Schottky Barrier Height Enhancement Research Articles

Gate leakage mechanisms of the AlGaN/GaN HEMT with fluorinated graphene passivation

The AlGaN/GaN high-electron-mobility transistor (HEMT) passivated by fluorinated graphene (FG) has been investigated. The performances of the HEMTs without passivation before and after F plasma treatment, with FG, Silicon nitride (SiNx), FG/SiNx passivation were contrasted. Compared with the HEMT without F plasma treatment and passivation, the gate leakage current decreases one and a half orders of magnitude after F plasma treatment and SiNx passivated, and four orders of magnitude after FG and FG/SiNx passivated. To study the leakage mechanisms, the temperature dependences of gate leakages have been tested at 323 K–473 K. Through analysis and fitting, the leakages are composed of three components, which are thermionic emission (TE) current, two-dimensional variable range hopping (2D-VRH) current, and Fowler–Nordheim tunneling (FNT) current. TE dominates in the high forward bias region. 2D-VRH dominates in low forward bias. And the chief leakage mechanisms at reverse bias are 2D-VRH and FNT. At 473 K, Schottky barrier height of the HEMT with FG passivation is 1.21 eV. The activation energy and the effective barrier height on the HEMT with FG passivation are 0.64 eV and 0.33 eV respectively. Furthermore, the reasons for the decrement of the gate leakage on the HEMT with FG and FG/SiNx passivation are the enhancement of Schottky barrier heights and augmentation of activation energy. And the improvement in gate leakages for the HEMT passivated by FG/SiNx mainly results from the effect of FG.

Control of Schottky barrier height in metal/β-Ga2O3 junctions by insertion of PdCoO2 layers

Control of Schottky barrier heights (SBHs) at metal/semiconductor interfaces is a critically important technique to design switching properties of semiconductor devices. In this study, we report the systematic variations of SBHs in metal/PdCoO2/β-Ga2O3 junctions with an increase in the thickness of the PdCoO2 insertion layer. The PdCoO2 insertion layer consists of ionic Pd+ and [CoO2]− sublattices alternatingly stacked along the normal of the Schottky interface. This polar layered structure of PdCoO2 spontaneously induces interface dipoles that increase the SBH in β-Ga2O3 devices. We fabricated Schottky junctions composed of metal/PdCoO2/β-Ga2O3 (−201) with the PdCoO2 thickness of 0–20 nm. With an increase in the PdCoO2 thickness, we observed a systematic shift of current density–voltage (J–V) characteristics to larger forward driving voltage. The shift of J–V characteristics indicates the enhancement of SBH by insertion of the PdCoO2 layer, which was confirmed by the capacitance measurement as the consistent shift of the built-in potential. These results demonstrate a controllable SBH in a wide range of 0.7–1.9 eV driven by a decisive contribution of the interface dipole effect. The Schottky junctions based on β-Ga2O3 with variable barrier heights could fit a wide range of applications, with the significant merits of optimizable switching properties.

A different approach to solar cell simulation

Zero barrier height inhomogeneity in the device is generally assumed to conform to Gaussian distribution in the literature. In this study, zero barrier height inhomogeneity has been adopted to obey random distribution. Cell was divided into elementary diodes, which were connected in parallel to each other. The current–voltage characteristics of the cell were obtained by developed device modeling program for various zero barrier height inhomogeneity levels at room temperature in dark and under light conditions. The cell parameters were then calculated by using simulated current–voltage data. It is displayed that increase in zero barrier height inhomogeneity results in Schottky barrier height enhancement and decrease in the diode factor of the cell. Fill factor and Voc values showed a decreasing trend with increasing zero barrier height inhomogeneity. Also, random distribution of zero barrier height effect on interface state density was examined. Interface state density increases with increasing zero barrier height inhomogeneity.

Enhanced photoresponse of ZnO nanorods-based self-powered photodetector by piezotronic interface engineering

Strain-induced piezopolarization can effectively engineer the interfacial electronic properties of a piezo-semiconductor junction, and thereby improve the performance of corresponding electronic devices. In this work, a metal–insulator–semiconductor (Pt/Al2O3/ZnO) based self-powered (SP) photodetector has been developed. The photodetector has sensitive response to the light illumination without any external bias. Applying an ultrathin dielectric layer and piezotronic effect are used as two effective strategies for interface engineering to enhance the photoresponse properties. The dielectric layer can significantly enhance the effective Schottky barrier height (SBH). In addition, the SBH can be actively modulated by the piezopolarization induced built-in electric field variation under compressive strains. Thus, the photoresponse properties of the SP photodetector are largely improved by the SBH enhancement. The responsivity and detectivity of the SP photodetector are increased by 2.77 times and 2.78 times, respectively under a compressive strain of −1.0%. According to the Schottky junction principle, it can be concluded that the piezotronic effect occurs strongly at the interface and gradually decays towards the quasi-neutral region of the junction.

Effect of Inverse Doped Surface Layer in Schottky Barrier Modification: A Numerical Study

Poisson’s equation and the drift–diffusion equations are used to simulate the current–voltage characteristics of a Schottky diode with an inverse doped surface layer. The potential inside the bulk semiconductor near the metal–semiconductor contact is estimated by simultaneously solving these equations, and then current as a function of bias through the Schottky diode is calculated. The Schottky diode parameters are extracted by fitting of simulated data to the thermionic emission diffusion equation. The simulation is carried out for various inverse layer thicknesses and doping concentrations. The obtained diode parameters are analyzed to study the effect of the inverse layer thickness and doping concentration on Schottky diode modification and its behavior at low temperatures. It is shown that an increase in the inverse layer thickness and doping concentration leads to Schottky barrier height enhancement and a change in the ideality factor. The temperature dependences of the Schottky barrier height and ideality factor are also studied.

Numerical simulation study of current–voltage characteristics of a Schottky diode with inverse doped surface layer

The Poisson’s equation and drift–diffusion equations are used to simulate the current–voltage characteristics of Schottky diode with an inverse doped surface layer. The potential inside the bulk semiconductor near the metal–semiconductor contact is estimated by simultaneously solving these equations, and current as a function of bias through the Schottky diode is calculated for various inverse layer thicknesses and doping concentrations. The Schottky diode parameters are then extracted by fitting of simulated current–voltage data into thermionic emission diffusion equation. The obtained diode parameters are analyzed to study the effect of inverse layer thickness and doping concentration on the Schottky diode parameters and its behavior at low temperatures. It is shown that increase in inverse layer thickness and its doping concentration give rise to Schottky barrier height enhancement and a change in the ideality factor. The temperature dependences of Schottky barrier height and ideality factor are studied. The effect of temperature dependence of carrier mobility on the Schottky diode characteristics is also discussed.

Effects of a a-Si:H layer on reducing the dark current of 1310 nm metal–germanium–metal photodetectors

Two approaches of hydrogenated-amorphous-silicon (a-Si:H), as Schottky-barrier height (SBH) enhancement and passivation layers, were investigated to suppress dark current of 1310nm metal–germanium–metal photodetectors (MGM-PDs). Observations show that when a-Si:H is inserted between metal and Ge, the dark current is effectively reduced due to SBH enhancement, but similarly lowers photocurrent resulting from the blocking of a-Si:H. In contrast with a-Si:H acting as a passivation layer a very high photo-to-dark current ratio of 6530 is achieved with a high responsivity of 0.72A/W, attributing to the defect centers on the Ge surface which are passivated. Such a result suggests that the a-Si:H passivation layer is a good candidate in fabricating high-quality 1310nm MGM-PDs.

Electrical and optical characteristics of Au/PbS/n-6H–SiC structures prepared by electrodeposition of PbS thin film on n-type 6H–SiC substrate

To realize Schottky barrier height (SBH) modification in the Au/n-6H–SiC Schottky diodes, lead sulfide (PbS) thin films were grown on n-6H–SiC by electrodeposition method. At first, XRD experiments were performed to investigate the crystal structure of the PbS film electrodeposited on n-6H–SiC. It has been deduced from the diffraction profile that the PbS thin film has a crystal structure more strongly oriented along the [2 0 0] direction. An optical energy band gap value of 1.42 eV for the PbS film was obtained from its optical absorption spectra. Then, we have prepared Au/PbS/n-6H–SiC Schottky barrier diodes (SBDs) with interface layer and reference Au/n-6H–SiC/Ni SBDs. The SBH enhancement has been succeeded by the PbS interlayer, influencing the space charge region of the SiC. The SBH values of 1.03 and 0.97 eV for the samples with and without the interfacial PbS layer were obtained from the forward bias current–voltage ( I– V) characteristics. The SBH increase in the Au/PbS/n-6H–SiC SBD with the interfacial PbS layer has been attributed to the fact that the interface states contain a net negative interface charge in metal/n-type semiconductor contact due to the presence of the interfacial PbS layer.

A comparative study of Schottky barrier height enhancement by realized pseudo-Schottky diodes on p-InP

Abstract In a metal/p-InP Schottky diode, interface states existing at the surface of the semiconductor are responsible for Fermi level pinning. The value of the Schottky barrier height contact is thus limited by this phenomenon. In gas sensor application, the sensitivity varies according to the Schottky barrier height. In order to reduce the effect of Fermi level pinning, we have developed pseudo-Schottky junctions on p-InP. The rectifying contact on p-InP using Ge-based metallization followed by moderate annealing temperatures is studied. Diffusion of Ge atoms at the metal–semiconductor interface creates a thin n + -InP layer. Pseudo-Schottky junctions are obtained with a significant barrier height enhancement, typically by 0.06 eV for Pd diodes and 0.12–0.14 eV for Au diodes. The metallization process involved throughout the present work leads to high-quality Schottky diodes within a rather simple procedure similar to those used in general to obtain good ohmic contacts. The behavior of pseudo-Schottky devices is thoroughly analyzed as a function of the annealing procedure. The best performances are obtained by applying cumulative annealing sequences, increasing the temperature while decreasing the time of thermal treatment. Comparisons of electrical characteristics between Au and Pd pseudo-Schottky diodes are realized.

Effects of Hydrogenated–Amorphous–Silicon Layer on the Performance of SiGe Metal–Semiconductor–Metal Photodetectors

A thin hydrogenated-amorphous-silicon (a–Si:H) layer has been introduced to dramatically suppress the dark current of metal–semiconductor–metal photodetectors (MSM-PDs) and enhance their photocurrent, around wavelength. The effects of a–Si:H as a passivation and a Schottky-barrier-height (SBH) enhancement layer on reducing the dark current of MSM-PDs have been studied in detail. It was found that the a–Si:H as a passivation layer could effectively suppress the dark current better than the a–Si:H as a SBH enhancement layer. Compared to uncapped samples, the samples with a–Si:H passivation layer could enhance the photo–to–dark-current ratio and responsivity by a magnitude of and 21, respectively. The related mechanisms have been proposed in this paper.

Enhancement of Schottky barrier height on p-type GaN by (NH4)2Sx treatment

Barrier height values of Ni contacts to (NH4)2Sx-treated p-type GaN (p-GaN) were obtained from current-voltage and x-ray photoelectron spectroscopy (XPS) measurements in this study. The induced deep level defect band through high Mg doping led to a reduction of the depletion layer width in the p-GaN near the interface and an increase in the probability of thermionic field emission (TFE). Furthermore, the calculated barrier height value of Ni contacts to (NH4)2Sx-treated p-GaN using the TFE model is close to the Schottky limit, which is in good agreement with the observed result by XPS measurements and suggests that (NH4)2Sx surface treatment leads to the removal of native oxides and the reduction of the surface state related to oxygen-induced and nitrogen-vacancy defects.

Hole Schottky barrier height enhancement and its application to metal–semiconductor–metal photodetectors

Hole Schottky barrier heights on GaAs have been studied experimentally by using a conventional metal–semiconductor–metal photodetector (MSMPD) structure. The Schottky barrier height for holes was obtained directly by the hole-current dominated dark current measurement of the MSMPD. With a thin, highly doped surface layer, control of the Schottky barrier heights for holes from 0.48 to 0.79 eV was obtained. By using these engineered Schottky contacts in the MSMPDs, over three orders of magnitude reduction in the dark currents of the MSMPDs was achieved.

Enhancement of metal–semiconductor barrier height with superthin silicon dioxide films deposited on gallium arsenide by liquid phase deposition

This study presents a method for surface passivation using silicon dioxide (SiO2). The proposed method has shown great effectiveness on metal–semiconductor barrier height enhancement. A high quality SiO2 layer is developed via liquid phase deposition, a method which naturally leaves a doping-level fluorine residue in the SiO2. The addition of fluorine to enhance the Schottky barrier height (SBH) is first discussed. Experimental results are presented. It is found that this fluorine addition enhances the Schottky barrier height, which allows a larger positive gate bias for enhancement mode metal–semiconductor field-effect transistors, thus permitting the fabrication of digital logic circuits with improved noise margins and relaxed tolerance with regard to device threshold voltage uniformity. The SBH to n-gallium arsenide (GaAS) is found to be approximately 0.7 eV. Finally, the effective barrier height of the metal–insulator–semiconductor structure reached 1.03 eV after annealing. The enhancement of SBH has been attributed to the formation of these stable interface layers. A model for fluorine-enhanced SiO2 SBH enhancement is also presented.

Barrier height enhancement of Ag/n-GaAs and Ag/n-InP Schottky diodes prepared by P2S5/(NH4)2Sx and HF treatments

A method for surface passivation using both the phosphorus sulfide/ammonia sulfide [P2S5/(NH4)2Sx] solution and hydrogen fluoride (HF) solution has shown great effectiveness on the barrier height enhancement of Ag/n-GaAs and Ag/n-InP Schottky diodes. It is found that, even though the Ag/n-GaAs and Ag/n-InP diodes were baked for 18 h at 300 °C, their Schottky barriers could still reach as high as 1.1 and 0.95 eV, respectively. After the bare semiconductor substrates were bathed successively in P2S5/(NH4)2Sx and HF solutions and then shone by an ultraviolet light, the analysis with x-ray photoelectron spectroscopy indicates a possible formation of ultrathin and stable sulfur fluoride or phosphorus fluoride layers on the substrate surfaces. The formation of these stable interface layers has been attributed to the enhancement of Schottky barrier heights.

Iridium-based multilayer contacts to n-GaAs

We report on the formation of Ir–Al/ n-GaAs Schottky contacts via an Al–Ga exchange mechanism. Direct correlation between the electrical properties of the Schottky contacts and the shape of their Auger depth profile was observed. An Al–Ga exchange mechanism was found to be responsible for the Schottky barrier height enhancement. Based on the Ir–Al/ n-GaAs contact formation, a multilayer Ir–In/ n-GaAs contact system is proposed to form ohmic contacts through an In–Ga exchange mechanism. Ohmic contact behavior was observed when annealing the structure above 750°C for 10 s. Auger depth profiles of as-deposited and annealed contacts are consistent with the proposed model of ohmic contact formation.

Schottky barrier height enhancement on n-In0.53Ga0.47As using delta-doping

We describe the use of n- and p-type delta-doping layers in n-In0.53Ga0.47As for Schottky barrier enhancement. The delta-doping layers are introduced by MOCVD using silicon and zinc dopants respectively. From current-voltage characteristics of Au/In0.53Ga0.47As diodes measured at room temperature, we find substantial effective Schottky barrier height enhancement, with a best value of 0.69 eV and corresponding ideality factor of 1.06. Numerical modelling of Poisson's equation for these structures predicts effective barrier heights in good agreement with those measured.

Roles of top and first Ni-layers in the improvement of electrical property and surface morphology in Ni/Al/Ni/n-InP contacts

The formation of wide band gap material (AlP) in Al/n-InP contacts leads to an enhancement of Schottky barrier height (E-SBH) upon rapid thermal annealing (RTA), but the alloying reaction was irregular. The addition of 5 nm first- and/or 14 nm top-Ni layers gives an excellent improvement in the electrical uniformity as well as the surface morphology for Al/n-InP contacts. The Ni first layer provides the formation of AlP and Ni 2P by the solid-phase reaction between Ni and InP at rather low temperatures (around 450°C) and results in the uniform interface. The addition of the Ni top layer further gives the interfacial uniformity thanks to prevention of irregular alloying.

Morphological and electrical characterization of AI/Ni/n-lnP contacts with tapered insertion Ni-Layer

The addition of a thin Ni layer has improved the surface morphology of Al/n-InP contacts which show an enhanced Schottky barrier height (SBH) after rapid thermal annealing. In order to determine the optimum thickness of the insertion Ni layer, we have fabricated a unique sample in which the thickness of the insertion Ni layer tapered off in space. The improvement of the surface morphol-ogy as well as the SBH enhancement were realized by inserting 35 nm Ni layer annealed at rather low temperatures (around 450°C). The solid-phase reaction between Ni and InP might play an important role in the low-temperature formation of A1P which was responsible for the SBH enhancement.

Enhancement of Schottky barrier height to n-GaAs using NiAl, NiAl/Al/Ni, and Ni/Al/Ni layer structures

The Schottky barrier height of NiAl/n-GaAs, NiAl/Al/Ni/n-GaAs, and Ni/Al/Ni/n-GaAs diodes has been studied by the current–voltage (I–V) and the capacitance–voltage (C–V) techniques. A NiAl alloy with 50 at. % Al was sputter deposited. An overall concentration of 50 at. % Al in NiAl/Al/Ni/n-GaAs contact structure, and two different overall concentrations of 25 and 60 at. % Al in Ni/Al/Ni/n-GaAs contact structure were prepared by sputter depositing different thicknesses of Ni and Al. An enhancement of the Schottky barrier height ranging from 0.1 to 0.13 eV was observed for each of the above contacts. The maximum barrier heights range from 0.95 to 0.98 eV for both the alloy and layered structure contacts, with ideality factors smaller than or equal to 1.1. The interfacial stability between the contacts and GaAs has been examined by cross-sectional transmission electron microscopy, glancing angle x-ray diffraction, and scanning Auger microscopy. A planar interface between contacts and GaAs was observed for both the alloy and layered contacts. A regrowth mechanism has been demonstrated to explain the enhancement of Schottky barrier height for these contacts.

A Proposed Regrowth Mechanism for the Enhancement of Schottky Barrier Height to N-GAAS

ABSTRACTA systematic study of the enhancement of Schottky barriers to n-GaAs diodes has been carried out using the Ni-Al binary system. The diodes, Ni2Al3/n-GaAs, Ni2Al3/Ni/n-GaAs, Ni/Al/Ni/n-GaAs and NiAl/Al/Ni/n-GaAs, have been realized by sputter deposition at a base pressure ∼2xl0-7 Torr. A high Schottky barrier height ranging from 0.95 to 0.98 eV (deduced from current-voltage measurements) was observed for all the annealed contacts except for Ni2Al3/n-GaAs contacts. The enhancement of the Schottky barrier height in all the contacts was attributed to the formation of a high Al content (Al,Ga)As layer at the metal/semiconductor interface. The formation of this (Al,Ga)As layer was explained in terms of a regrowth mechanism. In this mechanism, Ni reacts with GaAs initially at low temperatures, forming NixGaAs. The NixGaAs layer is believed to react with the Ni-Al layer to form the (Al,Ga)As layer when subjected to a high temperature annealing. A (200) dark field XTEM image of the annealed contact was used to demonstrate the existence of this (Al,Ga)As phase.