An investigation of the formation mechanisms of electric field domains in GaAs/AlAs superlattices

We have studied the vertical transport and formation mechanisms of electric field domains in doped weakly-coupled GaAs/AlAs superlattices. Under hydrostatic pressure two kinds of sequential resonant tunneling are observed within the pressure range from 0 to 4.5 kbar. A transition from Gamma-Gamma to Gamma-X sequential resonant tunneling occurs at P-t approximate to 1.6 kbar. For P < P-t, the high electric field domain is formed by the Gamma-Gamma process, while for P > P-t it is preferentially formed by the Gamma-X process.

Some new observation on the formation and optical properties of CdS clusters in zeolite-Y

CdS clusters in zeolite-Y have been prepared by the exchange of Cd2+ into the zeolite following by sulfurization with Na2S in solution. Blue-shifts from the bulk caused by quantum size effect and the change of absorption upon CdS loading are observed. Two absorption bands are detected for one of the sample and are assigned to the 1s-1s band and exciton transition, respectively. The exciton feature is more pronounced in the excitation spectrum than in the absorption spectrum, and the luminescence excited at the exciton band is stronger than that at the 1s-1s band. Copyright (C) 1996 Elsevier Science Ltd

Formation of Fe-N films containing Fe6N2 phase by ion beam assisted deposition

Fe-N films were deposited on Si(100) and GaAs(100) substrates at room temperature by ion beam assisted deposition under various N/ Fe atomic arrival ratio, 0.09, 0.12, 0.15. The results of X-ray diffraction indicated that the film deposited at 0.12 of N/Fe arrival ratio contained a considerable fraction of the Fe16N2 phase which had grown predominantly in the [001] orientation. For the larger N/Fe arrival ratio, a martensite phase with 15 at.% nitrogen was obtained. It was found that a lower deposition temperature (<200 degrees C) was necessary for the formation of the Fe16N2 phase.

New observation on the formation of PbS clusters in zeolite-Y

PbS clusters in zeolite-Y have been prepared with the reaction of Pb2+-ion-exchanged zeolite-Y with Na2S in solution at room temperature. Their absorption spectra show dramatic blue shifts from that of the bulk PbS. Obvious change of both the absorption edges and peak positions upon PbS concentrations have been observed. These phenomena provide evidences that PbS clusters have been formed within the zeolite. The absorption spectra show featureless structure and have no tails near the absorption edges. As the PbS loading density becomes higher, the absorption bands become stronger and sharpen. Order PbS clusters lattice with high quality might be formed in the supercages of zeolite-Y. (C) 1996 American Institute of Physics.

Influence of Fe Doping Concentration on Some Properties of Semi-Insulating InP

Properties of Fe-doped semi-insulating (SI) InP with different iron concentrations are studied by using Hall effect, current-voltage (I-V), photoluminescence spectroscopy (PL) and photocurrent spectroscopy (PC) measurements. I-V characteristics of SI InP strongly depend on Fe doping concentration. Fe doping concentration also influences optical properties and defective formation in as-grown SI InP. Band-gap narrowing phenomenon and defects in Fe doped SI InP are studied using PI and PC.

Preparation of Semi-Insulating Material by Annealing Undoped InP

Semi-insulating (SI) InP wafers of 50 and 75mm in diameter can be obtained by annealing of undoped liquid encapsulated Czochralski (LEC) InP at 930 ℃ for 80h. The annealing ambient can be pure phosphorus (PP) or iron phosphide (IP). The IP-SI InP wafers have good electrical parameters and uniformity of whole wafer. However, PP-SI InP wafers exhibit poor uniformity and electrical parameters, Photoluminescence which is subtle to deep defect appears in IP-annealed semi-insulating InP. Traps in annealed SI InP are detected by the spectroscopy of photo-induced current transient. The results indicate that there are fewer traps in IP-annealed undoped SI InP than those in as-grown Fe-doped and PP-undoped SI-undoped SI InP. The formation mechanism of deep defects in annealed undoped InP is discussed.

Formation of ZnS clusters in xeolite-Y

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Annealing ambient controlled deep defect formation in InP

Deep defects in annealed InP have been investigated by deep level transient capacitance spectroscopy (DLTS), photo induced current transient spectroscopy (PICTS) and thermally stimulated current spectroscopy (TSC). Both DLTS results of annealed semiconducting InP and PICTS and TSC results of annealed semi-insulating InP indicate that InP annealed in phosphorus ambient has five defects, while lid? annealed in iron phospbide ambient has two defects. Such a defect formation phenomenon is explained in terms of defect suppression by the iron atom diffusion process. The correlation of the defects and the nature of the defects in annealed InP are discussed based on the results.

Effects of polarization field on formation of two-dimensional electron gas in (0001) and (11(2)over-bar0) plane AlGaN/GaN heterostructures

Photoluminescence (PL) and temperature-dependent Hall effect measurements were carried out in (0001) and (11 (2) over bar0) AlGaN/GaN heterostructures grown on sapphire substrates by metalorganic chemical vapor deposition. There are strong spontaneous and piezoelectric electric fields (SPF) along the growth orientation of the (0001) AlGaN/GaN heterostructures. At the same time there are no corresponding SPF along that of the (1120) AlGaN/GaN. A strong PL peak related to the recombination between two-dimensional electron gas (2DEG) and photoexcited holes was observed at 3.258 eV at room temperature in (0001) AlGaN/GaN heterointerfaces while no corresponding PL peak was observed in (11 (2) over bar0). The existence of a 2DEG was observed in (0001) AlGaN/GaN multi-layers with a mobility saturated at 6000 cm(2)/V s below 80 K, whereas a much lower mobility was measured in (11 (2) over bar0). These results indicated that the SPF was the main element to cause the high mobility and high sheet-electron-density 2DEG in AlGaN/GaN heterostructures. (C) 2004 Elsevier B.V. All rights reserved.