摘要:

Photoluminescence studies as well as reflectance and transmittance measurements were performed on high‐purity epitaxial InAs grown by metal‐organic chemical‐vapor deposition. We report the optical identification of excitonic, donor, and acceptor impurity related transitions at a temperature of 1.4 K. Measurements at higher temperature and in the presence of magnetic fields up to 7 T support these identifications. We find the excitonic band gap at 415.65±0.01 meV according to the minimum in the polariton reflectance feature. The donor–acceptor‐pair and acceptor‐bound exciton transitions for three different acceptors are observed by photoluminescence, and we tentatively associate one of them to a double acceptor formed by a Ga impurity on an As lattice site. A donor‐bound exciton transition is observed with a binding energy of 0.42 meV. The magnetic field dependence yields values of the electron effective mass andgfactor of (0.026±0.002)m0and −15.3±0.2, respectively, in good agreement with values obtained by other techniques. Furthermore, we report a deep luminescence band of unknown origin at ∼375 meV, related to drastic temporal changes in the band‐edge photoluminescence intensity. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363660

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Surprising concentrations of hydrogen and deuterium, as high as 5×1020cm−3, were incorporated into nitrogen‐doped ZnSe grown on GaAs by molecular beam epitaxy. Infrared absorption bands due to local vibration modes were observed at 3193 and 783 cm−1for ZnSe:N,H samples, and at 2368 cm−1for ZnSe:N,D samples using Fourier transform infrared spectroscopy. The isotopic shift in the absorption band agrees with predictions of a simple harmonic oscillator approximation for N–H bonding. The variation of the absorption band associated with substitutional nitrogen with nitrogen concentration indicates that not all nitrogen is substitutional, and also exhibited significant changes related to hydrogen incorporation. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363661

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The intensity of visible photoluminescence from thin films of silicon nanoparticles is shown to be dependent upon the degree of surface passivation on the nanoparticles, while the emission energy is independent of the specific chemical nature of the passivating species. Nanoparticles are deposited into films using a pulsed laser ablation supersonic expansion source. Surface chemistry is controlled with a variety of postdeposition processing steps, including acid, methanol, and iodine treatments. These steps are then correlated with the visible photoluminescence behavior of the sample and the surface chemistry as characterized by x‐ray photoelectron spectroscopy. Surface passivation controls the emission intensity through the elimination of competing nonradiative carrier relaxation pathways. The chemical nature of the passivating species does not determine the emission energy and can be easily changed with no anomalous photoluminescence behavior resulting. All results are consistent with a simple quantum confinement model of emission where particle size determines emission energy and surface passivation determines emission intensity. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363662

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The two‐dimensional spectral distribution of photoluminescence (PL) was analyzed forp‐type andn‐type porous silicon (PS) prepared under different illumination conditions. In thep‐type PS fabricated under strong illumination, the peak position of PL distribution in the depth direction moves inside the PS as the wavelength becomes longer. On the other hand, the PS prepared in the dark has an intensity peak of longer wavelength near surface. In then‐type PS formed under illumination, PL intensity has a peak near the PS surface and the peak position of the PL intensity does not move much. The difference betweenp‐type andn‐type PS suggests that the penetration depth of the light becomes greater as the PS layer grows and thus the effect of illumination may extend far insidep‐type PS. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363663

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Decay kinetics of photoluminescence (PL) existing around 2.7 eV has been studied in various ion‐implanted thermal SiO2films as a function of implantation conditions. The PL observed in many samples shows decay constants shorter than 10 ms, which is a well‐observed decay constant for silica glass. The change in the decay constant and that in the PL intensity have been found to be systematically related with the mass and the dose of the implanted ions. Therefore, despite the short decay constant, the present 2.7 eV PL is attributable to a triplet‐to‐singlet transition of oxygen deficient centers, as in the case of silica glass. The rapid decay is interpreted as the increase in spin‐orbit coupling interaction due to structural deformations by ion implantation such as the formation of paramagnetic defects and/or densification. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363713

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We propose and demonstrate a novel approach to the coating of semiconductor laser facets. In this approach, processed semiconductor lasers are cleaved in a high‐vacuum system immediately followed by coating of the vacuum‐exposed facet with a very thin Si layer (≤100 A˚) and a large band gap dielectric (Al2O3) layer. The Si layer is sufficiently thin to avoid the formation of quantized bound states in the Si. GaAs coated with thin Si and Al2O3have a higher luminescence yield and a lower surface recombination velocity than bare GaAs surfaces as well as GaAs surfaces coated with Al2O3only. A surface recombination velocity of 3×104cm/s has been obtained using a modified dead layer model for the Si/Al2O3sample. It is also shown that lasers which are cleaved in vacuum and subsequently coated with Si and Al2O3have improved properties including an increased threshold for catastrophic optical damage. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363664

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report quadrupole mass‐selected, time‐of‐flight measurements of Mg+from polished, single crystal MgO and Na+from cleaved, single crystal NaNO3exposed to 248 nm (5 eV) laser radiation. A large fraction of the ions emitted from these materials have energies well above the energy of the incident photon. As the fluence is raised from low values, the ion intensities show thresholdlike behavior with a high‐order fluence dependence (roughly sixth order). At still higher fluences, the fluence dependence of Mg+from MgO decreases to roughly second order. We attribute these emissions to weakly bound ions adsorbed atop surface electron traps; when the underlying vacancy is photoionized, the adsorbed ion is electrostatistically ejected at high energy. We argue that several photons are required to ionize a surface electron trap beneath an adsorbed ion, accounting for the high‐order fluence dependence and satisfying conservation of energy. (Several 5 eV photons are required to produce a 10 eV ion.) We show that a sequence of single‐photon absorption events involving photoionization, charge transfer, and retrapping account for this unusual fluence dependence. These emission intensities are strong functions of surface treatments which increase defect densities, e.g., abrasion in the case of MgO and electron bombardment in the case of NaNO3. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363665

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We deal with the formation of thin aluminum oxynitride (AlON) layers after adsorption of nitric oxide (or coadsorption of oxygen and ammonia) on NiAl(001) at 75 K and subsequent annealing at 1200 K. The adsorption of NO and formation of the AlON films are investigated by means of high‐resolution electron energy loss spectroscopy (HREELS), low‐energy electron diffraction (LEED), and Auger electron spectroscopy (AES). The AlON film shows a distinct (2×1) LEED pattern and the HREEL spectrum exhibits five loss peaks. An oxygen to nitrogen atomic ratio of &bartil;2 has been estimated from the AES analysis. The energy gap is determined to beEg=6.6±0.2 eV. The structure of &thgr;‐AlON is derived from that of &thgr;‐Al2O3. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363666

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

One‐dimensional direct simulation Monte Carlo calculations have been carried out on H/H2and H/H2/CO mixtures under operating conditions typical of diffusion‐dominated diamond chemical vapor deposition processes. Mechanisms have been included in the model for the adsorption and recombination of hydrogen atoms on the diamond surface and the dissociation of molecular hydrogen at the interior of the reactor. Hydrogen atom fluxes and recombinative and conductive heat fluxes to the diamond surface are calculated as a function of pressure, gas composition, hydrogen dissociation and surface reaction probabilities, reactor temperature, and distance between the activating source and substrate. The numerical calculations are shown to be in excellent agreement with analytical results in the limiting regimes of free‐streaming particles at low pressures and continuum hydrodynamics at high pressures. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363667

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Real time spectroellipsometry has been applied to determine the deposition rate and thickness evolution of the nondiamond (sp2‐bonded) carbon volume fraction in very thin (<1000 A˚), but fully coalesced, nanocrystalline diamond films prepared on Si substrates by microwave plasma‐enhanced chemical vapor deposition from gas mixtures of CO and H2. At a substrate temperature of ∼800 °C, high quality diamond films can be obtained over two orders of magnitude in the CO/H2gas flow ratio, from 0.04, the lowest value explored, to ∼5. A well‐defined minimum in thesp2C volume fraction (0.03 in a 600 A˚ film) is observed for a CO/H2ratio of 0.2, corresponding to the C–H–O diamond‐growth phase‐diagram coordinateXH/&Sgr;=[H]/{[H]+[C]} of 0.9. Under these conditions, the deposition rate increases with increasing temperature over the range of ∼400–800 °C with an activation energy of 8 kcal/mol, behavior identical to that observed for diamond film growth from a CH4/H2ratio of 0.01. This observation shows that the dominant film precursors in the diamond growth process from CO/H2=0.2 are hydrocarbons whose flux at the growing film surface is controlled through the reaction of excited CO with H or H2in the plasma. A broad subsidiary minimum in thesp2C content is observed, centered near a CO/H2ratio of 2, corresponding to anXH/&Sgr;value of ∼0.5. Under these gas flow conditions, the deposition rate is a complicated function of temperature, exhibiting a peak near 550 °C. This peak shifts to lower temperature with further increases in the CO/H2ratio above 2, suggesting a nonhydrocarbon precursor and a different growth mechanism for diamond prepared at high CO/H2ratio and low temperature. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363668

出版商:AIP    

年代:1996

数据来源: AIP