摘要:

A position controlled or density controlled GaAs microcrystal growth from Ga droplets was attempted using a low energy focused ion beam system. Ga ions from a liquid Ga ion source were accelerated up to 10 kV to produce a focused ion beam. Subsequently the ions were given a positive bias to reduce their kinetic energy by a four-element retarding lens system. The Ga ions with a 30 eV kinetic energy softly landed on a S-terminated GaAs surface and formed a series of Ga droplets or Ga droplets matrix. After initiating the As molecule supply, GaAs microcrystals were found to grow from these Ga droplets. The low energy focused ion beam was also applied to create nucleation sites of Ga droplets on an As-terminated Si (001) surface at 100 eV. Ga droplets with high density were formed on a region where As atoms were removed partially on the Si surface. From these results, the low energy focused ion beam was found useful for position control or density control of GaAs microcrystals on semiconductor materials.

ISSN:1071-1023    

DOI:10.1116/1.590205

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Novel structures, in which an AlGaAs/GaAs modulation doped structure is overgrown on an underlying Be-implantedp-type region, are successfully fabricated using a system in which focused-ion-beam (FIB) implantation and molecular-beam epitaxy chambers are connected through a high vacuum tunnel. The two-dimensional electron gas (2DEG) at the heterointerface is well controlled by a voltage applied to the Be-FIB written backgate. Though Be out diffusion into the overgrown layer is observed, the sharp front of the out diffusion enables us to fabricate devices with a small separation between the 2DEG andp-type backgate. The three-dimensional hole gas (3DHG) formed by the Be-FIB implantation is used not only as a backgate but also for measuring the interaction between 2DEG and 3DHG.

ISSN:1071-1023    

DOI:10.1116/1.590206

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

We report on the fabrication ofn-AlGaAs/GaAs constricted-channel field-effect transistor (FET) structures by focused ion beam (FIB) implantation, and study transport properties of low-dimensional electrons via FIB induced localized states. In this work, quantum wire FET samples with in-plane gates and top gate were formed by using a focused Ga ion beam by which Ga ions of a high dose density(>1015cm−2)are introduced in the vicinity of a conductive channel at room temperature. The drain conductanceGdwas studied in constricted channels with various nominal widths,W.It is found thatGdof a narrow channel(W∼1 μm)becomes quite small and nonlinear at low temperatures. WhenGdis measured as a function of gate voltage,Vg,periodic oscillations are clearly observed at 15 K with a typical spacing ofVg∼60 mV,whereas the oscillation weakens and transforms to steplike structures at higher temperature (250 K). This oscillatory characteristic may possibly result from single electron transport through quantum dots associated with FIB-induced random potentials in the channel.

ISSN:1071-1023    

DOI:10.1116/1.590207

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Localized states in p-Si wires formed in n-Si(100) substrates by selective ion implantation using a focusedGa+ion beam have been investigated. The electrical conductance has the temperature dependence of one-dimensional (1D) variable-range-hopping conduction in the temperature range below 50 K,σ=σ0 exp[−(T0/T)1/2].The magnetoresistanceR(H)of p-Si wires at 4.2 K shows the negative and positive magnetoresistances at weak and strong magnetic fields, which have the relation thatR(H)/R0 ∝exp(−βH)andR(H)/R0 ∝exp(αH2),respectively, whereR0is the resistance without the magnetic fieldH.These characteristics can be explained by the 1D hopping conduction mechanism under the magnetic field. By expanding a three-dimensional model, we derive an equation of positive magnetoresistance in 1D hopping conduction. From the temperature dependence of conductance and positive magnetoresistance, the localization length, hopping distance, and density of localized states are estimated to be about 2 nm, 8–9 nm and about109cm−1 eV−1,respectively. This result indicates that the carrier transport is confined with the region of a few tens of nanometers.

ISSN:1071-1023    

DOI:10.1116/1.590208

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

An experimental instrument was made for the end-point detection of a deep small hole milled in large scale integrated circuit using focused ion beam (FIB). The SCANIIR method using photon-counting technique is adopted for detecting a very weak photoemission. The objective lens and imaging lens made by a quartz single lens are arranged in a parallel beam configuration. Observing optics,XYstage andZcontrolling mechanism for the optics are also used. To avoid the noise from the wall of the hole, a blanking circuit for detected signals was used. Experiments using a wide angle objective optical system showed an aluminum layer lower than 10 μm and theSiO2layer below were able to be clearly discriminated.

ISSN:1071-1023    

DOI:10.1116/1.590209

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Focused ion beam implantation is a powerful technology for the fabrication of opto- and microelectronic devices. Optoelectronic devices like gain coupled distributed feedback lasers and nonabsorbing waveguides can be defined in semiconductor heterostructures by the band gap shift due to highly spatially resolved implantation induced thermal intermixing. Single mode emitting devices were fabricated with emission wavelengths of 1 and 1.55μm in the material systems GaInAs/(Al)GaAs and GaInAsP/InP, respectively. Band gap shifts of more than 65 meV could be reached in GaInAsP quantum film structures which simplifies the integration of nonabsorbing waveguide sections with, e.g., lasers, modulators, and detectors. In highly doped semiconductor layers semi-insulating areas could be defined by focused ion implantation. Depletion lengths down to 50 nm can be controlled and were demonstrated on current injection restricted resonant tunneling devices. By using this technique collector-up heterobipolar transistors were fabricated which exhibit current amplification factors up to 45.

ISSN:1071-1023    

DOI:10.1116/1.590210

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

With a 100 nm focus of a focusedGa+ion beam with 100 keV, we write insulating lines in electronic layers ofIn0.21Ga0.79Asquantum wells. In this way, in-plane-gate (IPG) transistors are formed which can be operated at room temperature. In a typical integration application of a common source circuit, the pull-up resistance represents a serious problem due to the high geometric aspect ratio necessary for it. For example, the typical specific sheet resistivity of theIn0.19Ga0.79Asquantum well of 1.2 kΩ needs to be increased to 100 kΩ by a 1 μm wide, about 83 μm long channel. In order to save this waste of area we introduce active loads in the form of a narrow channel. In this way, the pull-up resistor requires orders of magnitude less area and stabilizes the drain current due to velocity saturation, leading to lower supply voltages. Inverters in this technology are presented and characterized. In finite element simulations these circuits are further investigated. The operation of these systems is based on the lateral depletion of adjacent quantum well areas. The basic differences between depletion withinpnhalf spaces andpnhalf planes are discussed analytically, showing a marked dependence on dimensionality. In particular, it is shown that the ruggedness of IPGs can be explained by these phenomena.

ISSN:1071-1023    

DOI:10.1116/1.590211

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

The profile of an ion beam line exposure ofGa+ions into GaAs(100) was characterizedin situusing scanning probe microscopy. Current imaging tunneling spectroscopy was used to characterize the surface defects induced by the high-energyGa+ions. Spatially reproducible features, approximately one per ion and 2–3 nm in diameter, were observed on the irradiated surface. Differential conductance spectra of these features indicated that the image contrast was due to acceptor states induced in the surface band gap. The density of these defects was used to form a profile of the ion beam in the semiconductor surface. The resulting profile was in excellent agreement with the two-Gaussian fit reported in previous work.

ISSN:1071-1023    

DOI:10.1116/1.590212

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Cobalt disilicide layers were formed by cobalt focused ion beam implantation into silicon. It was found that theCoSi2layer formation strongly depends on the pixel dwell time. In order to obtain continuous layers, short dwell times of a few μs are needed. Rutherford backscattering and channeling measurements were carried out to understand this effect. The results suggest that the accumulated irradiation damage is larger for longer dwell times. The sputtering yield of cobalt ions was measured and the formation ofCoSi2in noncrystalline silicon investigated.

ISSN:1071-1023    

DOI:10.1116/1.590154

出版商:American Vacuum Society    

年代:1998

数据来源: AIP