摘要:

We have carried out a detailed structural and optical characterization of Ga0.47In0.53As/InP multiple quantum wells grown by chemical beam epitaxy using a well‐defined sequence of growth interruption times between successive layers. These growth interruption times result in the formation of interfacial layers which drastically alter the structural properties of Ga0.47In0.53As/InP multiple quantum wells. An analysis of double‐crystal x‐ray diffraction data reveals that exposure of InP to arsine for 2 s is sufficient to create approximately 3 monolayers of InAs0.55P0.45ternary under biaxial compressive strain at the InP/Ga047In0.53As interface. Moreover, exposure of Ga0.47In0.53As to phosphine for 2 s results in the formation of approximately 2 monolayers of Ga0.48In0.52As0.21P0.79quaternary under biaxial tensile strain at the Ga0.47In0.53As/InP interface. We find that long exposures to hydrides (over 5 s) rather than short ones give rise to interfacial layers with less compositional disorder and/or thickness fluctuation. Moreover, photoluminescence and absorption spectroscopy data reveal the negligible effect of InAsxP1−xand GaxIn1−xAsyP1−yinterfacial layers on the emission and optical absorption properties of Ga0.47In0.53As/InP multiple quantum wells with sufficiently thick Ga0.47In0.53As layers. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361134

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Photocurrent correlation measurements used for the characterization of ultrafast photoconductive switches based on GaAs and silicon‐on‐sapphire are demonstrated. The correlation signal arises from the interplay of the photoexcited carriers, the dynamics of the bias field and a subsequent recharging of the switch. By using both photocurrent measurements and terahertz spectroscopy we verify the importance of space‐charge effects on the carrier dynamics. Photocurrent nonlinearities and coherent effects are discussed as they appear in the correlation signals. An analysis based on a simple model allows an estimate of the carrier lifetimes associated with the photoconductive switching process. We illustrate how pulse propagation can be studied sequentially using this technique and how a minor modification of the experimental setup enables the study of screening from long‐lived carriers. We emphasize in what ways the different techniques of measuring ultrashort electrical pulses are sensitive to different aspects of the pulse forming mechanisms. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361135

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Erbium is incorporated in crystalline silicon during molecular beam epitaxy on Si(100) at 600 °C, either in vacuum (6×10−11mbar) or in an O2ambient (4×10−10mbar). Strong Er segregation takes place during growth in vacuum, and only 23% of the total deposited Er is incorporated in the epitaxial layer. Films grown in an O2ambient show no Er segregation, and an Er concentration of 1.5×1019Er/cm3is incorporated in the crystal. The O content is 4×1019O/cm3. Photoluminescence spectra taken at 10 K show the characteristic intra‐4fluminescence of Er3+at 1.54 &mgr;m for both samples, grown with and without O2. Differences found in the spectral shape indicate a difference in the local environment (presumably O coordination) of Er for the two cases. The O codoped film shows a 7 times higher Er luminescence peak intensity than the film grown without O. This is due to the higher incorporated Er concentration as well as an increased luminescence efficiency (lifetime without O: 0.33 ms, with O: 1.81 ms). The Er excitation efficiency is lower in the O codoped film than in the O‐undoped film, which is attributed to the lower minority carrier lifetime in the O‐doped material. Thermal annealing of the O codoped film at 1000 °C increases the excitation efficiency and hence the Er luminescence intensity. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361136

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The optical constants for thin layers of strained InAs, AlAs, and AlSb have been investigated by spectroscopic ellipsometry and multi‐sample analyses. These materials are important for high‐speed resonant tunneling diodes in the AlAs/InAs/In0.53Ga0.47As and AlSb/InAs material systems. Understanding the optical properties for these thin layers is important for developinginsitugrowth control using spectroscopic ellipsometry.Exsituroom‐temperature measurements were made on multiple samples. The resulting fitted optical constants are interpreted as apparent values because they are dependent on the fit model and sample structure. These apparent optical constants for very thin layers can be dependent on thickness and surrounding material, and are generally applicable only for layers found in a similar structural context. The critical point features of optical constants for the strained layers and for the thin unstrained cap layers were found to differ from bulk values, and three principle effects (strain, quantum confinement, and thin‐barrier critical‐point broadening) have been identified as responsible. Of these three, the broadening of theE1andE1+&Dgr;1critical points for thin barrier material is the newest and most pronounced. This thin barrier effect is shown to be a separate effect from strain, and is also observable for the AlAs/GaAs system. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361137

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Continuous‐wave and time‐resolved photoluminescence spectroscopies have been employed to study the band‐edge transitions in GaN epitaxial layers grown by plasma assisted molecular beam epitaxy. In addition to the neutral‐donor‐bound exciton transition (theI2line), a transition line at about 83 meV below the band gap has been observed in an epitaxial layer grown under a lower plasma power or growth rate. This emission line has been assigned to the band‐to‐impurity transition resulting from the recombination between electrons bound to shallow donors and free holesD0,h+). Systematic studies of these optical transitions have been carried out under different temperatures and excitation intensities. The temperature variation of the spectral peak position of theD0,h+) emission line differs from the band gap variation with temperature, but is consistent with an existing theory forD0,h+) transitions. The dynamic processes of theD0,h+) transition have also been investigated and subnanosecond recombination lifetimes have been observed. The emission energy and the temperature dependencies of the recombination lifetime have been measured. These results have provided solid evidence for the assignment of theD0,h+) transition and show that the motions of the free holes which participated in this transition are more or less restricted in the plane of the epitaxial layer at temperatures below 140 K and that the thermal quenching of the emission intensity of this transition is due to the dissociation of neutral donors. Our results show that time‐resolved photoluminescence spectroscopy can be of immense value in understanding the optical recombination dynamics in GaN. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361138

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Photoluminescence in hydrogenated amorphous carbon thin films deposited using the dc saddle‐field glow‐discharge technique onto glass and single‐crystal silicon substrates was studied. Samples prepared using positive substrate bias exhibited strong broad‐band photoluminescence at room temperature. The luminescence spectrum had a major peak at 1.9 eV and two smaller peaks at 2.3 and 2.6 eV. Samples prepared using grounded or negatively biased substrates exhibited only weak photoluminescence near 2.6 eV. Infrared spectroscopy indicates that the luminescence at 1.9 and 2.3 eV is related to the presence of C–OH bonds, whereas the photoluminescence at 2.6 eV appears to be an intrinsic property of thea‐C:H films. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361139

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Cavitation bubbles were generated by the 193 nm argon fluoride excimer laser delivered with a specially designed tip into absorbing NaCl solution. The dynamics of bubble formation and collapse have been studied using fast flash photomicrography. The bubble dimensions were measured at different time delays as a function of the tip exit diameter, the energy fluence of the laser, and the NaCl concentration. The dynamics of the cavitation bubble created on the tip is compared with the well‐studied dynamics of bubbles resulting from dielectric breakdown near a boundary. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361140

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An approach is proposed which combines simultaneously advantages both of pulse (PT) and modulated infrared thermography. In a nondestructive evaluation perspective, the specimen is pulse heated as in PT and the mix of frequencies of the thermal waves launched into the specimen is unscrambled by performing the Fourier transform of the temperature evolution over the field of view. Of interest is the maximum phase image with many attractive features: deeper probing, less influence of surface infrared and optical characteristics, rapid image recording (pulse heating, surface‐wide inspection), and the possibility to inspect high thermal conductivity specimens. Several results are presented and the theory is discussed as well. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362662

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Amorphous hydrogenated silicon (a‐Si:H) was deposited by SiH4decomposition on a hot tungsten filament. The substrate temperature was held at 400 °C for all samples, maintaining conditions where material combining a low defect density and a low hydrogen content is obtained. A systematic study of the effects of gas pressure, substrate‐to‐filament distance, and filament temperature on film properties is presented, allowing insight into the growth condition required for this material as well as the significance of secondary gas phase reactions. Material of good optoelectronic quality is obtained at high growth rates. The stability with respect to light degradation was compared to typical plasma deposited films. Conditions for the transition from amorphous to microcrystalline films, observed under gas phase dilution with hydrogen, were investigated. Byinsituellipsometry and atomic force microscopy the nucleation and film morphology were shown to be significantly different from those for plasma‐chemical vapor deposition material. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361100

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The effect of rapid thermal annealing at 1200 °C as a pretreatment on the precipitation of oxygen during a three‐step internal gettering process is studied thanks to infrared analyses. The influence of both the duration and the ambient of this pretreatment is considered. We define a limit duration of the rapid thermal annealing from which the further precipitation is greatly enhanced through a precipitation path leading to the formation of quasispherical precipitates different from the platelets. It is also shown that hydrogen introduced during the rapid thermal anneal delays the oxygen precipitation during the internal gettering process. Finally, considering the inefficiency of the internal gettering of chromium after a rapid thermal annealing at 1200 °C under argon/hydrogen, a new interpretation is proposed: a rapid thermal annealing would produce a modification in the oxygen precipitation path, leading to the formation of precipitates which would not be suitable for an efficient gettering effect. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361141

出版商:AIP    

年代:1996

数据来源: AIP