摘要:

The dielectric response functions in the valence bands and in the conduction band of heavily doped zincblende semiconductors have been evaluated using the self‐consistent field method and incorporating thefinitelifetime of particles in the relaxation time approximation. Scattering rates of injected electrons are calculated with the Born approximation in the dielectric response function formalism atfinitetemperature. The finite particle lifetime introduces significant modifications to the spectral density function {Im[−1/&egr;(q,&ohgr;)]} at smallq, where collective excitations (i.e., coupled phonon‐plasmon modes) are heavily damped due to collisions. However, these modifications are small at largeq. At the same time, the scattering rates of injected electrons are strongly affected by the temperature dependence of these effects, which are particularly significant forp‐type semiconductors.

ISSN:0021-8979    

DOI:10.1063/1.352222

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Conduction current in the phosphor layer of ZnS:Mn ac thin film electroluminescent (ACTFEL) display device was measured as a function of the amplitude and the rise time of the bipolar voltage pulses: electric field in the phosphor was also determined. It was found that the clamping field of an ac thin film electroluminescent device is not a single‐valued device characteristic. The clamping field depended upon the rise time of the applied voltage pulse increasing in value as the rise time became smaller. These data were interpreted in terms of a nonideal breakdown of the insulator‐phosphor interface and a time delay involved in the emission of electrons from this interface. To account for the nonideality in the interface breakdown the ac equivalent circuit of the ACTFEL device was modified by including a voltage‐dependent resistor in parallel with the phosphor capacitance. The phosphor current measurements, transferred charge measurements and tunneling current calculations indicate that in the nonhysteretic ZnS:Mn devices under investigation, impact ionization in the phosphor layer, if present at all, leads to relatively small carrier multiplication factors.

ISSN:0021-8979    

DOI:10.1063/1.352223

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The native oxide, thermally oxidized and hydrofluoric acid rinsed surfaces of Si(100) have been characterized by photon stimulated ion desorption (PSD), and both photoelectron and Auger electron spectroscopies. The only species detected by PSD were H+ions with different kinetic energies. Low kinetic energy H+ions were detected only from the HF rinsed surfaces presumably arising from scission of Si—H bonds while higher kinetic energy ions attributed to adsorbed hydrocarbon dissociation were observed for all of the surfaces.

ISSN:0021-8979    

DOI:10.1063/1.352224

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Accurate measurements of the minority carrier‐ and lattice scattering‐diffusion constant and mobility in float zone silicon have been determined using photoconductance decay. For the more lightly doped specimens our results indicate slightly higher mobility than published majority carrier values. This is attributed to purer samples which allow a more accurate measurement of the lattice scattering mobility. In the dopant range 1015–1017cm−3the results for both electrons and holes are, within experimental error, equal to the majority carrier values. Unlike other methods this technique is a very direct measurement of the diffusion constant as only the thickness and decay time of the wafer need to be determined. The method is estimated to have a one standard deviation uncertainty of 2%–4% which is comparable to the best accuracy previously obtained for majority carrier measurements.

ISSN:0021-8979    

DOI:10.1063/1.352225

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have investigated the effect of oxygen plasma treatment on GaAs surface prior to plasma enhanced chemical vapor deposition of silicon nitride cap on the activation efficiency of implanted Si in GaAs. The oxygen plasma treatment improved the activation efficiency by ∼35% over (1:10) NH4OH:H2O treatment. In addition, the oxygen plasma treated samples had uniform sheet resistance across the wafer with minimum wafer‐to‐wafer variations. X‐ray photoelectron spectroscopy analysis of oxygen plasma treated GaAs surface indicated the formation of ∼25‐A˚‐thick oxide layer consisting of Ga2O3, As2O3, As2O5, and elemental As. During the activation anneal, the arsenic‐containing oxides react with the GaAs substrate to form Ga2O3and elemental As which increases the probability that the implanted Si incorporates in the Ga sites over the As sites, and thereby improves the activation efficiency. This surface related mechanism suggests that the variation in activation efficiency is mostly attributed to variation in surface conditions, and may explain the wide variety of reported values of activation efficiency. The higher and uniform activation efficiency for high Si implants improved the wafer scale variation of ohmic contact resistance ton+‐GaAs.

ISSN:0021-8979    

DOI:10.1063/1.352226

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Studies on electrical properties of highly ordered and amorphous thin films of pentacene (PEN) doped with iodine have been made. Highly ordered film heavily doped with iodine (PEN1I2.2) showed electrical conductivity of 150 &OHgr;−1 cm−1with a hole mobility of 0.2 to 1 cm2 V−1 s−1at room temperature. Metallic temperature dependence of the conductivity of the film from 240 to 4 K was observed as the first metallic transport phenomenon ever noted in an acenic compound. In contrast, amorphous film of PEN doped with iodine showed a conductivity of 10−3&OHgr;−1 cm−1with an estimated hole mobility of 2×10−5cm2 V−1 s−1and semiconductive transport. These results revealed that the electrical properties of PEN thin films are strongly correlated with the degree of molecular orientation.

ISSN:0021-8979    

DOI:10.1063/1.352227

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

‘‘Nongold’’ NiGe Ohmic contacts were developed by a lift‐off and annealing technique that was extensively used to fabricate the conventional AuGeNi contacts. The optimum conditions to prepare thermally stable, low resistance NiGe Ohmic contacts were determined by changing the Ge concentrations of the NiGe contacts from 13 to 43 at. %, and the deposition sequences of the Ni and Ge layers. Contact resistances of ∼0.8 &OHgr; mm were obtained for both two‐layered Ni/Ge and three‐layered Ni/Ge/Ni contacts, with Ge concentrations of ∼38 at. % after annealing at 600 °C. The thermal stability of the electrical properties during subsequent annealing at 400 °C after contact formation was found to be influenced by the microstructure at the GaAs/metal interface. The excellent stability was obtained only when the NiGe contacts formed high melting point NiGe compounds. The present result indicated that removal of Au from the AuGeNi contacts was not satisfactory enough to improve the thermal stability of the AuGeNi contacts after contact formation. A model for the current transport mechanism through the GaAs/NiGe interface was also proposed by correlating the electrical properties and the microstructure. This model explained well the dependences of the contact resistances on the Ge concentrations and the deposition sequence of the Ni and Ge layers.

ISSN:0021-8979    

DOI:10.1063/1.352228

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

New ‘‘nongold’’ NiSiW Ohmic contacts ton‐type GaAs have been developed using an electron beam evaporator and a rapid thermal annealer. Ohmic behavior was found to have dependencies on the Si concentrations of the NiSiW contacts and the annealing condition. The Ohmic contacts with 40 at. % Si, prepared by annealing at 650 °C, had smooth surfaces and yielded excellent thermal stability during subsequent annealing at 400 °C after contact formation. The microstructural analysis of the interface between the contact metal and the GaAs substrate was carried out using x‐ray diffraction, Auger electron spectroscopy, and cross‐sectional transmission electron microscopy. It was concluded that the key parameter that influenced the electrical properties was the NiAs compounds formed during contact annealing.

ISSN:0021-8979    

DOI:10.1063/1.352229

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have investigated the influence of structural characteristics on the band gap of rf sputtered CdTe thin films grown at substrate temperatures in the 69–232 °C range. The results of scanning electron microscopy and x‐ray diffraction studies indicated that the films are a polycrystalline mixture of cubic and hexagonal phases with preferential growth of columnar type parallel to the cubic [111] direction. The band gap of the films was obtained from photoreflectance spectroscopy experiments carried out at room temperature. It was found that the films had a band gap larger than that of CdTe single crystals. This result has been correlated with the existence of lattice strain, quantum size effects, and hexagonal phase regions. By using theoretical models it was possible to estimate the contribution to the band gap shift due to strain and quantum size effects obtaining results in good agreement with the experiment. The study of annealed samples indicated that the effects of thermal treatments were to promote the change of the hexagonal phase to cubic, increase grain size, and shift the band gap towards lower energies reducing its difference with respect to that of single crystals.

ISSN:0021-8979    

DOI:10.1063/1.352230

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

c‐axis‐oriented ZnO films were prepared in O2atmosphere by chemical vapor deposition using zinc acetylacetonate for source material. A minimum value of resistivity, 2.44 &OHgr; cm, was obtained at a film formation temperature of 550 °C. The resistivity of the films was measured at low temperatures (87–297 K). For temperatures between 200 and 297 K band conduction included boundary scattering due to both thermionic emission and thermal‐field emission at the grain‐boundary barriers in the films, and the activation energy obtained ranged from 1.45 to 6.32×10−2eV. For temperatures lower than about 200 K, the conductivity deviated from linear Arrhenius plots suggesting variable range‐hopping conduction. Discussions based on assumed electron mobility and concentration lead to variable range‐hopping conduction by localization of electrons in impurity levels in the intermediate concentration region. Mott’s parameters in the variable range‐hopping conduction were estimated for the films.

ISSN:0021-8979    

DOI:10.1063/1.352231

出版商:AIP    

年代:1992

数据来源: AIP