摘要:

The effects of various structure parameters such as graded potential, strain, quantum‐well size, barrier heights, and temperature on the optical gain of single quantum‐well lasers are studied for a potential solution to the problem of device optimization from the unified point of view with a rigorous model for gain. This study on the structure parameter dependence of the gain with the valence band mixing as well as intraband relaxation is new and presents a unified scheme for the optical gain control. Significant enhancement of gain in the graded quantum well as compared with that of the ordinary square quantum well is predicted. With the uniaxial stress, the TE mode gain is suppressed while the TM mode gain is enhanced due to the change of valence band structure. Calculated results show that the roles played by structure parameters such as well width, barrier heights, and temperature on the optical gain becomes of great importance for the device optimization.

ISSN:0021-8979    

DOI:10.1063/1.350373

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Indentation/crack length measurements were used to determine hardness and fracture toughness in twinned and detwinned single crystals of YBa2Cu3O6+&dgr;(YBCO). Hardness was found to be isotropic and unaffected by twin boundaries or moisture; the average hardness value was 9.5 GPa. Fracture toughness (Kc) was determined to be anisotropic with the average value for cracks running perpendicular to the basal plane being approximately twice that of cracks parallel to the basal plane; thus, cleavage is easier along basal planes. In addition, the results suggest a small but measurable anisotropy inKcbetween theaandbdirections. Twin boundaries were found to toughen YBCO, enhancingKcby about 25%. Moisture promoted crack growth, degradingKcby about 35%.

ISSN:0021-8979    

DOI:10.1063/1.350234

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A fixed volume of liquid is placed on a horizontal disk spinning at a constant angular speed. The liquid forms a film that thins continuously due to centrifugal drainage and evaporation or thins to a finite thickness when surface absorption counterbalances drainage. A nonlinear evolution equation describing the shape of the film interface as a function of space and time is derived, and its stability is examined using linear theory. When there is either no mass transfer or there is evaporation from the film surface, infinitesimal disturbances decay for small wave numbers and are transiently stable for larger wave numbers. When absorption is present at the free surface, the film exhibits three different domains of stability: disturbances of small wave numbers decay, disturbances of intermediate wave numbers grow transiently, and those of larger wave numbers grow exponentially.

ISSN:0021-8979    

DOI:10.1063/1.350235

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A thin liquid film drains radially off the surface of a horizontal, rotating substrate. Evaporation of solvent from the film increases the fluid viscosity and reduces the radial outflow. Governing equations are developed for the shape of the film interface as a function of space and time, as well as the axisymmetric solvent‐concentration distribution, for both unit order and large Peclet numbers. The numerical solution of these equations elucidates how a spinning film with either a corrugated or a flat free surface evolves over time in the presence of a time‐varying concentration (and viscosity) field. A correlation for the final film thickness in terms of the physical variables of the system is deduced from the governing equations, the result of which shows good agreement to published experimental results.

ISSN:0021-8979    

DOI:10.1063/1.350236

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Using a low‐pressure reactive ion etching reactor in a pulsed radio‐frequency (rf) power mode the rise time of the plasma induced emission of O at 777 and 844 nm was monitored on a ms time scale. With a two‐photon excitation scheme the rise time of the oxygen atom ground state concentration was followed by measuring the laser induced fluorescence (LIF) at 844 nm. An absolute density measurement was performed by comparing the LIF signal in the reactor to the LIF signal of a known concentration of O in a microwave discharge. Using these time resolved measurements the reliability of optical emission actinometry in low pressure O2rf plasmas for a determination of relative atomic oxygen densities was examined. By comparing the rise times with the ignition time of the plasma it is concluded that both emission lines are caused by dissociative excitation. The consequences for the applicability of actinometry will be discussed. A comparison of experimental emission intensities to calculated ones suggests that highly energetic (e.g., secondary) electrons are responsible for the dissociative excitation of O2.

ISSN:0021-8979    

DOI:10.1063/1.350237

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

An asymptotic analysis of the Elenbaas–Heller equation for a radiating wall‐stabilized high‐pressure gas‐discharge arc is given. This analysis applies when the operating temperatures within the arc are lower than the ionization temperature by an order of magnitude. It is shown that for arcs that are radiating highly efficiently a further asymptotic treatment can be given. It is shown under what conditions, governed by a dimensionless parameterM, this limiting case prevails. Comparison with earlier results put forward by Zollweg [J. Appl. Phys.49, 1077 (1978)] shows satisfactory agreement.

ISSN:0021-8979    

DOI:10.1063/1.350238

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Ion inertial confinement fusion requires beam transport over distances of a few meters for isolation of the diode hardware from the target explosion and for power compression by time‐of‐flight bunching. This paper evaluates light ion beam transport in a wall‐stabilizedz‐discharge channel, where the discharge azimuthal magnetic field radially confines the ion beam. The ion beam is focused onto the entrance aperture of the transport channel by shaping the diode to achieve beam convergence in a field‐free drift region separating the diode from the transport section. Ion orbits are studied to determine the injection efficiency (i.e., the fraction of the beam emitted from the diode which is transported) under various conditions. Ions that are focused onto the channel entrance at too large of an angle for confinement hit the wall and are lost. For a multimodular scheme (10–30 beams), individual transport channels are packed around the target with the exit apertures at some standoff distance from it. The fraction of the beam that is lost in this field‐free standoff region is also evaluated under various conditions. The standoff efficiency is then combined with the injection efficiency to give the dependence of the total transport efficiency &eegr;ton diode, focusing, transport and standoff parameters. It is found that &eegr;tcan be in the range of 75%–100% for parameter values that appear to be achievable.

ISSN:0021-8979    

DOI:10.1063/1.350239

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We present time‐resolved experimental measurements of the electron distribution functionf(v∥,v⊥,t) in a pulsed, partially ionized, electron cyclotron resonance (ECR)‐produced plasma. The discharge has some characteristics similar to those used in plasma processing applications. These properties include ECR production in a strong magnetic field and low electron temperature (Te<5 eV). In addition, electron‐neutral collisions play an important role. A novel analyzer is used to study the dependence off(v∥,v⊥,t) on velocities both parallel and perpendicular to the magnetic field. This information cannot be obtained with a simple Langmuir probe. The temporal evolution off(v∥,v⊥,t) is examined during plasma formation, with the source biased, with the source grounded and in the afterglow.

ISSN:0021-8979    

DOI:10.1063/1.350240

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The localized charging of a rectangular trench during the plasma etching of a perfectly insulating surface was modeled assuming an isotropic electron flux and monodirectional ion bombardment. The field set up by the localized charging acts to deflect arriving ions, modifying the ion flux densities within the feature, and thus, etching rates. Preliminary simulations indicate that this may be important in the shaping of etching profiles.

ISSN:0021-8979    

DOI:10.1063/1.350241

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

As the dimensions of semiconductor devices are reduced, changes in the structure of the devices can have a pronounced effect on their electrical parameters. In some cases it may no longer be correct to assume that the electrical parameters can simply be scaled with device area. In the present study it will be shown that when polysilicon‐emitter bipolar transistors are reduced to submicron dimensions, shadowing of the ion implant into the emitter sidewalls can alter the dopant concentration in the polysilicon diffusion source, thereby changing the dopant profiles in the single‐crystal silicon, and hence the junction depths. This shadowing effect, although present in all devices, is only found to affect the electrical parameters of transistors when the emitter size approaches submicron dimensions.

ISSN:0021-8979    

DOI:10.1063/1.350242

出版商:AIP    

年代:1991

数据来源: AIP