摘要:

Ballistic electron emission microscopy (BEEM) has been used to study electron transport across single barrier AlxGa1−xAs/GaAs heterostructures. The structures, grown by molecular beam epitaxy, utilized ap‐type δ‐doped sheet to cancel the band bending near the Schottky interface, enabling a direct measurement of the conduction band offset at room temperature. The band offset at room temperature forx=0.21 is 0.19 eV and forx=0.42 is 0.33 eV. Measurements at 77 K gave values of 0.20 eV forx=0.21 and 0.35 eV forx=0.42. These results demonstrate that BEEM can be used to probe the transport properties of semiconductor heterostructures which are spatially beneath the Schottky barrier.

ISSN:1071-1023    

DOI:10.1116/1.587221

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

We have performedinsituballistic‐electron‐emission microscopy (BEEM) and spectroscopy (BEES) at 77 K on epitaxial CoSi2/Si(111) films grown by molecular beam epitaxy. The transport in the silicide was found to be essentially ballistic. With the help of atomic‐resolution scanning tunneling microscopy it has been found that the BEEM current depends significantly on the surface electronic structure. On strain‐relaxed layers, hot electron scattering at individual interfacial dislocations has been observed for the first time by BEEM. Apart from the surface‐ and dislocation‐induced contrast variations, the BEEM current is generally homogeneous.

ISSN:1071-1023    

DOI:10.1116/1.587222

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The lateral variation in the Schottky barrier height (SBH) formed at UHV prepared Au/PtSi/(100)Si (n=4.5×1014) diodes was measured on length scales ranging from a few to several hundred nanometers using ballistic electron emission microscopy (BEEM). The spatial profile and the statistical distribution of the SBHs thus obtained were compared to broad area current–voltage (I–V) and capacitance–voltage (C–V) characteristics of these metal–semiconductor contacts. This comparison showed that the macroscopic SBHs obtained fromI–VandC–Vmeasurements can be successfully interpreted using the parallel conduction model applied to the BEEM derived barrier height distribution. In addition, we found that the variations in the SBH were strongly correlated, with an autocovariance length of ∼20 nm at short wavelengths and with a strong peak in the spectral density at a spatial frequency of ∼(225 nm)−1.

ISSN:1071-1023    

DOI:10.1116/1.587223

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

A study of the ZnSe(100) surface and of its interfaces with Al and Au is presented. We find that the (2×1) reconstructed Se‐rich surface is terminated with a full monolayer of dimerized Se, whereas theC(2×2) reconstructed Zn‐rich surface corresponds to a half‐monolayer of nondimerized Zn atoms. These atomic configurations and corresponding surface electron affinities are consistent with the requirement of dangling bond saturation and fully accounted for by the electron counting rule. For the metal/ZnSe interfaces, we find that Au forms an abrupt junction, whereas Al reacts and forms Al2Se3, releasing Zn in the process. The stabilized Fermi level position is 2.1 eV above the valence band maximum for Al and 1.15 eV for Au, irrespective of doping type and in qualitative agreement with the Schottky limit for the barrier heights. The Au/p‐ZnSe Schottky barrier height can be reduced by 0.25 eV by introducing a 2–3 ML Se interlayer between the metal and the semiconductor.

ISSN:1071-1023    

DOI:10.1116/1.587224

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The electronic properties, chemistry, and spatial structure of Au/CaF2/n‐Si(111) metal–insulator–semiconductor (MIS) structures, with epitaxially grown CaF2layers of a few monolayers (ML) thickness, have been studied by photoelectron spectroscopy, scanning‐tunneling microscopy, and ballistic‐electron emission microscopy. CaF2films on Si are characterized by flat surfaces with defect lines about 500 Å apart, and band bending in Si reduces gradually with increasing CaF2layer thickness. Au grows on top of the CaF2layer in the form of hexagonal terraces. A Si segregation to the surface, as observed in case of the bare Au/Si interface, is strongly reduced by the CaF2intralayer. Ballistic‐electron emission microscopy shows a strong influence of the CaF2density of states for electron transport through the intralayer. For a 4 ML thick CaF2intralayer, the position of the CaF2conduction‐band minimum is derived from the onset of the collector current at 3.3 V. The valence‐band offset at the CaF2/Si interface is derived from the valance‐band edge observed in photoelectron spectroscopy.

ISSN:1071-1023    

DOI:10.1116/1.587225

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The Schottky barrier height in Al/Si/GaAs(001) junctions grown by molecular‐beam epitaxy was determinedinsituby means of x‐ray photoemission spectroscopy andexsituthrough current–voltage and capacitance–voltage measurements. We found that the barrier height can be tuned from a minimum value of 0.2 eV to a maximum of 1.1 eV provided that a sufficiently high As or Al flux is employed during the growth of the Si interface layer. The minimum and maximum values of the barrier are already established for Si layer thicknesses in the 1–2 monolayer range. We propose that the changes in barrier height derive from the establishment of a Si‐induced local interface dipole. The magnitude and orientation of the dipole reflects the detail of the atomic reconstruction achieved at the interface in the different growth conditions.

ISSN:1071-1023    

DOI:10.1116/1.587226

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The Pt/GaAs Schottky interfaces with excellent qualities were fabricated by a novelinsituelectrochemical etching and plating technology using the electrical and photo pulses. The etched GaAs surface was very smooth, and no oxidized and disordered layer was produced at the interface. This technology also prevents formation of process‐induced near‐surface defect levels of GaAs. The Pt/GaAs diodes exhibited nearly ideal thermionic emission characteristics with a barrier height larger than 1.0 eV and an ideality factor lower than 1.05. Selective deposition of Schottky barriers to the edge of a two‐dimensional electron gas in a GaAs/AlGaAs quantum well structure was truly achieved by this process, which is confirmed by the agreement of the experimentalC–Vresults with theoretical predictions, as well as the results of the electron beam‐induced current measurements.  

ISSN:1071-1023    

DOI:10.1116/1.587227

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Impact ionization and interface transmission, two important processes in hot‐electron transport in semiconductor structures, have been studied by ballistic electron emission microscopy (BEEM) at interfaces of NiSi2/n‐Si(111)7×7. The analysis of BEEM spectra taken in pinholes of thin NiSi2films allows a direct determination of the quantum yield of impact ionization in Si over a wide energy range (≳7 eV). BEEM images and spectra recorded on NiSi2terraces show evidence for the conservation of transverse momentum and a small probability for normal interface transmission up to high energies (≊4 eV above the Fermi energy), in accordance with dynamical calculations of the transmission probabilities.

ISSN:1071-1023    

DOI:10.1116/1.587228

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The surface‐stress tensor is an important quantity entering the elastic theory of interaction between atomic steps on solid surfaces. For the clean Si(001) surface the difference between its diagonal elements, the surface stress anisotropy Δσ, comes out by about a factor of two smaller in experiment than compared to the value obtained from previous first‐principles calculations. This discrepancy was usually assigned to the presence of surface defects; as other plausible causes one could quote unrealistic atomic surface structures used for the calculations or even a failure of the local‐density approximation (LDA) on which the calculations were based. This constituted a serious deficiency in the understanding of the Si(001) surface. We demonstrate that, when first‐principles LDA calculations are carried out for the perfect Si(001) surface with the correct character of reconstruction, the calculated and measured Δσ agree within the experimental and numerical uncertainties. We conclude that standard LDA calculations can properly describe elastic properties of the Si(001) surface and that the effect of surface defects on the measured surface stress anisotropy is, at least for the measurements reported in the literature, much smaller than it has been previously anticipated.

ISSN:1071-1023    

DOI:10.1116/1.587229

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

We have carried out first‐principles pseudopotential calculations to study the formation energies of various ZnSe(100) surface reconstructions. Both Zn‐ and Se‐terminated models are treated, using as a guide the satisfaction of the electron counting rule (i.e., charge compensation at the surface by the filling of all the Se dangling bonds and the emptying of the Zn dangling bonds). In order to treat structures with different stoichiometries, we determine the surface energy as a function of the Zn chemical potential, which is allowed to vary in a range determined by the energies of bulk Zn, Se, and ZnSe. Ac(2×2) reconstruction with half‐monolayer coverage of twofold coordinated Zn atoms is stable in the Zn‐rich limit. Under moderately Se‐rich conditions, the surface adopts a (2×1) Se‐dimer phase. In the extreme Se‐rich limit we predict the stability of a reconstruction with one and a half monolayer coverage of Se. The new structure can account for the high growth rates observed in atomic layer epitaxy and migration enhanced epitaxy experiments at relatively low temperatures.  

ISSN:1071-1023    

DOI:10.1116/1.587230

出版商:American Vacuum Society    

年代:1994

数据来源: AIP