AlOx Interlayer Research Articles

Experimental-Modeling Framework for Identifying Defects Responsible for Reliability Issues in 2D FETs.

In this work, a self-consistent method is used to identify and describe defects plaguing 300 mm integrated 2D field-effect transistors. This method requires measurements of the transfer characteristic hysteresis combined with physics-based modeling of charge carrier capture and emission processes using technology computer aided design (TCAD) tools. The interconnection of experiments and simulations allows one to thoroughly characterize charge trapping/detrapping by/from defects, depending on their energy position. Once the trap energy distribution is extracted, it is used as input in transient TCAD simulations to reproduce the experimental hysteretic transfer characteristics. Our method is widely applicable to any 2D channel/gate stack combination. Here, it is demonstrated on FAB-integrated devices with AlOx/HfO2 gate oxide. A Gaussian-approximated defect band in the AlOx interlayer centered at a position of about 0.1 eV below the conduction band minimum of WS2 is obtained. Based on this energy position, it is concluded that aluminum interstitial and oxygen vacancies are the defects giving rise to the observed hysteresis. These defects are detrimental to the stability of the studied devices as they are easily accessible by channel carriers during on-state operation. A prominent hysteresis obtained during measurements is consistent with this conclusion.

Sputtered AlOx interlayer for improving performance of a-InGaZnO TFTs: A study on hydrogen diffusion mitigation and electron modulation

In this study, we developed an a-InGaZnO (a-IGZO) thin film transistor (TFT) structure that inserts a sputtered AlOx intermediate layer (IL) within the active layer. The IL not only effectively blocks hydrogen (H) diffusion from the gate insulation (GI) layer to the upper region of a-IGZO but also modifies the energy band structure of the bottom channel region and creates a locally low electron concentration that counteracts the excess electron donated by diffused H. Compared to conventional TFTs, the TFT with the IL exhibits impressive electrical characteristics, including a high saturation mobility (μsat) of 14.5 cm2 V−1 s−1, an on/off current ratio (Ion/Ioff) of 6.2 × 108, and a low subthreshold swing (SS) of 0.16 V/dec. Furthermore, this structure exhibits remarkable stability under negative bias stress and negative bias illumination stress, with ΔVth values of 1.1 and 1.5 V, respectively. The integration of the IL provides a promising approach for enhancing the performance of a-IGZO TFTs, paving the way for next-generation display technologies.

From nano to giant grains: Optimizing Pt thermistors for microbolometers

Pt is a suitable thermistor for use in microbolometers due to its high melting point, chemical inertness, and low 1/f noise. This work explores mechanisms of grain growth to fabricate Pt thin film thermistors for maximizing the temperature coefficient of resistance (TCR). The interplay between the microstructure and TCR is examined by varying Pt film deposition parameters, AlOX interlayer deposition technique, patterning technique, and annealing parameters. A smooth thin film morphology having giant grains of several hundreds of micrometers is achieved by abnormal grain growth, which is not attainable through normal grain growth. The fabrication of thermistor meanders is demonstrated through a combination of processes including Pt film deposition in O2/Ar environment, annealing at 1000 °C in Ar, and ion beam etching. Pt thermistors with a TCR (0 °C – 100 °C) of 0.371 ± 0.001 %/ °C are compatible with microbolometers utilizing carbon nanotube absorbers.

28‐4: Positive Aging Resulted in Highly Efficient Blue Quantum Rod Light Emitting Diodes

The synthesis of blue quantum rods (QRs) is challenging due to fast kinetics and a significant shift in color during the synthesis of w‐CdSe seeds. Herein, we synthesized highly bright CdSe/ZnxCd1‐xS/ZnS core/shell blue QRs with an emission wavelength of 480 nm and fabricated blue QRLEDs. We found that the aging process of the QRLEDs significantly improved their performance by slowly reacting Al with ZnMgO and forming an AlOx interlayer among the ZnMgO/Al, which increased electron injection by over 3x times. The AlOx layer minimized the electron injection barrier and produced highly conductive ZnMgO by forming oxidation deficiency. Additionally, the exciton quenching suppressed at the QRs/ZnMgO/Al interface, and film morphology also changed among the QRs/ZnMgO stacks with the time. As a result, the aged QRLEDs showed an EQE of 9.4% and luminance of 61500 cd/m2, which is 2.6x and 3x times higher than the freshly made QRLEDs. These are the highest reported numbers in EQE and luminance of blue QRLEDs. Additionally, the durability of the blue QRLEDs significantly improved from 50 to 300 hours at 100 cd/m2 initial luminance. Overall, the use of QRs in LEDs greatly improves device efficiency and brightness.

Influence of AlOx Interlayers on LeTID Kinetics in Ga-Doped Cz-Si

Light and elevated temperature-induced degradation (LeTID) is causing a reduction in efficiency especially in p-type silicon based solar cells. It is assumed to be strongly influenced by the hydrogen content in the bulk material. The presented work focuses on the impact of differently thick (5-25 nm) atomic layer-deposited aluminum oxide (AlOx) interlayers underneath the hydrogen-rich silicon nitride (SiNy:H) capping layer. The interlayer acts as a diffusion barrier for H during the firing step. It is demonstrated that the AlOx interlayer has a comparable effect on the LeTID kinetics in Ga-doped Cz-Si (Cz-Si:Ga) as it is observed in B-doped Cz-Si (Cz-Si:B). Additionally, it substantially minimizes lifetime degradation in the Cz-Si:Ga sample. With a determined ratio of electron to hole capture cross sections k=26(3), the degradation phenomena are attributed to the LeTID kinetics. Deposition of AlOx barrier layers exceeding 10 nm in thickness does not yield additional positive effects. Resistivity measurements revealed that the change in hole concentration correlates with the defect density for varying AlOx layer thicknesses. The doping concentration seems to influence the change in maximum defect density for varying AlOx layer thicknesses.

A Universal Perovskite/C60 Interface Modification via Atomic Layer Deposited Aluminum Oxide for Perovskite Solar Cells and Perovskite-Silicon Tandems.

The primary performance limitation in inverted perovskite-based solar cells is the interface between the fullerene-based electron transport layers and the perovskite. Atomic layer deposited thin aluminum oxide (AlOX) interlayers that reduce nonradiative recombination at the perovskite/C60 interface are developed, resulting in >60 millivolts improvement in open-circuit voltage and 1% absolute improvement in power conversion efficiency. Surface-sensitive characterizations indicate the presence of a thin, conformally deposited AlOx layer, functioning as a passivating contact. These interlayers work universally using different lead-halide-based absorbers with different compositions where the 1.55 electron volts bandgap single junction devices reach >23% power conversion efficiency. A reduction of metallic Pb0 is found and the compact layer prevents in- and egress of volatile species, synergistically improving the stability. AlOX-modified wide-bandgap perovskite absorbers as a top cell in a monolithic perovskite-silicon tandem enable a certified power conversion efficiency of 29.9% and open-circuit voltages above 1.92 volts for 1.17 square centimeters device area.

High-quality MOCVD-grown heteroepitaxial gallium oxide growth on III-nitrides enabled by AlOx interlayer

We report high-quality Ga2O3 grown on an AlGaN/AlN/Sapphire in a single growth run in the same Metal Organic Chemical Vapor Deposition reactor with an AlOx interlayer at the Ga2O3/AlGaN interface. AlOx interlayer was found to enable the growth of single crystalline Ga2O3 on AlGaN in spite of the high lattice mismatch between the two material systems. The resulting nitride/oxide heterogenous heterostructures showed superior material qualities, which were characterized by structural, electrical, and optical characterization techniques. In particular, a significant enhancement of the electron mobility of the nitride/oxide heterogenous heterostructure is reported when compared to the individual electron mobilities of the Ga2O3 epilayer on the sapphire substrate and the AlGaN/AlN heterostructure on the sapphire substrate. This enhanced mobility marks a significant step in realizing the next generation of power electronic devices and transistors.

Fabrication of Schottky-Barrier-Oxide- Semiconductor Thin-Film Transistors via a Simple Aluminum Reaction Method

In this work, we proposed a simple method for fabricating Schottky-barrier thin-film transistors (TFTs) with tailorable device characteristics. Through a simple post annealing process, an AlOx interlayer was formed between Cu/Al source/drain electrodes and the amorphous indium gallium zinc oxide (IGZO) layer, which induced the formation of a Schottky-barrier between Cu and the IGZO layer at the edge of the electrodes to modulate the carrier injection. Consequently, we found TFTs with different IGZO thicknesses presented notably different operation characteristics. When the thickness of the IGZO layer was 30 nm, the fabricated TFT behaved like a high mobility Ohmic-contact device, with an apparent field effect mobility as high as 82.9 cm2 V−1 s−1. After the thickness of the IGZO layer was reduced to 10 nm, the TFT worked like a Schottky-contact TFT, which exhibited a low saturation voltage of 2.3 V and a high output current of up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$80~\mu \text{A}$ </tex-math></inline-formula> at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{{\mathrm {GS}}} =20$ </tex-math></inline-formula> V.

Enhancement of ionic conductivity in novel LiON-AlOx multilayer heterostructures prepared by atomic layer deposition

A novel heterostructured multilayer thin-film solid electrolyte consisting of LiON-AlOx was synthesized by atomic layer deposition (ALD). The ALD-derived films were grown about 200 °C on SiO2/Si substrate by an alternating deposition of lithium oxynitride (LiON) and AlOx sublayers with 1–6 nm thickness and then characterized by various methods for roughness, homogeneity, crystallinity, thickness, composition, chemical environment, and ionic conductivity. The desired layer-by-layer structure of the films was confirmed by both high-resolution transmission electron microscopy and time-of-flight secondary ion mass spectrometry. Compared to pure LiON films without insulating AlOx interlayers, the ionic conductivities of multilayer LiON-AlOx films with various nanoscale sublayers are enhanced due to channeling effects between the heterointerfaces of nanoscale sublayers, while the activation energies are increased due to the incorporation of non-conducting AlOx sublayers. Thickness-dependent conductivity of the multilayer LiON-AlOx films indicates that 3.2 nm of LiON sublayer alternatively combined with 1 nm AlOx sublayer has the best conduction performance. The film with 15 bilayers exhibits a conductivity of 6.2 × 10−4 S/cm at 160 °C with an activation energy of 0.57 eV.

Optical transitions in monolayer WS2 observed through transient photoconductivity in MIS structures

Excitonic and band-to-band transitions in monolayer WS2 were observed using transient photoconductivity in metal-insulator-silicon structures. Significant improvement in sensitivity was achieved by introducing an Al/WS2 contact scheme. We attribute this improvement to high density of traps in the AlOx interlayer formed at the interface which gives rise to displacement current due to capture of electrons or holes optically generated in WS2. This new method is found to be viable with transferred monolayer films.

Metal-induced n+/n homojunction for ultrahigh electron mobility transistors

A self-organized n+/n homojunction is proposed to achieve ultrahigh performance of thin film transistors (TFTs) based on an amorphous (Zn,Ba)SnO3 (ZBTO) semiconductor with sufficiently limited scattering centers. A deposited Al layer can induce a highly O-deficient (n+) interface layer in the back channel of a-ZBTO without damaging the front channel layer via the formation of a metal-oxide interlayer between the metal and back channel. The n+ layer can significantly improve the field-effect mobility by providing a relatively high concentration of free electrons in the front n-channel ZBTO, where the scattering of carriers is already controlled. In comparison with a Ti layer, the Al metal layer is superior, as confirmed by first-principles density functional theory (DFT) calculations, due to the stronger metal-O bonds, which make it easier to form a metal oxide AlOx interlayer through the removal of oxygen from ZBTO. The field-effect mobility of a-ZBTO with an Al capping layer can reach 153.4 cm2/Vs, which is higher than that of the pristine device, i.e., 20.8 cm2/Vs. This result paves the way for the realization of a cost-effective method for implementing indium-free ZBTO devices in various applications, such as flat panel displays and large-area electronic circuits.

Role of device architecture and AlOX interlayer in organic Schottky diodes and their interpretation by analytical modeling

Considering the pivotal role of interfaces in controlling the performance of organic electronic devices, implications of metal/organic interfacial quality in a Schottky barrier diode (SBD) are investigated. The nature of metal/organic interfaces and the thin film quality of regioregular poly (3-hexylthiophene) based SBDs fabricated in different device architectures are investigated using experimental and theoretical modeling. The importance of oxidized aluminum nanostructures as an interlayer at the Schottky interface for the dramatic enhancement of the rectification ratio (&amp;gt;106 at ±5 V) has been demonstrated, which is attributed to suppressed leakage current due to the oxide layer and the formation of a charge double layer. Furthermore, electrical performances of all the SBDs were modeled in terms of an underlying particular phenomenon solely or with the combination of multiple physical phenomena. The combined modeling equation used in this work fits well for the different device architectures, which validates its generality in order to extract the device parameters.

Origin of Positive Aging in Quantum-Dot Light-Emitting Diodes.

The phenomenon of positive aging, i.e., efficiency increased with time, is observed in quantum‐dot light‐emitting diodes (QLEDs). For example, the external quantum efficiency (EQE) of blue QLEDs is significantly improved from 4.93% to 12.97% after storage for 8 d. The origin of such positive aging is thoroughly investigated. The finding indicates that the interfacial reaction between Al cathode and ZnMgO electron transport layer accounts for such improvement. During shelf‐aging, the Al slowly reacts with the oxygen from ZnMgO, and consequently, leads to the formation of AlOx and the production of oxygen vacancies in ZnMgO. The AlOx interlayer reduces the electron injection barrier while the oxygen vacancies increase the conductivity of ZnMgO and, as a result, the electron injection is effectively enhanced. Moreover, the AlOx can effectively suppress the quenching of excitons by metal electrode. Due to the enhancement of electron injection and suppression of exciton quenching, the aged blue, green, and red QLEDs exhibit a 2.6‐, 1.3‐, and 1.25‐fold efficiency improvement, respectively. The studies disclose the origin of positive aging and provide a new insight into the exciton quenching mechanisms, which would be useful for further constructing efficient QLED devices.

Large room-temperature tunneling anisotropic magnetoresistance and electroresistance in single ferromagnet/Nb:SrTiO3 Schottky devices

There is a large effort in research and development to realize electronic devices capable of storing information in new ways - for instance devices which simultaneously exhibit electro and magnetoresistance. However it remains a challenge to create devices in which both effects coexist. In this work we show that the well-known electroresistance in noble metal-Nb:SrTiO3 Schottky junctions can be augmented by a magnetoresistance effect in the same junction. This is realized by replacing the noble metal electrode with ferromagnetic Co. This magnetoresistance manifests as a room temperature tunneling anisotropic magnetoresistance (TAMR). The maximum room temperature TAMR (1.6%) is significantly larger and robuster with bias than observed earlier, not using Nb:SrTiO3. In a different set of devices, a thin amorphous AlOx interlayer inserted between Co and Nb:SrTiO3, reduces the TAMR by more than 2 orders of magnitude. This points to the importance of intimate contact between the Co and Nb:SrTiO3 for the TAMR effect. This is explained by electric field enhanced spin-orbit coupling of the interfacial Co layer in contact with Nb:SrTiO3. We propose that the large TAMR likely has its origin in the 3d orbital derived conduction band and large relative permittivity of Nb:SrTiO3 and discuss ways to further enhance the TAMR.

High-quality multilayer graphene on an insulator formed by diffusion controlled Ni-induced layer exchange

The Ni-induced layer-exchange growth of amorphous carbon is a unique method used to fabricate uniform multilayer graphene (MLG) directly on an insulator. To improve the crystal quality of MLG, we prepare AlOx or SiO2 interlayers between amorphous C and Ni layers, which control the extent of diffusion of C atoms into the Ni layer. The growth morphology and Raman spectra observed from MLG formed by layer exchange strongly depend on the material type and thickness of the interlayers; a 1-nm-thick AlOx interlayer is found to be ideal for use in experiments. Transmission electron microscopy and electron energy-loss spectra reveal that the crystal quality of the resulting MLG is much higher than that of a sample without an interlayer. The grain size reaches a few μm, leading to an electrical conductivity of 1290 S/cm. The grain size and the electrical conductivity are the highest among MLG synthesized using a solid-phase reaction including metal-induced crystallization. The direct synthesis of uniform, high-quality MLG on arbitrary substrates will pave the way for advanced electronic devices integrated with carbon materials.

Improved longtime stability of highly efficient polymer solar cells by accurately self-formed metal oxide interlayer at metal electrode

Al as a cheap and air-stable metal material has been widely applied to polymer solar cells (PSCs) as an efficient electrode. However, there are few care whether Al is a right electrode in PSCs for longtime stability. The inverted PSCs with the structure of ITO/ZnO/PTB7-Th:PC71BM/MoO3/Metal electrode were fabricated and the performance and stability of inverted PSCs with Al and AgAl electrodes were investigated. PSCs with AgAl electrode got the highest PCE value of 9.3% without aging. While the PCE of PSCs with Al electrode can be gradually improved and reach the highest value of 7.8% after aging for 36h, which is attributed to the formation of AlOx interlayer at the interface of MoO3/Al. PSCs with AgAl electrode still retained 69% of the initial PCE value and got 6.6% of PCE aging for 796days, showing amazing stability. However, PSCs with Al electrode was dropped to 3.7% of PCE aging for 796days due to the continuously increased thickness of AlOx interlayer, which can greatly increase the series resistance of cells. PSCs with AgAl electrode can be further improved and reach 10.2% of PCE using AZO (Al doped ZnO) instead of ZnO and show better UV-light resistance. The enhanced stability of PSCs with AgAl electrode is attributed to the dense and limited thick AlOx interlayer self-formed at the MoO3/AgAl interface due to the low content of Al. Our results demonstrated that Ag alloy electrode such as AgAl is a good strategy to accurately control the thickness of the metal oxidation interlayer, which can overcome the disadvantage of Al electrode and greatly improve the longtime stability of devices.

Schottky source/drain germanium-based metal-oxide-semiconductor field-effect transistors with self-aligned NiGe/Ge junction and aggressively scaled high-k gate stack

Schottky source/drain (S/D) Ge-based metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated by combining high permittivity (high-k) gate stacks with ultrathin AlOx interlayers and Fermi level depinning process by means of phosphorous ion implantation into NiGe/Ge contacts. Improved thermal stability of the metal/high-k/Ge stacks enabled self-aligned integration scheme for Schottky S/D complementary MOS applications. Significantly reduced parasitic resistance and aggressively scaled high-k gate stacks with sub-1-nm equivalent oxide thickness were demonstrated for both p- and n-channel Schottky Ge-FETs with the proposed combined technology.

Insights into thermal diffusion of germanium and oxygen atoms in HfO2/GeO2/Ge gate stacks and their suppressed reaction with atomically thin AlOx interlayers

The thermal diffusion of germanium and oxygen atoms in HfO2/GeO2/Ge gate stacks was comprehensively evaluated by x-ray photoelectron spectroscopy and secondary ion mass spectrometry combined with an isotopic labeling technique. It was found that 18O-tracers composing the GeO2 underlayers diffuse within the HfO2 overlayers based on Fick's law with the low activation energy of about 0.5 eV. Although out-diffusion of the germanium atoms through HfO2 also proceeded at the low temperatures of around 200 °C, the diffusing germanium atoms preferentially segregated on the HfO2 surfaces, and the reaction was further enhanced at high temperatures with the assistance of GeO desorption. A technique to insert atomically thin AlOx interlayers between the HfO2 and GeO2 layers was proven to effectively suppress both of these independent germanium and oxygen intermixing reactions in the gate stacks.

Amazing stable open-circuit voltage in perovskite solar cells using AgAl alloy electrode

The progresses made in emerging perovskite solar cells, a promising alternative photovoltaic technology to the conventional solar cells, have quickly set the power conversion efficiency (PCE) record of 20%. Apart from the high PCE, the stability of perovskite solar cells is another important issue for them to be commercially viable. To investigate the impact of electrodes on the stability of the perovskite solar cells, cells with a structure of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Cathode, having different cathode contacts of Al, Ag and AgAl alloy, were fabricated. The cells with an AgAl alloy cathode reached a PCE of 11.76%, which is slightly higher than that (11.45%) of the structurally identical cells with Ag contact, much higher than that for the ones with Al electrode (7.95%). The stable open-circuit voltage (VOC) of cells having an AgAl contact was demonstrated, with almost no change in the VOC after 360h aging under a relative humidity of 10% in air. However, there is an obvious drop in the VOC of the structurally identical perovskite cells with Ag cathode, e.g., an 85% decrease from its initial VOC value for cells aged under the same condition. The enhancement in the PCE of cells with AgAl cathode is attributed to the formation of AlOX, which can improve built-in potential in the cell and allow an effective electron extraction at the PCBM/AgAl cathode interface. An interfacial AlOX interlayer could be formed at the interface between PCBM and AgAl contact during thermal evaporation and aging. The presence of the interfacial AlOX interlayer helps to prevent the diffusion of the Ag atoms into the active layer, to improve the adhesion of the metal contact on PCBM and also to avoid moisture encroachment.

High (1 1 1) orientation poly-Ge film fabricated by Al induced crystallization without the introduction of AlOx interlayer

High (111) orientation poly-Ge film was fabricated by Al induced crystallization (AIC), where Al and amorphous Ge (a-Ge) layers were continuously deposited by magnetron sputtering, avoiding the deliberate introduction of an AlOx interlayer. To improve the quality of poly-Ge film, the ratio of thicknesses of Al and a-Ge was adjusted. Electron backscattered diffraction (EBSD) results revealed that the (111) fraction of poly-Ge film reached 97% and the average crystal grain size surpassed 100μm.