摘要:

Though no boron signal is identified, with respect to their boron content the narrow and broad components of the electron spin resonance signal in boron doped polycrystalline film decrease from 1018to 1016cm−3. This is ascribed to two different structural defects with concentration decreasing with the boron content, in agreement with theoretical predictions. Finally, we suggest a spatial location for these defects. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115605

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We found that the use of relatively low temperatures during oxide desorption in organometallic vapor‐phase epitaxy of GaAs reduced the epilayer–substrate interface charge. No differences in Hall mobility were found between the samples grown with 550 and 650 °C desorption. O, C, Si, and S were the dominant impurities at the interface. Si and S, which are shallow donors, induce the interface‐charge accumulation. Low‐temperature desorption leaves oxygen at the surface, suppressing the activation of shallow dopants. A high level (≳1×1012/cm2) of Cl was detected on every GaAs substrate we measured, but its effect on epitaxy is not clear. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115606

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The observation of red‐, near‐infrared, and nonphotoluminescent porous silicon structures both by transmission electron microscopy as well as by atomic force microscopy provides a consistent structural picture of the species responsible for the visible luminescence observed in these samples. The topography of the tops are seen in detail by atomic force microscopy, while the valleys are better observed by transmission electron microscopy; the observation techniques are therefore complementary. By measuring the apex radius of curvature of the atomic force microscope tip, it is possible to determine the porous silicon particle size by simple geometrical arguments. For red‐photoluminescent porous silicon, the measured particle diameter using atomic force microscopy was 55 A˚ and the particle height 4 A˚. The corrected particle diameter of 17 A˚ is in close agreement with the 15 A˚ value measured by transmission electron microscopy. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115607

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We discuss the optical properties in thin quantum boxes based on a theoretical analysis that rigorously treats excitonic confinement effects in the intermediate regime between zero and two dimensions. Our theory can exactly analyze not only the excitonic ground state but also higher energy states, and thus can simulate whole absorption spectra near the band edge region. We also report novel exciton electro‐absorption effects found in the intermediate confinement regime. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115608

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have used the 830 nm, subpicosecond output of a mode‐locked Ti:sapphire laser, together with subpicosecond 3.55 &mgr;m pulses from a synchronously pumped optical parametric oscillator, to perform room‐temperature, time‐resolved, differential transmission measurements on a multiple quantum well structure with AlGaSb barriers and GaInSb/InAs superlattice wells. From these measurements, we have determined a Shockley–Read–Hall rate of 2.4×108s−1and an Auger coefficient of 7×10−27cm6/s. In addition, we estimate the carrier capture efficiency into the wells to be ∼52% and have demonstrated that carrier cooling, cross‐well transport, and capture are complete within ∼10 ps after excitation. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115609

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

During short‐pulse laser crystallization of amorphous silicon on quartz, surface roughening occurs via the freezing of capillary waves excited in the silicon melt. The velocity and viscous damping of these capillary waves is computed and discussed. Volume change of the silicon during solidification appears to drive liquid silicon toward the last areas of solidification. Film thickness variation observed by transmission electron microscopy and atomic force microscopy shows increased film thickness at grain boundaries, and vertices of single pulse irradiated films. This effect is most pronounced within a narrow laser fluence regime wherein large lateral grain growth occurs. For 100 nm thick amorphous silicon films on quartz, this regime extends from approximately 520 to 560 mJ/cm2; standard deviation roughness can be as large as 40 nm. These effects have important implications for large area thin film transistor manufacturing. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115610

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The preoxidation cleaning of silicon carbide surfaces (3C, 4H, 6H polytypes) by exposing them to ultraviolet radiation and oxygen is shown to produce a significant improvement in the electronic properties of SiC/SiO2interfaces. It is found that this treatment results in a removal of defect species, otherwise present at the SiC surface after thermal oxidation of SiC. Carbon clusters are proposed as the attacked species responsible for a substantial part of the SiC/SiO2interface states. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115611

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We investigate the &bgr;‐SiC(100)3×2 surface oxidation by core level and valence band photoemission spectroscopies using synchrotron radiation. Low molecular O2exposures on the (3×2) surface reconstruction leads to direct SiO2/&bgr;‐SiC(100)3×2 interface formation already at room temperature (RT). To our best knowledge, this is the first example of RT oxidation leading directly to dominant silicon dioxide growth by O2chemisorption only. The amount of SiO2is enhanced when the surface temperature is raised by few hundred degrees only (<500 °C) during O2exposures leading to ‘‘bulk oxide’’ formation already at small thicknesses. These findings are also relevant in low‐temperature semiconductor oxide processing. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115612

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Basal plane sapphire is a common substrate for the heteroepitaxy of GaN. This presents a challenge for fabrication of cleaved‐facet GaN lasers because the natural cleavage planes in (0001) &agr;‐Al2O3are not perpendicular to the wafer surface. This letter describes a method for achieving perpendicular cleaved facets through wafer fusion that can potentially be used to fabricate GaN based in‐plane lasers. We demonstrate successful fusion of GaN to InP without voids or oxide at the interface and fabricate optically flat cleaved GaN facets that are parallel to the crystallographic planes of the host InP.I–Vmeasurements have been performed across then‐N fused interface. These results show that the fused junction exhibits a barrier of several electron volts for electrons passing from the InP to the GaN and ohmic conduction of electrons moving in the opposite direction. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115613

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

By regarding intense electron beams (∼340 keV, ∼2 kA, ∼10 ns) of a single pulse mode as a magnetic field source, we observed diffusion velocities of self‐magnetic fields of the beams through a 1.5 mm thick wall of a sintered superconducting Bi(2223) tube. Contrary to our prediction, fields of about 900 G out of the self‐magnetic fields diffused through the wall with an average diffusion velocity of 4×104m/s, almost independently of the operation temperatures for the range fromTc(∼103 K) to 80 K. Such a slow, viscous diffusion process accounts for effective functioning of superconducting tubes as lenses (Supertrons) for the short electron beams. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115614

出版商:AIP    

年代:1996

数据来源: AIP