摘要:

The use of localized Gaussian basis functions for large scale first principles density functional calculations with periodic boundary conditions (PBC) in 2 dimensions and 3 dimensions has been made possible by using a dual space approach. This new method is applied to the study of electronic properties of II–VI (II=Zn, Cd, Hg; VI=S, Se, Te, Po) and III–V (III=Al, Ga; V=As, N) semiconductors. Valence band offsets of heterojunctions are calculated including both bulk contributions and interfacial contributions. The results agree very well with available experimental data. Thep(2×1) cation terminated surface reconstructions of CdTe and HgTe (100) are calculated using the local density approximation (LDA) with two‐dimensional PBC and also using theabinitioHartree–Fock (HF) method with a finite cluster. The LDA and HF results do not agree very well.

ISSN:0734-211X    

DOI:10.1116/1.587883

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

We have used ultraviolet and x‐ray photoelectron spectroscopy to study the strain dependence of the valence‐band offset (VBO)insitufor binary arsenide compound semiconductor heterojunctions grown by molecular beam epitaxy; i.e., we have measured the VBO of InAs/GaAs, InAs/AlAs, and AlAs/GaAs(100) heterojunctions as it changes when these heterojunctions are pseudomorphically strained to lattice constants ranging from 5.653 Å (GaAs) to 6.058 Å (InAs). Intermediate lattice constants have been realized by using fully relaxed InxGa1−xAs buffer layers as virtual substrates. The spectrum of two distinct core‐levels, one from either side of the coherently strained junction, monitors the energetic alignment across the junction. To establish the band offset, one has to know in addition the binding‐energy separation of the core‐level to the respective valence‐band maximum (VBM) for each of the junction’s two components and corresponding to their correct bulk strain state. Here, we have recorded valence‐band and core‐level spectra of strained ‘‘bulk’’ samples to determine this energy difference experimentally. We have accounted for the true shape of the density of states near the VBM by using results ofk⋅ptheory, thus avoiding a full pseudopotential calculation. GaAs/InAs and AlAs/InAs heterojunction VBOs are heavily strain dependent.For example, one can alter the GaAs/InAs VBO by 480 meV on going from the GaAs to the InAs lattice constant, the InAs VBM being 0.04±0.10 eVlowerthan the GaAs VBM when InAs is strained to the GaAs lattice constant and 0.52±0.10 eVlowerwhen the strain is vice versa. The AlAs/InAs heterojunction VBO changes from +0.29±0.11 eV (type‐I), when InAs is strained to AlAs, to −0.10±0.17 eV (type‐II) for the opposite case. The AlAs/GaAs heterojunction VBO is independent of strain within our limits of accuracy. The results are compared with recent theoretical data, both ‘‘model’’ theories and self‐consistent calculations, shedding some light on the features that are important for the band alignment at polar heterojunctions. The results can be interpolated in a straightforward manner to estimate the VBO for the more realistic case of heterojunctions built up ofanytwoternaryarsenide compounds strained toanyreasonable lattice constant.

ISSN:0734-211X    

DOI:10.1116/1.587884

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

Theoretical studies are summarized which show that (i) anion‐site antisite defects AlSbin AlSb barriers and (ii) interfacial native defects such as AsAlat AlAs‐like interfaces are the origin of electrons in nominally undoped InAs quantum wells of AlSb/InAs heterojunctions. Tamm interface states, while present at the InSb‐like interfaces, lie at too low energy to account for the observed carrier densities.

ISSN:0734-211X    

DOI:10.1116/1.587885

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

A method of fabricating 40‐nm gate‐lengthn‐metal–oxide–semiconductor field effect transistors (MOSFETs) is described in detail. The fabrication of MOSFETs with gate lengths of this order poses two major problems: how to fabricate such small‐geometry gate electrodes, and how to fabricate the ultrashallow source and drain junctions required. Two special techniques are used to overcome these problems: a resist‐thinning process using isotropic oxygen plasma ashing for the fabrication of the gate electrodes, and a process of solid‐phase diffusion from phosphorus‐doped silicated‐glass gate sidewalls for fabrication of the source and drain junctions. The resulting 40‐nm gate electrodes and ultrashallow 10‐nm junctions have an adequate impurity concentration and have been shown to function successfully. It has been confirmed that these 40‐nm gate‐lengthn‐MOSFETs have good electrical characteristics at room temperature. Certain details of small‐geometry MOSFET electrical characteristics are studied using these devices.

ISSN:0734-211X    

DOI:10.1116/1.587886

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

By employing the technique of Z‐contrast imaging in a 300 kV scanning transmission electron microscope, we show that it is possible to obtain directly interpretable, atomic resolution images of interface structures in semiconductor materials. With particular emphasis on the study of the CdTe/GaAs(001) system, we demonstrate that such an approach enables the direct observation of the sublattice in compound semiconductors and, as a direct consequence of this, facilitates the observation of atomic arrangements (in some cases unexpected) at dislocation cores on the column‐by‐column level. In addition, we demonstrate that the technique can also be applied to the study of grain boundary structures, by showing examples taken from boundaries in Si and SrTiO3.

ISSN:0734-211X    

DOI:10.1116/1.587807

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

Most samples of Ga0.5In0.5P grown by metalorganic chemical vapor deposition (MOCVD) on (001)‐like surfaces are partially ordered and exhibit distinctive reflectance difference spectral (RDS) features associated with the anisotropic properties of the ordered bulk structure. It is known that the ordering is not a ground‐state property of the bulk but is surface‐induced during growth. On the other hand, Ga0.5In0.5P grown by liquid‐phase epitaxy (LPE) is completely disordered, and it has been shown that its RD spectrum is essentially featureless. In this article, we present a study of the effects of annealing (in a PH3/H2atmosphere) on LPE‐grown Ga0.5In0.5P usingexsituandinsituRDS. The annealing temperatures and times used in this study (650°C and tens of minutes) have virtually no effect on thebulkoptical or structural properties of MOCVD‐grown Ga0.5In0.5P. For LPE‐grown Ga0.5In0.5P, we find that annealing induces bulk‐like RDS features at bothE0andE1with line shapes similar to those observed for MOCVD‐grown ordered Ga0.5In0.5P. These bulk‐like spectral features are, however, due to near‐surface reconstruction of Ga and In because they are effectively quenched by exposure to air. Also, theE0feature becomes sharper and both theE0and theE1features red‐shift as the annealing process is prolonged. This indicates that this reconstruction is kinetically limited, presumably by the slow interdiffusion of Ga and In necessary to achieve the ordered bulk‐like structure.

ISSN:0734-211X    

DOI:10.1116/1.587808

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

We have quantitatively characterized the heterointerfaces in type‐II GaAs/AlAs short‐period structures with various types of growth interrupts. The quality of the heterointerfaces is governed by two factors: the magnitude of the potential fluctuations or interface roughness and the density of nonradiative defect centers incorporated at the heterointerfaces during growth. We have quantified these aspects of the heterointerfaces through photoluminescence (PL), PL time‐decay, and time‐resolved PL‐imaging measurements. We find that growth interrupts at thenormalheterointerfaces significantly improves the quality of the interfaces over growth withnointerruptsin regard to the interface roughness. Further, the transport of the excitons along the heterointerfaces may be explained by interface roughness induced scattering. We also find that growth interrupts at only thenormalinterfaces substantially reduces the nonradiative trap densities at the heterointerfaces.

ISSN:0734-211X    

DOI:10.1116/1.587809

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

Local variations in the optical properties of thick In0.13Ga0.87As films grown on GaAs(001) substrates misoriented toward {111} planes have been studied with polarized and spectrally‐resolved cathodoluminescence (CL) imaging. The degree of anisotropic relaxation and density of dark line defects (DLDs) in CL was found to depend on the choice of the substrate miscut orientation. An enhanced anisotropy in DLD density and strain relaxation was found for a misorientation towards (111)Arelative to that for a misorientation towards (111)B. Local variations and spatial correlations in polarization anisotropy, band‐gap energy shifts, luminescence efficiency, and defect‐induced long‐wavelength luminescence were examined.

ISSN:0734-211X    

DOI:10.1116/1.587810

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

Heterointerface flatness and abruptness of GaAs/AlGaAs quantum wells are controlled during metalorganic vapor phase epitaxy (MOVPE). Various growth modes such as two‐dimensional (2D) nucleation, step flow, and step bunching are achieved by changing the growth temperature and substrate surface misorientation angle. The degree of monolayer step smoothness and ordering are also changed. The effects of these nanometer‐scale morphologies and interface abruptness on the full width at half maximum (FWHM) of 4.2‐K photoluminescence spectra from quantum wells (QWs) are individually determined. The FWHM is increased in order by degraded interface abruptness, step roughness, multisteps, and 2D islands. Effective thickness variations introduced by these features are roughly ≳2.0, 1.0, 0.6, and 0.2 monolayers (ML), respectively, for 7‐ML‐thick QWs. Some of these effects on current–voltage characteristics of double barrier resonant tunneling diodes (DBRTDs) are also investigated. The factor most strongly affecting the characteristics of DBRTDs is step disordering, that is, a difference in step edge location between the top and the bottom surfaces of barriers. By making this difference smaller than the electron’s de Broglie wavelength using vicinal substrates, we obtain the best negative resistance characteristics ever reported for MOVPE growth.

ISSN:0734-211X    

DOI:10.1116/1.587811

出版商:American Vacuum Society    

年代:1995

数据来源: AIP

摘要:

It has been shown that trap generation inside thin oxides during high voltage stressing can be coupled to time‐dependent‐dielectric‐breakdown distributions through the statistics linking wearout to breakdown. Since the traps play a crucial role in the wearout/breakdown process, it is important to understand the properties of these traps. Oxides with thicknesses between 2.5 nm and 22 nm have been studied with emphasis on oxides in the 6 nm to 13 nm thickness range. The cross‐section of the traps responsible for the scattering of electrons in the tunneling barrier, the thickness dependence of measured trap density, the spatial and energy distribution of the traps, and the charging/discharging properties of the traps have been measured.

ISSN:0734-211X    

DOI:10.1116/1.587812

出版商:American Vacuum Society    

年代:1995

数据来源: AIP