Showing papers on "Schottky diode published in 1999"

Barrier heights of real Schottky contacts explained by metal-induced gap states and lateral inhomogeneities

Abstract: Most metal–semiconductor contacts are rectifying. For moderately doped semiconductors, the current transport across such Schottky contacts occurs by thermionic emission over the Schottky barrier. The current–voltage characteristics of real Schottky contacts are described by two fitting parameters that are the effective barrier heights ΦBeff and the ideality factors n. Due to lateral inhomogeneities of the barrier height, both parameters differ from one diode to another. However, their variations are correlated in that ΦBeff becomes smaller with increasing n. Extrapolations of such ΦBeff-versus-n plots to the corresponding image-force-controlled ideality factors nif give the barrier heights of laterally homogeneous contacts. They are then compared with the theoretical predictions for ideal Schottky contacts. Data of Si, GaN, GaAs, and CdTe Schottky contacts reveal that the continuum of metal-induced gap states is the fundamental mechanism that determines the barrier heights. However, there are additional b...

Electron-Hole Pair Creation at Ag and Cu Surfaces by Adsorption of Atomic Hydrogen and Deuterium

Abstract: Hot electrons and holes created at Ag and Cu surfaces by adsorption of thermal hydrogen and deuterium atoms have been measured directly with ultrathin metal film Schottky diode detectors on Si(111). When the metal surface is exposed to these atoms, charge carriers are excited at the surface, travel ballistically toward the interface, and have been detected as a chemicurrent in the diode. The current decreases with increasing exposure and eventually reaches a constant value at the steady-state coverage. This is the first direct evidence of nonadiabatic energy dissipation during adsorption at transition metal surfaces.

2.5-THz GaAs monolithic membrane-diode mixer

Abstract: A novel GaAs monolithic membrane-diode (MOMED) structure has been developed and implemented as a 2.5-THz Schottky diode mixer. The mixer blends conventional machined metallic waveguide with micromachined monolithic GaAs circuitry to form, for the first time, a robust, easily fabricated, and assembled room-temperature planar diode receiver at frequencies above 2 THz. Measurements of receiver performance, in air, yield at T/sub receiver/ of 16500-K double sideband (DSB) at 8.4-GHz intermediate frequency (IF) using a 150-K commercial Miteq amplifier. The receiver conversion loss (diplexer through IF amplifier input) measures 16.9 dB in air, yielding a derived "front-end" noise temperature below 9000-K DSB at 2514 GHz. Using a CO/sub 2/-pumped methanol far-infrared laser as a local oscillator at 2522 GHz, injected via a Martin-Puplett diplexer, the required power is /spl ap/5 mW for optimum pumping and can be reduced to less than 3 mW with a 15% increase in receiver noise. Although demonstrated as a simple submillimeter-wave mixer, the all-GaAs membrane structure that has been developed is suited to a wide variety of low-loss high-frequency radio-frequency circuits.

High-voltage Ni- and Pt-SiC Schottky diodes utilizing metal field plate termination

Abstract: We have fabricated 1 kV 4H and 6H SiC Schottky diodes utilizing a metal-oxide overlap structure for electric field termination. This simple structure when used with a high barrier height metal such as Ni has consistently given us good yield of Schottky diodes with breakdown voltages in excess of 60% of the theoretically calculated value. This paper presents the design considerations, the fabrication procedure, and characterization results for these 1 kV Ni-SiC Schottky diodes. Comparison to similarly fabricated Pt-SiC Schottky diodes is reported. The Ni-SiC ohmic contact formation has been studied using Auger electron spectroscopy and X-ray diffraction. The characterization study includes measurements of current-voltage (I-V) temperature and capacitance-voltage (C-V) temperature characteristics. The high-temperature performance of these diodes has also been investigated. The diodes show good rectifying behavior with ON/OFF current ratios, ranging from 10/sup 6/ to 10 at 27/spl deg/C and in excess of 10/sup 6/ up to 300/spl deg/C.

High temperature Pt Schottky diode gas sensors on n-type GaN

Abstract: The characteristics of Pt Schottky diodes on n-type GaN in hydrogen and propane are reported for the first time. This response from 200–400°C has been characterized by current–voltage measurements, revealing that the diodes are able to detect hydrogen from 200–400°C and propane from 300–400°C. The high temperature stability of Pt diodes on GaN has been investigated by long term annealing at 400°C in Ar or 20% O2 in Ar. The diodes have been held at 400°C for 500 h without degradation of their electrical characteristics or response to hydrogen-containing gases.

Sub-40 nm ptsi schottky source/drain metal-oxide-semiconductor field-effect transistors

Abstract: PtSi source/drain p-type metal–oxide–semiconductor field-effect transistors (MOSFETs) have been fabricated at sub-40 nm channel lengths with 19 A gate oxide. These devices employ gate-induced field emission through the PtSi ∼0.2 eV hole barrier to achieve current drives of ∼350 μA/μm at 1.2 V supply. Delay times estimated by the CV/I metric extend scaling trends of conventional p-MOSFETs to ∼2 ps. Thermal emission limits on/off current ratios to ∼20–50 in undoped devices at 300 K, while ratios of ∼107 are measured at 77 K. Off-state leakage can be reduced by implanting a thin layer of fully depleted donors beneath the active region to augment the Schottky barrier height or by use of ultrathin silicon-on-insulator substrates.

High-speed, low-noise metal–semiconductor–metal ultraviolet photodetectors based on GaN

Abstract: We present the fabrication and characterization of nonintentionally doped GaN and GaN:Mg Schottky metal–semiconductor–metal (MSM) photodetectors, grown on sapphire by metalorganic chemical vapor deposition. Low-leakage, Schottky contacts were made with Pt/Au. The devices are visible blind, with an ultraviolet/green contrast of about five orders of magnitude. The response times of the MSM devices were <10 ns and about 200 ns for GaN and GaN:Mg, respectively. The noise power spectral density remains below the background level of the system (10−24 A2/Hz) up to 5 V, for the undoped GaN MSM detector.

High voltage (450 V) GaN Schottky rectifiers

Abstract: We fabricated high standoff voltage (450 V) Schottky rectifiers on hydride vapor phase epitaxy grown GaN on sapphire substrate. Several Schottky device geometries were investigated, including lateral geometry with rectangular and circular contacts, mesa devices, and Schottky metal field plate overlapping a SiO2 layer. The best devices were characterized by an ON-state voltage of 4.2 V at a current density of 100 A/cm2 and a saturation current density of 10^–5 A/cm2 at a reverse bias of 100 V. From the measured breakdown voltage we estimated the critical field for electric breakdown in GaN to be (2.2 ± 0.7) × 10^6 V/cm. This value for the critical field is a lower limit since most of the devices exhibited abrupt and premature breakdown associated with corner and edge effects.

Barrier inhomogeneities and electrical characteristics of Ti/4H-SiC Schottky rectifiers

Abstract: Forward density-voltage (J-V) measurements of titanium/4H-SiC Schottky rectifiers are presented in a large temperature range. While some of the devices present a behavior in accordance with the thermionic current theory, others present an excess forward current at low voltage level. This anomaly appears more or less depending on the rectifier and on the temperature. A model based on two parallel Schottky rectifiers with different barrier heights is presented. The characteristics show good agreement. It is shown that the excess current at low voltage can be explained by a lowering of the Schottky barrier in localized regions. A proposal for the physical origin of these low barrier height areas is given.

Depletion layer thickness and Schottky type carrier injection at the interface between Pt electrodes and (Ba, Sr)TiO3 thin films

Abstract: The electrical conduction properties of rf sputter-deposited (Ba, Sr)TiO3 (BST) films on Pt and IrO2 electrodes and metalorganic chemical vapor deposited (MOCVD) BST films on a Pt electrode were investigated and a new energy band model that satisfactorily explains the observed leakage current characteristics and film thickness dependent dielectric properties is proposed. The BST and Pt junction constituted a blocking contact with interface potential barrier heights of 1.6–1.7 eV and 1.2 eV for the sputtered and MOCVD films, respectively. Schottky emission behavior was observed at measurement temperatures higher than 120 °C and tunneling related conduction behavior appeared below that temperature for a film thickness of 40 nm. A partial depletion model with a very thin (about 1 nm) layer devoid of space charge at the interface with the Pt electrode is proposed to explain the V1/2 dependent variation of ln(Jo) as well as the decreasing dielectric constant with decreasing film thickness.

High-resolution Schottky CdTe diode for hard X-ray and gamma-ray astronomy

Abstract: We report a significant improvement of the spectral properties of cadmium telluride (CdTe) detectors, fabricated in the form of a Schottky CdTe diode. With the use of high quality CdTe wafer, we formed a Schottky junction by evaporating indium on the Te-face and operated the detector as a diode. This allows us to apply much higher bias voltage than was possible with the previous CdTe detectors. A 2 mm×2 mm detector of thickness 0.5 mm, when operated at a temperature of 5°C, shows leakage current of only 0.2 and 0.4 nA for an operating voltage of 400 and 800 V, respectively. We found that, at a high-electric field of several kV cm−1, the Schottky CdTe diode has very good energy resolution and stability, suitable for astronomical applications. The broad low-energy tail, often observed in CdTe detectors due to the low mobility and short lifetime of holes, was significantly reduced by the application of a higher bias voltage which improves the charge collection efficiency. We achieved very good FWHM energy resolution of 1.1% and 0.8% at energies 122 and 511 keV, respectively, without any rise time discrimination or pulse height correction electronics. For the detection of hard X-rays and gamma-rays above 100 keV, we have improved the detection efficiency by stacking a number of thin CdTe diodes. Using individual readout electronics for each layer, we obtained high detection efficiency without sacrificing the energy resolution. In this paper, we report the performance of the new CdTe diode and discuss its proposed applications in future hard X-ray and gamma-ray astronomy missions.

Depth and thermal stability of dry etch damage in GaN Schottky diodes

Abstract: GaN Schottky diodes were exposed to N2 or H2 inductively coupled plasmas prior to deposition of the rectifying contact. Subsequent annealing, wet photochemical etching, or (NH4)2S surface passivation treatments were examined for their effect on diode current–voltage (I–V) characteristics. We found that either annealing at 750 °C under N2, or removal of ∼500–600 A of the surface essentially restored the initial I–V characteristics. There was no measurable improvement in the plasma-exposed diode behavior with (NH4)2S treatments.

Semiconductor near-ultraviolet photoelectronics

Abstract: After a brief review of classification, application and sources of near-ultraviolet (UV) radiation the methods for fabricating UV photodetectors and characteristics of the photoconductive cells, p-n junction structure and Schottky barrier photodiodes are discussed. Characteristics of some light filters used in photodetectors and measuring devices are also reported. Now Si p-n structures are commonly used but Schottky diodes based on wide-gap (GaAsP, GaP, GaN, AlGaN, SiC) semiconductors are very attractive. They are insensitive to the infrared radiation and if necessary simple glass filters can be used for correcting the spectrum in such way that it covers just the near-UV region.

Submicron transferred-substrate heterojunction bipolar transistors

Abstract: We report submicron transferred-substrate AlInAs/GaInAs heterojunction bipolar transistors (HBT's). Devices with 0.4-/spl mu/m emitter and 0.4-/spl mu/m collector widths have 17.5 dB unilateral gain at 110 GHz. Extrapolating at -20 dB/decade, the power gain cutoff frequency f/sub max/ is 820 GHz. The high f/sub max/, results from the scaling of HBT's junction widths, from elimination of collector series resistance through the use of a Schottky collector contact, and from partial screening of the collector-base capacitance by the collector space charge.

Intrinsic electrical properties of Au/SrTiO3 Schottky junctions

Abstract: Intrinsic electrical properties of Au/Nb-doped SrTiO3(001) (STO:Nb) Schottky junctions, fabricated using a proper surface treatment of the STO:Nb and in situ deposition of Au, were investigated in detail. Current–voltage characteristics and photocurrent–wavelength characteristics have shown a temperature-dependent and voltage-dependent Schottky barrier height, while capacitance–voltage characteristics have shown a temperature-independent flat band voltage. Using a temperature-dependent and field-dependent permittivity of the STO in the framework of Devonshire theory, we have performed computer simulation of the Schottky barrier potential to analyze the electrical properties of the junction. It is found that an intrinsic low permittivity layer at the Au/STO:Nb interface explains all the temperature dependence of the electrical properties.

Electrical characteristics of Schottky barriers on 4H-SiC: the effects of barrier height nonuniformity

Abstract: Electrical properties, including current-voltage (I-V) and capacitance-voltage (C-V) characteristics, have been measured on a large number of Ti, Ni, and Pt-based Schottky barrier diodes on 4H-SiC epilayers. Various nonideal behaviors are frequently observed, including ideality factors greater than one, anomalously low I-V barrier heights, and excess leakage currents at low forward bias and in reverse bias. The nonidealities are highly nonuniform across individual wafers and from wafer to wafer. We find a pronounced linear correlation between I-V barrier height and ideality factor for each metal, while C-V barrier heights remain constant. Electron beam induced current (EBIC) imaging strongly suggests that the nonidealities result from localized low barrier height patches. These patches are related to discrete crystal defects, which become visible as recombination centers in the EBIC images. Alternative explanations involving generation-recombination current, uniform interfacial layers, and effects related to the periphery are ruled out.

Analysis of Short-Channel Schottky Source/Drain Metal-Oxide-Semiconductor Field-Effect Transistor on Silicon-on-Insulator Substrate and Demonstration of Sub-50-nm n-type Devices with Metal Gate

Abstract: The Schottky source/drain metal-oxide-semiconductor field-effect transistor (MOSFET) has potential for scaling to the nanometer regime, because low electrode resistances with very shallow extension can be realized using metal source/drain. In this study, very short channel n- and p-type Schottky source/drain MOSFETs with silicon-on-insulator (SOI) structure were analyzed theoretically, and n-type devices were demonstrated experimentally. It was shown theoretically that a drivability of the Schottky source/drain MOSFET comparable to that of conventional MOSFETs can be realized with a low Schottky barrier height. The short-channel effect can be suppressed even with a 15-nm-long channel at tOX = 1 nm and tSOI = 3 nm. The room-temperature operation of sub-50-nm n-type ErSi2 Schottky source/drain MOSFETs on a separation by implanted oxygen (SIMOX) substrate was demonstrated.

Visible and infrared rare-earth-activated electroluminescence from indium tin oxide schottky diodes to gan:er on si

Abstract: Visible and infrared rare-earth-activated electroluminescence (EL) has been obtained from Schottky barrier diodes consisting of indium tin oxide (ITO) contacts on an Er-doped GaN layer grown on Si. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources for Ga, Mg, and Er and a plasma source for N2. RF-sputtered ITO was used for both diode electrodes. The EL spectrum shows two peaks at 537 and 558 nm along with several peaks clustered around 1550 nm. These emission lines correspond to atomic Er transitions to the 4I15/2 ground level and have narrow linewidths. The optical power varies linearly with reverse bias current. The external quantum and power efficiencies of GaN:Er visible light-emitting diodes have been measured, with values of 0.026% and 0.001%, respectively. Significantly higher performance is expected from improvements in the growth process, device design, and packaging.

Schottky energy barriers and charge injection in metal/Alq/metal structures

Abstract: We present internal photoemission, photocurrent versus bias voltage, and current–voltage measurements of metal/tris-(8-hydroxyquinoline) aluminum [Alq]/metal structures. Internal photoemission and photocurrent versus bias measurements were used to determine metal/Alq Schottky energy barriers for a range of contact metals with work functions from 2.7 eV (Sm) to 5.6 eV (Pt). The electron Schottky barrier for low work-function metals ( about 3.6 eV) the ideal Schottky model is generally accurate. A previously established device model was used to describe the current–voltage characteristics using the measured Schottky barriers. The results imply comparable electron and hole mobilities of about 2×10−5 cm2/V s at an electric field of 106 V/cm.

Effects of interfacial oxides on Schottky barrier contacts to n- and p-type GaN

Abstract: Schottky contacts were formed on n- and p-type GaN after either a conventional surface cleaning step in solvents, HCl and HF or with an additional treatment in (NH4)2S to prevent reformation of the native oxide. Reductions in barrier height were observed with the latter treatment, but there was little change in diode ideality factor. A simple model suggests that an interfacial insulating oxide of thickness 1–2 nm was present after conventional cleaning. This oxide has a strong influence on the contact characteristics on both n- and p-type GaN and appears to be responsible for some of the wide spread in contact properties reported in the literature.

Current status of silicon carbide based high-temperature gas sensors

Abstract: Silicon carbide (SiC) based field effect gas sensors can be operated at very high temperatures. Catalytic metal-insulator-silicon carbide (MISiC) Schottky diodes respond very fast to a change between a reducing and an oxidizing atmosphere, and cylinder-specific combustion engine monitoring has been demonstrated. The sensors have also been suggested for high-temperature electronic nose applications. Car applications and other harsh environments put very strong requirements on the long-term stability of the sensors. Here we review the current status of the field of SiC based Schottky diode gas sensors with emphasis on the work in our group. Basic work on understanding of the detection mechanism and the influence of interfacial layers on the long-term stability of the sensors is reviewed. The direction of future research and device development in our group is also discussed.

Resonant-tunneling mixed-signal circuit technology

Abstract: A large-scale integration (LSI) InP-based technology is described for high-speed mixed-signal circuits. The monolithic 75-mm wafer process uses molecular beam epitaxy, InP etch stop layers, an electron-beam-defined gate, non-alloyed ohmic contacts, and 10 mask levels to provide resonant tunneling diodes (RTD's), 0.25- or 0.5-μm gate-length high electron mobility transistors (HEMT's), Schottky diodes, resistors, capacitors and two and a half levels of interconnect. Resonant tunneling circuits described here for the first time include a 2.5-GHz, ten stage, tapped shift register, a 6.5-GHz clock generator and a multivalued-to-binary converter.

On-state and off-state breakdown in GaInAs/InP composite-channel HEMT's with variable GaInAs channel thickness

Abstract: Short-channel Ga/sub 0.47/In/sub 0.53/As high electron mobility transistors (HEMTs) suffer from low breakdown voltages due to enhanced impact-ionization effects in the narrow bandgap channel. This could limit the application of single-channel devices to medium power millimeter-wave systems. A composite Ga/sub 0.47/In/sub 0.53/As/InP channel, which exploits the high electron mobility of Ga/sub 0.47/In/sub 0.53/As at low electric fields, and the low impact-ionization and high electron saturation velocity of InP at high electric fields can overcome this limitation. In this paper we study on-state and off-state breakdown of Ga/sub 0.47/In/sub 0.53/As/InP composite-channel HEMT's with a variable GaInAs channel thickness of 30, 50, and 100 /spl Aring/. Reduction of channel thickness leads to the improvement of both on-state and off-state breakdown voltages. In on-state conditions, the enhancement in the effective Ga/sub 0.47/In/sub 0.53/As channel bandgap that takes place when the channel thickness is reduced to the order of the de Broglie wavelength (channel quantization) effectively enhances the threshold energy for impact-ionization, which is further reduced by real space transfer of electrons from the Ga/sub 0.47/In/sub 0.53/As into the wider bandgap InP. Channel thickness reduction also causes a decrease in the sheet carrier concentration in the extrinsic gate-drain region and therefore, a reduction of the electric field beneath the gate. This, together with the adoption of an Al/sub 0.6/In/sub 0.4/As Schottky layer (increasing the gate Schottky barrier height), leads to excellent values of the gate-drain breakdown voltage. In conclusion, composite channel InAlAs/GaInAs/InP HEMTs, thanks to the combined effect of effective band-gap increase, enhanced real space transfer into InP, and sheet carrier density reduction, allow a good trade-off between current driving capability and both on-state and off-state breakdown voltage.

On the extraction of linear and nonlinear physical parameters in nonideal diodes

Abstract: We describe a parameter extraction technique for the simultaneous determination of physical parameters in nonideal Schottky barrier, p-n and p-i-n diodes. These include the ideality factor, saturation current, barrier height, and linear or nonlinear series, and parallel leakage resistances. The suggested technique which deals with the extraction of bias independent parameters makes use of the forward biased current–voltage (I–V) characteristics and the voltage-dependent differential slope curve α(V)=[d(ln I)]/[d(ln V)]. The method allows (a) establishment of the current flow mechanisms at low and high bias levels, (b) extensive of the permissible ranges of determined parameters beyond what is possible in other published methods, and (c) to automation and computerization of the measurement processes. The method is verified experimentally using metal–semiconductor structures based on Si, InGaP, and HgCdTe as well as an InGaAs/InGaAsP multiple quantum well laser diode exemplifying a p-n junction.

Influence of dioxygen and annealing process on the transport properties of nickel phthalocyanine Schottky-barrier devices

Abstract: Schottky-barrier cells of the type (Al/p-NiPc/Au) are fabricated by successive vacuum depositions of p-NiPc thin films and aluminium fingers onto an ohmic gold electrode. The electrical conductivity has been measured both after exposure to oxygen for 10 days and after annealing at temperature up to 423 K. These cells showed high rectification in the oxygen-doped process. Current density–voltage characteristics under forward bias (aluminium electrode negative) are found to be due to space-charge-limited conduction controlled by a discrete trap level at lower voltage sections and by an exponential distribution of traps at higher voltage regions. Under reverse bias, the conduction processes are interpreted in terms of a transition from electrode-limited Schottky emission to the bulk-limited Poole–Frenkel effect. The effect of annealing showed similar behaviour and resulted in lowering the current density due to oxygen desorption. The linearity of the C −2 –V dependence for oxygen-doped devices is associated with a homogenous distribution of the impurities inside the space-charge region and also provided evidence of uniform doping.

Anomalous current transport in Au/low-doped n-GaAs Schottky barrier diodes at low temperatures

Abstract: The current-voltage characteristics of Au/low-doped n-GaAs Schottky diodes were determined at various temperatures in the range of 77-300 K, The estimated zero-bias barrier height and the ideality factor assuming thermionic emission (TE) show a temperature dependence of these parameters. While the ideality factor was found to show the $T_o$ effect, the zero-bias barrier height was found to exhibit two different trends in the temperature ranges of 77-160 K and 160-300 K, The variation in the Bat-band barrier height with temperature was found to be - (4.7 +/- 0.2) $210^4$ $eVK^1$, approximately equal to that of the energy band gap, The value of the Richardson constant, A**, was found to be $0.27 A cm^-^2 K^-^2$ after considering the temperature dependence of the barrier height. The estimated value of this constant suggested the possibility of an interfacial oxide between the metal and the semiconductor. Investigations suggested the possibility of a thermionic field- emission-dominated current transport with a higher characteristic energy than that predicted by the theory, The observed variation in the zero-bias barrier height and the ideality factor could be explained in terms of barrier height inhomogenities in the Schottky diode.

SiC power devices for high voltage applications

Abstract: Silicon Carbide device technology is now evolving from a pure vision to a real alternative to silicon devices. The feasibility of SiC devices has been shown for many different types of devices, the development of a working production technology has started, yield, reliability and costs now being the key issues. At present the high substrate prices keep the manufacturing costs of SiC high, making it very difficult to enter the device market with SiC on economic terms. Prime applications are those for which SiC offers substantial benefits or even a technological breakthrough on the system level. The main application is power conversion where the latest development efforts on silicon based power switches (e.g. IGBT) allow utilisation of much higher switching frequencies, putting very high demands on the free wheeling diode. The system performance is to a large extent limited by the diode recovery charge—a major source of switching losses. Depending on the voltage range, different device concepts are of interest: In the lower voltage range the junction–barrier controlled Schottky (JBS) device is a promising candidate while at voltages beyond 2.5 kV the PIN diodes is the device of choice. Different system requirements—e.g. surge current capability—make the PIN junction superior to a Schottky device for certain applications. With progress in material and technology development the ‘world’s best’ result is becoming less and less important and reproducibility is the issue. Failure analysis of defective devices needs to be established with a high number of substrate defects being still an obstacle in SiC. High leakage/soft reverse characteristics are often encountered and can usually be attributed to localised defects. It is important to identify their origin and to separate process-induced defects from those already present in the epilayer or substrate. In order to use the high power handling capability of SiC reduction of margins (e.g. in epilayer thickness and doping) is necessary. This requires narrow bandwidth of process and material variations. For paralleling of SiC devices equal current sharing under static and dynamic conditions is a fundamental requirement from the system side. Top-down calculation gives material specifications, which the supplier has to meet.

Epitaxial silicon carbide charge particle detectors

Abstract: The radiation detection properties of Schottky detectors made on epitaxial layers of 4H silicon carbide were evaluated. Exposure to 5.48 MeV alpha particles from a 241 Am source in vacuum led to robust signals from the detectors. The collection of the charge carriers was found to increase linearly with the square root of the applied reverse bias.

Numerical study of electrical transport in inhomogeneous Schottky diodes

Abstract: The Poisson equation together with the drift-diffusion equations have been used to simulate both forward and reverse I–V and C–V characteristics of inhomogeneous Schottky diodes. The barrier height distribution has been modeled by a single Gaussian. It is shown that the I–V and C–V curves and consequently extracted apparent Schottky diode parameters depend only slightly, if at all, on a lateral correlation between the single barrier patches in the structure for larger dimension of patches. The apparent barrier height of ordered structures differ only in several thousandths of volt from that of uncorrelated barrier patches. Very small differences were also found between the currents through the diodes with large inhomogeneities and nanosize inhomogeneities. The numerical results show that there is almost no dependence of the current on a pinch-off effect of electric potential. The diminishing of a drift part of the total current in the area of pinched-off potential is probably compensated by a greater diffusion current in the region. Consequently, very small and not unambiguous differences were found between the so called interacting and noninteracting diodes and this division is, according to the above results, questionable.

Si/SiGe optoelectronic integrated circuits

Abstract: An integrated optoelectronic circuit and process for making is described incorporating a photodetector and a MODFET on a chip. The chip contains a single-crystal semiconductor substrate, a buffer layer of SiGe graded in composition, a relaxed SiGe layer, a quantum well layer, an undoped SiGe spacer layer and a doped SiGe supply layer. The photodetector may be a metal-semiconductor-metal (MSM) or a p-i-n device. The detector may be integrated with an n- or p-type MODFET, or both in a CMOS configuration, and the MODFET can incorporate a Schottky or insulating gate. The invention overcomes the problem of producing Si-manufacturing-compatible monolithic high-speed optoelectronic circuits for 850 nm operation by using epixially-grown Si/SiGe heterostructure layers.