摘要:

Landau level formations have been observed in the photoluminescence spectra of highly optically populated InP strained self-organized quantum dots in between barriers ofIn0.5Ga0.5Pat a high magnetic field. The results clearly show the evolution of the discrete states caused by 3D confinement at 0 T into Landau level-like structures at 40.9 T. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120070

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The recently synthesized Engelhard titanosilicate (ETS-10) represents a material which contains in the structure well defined atomic &cellip;O–Ti–O–Ti–O&cellip; quantum wires embedded in a highly insulating siliceous matrix. We report and discuss the UV-Vis spectrum of this material and compare the experimentally determined optical band gap with the results predicted by simple modeling of a titanium oxide semiconductor wire unidimensionally confined by an infinite potential barrier. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120060

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of total deposition pressure on the structure of chemically vapor deposited polycrystalline-silicon films was examined over the pressure range from 10–600 Torr using thermal decomposition ofSiH4 in a hydrogen carrier gas in the 625–675 °C temperature range in a cold-wall, lamp-heated reactor. The temperature and deposition rate were kept constant for each set of experiments to isolate the effect of hydrogen on the surface diffusion of the silicon species. Both the amorphous-to-polycrystalline transition and the dominant crystal orientation depend on the total deposition pressure; however, the dependence is only moderate. Differences in gas purity and system integrity between different reactors also play a strong role in controlling the structure. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120061

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report a study of the dynamics of coherent island formation in InAs/GaAs films grown by molecular beam epitaxy. A comparison of the temperature dependence of the critical layer thickness for islanding between the migration-enhanced and the continuous growth modes confirms that surface adatom diffusion and indium desorption are the controlling processes which determine the variation of the measured critical layer thickness with temperature. We find that under conditions in which indium desorption is significant, the islanding transition is reversible, which provides a new way to study the dynamics of the islanding transition. Applying this technique, we find that the size distribution of the three-dimensional islands evolves into a bimodal distribution during the reverse process. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120062

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Effects of isolation materials on facet formation for low temperature Si selective epitaxial growth (SEG) usingSi2H6have been demonstrated by ultrahigh vacuum-chemical molecular epitaxy (UHV-CME) system. The activation energy of the Si epitaxial growth is 47.35 Kcal/mol. The isolation material includes silicon nitride, wet oxide, and tetraethylorthosilicate (TEOS) oxide. Different isolation materials have different faceting behaviors for the Si epilayer. A silicon nitride mask and a wet oxide mask result in a preferred faceting plane of (111) and (311), respectively. Using a TEOS oxide mask, we obtain a low temperature Si SEG layer without facet and twin formation. The preferred faceting plane orientation for different isolation materials is ascribed to the difference in the interface free energy between the Si layer and the isolation material. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120033

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report evidence of a large blue shift (up to 70 meV) in the photoluminescence spectra of InAs/InP island like quantum wells following the reduction of the InP top barrier layer thickness from 6 nm to near zero. The photoluminescence intensity only starts to decrease when the top barrier thickness falls below 1.5 nm, indicating that radiative recombinations in the islands are very efficient. These results are well understood by a model assuming a vacuum confinement energy close to 5 eV. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120022

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on the fabrication and characterization ofp-&pgr;-nGaN ultraviolet detectors. The peak responsivity at∼363  nmis measured to be 0.1 A/W in the photovoltaic mode, and 0.14 A/W with a bias of −15 V. Speed measurements have shown the photoresponse to be RC-limited with the response time decreasing from 17.4 ns at zero bias to 10.3 ns at −6 V bias. For a200×200 &mgr; m2device, we measure the dark current to be 2.7 pA at −3 V bias, and a noise density of less than10−25 A2/Hz, the noise floor of the measurement. Extrapolating the noise data taken at higher reverse biases, we estimate the noise equivalent power to be6.6×10−15 W/Hz1/2. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120023

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Field emission properties of diamond films were studied by macroscopicI–Vmeasurement. A lower turn-on field and a higher emission current were observed for diamond films produced by higher methane concentration, or with higher density of defects, introduced by ion implantation. However, diamond films of poorer quality experience a severe reliability problem. Cold implantation followed by rapid thermal or laser annealing produced diamond emitters with a turn-on field as low as 5 V/&mgr;m and the desired reliability. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120024

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A very small amount of pre-deposited C on a Si substrate causes island formation after epitaxial growth of less than 2 monolayers Ge. These C-induced Ge dots can be as small as 10 nm in lateral size and 1 nm in height. Their areal density is1011 cm−2. Intense photoluminescence signal from these small Ge quantum dots is observed reaching a maximum for 2.1±0.3 monolayers of Ge. In the initial stages of island formation, the optical transition of the wetting layer is blue-shifted by strain compensation effects. We propose spatially indirect mechanisms of radiative recombination between electrons confined in the underlying wetting layer and holes confined in the Ge islands. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120072

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report a combined &mgr;m-level topography and high-frequency magnetic field probe, a 6 &mgr;m loop defined on a scanning-force microscope cantilever. Since it functions as a near-zone antenna, it can be used with any suitable detector, and can probe both active and passive samples. We demonstrate its performance by scanning a coplanar waveguide sample at 10 GHz using a microwave network analyzer. With this instrument, the device noise at this frequency is∼2&mgr;&Fgr;0/Hz1/2atT=300 K, comparable to that found for a superconducting quantum interference device (SQUID) at DC. Unlike the SQUID, however, the thermally limited minimum-detectable field of this system scales with frequency. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120073

出版商:AIP    

年代:1997

数据来源: AIP