摘要:

A sacrificial Ti layer on electron‐beam deposited AuBe ohmic metallization top‐type GaAs is shown to prevent oxidation of Be that segregates to the surface of the AuBe during its deposition. In the absence of this Ti layer, the oxidation of the surface Be upon removal from the vacuum chamber creates a current blocking layer on the overlayer contact. For nonalloyed ohmic contacts top‐GaAs, Ti/Pt/Au metallization is found to be superior to Ti/Ag/Au because of its thermal stability and the fact that Au–Ag alloys have higher resistivities than either of the pure component metals. For the sputtered refractory metals, surface displacement damage to GaAs during sputter deposition of W or WSixcan be prevented by protecting the semiconductor with a thin (400 Å) Ti layer. This is particularly relevant for heterojunction bipolar transistors and other devices that cannot be annealed at the high temperatures (800 °C) needed to remove displacement damage.

ISSN:1071-1023    

DOI:10.1116/1.588368

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

The surface of GaAs (110) cleavage faces treated with (NH4)2Sxand SeS2solutions were studied by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) in air. Sulfur passivation using a (NH4)2Sxsolution removes the native oxide and leaves a thin unreactive sulfur layer, while selenium passivation using a SeS2solution neither removes the native oxide nor produces a selenium‐terminated surface. With sulfur passivation, an atomically flat surface of the GaAs (110) cleavage face was obtained in the STM image. The topographic contrast over thep‐njunction in the STM image obtained with sulfur passivation shows thenregion to be higher than thepregion, while there was no height difference seen in the AFM image.

ISSN:1071-1023    

DOI:10.1116/1.588369

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

We report the first time‐resolved luminescence measurements using the tunneling current of a scanning tunneling microscope for excitation with its high spatial resolution. This new technique enabled us to measure the minority‐carrier lifetime and the doping concentration in the intrinsic region of a specially tailoredn+‐n‐i‐n+‐GaAs homostructure. Further, we show that the minority‐carrier lifetime depends, as expected, strongly on surface recombination which demonstrates that this technique may be used to determine the local surface state density.

ISSN:1071-1023    

DOI:10.1116/1.588370

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

A single AlGaAs/GaAs quantum well (QW)/quantum wire (QWR) structure was grown by metalorganic vapor phase epitaxy on a submicron period grating of V grooves. High resolution transmission electron microscopy studies of the sample identifies three regions of the QW; between the grooves, approximately 3.5 nm thick and oriented along (100), on the sidewalls of the V groove slightly thinner and oriented along {111}. At the bottom of the groove an approximately 70 nm wide crescent shaped region forms a QWR. In addition, a vertical quantum well (VQW) extends from the bottom of each V groove in the GaAs substrate to the surface. The luminescence spectra of the sample are dominated by a peak originating in the QW, with additional peaks of the QWR, the VQW and the AlGaAs barrier. The striped nature of the sample is revealed in the top view cathodoluminescence (CL) images of all four peaks. In side view CL images, the QWR emission appears spot like, whereas the emission of the VQW is elongated in the direction perpendicular to the surface. Photoluminescence excitation spectroscopy reveals that the main source for excitation in the QWR comes from the VQW, even though a small contribution comes from the QW.

ISSN:1071-1023    

DOI:10.1116/1.588371

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

A high current density NbN/MgO/Nb superconducting tunnel junction has been modified using a focused ion beam to trim the junction area following fabrication and measurement. After milling, the exposed edge of the junction was cleaned of resputtered material using a low current ion beam combined with gas assisted etching. Some remaining shorts across the barrier were then removed by anodization. The modified junction showed a resistance increase correlating exactly with the decrease in area and very little change in quality. This technique may be used on fully fabricated circuits to trim accurately the resistance of selected junctions in order to overcome variations in barrier conductance and junction area.

ISSN:1071-1023    

DOI:10.1116/1.588372

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

A metrological study with a Leica Cambridge (microfabrication) MF 10 cs/120 electron‐beam (e‐beam) machine on metal structures in the nanometer region is presented. The nanometer region (below 100 nm) considered in this study is very challenging when an e‐beam machine is used in the metrological mode, because the feature sizes, in this work ranging between 60 and 170 nm, become comparable to the probe spot size. Thus, a more detailed analysis is necessary in order to extract metrological information properly. Electrons detected by an annular channel plate form the signal from which the metrological data are extracted. Based on this feature, two algorithms, one computational and the other graphical, are proposed and compared. A good agreement between e‐beam‐based and independent scanning electron microscope measurements is found. A statistical study shows an accurate reproducibility below 10 nm with high speed performances. Finally, dimensional control requirements are fulfilled, making the e‐beam machine one of the most reliable metrological tools for metal structures even in the nanometer region down to 60 nm.

ISSN:1071-1023    

DOI:10.1116/1.588373

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

Scanning tunneling microscopy (STM) has been used to obtain images and current–voltage (I–V) curves of carbon nanotubes produced by arc discharge of carbon electrodes. The STMI–Vcurves indicate that carbon nanotubes with diameters from 2.0 to 5.1 nm have a metallic density of states. Using STM, we also observe nanometer‐size graphene sheets which are four graphite layers thick. The STM images of carbon nanotubes are in good agreement with transmission electron microscope images.

ISSN:1071-1023    

DOI:10.1116/1.588374

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

A microprobe having an ultrasharp and high‐aspect‐ratio stylus was made using a directly bonded silicon‐on‐insulator (SOI) wafer. The stylus and cantilever were made of 8 μm‐thick (100)‐Si film and 2 μm‐thick dioxide film of the SOI wafer with sufficient reproducibility. The cantilever is 100 μm in length, 20 μm in width, and 1.6 μm in thickness; the stylus is 7 μm in height with an aspect ratio exceeding 2. The stylus was formed first by reactive ion etching and sharpened by orientation dependent etching with KOH solution. The apex of the stylus is 10 nm in radius of curvature. The present microprobe was found adequate for atomic force microscopy (AFM) measurement with spatial resolution better than 10 nm in noncontact‐mode topographic imaging. The mode of fabrication, mechanical properties of the microprobe, and results of AFM measurement are discussed.

ISSN:1071-1023    

DOI:10.1116/1.588375

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

We have used a Ga+focused ion beam (FIB) milling technique to produce sharp scanning‐probe microscope tips. The FIB procedure employs a roughly 0.2‐μm‐diam 20 keV Ga ion beam vector scanned in an annular pattern across the apex of an electrochemically etched wire. This method usually produces exceptionally sharp conical tips, but occasionally it generates a nearly cylindrical spike at the apex. In this paper, we show examples of the spikes, and we discuss possible mechanisms by which they are produced.

ISSN:1071-1023    

DOI:10.1116/1.588376

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

Overcoating Spindt‐type field‐emitter‐array cathodes with several monolayers of Ti, Zr, or Hf leads to a decrease in the voltage for the same emission current by 30 to 40%. This change is entirely ascribable to a 1 eV decrease in surface work function and an increase by a factor of 10 to 100 in the pre‐exponential term of the Fowler–Nordheim relation. The postdeposition current voltage characteristics have been observed to remain essentially unchanged for periods of greater than 100 hours at current levels of 10 μA/tip. Field‐emission micrographs indicate that the increase in pre‐exponential term cannot be attributed to an increase in the emitting area. A plausible explanation is that the electron supply function for these overcoatings is larger than that of the as‐fabricated emitter.

ISSN:1071-1023    

DOI:10.1116/1.588377

出版商:American Vacuum Society    

年代:1995

数据来源: AIP