal or O2-plasma-assisted atomic layer deposition was studied by means of spectroscopic ellipsometry, Fourier-transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy coupled with energy dispersive X-ray spectroscopy as well as photoluminescence method. An annealing at 500–800 °C resulted in the film crystallization mainly. Thermal treatment at high temperatures caused the formation of Er silicate phase due to the diffusion of Si atoms from the substrate in the films depth. This phase was found to be Er2SiO5 being crystallized at 1100 °C. Light emitting properties of the films are determined by Er2O3 native defects (like oxygen vacancies) and intra-4f shell transition in Er3+ ions. The latter dominated in the films annealed at 1000–1100 °C. The most intense Er3+ emission, observed in the films grown with O2-plasma-assisted approach, was explained by a lower contribution of oxygen vacancies as well as by pronounced crystallization of Er silicate phase. In this latter, the effect of concentration quenching of Er3+ luminescence was lower due to a larger distance between Er3+ neighbor ions.

Microstructure, hardness and optical properties of Er2O3 films deposited on diamond-coated and Si(100) substrates by radio frequency magnetron sputtering

Er2O3 anti-reflection films were deposited on the surface of the chemical vapor deposited diamond films and Si(100) substrates by radio frequency magnetron sputtering. The microstructure of the Er2O3 thin films and the interfacial layer were investigated by means of scanning electron microscopy, X-ray diffraction, atomic force microscopy and transmission electron microscopy. The refractive index, hardness and transmittance of the films were measured by ellipsometry, nanoindentation measurements, and Fourier transformed infrared spectroscopy. Results revealed that the bias induces the formation of a monoclinic phase and the nucleation of the Er2O3 thin films is mainly observed along the (222) plane. A high-resolution TEM image revealed a 2.5-nm-thick amorphous layer at the interface between the Si substrate and Er2O3 film. Notably, monoclinic Er2O3 films can considerably improve the transmittance of the diamond film in the long-wavelength infrared range of 8–12 μm via the reduction of the refractive index. However, the introduction of the monoclinic phase led to the decrease of the hardness and elastic modulus of the films; hence, controlling a suitable amount of the monoclinic phase may play an extremely important role in the mechanical and optical properties of the Er2O3 films.

Temperature Dependence of the Stark Shifts of Er3+ Transitions in Er2O3 Thin Films on Si(001)

Optical transitions of an Er$_2$O$_3$ film on a Si substrate grown by using a metal-organic chemical vapor deposition technique were investigated in a wide temperature (300 K $\sim$ 5 K) and spectral (500 nm and 850 nm) ranges. Numerous sharp transitions corresponding to the Er$^{3+}$ ionic levels were observed, which show Stark shifts induced by the crystal field. With decreasing temperature from 300 K to 5 K, all transition peaks exhibit spectral red-shift. We believe that such red-shift behavior is due to the change of the crystal field together with the change of strain field induced by the film and the substrate in varying temperature. An interesting result is the total amount of red-shifts between 300 K and 5 K. We obtain that the higher transition energy peaks show bigger red-shifts. This is very consistent to all transition peaks. This is because the dipole moments between the transition levels are different that lead to different amounts of Stark shifts.

Wet etching mechanism of Er2O3 grown on Si by molecular beam epitaxy

We report on wet etching mechanism of erbium oxide in a sulfuric acid solution within the nanometer scale. The experiments were performed on 300 nm thick Er2O3 thin films formed on Si substrate by molecular beam epitaxy (MBE). The etching mechanism was greatly effected by surface morphology and was different for Er2O3 on Si(111) compared to Er2O3 on Si(100) orientation samples. The chemical etching kinetics was analysed in detail by determining the etching rates and activation energy. The well-defined patterns were formed to explain etching anisotropy. The lateral isotropic etching can be achieved for both orientation Er2O3 (110), (111) samples, however the macroscopic etching anisotropy of Er2O3(110) thin film is governed by the shape of nanometer size crystalline grains and their in-plane alignment. The model based on surface morphology was introduced to explain the lateral etching anisotropy of Er2O3(110) thin film, finally.

Formation of Erbia-Yttria double layer fabricated by metal organic chemical vapor deposition process with changing oxygen flow rates

Er2O3 and Y2O3 are promising materials for advanced breeding blanket system of nuclear fusion reactor because they have high electrical resistivity and effective tritium permeation suppression. In this report, Er2O3 thin films were fabricated by metal organic chemical vapor deposition (MO-CVD) process with changing oxygen flow rates on the stainless steel 316 (SUS316) substrate with Y2O3 layer fabricated via radio frequency (RF)-sputtering. Samples were prepared with four conditions of oxygen rate, 0.08, 0.13, 0.25, 0.42 Pa∙m3/s (50, 75, 150 and 250 sccm, respectively) and only on Er2O3 / Y2O3–0.42 Pa∙m3/s sample was added thermal cycles. Four samples were observed with using X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Increasing oxygen flow rate during MO-CVD process increased the thickness of Er2O3 thin film and decreased columnar width and succeeded in fabricating Er2O3 thin film and dense microstructure on the SUS 316 substrate with Y2O3 layer.

Photon up‐converting (Yb,Er)2O3 thin films by atomic layer deposition

We report up‐converting (Yb,Er)2O3 thin films grown with the atomic layer deposition (ALD) technique. The films are crystalline and show a homogeneous morphology with a roughness less than 1 nm for 40 nm thick films. High‐intensity near‐infrared (NIR) to green and red two‐photon up‐conversion emission is obtained with 974 nm excitation through an absorption by Yb3+, followed by a Yb3+‐Er3+ energy transfer and emission from Er3+. The ALD technique promises to be excellent for producing up‐converting films for many applications such as near‐infrared radiation absorbing layers for solar cells and sensors in point‐of‐care biomedical diagnostics.Schematic picture of the ALD‐grown (Yb,Er)2O3 thin film including the up‐conversion emission spectra.

Preparation of Er2O3 and TiO2 Multilayer Films as Optical Filter Using Magnetron Sputtering Deposition

Dispersion relations of refractive indexes and extinction coefficients of constituent materials were obtained by comparing the experimental and simulated transmission spectra of single-layer Er2O3 and TiO2 films. We designed multilayer thin films of [Er2O3/TiO2]6/[Er2 O3]2/[TiO2/Er2O3]6 such that they can act as photonic crystals exhibiting a resonance wavelength of 514 nm. We prepared single-layer TiO2 and Er2O3 thin films on quartz glass substrates by employing a magnetron sputtering deposition method. Uniform films exhibiting very high transmittance values were obtained. Deposition rates of the TiO2 and Er2O3 films were 0.44 and 0.82 nm/s, respectively. [Er2O3/TiO2]6/[Er2 O3]2/[TiO2/Er2O3]6 multilayer films, to be used for optical bandpass filter applications, were also prepared using a multitarget sputtering deposition method. Uniform and transparent films were obtained; however, the wavelength corresponding to the highest transmittance was observed around 490 nm through ultraviolet-visible near-infrared spectroscopic measurements. The shift in the wavelength can be attributed to the low crystallinity and variations in the thicknesses of Er2O3 and TiO2 films.

Fabrication and Hydrogen Permeation Properties of Epitaxial Er2O3 Films Revealed by Nuclear Reaction Analysis

In order to evaluate the potential of erbium oxide films in applications such as hydrogen (H) permeation barriers, we fabricated high-quality Er2O3 thin films by ion beam sputter deposition on Si(100) as an epitaxial substrate. The physical structures of the thin films were characterized by scanning X-ray diffraction, and the process of hydrogen permeation through the Er2O3 films upon annealing in H2 was elucidated by H depth profiling with nuclear reaction analysis. The results show that quasi-single-crystalline Er2O3(110) thin films can be produced that feature a hydrogen solubility, diffusivity, and permeability at 873 K of (1.1 ± 0.2) × 102 mol m–3, (7.2 ± 1.4) × 10–22 m2 s–1, and (3.8 ± 1.5) × 10–22 mol Pa–1/2 m–1 s–1, respectively. The remaining difference in hydrogen permeability between our quasi-single-crystalline Er2O3(110) thin films and that expected for ideal bulk Er2O3 attests to the negative role of residual defects (e.g., pores) that exist in the thin films.

Hydrogen isotope dissolution, diffusion, and permeation in Er2O3

We report the fabrication and characterization of nanocrystalline Er2O3 thin films, as well as the calculations of interstitial deuterium (D) behaviors in bulk Er2O3 using first-principles calculations based on density-functional theory. Our results show that the prepared Er2O3 thin films possess a regular cubic phase with a phase structure consisting mainly of bulk and grain boundaries. Transport of hydrogen isotopes in bulk is predicted to occur by translocation between empty interstitials (e.g., tetrahedral or octahedral sites), and involves hopping from one empty interstitial to another. The rate-determining process of diffusion and permeation is hydrogen isotope movement from tetrahedral site to octahedral site. Transport of hydrogen isotopes within grain boundaries is predicted to be dominant based on the comparison of D permeability or permeation activation energy between experiments and DFT calculations. At a typical temperature of 873 K, the solubility, diffusion coefficient, and permeability of D in bulk Er2O3 are predicted to be 2.94 × 10−15 mol m−3, 3.56 × 10−10 m2 s−1, and 3.68 × 10−27 mol m−1 s−1 Pa−1/2, respectively.

Growth of single-phase nanostructured Er2O3 thin films on Si (100) by ion beam sputter deposition

Single-phase nanocrystalline thin films of Er2O3 (440) has been first prepared using Si (100) substrates by ion beam sputter deposition at 700 °C at a pressure of < 10− 7 Torr and in-situ annealing at 750 °C at a pressure of < 10− 9 Torr. Er silicides formed during the deposition are eliminated via the annealing, which results in the single phase and the smooth surface of the Er2O3 thin films. The epitaxial relationship between Si (100) and Er2O3 (110) is clarified by X-ray diffraction and reflection high energy electron diffraction. The silicide phase of ErSi2 appears again when an annealing temperature is higher than 800 °C.

Easy and General Synthesis of Large-Sized Mesoporous Rare-Earth Oxide Thin Films by 'Micelle Assembly'.

Large-sized (ca. 40 nm) mesoporous Er2O3 thin films are synthesized by using a triblock copolymer poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-b-P2VP-b-PEO) as a pore directing agent. Each block makes different contributions and the molar ratio of PVP/Er(3+) is crucial to guide the resultant mesoporous structure. An easy and general method is proposed and used to prepare a series of mesoporous rare-earth oxide (Sm2O3, Dy2O3, Tb2O3, Ho2O3, Yb2O3, and Lu2O3) thin films with potential uses in electronics and optical devices.

Energy transfers in telecommunication-band region of (Sc,Er)2O3 thin films grown on Si(111)

The energy transfer dynamics in 1.5-μm region of (ErxSc1-x)2O3 epitaxial thin films grown on Si(111) were investigated via temperature-dependence of the time-resolved photoluminescence (TR-PL). In order to exclude the dissipation via the cooperative up- conversion, the low power and resonant excitation of the third crystal-field level (4I13/2 : Y'3) of the Er3+ site with C3i symmetry was employed. The TR-PL measurements of the Y'1- Z'1 transition have proved the existence of two decay components having fast (10-100 μs) and slow (0.1-1 ms) relaxation times in the range of 4-60 K. The model calculation including the temperature-sensitive and -insensitive non-radiative relaxations could explain well all the observed results. Moreover, the long averaged inter-Er-ion distance by decreasing Er density was found to be very effective to reduce both non-radiative relaxation rates.

Cyclopentadienyl Precursors for the Atomic Layer Deposition of Erbium Oxide Thin Films

In this article, three novel cyclopentadienyl precursors are evaluated for the atomic layer deposition (ALD) of erbium oxide, with either ozone or water as the oxygen source. The erbium precursors evaluated are Er(iPrCp)3, Er(MeCp)2(iPr‐amd), and Er(nBuCp)3. The films are deposited on silicon within the temperature range 200–400°C. Self‐limiting growth is achieved with all three precursors, with both ozone and water. It is found that the water processes of all three precursors present significantly higher growth rates when compared to the ozone processes. An up to three‐fold increase in the growth rate is observed for the water processes of Er(iPrCp)3 and Er(MeCp)2(iPr‐amd) (amd: amidinate) when compared to their ozone processes. The films are smooth and uniform, as determined by atomic force microscopy (AFM) (rms roughness &lt; 3% of film thickness). The composition of the films is investigated by means of X‐ray photoelectron spectroscopy (XPS). It is found that the films contain small amounts of carbon as an impurity, especially in the case of ozone‐processed films. Using Er(nBuCp)3 together with ozone as the oxygen source, a highly conformal Er2O3 thin film is deposited on a 1:60 high‐aspect‐ratio substrate. This is the first report of the conformal growth of Er2O3 thin films by ALD on a high‐aspect‐ratio structure.

Nanostructured Er2O3 thin films grown by metalorganic chemical vapour deposition.

Metalorganic chemical vapor deposition (MOCVD) of nanostructured Er2O3 thin films was performed using the Er-tris-guanidinate precursor [Er(DPDMG)3] (DPDMG = diisopropyl-2-dimethylamidoguanidinato) as the Er source and oxygen. Film deposition was carried out on Si(100) and quartz glass substrates and the process parameters namely temperature, pressure and oxygen flow rate were varied. The resulting thin films were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) for investigating the crystallinity and morphology, respectively. The chemical composition of the film was investigated by X-ray photoelectron spectroscopy (XPS) measurements. Transmittance and absorption spectra of the 600 degrees C film grown on glass substrates were performed by UV-vis measurements revealing more than 80% transmittance. The potential of Er2O3 thin films as gate dielectrics was verified by carrying out capacitance-voltage (C-V) and current-voltage (I-V) measurements. Dielectric constants estimated from the accumulation capacitance were found to be in the range of 10-12 in AC frequencies of 1 MHz down to 10 kHz and the leakage current of the order of 2 x 10(-8) A/cm2 at the applied field of 1 MV cm(-1) was measured for films deposited under optimised process conditions. The low leakage current and high dielectric constant implies good quality of the Er2O3 layers relevant for high-k applications. These layers were found to be paramagnetic with a slightly reduced magnetic moment of the Er3+ ions.