Ga Focused Ion Beam Implantation Research Articles

Synthesis of Diamond‐Like Carbon Films Deposited by the Ionization Vapor Method and Development of its Semiconductive Devices Fabricated by the Focused Ga Ion Beam Implantation

SUMMARYIn this study, we have attempted to synthesize the Gallium (Ga)‐implanted diamond‐like carbon (DLC) film for new functional devices as substituting Si‐based materials. Intrinsic‐DLC (i‐DLC) films (energy gap: 1.45 eV) were deposited by the ionization vapor method with applying the negative pulsed bias voltage (frequency: 2 kHz, duty ratio: 30%, peak voltage: 500 V) to SiO2 substrates. Ga atoms were implanted to i‐DLC films as accepters utilizing by focused ion beam irradiation system. The Raman scattering spectra of i‐DLC and Ga‐DLC films showed typical DLC characteristics which consisted of I(D) and I(G) peaks. In order to evaluate working function of the Ga‐DLC film, several electrode materials (Au, Pt, Cu, Al, and Sn) were deposited on the films. Current–voltage characteristics of Au and Pt electrodes on Ga‐DLC films showed Ohmic contacts, and Cu, Al, and Sn electrodes were Schottky contacts. These results suggested that a work function of the Ga‐DLC film was in the range of 4.47 eV to 4.58 eV. To apply these contact properties to DLC semiconductive devices, we produced the DLC Schottky diode using Al and Pt electrodes deposited on the Ga‐DLC film. A current–voltage characteristic of DLC Schottky diode showed diode property in which amount of forward and backward voltage were 7.0 V and 17.0 V, respectively. The ideality factor n of produced diode was 11.3.

イオン化蒸着法によるダイヤモンド状炭素の成膜と集束イオンビームによるデバイスの作製

イオン化蒸着法によるダイヤモンド状炭素の成膜と集束イオンビームによるデバイスの作製

Site-selective growth of self-assembled InAs quantum dots on focused ion beam patterned GaAs

A site-selective growth of self-organized InAs quantum dots (QDs) employing a combination of in-situ focused ion beam (FIB) implantation and self-organized molecular beam epitaxy (MBE) growth has been successfully demonstrated. First, a buffer layer of GaAs was grown by MBE before a square lattice of shallow holes with a pitch of 1–2 μm was fabricated by FIB implantation of Ga and In ions. Before InAs deposition, different procedures to remove the implantation damage were tested. The best results were obtained after re-evaporation of 3–5 nm GaAs. Another critical parameter that was carefully optimized is the deposited InAs amount. For the optimized process it was possible to induce growth of single QD in the hole with more than 50% probability. Between the shallow holes of 2 nm depths, no QD growth was observed. The optical quality of positioned dots was investigated by photoluminescence spectroscopy, employing a separate sample where the QDs were overgrown by GaAs cap layer. Excited-state interband transitions up to n=5 were observed from positioned QDs.

Nanostructure fabrication and the science using focused ion beams

We describe the fabrication of nanostructures and the physics of the devices formed in InGaAs-based modulation doped heterostructures using Ga focused ion beam implantation. The two-dimensional electron gas in this heterostructure has a high electron density, a small effective mass, and a high mobility at high temperature, all of which are advantageous for low-dimensional quantum devices and ballistic devices. Ballistic transport at high temperature, quantized conductance with a large spacing of one-dimensional subbands, and a single electron transistor action with nonperiodic Coulomb oscillations are demonstrated.

AlGaAs/InGaAs/GaAs single electron transistors fabricated by Ga focused ion beam implantation

Single electron transistors are formed in an AlGaAs/InGaAs/GaAs modulation-doped heterostructure by Ga focused ion beam implantation. The AlGaAs/InGaAs/GaAs system has a high two-dimensional electron gas density and facilitates a lateral constriction whose depletion length is much smaller than that in a conventional AlGaAs/GaAs system. A dot structure confined by a small depletion spreading of less than 0.15 μm is formed by the ion implantation. This ion implantation is also employed to form in-plane gates for controlling the tunneling junctions between the dot and reservoirs, and the number of electrons in the dot. Coulomb oscillations and a Coulomb staircase have been clearly observed by controlling three in-plane gates.

Improved quantification in secondary-ion mass spectrometry detecting MCs+ molecular ions

Molecular secondary ions composed of a sample atom M and a resputtered Cs+ projectile (MCs+) are successfully used for the quantification of secondary-ion mass spectrometry (SIMS) data. For a variety of different specimens it is demonstrated that the yields of these rather ubiquitous species exhibit little or no dependence on sample composition (matrix effect) even in the presence of electronegative elements and are thus well suited for quantitative SIMS evaluation. Specifically, for series of binary and ternary systems (a-Si:H, a-SiGe:H, a-SiC:H, and HCN) composition independent relative sensitivity factors could be established; thus, quantification by means of a single standard is feasible. Furthermore, from the correlation of the measured MCs+ secondary ion intensities relative sensitivity factors (and hence concentrations) can directly be derived, i.e., without any standard. The applicability of this quantification scheme is exemplified for a AlGaAs/GaAs multilayer structure and for the Ga focused ion beam implantation in InP. The results indicate that utilizing MCs+ molecular ions an accurate quantification of major components by SIMS is possible.

Deep level transient spectroscopy on focused ion beam written in-plane capacitances

We discuss defects created by focused Ga ion beam implantation in GaAs or AlGaAs/GaAs heterostructures using deep level transient spectroscopy (DLTS). A novel contact configuration which is sensitive to defects located at the boundary between implanted and unperturbed regions at a well-defined depth is presented. The DLTS spectra for these samples are dominated by a peak with an activation energy of Ea=0.38 eV. The results show that this peak is associated with implantation-induced damage independent of the ion species. The defect is also found in a sample with Schottky contacts on top of a Ga-implanted GaAs layer.

Electrical properties of Si p/sup +/-n junctions for sub-0.25 mu m CMOS fabricated by Ga FIB implantation

p/sup +/-n junction diodes for sub-0.25- mu m CMOS circuits were fabricated using focused ion beam (FIB) Ga implantation into n-Si

Anisotropic electron transport through a rectangular antidot lattice

Rectangular antidot lattices are prepared by Ga focused ion beam implantation with lateral periodicities in the range of 0.1–2.0 microm. For current flow along the long periodicity of the antidot lattice the carrier density determined from the slope of the classical Hall resistance ϱ xy is 30% larger than the carrier density deduced from the minima of the magnetoresistance oscillations. Furthermore the Hall plateaus are shifted to the low field side of the extrapolation of the classical Hall resistance. For current flow along the short periodicity a dramatic negative magnetoresistance is observed similar to a square antidot lattice. We conclude that the transport properties of the rectangular antidot lattices are dominated by the strongly modulated charge distribution in these systems.

InGaAsP/InP quantum wires fabricated by focused Ga ion beam implantation

InGaAsP/InP quantum-wire structures are fabricated by focused Ga ion beam implantation onto InGaAs/InP single quantum well (QW) structures. It is found that InGaAsP layers produced by the intermixing of InGaAs/InP QW's by Ga ion implantation and subsequent thermal annealing are nearly lattice matched to the InP substrate. Fabricated quantum-wire structures exhibit photoluminescence spectra showing a large blue shift, which is induced by the carrier confinement into wire structures and the change of well composition.

Creation of 3D Patterns in Si by Focused Ga-Ion Beam and Anisotropic Wet Chemical Etching

ABSTRACTWe report the realization of free standing 3D structures as tall as ∼ 7μm with nano-scale thickness in Si using the technique of Ga focused ion beam implantation and sputtering followed by wet chemical etching. Some of the previously investigated subjects such as anisotropie etching behavior of crystalline Si and etch stop effect of Ga+implanted Si etched in certain anisotropie chemical etchants have been further explored with the emphasis on exploiting them in realizing free standing structures. The design and fabrication considerations in achieving such free standing structures are discussed and some typical structures fabricated by this technique are shown.

Resonant tunneling through one-dimensional states constricted by Al xGa 1−xAs/GaAs/Al xGa 1−xAs heterojunctions and high-resistance regions induced by focused Ga ion beam implantation

Resonant tunneling characteristics originating from subband mixing at the emitter-barrier interface were studied in double-barrier diodes with a restricted lateral dimension. The current vs. voltage characteristics exhibited a series of peaks spaced by the voltages corresponding to subband splittings in the double-barrier region when a large number of emitter subbands contributed to the tunneling current. These characteristics exhibited peaks spaced by approximately twice the voltages corresponding to the subband splittings in the double-barrier region when the laterally confined lowest emitter subband mainly contributed to the tunneling current. These differences were well explained by the calculation of tunneling of electrons from two-dimensional subbands in the emitter to one-dimensional subbands in the double-barrier region with subband mixing taken into account. Application of a magnetic field parallel to the tunneling direction also revealed the subband mixing effects on the tunneling current. The observed field dependence of the current peaks compared well to tunneling generated by mixing electromagnetic subbands at the emitter-barrier interface.

Si Nanostructure Fabrication by Ga+ FIB Selective Doping and Anisotropic Etching

ABSTRACTA novel fabrication technique involving the use of focused ion beam (FIB) selective implantation to fabricate nanostructures on crystalline Si substrates in conjunction with anisotropic etching is described. Using this maskless & resistless approach, Si nanostructures were fabricated by FIB implantation of Ga+ at doses from 1015 to 1016/cm 2. Wet etching in KOH/IPA does not attack the implanted region, while it removes the underlying Si anisotropically, with a very low etch rate on the {111} planes. The result is a cantilever-like structure whose thickness is dependent on the implantation energy and dose. Pre-etching rapid thermal annealing at 600°C for 30 sec does not prevent structure fabrication and post-etching RTA does not affect the shape of the structures.

Magnetotransport through an antidot lattice in GaAs-AlxGa1-xAs heterostructures.

Regular two-dimensional arrays of antidots with periodicities in the range of 200--500 nm are prepared in GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterostructures by means of Ga-focused ion-beam implantation. Transport measurements at low magnetic fields reveal a strong negative magnetoresistance originating from the localization of the electrons in the potential valleys between antidots. The low-temperature mobilities of the carriers deduced from the B=0 resistance are in the range of 1000--30 000 ${\mathrm{cm}}^{2}$/V s. Under illumination mobility changes by more than a factor of 20 can be achieved. For high magnetic fields well-defined Shubnikov--de Haas oscillations and quantum Hall plateaus are observed. Close to B=0 a very small structure in the magnetoresistance occurs reflecting the commensurability of the cyclotron diameter and the periodicity of the antidot array.

Resonant tunneling through one- and zero-dimensional states constricted by AlxGa1-xAs/GaAs/AlxGa1-xAs heterojunctions and high-resistance regions induced by focused Ga ion-beam implanation.

Lateral dimensions of ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/GaAs double-barrier diodes were restricted by use of focused Ga ion-beam implantation. The diode with a restricted lateral dimension exhibited a series of resonant-tunneling current peaks corresponding to the laterally confined one-dimensional levels superimposed on to the ground state confined by the heterojunctions. The resonant peaks were more pronounced in the diode with the smaller lateral dimension and consequently stronger lateral confinement. The spectral feature of the resonant peaks suggests mixing of even- (odd-) parity one-dimensional subbands in the double-barrier structure with two-dimensional subbands of the same parity in the contact. The diode with two restricted lateral dimensions also exhibited a series of resonant peaks corresponding to the laterally confined zero-dimensional levels.

GaAs/AlGaAs material modifications induced by focused Ga ion beam implantation

Two aspects of the material property modifications of the GaAs/AlGaAs system induced by Ga focused ion beam implantation have been studied. One is the formation of a highly resistive region in an n-type GaAs layer, and the other is the enhanced interdiffusion of GaAs/AlGaAs heterointerfaces. Both modifications enable us to change material properties with a minimum dimension of <100 nm. Quantum-well-wire structures were successfully fabricated by using the latter technique.

Defects induced by focused ion beam implantation in GaAs

The characteristics of defects induced by Si and Ga focused ion beam (FIB) implantation in n-GaAs have been investigated by means of deep-level transient spectroscopy (DLTS), C–V carrier profiling, and resistance measurements. The DLTS spectra of Si and Ga FIB implanted samples annealed at temperatures up to 500 °C are apparently identical to one another and show three different electron traps with an activation energy between 0.25 and 0.6 eV. The resistance increases by more than five orders of magnitude by Si and Ga FIB implantation due to the induced defects. However, it is restored to initial values after annealing at 600 °C, except for a sample of Ga implantation with a dose higher than 1014 /cm2 . For annealing of induced defects, there are no intrinsic problems for FIB implantation with a dose lower than 1013 /cm2 .

Formation of submicron isolation region in GaAs by Ga focused ion beam implantation

Highly resistive regions formed by Ga focused ion beam (FIB) were investigated. The submicron isolation region can be formed into n-GaAs layers by Ga FIB single line implantation with the conductive layer carrier concentration up to 1×1018 cm−3 and with the annealing temperature up to 900 °C. Using Ga FIB raster scanning implantation, the resistivity of the highly resistive region was evaluated to be more than 2×104 Ω cm for doses around 1×1014 cm−2. Exceeding this dose, n-type carrier generation was observed for S-doped layers, while p-type carrier generation was observed for Si-doped layers. No highly resistive region could be observed for p-GaAs layers. For conventional Ga unfocused ion beam (UIB), similar results were obtained.

Toward Realization of Quantum Well Wire Structures : Intermixing of Superlattice Structures by Focused Ga Ion Beam Implantation

Toward Realization of Quantum Well Wire Structures : Intermixing of Superlattice Structures by Focused Ga Ion Beam Implantation

VIA-5 planar-type GaAs avalanche photodetector fabricated by focused Ga ion-beam implantation

VIA-5 planar-type GaAs avalanche photodetector fabricated by focused Ga ion-beam implantation