摘要:

We have studied the effect of uniaxial stress on the long-wavelength optical phonons of InSb at room temperature using Raman spectroscopy. From the observed frequency shifts and degeneracy splittings we obtain values for the phonon deformation potentials. The results are used to analyze previously reported Raman measurements of phonons in strainedInSb/In1−xAlxSbsuperlattices. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366509

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have measured electroluminescence (EL) spectra of GaAs/InGaAs and AlGaAs/GaAs single quantum well (QW)p-i-nphotodiodes at temperatures between 200 and 300 K and forward biases close to the open circuit voltage. Integrated EL spectra vary likeeqV/nkTwith an ideality factorn=1.05±0.05over five decades, indicating purely radiative processes. The spectra are calibrated into absolute units enabling comparison to be made with the predictions of a theoretical model. For each temperature and bias we calculate the EL spectrum and radiative current expected in the detailed balance limit, integrating the theoretical emission spectrum over the surface of the device, in order to establish the quasi-Fermi potential separation,&Dgr;&fgr;f,in the QW and, where possible, in the host material. For the GaAs/InGaAs cell we are able to model emission from the QW and the host material simultaneously. We find that, in all cases, the QW emission is overestimated by theory if it is assumed that&Dgr;&fgr;f=V.QW emission corresponds instead to a value of&Dgr;&fgr;fwhich a few tens of mV less thanV.In contrast, emission from the host material, where visible, is well fitted by the model with&Dgr;&fgr;f=Vat all biases and temperatures. We attribute the variation in&Dgr;&fgr;fto irreversible thermally assisted escape from the QWs. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366510

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We measured the Raman spectra of GaAs wirelike crystals grown on porous silicon (PS) using two different excitation radiations which probe the near surface and the bulk. The transverse optic and longitudinal optic vibrational bands appear redshifted and broadened when compared to bulk GaAs, and with shoulders on their low frequency sides. These features are attributed to a disorder-induced relaxation in the selection rules for Raman activity arising from point defects. In addition, the bands show a strong frequency and bandwidth dependence on excitation energy. Differences in penetration depth together with a gradient in defect density are invoked to account for the observations. This analysis yields a picture in which there is a predominantly amorphous GaAs region buried at the PS–GaAs interface followed by microcrystalline GaAs cylindrical structures that become less defective as they grow farther from the interface. The near surface tends to approach the low defect density of crystalline GaAs. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366511

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A model is developed for the polarization dependent refractive index of interdiffused AlGaAs/GaAs quantum well at room temperature for wavelengths ranging from 0.6 to 2 &mgr;m. The present model is based on a semianalytic and semiempirical method through the Kramers–Kro¨nig transformation. The multi-quantum-well structures, including the exciton effect and above barrier gap contributions, are fully considered in this model. The distinct structures at energies of theE0,E0+&Dgr;0,E1,andE2critical points are revealed. Moreover, the birefringence at room temperature is also analyzed in the wavelength range varying from 0.7 to 1.0 &mgr;m. The calculated refractive index results are in satisfactory agreement with the experimental measurements over the quantum well band edge, i.e., 0.8–0.9 &mgr;m. The effect of interdiffusion on the change of refractive index is discussed. The polarization dependent absorption coefficients are also calculated with all the bound excitons, and results agree well with experiments. These results are important, since refraction index in a particular wavelength region of interest, where experimental data are not available, can be determined and thus are very useful in the design of devices. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366512

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Optical absorption and emission properties of Er3+ions inZnCl2-based glasses are investigated. The electric dipole line strengths for various transitions were estimated from the measured optical absorption spectra. The spontaneous emission probabilities for various transitions were predicted using the Judd–Ofelt theory. Among&OHgr;t(t=2, 4, 6)phenomenological intensity parameters, the&OHgr;2value is larger than that measured for ZrF4-based glass. On the contrary, the&OHgr;4and&OHgr;6values are comparatively small. Multiphonon relaxation rates follow a so-called “energy-gap law” which is given byWMPR=C exp(−&agr;&Dgr;E). TheCvalue is quite smaller than that of the ZrF4-based glass by about two orders of magnitude. This result is attributed to the very low-phonon-energy of the chloride glass matrix. On the other hand, the&agr;value is almost the same as those of other glass hosts. Because of the low-phonon-energy and the host-independent&agr;value, the electron–phonon coupling constant&egr;of theZnCl2-based glass is extremely large compared with those of oxide and fluoride glasses. It was also found that several emissions due to transitions between the excited 4f-levels are detectable, which are hardly observed in other glass hosts. Radiative quantum efficiency is definitively high even for emitting levels of which the energy-gap to the next-lower level is small. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366545

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effects of thermal annealing below 500 °C on Spindt-type Mo field emitter arrays (FEAs) were studied through emission characteristics and Mo surface analysis. The anode current of the FEAs increases with increasing annealing time and then saturates after a certain period that is shorter for higher-temperature annealing. X-ray photoelectron spectroscopy and temperature programmed desorption show thatMoO3formed on the Mo surface desorbs at around 500 °C. The enhancement of the anode current is caused mainly byMoO3desorption, since the period required forMoO3desorption corresponds to that required for current saturation.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366513

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This article presents results on the surface etching of a Novolak-type polymer (Shipley, SPR2) on Si wafers using dielectric barrier discharges in oxygen at high pressures and room temperature. The etching depth is measured by mechanical profilometry as a function of gap spacing and gas pressure. Figures of merit are generated allowing comparison with conventional plasma surface treatment, as etch rate per power density coupled onto the sample surface(nm J−1 cm2),or coupled into the gas volume(nm J−1 cm3).Energy-density specific etch rates were measured as a function of the gap spacing(d)and the total oxygen gas pressure(p),as well as a function of the product ofpdin the gas pressure range of 50–1500 mbar and of the gap spacing range of 1–20 mm. At a constant gap spacing and pressure, the removal rate is a linear function of the applied power density. The highest achieved etching rate per surface energy density is2.2 nm J−1 cm2at 730 mbar and 1 mm(0.2 nm J−1 cm3)and the highest etching rate per volumetric energy density is0.85 nm J−1 cm3at 290 mbar and 7 mm(0.87 nm J−1 cm2).The surface of the etched photoresist is characterized using mechanical profilometry and scanning electron microscopy. The results obtained in this work suggest that dielectric barrier discharges can be an efficient, alternative plasma source for general surface processing, because they can provide nonthermal discharges also near atmospheric pressures and thereby eliminate the need of costly vacuum systems. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366514

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Supersonic jets of silane were employed to deposit silicon on both polysilicon and Si(100) at substrate temperatures ranging from 500 to 650 °C. The growth rate and film uniformity were studied as a function of silane kinetic energy. Increasing theSiH4precursor kinetic energy from 0.4 eV (10&percent;SiH4in He mixture) to 1 eV (1&percent;SiH4inH2mixture) results in as much as an order of magnitude increase in reaction probability. The advantage of using high kinetic energy precursors to enhance deposition is reflected in the centerline growth rates obtained employing supersonic jets ofSiH4.At higher substrate temperatures, the high kinetic energySiH4jet has a higher growth rate than the low kinetic energySiH4jet, although, the flux of the high energy jet at the centerline is a factor of 8 less than the flux of the low energy jet. The silane flux distribution from the supersonic jet is dependent on the gas mixture; a flux distribution ofcos55 &thgr;results from the 1&percent; silane in hydrogen jet (1 eV) compared to acos28 &thgr;distribution from the 10&percent; silane in helium jet (0.4 eV). ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366515

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of electron beam impact on the oxidation of Si (100) by oxygen has been studied using x-ray photoelectron spectroscopy and Auger electron spectroscopy. It was found that electron beam impact can enhance the oxidation of Si (100) by oxygen at low temperatures, resulting in silicon dioxide formation. Furthermore, electron energy-dependent film growth experiments were carried out onO2(a) and an electron attachment resonance energy of∼10.1 eVwas found. A possible electron-induced oxidation mechanism is proposed which involves dissociative electron attachment for adsorbedO2species and the formation of O andO−species from adsorbedO2−.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366516

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a method for simulating the chemical vapor deposition (CVD) of thin films. The model is based upon a three-dimensional representation of film growth on the atomic scale that incorporates the effects of surface atomic structure and morphology. Film growth is simulated on lattice. The temporal evolution of the film during growth is examined on the atomic scale by a Monte Carlo technique parameterized by the rates of the important surface chemical reactions. The approach is similar to the N-fold way in that one reaction occurs at each simulation step, and the time increment between reaction events is variable. As an example of the application of the simulation technique, the growth of {111}-oriented diamond films was simulated for fifteen substrate temperatures ranging from 800 to 1500 K. Film growth rates and incorporated vacancy and H atom concentrations were computed at each temperature. Under typical CVD conditions, the simulated growth rates vary from about 0.1 to 0.8 &mgr;m/hr between 800 and 1500 K and the activation energy for growth on the {111}: H surface between 800 and 1100 K is 11.3 kcal/mol. The simulations predict that the concentrations of incorporated point defects are low at substrate temperatures below 1300 K, but become significant above this temperature. If the ratio between growth rate and point defect concentration is used as a measure of growth efficiency, ideal substrate temperatures for the growth of {111}-oriented diamond films are in the vicinity of 1100 to 1200 K. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366532

出版商:AIP    

年代:1997

数据来源: AIP