High Schottky Barrier Research Articles

Metamorphic In0.3Ga0.7As/In0.29Al0.71As layer on GaAs: A new structure for high performance high electron mobility transistor realization

A new high electron mobility transistor (HEMT) using InAlAs/InGaAs grown on GaAs has been successfully realized. This structure, with an In content close to 30%, presents several advantages over conventional pseudomorphic HEMT on GaAs and lattice matched HEMT on InP. To accommodate the mismatch between the active layer and the GaAs substrate, a metamorphic buffer has been grown. High electron mobility with high two-dimensional electron gas density (20 700 cm2/V s with 4×1012 cm−2) and high Schottky barrier quality (Vb=0.68 V with η=1.1) have been obtained. A 3 μm gate length device has shown intrinsic transconductance as high as 530 mS/mm.

Vacuum annealing characteristics of electron beam evaporated ruthenium contacts to n-GaAs grown by organometallic vapour phase epitaxy

High quality ruthenium Schottky barrier diodes were fabricated on organometallic vapour phase epitaxially grown n-GaAs, with a carrier density of 1 x 10 16 cm −3, by electron beam evaporation of ruthenium at a rate of 1 Å s −1. The annealing studies were carried out in vacuum over the temperature range from 225 °C to 600 °C. The electrical characteristics of the Schottky contacts were evaluated by standard current-voltage I–V and capacitance-voltage C–V measurements. The effective barrier height ϕ e I–V and the flat band barrier height ϕ b C–V of the as-deposited R u-n-GaAs Schottky contacts were 0.865 eV and 0.916 eV respectively. These barrier heights reached their respective maximum values of 0.925 eV and 0.955 eV after annealing at 450 °C. Auger electron spectroscopy results indicated that ruthenium forms structurally a very stable contact to GaAs, with no evidence of any chemical reactions between ruthenium and GaAs up to 500 °C. Very limited diffusion of arsenic through the ruthenium layer was observed after annealing at 400 °C. Diffusion of arsenic increased sharply after annealing at temperatures above 500 °C.

Annealing characteristics and thermal stability of electron beam evaporated ruthenium Schottky contacts to n-GaAs

High quality ruthenium Schottky barrier diodes were fabricated on epitaxially grown n-GaAs, by the electron beam evaporation of Ru. Annealing studies were carried out in vacuum and in air. The effective barrier height and the flatband barrier height of the as-deposited Schottky contacts were 0.86 and 0.91 eV, respectively. These barrier heights reached their respective maximum values of 0.93 and 0.96 eV, after annealing at 450 °C in vacuum. The electrical characteristics of a third set of contacts, which was subjected to prolonged (1000 min) annealing at 400 °C in vacuum, showed no measureable signs of degradation.

Annealed indium oxide transparent ohmic contacts to GaAs

The current–voltage characteristics of annealed In2O3–GaAs devices have been investigated for the purpose of fabricating transparent ohmic contacts to GaAs. A detailed study of the reverse current for as-deposited structures with degenerately doped n-type In2O3 on lightly doped n-type GaAs yields a 0.67-V high Schottky barrier. After annealing, the barrier height is only slightly modified, but the reverse current increases dramatically. This reverse current follows a voltage dependence that is consistent with a Fowler–Nordheim tunneling mechanism, for which the electric field is enhanced around localized asperities. These data suggest that an optimized annealing schedule might be used to fabricate low-resistance, transparent In2O3 ohmic contacts to GaAs-based optoelectronic devices.

Planar 100 GHz silicon detector circuits

On high resistive silicon substrates Schottky barrier diodes have been monolithically integrated with planar antenna structures. The Schottky barrier diodes were fabricated on n+ diffusion regions with thin epitaxial layers grown by molecular beam epitaxy. Low series resistance (≪ 6 ?), ideality factor of less than 1.1 and cut-off frequencies up to 1 THz have been achieved. The maximum sensitivity of the detector-was 90 mV/(mW cm?2) at 94 GHz.

High Schottky Barriers between Amorphous-Si-P Alloy and P-Type Gallium Arsenide

Schottky barriers of as high as 0.75 V are formed between p-type GaAs and amorphous Si-P alloy films. These high barriers are probably caused by P atoms on the GaAs surface. Because this contact is temperature-stable and easily formed simply by conventional chemical vapor deposition (CVD), it is suitable for fabrication of GaAs complementary metal-semiconductor field effect transistors (MESFETs).

Large Schottky barrier heights on n-InP−A novel approach

An unusually high Schottky barrier height (SBH) of 0.82 eV has been observed at Au/n-InP(110) interfaces with one monolayer of Sb as an interlayer using photoemission techniques. For Au deposited on clean cleaved InP(110), Au-In alloying that occurs with increasing Au coverage destroys interfacial perfection. The resulting Fermi level position lies ∼ 0.5 eV below the conduction band minimum, as is common for metal interfaces with clean cleaved InP. However, for InP surfaces first passivated with one monolayer of Sb, this Au–In alloying is completely inhibited. An abrupt interface results in an increased possibility of a low interface defect density. This represents a possible way to control of SBH and produces high SBH for n-InP.

Application of photodeposited Cd to Schottky barrier diode and transistor fabrication on InP and In0.53Ga0.47As substrates

We report on using a thin (∼200 Å) layer of photodeposited Cd to form high Schottky barrier height contacts to InP and In0.53Ga0.47As. Current-voltage measurements of the Schottky diodes yield barrier heights of 0.70 and 0.55 eV to InP and In0.53Ga0.47As, respectively. The photodeposition process has been integrated with conventional clean room processing to fabricate Au/Cd/In0.53Ga0.47As transistors with high transconductances (∼200 mS/mm) and operating frequencies ( fmax∼30 GHz). X-ray photoelectron spectroscopy of thin Cd photodeposits on InP shows that the process produces an interfacial (∼10 Å thick) Cd-InP reaction zone covered by metallic Cd.

Interface structure and Schottky barriers of epitaxial Pb on Si(111)

Schottky barrier (SB) heights of epitaxialSi(111)Pb Schottky contacts having different interface structures were found to be very different (0.70 and 0.93 eV for the (7×7) and(√3 × √3)R30° type interfaces, respectively). For monolayer coverages even higher values were found from photoelectron spectra (0.94 and 1.04 eV, respectively). The discrete interface states which must be responsible for these exceptionally high SB could be identified in the ARUPS spectra. Because they appear in regions of k-space where there is a common gap of the metal and the semiconductor, they may be true interface states.

Carrier recombination and high-barrier Schottky diodes on silicon

Small-area high-barrier Schottky diodes have a very high dynamic resistance. Consequently, special care is needed when measuring the current-voltage characteristic of such diodes. The reported observation of carrier recombination in the depletion layer of high-barrier IrSi/Si Schottky diodes at room temperature is shown to be due to instrumental loading of the diodes. Careful measurements show that carrier recombination is observed only below 200 K and is dependent on the dimension of the diode.

From synchrotron radiation to I-V measurements of GaAs schottky barrier formation

Through the use of synchrotron radiation photoemission spectroscopy (PES) and related techniques, we have gained detailed knowledge of Fermi level pinning, interfacial chemistry and disruption of GaAs for coverages up to several monolayers (ML). A link has been made between these data and that in the thick layer regime (hundreds of ML), which characterizes practical Schottky diodes. PES results for thin layers deposited at room temperature (RT) and low temperatures of about 80 K (LT) as well as thick films deposited at RT and annealed to higher temperatures are considered. At LT where GaAs disruption is minimized for thin films, metal-induced gap states seem to dominate the Fermi level pinning process except where GaAs metal reactions are strong. For RT thin and thick films, the effects of defects must be considered, and the advanced unified defect model (AUDM) is applied. In the AUDM the key defects are identified as the AsGa (double donor with levels at 0.75 and 0.5 eV above the valence band maximum) and the GaAs antisite (double acceptor) with the AsGa normally dominating due to the excess As which characterizes LEC GaAs crystals. The literature is reviewed and a number of phenomena are explained in terms of this model including the Fermi level position on MBE grown GaAs observed by Svensson et al. and the anomolously high Schottky barrier height (SBH) of thick Ga on n-GaAs observed by several groups. By performing electrical, TEM, and chemical studies of thick diodes and by evaluating the changes upon thermal annealing of diodes it is found that the AUDM successfully predicts the increase or decrease of barrier height on annealing.

Composition and Structure Characterization of WNx Films Produced by RF Reactive Sputtering

AbstractWNx film is one of the most promising materials for self-aligned GaAs NASFET because of its low electrical resistivity and high Schottky Barrier Height at the WNx /GaAs contact.In this paper, the effect of the sputtering conditions and the annealing environment on the chemical composition and structure of the WNx films deposited on Si and GaAs by RF reactive sputtering are studied.The results show that with the increase of the partial pressure ratio of nitrogen gas or decrease of the working pressure, deposition rate of WNx film decreases, whereas the atomic percentage of N in the deposited film increases before approaching saturation. The WNx films formed at high working pressure (≈5 × 10−2 torr) consist of W, WN or W2N phases depending on the nitrogen partial pressure ratio. Whereas the films formed at low working pressure (≈ 3 × 10−3 torr) are usually amorphous. Annealing in a flowing N2 gas causes the crystallization of the amorphous films, which mainly consist of W+W2N. There is no change for the crystalline films. However, annealing in H2 gas causes severe loss of nitrogen of the film, the film becoming single W phase eventually.

Superconducting InGaAs junction field-effect transistors with Nb electrodes

We describe the design, fabrication, and characterization of superconducting In0.47Ga0.53As junction field-effect transistors (JFETs) with Nb source and drain electrodes. In0.47Ga0.53As has the advantage of combining large coherence length and high Schottky barrier transmission, making it a very attractive material on which to base superconducting FETs. At large voltages these devices behave as normal FETs in either enhancement or depletion modes, while at small voltages they act as Josephson junctions or super-Schottky diodes. Both normal and super- currents are controlled by the gate.

Deep level transient spectroscopy study of GaAs surface states treated with inorganic sulfides

Surface states of liquid-encapsulated Czochralski and molecular beam epitaxy grown n-type GaAs samples coated with Na2S and (NH4)2S films are studied with deep level transient spectroscopy measurements employing metal-insulator-semiconductor structures. Two deep levels at 0.58 and 1.15 eV below the conduction-band edge are found in the as-grown samples. The Ec−0.58 eV deep level is found to be greatly reduced after sulfide treatment, while the Ec−1.15 eV deep level remains with a very high density. The surface Fermi level is shifted deeper into the energy band gap toward the Ec−1.15 eV deep level after surface treatment. This new, deeper pinning position is believed to be the cause of the greatly enhanced photoluminescence intensity recently reported. This new pinning position is deeper than some of the recently reported sodium sulfide/GaAs results but consistent with the high Schottky barrier height, 1.15 eV measured for the gallium-rich GaAs surface.

Intermetallic contacts to gallium arsenide: Doping and alloying by limited solid-phase reactions

Further advances in the miniaturization and integration of GaAs-based electronic and photonic devices necessitate the development of low-resistance (ohmic) and rectifying (Schottky) contacts that are thermally stable and morphologically uniform. In principle, optimum stability and morphology can be achieved by codepositing intermetallic phases (e.g. NiGa, CoGa and AuGa2) that are known to be in thermodynamic equilibrium with GaAs at the relevant temperatures. Such an approach must, however, be combined with a mechanism by which the GaAs may be doped or alloyed to yield contacts with a range of electrical properties (e.g. low-barrier ohmic, tunneling ohmic or high-barrier Schottky contacts). In this paper, the fabrication of stable and uniform ohmic and Schottky contacts using limited reactions between GaAs and intermetallic phases that contain the doping (e.g. Ge or Si) or alloying (e.g. Al or In) element is described. The fact that these reactions are limited - involving only 5-10 nm of GaAs at the metallization/GaAs interface - makes TEM an essential tool for characterizing these contacts.

Ga0.4In0.6As/Al0.55In0.45As pseudomorphic modulation-doped field-effect transistors

High-performance pseudomorphic Ga 0.4 In 0.6 As/ Al 0.55 In 0.45 As modulation-doped field-effect transistors (MODFET's) grown by MBE on InP have been fabricated and characterized. DC transconductances as high as 271, 227, and 197 mS/mm were obtained at 300K for 1.6-µm and 2.9-µm gate-length enhancement-mode and 2-µm depletion-mode devices, respectively. An average electron velocity as high as 2.36 × 107cm/s has been inferred for the 1.6-µm devices, which is higher than previously reported values for 1-µm gate-length Ga 0.47 In 0.53 As/Al 0.48 In 0.52 As MODFET's. The higher bandgap Al 0.55 In 0.45 As pseudomorphic barrier also offers the advantages of a larger conduction-band discontinuity and a higher Schottky barrier height.

Al/Si(100) Schottky barrier formation using nozzle jet beam deposition

High Schottky barrier height of φb=0.77 eV for Al/n-Si was obtained by the nozzle jet beam deposition method in a conventional vacuum condition without post-annealing. Previously, this high barrier height was only observable in the vacuum cleaved or sputter-etched samples in an ultrahigh vacuum condition. The Schottky barrier height was reduced if a partially ionized jet beam with 0.1% ions was used in the deposition process and if a bias of ≥0.5 kV was applied to the substrate. The reduction of the Schottky barrier height is attributed to the surface damage caused by the energetic ion bombardment. It is shown that a high barrier height (≂0.8 eV) and a low leakage current were retained after a relatively low-temperature (≂450 °C) annealing process if the applied bias was ≤1 kV.

Evidence for the formation of polycrystalline silicon by argon implantation and its passivation by atomic hydrogen

Evidence is presented through electrical measurements for the presence of microcrystallites in the surface damage layer resulting from the implantation of 20 keV Ar at a moderate dose (1013 cm−2). Low-energy (0.4 keV) atomic hydrogen is found to passivate the polycrystalline grain boundaries resulting from the argon implant. Extremely high Schottky barrier heights on p-type Si, up to 0.88 eV, are also found to result from the implantation of both argon and atomic hydrogen.

Computer modeling and comparison of different rectifier (M-S, M-S-M, p-n-n+) diodes

A computer method is used to investigate the forward characteristics of high-barrier Schottky diodes with different back contacts. A discussion of rectifier-parameter optimization is presented, together with comparisons of different diode types, including p-n-n+diodes. The superiority, in certain voltage ranges, of the high-barrier Schottky diodes over p-n-n+diodes is demonstrated.

A High Schottky Barrier Contact of Metallic Amorphous Si-P on P-Type Si

ABSTRACTA high Schottky barrier contact is formed when amorphous Si-P solid solution film and p-type Si are brought into contact. Amorphous Si-P films were deposited by thermal decomposition of a Si2H6-PH3 mixture at 500°C. It was found that conductivity increases rapidly when PH3/Si2H6, is increased from 0.2 to 2. When PH3/i2H6 = 2, conductivity is 0.15 S/cm, and the dominant conduction mechanism is variable-range hopping. Barrier height of amorphous Si-P/p-type Si Schottky contact is estimated to be 0.8 – 0.85 V. This value exceeds the barrier height formed by any normal metal.