摘要:

In this work, the electrical influence of carbon onW/SiGeC-p/Si(100)-pSchottky diodes is investigated. Analyzed samples consist of fully strained SiGe and SiGeC layers grown by room temperature chemical vapor deposition, deep level transient spectroscopy, (DLTS),I–V,C–V,and secondary ion mass spectroscopy measurements have been carried out. These experiments have shown that carbon incorporation leads to a full depletion of the epitaxial layer. In order to explain this phenomenon, we propose two assumptions: (1) electrical compensation of the active dopant due to a bulk defect, (2) important charge trapping mechanism at the interfaces. Three groups of defects have been detected by DLTS. Their binding energies are respectively 0.21, 0.36 and 0.62 eV above the valence band. Considering the possible origin of these defects, the hypothesises proposed before are discussed.

ISSN:1071-1023    

DOI:10.1116/1.590229

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

We discuss a set of atomistic calculations of the structure of Si geometries with substitutional carbon atoms, involving the (100) surface or bulk features related to thin films grown in the (100) direction. We use both quantum mechanical density functional theory and empirical potential calculations at finite temperature and constant pressure to study the local structure, bonding characteristics and overall distribution of the carbon atoms in the host silicon lattice. These calculations reveal a strong nearest neighbor repulsion between substitutional carbon atoms, to the point where these atoms prefer to have fewer bonds than normally in order to avoid each other. This effect still holds for high temperatures and high carbon concentrations. As a result, bulk ordering of the type observed in Si–Ge alloys is unlikely to occur.

ISSN:1071-1023    

DOI:10.1116/1.590035

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

The electronic structure and bonding geometry of acetylene adsorbed at room temperature on Si(111)-7×7 is studied by a combination of synchrotron radiation x-ray photoemission spectroscopy and of near-edge x-ray absorption fine structure spectroscopy. Then the stability of the molecule, submitted to thermal annealings and to synchrotron white beam irradiation is examined. The possibility of using acetylene gas as a carbon source for the fabrication of silicon-carbon compounds (or for the formation of abrupt carbon/silicon interfaces) is discussed.

ISSN:1071-1023    

DOI:10.1116/1.590036

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

An experimental study of the infrared properties of pseudomorphically grownSi1−xGexquantum wells is presented. Undoped quantum wells grown by ultrahigh vacuum chemical vapor deposition are investigated by photoinduced absorption and emission spectroscopies. The 2 nm thickSi0.7Ge0.3quantum wells exhibit infrared absorption around 10 μm wavelength which is associated with bound-to-continuum intersubband transitions. We show that the study of photoinduced intersubband absorption gives valuable information on the dynamics of photocarriers. An average lifetime τ≈2.5 μs is deduced from the frequency dependence of the photoinduced infrared absorption. We show that the temperature dependence of the photoinduced absorption is governed by the thermal excitation of the carriers above the barriers. The infrared emission of the quantum wells is studied in a second part. In III–V quantum wells, intersubband transitions around 10 μm wavelength are clearly evidenced by room temperature infrared emission spectroscopy. In the case of Si-SiGe quantum wells, only blackbody and defect-related emissions have been observed in the mid-infrared spectral range. The vanishing room-temperature emission is correlated with the weak photoinduced room-temperature absorption.

ISSN:1071-1023    

DOI:10.1116/1.590037

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Studying the structural and photoluminescence properties of pseudomorphicSi1−yCyandSi1−x−yGexCymultiple quantum well (QW) structures on (001) Si substrates offer a quantitative characterization of the band gap and band offset shifts caused by C alloying fory<3%.The main features ofSi1−yCyalloys, which are a reduced lattice constant and a strong lowering of the conduction band energy, promise that C may serve as a counterpart to Ge in Si heteroepitaxy. The photoluminescent properties ofSi1−yCyand SiGeC QWs are comparable to SiGe. Novel pseudomorphicSi1−yCy/SiGecoupled QW structures andSi1−yCy/Gequantum dot structures result in a strong enhancement of the photoluminescent efficiency. The ternary SiGeC material system offers a higher degree of freedom in strain and band edge engineering of structures. We focus on our recent results onSi1−yCyand SiGeC QW layers embedded in Si concerning the growth by solid-source molecular beam epitaxy, structural properties, thermal stability, optical properties, and band offsets. The prospects of SiGeC alloys for realization of optoelectronic structures are discussed. First characteristics from 0.75μmp-channel modulation-doped field-effect transistor devices containing an active SiGeC layer demonstrate good electrical properties.

ISSN:1071-1023    

DOI:10.1116/1.590038

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Bright quantum confined luminescence due to band-to-band recombination can be obtained fromSi/SiO2superlattices. To further enhance their light emitting properties, we have studied the effect of placing them in a one-dimensional optical microcavity. TheSi/SiO2superlattices were grown on various substrates in a magnetron sputtering system. The effect of the additional optical confinement on the photoluminescence (PL) results in a pronounced modulation of the PL intensity with emission wavelength, as a consequence of the standing wave set up between the substrate and air interfaces. The modulation in the case of a quartz substrate is much weaker, because of the low reflectance(∼1%)between the superlattice and the quartz. For a Si substrate, absorption of light reduces the PL efficiency, but for an Al-coated glass substrate the PL intensity is twice that of the quartz substrate case. These results show that a suitably designed planar microcavity cannot only considerably increase the efficiency of luminescence inSi/SiO2superlattices but can also be used to decrease the bandwidth and selectively tune the peak wavelength.

ISSN:1071-1023    

DOI:10.1116/1.590299

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Efficient no-phonon (NP) luminescence was observed from a pair of pure-Ge/pure-Si on relaxedSi0.82Ge0.18which separately confines electrons and holes in neighboring quantum wells. Anomalous broadening of the photoluminescence linewidth from the wetting layer occurred at around critical Ge coverage of Ge island formation, indicating that the microscopic interface roughness becomes significant at the initial stage of the island formation. At around the critical coverage, the enhanced NP feature was clearly observed at 77 K owing to the realization of rigorous confinement potential for exciton localization.

ISSN:1071-1023    

DOI:10.1116/1.590039

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

We observe near band edge photoluminescence (PL) from pseudomorphicSi/Si1−yCymultiple quantum wells and thickSi1−yCyepilayers, which were grown by molecular beam epitaxy on Si substrates. Pieces of these structures were annealed at temperatures between 500 and 1000 °C to investigate their thermal stability. While annealing at 900 °C or more leads to a reduction of the amount of substitutionally incorporated carbon and to a quenching of the PL signal, annealing at temperatures between 500 and 700 °C results in increased PL intensities and reduced linewidths. Although no decrease in the carbon content is observed under these conditions, we also observe a blue shift of the PL lines after annealing. In addition, increasing the temperature, at which the PL is recorded, leads to a red shift of the lines. We show that these findings are consistent with a recombination model of excitons bound to alloy fluctuations and a homogenization of not statistically distributed carbon atoms upon annealing.

ISSN:1071-1023    

DOI:10.1116/1.590040

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

We have investigated Si-(0⩽x⩽0.13)and Ge-rich(0.90⩽x⩽1)Si1−xGexbulk crystals by photoluminescence and photoconductivity measurements. The small linewidths of the near band edge luminescence of less than 4 meV demonstrate the high quality of the crystals. Luminescence linewidth, line shape, and intensity ratios of transitions with and without phonon participation reveal a stronger influence of alloy effects on excitons on the Ge-rich side compared with the Si-rich side. Photoconductivity spectra of boron doped Si-rich and phosphorus doped Ge-richSi1−xGexcrystals show the influence of alloy composition and alloy fluctuations on the impurity levels. The shift of the photoconductivity spectra with increasing Si or Ge concentration indicates the change of the ground state energy of the impurity with changing alloy composition.

ISSN:1071-1023    

DOI:10.1116/1.590041

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

In the present work we report on the evolution of the electronic states as a function of Ge overlayer thickness ranging from a fraction of a monolayer to few tens of monolayers. The Ge states above the Si valence band top could be clearly detected at every overlayer thicknessd.Ford∼6 Å,i.e., at the critical thickness for the transition from strained to unstrained overlayers. For these larger thicknesses, the Ge edge becomes broad and featureless. The energy separation between the Ge onset and the Si valence top increases up to 0.70 eV at larger overlayer thicknesses.

ISSN:1071-1023    

DOI:10.1116/1.590042

出版商:American Vacuum Society    

年代:1998

数据来源: AIP