摘要:

Monolayer coverages of C60on a gold substrate have been studied using scanning tunneling microscopy. The images reveal various packing arrangements and reproducible intramolecular contrasts of the C60molecules. We find thatapproximatelyeveryothercarbonatomis highlighted on the π‐electron surface of the molecule as a result of a preferential electron transfer from the gold substrate, in agreement with a theoretical analysis of the high‐lying π‐electron density of a C60molecule adsorbed on metallic surfaces.

ISSN:0734-211X    

DOI:10.1116/1.585719

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

High quality rapid thermal annealing of InP and GaAs at elevated temperatures was achieved in a load‐locked rapid‐thermal‐low‐pressure‐metalorganic‐chemical‐vapor deposition (RT‐LPMOCVD) reactor, under phosphorus and arsenic controlled ambient, using tertiarybutylphosphine (TBP) and tertiarybutylarsine (TBA) organometallic liquid sources. Damage‐free surfaces of InP and GaAs were obtained for temperatures up to 700 °C for InP under TBP ambient, or above 900 °C for GaAs under TBA ambient, respectively. Annealing the III–V substrates at low protective ambient pressure (50 mTorr) provided an excellent surface protection through the heating cycle without resulting in deposition of the group‐V elements on the surface and without reducing the efficiency of the process.

ISSN:0734-211X    

DOI:10.1116/1.585720

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A self‐consistent calculation of the energy levels ofn‐doped quantum wells (MQW) is reported. The eigenstates of the system are calculated from a four‐band k.p Hamiltonian. The Hartree and exchange–correlation components of the Coulomb interaction are included self‐consistently. The Hartree component is included by solving the Poisson equation; the exchange–correlation interaction is incorporated within the density–functional scheme. Also included are the vertex and depolarization effects which modify the intersubband transition energies. All of these many‐body corrections are shown to strongly influence the ground to excited state transition within the conduction band. Further, it is revealed that contrary to previous claims, the many‐body effects in these structures are insensitive to temperature. Consequently, such effects cannot account for the observed blue shift of the principal infrared peak as a function of decreasing temperature.

ISSN:0734-211X    

DOI:10.1116/1.585721

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The over‐passivations of sulfur treated GaAs were investigated by the photoluminescence measurement and device characteristics of AlGaAs/GaAs heterojunction bipolar transistors. The two chemical vapor deposition systems of the conventional plasma enhanced process and electron cyclotron resonance process were employed. The surface recombination current density calculated from the current gain and the base current noise was reduced to 25% by sulfur treatment and over‐passivation process using the electron cyclotron resonance deposition system, whereas over‐passivation by the plasma enhanced deposition system gave some damage to the sulfur treated surface.

ISSN:0734-211X    

DOI:10.1116/1.585722

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The application of ellipsometry in conjunction with step etching is demonstrated for determining compositional profiles of Hg1−xCdxTe heterostructures. Measurements of the ellipsometric ψ parameter can be directly correlated with composition,x, for 0.2

ISSN:0734-211X    

DOI:10.1116/1.585723

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Damage introduction into GaAs/AlGaAs high electron mobility transistor (HEMT) structures during either pattern transfer or gate mesa etching steps has been characterized. For O2reactive ion etching of the polydimethylglutarimide (PMGI) planarizing layer in a trilevel resist mask, the threshold dc bias for observable damage introduction in the AlGaAs donor layer is ∼200 V. This threshold bias for damage is a function of the PMGI overetch time and for extended times (>10 min), a decrease in saturated drain‐source current (IDSS) of the HEMTs can be detected for oxygen ions accelerated through a bias of ∼150 V. The use of combined electron cyclotron resonance (ECR)/radio frequency (rf) O2discharges enhances the PMGI etch rate without creating additional damage to the device, and 0.25‐μm gate widths have been demonstrated. Gate mesa formation by etching the GaAs cap with CCl2F2/O2or CH4/H2/Ar discharges is shown to produce damage in the underlying AlGaAs at dc negative biases of 125–150 V. In addition, substantial hydrogen passivation of the Si dopants occurs for the latter mixture. Recovery of the initial carrier concentration in the damaged HEMT occurs around 400 °C, provided the maximum dc biases were kept to ≤400 V during the dry etch step. Finally, changes in the surface chemistry of the exposed AlGaAs after various post‐RIE processing steps have been monitored by x‐ray photoelectron spectroscopy. Complete removal of AlF3was obtained only after careful H2O and NH4OH: H2O rinsing, while chlorides are removed by H2O alone.

ISSN:0734-211X    

DOI:10.1116/1.585724

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Reactive ion etching of III–V heterostructures was monitored using laser interferometry at 632.8 nm and optical emission spectroscopy (OES) between 200 and 800 nm, simultaneously. Three standard plasma chemistries were investigated: (i) CCl2F2/He for the selective etching of GaAs on AlGaAs, (ii) SiCl4/He for the nonselective etching of GaAs/AlGaAs heterostructures, and (iii) CH4/H2for the etching of In‐based III–V compounds. Laser interferometry provided local monitoring of etch rate, independent of etch chemistry. During GaAs and AlGaAs etching, optical emission from etch products was detected, identified, and selected to monitor etching. Using AlCl emission line at 261.4 nm, accurate etch monitoring of GaAs/AlGaAs heterostructures in SiCl4‐based plasma was demonstrated. The high resolution capacity of OES thereby allowed the discrimination of AlGaAs layers as thin as 5 nm. Accurate etch monitoring of InP/In0.53GaAs heterostructures in CH4/H2plasma was also demonstrated using the In atomic emission line at 325.6 nm: detection of In0.53GaAs layers as thin as 3 nm was possible. The combination of laser interferometry and OES was shown to be a suitable tool for III–V device etching.

ISSN:0734-211X    

DOI:10.1116/1.585681

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Silicon etching using ClF3gas has been carried out at various substrate temperatures from −20 to 120 °C. The etching properties (etch rate, pressure effect, and surface morphology) depend remarkably on the temperature. Based on the mass spectroscopic measurements, SiF4is specified as a main product. The minor product SiF2is also found, and the ratio of the signal intensity of SiF2to that of SiF4decreases with temperature. From Auger electron analyses on the etched surface, the density of fluorine atoms on the surface decreases with increasing the temperature. It is concluded that the density of the fluorosilyl species greatly influences the etching reaction process.

ISSN:0734-211X    

DOI:10.1116/1.585682

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The effects of oxygen addition on the synchrotron radiation‐excited etching of crystal Si, poly‐Si, and SiO2using SF6reaction gas are investigated. Without oxygen, two phenomenologically classified reaction mechanisms are observed: gas phase and surface excitation mechanisms. With oxygen addition, the gas phase excitation mechanism disappears and only the surface excitation mechanism becomes dominant. Oxygen addition is extremely effective in the microfabrication of SiO2line and space patterns using poly‐Si as an etching mask. Its addition creates high selectivity between SiO2and crystal Si. Furthermore, it is considered that the added oxygen removes some etching suppressing species generated on the poly‐Si surface.

ISSN:0734-211X    

DOI:10.1116/1.585683

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The interaction between ion beam and polyamidoimide (PAI) is studied by means of low‐temperature infrared spectroscopy. 200 keV Ar+and 250 keV He+beams with fluences ranging from 1013ions cm−2to 5×1016ions cm−2are found to induce atomic bond breaks leading to absorption bands at 2344, 2261, and 2125 cm−1corresponding respectively to CO2, C=N=N and C=N–R vibrations. Shrinkage of the polymer along with a drastic decrease of the resistivity during Ar+and He+irradiation are observed. Speculations on the respective role of electronic processes and atomic collisions in the evolution of the polymer are made. No evidence of PAI modification through knock‐on mechanism for fluences lower than 5×1015ions cm−2is noticed. In fact, our results would suggest a predominant role of the electronic processes for the low fluences (up to 5×1015ions cm−2), whereas a degradation mechanism based on atomic collisions is more likely to take place for higher fluences. A theoretical mechanism of reactions based upon our Fourier transform infrared (FTIR) and secondary ion mass spectroscopies (SIMS) results, describing the chemical changes occurring in the PAI, is presented and briefly discussed.

ISSN:0734-211X    

DOI:10.1116/1.585684

出版商:American Vacuum Society    

年代:1991

数据来源: AIP