Ag Schottky Contacts Research Articles

Plasmonic internal-photoemission-based Si photodetector design suitable for optical communication.

We propose a high-performance plasmonic photodetector based on the internal photoemission (IPE) process for the C-band communication wavelength. This photodetector takes advantage of an embedded nanohole array in Schottky metal. Owing to localized surface plasmon resonance, the absorption of the active metal layer increases, which results in the generation of more hot carriers and subsequently compensates for the low efficiency of IPE-based photodetectors. Simulations show that for the proposed photodetector with 2-nm-thick Au, Cu, and Ag Schottky contacts, the absorptance dramatically enhances to 95.1%, 93.2%, and 98.2%, respectively, at the wavelength of 1.55 µm. For the detector based on Au, the highest external quantum efficiency of 25.3% and responsivity of 0.32 A/W are achieved at a reverse bias voltage of 1 V. Furthermore, the 3 dB bandwidth can exceed 369 GHz owing to the low capacitance of the structure and the fast transit time of carriers from the thin p-Si layer. Finally, by studying the current-voltage characteristics of the photodetector, it is shown that under the reverse bias voltage of 1 V, the dark current is 665 nA at room temperature, and by reducing the temperature to 200 K, it improves three orders of magnitude and decreases to 810 pA.

Oxidized Metal Schottky Contacts on (010) <inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math> </inline-formula>-Ga2O3

Oxidized Ir, Pd, Pt, Ag and Au Schottky contacts (SCs) were fabricated on (010) β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> single crystal substrates via reactive RF sputtering using an O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> : Ar plasma. The use of in situ oxidizing conditions resulted in SCs with very high rectifying barriers in excess of 2.0 eV for all the metals investigated, representing an increase of 0.4-0.9 eV compared with the corresponding plain metal versions. Both the plain and oxidized metal SCs showed evidence of Fermi level pinning with their laterally homogeneous barrier heights lying in narrow ranges of ~1.3-1.5 eV and ~2.2-2.4 eV, respectively, with little correlation with metal work function. This was attributed to the influence of metal-induced oxygen vacancies and gap states at the SC interface, respectively. The very high barriers of the oxidized SCs resulted in excellent high-temperature performance with ~10 orders of magnitude of rectification at 180 °C, indicating the potential of this technique for the fabrication of high-temperature unipolar devices.

Direct comparison of plain and oxidized metal Schottky contacts on β-Ga2O3

High quality Ru, Ir, Pd, Pt, Ag, and Au Schottky contacts (SCs) were fabricated on 2¯01 β-Ga2O3 single crystal substrates via rf sputtering under inert and oxidizing plasma conditions. The oxidized SCs exhibited significantly higher rectifying barriers and, with the exception of gold oxide, significantly improved high temperature performance, with more than 12 orders of magnitude of stable rectification at 180 °C. With the exception of Ag, the image-force-corrected laterally homogeneous barrier heights of the plain metal SCs were pinned close to 1.3 eV, irrespective of the metal work function, with the Fermi level at the SC interface close to the predicted VO (2+/0) transition level of fourfold coordinated oxygen vacancies. The equivalent barrier heights of the oxidized SCs were consistently 0.5–0.8 eV higher than their plain metal counterparts, lying in the range of 1.8–2.5 eV, with the increase attributed to the passivation of interfacial oxygen vacancies and a significant increase in the work function of the oxidized metals. The highest Schottky barriers for both the plain and oxidized metal SCs involved Ag, which may be linked to the relative ease of its unintentional and intentional oxidation, respectively. The very high rectifying barriers and the thermal stability of oxidized Schottky contacts to β-Ga2O3 indicate their potential for high temperature device applications.

Effect of surface treatment of printed Ag Schottky contacts on n-GaN epitaxial layers using Ag nanoink: Two dimensional characterization by scanning internal photoemission microscopy

We report the basic electrical characteristics of Ag Schottky contacts printed on n-GaN epitaxial wafers using Ag nanoink with surface treatment using HCl or an organic solvent. The Ag Schottky contacts treated with HCl showed better current–voltage characteristics and a larger Schottky barrier height than those treated with the organic solvent. Scanning internal photoemission microscopy revealed that the HCl-treated samples exhibited a higher uniformity owing to their higher wettability to the Ag nanoink and electrodes than the organic-solvent-treated samples. These results indicate that the removal of surface oxide layers using HCl is effective even though the GaN surface is printed and annealed in air.

Characterization of Ag/ZnO Nanorod Schottky Diode-Based Low-Voltage Ultraviolet Photodetector

Ultraviolet (UV) detection characteristics of Ag Schottky contacts with ZnO nanorods (ZnO-NRs) grown on Indium Tin Oxide (ITO)-coated glass substrates have been investigated. A low-temperature hydrothermal method was used for growing ZnO-NRs. Circular contacts of Ag were deposited above the ZnO-NRs/ITO samples using the shadow mask technique. The structural properties of the ZnO-NRs were characterized by using scanning electron microscopy (SEM), atomic force microscope (AFM) and X-ray diffraction (XRD). The results revealed a (0002) crystal orientation and a wurtzite hexagonal structure. The electrical characteristics of the Ag/ZnO-NR Schottky contacts were studied at forward applied bias over the range 0[Formula: see text]V to 1[Formula: see text]V, under dark and UV illumination. The dark and photocurrents were [Formula: see text][Formula: see text]A and [Formula: see text][Formula: see text]A, respectively, and the contrast ratio (ratio of photocurrent to dark current) was 1.67 at [Formula: see text]1.0[Formula: see text]V for these devices. The results show that these devices could be useful for cost-effective and low-voltage UV detection applications.

Room temperature current-voltage (I-V) characteristics of Ag/InGaN/n-Si Schottky barrier diode

Metal-semiconductors (MSs) or Schottky barrier diodes (SBDs) have a significant potential in the integrated device technology. In the present paper, electrical characterization of Ag/InGaN/n-Si Schottky diode have been systematically carried out by simple Thermionic method (TE) and Norde function based on the I-V characteristics. Ag ohmic and schottky contacts are deposited on InGaN/n-Si film by thermal evaporation technique under a vacuum pressure of 1×10−5mbar. Ideality factor, barrier height and series resistance values of this diode are determined from I-V curve. These parameters are calculated by TE and Norde methods and findings are given in a comparetive manner. The results show the consistency for both method and also good agreement with other results obtained in the literature. The value of ideality factor and barrier height have been determined to be 2.84 and 0.78eV at room temperature using simple TE method. The value of barrier height obtained with Norde method is calculated as 0.79eV.

Preparation of Ag Schottky contacts on n-type GaN bulk crystals grown in nitrogen rich atmosphere by the hydride vapor phase epitaxy technique

Electrical properties of Schottky contacts on n-type GaN grown in nitrogen rich atmosphere with different N/Ga ratios by hydride vapor phase epitaxy were investigated. We show that tunneling of electrons from the conduction band of GaN to the metal is dominant in our samples. The quality of Schottky contacts does not only depend on surface preparation but also on the growth conditions of the crystals. Schottky contacts on these crystals show an increasing deterioration when higher N/Ga growth ratios are used. We correlate our results with the presence of negatively charged gallium vacancies in the samples. These charges compensate the positively charged donors and lead to a significant increase in series resistance.

Effect of oxygen plasma treatment on the electrical properties in Ag/bulk ZnO Schottky diodes

Using current–voltage (I–V) and capacitance–voltage (C–V) measurements, the effect of oxygen plasma treatment on the electrical properties of Ag Schottky contacts to hydrothermally-grown O-polar bulk ZnO was investigated. Schottky contacts to untreated ZnO had higher barrier heights and lower ideality factors than those to oxygen plasma treated ZnO. The measured C–V and conductance–voltage (G/ω–V) characteristics for both samples showed strong dependences on bias voltage and frequency. The increments of series resistance in small forward bias region (0–0.5 V) was larger for oxygen plasma treated ZnO, indicating that the contribution of interface states to series resistance was more significant. The interface state density was obtained from the corrected C–V and G/ω–V characteristics with considering series resistance. The higher interface state density was found for oxygen plasma treated ZnO, implying that oxygen plasma induced the interface states near the ZnO surface.

Temperature-Dependent Electrical Characteristics of Ag Schottky Contacts to Differently Grown O-Polar Bulk ZnO

The temperature-dependent electrical properties of Ag Schottky contacts to differently grown O-polar bulk ZnO single crystals were comparatively investigated in the temperature range of 100–300 K. Schottky contact to hydrothermal ZnO produced the higher barrier heights (lower ideality factors) than that of pressurized melt-grown ZnO. The modified Richardson plots for two samples produced the larger Richardson constant compared to the theoretical value of 32 A cm−2 K−2 for n-type ZnO, indicating that the inhomogeneous barrier height with the thermionic emission (TE) model could not explain the current transport. The conductive accumulation layers on the ZnO surfaces might not be removed effectively for two samples, which degraded the rectifying characteristics. The different electron transport characteristics between hydrothermal and pressurized melt-grown ZnO could be explained by the different degree of Ag-O formation at the interface.

Electrical properties of Ag Schottky contacts to hydrothermally-grown polar and nonpolar bulk ZnO

The electrical properties of Ag Schottky contacts to hydrothermally-grown polar (Zn- and Opolar) and nonpolar (m-plane) bulk ZnO were investigated. Ohmic-like behavior for Zn-polar ZnO and rectifying behaviors for O-polar and m-plane ZnO were observed from current-voltage (I–V ) measurements. Schottky contacts to O-polar ZnO were found to have higher barrier heights and lower ideality factors than those to m-plane ZnO. Higher series resistances were found for both the Zn-polar and the m-plane ZnO compared to the O-polar ZnO probably due to the presence of the interfacial layer and interface states. The homogeneous barrier heights obtained from linear fitting to the effective barrier height vs. ideality factor plots were similar to those obtained from capacitance-voltage (C–V ) measurements. A higher degree of oxidation at the Ag-ZnO interface might occur for O-polar ZnO than for m-plane ZnO, increasing the barrier heights. The large dispersion in the capacitance for m-plane ZnO was related to the excess capacitance due to the interface states.

Barrier inhomogeneity in Ag Schottky contacts to bulk ZnO grown by different methods

The electrical properties of Ag Schottky contacts to differently grown bulk ZnO single crystals were comparatively investigated. Schottky contacts to O-polar ZnO revealed higher barrier heights and lower ideality factors than those to Zn-polar ZnO. A higher degree of oxidation at the Ag-ZnO interface might occur for the O-polar ZnO, increasing the barrier heights. Compared to the current values measured under vacuum, those measured in an air ambient were decreased, suggesting that compensation of the surface conductive layer by acceptor-like adsorbates such as O2 and H2O plays an important role in the current transport of Ag/ZnO contacts.

Silver Schottky contacts to Zn-polar and O-polar bulk ZnO grown by pressurized melt-growth method

The current transport mechanisms of Ag Schottky contacts to Zn-polar and O-polar bulk ZnO single crystals were investigated over the temperature range of 100–300 K. Using the thermionic emission (TE) model, Schottky contacts to Zn-polar face were found to have higher barrier heights (lower ideality factors) than those to O-polar face. Compared to the theoretical value of n-type ZnO, the higher Richardson constant was obtained for both polar faces in the modified Richardson plot, indicating that the TE model, which considers barrier inhomogeneity, cannot adequately explain the current transport. Temperature-dependent tunneling characteristics showed that the tunneling current was dominant for the Zn-polar face over the entire temperature range (100–300 K). For the O-polar face, the tunneling current was dominant mainly at low temperatures (100–200 K) and the TE component contributed strongly to the current transport above 200 K.

Electrical characteristics of Au and Ag Schottky contacts on Nb-1.0 wt %-doped SrTiO3

The (Au,Ag)/Nb-1.0 wt %-doped SrTiO3 (NSTO), i.e., Au/NSTO, Ag/NSTO, Ag/Au/NSTO, and Au/Ag/NSTO junctions were fabricated by magnetic controlled sputtering and annealing process. Backward diodelike behaviors were observed in all as-prepared samples, and forward rectifying characteristics were gradually developed in the four junctions after annealed in oxygen at 400 °C, 550 °C, 700 °C, and 850 °C, respectively. Compared with the Ag/NSTO junctions, the Au/NSTO junctions showed higher temperature evolving procedure of forward rectifying behavior. Moreover, ideal Schottky behaviors appeared in the samples annealed at 850 °C, which were attributed to the formation of interface states. X-ray photoelectron spectroscopy and secondary ion mass spectrometry analysis showed that the interface states mainly originated from the migration of metal into NSTO matrix and the changes in chemical composition at the metal/NSTO interfaces. The results of current-voltage measurements reveal that annealing at higher temperature alters the interface barrier and thereby ameliorates the stability of leakage current remarkably.

Silver Schottky contacts to a-plane bulk ZnO

The temperature dependent electrical properties of Ag Schottky contacts to a-plane bulk ZnO single crystal were investigated in the temperature range of 100–300 K. The variation in the barrier heights was described by a double Gaussian distribution with two different regions in the temperature range of 200–300 and 100–180 K. The modified Richardson plot in the temperature range of 200–300 K produced the Richardson constant of 29 A cm−2 K−2 which is similar to the theoretical value of 32 A cm−2 K−2 for n-type ZnO, indicating that the inhomogeneous barrier height with the thermionic emission model can explain the current transport well in this region. Below 200 K, the bulk carriers start to freeze out and the induced oxygen vacancies in the interface region, probably due to the formation of silver oxide at the Ag–ZnO interface, will influence significantly the current transport by creating very thin interfacial layer that is susceptible to electron tunneling.

Properties of reactively sputtered Ag, Au, Pd, and Pt Schottky contacts on n-type ZnO

Highly rectifying Ag, Au, Pd, and Pt Schottky contacts have been fabricated on heteroepitaxial pulsed-laser deposited ZnO-thin films by reactive sputtering. X-ray photoelectron spectroscopy revealed an oxidation of the Ag, Pd, and Pt contact material; the gold contacts are purely metallic. The necessity of a conductive capping of the oxidized contacts is proven by photocurrent measurements of AgxO contacts. The ideality factors and the effective barrier heights were determined by current-voltage measurements. Capacitance-voltage and temperature dependent current-voltage measurements were furthermore carried out to determine the mean barrier height, the standard deviation and the respective voltage dependencies taking lateral fluctuations of the barrier height into account.

Characteristics of aligned ZnO nanorods grown on stainless‐steel foil by successive chemical solution deposition

AbstractWell‐aligned ZnO nanorods with a hexagonal cross section of size 200–300 nm and length 1000–1400 nm were grown along their c‐axis normal to the stainless steel substrate. The growth was performed for the first time by successive chemical solution deposition. Their structure, photoluminescence and electrical properties were characterized. Schottky diodes could be fabricated on nanorods which have a high optical transmittance and a band gap energy 3.25–3.28 eV. The Ag Schottky contacts have a large barrier height 0.99 eV and an ideality factor 2.35. The density of uncompensated donors in nanorods is 7 × 1014 cm–3. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Series resistance calculation for Ag contacts on single crystal layered p-SnS and p-SnSe compound semiconductors in the wide temperature range

This paper summarizes the first results of characteristics parameters obtained from current–voltage ( I– V) measurements for Ag/p-SnS and Ag/p-SnSe structure. The reverse and forward bias current–voltage characteristics of Ag Schottky contacts on a Bridgman–Stockbarger grown p-SnS and p-SnSe layered semiconducting material have been measured at various temperatures. We have tried to determine contact properties such as apparent barrier heights Φ B0, ideality factor n and series resistance R s. The apparent barrier height and ideality factor calculated by using thermionic emission theory were found to be strongly temperature dependent. Evaluating forward I– V data reveals a decrease at the apparent barrier height, but an increase at the ideality factor with decrease in temperature. It is shown that the values of R s estimated from Cheung’s method were strongly temperature dependent and decreased with increasing temperature. It has been found that both contacts are of Schottky type.

Temperature-dependent barrier characteristics of Ag/p-SnSe Schottky diodes based on I–V–T measurements

The current–voltage (I–V) characteristics of Ag Schottky contacts on a Bridgman–Stockbarger grown p-type SnSe layered semiconducting material have been measured over the temperature range of 80–350 K. Their analysis based on the thermionic emission (TE) theory has revealed an abnormal decrease of zero-bias barrier height and increase of ideality factor at lower temperatures. This behaviour has been interpreted on the basis of the assumption of a Gaussian distribution of barrier heights due to barrier height inhomogeneities that prevail at the interface. The inhomogeneities are considered to have Gaussian distribution with a mean barrier height of and standard deviation of σs0 = 0.075 V at zero-bias. Furthermore, the mean barrier height and the Richardson constant values were obtained by means of the modified Richardson plot, ln(I0/T2) − (q2σ2s0/2k2T2)versus 1000/T, as 0.603 eV and 7.72 A K−2 cm−2 respectively, of which latter is close to its theoretical value of 18 A K−2 cm−2 used for the determination of the zero-bias barrier height. Hence, it has been concluded that the temperature dependence of the I–V characteristics of the Schottky barrier on p-type SnSe can be successfully explained on the basis of TE mechanism with Gaussian distribution of the barrier heights.

Electrical characteristics of Au and Ag Schottky contacts on n-ZnO

Au and Ag Schottky contacts on the epiready (0001)Zn surface of bulk n-ZnO crystals show Schottky barrier heights of 0.65–0.70 eV from capacitance–voltage measurements, activation energies for reverse saturation currents of 0.3–0.4 eV and saturation current densities ranging from 10−5 A cm−2 on surfaces etched in HCl to 8×10−7 A cm−2 on solvent cleaned samples. The diode ideality factors were in the range 1.6–1.8 under all conditions. The properties of both the Au and the Ag Schottky diodes were degraded by heating in vacuum to temperatures even as low as 365 K. The degradation mechanisms during annealing were different in each case, with the Au showing reaction with the ZnO surface and the Ag contacts showing localized delamination. Mechanical polishing of the ZnO surface prior to contact deposition produced a high-resistivity damaged layer with prominent deep level defects present with activation energies of 0.55 and 0.65 eV.

Transport gap of organic semiconductors in organic modified Schottky contacts

Two different organic molecules with similar structure, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and N,N′-dimethyl-3,4,9,10-perylenetetracarboxylic diimide (DiMe-PTCDI), were used for the modification of Ag Schottky contacts on sulphur passivated GaAs(100) (S-GaAs). Such diodes were investigated recording in situ current–voltage (I–V) characteristics. As a function of the PTCDA thickness the effective barrier height of Ag/PTCDA/S-GaAs contacts initially increases from 0.59±0.01 to 0.72±0.01 eV, and then decreases to 0.54±0.01 eV, while only a decrease in barrier height from 0.54±0.01 to 0.45±0.01 eV is observed for DiMe-PTCDI interlayers. The initial increase and decrease in effective barrier height for PTCDA and DiMe-PTCDI respectively, is correlated with the energy level alignment of the lowest unoccupied molecular orbital (LUMO) with respect to the conduction band minimum (CBM) of S-GaAs at the organic/inorganic semiconductor interface. Whilst there is an additional barrier for electrons at the PTCDA/S-GaAs interface of about 150meV, i.e. the LUMO lies above CBM, the LUMO is aligned or below CBM in the DiMe-PTCDI case. The results also shine light on the important issue of the transport gap in organic semiconductors for which an estimation can be obtained.