Schottky Barrier Height Inhomogeneity Research Articles

Electrical Characteristics of Metal–Insulator Diamond Semiconductor Schottky Barrier Diode Grown on Heteroepitaxial Diamond Substrate

Herein, the growth of lateral‐structure p‐type diamond Schottky barrier diodes (SBDs) on a heteroepitaxial diamond substrate using a thin atomic‐layer‐deposited hafnium oxide () interfacial layer is demonstrated. The diamond SBD is grown using the microwave plasma chemical vapor deposition (MPCVD) with 1 kW microwave power at 2.45 GHz. Two kinds of samples are grown on heteroepitaxial diamond substrates under the same growth conditions for identical epi structures. And the 10 nm thickness of is used as an insulator for MIS SBD. The effects of the interlayer on the electrical properties of the SBDs are investigated using current–voltage (I–V curve) and capacitance–voltage (C–V curve) characteristics at room temperature. Compared with the metal–semiconductor (MS) SBD, the metal–insulator–semiconductor (MIS) SBD exhibited a lower reverse leakage current. The Schottky barrier height in the MIS SBD is almost 0.2 eV higher than in the MS SBD. The insertion of the interlayer reduces the inhomogeneous Schottky barrier height and enhances the barrier height because of the reduction in the interface state density.

Inhomogeneous heterojunction performance of Zr/diamond Schottky diode with Gaussian distribution of barrier heights for high sensitivity temperature sensor

Herein, we demonstrated the fabrication and operation of vertical diamond Schottky barrier diode (SBD) as a high-performance temperature sensor. The current transport mechanism and temperature sensor properties of Zr/p-diamond SBD were comprehensively investigated with operating temperatures up to 448 K. At room temperature, Zr/p-diamond SBD exhibits outstanding performances with a high rectification ratio of 2.28 × 1010, a low specific on-resistance of 0.5 mΩ•cm2, a large Schottky barrier height (SBH) of 1.43 eV, a low ideality factor of 1.77, and an extremely low saturation current of 4.42 × 10−22 A. The enhanced-performance with a higher forward current and a lower reverse leakage current is observed to be across a wide temperature range from 323 to 448 K. Additionally, a significant improvement of rectifying current curve with a highest rectification ratio over 1012 is obtained at 423 K. The SBH increases whereas the ideality factor decreases with temperature increasing, indicating barrier inhomogeneities at Zr/p-diamond interface. The temperature-dependent electrical transport characteristics on spatially inhomogeneous Schottky contacts can be successfully described by potential fluctuations model. The extracted original value of Richardson constant (A*) is 0.0153 A/cm2•K2, which is much lesser than theoretical value of 96 A/cm2•K2. The discrepancy of A* value from theoretical value has been well explained by thermionic emission model with Gaussian distribution of barrier inhomogeneity. The values of mean SBH and A* extracted from modified Richardson plot depending on SBH inhomogeneity are 1.76 eV and 105.51 A/cm2•K2, respectively. With a Gaussian distribution take into account, the A* value is close to the theoretical value, and confirmed the existence of SBH inhomogeneity at Zr/p-diamond interface. Furthermore, for Zr/p-diamond SBD operating as a temperature sensor, the voltage drop across the diode decreases linearly with increasing temperature at a specific forward current level, contributing to a highest sensor sensitivity of 6.8 mV/K. The reported results in this work are among the best to date in diamond SBD temperature sensor. Although not optimized for temperature sensor, the high and thermally stable rectifying barriers make Zr/p-diamond SBD a strong candidates for high-performance diamond rectifying diode and temperature sensor.

Temperature-dependent electrical characteristics of neutron-irradiated GaN Schottky barrier diodes

Temperature-dependent electrical characteristics were explicitly investigated for a 400-μm diameter neutron-irradiated (NI) GaN Schottky barrier diode (SBD). Based on C-V measurements, a marked decrease in electron concentration has been revealed for the NI diode compared with the pristine sample, suggesting a thermal-enhanced carrier removal effect. Neutron irradiation causes noticeable Schottky barrier height inhomogeneity, which was studied by a two-barrier model. Data indicates that neutron irradiation affects a small but measurable suppression of leakage current as well as low frequency noise level. Despite a new deep-level trap was identified, the temperature-dependent electrical results specified GaN SBD's outstanding resistance to neutron irradiations and robustness in extreme operation temperatures.

Impact of Al2O3 Passivation on the Photovoltaic Performance of Vertical WSe2 Schottky Junction Solar Cells.

Transition metal dichalcogenide (TMD) materials have emerged as promising candidates for thin-film solar cells due to their wide bandgap range across the visible wavelengths, high absorption coefficient, and ease of integration with both arbitrary substrates and conventional semiconductor technologies. However, reported TMD-based solar cells suffer from relatively low external quantum efficiencies (EQE) and low open circuit voltage due to unoptimized design and device fabrication. This paper studies Pt/WSe2 vertical Schottky junction solar cells with various WSe2 thicknesses in order to find the optimum absorber thickness. Also, we show that the devices' photovoltaic performance can be improved via Al2O3 passivation, which increases the EQE up to 29.5% at 410 nm wavelength incident light. The overall resulting short circuit current improves through antireflection coating, surface doping, and surface trap passivation effects. Thanks to the Al2O3 coating, this work demonstrates a device with an open circuit voltage (VOC) of 380 mV and a short circuit current density (JSC) of 10.7 mA/cm2. Finally, the impact of Schottky barrier height inhomogeneity at the Pt/WSe2 contact is investigated as a source of open circuit voltage lowering in these devices.

Theoretical and experimental investigations of barrier height inhomogeneities in poly-Si/4H-SiC heterojunction diodes

p-Si/4H-SiC heterojunction diodes are realized by sputter-deposition of the Si top contact and subsequent post-deposition annealing at either 900 °C or 1000 °C. The high Schottky barrier height (SBH) of this junction architecture of around 1.65 V is ideal to analyze SBH inhomogeneities present in most Schottky- and heterojunctions. Current-voltage-temperature (IVT) and capacitance-voltage-temperature (CVT) measurements are conducted in a wide temperature range from 60 K up to 460 K while applying standard techniques for SBH extraction. Strong deviations from ideal IV characteristics are present especially at lowest temperatures when assuming a homogenous SBH. Additionally, the extracted SBHs at low temperatures differ a lot between the two methods, indicating the presence of low barrier conduction paths. The presence of at least two distinct SBH inhomogeneities is found, which are labeled as ‘intrinsic’ and ‘extrinsic’. Next, the Tung model was applied to fit the measured IVT data using a discretized Gaussian distribution of patch parameters to account for spreading resistance effects. By using multiple Gaussian distributions, excellent fitting results were achieved, giving the density values of the different patches and a background barrier height from the IVT data, which are in excellent agreement with the CVT data over a wide temperature range of 400 K.

Impact of tin-oxide nanoparticles on improving the carrier transport in the Ag/p-GaN interface of InGaN/GaN micro-light-emitting diodes by originating inhomogeneous Schottky barrier height

The effect of tin-oxide (SnO) nanoparticles, which are obtained by indium-tin-oxide (ITO) treatment, on the p-GaN surface of GaN-based flip-chip blue micro-light-emitting diode ( μ -LED) arrays is investigated. A thin Ag layer is deposited on the ITO-treated p-GaN surface by sputtering. SnO nanoparticles originate from inhomogeneous Schottky barrier heights (SBHs) at Ag/p-GaN contact. Therefore, effective SBH is reduced, which causes carrier transport into the μ -LED to enhance. 10 nm thick ITO-treated μ -LEDs show better optoelectronic characteristics among fabricated μ -LEDs owing to improved ohmic contact and highly reflective p-type reflectors. Basically, SnO nanoparticles help to make good ohmic contact, which results in improved carrier transport into μ -LEDs and thus results in increased optoelectronic performances.

Temperature dependent characteristics of Ni/Au vertical Schottky diode based on mechanically exfoliated beta-Ga<sub>2</sub>O<sub>3</sub> single crystal

In this paper, a Ni/Au vertical structure Schottky diode based on mechanically exfoliated β-Ga<sub>2</sub>O<sub>3</sub> is fabricated. The temperature dependent characteristics of <i>I</i>-<i>V</i> curves are measured. The device shows a good rectifying behavior. As the temperature increases from 300 K to 473 K, the barrier height increases from 1.08 eV to 1.35 eV, and the ideal factor decreases from 1.32 to 1.19. Both of them show strong temperature dependence, which indicates that the Schottky barrier of the device is inhomogeneous. The device has a double exponential forward I-V characteristic curve, which may be related to crystal defects, surface states, surface energy band bending and the effect of mechanical exfoliation from the crystal surface. Through Cheung's method and Norde's method, the series resistances and barrier heights of the device at different temperatures are extracted. It is found that the parameters extracted by the Norde's method are in good agreement with the values obtained from the forward <i>I</i>-<i>V</i> curve. The series resistance decreases with temperature increasing, which is mainly caused by the increase of the concentration of thermally excited carriers. In this paper, the temperature characteristics of the device are modified by the Gauss distribution of the barrier height. The corrected barrier height is 1.54 eV and Richardson's constant is 26.35 A·cm<sup>–2</sup>·K<sup>–2</sup>, which is closer to the theoretical value. It shows that the <i>I</i>-<i>V</i> temperature characteristics of Au/Ni/β-Ga<sub>2</sub>O<sub>3</sub> Schottky diodes can be described by the thermionic emission model of the Gauss distribution barrier height accurately. There are a lot of surface states on the surface of Ga<sub>2</sub>O<sub>3</sub> single crystal obtained by Mechanical exfoliation, which has a great influence on the Schottky contact of the device and may lead to the inhomogeneity of Schottky barriers. At the same time, due to mechanical exploiation, the surface of gallium oxide single crystal material is not completely continuous, and the single crystal surface has layered or island structure. This will also cause the inhomogeneous Schottky barrier height. Considering the influence of inhomogeneous barrier on Schottky diode, the method of measuring the temperature characteristics is more suitable to extracting the electrical parameters of β-Ga<sub>2</sub>O<sub>3</sub> Schottky diodes than the method of fitting <i>I</i>-<i>V</i> forward curve by TE model.

Temperature Effect on Al/p-CuInS2/SnO2(F) Schottky Diodes

In this paper, Schottky diodes (SDs) obtained by evaporated thin films of aluminum on pulverized p-CuInS2/SnO2:F have been studied using J-V-T characteristics in a temperature range of 200-340K. These characteristics show that aluminum acts as a rectifier metal-semiconductor contact. Characteristic variables of the Al/p-CuInS2/SnO2:F junctions, such as the current density, the serial resistance, the parallel conductance, the Schottky barrier height (SBH), and the ideality factor of the SD were obtained by fitting the J-V-T data using the Lambert function. Data analysis was conducted with the use of MATLAB. Results showed that n is greater than 1, which could be explained by the existence of inhomogeneities due to the grain boundaries in CuInS2. Through this analysis, one can see a good agreement between experimental and modeled data. The study has shown that the main contribution in the current conduction in such heterostructures is the thermionic emission (TE) supported by the recombination of the carriers. The last phenomenon appears mainly in the grain boundaries, which contain both intrinsic and extrinsic defects (secondary phases, segregated oxygen). An investigation of the J-V-T characteristics according to TE theory has demonstrated that the current density and the SBH increase while serial resistance, parallel conductance decrease with an increase in temperature. After an SBH inhomogeneity correction, the modified Richardson constant and the mean barrier height were found to be 120AK-2cm-2 and 1.29eV respectively. This kind of behavior has been observed in many metal-semiconductor contacts.

Barrier Height Inhomogeneity in Mixed-Dimensional Graphene/Single CdSe Nanobelt Schottky Junctions

Mixed-dimensional graphene/single CdSe nanobelt (NB) Schottky junctions are fabricated, and the influence of Schottky barrier inhomogeneity on the electrical transport mechanism is investigated. The ideality factor increases and the zero-bias Schottky barrier height (SBH) decreases monotonically, as temperature decreases from 300 to 80 K. The temperature-dependent electrical transport characteristics can be explained by the SBH inhomogeneity. We use a spatial potential fluctuation model to analyze the conduction mechanism, where the SBH with a Gaussian distribution is assumed. The standard deviations of SBH distribution are up to 13.06% and 14.09% of the mean value of zero-bias SBH in 80–140 and 140–300 K, respectively, implying strong SBH inhomogeneity in typical graphene/CdSe NB junctions.

Temperature- and doping-dependent nanoscale Schottky barrier height at the Au/Nb:SrTiO3 interface

We use ballistic electron emission microscopy to investigate prototypical Au/Nb-doped SrTiO3 (NSTO) Schottky barrier diodes for different temperatures and doping levels. To this end, ultrathin Au overlayers are thermally evaporated onto TiO2-terminated NSTO single crystal substrates. We show that at room temperature, regardless of the nominal doping, rectification is controlled by a spatially inhomogeneous Schottky barrier height (SBH), which varies on a length scale of tens of nanometers according to a Gaussian distribution with a mean value of 1.29–1.34 eV and the standard deviation in the range of 80–100 meV. At lower temperatures, however, doping effects become relevant. In particular, junctions with a low Nb content of 0.01 and 0.05 wt. % show an ∼300 meV decrease in the mean SBH from room temperature to 80 K, which can be explained by an electrostatic analysis assuming a temperature-dependent dielectric permittivity for NSTO. In contrast, this model fails to predict the weaker temperature dependence of SBH for junctions based on 0.5 wt. % NSTO. Our nanoscale investigation demands to reassess conventional models for the NSTO polarizability in high-intensity electric fields. Furthermore, it contributes to the comprehension and prediction of transport in metal/SrTiO3 junctions and devices.

Research on the growth of β-(AlGa)2O3 film and the analysis of electrical characteristics of Ni/Au Schottky contact using Tung's model

Single crystalline β-(AlGa)2O3 epilayer was grown on β-Ga2O3 (010) substrate using pulsed laser deposition. By high resolution X-ray diffraction and X-ray photoelectron spectroscopy measurements, the Al composition was determined to be 11%–13%, somewhat larger than that of target. In addition, Schottky diodes were fabricated on epitaxial β-(Al0.11Ga0.89)2O3 film using Ni/Au as the anode contacts and the electrical characteristics were performed in the temperature range from 300 K to 573 K. From the forward I-V curves, the Φb and n were obtained and they are both strongly dependent on the temperature, which was attributed to the inhomogeneous Schottky barrier height distribution. According to the Tung's model, the mean barrier height of 1.38 eV and A* of 46.52 Acm−2K−2 are extracted by the modified Richardson plot.

Effect of inhomogeneous Schottky barrier height of SnO2 nanowires device

The current–voltage (I–V) characteristics of metal–semiconductor junction (Au–Ni/SnO2/Au–Ni) Schottky barrier in SnO2 nanowires were investigated over a wide temperature range. By using the Schottky–Mott model, the zero bias barrier height ΦB was estimated from I–V characteristics, and it was found to increase with increasing temperature; on the other hand the ideality factor (n) was found to decrease with increasing temperature. The variation in the Schottky barrier and n was attributed to the spatial inhomogeneity of the Schottky barrier height. The experimental I–V characteristics exhibited a Gaussian distribution having mean barrier heights of 0.30 eV and standard deviation σs of 60 meV. Additionally, the Richardson modified constant was obtained to be 70 A cm−2 K−2, leading to an effective mass of 0.58m0. Consequently, the temperature dependence of I–V characteristics of the SnO2 nanowire devices can be successfully explained on the Schottky–Mott theory framework taking into account a Gaussian distribution of barrier heights.

Investigation of barrier inhomogeneities and interface state density in Au/MgZnO: Ga Schottky contact

The electrical characteristics of Au/MgZnO:Ga (GMZO) Schottky contact, which is fabricated using a dual ion beam sputtering system, have been investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements over a wide temperature range of 80 to 300 K. The apparent Schottky barrier height (SBH) and ideality factor obtained from the I–V measurements are observed to increase and reduce, respectively, with increasing measurement temperature. This anomalous observation in the behaviour of the SBH is in good agreement with the predictions of a double Gaussian distribution (DGD) of the inhomogeneous SBH at a metal–semiconductor (MS) interface. The values of the SBH as determined from C–V measurements are expectedly higher than those extracted from I–V measurements. The DGD model is observed to fit with experimentally obtained data for the temperature-dependent SBH with mean values of the SBH of 0.95 and 0.54 eV and standard deviations of 0.131 and 0.072 eV in the temperature range of 160–300 K and 80–160 K, respectively. The larger value of the SBH standard deviation confirms more SBH inhomogeneity at the MS interface, and these inhomogeneities are attributed to the presence of deep level or surface level interface states. The calculated interface states density is seen to vary from 6.46 × 1014 eV−1 cm−2 at EC-0.27 eV to 1.58 × 1014 eV−1 cm−2 at EC-0.74 eV, where EC is the bottom of a conduction band at 300 K.

Barrier height inhomogeneity and its impact on (Al,In,Ga)N Schottky diodes

III-N materials, especially ternary and quaternary alloys, are profoundly affected by barrier height inhomogeneity as evidenced by great variability in reported barrier height and Richardson constant values for Schottky diode samples involving epilayers with identical material composition. Research into AlInGaN-based devices is gaining traction due to its usefulness for strain engineering, polarization engineering, and vertical device design. Thus it is important to characterize the Schottky barrier height between AlInGaN and technologically relevant metals like nickel. It is proposed that alloy composition fluctuations inherent to low-temperature III-N alloys result in a Schottky barrier height inhomogeneity, and that the Schottky barrier height follows a Gaussian distribution. Current vs voltage data as a function of temperature was measured for three AlInGaN samples of varying composition. Utilizing a model tailored to thermionic emission over a Gaussian distribution of barriers, both the average barrier height and the standard deviation in the distribution were extracted from experimental data via multiple linear regression. Average barrier height was found to correlate with the AlInGaN band gap, while the standard deviation in barrier height increased with aluminum and indium concentration on the group-III sublattice.

Investigation of temperature dependent electrical properties of Ni/Al0.26Ga0.74N Schottky barrier diodes

The current–voltage (I–V) characteristics of the Ni/Al0.26Ga0.74N Schottky barrier diodes (SBDs) were measured in the temperature range of 100–310K by the step of 10K. The forward I–V characteristics were analyzed on the basis of the thermionic emission theory. The characteristics of diode parameters such as the Schottky barrier height (SBH) and the ideality factor were investigated as a function of temperature. An experimental SBH value of about 1.021eV was obtained for the Ni/Al0.26Ga0.74N SBD at 300K. The experimental results show that the values of the ideality factor decrease while the values of the SBH increase with increasing temperature. The temperature dependence of the SBH was explained on the basis of a thermionic emission mechanism with the Gaussian distribution of the SBHs due to the SBH inhomogeneities at the metal–semiconductor interface. The values of the mean barrier height Φ¯b0 and the standard deviation σs0 were 1.362eV and 133meV in the temperature range of 210–300K, 1.204eV and 111meV in the temperature range of 100–210K, respectively. The modified Richardson plots according to inhomogeneity of the SBHs have a good linearity in the corresponding temperature range. The values of Richardson constant A* were found to be 31.46Acm−2K−2 and 33.36Acm−2K−2 in the temperature ranges of 210–310K and 100–210K, respectively. The obtained Richardson constant values are in good agreement with the theoretical value of 34.56 Acm−2K−2 known for n-type Al0.26Ga0.74N.

Scattering due to Schottky barrier height spatial fluctuation on two dimensional electron gas in AlGaN/GaN high electron mobility transistors

A scattering mechanism related to the Schottky barrier height (SBH) spatial fluctuation of the two dimensional electron gas (2DEG) in AlGaN/GaN heterostructures is presented. We find that the low field mobility is on the order of 104–106 cm2/Vs. The 2DEG transport properties are found to be influenced by both the mobility and 2DEG density variations caused by the SBH fluctuation. Our results indicate that a uniform Schottky contact is highly desired to minimize the influence of SBH inhomogeneity on the device performance.

Electronic properties of Al/p-Si/C70/Au MIS-type diode

The electrical characteristics of the Al/p-Si/C70/Au diode were investigated by current–voltage and capacitance–voltage measurements. The current–voltage characteristics confirm that the diode is a metal–insulator–semiconductor type device. The decrease in ideality factor and increase in barrier height values of the diode were observed with temperature. This behavior was explained on the basis of Schottky barrier height inhomogeneities. The zero-bias mean barrier height ϕ¯bo and Richardson values for the diode were found to be 1.06eV and 33.12A/cm2K2, respectively. The obtained Richardson constant (A*=33.12A/cm2K2) is in agreement with the theoretical value of A*=32A/cm2K2. The interface state density properties of the diode were analyzed and the shape of the interface state density is changed with temperature. The ϕB value obtained from C–V measurement is higher than that of ϕB value obtained from I–V measurements. The discrepancy between ϕB(C–V) and ϕB(I–V) values was explained by distribution of Schottky barrier height due the inhomogeneities.

Modification of Schottky barrier height on Si (111) by Ga-termination

The method of “partisan interlayer” (PI) was recently applied to the As-, S- and Cl-terminated surfaces of silicon and was demonstrated effective in reducing the n-type Schottky barrier height (SBH) and increasing the p-type SBH. These SBH shifts were likely driven by the expected transfer of charge from silicon to the adsorbates with larger electronegativity. In the present work, SBHs for Ag, Au and In on Si(111)3×3-Ga R30° and Si(111)6.3×6.3-Ga surfaces are studied and found to be shifted by as much as 0.2eV from those on clean Si(111)7×7, but in directions opposite to those observed previously. The present results are thus in agreement with the expected Ga to Si charge transfer and illustrate the general validity of the PI technique. However, large degrees of SBH inhomogeneity are observed for diodes on Ga-terminated surfaces, likely due to insufficient stability of these surfaces to withstand metal interaction, i.e., breakage of silicon–adsorbate bonds on the interface and the simultaneous/subsequent bond formation between metal and silicon and/or adsorbate atoms, as a result of metal deposition.

Barrier characteristics of Pt/Ru Schottky contacts on n-type GaN based on I–V–T and C–V–T measurements

We have investigated the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of Ru/Pt/n-GaN Schottky diodes in the temperature range 100–420 K. The calculated values of barrier height and ideality factor for the Ru/Pt/n-GaN Schottky diode are 0·73 eV and 1·4 at 420 K, 0·18 eV and 4·2 at 100 K, respectively. The zero-bias barrier height (Φb0) calculated from I–V characteristics is found to be increased and the ideality factor (n) decreased with increasing temperature. Such a behaviour of Φb0 and n is attributed to Schottky barrier (SB) inhomogeneities by assuming a Gaussian distribution (GD) of barrier heights (BHs) at the metal/semiconductor interface. The current–voltage–temperature (I–V–T) characteristics of the Ru/Pt/n-GaN Schottky diode have shown a double Gaussian distribution having mean barrier heights (\( {\bar{{\Phi}}_{\text{b}0}} \)) of 1·001 eV and 0·4701 eV and standard deviations (σ 0) of 0·1491 V and 0·0708 V, respectively. The modified \({ln} ({{J}_{0} /{T}^{2}} )-( {{q}^{2}{\sigma} _{0}^{2}/{2}{k}^{2}{T}^{2}} )\) vs 103/T plot gives \(\bar{{\Phi}}_{\text{b}0} \) and Richardson constant values as 0·99 eV and 0·47 eV, and 27·83 and 10·29 A/cm2K2, respectively without using the temperature coefficient of the barrier height. The difference between the apparent barrier heights (BHs) evaluated from the I–V and C–V methods has been attributed to the existence of Schottky barrier height inhomogeneities.

Schottky Barrier Height Inhomogeneity-Induced Deviation From Near-Ideal Pd/InAlN Schottky Contact

A Pd/InAlN Schottky diode with leakage current as low as 1.01 × 10-6 A/cm2 at -5 V at 300 K has been fabricated. It is found that the current-voltage (I-V) characteristics of Pd/InAlN Schottky contact can be quantitatively described by taking into account the inhomogeneity of Schottky barrier height (SBH), and the SBH inhomogeneity is the main cause for the significant deviation from an ideal Schottky contact. The SBH inhomogeneity is suggested to be related to the quantum dotlike structure on InAlN surface, indicating the importance of surface effect to the investigations on those devices involving InAlN-based Schottky contact.