摘要:

A previously reported ac magnetic‐field technique has here been applied to selective recrystallization on quartz substrates of polysilicon thin films which had been patterned into specific microblock designs. With the recrystallization it has been possible to produce single‐crystal silicon microblocks of a maximum size of approximately 60×40×2 &mgr;m,3large enough for the fabrication of high‐performance thin‐film transistors. Microblocks used in the experiments were of two types: ‘‘network’’ rectangles, connected on the wafer two dimensionally with polysilicon paths, and ‘‘isolated’’ rectangles adjacent to the network rectangles. The surface morphology of the recrystallized silicon films was observed with scanning electron microscopy. While no grain boundaries were found on the surfaces of the recrystallized network rectangles, many grain boundaries were observed to remain on the recrystallized isolated rectangles. X‐ray diffractions for the recrystallized network rectangles were measured with a microfocused x‐ray beam, and the recrystallized network rectangles were confirmed to be single‐crystal silicon microblocks of good crystal quality. It had been expected that network rectangles would be more greatly heated, as compared to isolated rectangles, by the eddy currents induced by the ac magnetic fields, and the observed higher quality of network‐rectangle recrystallization has verified that anticipated eddy‐current contribution.

ISSN:0021-8979    

DOI:10.1063/1.354307

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Liquid phase epitaxy of GaAs from Bi melt was studied for growth temperatures between 670–750○C. The layers were characterized by Van der Pauw and photoluminescence measurements. All epitaxial layers were n‐type and exhibit low compensation and electron mobilities up to 6×104cm2/V s at 77 K. A gradual increase in then‐type doping was observed with growth temperature. Intentional doping of GaAs with Sn leads to a Sn distribution coefficient ∼60 times larger for the Bi melt in comparison to the Ga melt. Extremely low compensation of the Sn‐doped layers (K≤0.1 forNd=2.5×1017cm−3) is obtained.

ISSN:0021-8979    

DOI:10.1063/1.354308

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Microstructure and texture of Cr thin films sputter deposited on NiP‐coated AlMg substrates were studied using transmission electron microscopy (TEM). The sample tilt method in TEM has proven to be very effective in determining the fiber axis of weakly textured films. It was found that both the grain size and texture of the Cr films are strongly dependent on their thickness and deposition conditions. For Cr films deposited on 300 °C preheated substrates, the grain size increases monotonically with the film thickness. The texture changes from no texture (∼100 A˚) to a [001] fiber texture (200–2000 A˚), and then to a [011] fiber texture (∼5000 A˚). A 2000‐A˚‐thick film deposited on a room‐temperature substrate shows a strong [011] texture and a smaller grain size than that of a film with the same thickness but deposited on a preheated substrate. Correlations between the in‐plane coercivity of Co‐based alloy thin films for longitudinal magnetic recording and the grain size and texture of Cr underlayers are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.354283

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We report on the gas source molecular beam epitaxy/migration enhanced epitaxy (MEE) growth of InAs/AlSb superlattices. The incorporation behavior of constituent group III and group V atoms during growth is investigated in detail using reflection high energy electron diffraction. In and Sb atoms are found to move towards the surface during MEE growth, although the movement of In atoms can be reduced by lowering the growth temperature. Raman scattering measurement of InAs/AlSb superlattices shows that the formation of atomically controlled heterointerfaces (InSb‐ or AlAs‐type interfaces in InAs/AlSb superlattices) is difficult. However, photoluminescence (PL) measurement shows that the optical properties of quantum well structures are strongly dependent on the shutter sequence at the interfaces. 77 K PL from InAs/AlSb quantum well structures with an InSb‐type interface shutter sequence is one order of magnitude stronger than that of the AlAs‐type interface.

ISSN:0021-8979    

DOI:10.1063/1.354284

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

GaN films were grown on thec‐plane of sapphire substrates by plasma‐enhanced molecular beam epitaxy equipped with an electron‐cyclotron resonance (ECR) source. Sapphire substrates were cleaned by a hydrogen plasma treatment, obviating the need for perilous elevated temperatures. ECR sources are plagued with high energetic ions, particularly at high microwave power levels, where they cause damage in the growing films. To circumvent this problem, we systematically optimized the growth conditions and other pertinent parameters for optimum layer quality. Among the parameters optimized were the magnetic field strength, microwave power, nitrogen over‐pressure, and growth temperature. The quality of the GaN layers were evaluated by electrical and structural measurements as well as observing the surface morphology.

ISSN:0021-8979    

DOI:10.1063/1.354285

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The valence and conduction band states of crystalline silicon nitride &agr;‐Si3N4have been studied by using two complementary experimental methods. The total valence band distribution has been analyzed by x‐ray induced photoelectron spectroscopy. The Si 3pvalence states and the Sipconduction states have been probed selectively by x‐ray emission and absorption spectroscopies, respectively. The experimental curves have been compared in the same energy scale referred to the Fermi level. Our results show clearly that the N 2p&pgr; states of Si3N4are located at the top of the valence band while Si 3pstates, mixed to N 2pstates and, respectively, to N 2sstates are located at aboutEF−8.4 eV andEF−19.6 eV. Our experimental results are in very good agreement with theoretical simulations of the spectra made from recent density of states calculations by Robertson [Philos. Mag. B63, 47 (1991)] in a tight binding approach.

ISSN:0021-8979    

DOI:10.1063/1.354286

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We report resonant Raman scattering (RRS) and ‘‘hot’’ exciton luminescence (HEL) from dry etched GaAs‐AlGaAs quantum dots in which quantum confinement effects have been found with decreasing dot sizes. Up to fourth‐order multiphonon processes have also been observed for the first time via photoluminescence and photoluminescence excitation in quantum dots. These results are direct evidence of the bottleneck effect. Hot carriers are maintained due to the slowed‐down electron‐phonon scattering in one‐ and zero‐dimensional semiconductors. The competition between resonant relaxation via LO phonons and sidewall nonradiative recombination results in stronger multiphonon processes with increasing quantum confinement. Furthermore, lateral patterning of quantum wells strongly localizes excitons in three‐dimensional quantum confinement regime. The observation of RRS and HEL up to high temperature demonstrates the high stability of localized excitons.

ISSN:0021-8979    

DOI:10.1063/1.354287

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We present a numerical study of the &Ggr;‐Xmixing in GaAs/AlAs/GaAs quantum well structures. A &Ggr;‐Xmixing model proposed by Liu [Appl. Phys. Lett.51, 1019 (1987)] is extended to include the effects of self‐consistency and nonzero transverse momentum. In the present model, the coupled Schro¨dinger equations for &Ggr; andXelectron envelope wave functions are solved self‐consistently with Poisson’s equation to calculate the electron transmission probability and wave functions, which lead to the current‐voltage (I‐V) characteristics of single barrier and double barrier resonant tunneling diode structures. The quantum transmitting boundary method is employed in the model for numerical solution of the coupled Schro¨dinger equations, which proves to be very stable and efficient, even for large (≳2000 A˚) structures. The features of &Ggr;‐Xmixing, such as the resonance/antiresonance in the transmission probability and the virtual bound states, are clearly demonstrated. Additional physical features are observed in the transmission probability and the wave functions under applied bias conditions. Our work shows that inclusion of transverse momentum, variable effective mass, and the self‐consistent potential is important in the realistic modeling ofI‐Vcharacteristics for structures exhibiting &Ggr;‐Xcoupling.

ISSN:0021-8979    

DOI:10.1063/1.354288

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The problem of combining different methods of deriving bounds on the conductivity of composite materials is addressed. We combine the translation method and the Hashin‐Shtrikman variational principle and apply the combined method to a composite where the two methods, separately, give bounds that partly improve on each other; an equiaxed polycrystal. As a result we get a lower bound which improves on all previously known bounds for this composite.

ISSN:0021-8979    

DOI:10.1063/1.354289

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Deep localized‐state distribution in amorphous arsenic triselenide thin films has been measured with a modulated photocurrent technique. A peak in the deep localized‐state distribution is found at 0.79 eV above the valence‐band mobility edge. It is also found that the thermal emission rate of holes from the localized state at the peak is almost constant in the room‐temperature range but exhibits thermally activated behavior below and above the room‐temperature range. This anomalous temperature dependence of the thermal emission rate is interpreted on the basis of a thermally created defect.

ISSN:0021-8979    

DOI:10.1063/1.354290

出版商:AIP    

年代:1993

数据来源: AIP