摘要:

The electronic properties of metal‐semiconductor or Schottky contacts are characterized by their barrier heights. At ideal contacts, they are determined by the continuum of metal‐induced gap states. Extrinsic interface defects and dipoles as well as interlayers may be present in real contacts and will modify the barrier heights. The zero‐charge‐transfer barrier height and a slope parameter describe the chemical trends of the barrier heights of Schottky contacts on a specific semiconductor. The zero‐charge‐transfer barrier heights may be calculated by using the empirical tight‐binding method with universal parameters and the width of the dielectric band gaps and the slope parameters are given by the optical dielectric constants of the semiconductors. This is verified by comparison with numerical data from well‐established theoretical approaches. Hydrogen doping of metal–diamond and metal–silicon interfaces changes their barrier heights with opposite sign. This is explained by a different orientation of H–C and H–Si interface dipoles. Ag and Pb/Si(111) contacts may be prepared with a ‘‘7×7’’ and a 1×1 interface structure. The difference of their barrier heights is explained by the electric dipole correlated with the stacking fault which is a characteristic of 7×7 reconstructions. Interlayers will also alter the barrier heights of Schottky contacts. Typical examples are SiO2and Si3N4, i.e., MOS and MNS structures. Previous investigations found their barrier heights to vary as a function of the metals used. The chemical trends of these two data sets are described by the slope parameters predicted from the optical dielectric constants of SiO2and Si3N4.

ISSN:0734-211X    

DOI:10.1116/1.588947

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Silicon layers grown by molecular beam epitaxy in the interface region of Al/n‐GaAs(001) Schottky diodes have been shown to tune the Schottky barrier height in the 0.3–1.1 eV range, provided that high enough excess fluxes of As or Al are employed during Si deposition. We studied the incorporation of As and Al in the interface layer for Si growth temperatures of 300 and 400 °C, and for interlayer thicknesses in the 10–150 Å range. Following deposition under an excess As flux we found an As atomic concentrationcAs=0.4–0.5 at 300 °C andcAs=0.2 at 400 °C. The excess Al flux yielded an Al atomic concentrationcAl=0.7–0.8 at 300 °C, andcAl=0.6–0.7 at 400 °C. Correspondingly, the lattice structure of the interlayers appears dramatically different from that of Si. We conclude that the 10–100 Å interface layers used by some authors to change the barrier height bear little resemblance to degenerate bulk Si, so that several of the mechanisms proposed to explain Schottky barrier tuning should be reevaluated.

ISSN:0734-211X    

DOI:10.1116/1.588948

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Using anabinitiopseudopotential approach, we have investigated the electronic structure of ideal Al/GaAs(100) and Al/Ga1−xAlxAs(100) junctions, and the change of the corresponding Schottky barrier height versus the alloy compositionxand in the presence of ultrathin group‐IV atom interlayers. We find large changes in the Schottky barrier height which agree well with the experimental data. In order to interpret the observed trends we have analyzed the charge density response to chemical substitutions near the junction. This allowed us to extend to metal/semiconductor interfaces a microscopic linear‐response theory approach previously employed to interpret band‐offset trends at semiconductor heterojunctions.

ISSN:0734-211X    

DOI:10.1116/1.588949

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Recent advances in wet‐chemical surface treatment of silicon has resulted in unreconstructed, hydrogen terminated Si(111) surfaces with extremely low surface recombination velocity of only 0.25 cm/s [E. Yablonovitchetal., Phys. Rev. Lett.57, 249 (1986)]. This points towards a surface free of surface states that normally pin the Fermi levelEFon Si(111) somewhere near midgap depending on the surface reconstruction. This expectation is not borne out, however, by experiment. Using Si 2pcore level spectra, we find consistently a surface Fermi level position near midgap for 16 heavily dopedn‐ andp‐type samples. Checks for surface photovoltage and ion concentrations sufficient to induce the observed band bending were negative. All samples attain their bulk Fermi level position at the surface after annealing to about 400 °C, a temperature at which the surface hydrogen coverage is unchanged as monitored by ultraviolet excited photoemission. Above 400 °C, hydrogen starts to desorb from the surface and only with the onset of the 7×7 reconstruction doesEFmove back towards midgap. We suggest that the initial position ofEFnear midgap is due to a hydrogen induced passivation of dopants that leaves an intrinsic surface layer. Annealing at ∼400 °C reactivates the dopants by breaking the B–H and P–H complexes as is known from plasma passivation. The necessary passivation depth has been calculated as a function of bulk doping yielding values of the order of one micrometer.

ISSN:0734-211X    

DOI:10.1116/1.589056

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Ga and In atoms in Ga0.52In0.48P layers spontaneously segregate to form alternating In‐ and Ga‐rich {111} monolayers during organometallic vapor phase epitaxial (OMVPE) growth on (001) oriented GaAs substrates, thus forming the CuPt ordered structure. This ordering phenomenon is believed to be driven by surface processes, although little direct experimental information is available. This work presents evidence, based on surface photoabsorption data, that [1̄10] oriented P dimers are present on the surface during OMVPE growth using trimethylgallium and ethyldimethylindium combined with tertiarybutylphosphine, suggesting a (2×4)‐like surface reconstruction. Furthermore, when the growth temperature is increased above 620 °C, with other parameters constant, both the concentration of these P dimers and the degree of order are observed to decrease. A similar correlation of decreased P‐dimer concentration with decreased degree of order is observed for decreases in V/III ratio. Thus, the changes in order parameter for variations in temperature and TBP flow rate are found to be closely correlated with the changes in the order parameter. A third parameter studied was the misorientation of the substrate from (001) toward either the {111}Aor {111}Bplanes. The concentration of P dimers decreased as the misorientation increased in either direction. The degree of order was also observed to generally decrease, supporting the connection between surface reconstruction and ordering. However, the difference in order parameter observed for the two misorientation directions suggests the importance of a second parameter, the step structure, itself. For exactly (001) oriented substrates the surface was observed, using high resolution atomic force microscopy, to consist of islands, elongated in the [110] direction, with heights of 30–60 Å. Monolayer steps are observed for some growth conditions, but for most conditions the boundaries are formed exclusively of bilayer (5.7 Å) steps. Predominantly monolayer steps are formed for low V/III ratios and bilayer steps for high V/III ratios.

ISSN:0734-211X    

DOI:10.1116/1.589057

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

In this article, we analyze the kinetics of heteroepitaxial growth of GaP on Si(100) by pulsed chemical beam epitaxy on the basis of results obtained by real‐time optical process monitoring. In view of the large barrier to epitaxial growth on oxygen or carbon contaminated silicon surface elements and the low stacking fault energy for GaP, residual contamination of the silicon surface contributes to defect formation in the initial phase of GaP heteroepitaxy on Si, and requires special measures, such as surface structuring, to limit the propagation of defects into the epitaxial film. The control of the supersaturation during the first 10–20 s of film formation is essential for the quality of subsequent epitaxial growth and is limited to a narrow process window between three‐dimensional nucleation and overgrowth at low Ga supersaturation and gallium‐cluster formation at high Ga supersaturation. Steady state heteroepitaxial growth is described by a four‐layer stack substrate/epilayer/surface reaction layer (SRL)/ambient and, depending of the source vapor flux, allows for more than monolayer coverage. Under this special condition of low‐temperature CBE, the kinetics of chemical reactions in the SRL is composed of homogeneous reactions creating/consuming intermediates that participate in surface reactions including the incorporation of Ga and P atoms into the epitaxial film. For the homogeneous part of the surface kinetics the dipole approximation provides an adequate correlation of the changes in the dielectric function of the SRL to the activities of randomly distributed reactants and products. No adequate correlation of the dielectric function exists to the concentrations of strongly bonded surface atoms and surface molecules. Therefore, quantitative assessments of the heterogeneous kinetics on the crystal surface cannot use real‐time optical monitoring as a reliable basis.

ISSN:0734-211X    

DOI:10.1116/1.589058

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Si/Si0.97C0.03superlattices grown on Si(001) substrates by Sb surfactant assisted molecular beam epitaxy are characterized byinsitureflection high energy electron diffraction (RHEED), atomic force microscopy, transmission electron microscopy (TEM), and high resolution x‐ray diffraction. The RHEED shows that, in the absence of Sb, the growth front roughens during Si0.97C0.03growth and smooths during subsequent Si growth. In contrast, when Sb is present, the growth front remains smooth throughout the growth. This observation is confirmed by cross‐sectional TEM, which reveals that for samples grown without the use of Sb, the Si/Si0.97C0.03interfaces (Si0.97C0.03on Si) are much more abrupt than the Si0.97C0.03/Si interfaces. In the case of Sb assisted growth, there is no observable difference in abruptness between the two types of interfaces. Atomic force microscopy micrographs of the Si0.97C0.03surface reveal features that could be the source of the roughness observed by RHEED and TEM.

ISSN:0734-211X    

DOI:10.1116/1.589059

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Surface processes during the heteroepitaxy of GaP on Si under pulsed chemical beam epitaxy conditions were investigated simultaneously by the optical methods reflectance difference/anisotropy spectroscopy,p‐polarized reflectance spectroscopy (PRS), and laser light scattering. Our studies were performed during both cyclic and interrupted growth, where the surface was exposed to individual pulses of the precursors triethylgallium (TEG) and tertiarybutylphosphine (TBP). The data show that the three optical probes provide different perspectives of growth. Several surface processes exhibit time constants of the order of 1 s. One such process is the clustering of Ga atoms, or less likely, of TEG fragments, that occurs with TEG exposure. The optical data also show that TBP dealkylation occurs essentially instantaneously upon arrival at the surface, and that TEG dealkylation is the rate‐limiting step. The PRS data exhibit fine structure that shows that heteroepitaxial growth can be described by a four‐phase model consisting of the substrate, a GaP layer, a surface reaction layer containing all adsorbed species not yet incorporated in the growing layer, and the ambient. By assuming that this surface layer is very thin we derive approximate equations that allow us to treat the PRS response quantitatively.

ISSN:0734-211X    

DOI:10.1116/1.589061

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The As/P exchange behavior at interfaces of As compound/P compound heterojunction superlattices has been assessed by observing changes in average lattice spacing when very thin but different thickness As compound layers are inserted into InP, or P compound layers inserted into GaAs. Compositional changes are inferred from strain behavior measured by x‐ray diffraction. Implications of the data are: (1) As rapidly displaces P and P slowly displaces As; (2) As atoms displace P atoms and reconstruct as a discrete single layer above 600 °C and as a double layer below 600 °C when InP surfaces are exposed to AsH3; and (3) interfaces and layers of different P compounds on GaAs show the same temperature‐dependent inclusion of As.

ISSN:0734-211X    

DOI:10.1116/1.589062

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

We discuss the structure and formation mechanism of ZnSe/GaAs(100) interfaces as probed by reflectance difference spectroscopy (RDS). First we describe a simple analytic procedure that separates the surface and interface contributions in the RD spectra obtained for a heterostructure. The procedure opens up the new possibilities of RDS as aninsituinterface probe. We have applied this technique to characterize the ZnSe/GaAs interfaces prepared on various GaAs(100) surfaces. The interface‐anisotropy spectra thus obtained and the cross‐sectional transmission electron microscopy, show clearly that the chemical composition of the interfacial layer can be changed by controlling the reconstruction and the pregrowth Zn and Se treatments of the initial GaAs surface.

ISSN:0734-211X    

DOI:10.1116/1.589063

出版商:American Vacuum Society    

年代:1996

数据来源: AIP