摘要:

In a study of (100)Si growth by molecular‐beam epitaxy, we have observed an interesting phenomenon associated with the breakdown of (100)‐oriented growth at low temperatures (<∼400 °C). Electron microscope imaging revealed that the (100) surface no longer remains planar but develops a series of cusps with {111} oriented facets. At the base of each cusp a small (∼3 nm) cylindrically shaped defect region is formed, but this is morphologically unstable and breaks down to form a linear array of spherical defects trailing behind the growing interface, aligned parallel to the growth direction. The similarities observed between these structures and those found in the unidirectional solidification of rod eutectoids or monotectoids are striking, although the scale of the microstructure in the present case is much smaller. From a series of electron microscopy experiments using both cross‐sectional and plan‐view specimen geometries it has been found that the cylindrical–spherical defects are microvoid regions. Furthermore, the microvoid defect structure was found to be stable as the epitaxial Si matrix transformed to the polycrystalline and amorphous states beyond an epitaxial critical thickness.

ISSN:1071-1023    

DOI:10.1116/1.585772

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We grewn‐type modulation doped Si/SiGe multiple quantum well structures with the highest electron mobilities reported so far for this heterosystem. The samples were annealed at temperatures between 750 and 950 °C for 1000 s and subsequently characterized by x‐ray rocking analysis, secondary ion mass spectroscopy, and temperature dependent Hall measurements. A moderate decrease in room temperature Hall mobility is observed up to annealing temperatures of 900 °C. Above 900 °C the samples become homogeneously doped and show strong Si/Ge interdiffusion at the heteroboundaries. The annealing effects are discussed in terms of dopant and Ge diffusion, and of metastability of the SiGe layers.

ISSN:1071-1023    

DOI:10.1116/1.585773

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Interdiffusion of Si/Ge short‐period superlattices is studied in detail with Raman spectroscopy. Folded acoustic modes and alloy modes from the interface region are found to be very sensitive to intermixing and concentration profile. Annealing at elevated temperature first leads to indiffusion of Si into the Ge layers. The diffusion constant depends strongly on the Si content and consequently varies during the interdiffusion process. The experimental results are qualitatively understood on the basis of a simple atomistic diffusion model. In high quality samples with sharp interfaces the onset of intermixing is observed already at temperatures as low as 450 °C.

ISSN:1071-1023    

DOI:10.1116/1.585774

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Elastic scattering of laser light has been used to monitor surface topography in real time during growth of Si1−xGexheterostructures. Large increases in scattered intensity were caused by surface height fluctuations in the alloy layers which, after growth, could be imaged in cross section by transmission electron microscopy and in plan view by scanning optical microscopy. For pseudomorphic alloy layers (x=0.19±0.01) grown at 750 °C the surface height fluctuations were periodic, the wavelength of approximately 270 nm giving strong laser scattering. Plan view transmission electron micrographs on such a layer showed periodic strain fluctuations with the same wavelength, whereas an equivalent layer grown at 610 °C showed strain fluctuations which were irregular in shape and spatial distribution. The intensity of light scattered from the surface of this layer was much lower. Thick alloy layers grown beyond the critical thickness for appearance of misfit dislocations showed strong scatter which increased more quickly in intensity at higher growth temperature.

ISSN:1071-1023    

DOI:10.1116/1.585775

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

X‐ray techniques have been applied to the characterization of various device type Si–Ge heterostructures. Double crystal diffractometry was used to evaluate the crystal perfection and thermal stability of buried Si1−xGexlayers used in heterojunction bipolar transistors and of Si1−xGex/Si superlattices used inp‐i‐nphotodetectors. The glancing incidence x‐ray technique is more sensitive to the near surface region and better suited to study thin layered structures. This method was used to obtain the structural parameters of SimGenshort‐period superlattices. Ultrathin buried Ge layers (1–12 monolayers) on (100) Si were also investigated by analyzing intensity oscillations in the reflected x rays arising from interference effects. This technique is sensitive enough to detect Ge layers one atomic layer thick. Comparison of the measured and calculated reflected intensity also provided an estimate of the morphology and interface sharpness of these heterostructures. The same technique was also applied to the study of a very thin heavily erbium‐doped Si epilayer.

ISSN:1071-1023    

DOI:10.1116/1.585776

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Temperature dependent transport through strained Si/SiGe hole resonant tunneling diodes has been studied. A quantitative measure of the different current components due to the conduction through the light hole and heavy hole resonant states at any particular bias and temperature has been obtained, and energy values for states in the SiGe well have been extracted. We also show that the quenching of the negative differential resistance at room temperature in hole resonant tunneling diodes is due to thermally assisted tunneling through higher resonant states.

ISSN:1071-1023    

DOI:10.1116/1.585777

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Strained‐layer Si1−xGex/Si heterostructures have created a great deal of interest due to the potential of integration with the conventional silicon very large scale integrated technology. With the current advances in silicon molecular beam epitaxy (Si‐MBE) and other low‐temperature epitaxial techniques, many Si1−xGex/Si heterojunction devices have been realized. For example, among those realized are avalanche photodiodes, modulation‐doped field‐effect transistors, heterojunction bipolar transistors, and more recently, resonant tunneling structures, hot‐carrier transistors, and quantum well metal‐oxide‐semiconductor field‐effect transistors. In this paper, several quantum size effects in strained Si1−xGexlayers and their potential in device applications will be reviewed. Among those to be discussed are resonant tunneling, miniband transport, and intersubband absorption in Si1−xGex/Si superlattice structures, optical properties of monolayer SimGensuperlattices, and observation of large Stark effect associated with interband transition between quantized states in Si1−xGex/Si quantum well structures.

ISSN:1071-1023    

DOI:10.1116/1.585778

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Contact potential difference (CPD) measurements using a Kelvin probe coupled with synchrotron radiation are used to investigate various aspects of the problem of surface photovoltage (SPV) induced by the synchrotron radiation at (110) and (100) GaAs surfaces. A large and quasipermanent SPV is found at surfaces of low doped and low temperature (110) samples. SPV discharge mechanisms are investigated. Finally, the CPD technique is used to define conditions which minimize SPV and allow accurate measurements of band bending at low temperature. Band bending measurements are reported for interfaces between metals and (110) and (100) GaAs surfaces.

ISSN:1071-1023    

DOI:10.1116/1.585779

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Soft x‐ray photoemission spectroscopy has been used to investigate the initial stages of Schottky barrier formation on GaAs (100) surfaces prepared by the thermal desorption of an As cap. This work was motivated by a previous study [Brillsonetal., J. Vac. Sci. Technol. B6, 1263 (1988)] of identically grown and capped samples which reported ‘‘unpinned’’ Schottky barrier formation, with barrier heights falling over a wide range (0.75 eV) of energies. This large energy range is a striking result, as a considerable number of prior studies on both (110) and (100) surfaces have found that all metals will pin in a narrow (0.25 eV) range near midgap. Since Au and Al are the extremes of the larger 0.75 eV span of Schottky barriers, we have studied the deposition of these two metals. We found that the barrier height measurements on the low dopedn‐type samples used in this work and in the paper referenced above are affected by photovoltaic effects, even at room temperature. These photovoltaic effects cause shifts in the band bending, which are an artifact of the measurement. We also performed measurements on more heavily doped samples, and the photovoltaic effects were removed. In addition, we point out that Au–Ga alloying makes the case of Au potentially misleading. With the photovoltaic effects removed, and the Au–Ga alloying carefully accounted for, we found that the barriers heights for Au and Al differ by only 0.25 eV.

ISSN:1071-1023    

DOI:10.1116/1.585780

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Surface photovoltage (SPV) needs to be considered in optical studies of electronic properties of semiconductor surfaces. We used a Kelvin probe (CPD), ultraviolet photoemission spectroscopy (UPS), and electric‐field‐induced Raman spectroscopy (EFIRS) to investigate the effect of SPV on adsorbate‐induced variations of surface band bending at InP(110) and GaAs(110) surfaces at low temperatures. On InP(110) surfaces, which were exposed to Cs, H, and Cl2at ≊170 K, the SPV was found to depend on the type of adsorbate and its coverage. After the light was switched off, the SPV was found to decay with time constants varying between some minutes up to a few hours. For GaAs(110) surfaces exposed to atomic hydrogen at 140 K, we observed the light of a discharge lamp to flatten the bands. By using EFIRS, on the other hand, the buildup of surface band bending was unambiguously detected as a function of exposure to atomic hydrogen. The H‐induced changes of surface band bending determined from variations of the work function measured in the dark with a Kelvin probe and of the ionization energy evaluated from the widths of UPS spectra excellently agree with the EFIRS‐derived data.

ISSN:1071-1023    

DOI:10.1116/1.585781

出版商:American Vacuum Society    

年代:1991

数据来源: AIP