摘要:

The influence of a titanium‐titanium nitride (Ti/TiN) barrier metallization on the behavior of junctions has been investigated. Different geometries have been used in order to separate the various contributions to the electrical behavior of junctions. An increase of the reverse current of junctions is observed in the presence of Ti/TiN/Al:Si contacts. This fact does not produce an increase of junction defect density, since the reverse current of junctions remains within an acceptable range. The contribution to junction reverse current induced by Ti/TiN/Al:Si contacts has been characterized; it has been shown that it is related to contact perimeter, it is independent of many relevant process steps, and it is reduced by thermal treatments after metal deposition. By assuming that this contribution is due to a generation‐recombination center induced by Ti/TiN contacts, the analysis of current‐voltage characteristics versus temperature gives an activation energy for this contribution. However, at present the available data do not allow us to identify its cause.

ISSN:0021-8979    

DOI:10.1063/1.346576

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Slow moving material (velocity ≊3×104cm/s) ejected from polycarbonate and poly(&agr;‐methylstyrene) targets by ultraviolet laser photoablation is probed using time‐of‐flight mass spectroscopy. The product distribution seen from polycarbonate, using resonant‐two‐photon ionization with 248‐ or 266‐nm light, consists of aromatic species smaller than the monomer. Mass spectra are similar for 355‐, 266‐, and 193‐nm ablation, and the products differ structurally from the starting material; both observations suggest that slow moving species are ejected by a thermal mechanism at all three wavelengths. 248‐nm ablation of polycarbonate near the ablation threshold, gives a different product distribution and it is argued that a cooler thermal regime is being sampled or, that photochemical effects are important. The dominant product seen in 266‐, 248‐, and 193‐nm ablation of poly(&agr;‐methylstyrene) is the monomer in each case. Subtle differences present in the resulting mass spectra may be due to photochemical effects, but major similarities suggest that slow movers are ejected by a photothermal mechanism.

ISSN:0021-8979    

DOI:10.1063/1.346577

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The bare work functions of etched and unetched plasma‐sprayed tungsten were found to be 4.8 and 4.5 eV, respectively. The electron emission of plasma‐sprayed tungsten, both etched and unetched, was measured over a wide range of temperatures in a cesium atmosphere. Work functions were derived from the saturation current densities. In the ignited mode, current‐voltage (I‐V) characteristics were measured. The influence of the emitter, collector, and cesium reservoir temperatures on theI‐Vcharacteristics was investigated. Barrier indexes of 2.06 and 2.30 eV were found for etched and unetched tungsten emitters, respectively. At an emitter temperature of 1400 °C, in the case of an unetched tungsten emitter a power density of 1.5 W/cm2was found, while for an etched tungsten emitter it was 4.5 W/cm2. This increased power density could be attributed to a lower collector work function. The lower cesiated collector work function resulted from the evaporation of oxygen, as WO3, from the etched tungsten emitter.

ISSN:0021-8979    

DOI:10.1063/1.346578

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Theoretical efficiencies are calculated for two‐junction, series‐connected solar cells using air mass 1.5 global and direct irradiance spectra. For band‐gap combinations previously limited by a low bottom‐cell current, thinning of the top cell is shown to result in significant increases in the theoretical efficiencies. The increases are primarily due to increased short‐circuit currents, since current matching is achievable. Smaller gains are also seen in the open‐circuit voltages of the thinner cells when a low surface‐recombination velocity is assumed. Thus, a number of material combinations which previously could only be used in four‐terminal configurations can now be considered for series‐connected two‐junction solar cells.

ISSN:0021-8979    

DOI:10.1063/1.347177

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The current‐voltage characteristics ofp‐channel MOSFETs (metal‐oxide‐semiconductor field‐effect transistors) in the temperature range 4.2‐50 K have been investigated in detail. A peak is observed at the beginning of the drain‐current–drain‐voltage (Id,Vd) curves for lowVgvalues, which is not observed in the case ofn‐channel MOSFETs and is found to be a very slow transient effect. This time‐dependent peak is observed for temperatures below ∼25 K and for channel lengths greater than ∼3 &mgr;m. In this temperature range a strong hysteresis effect is also observed at lowVgvoltages. The above behavior will be explained in terms of a very slow depletion layer formation in the drain region, introduced by the large time constant of the field‐assisted thermal emission of carriers inn‐type bulk semiconductors at temperatures below ∼20 K. Another effect, analogous to the ‘‘kink effect’’ observed inn‐channel MOSFETs at temperatures below 16 K, is also observed for lowVgandVdvalues. This effect is observed with difficulty and is less pronounced than inn‐channel MOSFETs.

ISSN:0021-8979    

DOI:10.1063/1.346579

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The memory retention characteristics of silicon‐nitride‐oxide‐silicon nonvolatile memory devices are found to be strongly thermally activated. A model is developed based on thermal emission of charge from traps. This model accurately predicts the threshold voltage decay of transistors stored in varying thermal environments. The model is demonstrated to be accurate over 7 decades of time and for temperatures between −40 and 200 °C.

ISSN:0021-8979    

DOI:10.1063/1.346580

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have investigated solid state amorphization reactions in mechanically deformed composites in both the Ni‐Ti system and the Ni‐Zr system. The growth of amorphous material in our Ni/Ti composites is apparently facilitated by the relatively large degree of disorder induced in the metal layers by the mechanical deformation process. The growth of amorphous material is slower in Ni/Ti composites than in Ni/Zr composites, while we found similar kinetic constraints on the formation of equilibrium compounds in both systems. Thus the maximum thickness of amorphous Ni‐Ti layers was an order of magnitude less than the 1000‐A˚ layers grown in the Ni‐Zr system.

ISSN:0021-8979    

DOI:10.1063/1.346581

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The far infrared (FIR) photoconductivity of GaAs/AlGaAs multiquantum wells (MQWs) doped with silicon has been investigated. The spectral response is consistent with extrinsic photoconductivity from shallow donors with an effective Rydberg of approximately 10.5 meV. The time‐resolved photoconductivity due to stimulation with a cavity‐dump FIR laser is measured. Subnanosecond rise and decay times are implied for the MQWs investigated; these times are shorter than for the corresponding bulk cases. Possible effects of geometric confinement on recombination rates are discussed. For a 150‐period MQW, the responsivity at 118 &mgr;m is approximately 105V W−1.

ISSN:0021-8979    

DOI:10.1063/1.346582

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Graded‐index separate‐confinement heterostructure single‐quantum‐well GaAs/AlGaAs diode lasers exhibiting continuous (cw) operation at room temperature have been grown on a Si substrate by organometallic vapor‐phase epitaxy, without the use of molecular‐beam epitaxy. To improve the quality of the laser structure, a defect‐filtering layer was incorporated between this structure and a GaAs buffer layer about 1.5 &mgr;m thick grown on the substrate. Of four types of defect‐filtering layers investigated, the most effective was one grown with thermal cycling, which made it possible to obtain pulsed threshold current densities as low as 350 A/cm2for broad‐stripe lasers with a cavity length of 500 &mgr;m. Ridge‐waveguide lasers with this type of defect‐filtering layer have exhibited cw threshold currents as low as 25 mA and a differential quantum efficiency of 55%.

ISSN:0021-8979    

DOI:10.1063/1.346583

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Pseudomorphic In0.6Ga0.4As/In0.52Al0.48As 1 &mgr;m gate modulation‐doped field‐effect transistors have been monolithically integrated with In0.53Ga0.47As photodiodes for front‐end photoreceivers using one‐step molecular‐beam epitaxy and lithography techniques. A 1‐&mgr;m thick undoped In0.52Al0.48As layer is used to isolate the two devices. The transistors are characterized bygm(ext) =500 mS/mm andfT=9 GHz. The temporal response of the photodiodes is characterized by a linewidth of 60 ps. The eye pattern of the photoreceiver circuit for 1.7 Gbit/s pseudorandom optical signal is open and it is expected that the circuit can perform at bandwidths up to 2.5 GHz. Measured bandwidths of ∼6.5 GHz are obtained by using regrowth.

ISSN:0021-8979    

DOI:10.1063/1.346584

出版商:AIP    

年代:1990

数据来源: AIP