Showing papers on "Schottky diode published in 2007"

Evidence for strong Fermi-level pinning due to metal-induced gap states at metal/germanium interface

Abstract: The purpose of this paper is to understand metal/germanium (Ge) junction characteristics. Electrode metals with a wide work function range were deposited on Ge. All metal/p-Ge and metal/n-Ge junctions have shown Ohmic and Schottky characteristics, respectively, with the strong Fermi-level pinning. The charge neutrality level (CNL) at metal/Ge interface is close to the branch point calculated for the bulk Ge. Moreover, the pinning level is hardly modulated by annealing in forming gas, forming metal-germanide/Ge interfaces or changing the substrate orientation. These results suggest that Fermi level at metal/Ge interface is intrinsically pinned at the CNL characterized by the metal-induced gap states model.

Power Conversion With SiC Devices at Extremely High Ambient Temperatures

Abstract: This paper evaluates the capability of SiC power semiconductor devices, in particular JFET and Schottky barrier diodes (SBD) for application in high-temperature power electronics. SiC JFETs and SBDs were packaged in high temperature packages to measure the dc characteristics of these SiC devices at ambient temperatures ranging from 25degC (room temperature) up to 450degC. The results show that both devices can operate at 450degC, which is impossible for conventional Si devices, at the expense of significant derating. The current capability of the SiC SBD does not change with temperature, but as expected the JFET current decreases with rising temperatures. A 100 V, 25 W dc-dc converter is used as an example of a high-temperature power-electronics circuit because of circuit simplicity. The converter is designed and built in accordance with the static characteristics of the SiC devices measured under extremely high ambient temperatures, and then tested up to an ambient temperature of 400degC. The conduction loss of the SiC JFET increases slightly with increasing temperatures, as predicted from its dc characteristics, but its switching characteristics hardly change. Thus, SiC devices are well suited for operation in harsh temperature environments like aerospace and automotive applications.

A New Degradation Mechanism in High-Voltage SiC Power MOSFETs

Abstract: The phenomenon of recombination-induced stacking faults in high-voltage p-n diodes in SiC has been previously shown to increase the forward voltage drop due to reduction of minority carrier lifetime. In this paper, it has been shown that, for the first time, this effect is equally important in unipolar devices such as high-voltage MOSFETs. If the internal body diode is allowed to be forward biased during the operation of these devices, then the recombination-induced SFs will reduce the majority carrier conduction current and increase the leakage current in blocking mode. The effect is more noticeable in high-voltage devices where the drift layer is thick and is not expected to impact 600-1200-V devices.

A Wireless Power Interface for Rechargeable Battery Operated Medical Implants

Abstract: This brief presents a highly integrated wirelessly powered battery charging circuit for miniature lithium (Li)-ion rechargeable batteries used in medical implant applications. An inductive link and integrated Schottky barrier rectifying diodes are used to extract the DC signal from a power carrier while providing low forward voltage drop for improved efficiency. The battery charger employs a new control loop that relaxes comparator resolution requirements, provides simultaneous operation of constant-current and constant-voltage loops, and eliminates the external current sense resistor from the charging path. The accuracy of the end-of-charge (EOC) detection is primarily determined by the voltage drop across matched resistors and current-sources and the offset voltage of the sense comparator. Experimental results in 0.6-mum 3M-2P CMOS technology indicate that plusmn1.3% (or plusmn20 muA) EOC accuracy can be obtained under worst case conditions for a comparator offset voltage of plusmn5 mV. The circuit measures roughly 1.74 mm2 and dissipates 8.4 mW in the charging phase while delivering a load current of 1.5 mA at 4.1 V (or 6.15 mW) for an efficiency of 73%.

Reproducible unipolar resistance switching in stoichiometric ZrO2 films

Abstract: The resistance switching characteristics of stoichiometric ZrO2 film were investigated for nonvolatile memory. The Al∕ZrO2∕Al device presents reliable and reproducible switching behaviors. The on/off ratio of two stable states is larger than 2×103. It is suggested that the current-voltage characteristics are governed by the Schottky conduction mechanism in high voltage region, while the filament conduction is suggested in low voltage region. The switching process is explained in terms of the spontaneous reversible reaction between electrode and ZrO2 films with the contribution of Joule heating effect by the external current. It provides a possible solution for low device yield of nonstoichiometric oxides.

Barrier inhomogeneity and electrical properties of Pt∕GaN Schottky contacts

Abstract: The temperature dependence of the electrical properties of Pt∕GaN Schottky barrier was studied. In particular, a Schottky barrier height of 0.96eV and an ideality factor of 1.16 were found after a postdeposition annealing at 400°C. Nanoscale electrical characterization was carried out by the conductive biased tip of an atomic force microscope both on the bare GaN surface and on the Pt∕GaN contacts. The presence of a lateral inhomogeneity of the Schottky barrier, with a Gaussian distribution of the barrier height values, was demonstrated. Moreover, GaN surface defects were demonstrated to act as local preferential paths for the current conduction. The temperature dependent electrical characteristics of the diodes were discussed in terms of the existing models on inhomogeneous barriers and correlated to the nanoscale electrical characterization of the barrier. In this way, the anomalous electrical behavior of the ideality factor and of the Schottky barrier and the low experimental value of the Richardson’s ...

Dominant effect of near-interface native point defects on ZnO Schottky barriers

Abstract: The authors used depth-resolved cathodoluminescence spectroscopy and current-voltage measurements to probe metal-ZnO diodes as a function of native defect concentration, oxygen plasma processing, and metallization. The results show that resident native defects in ZnO single crystals and native defects created by the metallization process dominate metal-ZnO Schottky barrier heights and ideality factors. Results for ZnO(0001¯) faces processed with room temperature remote oxygen plasmas to remove surface adsorbates and reduce subsurface native defects demonstrate the pivotal importance of crystal growth quality and metal-ZnO reactivity in forming near-interface states that control Schottky barrier properties.

Electrical characterization of Al/MEH-PPV/p-Si Schottky diode by current-voltage and capacitance-voltage methods

Abstract: The electrical characterization of the Al/poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)/p-Si structure has been investigated by current–voltage and capacitance–voltage methods. The Al/MEH-PPV/p-Si Schottky diode with the ideality factor value of 1.88 obeys a metal–interfacial layer–semiconductor (MIS) configuration rather than an ideal Schottky diode due to the existence of an insulating layer on the organic semiconductor. The barrier height ( Φ b , o = 0.80 eV ) obtained from the I–V characteristic is lower than the barrier height ( Φ b , o = 1.19 eV ) obtained from the C–V characteristic. The discrepancy between Φ b , o ( I – V ) and Φ b , o ( C – V ) can be due to the existence of the interfacial native oxide and the organic MEH-PPV layers between the semiconductor and Schottky contact metal. The barrier height value for the Al/MEH-PPV film/p-Si/Al contact obtained at the room temperature that is significantly larger than that for the conventional Al/p-Si Schottky diode. The density distribution curves of the interface states is in the range (0.32-Ev) to (0.68-Ev)eV. The interface state density Nss ranges from 3.84×1014 cm−2 eV−1 in (0.32-Ev)eV to 1×1014 cm−2 eV−1 in (0.68-Ev)eV, of the Al/MEH-PPV/p-Si. The interface state density has an exponential rise with bias from the midgap towards the top of the valence band of the p-Si.

Silver oxide Schottky contacts on n-type ZnO

Abstract: A method of fabricating highly rectifying Schottky contacts on n-type ZnO using silver oxide has been developed and used to compare diode performance on hydrothermal and melt grown, bulk, single crystals. Silver oxide diodes on hydrothermal ZnO have lower ideality factors, lower reverse current voltage dependence, higher series resistance, and larger surface-polarity related differences in barrier height, compared to those on melt ZnO. These effects are explained by the large difference in resistivity between hydrothermal and melt ZnO. Barrier heights of 1.20eV were achieved on the Zn-polar face of hydrothermal ZnO which are the highest reported for n-type ZnO.

Mechanisms of current flow in metal-semiconductor ohmic contacts

Abstract: Published data on the properties of metal-semiconductor ohmic contacts and mechanisms of current flow in these contacts (thermionic emission, field emission, thermal-field emission, and also current flow through metal shunts) are reviewed. Theoretical dependences of the resistance of an ohmic contact on temperature and the charge-carrier concentration in a semiconductor were compared with experimental data on ohmic contacts to II–VI semiconductors (ZnSe, ZnO), III–V semiconductors (GaN, AlN, InN, GaAs, GaP, InP), Group IV semiconductors (SiC, diamond), and alloys of these semiconductors. In ohmic contacts based on lightly doped semiconductors, the main mechanism of current flow is thermionic emission with the metal-semiconductor potential barrier height equal to 0.1–0.2 eV. In ohmic contacts based on heavily doped semiconductors, the current flow is effected owing to the field emission, while the metal-semiconductor potential barrier height is equal to 0.3–0.5 eV. In alloyed In contacts to GaP and GaN, a mechanism of current flow that is not characteristic of Schottky diodes (current flow through metal shunts formed by deposition of metal atoms onto dislocations or other imperfections in semiconductors) is observed.

Comparisons of SiC MOSFET and Si IGBT Based Motor Drive Systems

Abstract: With the rapid development of silicon carbide (SiC) material quality, SiC power devices are gaining tremendous attentions in power electronics. In this paper, a SiC device based motor drive system is performed to provide a quantitative estimate of the system improvement. Two 60 kW motor drive systems based on SiC MOSFET/Schottky diode and Si IGBTs are designed. The power losses of the two inverters with sinusoidal pulse width modulation (SPWM) control are calculated analytically. By comparing the efficiencies, sizes and temperatures of the two designed systems, SiC device shows the superior advantages of smaller loss, better efficiency and smaller size in the same motor drive application.

Schottky barriers to colloidal quantum dot films

Abstract: We elucidate experimentally a quantitative physical picture of the Schottky barrier formed at the junction between a metallic contact and a semiconducting colloidal quantum dot film. We used a combination of capacitance-voltage and temperature-dependent current-voltage measurements to extract the key parameters of the junction. Three differently processed Al∕PbS colloidal quantum dot junction devices provide rectification ratios of 104, ideality factors of 1.3, and minimal leakage currents at room temperature. The Schottky barrier height is 0.4eV and the built-in potential 0.3V. The depletion width ranges from 90to150nm and the acceptor density ranges from 2×1016to7×1016cm−3.

High-performance nano-Schottky diodes and nano-MESFETs made on single CdS nanobelts.

Abstract: Nano-Schottky diodes and nanometal-semiconductor field-effect transistors (MESFETs) on single CdS nanobelts (NBs) have been fabricated and studied. The Au/CdS NB Schottky diodes have very low reverse current density ( approximately 3.0 x 10-5 A.cm-2 at -10 V reverse bias) and the highest on/off current ratio (approximately 108) reported so far for nano-Schottky diodes. The single CdS NB MESFETs exhibit n-channel normally on (depletion) mode, low threshold voltage (approximately -1.56 V), high transconductance ( approximately 3.5 microS), low subthreshold swing ( approximately 45 mV/dec), and the highest on/off current ratio (approximately 2 x 108) reported so far for nanofield-effect transistors. We also show that the absolute value of threshold voltage for a metal-insulator-semiconductor field-effect transistor made on a single CdS NB can be reduced from approximately 12.5 to approximately 0.4 V and its transconductance can be increased from approximately 0.2 to approximately 3.2 microS by adding an extra Au Schottky contact on the CdS NB, the mechanism of which is discussed.

Imaging of the Schottky barriers and charge depletion in carbon nanotube transistors.

Abstract: The photovoltage produced by local illumination at the Schottky contacts of carbon nanotube field-effect transistors varies substantially with gate voltage. This is particularly pronounced in ambipolar nanotube transistors where the photovoltage switches sign as the device changes from p-type to n-type. The detailed transition through the insulating state can be recorded by mapping the open-circuit photovoltage as a function of excitation position. These photovoltage images show that the band-bending length can grow to many microns when the device is depleted. In our palladium-contacted devices, the Schottky barrier for electrons is much higher than that for holes, explaining the higher p-type current in the transistor. The depletion width is 1.5 mum near the n-type threshold and smaller than our resolution of 400 nm near the p-type threshold. Internal photoemission from the metal contact to the carbon nanotube and thermally assisted tunneling through the Schottky barrier are observed in addition to the photocurrent that is generated inside the carbon nanotube.

Shielded gate trench (SGT) MOSFET cells implemented with a schottky source contact

Abstract: This invention discloses a semiconductor power device that includes a plurality of power transistor cells surrounded by a trench opened in a semiconductor substrate. At least one active cell further includes a trenched source contact opened between the trenches wherein the trenched source contact opened through a source region into a body region for electrically connecting the source region to a source metal disposed on top of an insulation layer wherein a trench bottom surface of the trenched source contact further covered with a conductive material to function as an integrated Schottky barrier diode in said active cell. A shielding structure is disposed at the bottom and insulated from the trenched gate to provide shielding effect for both the trenched gate and the Schottky diode.

Responsivity and Noise Measurements of Zero-Bias Schottky Diode Detectors

Abstract: Schottky barrier diodes can be used as direct detectors throughout the millimeterand submillimeterwave bands. When the diodes are optimized to have a low forward turn-on voltage, the detectors can achieve excellent frequency response and bandwidth, even with zero-bias. This paper reports on the characterization of VDI’s zerobias Schottky detectors. Responsivity typically ranges from 4,000 V/W at 100 GHz to 400 V/W at 900 GHz and each detector achieves good responsivity across the entire singlemoded bandwidth of the input rectangular waveguide. Under low power operation the detectors achieve a measured noise-equivalent-power (NEP) of about 1.5x10 W/√Hz, even without signal modulation. Such high sensitivity is expected for any zero-bias diode detector with high responsivity when there is no incident RF power; since only thermal noise can be generated under this condition. However, as the input power is increased, excess noise is generated. This noise typically has a 1/f power spectrum and is commonly known as flicker noise. Flicker noise becomes increasingly important as the input power is increased and signal modulation is generally required to achieve maximum sensitivity. The signal-to-noise of the VDI zero-bias detectors has been carefully measured as a function of input power and modulation rate. This data allows the user to understand the sensitivity of the detector under real operating conditions, and is therefore far more useful than the simple measurement of detector NEP with zero RF power, which is commonly quoted in the literature for new diode detector designs. Index Terms — Terahertz detectors, zero-bias detectors, noise-equivalent power, flicker noise.

Electronic and Thermoelectric Properties of Polyaniline Organic Semiconductor and Electrical Characterization of Al/PANI MIS Diode

Abstract: The electrical conductivity, thermoelectric power, and metal−insulator−semiconductor diode properties of polyaniline prepared in ionic liquid (PANI) have been investigated. The electrical conductivity of the polyaniline increases exponentially with increasing temperature. The electrical conductivity value at 28 °C is 0.21 S/cm. The Seebeck coefficient of the PANI decreases with increasing temperature. The electrical conductivity and thermoelectric power results suggest that the PANI is a p-type semiconductor polymer. The Al/PANI Schottky diode was fabricated and is a metal−insulator−semiconductor type device. The ideality factor n and barrier height φb values of the diode at 298 K were found to be 2.78 and 0.85 eV, respectively. The barrier inhomogeneities are a very important explanation of the higher values of the ideality factor. The Gaussian distribution function was suggested for describing barrier height inhomogeneities. The standard deviation of the barrier height distribution σo indicates the pres...

Leakage current analysis of diamond Schottky barrier diode

Abstract: The current-voltage characteristics of non-punch-through-type diamond Schottky barrier diodes (SBDs) are analyzed by using thermionic and thermionic-field emission (TFE) models. Diamond SBD with defects such as nonepitaxial crystallites (NCs) shows shunt path conductance both under forward and reverse bias conditions. However, SBD without NCs shows a low reverse leakage current density of less than 1×10−11A∕cm2, which is more than 12 orders of magnitude smaller than the forward current density. From the fitting of the reverse leakage current of SBD without NCs, TFE current dominates when the reverse electric field is larger than 1.2MV∕cm and its current density value reaches 10−6A∕cm2 even at 1.6MV∕cm, which is lower than the avalanche limit.

Schottky contact on a ZnO (0001) single crystal with conducting polymer

Abstract: High quality Schottky junctions were fabricated on a ZnO (0001) bulk single crystal by spin coating a commercial conducting polymer, poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), as the metal electrodes. The junctions exhibited excellent rectifying behavior with a typical ideality factor of 1.2. Such parameters as Schottky barrier height (ϕb) and built-in potential (Vbi) show negligible variation among junctions. The electron affinity of ZnO derived from ϕb and qVbi values show a slight deviation (∼0.2eV), suggesting the existence of spontaneously formed interfacial dipole layer between ZnO (0001) polar surface and anionic PSS molecules.

Schottky ultraviolet photodiode using a ZnO hydrothermally grown single crystal substrate

Abstract: A Schottky ultraviolet photodiode using a (0001) ZnO single crystal grown by the hydrothermal growth method is reported. The photodiode consisted of a semitransparent Pt film for the Schottky electrode and an Al thin film for the Ohmic electrode. The photodiode had polarity dependences on current-voltage characteristics and on responsivity. In the case of the Schottky electrode on the zinc surface, the responsivity was 0.185A∕W at a wavelength of 365nm. On the other hand, the responsivity was 0.09A∕W for an oxygen surface. The results are attributed to the polarity dependences of surface chemical reactivity and the surface state density on ZnO surfaces.

One transistor dram cell structure and method for forming

Abstract: A one-transistor dynamic random access memory (DRAM) cell includes a transistor (10) which has a first source/drain region (26) a second source/drain region (24), a body region (36) between the first and second source/drain regions, and a gate (28) over the body region. The first source/drain region includes a Schottky diode junction with the body region and the second source/drain region includes an n-p diode junction with the body region.

Schottky-Barrier Height Tuning by Means of Ion Implantation Into Preformed Silicide Films Followed by Drive-In Anneal

Abstract: An experimental study on Schottky-barrier height (SBH) tuning using ion implantation followed by drive-in anneal of As, B, In, and P in preformed NiSi and PtSi films is presented. Measured on B-implanted NiSi and PtSi Schottky diodes, the effective SBH on n-type Si is altered to ~1.0 eV. For As- and P-implanted diodes, the SBH on p-type Si can be tuned to around 0.9 eV. The process window for the most pronounced SBH modification is dopant dependent.

Electrical properties of individual tin oxide nanowires contacted to platinum electrodes

Abstract: A simple and useful experimental alternative to field-effect transistors for measuring electrical properties free electron concentration nd, electrical mobility , and conductivity in individual nanowires has been developed. A combined model involving thermionic emission and tunneling through interface states is proposed to describe the electrical conduction through the platinum-nanowire contacts, fabricated by focused ion beam techniques. Current-voltage I-V plots of single nanowires measured in both two- and four-probe configurations revealed high contact resistances and rectifying characteristics. The observed electrical behavior was modeled using an equivalent circuit constituted by a resistance placed between two back-to-back Schottky barriers, arising from the metal-semiconductor-metal M-S-M junctions. Temperature-dependent I-V measurements revealed effective Schottky barrier heights up to BE=0.4 eV.

Temperature dependence of characteristic parameters of the Au/SnO2/n-Si (MIS) Schottky diodes

Abstract: The variation in electrical characteristics of Au/SnO2/n-Si (MIS) Schottky diodes have been systematically investigated as a function of temperature by using forward bias current–voltage (I–V) measurements The main diode parameters, ideality factor n and zero-bias barrier height ΦB0, were found strongly temperature dependent and while the zero-bias barrier height ΦB0(I–V) increases, the n decreases with increasing temperature This behavior has been interpreted by the assumption of a Gaussian distribution of barrier heights due to barrier inhomogenities that prevail at the metal–semiconductor interface The zero-bias barrier height ΦB0 vs q/(2kT) plot has been drawn to obtain evidence of a Gaussian distribution of the barrier heights, and values of Φ ¯ B 0 = 1101 eV and σ0 = 0158 V for the mean barrier height and zero-bias standard deviation have been obtained from this plot, respectively Thus a modified ln(I0/T2) − ( q 2 σ 0 2 ) /2k2T2 vs q/(kT) plot has given mean barrier height Φ ¯ B 0 and Richardson constant (A*) as 1116 eV and 12786 A cm−2 K−2, respectively The A* value 12786 A cm−2 K−2 obtained from this plot is in very close agreement with the theoretical value of 120 A cm−2 K−2for n-type Si Hence, it has been concluded that the temperature dependence of the forward bias I–V characteristics of the Au/SnO2/n-Si (MIS) Schottky diode can be successfully explained on the basis of a thermionic emission (TE) mechanism with a Gaussian distribution of the Schottky barrier heights (SBHs) In addition, we have reported a modification by the inclusion of both n and αχ05δ in the expression of I0 to explain the positive temperature dependence of ΦB0 against that of energy band-gap of Si Thus, the values of temperature coefficient of the effective barrier height ΦBef(−364 × 10−4 eV/K) is very close agreement with the temperature coefficient of Si band-gap (−473 × 10−4 eV/K)

Electron mobility related to scattering caused by the strain variation of AlGaN barrier layer in strained AlGaN∕GaN heterostructures

Abstract: Using the measured capacitance- voltage curves of Ni Schottky contacts with different areas on strained AlGaN/ GaN heterostructures and the current- voltage characteristics for the AlGaN/ GaN heterostructure field- effect transistors at low drain- source voltage, we found that the two- dimensional electron gas (2DEG) electron mobility increased as the Ni Schottky contact area increased. When the gate bias increased from negative to positive, the 2DEG electron mobility for the samples increased monotonically except for the sample with the largest Ni Schottky contact area. A new scattering mechanism is proposed, which is based on the polarization Coulomb field scattering related to the strain variation of the AlGaN barrier layer. (C) 2007 American Institute of Physics.

Influence of spontaneous polarization on the electrical and optical properties of bulk, single crystal ZnO

Abstract: Hall effect, photoluminescence, and Schottky diode measurements were made on the Zn-polar and O-polar faces of undoped, bulk, single crystal, c-axis ZnO wafers. Significant polarity related differences were observed in the PL and Schottky diode characteristics of low carrier concentration, hydrothermally grown wafers. Increased emission from free exciton recombinations and from recombinations between 3.3725 and 3.3750eV was observed on the Zn-polar face. Conversely, emission between 3.3640 and 3.3680eV was more intense on the O-polar face. The barrier heights of silver oxide Schottky diodes were approximately 130meV larger on the Zn-polar face compared to the O-polar face.

Mechanism of surface conduction in the vicinity of Schottky gates on AlGaN∕GaN heterostructures

Abstract: Lateral surface leakage current (Is) on an AlGaN∕GaN heterostructure was systematically investigated by using a two-parallel gate structure with a gap distance (LGG) of 200nm–5μm. The surface current Is systematically increased as LGG decreased. A simple resistive layer conduction that should show 1∕LGG dependence failed to account for the drastic increase in Is when LGG was reduced to less than 1μm. However, no dependence on LGG was seen in vertical current that flows in the Schottky interface. The Is showed a clear temperature dependence proportional to exp(−T−1∕3), indicating two-dimensional variable-range hopping through high-density surface electronic states in AlGaN. A pronounced reduction in surface current of almost four orders of magnitude was observed in a sample with SiNx passivation.

Single Schottky-barrier photodiode with interdigitated-finger geometry: Application to diamond

Abstract: The authors propose a single Schottky-barrier photodiode (SPD) with interdigitated Ohmic and Schottky contacts. A homoepitaxial diamond layer with low boron concentration has been utilized as an example for the fabrication of solar-blind deep-ultraviolet detector. This device structure enables the operations in both photoconductive mode with large photocurrent gain and depletion mode with fast response speed. The photosensitivity and spectral response of such kind of device are greatly improved when compared with a conventional SPD with semitransparent dotted Schottky contact. The present device structure can be extended to other semiconductor photodetectors.

Method to form upward pointing p-i-n diodes having large and uniform current

Abstract: A method is disclosed to form an upward-pointing p-i-n diode formed of deposited silicon, germanium, or silicon-germanium. The diode has a bottom heavily doped p-type region, a middle intrinsic or lightly doped region, and a top heavily doped n-type region. The top heavily doped p-type region is doped with arsenic, and the semiconductor material of the diode is crystallized in contact with an appropriate silicide, germanide, or silicide-germanide. A large array of such upward-pointing diodes can be formed with excellent uniformity of current across the array when a voltage above the turn-on voltage of the diodes is applied. This diode is advantageously used in a monolithic three dimensional memory array.