摘要:

Laser ablative hole formation in amorphous Te‐Se‐I films was studied by microscopy and transient reflectivity measurements. Laser pulses of variable power and length were focused to either 0.8 or 10 &mgr;m spots on the films which were deposited on glass and polycarbonate substrates. The important feature of these films was that they did not crystallize upon pulsed laser irradiation. This allowed the examination of dependences on experimental parameters without the complication of phase transitions. The absence of a crystal‐melt interface in the films enabled the ablation of holes with exceptionally smooth rims. The experiments confirm that hole formation is by material flow, induced by the laser heating, radially away from the irradiation center. We show that the hole opening is a thermally activated process limited by viscous flow. A barrier of 0.7 eV is derived for the Te‐Se‐I films. Film viscosity and substrate thermal properties are identified as the key variables by which the dynamics of the process can be affected and the final shape of the hole thereby controlled.

ISSN:0021-8979    

DOI:10.1063/1.353385

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The effect of H2plasma exposure on CuInSe2was studied by synchrotron radiation soft‐x‐ray photoemission spectroscopy. The low‐power H2plasma was generated with a commercial electron cyclotron resonance plasma source using pure H2with the plasma exposure being performed at 200 °C.Insituphotoemission measurements were acquired after each plasma exposure in order to observe changes in the valence‐band electronic structure as well as changes in the In 4dand Se 3dcore lines. The results were correlated in order to relate changes in surface chemistry to the electronic structure. These measurements indicate that the H2plasma exposure type converts the CuInSe2surface to ann‐type surface as well as converting the In+3valency state to an In+1valency state.

ISSN:0021-8979    

DOI:10.1063/1.354063

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Understanding the mechanisms of reactive sputtering is thought to be crucial to obtain a better process control and widen applications of reactive sputtering. A model simulating reactive gas mass balance changes in reactive sputtering is described. The model is based on physical mechanisms involved in target and wall gettering behavior. This enables calculation of time‐dependent condition changes that occur until the process reaches a steady state, without assuming how the process reaches a steady state. Another important feature of the model is that hysteresis curves are obtained as a result of the calculation of time‐dependent target condition changes. This approach to obtain hysteresis curves is more similar to an actual reactive sputtering process. The proposed model clearly displays changes in target coverage, sputtered flux, and reactive gas partial pressure during compound‐layer formation and sputter etching processes as a function of elapsed time. Effects of reactive gas flow rate, pumping speed, and sputtering current on compound‐layer formation and sputter etching are also discussed. Hysteresis curves are yielded as a result of compound‐layer formation and sputter etching calculations. The obtained curves are in accord with experimental results. Further, the dependence of hysteresis on pumping speed, sputtering current, and the difference of sputtering yields between metallic and compound‐covered targets was investigated, resulting in showing a good agreement to that obtained experimentally. Mechanisms of hysteresis formation are also discussed on the basis of obtained results. It is concluded that hysteresis is formed because of the difference of gettering capacity before and after the target surface condition transition.

ISSN:0021-8979    

DOI:10.1063/1.353386

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

When Al alloys such as Al‐1%Si or Al‐2%Cu are sputtered on Si substrates at elevated temperatures, extruded single crystal precipitates are observed on the alloy films. The morphology and crystallography of the precipitates are studied in detail using scanning electron microscopy and transmission electron microscopy. The precipitates on the Al‐2%Cu films contain a few percent Cu and are single crystals with crystallographically low‐index facet planes. The temperature profiles during and after the deposition for the favorable occurrence of the precipitation are also investigated.

ISSN:0021-8979    

DOI:10.1063/1.353387

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The effects of incident ion/metal flux ratioJi/JMeand ion energyEion the microstructure, texture, and phase composition of polycrystalline metastable Ti0.5Al0.5N films produced by reactive magnetron sputtering have been investigated using x‐ray diffraction (XRD), plan‐view and cross‐sectional transmission electron microscopy, and Rutherford backscattering spectroscopy. The films, typically &bartil;1 &mgr;m thick, were deposited at a pressure of 20 mTorr (2.67 Pa) in pure N2on thermally oxidized Si(001) substrates at 250±25 °C. The N2+ion flux to the substrate was controlled by means of a variable axial magnetic field superimposed on the permanent magnetic field of the magnetron. Films deposited atEi=20 eV (&bartil;10 eV per incident accelerated N) withJi/JMe=1 exhibited a complete (111) texture with a porous columnar microstructure and an average column size of &bartil;30 nm. IncreasingEifrom 20 to 85 eV, while maintainingJi/JMeconstant at 1, resulted in a small change in texture as the XRD intensity ratioI002/(I111+I002) increased from &bartil;0 to 0.14, a decrease in average column size to 25 nm, and a reduction in intracolumn porosity.The stoichiometric ratio N/(Ti+Al) increased from 1 atEi=20 eV withJi/JMe=1 to 1.23 atEi=85 eV indicating trapping of excess N while the lattice constanta0increased from 0.4157 to 0.4188 nm due to compressive stress.Eivalues ≥100 eV led to alloy phase separation. In contrast, maintainingEiat &bartil;20 eV and increasingJi/JMefrom 1 to ≥5.2 resulted in a change from a porous (111) texture to a dense completely (002)‐oriented microstructure with an increase in the average column size to 35 nm. N/(Ti+Al) anda0remained essentially constant and the alloy remained single phase. Mechanistic pathways leading to microstructure and texture changes through variations inEiat constantJi/JMeand inJi/JMeat constantEiwere found to be quite different. The average energy deposited per metal atom, ⟨Ed⟩=Ei(Ji/JMe), is therefore not a universal parameter, as has been previously proposed, for describing film growth.

ISSN:0021-8979    

DOI:10.1063/1.353388

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Polycrystalline nickel lines as small as 1 &mgr;m in width were deposited by pyrolysis of nickel tetracarbonyl [Ni(CO)4] on polysilicon/silicon dioxide/monosilicon substrates. As heat source, a cw argon‐ion laser operating at several wavelengths around 0.5 &mgr;m was used. The growth kinetics, morphology, and electrical resistivity of the nickel microstructures were investigated at various scanning speeds of the laser spot, laser beam powers, and reactant gas pressures. From the deposition kinetics, the vertical deposition rate of nickel was calculated. For Ni(CO)4pressures below 0.3 mbar, deposition of flat‐topped nickel lines occurs. The deposition rate was proportional to the Ni(CO)4pressure and independent of the laser output power. For Ni(CO)4pressures above 0.3 mbar, lines with a Gaussian profile are obtained. The deposition rate was found to be independent of the Ni(CO)4pressure and exhibits an activation energy of 11.5 kcal mol−1. The measured electrical resistivity of the flat‐topped lines was about ten times higher than that of the bulk (7 &mgr;&OHgr; cm) while for the Gaussian lines this ratio falls below 1.5. Kinetic measurements with carbon monoxide (CO) as buffer gas were also performed. The nickel deposition rate was found to decrease as the CO partial pressure increases for all the Ni(CO)4partial pressures considered (0.2–20 mbar). The morphology and roughness of the deposited lines were investigated using both a scanning electron microscope and an atomic force microscope. The effect of the laser beam on the quality of the interfaces underlying the deposited lines was investigated by means of a focused ion beam system. On the basis of the experimental results, a decomposition mechanism of the Ni(CO)4molecules was elaborated.

ISSN:0021-8979    

DOI:10.1063/1.353389

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The actual performance of series‐connected photovoltaic multigap cells may substantially deviate from the design point performance. The influence of variations in cell temperature, solar irradiance, and its spectral distribution on thermodynamically ideal cells with one to five gaps is assessed. It is found that multigap cells behave equally sensitive to average meteorological conditions as one‐gap cells. When exposed to direct radiation only, the performance of multigap cells can decrease strongly for extreme conditions; however, generally these conditions give such small output that they do not significantly decrease the energy yield.

ISSN:0021-8979    

DOI:10.1063/1.353390

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A robust injector capable of controlling the radius and angle of incidence of the pulsed, intense, annular electron beam extracted from the HERMES III accelerator is described. The injector, called the compound lens, uses a tapered anode to control the beam electrostatically, followed by a gas cell with externally applied current to control the beam magnetically. Adjustment of the anode‐cathode gap and external current of the injector permits the radius and angle to be defined independently of one another. Measurements of these quantities confirm model expectations.  

ISSN:0021-8979    

DOI:10.1063/1.353391

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A new delta‐doped quantum well negative‐differential‐resistance (NDR) switch, grown by molecular beam epitaxy, has been fabricated and demonstrated. A delta‐doped sheet [&dgr;(p+)], located at the center of InGaAs quantum well, provides a potential barrier for electron injection. When a sufficiently high voltage bias is applied, an interesting S‐shaped NDR phenomenon can be observed due to the avalanche multiplication and potential redistribution process. From experimental results, it is known that the environmental temperature plays an important role on the NDR performance. The influence of temperature on the device performance is studied.

ISSN:0021-8979    

DOI:10.1063/1.353392

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The realization of collector‐up light‐emitting complementary charge injection transistors is reported. The devices have been implemented in molecular‐beam‐epitaxy‐grownn‐InGaAs/InAlAs/p‐InGaAs andn‐InGaAs/InP/p‐InGaAs heterostructures using a self‐aligned process for the collector stripe definition. Electrons, injected over the wide‐gap heterostructure barrier (InAlAs or InP) by the real‐space transfer (RST) process, luminesce in the low‐dopedp‐type InGaAs active layer. An essential feature of present devices, besides their self‐aligned collector‐up configuration, is a relatively heavy doping of then‐type emitter channel, with the sheet dopant concentration of 4×1012cm−2. This ensures a higher uniformity of the electric field in the channel and provides a relief from RST instabilities at a high level of collector current (linear density ∼10 A/cm). Devices with InAlAs and InP barriers show rather different optical characteristics, mainly due to the different band lineups &Dgr;EC/&Dgr;EVin InGaAs/InAlAs and InGaAs/InP heterostructures, leading to different ratios between the RST current and the parasitic leakage of holes from the collector into the channel. At high RST current densities, the effective carrier temperatureTein the active collector layer, determined from the high‐energy tails of the luminescence spectra, is strongly enhanced compared to the lattice temperature. This decreases the device radiative efficiency and leads to a thermionic emission of carriers out of the active layer.

ISSN:0021-8979    

DOI:10.1063/1.353393

出版商:AIP    

年代:1993

数据来源: AIP