摘要:

The concept of the capacitively coupled single-electron transistor (CSET) is generalized to a device based on a linear array ofNtunnel junctions. The basic characteristics of such multiple-junction CSETs are calculated for several distributions of tunnel junction and coupling capacitances. The results indicate that for optimized parameters, the operating temperature and parameter tolerances increase appreciably withN, with the most striking gains forN≲5. For example, a five-junction transistor may provide a 2.5-fold increase of the maximum operating temperature, for the same minimum feature size. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120644

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on the effect of external strain on the two-dimensional electron gas density in AlGaN/GaN heterostructures grown on sapphire by low pressure metalorganic chemical vapor deposition. The electron sheet concentration in the studied samples was4×1012–2×1013 cm−2and decreased with compressive strain. Lower doped heterostructures had a higher sensitivity to applied strain. The comparison between the experimental data and our model shows that the GaN layers are primarily nitrogen terminated at the heterointerface. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120645

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The capture of a flux of vacancies in Si by a band of extrinsic dislocation loops has been observed in Sb doping superlattices. Annealing Sb doping superlattices containing a band of dislocation loops inNH3results in an injection of vacancies, which enhances the diffusion of Sb spikes located between the surface and loop band. By extracting the diffusivity in the Sb spikes on either side of the loop band, we conclude that over 90&percent; of the injected vacancies are captured by the loops. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120646

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Continuous redshift of an emission from 3.23 to 2.85 eV with decreasing excitation density is observed in the photoluminescence spectra of highly doped GaN:Mg. It has been explained by the formation of minibands originating from the overlap of deep levels and shallow acceptor levels. For nominally undoped samples the intensity ratio of a donor-bound exciton line and a donor–acceptor pair line changes dramatically with excitation density due to the limited number of acceptors. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120647

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

NanocrystallineTiO2has been obtained by a sol-gel process by controlling the crystal size through the water/alkoxide ratio. Raman spectra of anatase nanocrystals with average sizes of 9.5–13.4 nm are reported and the correlation between the Raman band shape (peak position and linewidth) of the main feature at 144cm−1and the crystals dimension is discussed. While in this system a minor role is played by nonstoichiometry and pressure effects, a model based on the phonon confinement, which takes into account the size distribution as determined by the transmission electron microscopy images, correctly reproduces the Raman band shape change. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120648

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have studied the mobility and carrier concentration as a function of temperature between 4 and 300 K inn-type Si–Ge short-period superlattices. In the parallel transport configuration, we have measured a mobility ratio&mgr;77/&mgr;300>50in ann-type strained-layer superlattice with a carrier concentration in the mid1016 cm−3range. The peak mobility measured was 17 000cm2/V s−1at 70 K. Carrier freeze-out effects frustrated transport measurements below 60 K. Above 80 K the mobility is limited by optical phonon scattering with a characteristic phonon energy of 60 meV. These characteristics indicate electron transport via extended states. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120649

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Annealing ofSiO2/(100)Siinterfaces in hydrogen in the temperature range of 500–800 °C is found to introduce a considerable density of fixed positive charge. The charge is diamagnetic, and shows no correlation with any kind of dangling bond defects at the Si surface or in the oxide. The observed charged state is attributed to hydrogen bonding to a bridging oxygen atom at the interface (threefold coordinated oxygen center), which may account for the well-known oxidation-induced charge at theSi/SiO2interfaces. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120650

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Si- and Mg-doped GaN layers were grown onc-plane sapphire substrates by molecular beam epitaxy withNH3as the nitrogen precursor. Their optical and electrical properties were investigated by photoluminescence experiments and Hall measurements, respectively.P-type conductivity, with a net acceptor concentration of3×1017 cm−3and a mobility of 8cm2/V s, was obtained. Mesa-etched light-emitting diodes were processed fromp–njunctions. The turn-on voltage is 3 V and the forward current reaches 20 mA at 3.5 V. The room-temperature electroluminescence exhibits a strong emission at 390 nm. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120651

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In this letter, we report on the impact aluminum has on gallium desorption kinetics in AlGaN alloys grown by gas source-molecular beam epitaxy. Aluminum is found to preferentially incorporate into the AlGaN films over the range of fluxes and temperatures investigated[0.05⩽Ji(Ga)⩽0.5ML/s;0.1⩽Ji(Al)⩽0.2ML/s;700 °C⩽Ts⩽775 °C].As a result, Ga is not observed to incorporate into the film until theNH3flux exceeds that required to grow stoichiometric AlN. This preferential incorporation stems from two facts: (a) Al has an ammonia cracking efficiency ∼2.5 times greater than that of Ga, and (b) Al participates in a Al-for-Ga exchange. As a result of these factors and underNH3limited growth conditions, the aluminum mole fraction in a layer can be controlled by changing the incidentNH3flux. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120652

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

GaseousHN3reacts with surface-boundGa(CH3)xspecies slowly at 300 K to produce thin films containing azide-substituted gallium compounds. When mixtures ofHN3andGa(CH3)3over the surface are irradiated at 253.7 nm, the reaction is dramatically accelerated, and films containing GaN and complexedN2are produced. Heating of these films to 400 K drives off theN2leaving GaN. The mechanism of the reaction is thought to involve photodissociation ofHN3to produce excitedNH(a1&Dgr;)andN2,followed by insertion of theNH(a1&Dgr;)into the Ga–C bond of surface-boundGa(CH3)xmolecules. The insertion product eliminatesCH4to leave GaN. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120653

出版商:AIP    

年代:1998

数据来源: AIP