摘要:

Using the extended x‐ray absorption fine structure method, we have studied the local structures around Zn atoms in Zn‐doped GaAs crystal grown by the liquid‐encapsulated Czochralski technique. Zn atoms, whose concentration is about 2.4×1018cm−3, have the first nearest neighbor atoms at a very short distance of about 1.95 A˚ and the second nearest neighbor atoms at a distance of about 3.15 A˚. The Zn atom configuration forms ‘‘interstitialcy’’, not substitutional, tetrahedral, or hexagonal sites. As the Zn concentration increases, however, Zn atoms have a tendency to occupy substitutional sites.

ISSN:0003-6951    

DOI:10.1063/1.101123

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The early stages of diamond film nucleation and growth in a microwave plasma have been studied in detail as a function of important deposition parameters. The influence of the substrate temperature on the diamond nucleation rate, quality, and final film morphology has been elucidated through Raman spectroscopy and scanning electron microscopy measurements. Using transmission infrared spectroscopy and x‐ray diffraction, it is found that a carbide layer is initially formed on the substrate prior to the growth of the diamond film. Furthermore, the final film morphology is also a strong function of the plasma starting condition, the gas composition, and the substrate temperature.

ISSN:0003-6951    

DOI:10.1063/1.101124

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The effect of growth conditions on the stability of &agr;‐Sn films grown by molecular beam epitaxy on CdTe is studied. The growth conditions considered are substrate orientation, thickness, growth rate, and substrate temperature. The transition temperature from &agr;‐Sn to &bgr;‐Sn, as determined by optical microscopy, is used as the measure of stability. It is shown that CdTe(110) is a somewhat better orientation than CdTe(100), and CdTe(111)Bis totally unacceptable for the growth by molecular beam epitaxy of &agr;‐Sn films. The transition temperature from &agr;‐Sn to &bgr;‐Sn shows a dependence on the total film thickness, with thinner films having a somewhat higher transition temperature than thicker. The quality of the films is the best when the growth rate is about 0.5 A˚/s and the growth temperature is about 75 °C. Since the transition from &agr;‐Sn to &bgr;‐Sn starts at defects in the film, improving the quality of the film by lowering the growth rate and raising the growth temperature raises the transition temperature.

ISSN:0003-6951    

DOI:10.1063/1.101125

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The preferred crystallographic orientation, or texture, of aluminum films deposited on oxidized silicon by evaporation and by partially ionized beam (PIB) deposition is studied. Texture is quantified by the x‐ray diffraction pole figure technique. The pole figures reveal important details of the crystallite distribution not quantifiable by simply taking the 2&thgr; scan. It is found that the films deposited by the PIB technique possess a very strong {111} fiber texture whose strength can be controlled by deposition conditions. Correlation between the strength of the texture and the electromigration lifetime is discussed.

ISSN:0003-6951    

DOI:10.1063/1.101126

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

In an electron inversion layer on a degeneratep‐type InAs substrate, a resonance effect is observed in tunneling from the two‐dimensional electron gas into the continuum of valence states. The effect is confirmed by additional magnetotunneling measurements.

ISSN:0003-6951    

DOI:10.1063/1.101127

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The small mass of light holes in strained quantum wells leads to high mobility at low fields. However, at high fields, the holes become hot and populate the heavy hole band, thereby greatly reducing their mobility. An analysis shows that the high‐field mobility primarily depends on &Dgr;, the strain splitting of the light and heavy holes, and ℏ&ohgr;0, the optical phonon energy. If &Dgr;<ℏ&ohgr;0, the light holes transfer to the heavy hole band at relatively low power and small fields. If &Dgr;≊ℏ&ohgr;0, the low‐field mobility is greatly enhanced without producing negative differential mobility at high fields. If &Dgr;>ℏ&ohgr;0, the high mobility persists until the applied power per carrierPexceeds a characteristic powerP0. Above this power, negative differential mobility (a Gunn effect) occurs when the light holes transfer to the heavy hole band. For thinp‐doped In0.2Ga0.8As/GaAs single‐strained quantum wells, Monte Carlo calculations show thatP0≊5×10−8W/carrier.

ISSN:0003-6951    

DOI:10.1063/1.101128

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Using laser structures with a window in the contact stripe, we have observed recombination from the wells and barrier regions of GaAs‐AlGaAs quantum well lasers. The magnitude of the ratio of emission intensities from the barrier and the well, and the dependence of this ratio upon injection current, are in good agreement with a calculation in which the carrier populations in well and barrier are in thermal equilibrium at the lattice temperature (300 K).

ISSN:0003-6951    

DOI:10.1063/1.101129

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The electric field induced localization and decoupling of quantized levels (FILD) in double quantum wells is studied both theoretically and experimentally and is shown to result in a novel blue shift of optical absorption peaks. The absorption edge of doubly coupled 54 A˚ GaAs wells separated by a 5.7 A˚ AlAs inserted barrier is found to shift by 8 meV toward the higher energy under a moderate field (>30 kV/cm). Considering the field‐induced variation of quantized levels and excitonic effect, the observed shifts of most peaks are well explained by the simple effective mass theory. Device applications of this novel electro‐optic effect (FILD) are also discussed.

ISSN:0003-6951    

DOI:10.1063/1.101130

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The behavior of ideally soft ferromagnetic films in the presence of a weak coplanar magnetic field is explored by the method of characteristics. Solutions are found which have no internal field or in some cases have field‐free zones. Results are specifically given for circular and elliptic disks, the infinite strip, and the semi‐infinite plane. The disk solutions have internal domain walls.

ISSN:0003-6951    

DOI:10.1063/1.101131

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Simultaneous measurement of both the conduction‐ and valence‐band dispersion curves in single strained‐layer structures is presented. These measurements rely on the application of recent observations regarding breaking of the usual selection rules for interband magnetoluminescence transitions in modulation‐doped structures. Low‐temperature magneto‐luminescence data for three representative InGaAs/GaAsn‐type single‐strained quantum well structures are presented. For energies approaching 50 meV above the band gap, we find that the conduction band is parabolic with an effective mass of 0.071m0. Over the same energy range, the valence bands are highly nonparabolic.

ISSN:0003-6951    

DOI:10.1063/1.101367

出版商:AIP    

年代:1989

数据来源: AIP