Barrier Height For Hole Injection Research Articles

Drift of Schottky Barrier Height in Phase Change Materials.

Phase-change memory (PCM) devices have great potential as multilevel memory cells and artificial synapses for neuromorphic computing hardware. However, their practical use is hampered by resistance drift, a phenomenon commonly attributed to structural relaxation or electronic mechanisms primarily in the context of bulk effects. In this study, we reevaluate the electrical manifestation of resistance drift in sub-100 nm Ge2Sb2Te5 (GST) PCM devices, focusing on the contributions of bulk vs interface effects. We employ a combination of measurement techniques to elucidate the current transport mechanism and the electrical manifestation of resistance drift. Our steady-state temperature-dependent measurements reveal that resistance in these devices is predominantly influenced by their electrical contacts, with conduction occurring through thermionic emission (Schottky) at the contacts. Additionally, temporal current-voltage characterization allows us to link the resistance drift to a time-dependent increase in the Schottky barrier height. These findings provide valuable insights, pinpointing the primary contributor to resistance drift in PCM devices: the Schottky barrier height for hole injection at the interface. This underscores the significance of contacts (interface) in the electrical manifestation of drift in PCM devices.

The effect of terminal group of hole injection self-assembled monolayers on the performance of optoelectronic devices on ITO anodes

We demonstrate the effect on the performance of conventional (Indium tin oxide (ITO)/N,Nj-Di (1- naphthyl)-N,Nj-diphenyl-(1,1-biphenyl)-4,4-diamine (NPB)/Tris-(8-hydroxyquinoline)aluminum (Alq3)/LiF/Al) optoelectronic devices when the ITO surface is modified with various types of self-assembled monolayer (SAM)s such as 3-(trimethoxysilyl)propylamine (NH2SAM), Trimethoxy (propyl)silane CH3SAM, and Trimethoxy (3,3,3-trifluoropropyl)silane (F3SAM). The head functional group and chain configuration are trimethoxysilylpropyl (-(CH3O)3Si(CH2)2) and the tail groups distinguished SAMs (-NH2, -CH3, and -CF3). The contact angles of NH2SAM, CH3SAM, and F3SAM deposited on ITO and ITO were 70.7°, 81.42°, 68.23°, and 30.85°, respectively. The SAM-modified ITO's surface morphology Rpv and Rq parameters were reduced from 31.02 nm to 2.0 nm and 1.18 nm–0.26 nm. The work functions values of ITO, ITO/NH2SAM, ITO/CH3SAM and ITO/F3SAM measured by UPS were 4.99eV, 4.39, 5.09 and 5.69eV, respectively. The maximum luminance of the SAM-modified device increased to 166-fold, and the current density 105-fold, compared to the unmodified device when the operating voltage is set to 11 V. Current and power efficiency increased by 1.9 and 2-fold, respectively. The hole injection conditions are enhanced and the hole injection barrier height between ITO/NPB is reduced.

Contact‐Barrier Free, High Mobility, Dual‐Gated Junctionless Transistor Using Tellurium Nanowire

AbstractThe gate‐all‐around nanowire transistor, due to its extremely tight electrostatic control and vertical integration capability, is a highly promising candidate for sub‐5 nm technology nodes. In particular, the junctionless nanowire transistors are highly scalable with reduced variability due to avoidance of steep source/drain junction formation by ion implantation. Here a dual‐gated junctionless nanowire p‐type field effect transistor is demonstrated using tellurium nanowire as the channel. The dangling‐bond‐free surface due to the unique helical crystal structure of the nanowire, coupled with an integration of dangling‐bond‐free, high quality hBN gate dielectric, allows for a phonon‐limited field effect hole mobility of 570 cm2 V−1 s−1 at 270 K, which is well above state‐of‐the‐art strained Si hole mobility. By lowering the temperature, the mobility increases to 1390 cm2 V−1 s−1 and becomes primarily limited by Coulomb scattering. The combination of an electron affinity of ≈4 eV and a small bandgap of tellurium provides zero Schottky barrier height for hole injection at the metal‐contact interface, which is remarkable for reduction of contact resistance in a highly scaled transistor. Exploiting these properties, coupled with the dual‐gated operation, we achieve a high drive current of 216 μA μm−1 while maintaining an on‐off ratio in excess of 2 × 104. The findings have intriguing prospects for alternate channel material based next‐generation electronics.

Polarization-engineered AlGaN last quantum barrier for efficient deep-ultraviolet light-emitting diodes

AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) have been identified as a prospective mercury-free UV source. However, the observation of severe electron overflow and low hole injection efficiency in the conventional DUV LED deteriorates the device performance, attributing to the downward band bending as a result of the strong polarization-induced electric fields between the last quantum barrier (LQB) and the electron blocking layer (EBL). In this study, a composition-graded AlGaN layer with linearly increasing of Al composition from 0.5 to 0.65 is proposed to act as the LQB, replacing the conventional flat LQB to reduce the effective barrier height for hole injection while improving the electron blocking ability. Hence, a considerable enhancement of the output power can be obtained. Moreover, further investigations show that the thickness of graded LQB determine the band bending in the LQB and thus significantly suppress the electron leakage, eventually leading to a boosted output power. The thorough investigation on the LQB could pave the way towards the realization of efficient DUV LEDs of the future.

Impact of ambient environment on the electronic structure of CuPc/Au sample

The performances of organic devices are crucially connected with their stability in the ambient environment. The impact of 24 h. Ambient environment exposure to the electronic structures of about 12 nm thick CuPc thin film on clean Au substrate have been studied employing UV photoemission spectroscopy technique. X-ray photoemission spectroscopy (XPS) was used to find out the origin of the change of the electronic structures in the sample with the exposure. The XPS study suggests that the oxidation occurs at the CuPc thin film. Due to the adsorption of oxygen in the CuPc film from the ambient air, charge carriers are formed within the CuPc film. Moreover, the XPS results imply that the CuPc film is sufficiently thinner for diffusing oxygen molecules through it and gets physically absorbed on Au substrate during the ambient exposure. Consequently, the hole injection barrier height of pristine CuPc film, grown on Au substrate, is reduced by about 0.50 eV and work-function of the pristine CuPc sample is enhanced by around 0.25 eV in the exposure. The findings will help to understand the mechanism that governs the degradation of performance of CuPc based devices in ambient environment.

The feasibility of using solution-processed aqueous La2O3 as effective hole injection layer in organic light-emitting diode

Low-cost and scalable manufacturing boosts organic electronic devices with all solution process. La2O3 powders and corresponding aqueous solutions are facilely synthesized. Atomic force microscopy and scanning electron microscopy measurements show that solution-processed La2O3 behaves superior film morphology. X-ray diffraction and X-ray photoelectron spectroscopy measurements verify crystal phase and typical La signals. In comparison with the most widely-used hole injection layers (HILs) of MoOx and poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), enhanced luminous efficiency is observed in organic light-emitting diode (OLED) using solution-processed La2O3 HIL. Current-voltage, impedance-voltage and phase angle-voltage transition curves clarify that solution-processed La2O3 behaves nearly comparable hole injection capacity to MoOx and PEDOT:PSS, and favorably tailors carrier balance. Moreover, the hole injection mechanism of solution-processed La2O3 is proven to be predominantly controlled by Fowler-Nordheim tunneling process and the hole injection barrier height between ITO and NPB via La2O3 interlayer is estimated to be 0.098 eV. Our experiments provide a feasible application of La2O3 in organic electronic devices with solution process.

Performance enhancement of organic light-emitting diodes using fluorinated self-assembled monolayer

ABSTRACTIn order to enhance the performance of organic light-emitting diodes, fluorinated self-assembled monolayer (F-SAM) with long alkyl chain was introduced to the device between the anode and hole-transport layer. CF3-terminated F-SAM has a relatively high electric dipole moment, which may affect hole injection at the indium-tin-oxide (ITO) anode. Two kinds of F-SAM with different alkyl chain lengths (F3-SAM and F10-SAM) were formed on the ITO substrate through hydrolysis and dehydration process. Electric dipole moments of these F-SAMs were obtained from a simulation using Gauss View program. A device was made in a structure of ITO (170 nm) / F-SAM / TPD (40 nm) / Alq3 (60 nm) / Al (100 nm). Formation of the SAM was confirmed by contact-angle measurements. It was found that the contact angles for the F3-SAM and F10-SAM are about 84° and 112°, respectively. A device with properly treated self-assembled monolayer at the anode gives an improvement in turn-on voltage, luminance, and efficiency compared to those of the device without SAM. Turn-on voltage was lowered from 4.25 V to 3.50 V in the device with SAM compared to the one without SAM, which indicates a reduction of hole-injection barrier height due to the electric dipole moment of the F-SAM. An external quantum efficiency of the device with F3-SAM was increased by a factor of about 3.5 compared to the one without SAM.

Energy level alignment and molecular conformation at rubrene/Ag interfaces: Impact of contact contaminations on the interfaces

This paper addresses the impact of electrode contaminations on the interfacial energy level alignment, the molecular conformation, orientation and surface morphology deposited organic film at organic semiconductor/noble metal interfaces by varying of film thickness from sub-monolayer to multilayer, which currently draws significant attention with regard to its application in organic electronics. The UHV clean Ag and unclean Ag were employed as substrate whereas rubrene was used as an organic semiconducting material. The photoelectron spectroscopy (XPS and UPS) was engaged to investigate the evolution of interfacial energetics; polarization dependent near edge x-ray absorption fine structure spectroscopy (NEXAFS) was employed to understand the molecular conformation as well as orientation whereas atomic force microscopy (AFM) was used to investigate the surface morphologies of the films. The adventitious contamination layer was acted as a spacer layer between clean Ag substrate surface and rubrene molecular layer. As a consequence, hole injection barrier height, interface dipole as well as molecular-conformation, molecular-orientation and surface morphology of rubrene thin films were found to depend on the cleanliness of Ag substrate. The results have important inferences about the understanding of the impact of substrate contamination on the energy level alignment, the molecular conformation as well as orientation and surface morphology of deposited rubrene thin film at rubrene/Ag interfaces and are beneficial for the improvement of the device performance.

Hole-Injection Properties Characteristics of Fluorinated Self-Assembled Monolayer on Polymeric and Organic Light-Emitting Diodes

We examine the electro-optic effects of a fluorinated self-assembled monolayer (FSAM) on polymeric light-emitting diodes (PLEDs) and organic light-emitting diodes (OLEDs). Owing to the high electronegativity of fluorine atoms, which decreases the hole-injection barrier-height, the LEDs with FSAM as the hole-injection layer (HIL) have the highest current density. The current densities of the LEDs with FSAM, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), and without HIL were estimated to be approximately 1, 0.24, and 0.06 A/cm2 respectively at 10 V. During the operational lifetime of the PLEDs, the driving voltage with FSAM is suppressed owing to the ohmic contact of the FSAM-modified ITO.

Effects of transparent MPTMS/Ag/MoO3 structure as anode on the performance of green organic light-emitting diodes

A transparent 3-mercaptopropyl trimethoxysilane (MPTMS)/Ag/MoO3 composite anode is introduced to fabricate green organic light-emitting diodes (OLEDs). Effects of the composite anode on brightness and operating voltage of OLEDs are researched. By optimizing the thickness of each layer of the MPTMS/Ag/MoO3 structure, the transmittance of MPTMS/Ag (8 nm)/MoO3 (30 nm) reaches over 75% at about 520 nm. The sheet resistance is 3.78 Ω/□, corresponding to this MPTMS/Ag (8 nm)/MoO3 (30 nm) structure. For the OLEDs with the optimized anode, the maximum electroluminescence (EL) current efficiency reaches 4.5 cd/A, and the maximum brightness is 37 036 cd/m2. Moreover, the OLEDs with the optimized anode exhibit a very low operating voltage (2.6 V) for obtaining brightness of 100 cd/m2. We consider that the improved device performance is mainly attributed to the enhanced hole injection resulting from the reduced hole injection barrier height. Our results indicate that employing the MPTMS/Ag/MoO3 as a composite anode can be a simple and promising technique in the fabrication of low-operating voltage and high-brightness OLEDs.

Low driving voltage characteristics of polyaniline–silica nanocomposites as hole-injection material of organic electroluminescent devices

Polyaniline–fumed silica (PANI–SiO2) nanocomposites were synthesized through in-situ chemical oxidative polymerization of the aniline in the presence of SiO2 nanoparticles by using ammonium peroxydisulphate (APS) as an oxidant. The resulting PANI–SiO2 nanocomposites with different SiO2 contents were characterized using FT-IR, XRD, FE-SEM and UV–vis techniques. The influence of SiO2 contents on the sheet resistance of the nanocomposite was investigated by four-point probe system. The optical properties of poly [2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) in toluene solution studied by UV–vis and photoluminescence (PL) measurements at room temperature. For the first time, the application of the prepared PANI–SiO2 nanocomposites as a hole-injection layer (HIL) of electroluminescent (EL) devices was examined and the device performance (e.g., turn-on voltage and current density–voltage (J–V) characteristics) was investigated. The Fowler–Nordheim (FN) field-emission tunneling model was used to explain the J–V characteristics of the fabricated devices. The hole-injection barrier height (φ) values for the devices were obtained and reported.

Optoelectronic characteristics of MEH-PPV + BT blend thin films in polymer light emitting diodes

Due to the unique optical and electronic properties of conjugated polymers, much research has been conducted to study the effect of the incorporation of electron-transporting materials on the polymer blends’ compatibility and their capability for use in optoelectronic devices. In this work, to characterize the optoelectronic properties of blend thin films of poly [2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) with benzothiadiazole (BT), polymer light- emitting diodes (PLEDs) with single-emission layers of MEH-PPV + BT blends have been fabricated. The influence of MEH-PPV + BT blend weight ratios over ITO/PEDOT:PSS/MEH-PPV + BT/Al PLEDs performances, e.g., lifetime, turn-on voltage, and current density-voltage (J-V) characteristics, has been studied. According to the obtained results, the turn-on voltage of the devices successfully decreased with the addition of the BT as an electronic transportation material. At an optimum condition, we obtained a turn-on voltage as low as 5 V and a lifetime of about 190 h for a device incorporating 65% BT. The logarithmic plots of the J-V characteristics of the fabricated devices showed a power law behavior (J ∝ Vk+1) with three distinct regions. The J-V characteristics have been explained by the Fowler–Nordheim (FN) tunneling model. It was found that the hole-injection barrier height decreases with increasing BT content in the range of 0–65%. According to the obtained results, in all of our investigations, the electroluminescence (EL) originated exclusively from the MEH-PPV material, even for the high BT contents.

Electrically conductive polyaniline as hole-injection layer for MEH-PPV:BT based polymer light emitting diodes

Polyaniline (PANI) was synthesized by oxidative polymerization of aniline at different temperatures (5, 10, 15, 20 and 25 °C). The influence of polymerization temperature on sheet resistance of PANI was investigated, and the one prepared at 15 °C which showed lowest resistivity was chosen for further analysis. PANI was subsequently used as hole-injection layer (HIL) in polymer light emitting diodes (PLEDs) with structure of poly(ethylene terephthalate) (PET)/indium tin oxide (ITO)/PANI/MEH-PPV:BT/aluminum (Al). The PLEDs with emission layer made from a blend of poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and an electron transporting material, benzothiadiazole (BT), were fabricated at room conditions without using glove boxes. Our results showed an improvement in performance of our PANI-based fabricated PLEDs (PET/ITO/PANI/MEH-PPV:BT/Al) compared to the conventional devices that use poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PET/ITO/PEDOT:PSS/MEH-PPV:BT/Al) as their HIL. The hole injection barrier height (φ) of the fabricated PLEDs were then estimated using the Fowler–Nordheim (FN) field-emission tunneling theory and revealed that the barrier height decreases by increasing the BT concentration in the MEH-PPV:BT blend layer.

Energy-level alignment and electrical properties of Al/p-type Si Schottky diodes with sorbitol-doped PEDOT:PSS as an organic interlayer

The current–voltage (I–V) characteristics of Al/p-type Si Schottky diodes with pristine and 5wt.% sorbitol-doped organic PEDOT:PSS interlayers have been investigated. It was found that the barrier heights of the diodes with pristine and sorbitol-doped PEDOT:PSS are higher than those of a conventional Al/p-type Si Schottky diode because of the modification of the effective barrier height by the organic interlayer. It is noted that the Al/p-type Si Schottky diode with sorbitol-doped PEDOT:PSS interlayer exhibits higher barrier height and lower series resistance, as compared to Al/p-type Si Schottky diodes with pristine PEDOT:PSS interlayer. In addition, UPS measurements indicate that the position of the HOMO level is closer to the Fermi level for pristine PEDOT:PSS than for sorbitol-doped PEDOT:PSS. As a result, the hole injection barrier height is 0.15eV lower in the pristine PEDOT:PSS structure than in the sorbitol-doped PEDOT:PSS. This value closely matches the difference in barrier heights (0.12eV) seen in the I–V measurements. An energy-level alignment diagram is also presented and discussed for the structures studied. The Poole–Frenkel mechanism is found to dominate the reverse leakage current in both structures, indicating the presence of structural defects and trap levels in the organic film.

Fundamental insights into the threshold characteristics of organic field-effect transistors

We physically model the threshold characteristics of organic field-effect transistors (OFETs) using a two-dimensional finite-element method. The transfer characteristics are simulated for staggered OFETs with various electronic structures. A reliable method to extract a structure-unique threshold voltage is presented based on the second-derivative method. By changing the hole injection barrier height in such a manner that the flat-band voltage, defined from the difference of Fermi levels of gate and source electrode, is kept constant, we demonstrate a direct impact of the hole injection barrier height on the threshold voltage. Simulated charge carrier distribution shows the two-dimensional nature of channel creation process and physical insights into the threshold characteristics of OFETs.

Quantum chemical characterization and design of homoleptic Ir(III) complexes employing triphenylamine-featured thiazole-based ligand for efficient phosphors in OLEDs

The electronic structures and photophysical properties of a series of homoleptic Ir(III) complexes with triphenylamine-featured thiazole (1: fac-tris(2-phenylthiazole)iridium(III)) and benzothiazole (2: fac-tris[6-(1-naphthalenylphenylamino)-2-phenylbenzothiazole]iridium(III)) based ligands are investigated using the density functional method. By introducing the diphenylamine unit at 2-, 3- and 4-position of the phenyl ring in (C^N) ligands, 1a–1c (1a: fac-tris[2-(2-(N,N-diphenylamino)phenyl)thiazole]iridium(III); 1b: fac-tris[2-(3-(N,N-diphenylamino)phenyl)thiazole]iridium(III); 1c: fac-tris[2-(4-(N,N-diphenylamino)phenyl)thiazole]iridium(III)) and 2a–2c (2a: fac-tris[6-(1-naphthalenylphenylamino)-2-(2-(N,N-diphenylamino)phenyl)benzothiazole]iridium(III); 2b: fac-tris[6-(1-naphthalenylphenylamino)-2-(3-(N,N-diphenylamino)phenyl)benzothiazole]iridium(III); 2c: fac-tris[6-(1-naphthalenylphenylamino)-2-(4-(N,N-diphenylamino)phenyl)benzothiazole]iridium(III)) are studied to get insight into the influence of different ligation positions of diphenylamine unit on the photophysical properties. The calculated results showed that the incorporation of diphenylamine unit into (C^N) ligands is beneficial to raise the HOMO levels, reducing the barrier height for hole injection and enhancing the balance of charge-transfer process. In addition, a remarkable color tuning could also be realized by altering the ligation positions of the diphenylamine units. A 82–132nm blue shift is found for the thiazole-based 1a–1c compared with 1, while a relatively small red shift (7–35nm) is observed on the emissions of benzothiazole-based 2a and 2c compared with 2. Meanwhile, a qualitative analysis on the parameters that would affect the quantum yields (ΦPL) of the studied complexes has also been presented.

Interface modified thermally stable hole transporting layer for efficient organic light emitting diodes

Electrical transport in thermally stable 2, 7-bis [N, N-bis (4-methoxy-phenyl) amino]-9, 9-spirobifluorene (MeO-Spiro-TPD) thin films has been investigated as a function of temperature and organic layer thickness. ITO/MeO-Spiro-TPD interface was found to be injection limited and has been studied in detail to find barrier height for hole injection. The thickness of tetra-fluoro-tetracyano-quinodimethane thin films were optimized to be used as hole injection buffer layer which resulted in switching of charge transport mechanism from injection limited to space charge limited conduction above a critical thickness of 3 nm. Hole mobility has been measured using transient space charge limited conduction (SCLC), field dependent SCLC, and top contact transistor characteristics. The charge carrier transport in interface modified hole only devices was analysed using Gaussian disorder model. The thermal stability of MeO-Spiro-TPD has been investigated by atomic force microscopy and X-ray diffraction studies. The study indicates a thermally stable and highly efficient hole transport material for application in organic semiconductor based devices.

Design Considerations for GaN-Based Blue Laser Diodes With InGaN Upper Waveguide Layer

Effects of an inserted InGaN interlayer between active region and p-AlGaN electron blocking layer on electrical and optical characteristics of GaN-based blue laser diodes are numerically investigated. It is found that the inserted InGaN interlayer reduces the barrier height for hole injection into multiple quantum wells. Moreover, it is found that the background electron concentration of the undoped InGaN plays a critical role in the LD performance. A background electron concentration higher than 1 × 1017 cm-3 may induce undesired electron-hole recombination in this layer. In addition, we have calculated the dependences of optical confinement factor and internal absorption loss (IAL) on location, In composition, and thickness of the InGaN layer. A significant increase in OCF and a decrease in IAL are obtained by inserting the InGaN layer.

Efficient Charge Injection in p-Type Polymer Field-Effect Transistors with Low-Cost Molybdenum Electrodes through V2O5 Interlayer

Here we report high-performance polymer OFETs with a low-cost Mo source/drain electrode by efficient charge injection through the formation of a thermally deposited V2O5 thin film interlayer. A thermally deposited V2O5 interlayer is formed between a regioregular poly(3-hexylthiophene) (rr-P3HT) or a p-type polymer semiconductor containing dodecyl-substituted thienylenevinylene (TV) and dodecylthiophene (PC12TV12T) and the Mo source/drain electrode. The P3HT or PC12TV12T OFETs with the bare Mo electrode exhibited lower charge carrier mobility than those with Au owing to a large barrier height for hole injection (0.5-1.0 eV). By forming the V2O5 layer, the P3HT or PC12TV12T OFETs with V2O5 on the Mo electrode exhibited charge carrier mobility comparable to that of a pristine Au electrode. Best P3HT or PC12TV12T OFETs with 5 nm thick V2O5 on Mo electrode show the charge carrier mobility of 0.12 and 0.38 cm(2)/(V s), respectively. Ultraviolet photoelectron spectroscopy results exhibited the work-function of the Mo electrode progressively changed from 4.3 to 4.9 eV with an increase in V2O5 thickness from 0 to 5 nm, respectively. Interestingly, the V2O5-deposited Mo exhibits comparable Rc to Au, which mainly results from the decreased barrier height for hole carrier injection from the low-cost metal electrode to the frontier molecular orbital of the p-type polymer semiconductor after the incorporation of the transition metal oxide hole injection layer, such as V2O5. This enables the development of large-area, low-cost electronics with the Mo electrodes and V2O5 interlayer.

Enhanced Hole Injection in Phosphorescent Organic Light-Emitting Diodes by Thermally Evaporating a Thin Indium Trichloride Layer

An ultrathin layer of indium trichloride (InCl(3)) is thermally evaporated on the indium tin oxide (ITO) anode to enhance the hole injection in simplified phosphorescent organic light-emitting diodes (PHOLEDs). Comparing with the device with ultraviolet (UV)-ozone treatment, the device modified by InCl(3) exhibits a maximum current efficiency of 82.2 cd/A measured at about 2000 cd/cm(2) and 36% improvement in power efficiency measured at 20 mA/cm(2). More importantly, more than three times improvement in half lifetime estimated at an initial luminance of 1000 cd/cm(2) is achieved. The investigations using ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and the bias- and temperature-dependent current density-voltage characteristics in the related hole-dominated devices have revealed that the improved device performance is mainly attributed to the enhanced hole injection resulting from the lowered hole injection barrier height in the InCl(3)-modified devices.