摘要:

Atomic layer epitaxy (ALE) is not so much a new technique for the preparation of thin films as a novel modification to existing methods of vapor‐phase epitaxy, whether physical [e.g., evaporation, at one limit molecular‐beam epitaxy (MBE)] or chemical [e.g., chloride epitaxy or metalorganic chemical vapor deposition (MOCVD)]. It is a self‐regulatory process which, in its simplest form, produces one complete molecular layer of a compound per operational cycle, with a greater thickness being obtained by repeated cycling. There is no growthratein ALE as in other crystal growth processes. So far ALE has been applied to rather few materials, but, in principle, it could have a quite general application. It has been used to prepare single‐crystal overlayers of CdTe, (Cd,Mn)Te, GaAs and AlAs, a number of polycrystalline films and highly efficient electroluminescent thin‐film displays based on ZnS:Mn. It could also offer particular advantages for the preparation of ultrathin films of precisely controlled thickness in the nanometer range and thus may have a special value for growing low‐dimensional structures.

ISSN:0021-8979    

DOI:10.1063/1.337344

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Analytic expressions are presented for the components of the quasistatic electric and magnetic field dyadic Green’s functions for a conducting half‐space. Numerical results illustrate the effects of the conductor–air interface on electric and magnetic dipole fields. Applications to modeling of eddy current flaw detection are discussed.

ISSN:0021-8979    

DOI:10.1063/1.337326

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Using a convergent beam approach, a spatially resolved ellipsometry (SRE) has been achieved. The modifications and the limitations due to the use of such a nonplanar wave for an ellipsometric measurement are discussed. We first established the relations between the ellipsometric data (tan &psgr;,cos &Dgr;), the optical properties of the sample which are assumed to be spatially nonuniform [rp(x,y) andrs(x,y)], and the optical characteristics of the beam (i.e., electric field distribution of the light on the sample surface and its angular domain Fourier transform function). These relations are established for both a coherent and an incoherent light source. We use them to investigate the absolute accuracy achievable with SRE on an homogeneous sample. It is demonstrated that submonolayer sensitivity can be obtained using a 10×10‐&mgr;m spot. In the case of a step discontinuity ofrp(x,y) andrs(x,y), strong optical resonances can take place in SRE. Their quantitative analysis is performed in the (tan &psgr;,cos &Dgr;) plane. In this representation, the optical resonance corresponds to a trajectory, called ‘‘spatial trajectory.’’ Another type of trajectory can be observed for a multilayer structure in the case when one (or more) thickness is slowly varying versus the position (‘‘thickness trajectory’’). The combination of both cases leads to a generalized trajectory concept which allows for a quantitative analysis of two‐dimensional ellipsometric maps. This trajectory approach is illustrated on two practical situations: (i) a SiO2layer etched through a lithographic mask on top of a GaAs wafer; (ii) metallic patterns deposited on GaAs. It is shown that the trajectory concept is capable of analyzing patterns with lateral dimensions smaller than the actual spot size (i.e., direct optical resolution of SRE).

ISSN:0021-8979    

DOI:10.1063/1.337327

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We demonstrate laser emission by photopumping at room temperature from a distributed feedback structure for a surface‐emitting laser constructed by alternating growths of a GaAs/AlGaAs multiquantum well and an Al0.7Ga0.3As layer using molecular‐beam epitaxy. A threshold photoexcitation intensity lower than 3.1×105W/cm2, a 34‐nm longitudinal mode spacing, and a 2.3‐nm peak width of the laser emission were observed for the 6‐&mgr;m‐thick multilayer.

ISSN:0021-8979    

DOI:10.1063/1.337328

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A series of experiments was performed with an Applied‐Bion diode on the Particle Beam Fusion Accelerator‐I, with peak voltage, current, and power of approximately 1.8 MV, 6 MA, and 6 TW, respectively. The purpose of these experiments was to explore issues of scaling of Applied‐Bdiode operation from the sub‐TW level on single module accelerators to the multi‐TW level on a low impedance, self‐magnetically insulated, multimodule accelerator. This is an essential step in the development of the 100‐TW level light ion beam driver required for inertial confinement fusion. The accelerator and the diode are viewed as a whole because the power pulse delivered by the 36 imperfectly synchronized magnetically insulated transmission lines to the single diode affects module addition, diode operation, and ion beam focusability. We studied electrical coupling between the accelerator and the diode, power flow symmetry, the ionic composition of the beam, and the focusability of the proton component of the beam. Scaling of the diode impedance behavior and beam quality with electrical drive power is obtained from comparison with lower‐power experiments.The diode impedance lifetime was about 10 ns, several times shorter than for lower‐power experiments. Azimuthal and top‐to‐bottom variations of the diode and ion currents were found to be approximately ±10%, compared with an estimated requirement of 5%–7% uniformity to avoid focal blurring by self‐magnetic field effects. The ion production efficiency was 80%–90%. However, only 50%±10% of the ion current was carried by protons; the balance was carried by multiply charged carbon and oxygen ions. Activation measurements showed a proton beam energy of approximately 50 kJ. A gas cell filled with 5 Torr of argon was used for beam transport. The macroscopic divergence was 15±10 mrad and the microscopic divergence was 20±15 mrad, values that are similar to those from lower‐power experiments. A model of beam focusing is formulated that predicts the proton charge focused onto 0.47‐cm radius lithium targets, taking into account beam purity, magnetic bending, small‐angle multiple scattering, and intrinsic divergence. The model results and activation measurements of the number of protons focused onto targets agree, and indicate that the spatially averaged (over about 3 cm2) peak focal power was about 0.5 TW/cm.2The most important limitations on power concentration were found to be the low proton content of the beam, the short impedance lifetime of the diode, and the asymmetric current feed of the accelerator. The short impedance lifetime limited the power coupled to the diode, and caused the voltage at peak ion power to be low, which exacerbates the small‐angle scattering problem. The asymmetric feed caused focal blurring through nonuniform self‐magnetic bending. At least partly because of the experience gained with low impedance beams during these experiments, the next generation accelerator, the 100‐TW Particle Beam Fusion Accelerator‐II, has been configured to produce a 25–30‐MV Li+beam rather than a 5‐MV proton beam. off

ISSN:0021-8979    

DOI:10.1063/1.337329

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In this paper the physical and the mathematical model of a three‐temperature plasma is presented. The numerical algorithm used to solve this problem is also described. A special technique has been used to treat very rapid electron‐ion and electron‐radiation energy equipartition rates in inertial fusion plasmas. This model has been incorporated in the one‐dimensional computer codemedusa‐ka. (N. A. Tahir and K. A. Long, ‘‘medusa‐ka: A one‐dimensional computer code for inertial fusion target design,’’ Kernforschungszentrum Karlsruhe Report, KfK‐3454, 1983). Application of this model to study the problem of ignition and burn propagation in reactor‐size inertial fusion targets is also briefly discussed.

ISSN:0021-8979    

DOI:10.1063/1.337330

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Rare gas–halogen excimer lasers excited by electron‐beam‐sustained discharges (EBSD) will operate stably for only a limited length of time (hundreds of nanoseconds to a few microseconds). In this paper, results from a multidimensional model for an EBSD KrF laser are used to study various aspects of discharge ionization and geometric stability, and the relationship between the two. We examine the effects of photodetachment of electrons from the halogen negative ion, of circuit response, and of nonuniforme‐beam power deposition upon the onset of discharge instabilities. We find that both spontaneous emission from KrF* and laser oscillation resulting in photodetachment of electrons from F−can initiate an ionization instability. By operating with high impedance electrical circuits, the tendency towards instabilities by this effect can be reduced. We also find that the spatial uniformity of thee‐beam power deposition is directly correlated with both the rate of discharge constriction and the time at which the discharge suffers an ionization instability.

ISSN:0021-8979    

DOI:10.1063/1.337331

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The time evolution of the energy balance in a nitrogen discharge during its early phases of development is simulated using a self‐consistent calculation of the electron distribution function (EDF), the vibrational population (VP), and densities of some electronically excited states. The contribution of the V–T (vibration‐to‐translation), and V–V (vibration‐to‐vibration) energy exchanges is quantitatively analyzed. The contribution to the energy balance by self‐quenching reactions of the N2(A3&Sgr;+u) state is also analyzed. It is shown that the population of this state in a discharge and its contribution to the energy balance may be significant.

ISSN:0021-8979    

DOI:10.1063/1.337332

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Densities of the negative and positive ions of SF6in a 110‐liter Pyrex container were measured using a Gerdien ion counter. The current‐voltage characteristics were obtained for gas flows ranging from 40 to 200 cm3 s−1. A quantitative model of the counter was developed to interpret the measured data. The model includes appropriate representation of the developing gas flow and the electric field distribution near the ends of the accelerating electrode. The best‐fit value for the negative‐ion mobility was &mgr;n=0.38 cm2 V−1 s−1, as derived from a comparison of the calculated and the measured characteristics. The mobility of the positive ions was found to equal that of the negative ions within the limits of dispersion of experimental data. The negative‐ion density at a pressure of 760 Torr evaluated at the counter entry plane was 3000 cm−3; the value of the positive‐ion density was practically identical.

ISSN:0021-8979    

DOI:10.1063/1.337333

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Strong impurity effects upon introduction and annealing behavior of radiation‐induced defects in InP irradiated with 1‐MeV electrons have been found. The main defect center of  0.37‐eV hole trap H4 inp‐InP, which must be due to a point defect, is annealed even at room temperature. Its annealing rate is found to be proportional to the 2/3 power of the preirradiation carrier concentration in InP. Moreover, the density of the hole trap H5 (Ev+0.52 eV) inp‐InP, which must be due to a point defect–impurity complex, increases with increase in the InP carrier concentration. These results suggest that the radiation‐induced defects in InP must recover through long‐range diffusion mediated by impurity atoms. A model is proposed in which point defects diffuse to sinks through impurities so as to disappear or bind impurities so as to form point defect–impurity complexes. In addition to the long‐range diffusion mechanism, the possibility of charge‐state effects responsible for the thermal annealing of radiation‐induced defects in InP is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.337334

出版商:AIP    

年代:1986

数据来源: AIP