摘要:

We propose a process for fabricating one-dimensional Si nanowires with a point contact. The nanowire structure can be easily obtained through two steps: KOH etching of a {110} Si layer of a silicon on insulator substrate and sufficient oxidation of the Si patterns formed by etching. In the etching process, vertical sidewalls comprised of {111} planes are formed into a wire. In addition, other {111} planes, projecting obliquely along the vertical sidewalls, spontaneously appear in the etched substrate. This is due to the fact that the etching proceeds as {111} planes appear because the etch rate of the {111} plane is the lowest of all planes. The bottom-corner region of two inclined {111} planes becomes a point-contact structure by making the distance between two inclined planes appropriate. The oxidation process converts the two-dimensional wire into one-dimensional nanowire by the stress-dependent oxidation phenomena of the Si wire. Consequently, a Si nanowire with a point contact can be formed in the bottom region. The Si nanowires fabricated through this process show clear conductance steps with little fluctuation on plateaus at 45 K. In addition, we discuss the conductance step characteristics in connection with a calculated energy level for a nanowire in (110) Si.

ISSN:1071-1023    

DOI:10.1116/1.589356

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Cyclotron resonance and photoluminescence measurements were carried out on two types of modulation-doped field-effect transistor heterostructures whose channels were made of an InAs–GaAs short-period superlattice and of anInxGa1−xAsquantum well, respectively. From cyclotron resonance data a linear dependence of the channel electron effective mass on indium content was obtained for both series of samples. For a given mean value of the indium content in the channel, the effective mass is found to be systematically higher in samples where the channel is based on a short-period superlattice rather than on an alloy-based channel. This can be attributed to larger nonparabolic effects in the former. Calculations of nonparabolicity corrections are in agreement with these results. In our theoretical model, the energy of the electron and heavy hole levels were determined self-consistently.

ISSN:1071-1023    

DOI:10.1116/1.589357

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

High resolution photoluminescence (PL) measurements performed on several GaAs–AlAs quantum well structures revealed sharp excitonic transitions separated in energies corresponding to roughly half-monolayer fluctuations in well size. The narrow linewidths correlate with interface island structure whose lateral extent is either much larger or much smaller than the exciton diameter. The half-monolayer separation results from a sharply peaked PL intensity response occurring around those areas of the laterally nonuniform interface which have roughly 50% island coverage, with the average island size much smaller than the exciton diameter, about 225 Å.

ISSN:1071-1023    

DOI:10.1116/1.589358

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Epitaxial layers of InP and InGaAsP have been grown on (100) InP substrates by gas source molecular beam epitaxy over the temperature range 400–480 °C while simultaneously exposed to an Ar plasma stream produced by electron cyclotron resonance (ECR). Transmission electron microscopy, x-ray diffraction, and photoluminescence studies indicate improved structural and optical properties of the InGaAsP layers as compared to layers grown by conventional epitaxy without plasma. This improvement is attributed to a reduction in lateral composition modulation (LCM), which develops at the surface during growth due to the existence of a miscibility gap. Comparison of these results with that achieved by an independent thermal hydrogen cracker suggests that the reduced LCM results from molecular hydrogen, produced from the cracking of the group V hydride sources, backflowing into the ECR chamber and resulting in a flux of atomic hydrogen toward the growth front. Atomic hydrogen exposure of the growing surface may then result in surfactant-mediated epitaxy, thereby, reducing the adatom surface diffusion length and, hence, the LCM. Atomic hydrogen, therefore, appears to be the sole actor in reducing the LCM, while the effects of the plasma itself are negligible.

ISSN:1071-1023    

DOI:10.1116/1.589359

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

In this work, we present a correlation between the morphological characterization ofInyAl1−yAs/InxGa1−xAsheterostructures grown on InP substrates for high electron mobility transistors (HEMTs) applications as determined by transmission electron microscopy, and the electrical behavior of the two-dimensional electron gas (2DEG) confined in the InGaAs channel. Our main goal is to analyze the origin of the low and anisotropic values of 2DEG Hall mobilities, discussing the effect of the density and asymmetric distribution of stacking faults and the surface undulation induced by a three-dimensional (3D) growth mode, depending on the growth temperature(Tg)and thickness(tw)of theInxGa1−xAswell. Our results have shown that a high mobility for a matched channel is obtained if theIn0.53Ga0.47Aslayer is grown at 530 °C. Lower temperatures reduce the mobility values and lead to higher mobilities for [11̄0] due to the surface corrugation along [110]induced by lateral decomposition of the InGaAs at low growth temperatures. For HEMT structures with strainedIn0.75Ga0.25Aschannels grown at 530 °C, within the range of the well thickness considered (5–10 nm), Hall mobilities are also more influenced by the surface roughness than by fault distribution. However, in this case, the observed roughness is not driven by alloy decomposition but by a strain-induced 3D growth mode.

ISSN:1071-1023    

DOI:10.1116/1.589360

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

A one-step electron-beam lithography process for fabrication of submicron air bridges is described. The fabrication principle is based on differing sensitivities of three layers of resist. By modulating the exposure dose it is possible to develop through all layers, the top layers only, or the center layer only (tunnels). We have fabricated the gate structure for making a quantum ring of 1 μm diameter on GaAs material, with five separate Ti/Au Schottky gates around and in the center of the ring, including an air-bridge connection to the center gate.

ISSN:1071-1023    

DOI:10.1116/1.589361

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

High rate plasma etch processes for InP with smooth etched surfaces and highly anisotropic sidewall profiles were developed. ACH4:H2-based process using an electron cyclotron resonance (ECR) etcher and a reactive ion etcher (RIE) was investigated. Etch rates in excess of 120 nm/min in an ECR etcher usingCH4:H2:Arplasma and 135 nm/min in a RIE usingCH4:H2:O2were achieved in InP and produced minimal surface roughness. These etch rates are significantly faster than those previously reported.

ISSN:1071-1023    

DOI:10.1116/1.589362

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

The influence of the CH4-H2mixture composition on the etching process of InP is investigated by means of plasma diagnostics (optical emission spectroscopy and mass spectrometry) and quasiin situx-ray photoelectron spectroscopy (XPS) surface analysis. Increasing the mixture composition in methane increases the InP etch rate. For example, it rises from 230 to 380 Å/min when increasing the percentage in CH4from 2.5% to 75%. In pure methane discharge, at a pressure of 50 mTorr, amorphous carbon is deposited on InP. Quasiin situXPS reveals major changes in the surface chemistry. In particular P depletion decreases and the mean surface stoichiometry improves as the percentage of methane increases. The mass spectrometry PH3+signal(m/e=34 amu) corresponding to PH3molecules and the In*emission line(λ=451.1 nm), which are, respectively, characteristic signals of the individual removal rate of In and P, and the concentration of CH3radicals in the plasma as measured by the threshold ionization technique display good agreement with the etch rate and surface chemical modifications. These results confirm that the etching mechanism of InP is controlled by the etching mechanism of In, and that the latter is strongly correlated with the concentration of methane in the mixture. Variable photoelectron emission angle measurements are performed to determine precisely the location of the species in the damaged layer. A model for the representation of the surface in the process of etching is then proposed.

ISSN:1071-1023    

DOI:10.1116/1.589363

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Numerical simulations of charging and profile evolution during gate electrode overetching in high density plasmas have been performed to investigate the effect of long conductive sidewalls on profile distortion (notching). The results reveal that the angle of electron irradiance of the conductive portion of the sidewalls affects profoundly the charging potential of the gates. Larger angles, obtained for thinner masks and/or thicker polysilicon, result in reduced gate potentials which, through their influence on the local ion dynamics, cause more severe notching atalllines of the microstructure.

ISSN:1071-1023    

DOI:10.1116/1.589364

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Experimental studies of the deposition of films formed on the sidewalls of a photoresist pattern in the etching of platinum films with Ar and halogen mixed gas plasmas were performed. In platinum etching with Ar/halogen gas plasmas there is no enhancement of the etch rate by adding halogen gases, and deposition films are formed on the sidewall of a photoresist pattern. The thickness of the sidewall deposition film is minimized in etching with pure Ar plasma. The addition of halogens increases the thickness of the sidewall deposition film. These films were analyzed by x-ray photoelectron spectroscopy (XPS) to investigate their formation mechanism. Carbon was detected even in the deposition films formed during etching with gases that did not include carbon. From the results of XPS analysis it was found that the etching reaction products from the photoresist relate to the formation of these films, and that the reason for the increase in the film thickness is the increase in the etch rate of the photoresist by adding halogens. Therefore in the etching of platinum films it is important to suppress the etching of the photoresist to decrease the thickness of the sidewall deposition film.

ISSN:1071-1023    

DOI:10.1116/1.589519

出版商:American Vacuum Society    

年代:1997

数据来源: AIP