摘要:

Generation of native defects during growth of heavily Si-doped GaAs and their effects on carrier concentrations in heavily doped and adjoining lightly Si-doped GaAs layers are investigated. The mechanism of their intrusion from the heavily doped layer into the lightly doped layers is discussed. The behavior of the native defects during annealing after growth is also studied. As Si doping concentration increases, the concentration of triply ionized gallium vacancy (VGa3−), generated by a Frenkel-pair defect formation process, increases. The limit of free-carrier concentration in the heavily doped layers is caused by thisVGaand not by electron occupation of a highly localized state of the donor-related DX center.VGaalso causes carrier compensation in the adjoining underlayers. However, the carrier concentration in the adjoining overlayer grown on the heavily doped layer is not affected. We infer that drift is the predominant process forVGaflow into the lightly doped layers. This drift is caused by the electric field induced by a surface–Fermi-level pinning, mainly in an early growth stage of the heavily doped layer. On the other hand, the diffusion process ofVGafrom the heavily doped layer during growth is negligible. Therefore, the carrier concentration in the layers grown on the heavily doped layer is not affected. During annealing after growth theVGa, which is supersaturated in the lightly doped underlayer, disappears as the result of a first-order reaction, so the carrier concentration is recovered. These results not only suggest a carrier compensation mechanism, but are also useful in improving the characteristics of devices consisting of structures with heavily Si-doped GaAs layers. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364030

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new model of two species of electron–hole with shallow electron trap is presented. The model predicts that if the shallow trap accumulates large density of charge carriers, the photoconductivity can be a sublinear (or superlinear) function of light intensity, and the space-charge field increases (or decreases) and reaches a saturate value as intensity increases depending on the sign of dominant carrier. Comparison this model with previous ones shows that this model provides more common descriptions about photoconductivity and space-charge-field dependence of intensity. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364031

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The bulk low frequency noise has been investigated in the 4H silicon carbide polytype. In the temperature range of 300–550 K the noise spectral densitySis proportional tof−1.5, wherefis the measurement frequency. A very low noise level has been observed for the bulk noise. At 300 K, the Hooge constant &agr; is as small as (2–4)×10−6atf=20 Hz and &agr;⩽5×10−7atf=1300 Hz. AtT⩾600 K, the generation-recombination noise of a local level makes the main contribution into the total low frequency noise. The electron capture cross section &sgr; of this level depends very strongly on temperature. In the temperature range of 620–700 K, the temperature dependence of &sgr; can be expressed as &sgr;∼exp(−E1/kT), with an activation energyE1as high as 2.7 eV. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364007

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Better carrier confinement in 0.6-&mgr;m-band laser diodes can be achieved by incorporating an AlInP layer into the (Al0.7Ga0.3)0.5In0.5P cladding layers. The effectiveness of this heterostructure, though, cannot be analyzed without detailed knowledge of the energy band alignment at theXc, &Ggr;c, and &Ggr;vband extrema. We conducted photoluminescence and photoreflectance measurements at 12–100 K on (Al0.7Ga0.3)0.5In0.5P/AlxIn1−xP heterostructures (x=0.47–0.61) free from long-range ordering, and analyzed the results to obtain basic data on the alignment scheme. In these measurements we observed the &Ggr;cto &Ggr;vand theXcto &Ggr;vtransitions in bulk Al0.53In0.47P and (Al0.7Ga0.3)0.5In0.5P alloys, the AlxIn1−xPXcto (Al0.7Ga0.3)0.5In0.5P &Ggr;vtransition in (Al0.7Ga0.3)0.5In0.5P/AlxIn1−xP superlattices, and theXcto &Ggr;vand to the &Ggr;cto &Ggr;vtransitions in 20-nm-wide AlxIn1−xP layers in (AlyGa1−y)0.5In0.5P/AlxIn1−xP/(AlyGa1−y)0.5In0.5P double heterostructures (x=0.33–0.39,y=0.7–1.0). We found that the energy level ofXcin AlxIn1−xP decreased by 0.09 eV asxincreased from 0.47 to 0.61, theXcof AlxIn1−xP crossed the &Ggr;cat 0.340 (±0.008), and the &Ggr;vof AlxIn1−xP crossed the &Ggr;vof (Al0.7Ga0.3)0.5In0.5P atx=0.47(±0.01). The share of the band offset at &Ggr;cforx=0.53 was 75(±3)&percent;. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364064

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An experiment on detecting the influence of THz irradiation on coherent resonant electron tunneling through a short superlattice in an electric field is proposed. It is numerically shown that transmission via the upper levels of the lowest miniband, being suppressed down to the valuesT=10−2–10−1by applied voltage, is restored toT∼1by the THz field of certain amplitudes and frequencies. This is caused by electron delocalization due to stimulated multi-quantum transitions to the levels close to the center of the miniband. Thus, amplification of incident irradiation and higher-harmonics generation are possible. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364032

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The electron-optical phonon scattering rate and electron subband population in a semiconductor quantum well (QW) containing a phonon wall (Ph-wall) is calculated. It is shown that the Ph-wall (a barrier of one–two AlAs monolayers) inserted into an AlAs/GaAs/AlAs QW changes radically the intra- and intersubband scattering rates. Electron subband energy spectra, phonon frequencies, electron and phonon wave functions and scattering rates are found to depend on the Ph-wall position in the QW. The largest decrease of the intrasubband electron-phonon scattering rate takes place when the Ph-wall is located at the QW center. The intersubband scattering rate increases resonantly when the intersubband energy separation is equal to the interface phonon energy. The Ph-wall increases the electron mobility in the QW except the areas where the resonance scattering takes place. The Ph-wall position in the QW causing the subband population inversion is determined in the case of optical excitation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364033

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have examined carrier thermalization, recombination, and band filling in GaAs/AlGaAs quantum boxes with low-temperature cathodoluminescence (CL). The temperature dependence of the quantum box CL intensity forT⩽90 K exhibits an Arrhenius behavior, as a result of carrier thermalization between the quantum box and surrounding barrier regions. The width of the quantum box luminescence is found to increase rapidly with an increasing excitation density and reveals an enhanced phase-space and real-space filling, in comparison to the behavior observed for quantum wells. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364008

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Exciton radiative recombination lifetime in a thin quantum box in the intermediate spatial dimension between the two-dimension and the zero-dimension is investigated by a theoretical analysis which rigorously treats the electron-hole Coulomb interaction. The higher exciton states as well as the ground exciton state are explicitly taken into account to estimate the temperature dependence of exciton recombination lifetime. We clarify how the temperature dependence of the recombination lifetime varies with a change in the quantum confinement dimension which can be controlled by the lateral width of a thin quantum box. We also discuss the effect of the exciton localization due to structural imperfection on the radiative recombination lifetime. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364034

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Surface potentials of heat-treated polyimide (PI) Langmuir–Blodgett (LB) films deposited on Au, Cr, and Al electrodes were measured in a dark vacuum vessel at various temperatures as a function of the number of deposited layers. The potential depended on the thickness of PI LB films and the work function of base metal electrode. The spatial charge distribution in PI LB films on various electrodes was determined from the relationship between the surface potential and the number of deposited layers. Based on this result, distribution of the density of electronic state in PI LB films was determined. It was experimentally shown that the electrostatic phenomena in PI LB films at the metal/film interface were explained taking account of surface states which exist within the range of∼1nm from the interface and molecular–ion states which exist in the entire range. Further, it was found that distribution of electronic density in states of polyimides was broadened with the increment of temperature. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364035

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Surface plasmon interactions on a finite silver layer are theoretically investigated using a coupled dipole formalism. The studied system consists of several protruding particles located on the surface of the layer that are scanned with an optical probe. An optical scan-image of the silver surface is obtained by assigning the recorded far-field radiation to the momentary position of the optical probe. Both, probe and protrusions are considered as single dipolar particles. Interferences of the locally excited surface plasmons can be recorded by detecting the radiation emitted into the lower half-space at angles beyond the critical angle of total internal reflection (forbidden light). The resulting scan images show excellent agreement with recent experimental measurements. The theory of the coupled dipole formalism using Green’s functions of a layered reference system is outlined and electromagnetic properties of surface plasmons are discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364036

出版商:AIP    

年代:1997

数据来源: AIP