摘要:

Recently, a number of studies have reported a correlation between variations in threshold voltage of field effect transistors and the nonuniformity of the luminescence efficiency of semi‐insulating GaAs crystals grown by the liquid‐encapsulated Czochralski technique. The changes in luminescence efficiency and subsequently the variations in threshold voltages were dramatically reduced by postgrowth annealing of the GaAs crystals under a variety of conditions. In this study, we employ the technique of spatially resolved cathodoluminescence (CL) to carefully examine the changes in luminescence efficiency due to postgrowth annealing. In agreement with previous work, we find that the CL variations are greatly reduced from a factor of ∼2 to ∼5% by thermal annealing at 800 °C for 30 h or at 1200 °C for 6 h followed by slow cooling. The latter thermal treatment is the same as that experienced by crystals during growth by the horizontal gradient freeze (HGF) technique. The extremely uniform luminescence efficiency of HGF crystals is thus believed to be a result of the thermal treatment during growth. Using evacuated sealed ampoule annealing in the temperature range of 550–650 °C, we show for the first time that improvements in CL uniformity are a result of a diffusion process which involves an As vacancy. Due to the dependence on As loss, values of the diffusivity (D) depend on the surface conditions. Values ofD=9×106exp(−2.6 eV/kT) cm2/s andD=1×107exp(−2.5 eV/kT) cm2/s are obtained for polished and as‐cut surfaces, respectively.

ISSN:0021-8979    

DOI:10.1063/1.334363

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Pure blue light emission has been obtained from ZnSep‐njunctions. ZnSe crystals are grown by the temperature difference solution growth method under controlled vapor pressure. Ap‐type ZnSe crystal can be grown from Se solution by doping with a group I element under controlled Zn pressure. The properties ofp‐type crystals have been measured by the van der Pauw method. Ap‐njunction has been made by the formation of then‐type layer by Ga diffusion into thep‐type crystal. The fundamental properties of thep‐njunctions are as follows: the value ofnin the I‐V characteristics ranges from 1.4 to 1.8 and the diffusion potential is between 2.5 and 2.7 eV. The emission spectrum from thep‐njunction depends on the vapor pressure during growth and blue light emission is obtained with optimum pressure. The wavelength of the main emission peak is 460 nm at 77 °K and 480 nm at 300 °K. The brightness is 2 mcd at 2 mA.

ISSN:0021-8979    

DOI:10.1063/1.334364

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The influence of OH ion impurities on thermoluminescent sensitivity and supralinearity in LiF:Mg, Ti is analyzed. Available evidence is shown to be consistant with the presence of Ti‐OH and Mg‐OH complexes. The track interaction model is used to explain the data, with competing centers decreasing sensitivity and supralinearity at high concentrations.

ISSN:0021-8979    

DOI:10.1063/1.334365

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The effects of doping on the polysilicon etch rate in a CF4‐CF3Cl‐O2planar plasma reactor are described. The effect is related only to the active carrier concentration and not to the total doping level. No significant change in etch rate was observed for carrier concentrations below 1019cm−3. At higher concentrations the etch rate rapidly increases for phosphorus and arsenic doping and decreases for boron. A qualitative model, which explains experimental results, is described.

ISSN:0021-8979    

DOI:10.1063/1.334366

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The process of alloy generation during laser surface alloying was examined. A numerical model was developed that solved the two‐dimensional, transient equation for convection diffusion of matter in the melt pool using the alternate‐diagonal implicit method. Velocity distributions used were for steels for a laser power of 1.5 kW, a 0.001‐m beam diameter and a traverse speed of 0.01 m/s. Calculations were made for a uniform surface mass flux of 5 and 10 kg m2 s−1and values of 100 and 1000 for the Peclet number for diffusion. The results showed that powder particles injected into the melt pool melted practically instantaneously, that good mixing was determined by the pattern of fluid flow, that average solute contents increased linearly with increasing interaction time, and that a change in the solute diffusivity by a factor of 10 did not greatly alter the predicted solute distribution. Good mixing was also found with surface flux over only a part of the melt pool. The conclusions were that fluid flow dominates the process of mass transport and determines the nature of the solute distribution, that powder feed is an effective method for surface alloying, and that results of the model could be used to better understand the process of laser surface alloying.

ISSN:0021-8979    

DOI:10.1063/1.334367

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We have measured the crystal growth rateuof B2O3‐I in the amorphous phase, as it varied over five orders of magnitude with changes in temperature and pressure. We eliminated the crystal nucleation barrier by seeding the surface of boron oxide glass with crystals.ubecame measurable only when the pressure exceeded a threshold level near 10 kbar. Using the published thermodynamic information on the B2O3system and a crude free‐energy model for the crystal and glass phases, we account qualitatively for our results with the theory of crystal growth limited by the rate of two‐dimensional nucleation of monolayers. The constants for the prefactor, activation energy, activation volume, and ledge tension are determined by fitting. By adjusting the thermodynamic parameters to a set of values that are well within the ranges delineated by their experimental uncertainties, we account quantitatively for the measured growth rates from 300 to 500 °C and from 0 to 30 kbar with the following relation:u(T,P)=(785 m/s)[‖&Dgr;Gm‖/(RT)]1/6×exp[&pgr;×3 A˚(420 erg/cm2)2(28 cm3/mole)/(3kT&Dgr;Gm)]exp[−10 366 cal/mole/(RT)] ×exp[−P×16 cm3/mole/(RT)]×{1−exp[&Dgr;Gm/(RT)]}2/3, with the driving free energy given by &Dgr;Gm(T,P)=(13 cm3/mole) [PM(T)−P] and the melting curve given byPM(T)=(T−450 °C)/(42.6 K/kbar). The ‘‘B2O3crystallization anomaly’’, that crystals have never been observed to grow at atmospheric pressure, is explained, since according to our model, the frequency of two‐dimensional nucleation is negligible at all temperatures at pressures less than 10 kbar.

ISSN:0021-8979    

DOI:10.1063/1.334368

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The dehydrogenation of highly photoconductive amorphous silicon films has been studied using15N,pnuclear reaction hydrogen depth profiling and isochronal anneals at temperatures between 300 and 500 °C. The studies shown that neither diffusion nor a first‐order reaction are the rate limiting dehydrogenation mechanism for hydrogen concentrations between 5 and 40 at. %. Dehydrogenation is not rate limited by processes at the surface. The studies suggest that for concentrations above 5 at. % the dehydrogenation may be explained by second‐order reaction kinetics involving the reordering of bonds. Below about 5 at. % a first‐order process leading to dangling silicon bonds appears to dominate.

ISSN:0021-8979    

DOI:10.1063/1.334369

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The uniformity of epitaxial growth of GaAs by metalorganic chemical vapor deposition in a vertical‐flow rotating‐disk reactor has been investigated. Observations of the thickness of the epitaxial layer versus radial distance on the susceptor surface are made for various conditions of carrier gas flow and growth temperature. A model is proposed in consideration of hydrodynamic and thermal boundary layer effects at the susceptor surface. The effects of a parasitic processes in the limit of smaller boundary layers and transition to source input rate‐limited growth in the limit of thicker boundary layers are described.

ISSN:0021-8979    

DOI:10.1063/1.334370

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The room‐temperature oxidation of Ni, Pd, and Pt silicides has been studied using electron spectroscopy for chemical analysis. It has been found that (1) Si atoms oxidize predominantly, (2) the oxidation of Si is enhanced in the metal‐rich silicides, and (3) the growth of the surface oxide layer leaves behind a phase enriched with metal.

ISSN:0021-8979    

DOI:10.1063/1.334371

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Lattice defect structures within large grains of cast polycrystalline silicon have been investigated using optical microscopy, x‐ray topography, and electron‐beam‐induced conductivity (EBIC) measurements. Optical observations through a series of wafers of an ingot indicate that kinks in high‐angle grain boundaries develop by forming straight grain boundaries rather than curved boundaries. It is also observed that a junction of three grain forms a kink in the grain boundary. X‐ray topographic observations of lattice defects show that cumulative dislocations are generated at these kinks when the material is subjected to thermal stresses at sufficiently elevated temperatures during solidification. Subsequently the dislocations propagate into the grain volume and form subgrain boundaries. In some cases, they pile up in the coherent {111} twin boundary interfaces. Observed EBIC constrast has shown that both dislocations and subgrain boundaries are electrically active and serve to decrease the effective minority carrier diffusion length.

ISSN:0021-8979    

DOI:10.1063/1.334372

出版商:AIP    

年代:1985

数据来源: AIP