Scanning tunneling microscopy of semiconductor surfaces (original) (raw)
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Electronic structure of semiconductor surfaces
Applied Physics A Solids and Surfaces, 1985
Our present understanding of the electronic structure of semiconductor surfaces is reviewed. It is shown that photoemission and inverse photoemission are ideal techniques for probing occupied and unoccupied electronic states, respectively. All quantum numbers of an electron can be determined, i.e., energy, momentum, spin and angular symmetries. For simple systems, such as clean ordered surfaces with a small unit cell it is possible to understand the electronic structure from first-principles calculations. For complex systems, such as encountered during oxidation and dry etching one is restricted to measuring the properties determined by short-range order. Core level spectroscopy with synchrotron radiation is able to determine the oxidation state and the local bonding of surface and interface atoms.
S.T.M. studies on semiconductor surfaces and metal-semiconductor interfaces
Microscopy Microanalysis Microstructures, 1990
2014 Au cours des dernières années, la caractérisation en microscopie tunnel des surfaces à l'échelle nanométrique a permis une meilleure compréhension de leurs propriétés structurales et électroniques. Cet article fait état d'expériences de microscopie par effet tunnel sur des surfaces de silicium et sur des interfaces métal-silicium que nous avons effectuées dans notre groupe à Marseille. Nous discuterons les systèmes suivants: Si(111); B-Si(111) ~3 x ~3 R (30°); Sn/Si~3 x ~3 R (30°) et Ag/Si(111). L'obtention de la résolution atomique a été, depuis l'invention de la microscopie tunnel, la principale préoccupation dans l'étude des propriétés structurales des surfaces. Nous mettons ici l'accent sur la nécéssité d'avoir également une information sur la topographie de la surface à plus grande échelle. Ce type de microscopie tunnel a récemment été utilisé par notre groupe et nous a permis de relier la rugosité de la surface de silicium (111) à la méthode de préparation des échantillons.
Tunneling spectroscopy on semiconductors with a low surface state density
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1997
A detailed study of tunneling spectroscopy concerning semiconductors with a low surface state density is presented. For this purpose, I -V curves under dark conditions and under illumination were measured on the ͑0001͒ van der Waals surface of a p-type WS 2 single crystal, which is known to be free of intrinsic surface states. The measurements are interpreted by an analytical one-dimensional metal-insulator-semiconductor model, which shows that the presence of the finite tunneling current has to be considered in the calculation of the tip-induced bandbending. Rectification of the dark I -V curves is explained by the absence of an inversion layer at the semiconductor surface. In contrast, the I -V curves measured for different light intensities and tip-sample separations indicate the existence of an optically induced inversion layer. Since no surface recombination needs to be considered to model these spectra, we conclude that bulk recombination, diffusion and direct tunneling of photogenerated minority charge carriers are the dominant processes for semiconductors with a low density of surface states. In contrast to the standard interpretation of tunneling spectroscopy, which can be applied to semiconductors with a high surface state density, our results clearly show that in this case the normalized differential conductivity (dI/dU)/(I/U) cannot be used to determine the energetic distribution of the local surface state density.
Journal of Molecular Catalysis
A theoretical simulation of STM/STS has been performed for various surface systems, based on the first-principles local density functional (LDA) calculation. Cluster models made of lo-20 atoms are utilized for the tip, and slab models with several atomic layers are adopted for the sample surface. The tunnel current is almost concentrated on a single apex atom, if the other atoms on the top of the tip are not located on the same level. In such a case the STM image is normal, with atomic resolution. However, if the apex of the tip is formed by more than one atom, abnormal images tend to be formed. We verify this feature by numerical results for graphite, Si(loo), and Si (111) /Ag surfaces, and discuss the light emission from STM, based on realistic calculations of the electronic states of the tip/sample systems.
Theory of Scanning Tunneling Microscopy and Spectroscopy
1990
A method for simulating scanning tunneling microscopy (STM) and spectroscopy (STS) is proposed, 0 which is effective at realistic tip-to-surface distances of 5-10 A, and its application is reported for Si(100) reconstructed surfaces. The vacuum tails of wave functions cannot be accurately described either by linear combination of atomic orbitals or by pure plane-wave expansion. An attempt is made to effectively describe the tail parts by combining this method with realistic calculations of the sample surface electronic states. The method is applied to Si(100) reconstructed surfaces and the features of the STM images and STS spectra of 2X1 dimer structures are clarified. This method confirms that the experimental c(4X2) image of STM is actually obtained from the c (4X2) structure and reveals how the buckling of dimers is rejected on the STM image.
Low-temperature scanning tunneling spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 2000
Low-temperature scanning tunneling spectroscopy measurements on semiconductor surface are described. We consider both surface which do not possess surface states within the bulk bandgap, such as GaAs , and surfaces which do have states within the gap, such as Ge and Ge(111)c(2×8). Band bending in the semiconductor due to the electric field in the vacuum penetrating the semiconductor is found to be a substantial effect in the former case. Transport limitations in the semiconductor give rise to additional voltage drops, which can be observed by making measurements over a wide range of tunnel current magnitudes.
Physica E: Low-dimensional Systems and Nanostructures, 2002
A novel technique is developed to follow the energetic position of the conduction and valence bands with respect to the Fermi level as a function of the lateral position on semiconductor surfaces. By combining high-resolution scanning-tunneling spectroscopy measurements with model calculations it is possible to relate the apparent change in conduction and valence band position to their real counterparts. This method allows one to determine the charge on surface artifacts like steps or vacancies. For a single step on p-type GaAs we ÿnd a charge of 0:9 ± 0:3q nm −1 . ?
Fixing the Energy Scale in Scanning Tunneling Microscopy on Semiconductor Surfaces
Physical Review Letters, 2013
In scanning tunneling experiments on semiconductor surfaces, the energy scale within the tunneling junction is usually unknown due to tip-induced band bending. Here, we experimentally recover the zero point of the energy scale by combining scanning tunneling microscopy with Kelvin probe force spectroscopy. With this technique, we revisit shallow acceptors buried in GaAs. Enhanced acceptorrelated conductance is observed in negative, zero, and positive band-bending regimes. An Anderson-Hubbard model is used to rationalize our findings, capturing the crossover between the acceptor state being part of an impurity band for zero band bending and the acceptor state being split off and localized for strong negative or positive band bending, respectively.
An ultrahigh vacuum scanning tunneling microscope for the investigation of clean surfaces
A uhv scanning tunneling mircoscope (STM) operating at 1 x 10 -11 mbar has been incorporated into a VG surface analysis system equipped with LEED, XPS, UPS, SEM/SAM, in addition to several sample and tip preparation facilities. Calibration of the STM can be done routinely by imaging the atomic lattice of graphite and its performance was tested by resolving the Si x 7 surface structure. The main intended application is the investigation of well characterized, clean metal surfaces of single crystals, polycrystalline, quasicrystalline and amorphous materials. On a clean single crystal Au(1 11) surface, a series of monoatomic steps, the reconstruction of this surface as well as the atomic structure could be imaged. For comparison, we have also studied a polycrystalline Au film, vacuum deposited onto graphite. For the first time, atomic resolution could be obtained on a polycrystalline metal surface.