摘要:

In a series of Al0.3Ga0.7As epitaxial layers with Si doping concentrations varied from 1×1017to 1.5×1018 cm−3, carrier concentration saturation effect was observed by Hall measurements. When Si doping concentration was increased, the carrier concentration tended to saturate. This is due to the negativeUproperty of the donor DX center. The Fermi energy tends to be pinned at the free energy level of the DX center. This carrier concentration saturation effect should not be limit to onlyn‐AlxGa1−xAs semiconductors. It is a general effect inn‐type compound semiconductors when donor impurities induce negativeUDX levels, and will have a great influence in designing optoelectronic and fast speed microelectronic devices. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113211

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Amorphous Si films deposited by the low pressure chemical vapor deposition from disilane, and subsequently subjected to a combined furnace annealing at 600 °C/12 h and a sequential excimer laser annealing, results to polycrystalline silicon films with very large grains, low in‐grain defect density, and smooth‐free surface. Large but heavily defected grains are produced by the furnace annealing, the in‐grain defects are mainly microtwins, which are eliminated by a combined liquid–solid state process induced by the laser annealing. The two‐step annealing provides a very high quality polycrystalline material suitable for thin‐film transistor application. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113212

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effects of rapid thermal annealing on the materials properties of the carbon‐doped AlxGa1−xAs system have been systematically studied. The hole concentration in GaAs and AlGaAs layers doped up to 1021cm−3drop severely after annealing for 5 min at temperatures above 650 °C. The decrease in hole concentration produces a minimum of 8×1019–1020cm−3free carriers. The hole concentration for heavily doped AlAs is relatively stable up to 950 °C in material withp∼1020cm−3. Unlike GaAs, AlAs with a low hole concentration but a substantially higher total carbon background, exhibits a substantial drop in activation for annealing temperatures above 650 °C. High resolution x‐ray diffraction studies show that the lattice parameter of both the AlAs and GaAs becomes less strained relative to the GaAs substrate as the annealing temperature is increased. In both materials, the changes observed with annealing are believed to be due to pairing of the carbon atoms on the As sublattice, resulting in a decrease in the electrically active carbon and the strain in the layer. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113213

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

By the application of disorder, an indirect–direct band gap transition can be achieved in a random superlattice composed of GaP and AlP monolayers. In all random models studied here, optical absorption intensities are found to be larger than that of the ordered ultrathin‐layer GaP/AlP superlattice. With increasing disorder, a considerable optical enhancement, which is about 44 times stronger than that of the ordered structure with equal composition, is obtained in a proposed random system. These properties suggest that the disordered superlattice offers great potential for application to optical devices. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113214

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Plasma dry etching, used for the fabrication of low‐dimensional structures, is known to create defects in the material which affect both the optical and the transport properties of the sample. We compare the results obtained from three different methods of characterizing the damage induced by electron cyclotron resonance metalorganic reactive ion etching to the two‐dimensional electron gas (2DEG) in GaAs/AlGaAs heterostructures: photoluminescence, transport measurements, and electron paramagnetic resonance. Etching impairs the quality of luminescence and decreases the single‐particle relaxation time, while the concentration of a surface related paramagnetic defect (probably dangling bonds) is increased. However, detailed experiments show no correlation between the density of defects and transport or luminescence properties, nor between transport and luminescence properties. In particular, hydrogen passivation, which improves the luminescence properties after etching, leads to deteriorated transport properties. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113215

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In GaAs/AlGaAs modulation‐doped heterostructure, adopting triangular quantum well approximation and including the seven major scattering mechanisms, we considered the existence of the DX centers in the AlxGa1−xAs barrier and calculated the dependence of low‐temperature two‐dimensional electron gas (2DEG) density and mobility on spacer layer thickness, Al composition and Si‐doping concentration of the AlxGa1−xAs barrier. The calculated results explained the experimental results that cannot be explained by the previous studies. Our calculations demonstrate that DX centers in the AlxGa1−xAs barrier play an important role in determining low‐temperature 2DEG density and mobility. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113216

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Isochronal annealing experiments on defects produced by 1.5 MeV electron irradiation at room temperature have been performed onn‐type SiGe alloys. Two defects have been studied, labeled P1 and P2, with associated energy levels located atEC−0.32 eV andEC−0.49 eV, respectively, and capture cross sections equal to 1×10−15cm2and 2×10−15cm2. P1 anneals out at 560 K and P2 at 470 K. A comparison with the defects known in Si and Ge allows us to propose the following identification: P1 is associated with the 0/− charge state of the divacancy (V–V)Siand P2 is associated with the 0/− charge state of theEcenter (P–VSi). ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113217

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Exsitunonalloyed ohmic contacts were made ton‐ andp‐type GaAs using low‐temperature molecular beam epitaxy. Forn‐type GaAs, Ag, and Ti/Au nonalloyed contacts displayed specific contact resistitivities of mid 10−7&OHgr; cm2. Forp‐type GaAs, nonalloyed Ti/Au contacts with specific contact resistivities of about 10−7&OHgr; cm2were obtained. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113218

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The diffusivity of phosphorus is measured in silicon with nearly uniform arsenic or boron background dopingno>(0.1<n/ni<30) at temperatures of 915, 1015, and 1105 °C. It is found that diffusion via neutral and single negatively charged point defects are sufficient to account for the experimental data, with no need to include diffusion via double negatively charged point defects. Greatly reduced diffusivity is observed in the boron‐doped samples, which is consistent with the formation of immobile donor–acceptor pairs. Activated diffusion and pairing coefficients are calculated based on this work and combined with experimental results previously reported in the literature. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113219

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Two integrated, thin‐film multiloop magnetometers (fractional turn SQUIDs) have been fabricated using a YBa2Cu3O7−x‐SrTiO3‐YBa2Cu3O7−xmultilayer process. The magnetometers have 16 parallel loops, an outer diameter of 7 mm and effective areas of 1.84 and 1.89 mm2, respectively. The magnetic field noise of the better device, measured in a YBCO tube at 77 K with a bias reversal scheme, was 37 fT Hz−1/2at 1 Hz and 18 fT Hz−1/2at 1 kHz. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.113220

出版商:AIP    

年代:1995

数据来源: AIP