摘要:

GaAs quantum well (QW) lasers with distributed Bragg reflection (DBR) Al0.3Ga0.7As/GaAs superlattice gratings have been fabricated by the single‐step, maskless focused ion beam (FIB) mixing. 200 keV Si++FIB implantation with a beam diameter of ∼60–70 nm and a dose of 1014cm−2was used to obtain localized compositional mixing. The DBR grating period was 350 nm, corresponding to a third order grating matched to the emission from the 30 nm wide QW. Lasing operation was examined by optical pumping. With a pumping power 1.6× the threshold value, lasing modes were observed near 827 nm, with a spacing of 3 A˚ and a linewidth of 1.5 A˚. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114659

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Real‐time infrared imaging acquisition was used to measure the steady state intracavity spatial spontaneous emission profile along the active stripe of bulk Fabry–Pe´rot InGaAsP/InP lasers. The direct observation of spatially nonhomogeneous spontaneous emission profiles (relating to the spatial nonhomogeneity and redistribution of the quasi‐Fermi level along the gain guiding medium) is demonstrated. The three‐dimensional image mapping of the spatial redistribution of electrons along the active stripe well above lasing threshold is also discussed. We will demonstrate that the threshold saturation of spontaneous emission does not always occur along the entire length of the lasing cavity. Above threshold it was observed that the spatial redistribution of the spontaneous emission is highly wavelength dependent and that this observed phenomenon is a direct result of the optical cavity’s asymmetry. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114660

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report the observation of ultrahigh frequency oscillations of up to 240 GHz in optically gain switched vertical cavity surface emitting lasers. These oscillations are shown to be produced by multimode emission through mode competition (10–30 GHz) or mode beating (above 100 GHz). Although these oscillations are not related to the intrinsic modulation bandwidth, some of them could be mistaken for relaxation oscillations, calling for careful interpretation of the results of this type of experiments. The highest frequencies observed for single mode relaxation oscillations were about 9 GHz in agreement with values of modulation bandwidth reported in the literature. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114661

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The photorefractive effect in materials such as bismuth silicon oxide (BSO) depends on photoionizing deep defect levels inadvertently present rather than controllably introduced. Using thermal stimulated conductivity measurements, a preliminary attempt has been made at associating specific levels with a particular sillenite member and impurity dopants. While many of the features prevail throughout, significant changes occur when Ge is substituted for Si to give BGO and whenp‐ (Al) andn‐type (P) impurities are added to dope BSO.

ISSN:0003-6951    

DOI:10.1063/1.114662

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In low pressure, capacitively coupled rf discharges mode transitions in the shape of the electron energy distribution function on variation of the pressure have been observed previously, and have been interpreted as a transition from dominating stochastic to dominating Joule heating. In this letter we present a similar mode transition, which has been observed at constant discharge pressure on variation of the rf current density through the discharge. By comparison to a parametric kinetic model it is shown that a dependence of the sheath heating efficiency on the magnitude of the rf sheath potentials can be considered as a possible explanation of the mode transition. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114663

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A secondary discharge was used to enhance chemical nonequilibrium in the boundary layer of a stagnation point flow reactor during the atmospheric pressure deposition of chemically vapor deposited (CVD) diamond with a direct‐current (dc) arcjet. The secondary discharge was induced by means of a positive potential on the deposition surface to drive a current through the boundary layer and produce energetic electrons. These electrons can promote superequilibrium concentrations of radicals at the growth surface. It was found that with 3.5 A/cm2at 115 V in the secondary discharge, the growth rate of diamond in this reactor increased by a factor of 6 as compared with the floating or grounded substrate case. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114664

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The dynamics of laser‐ablated yttrium plume propagation through background argon have been investigated with fast time‐ and spatially‐resolved plasma diagnostics in order to characterize a general phenomenon believed to be important to film growth by pulsed laser deposition (PLD). During expansion into low‐pressure background gases, the ion flux in the laser ablation plasma plume is observed to split into fast and slow components over a limited range of distances including those typically utilized for PLD. Optical absorption and emission spectroscopy are employed to simultaneously identify populations of both excited and ground states of Y and Y+. These are correlated with intensified‐CCD (ICCD) photographs of visible plume luminescence and ion fluxes recorded with fast ion probes. These measurements indicate that plume‐splitting in background gases is consistent with scattering of target constituents by ambient gas atoms. The momentum transfer from these collisions produces a transition from the initial, ‘‘vacuum’’ velocity distribution into a velocity distribution which is significantly slowed in accordance with shock or drag propagation models. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114665

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report on measurements of the charge state distributions of ions formed in a vacuum arc plasma in a magnetic field. A vacuum arc ion source was used for plasma formation and ion beam extraction, and the charge state spectra were investigated using both magnetic and time‐of‐flight charge state diagnostics. We find that the charge states of all of the metal species investigated are significantly increased by a magnetic field of up to 6 kG. New high ion charge states are created, and the mean of the charge state distribution is increased by about 30% at 3.75 kG and 50% at 6 kG. The results are important fundamentally as well as being of relevance to vacuum arc ion source applications such as ion implantation and accelerator injection. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114666

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Crystalline carbon nitride/TiN composite coatings have been deposited using a dual‐cathode magnetron sputtering system onto polished silicon andM2 steel substrates held at room temperature. We propose that TiN provides a lattice‐matched structural template to seed the growth of carbon nitride crystallites. The resulting coatings are smooth, fully crystalline, with nanoindentation hardness in the range of 45–55 GPa. This hardness is in the low‐end range of diamond films. Suggestions for better seeding materials to further improve the hardness are proposed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114667

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Amorphous layer formation by irradiation of an intense pulsed ion beam (PIB) has been studied experimentally. A mixed carbon and fluorine PIB with energy of 180 keV, current density of 180 A/cm2, and pulse duration of 25 ns is exposed to a Ni65Cr15P16B4alloy, resulting in an amorphous layer on the substrate surface within 0.66 &mgr;m in depth. The cooling rate for a nickel substrate from the melting point to the glass transition temperature is estimated to be ∼3.8×105K/s. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114668

出版商:AIP    

年代:1995

数据来源: AIP