Defects in III-V semiconductor surfaces

Abstract

Abstract. This work reports the measurement of the nanoscale physical properties of surface vacancies and the extraction of the types and concentrations of dopant atoms and point defects inside compound semiconductors, primarily by crosssectional scanning tunneling microscopy on cleavage surfaces of III-V semiconductors. The results provide the basis to determine the physical mechanisms governing the interactions, the formation, the electronic properties, and the compensation effects of surface as well as bulk point defects and dopant atoms. 71.55.Eq; 73.20.Hb; 68.37.Ef The electrical properties of semiconductors and thus their applicability in electronic devices are to a large degree governed by defects and dopant atoms incorporated during growth and production processes. Although some defects and dopant atoms may be desired to achieve the optimum device properties, other defects may be formed unintentionally and counteract the desired electronic properties. Therefore, considerable research efforts were focussed on determining the nanoscale physics governing the formation of point defects, the incorporation behavior of impurities, and their respective electronic properties. PACS:Unfortunately, a direct experimental access to point defects in semiconductors is very difficult, because most experimental techniques rely on the interpretation of macroscopic data of differently processed crystals or on signals integrated over a large set of usually unknown defects. Conclusions about point defects on the atomic level were necessarily limited. In contrast, cross-sectional scanning tunneling microscopy (STM) allows us to directly image with atomic resolution individual point defects and dopant atoms. Crosssectional scanning tunneling microscopy is based on a simple concept: the defects inside the crystal are exposed by cleavage on a surface and subsequently imaged with atomic resolution using STM. Such images yielded a large variety of atomically resolved data about point defects and dopant * (Fax: +49-2461/61-6444, E-mail: p.ebert@fz-juelich.de) atoms. The results provided not only significant progress in the understanding of the fundamental physics of point defects in compound semiconductor surfaces, but it has even been possible to draw conclusions about properties of defects inside semiconductor crystals and the physics governing these bulk point defects [1].The present paper illustrates using selected examples of the progress we achieved in recent years in determining the physics governing the nano-scale properties of point defects in compound semiconductors and their surfaces. We concentrate, on the one hand, on anion surface vacancies as the purest example for surface defects in cleavage surfaces of III-V semiconductors and demonstrate the determination of the surface vacancies' key properties, such as chargetransition levels, electrical charge states, lattice relaxation, and interactions. On the other hand, it is shown how to extract the physics governing bulk point defects by STM. Particular focus will be on...

Low-Temperature Scanning Tunneling Microscopy of Ring-Like Surface Electronic Structures Around Co Islands on InAs(110) Surfaces

“…In particular, III-V semiconductors have been intensively investigated for many years by STM and STS, revealing detailed information about the surface band structure and the influence of various dopant atoms and defects on this band structure. 6 Of particular interest is InAs 7 for which it is well known that by deposition of only a small amount of different adsorbates onto the InAs(110) surface, the Fermi level can be shifted into the conduction band by up to 600 meV (see, e.g., Ref. [8][9][10] and references cited therein), thus causing strong downward band bending and creating a 2D surface electron channel.…”

Surface morphology of Au-free grown nanowires after native oxide removal

“…This is due to the vacancies being positively charged thereby inducing a local downward band bending. 10,29 The local band bending reduces the amount of valence band states available for tunneling at the negative sample bias (filled states) resulting in the observed darker appearance. For the positive sample bias (empty states), the band bending increases the amount of conduction band states available for tunneling leading to the observed brighter appearance.…”

“…Due to the high surfaceto-volume ratio of NWs, it is important to characterize these unique surfaces in terms of morphology, atomic structure, and defects (e.g. atomic vacancies) since these can alter the electronic properties of the entire NWs, 10,11 thereby affecting electric transport, gas adsorption, and shell growth properties. Characterization and control of the precise geometry of NWs are needed as they influence the optoelectronic response.…”

Cleavage induced rows of missing atoms on ZnTe (110) surface

“…We make use of norm-conserving Troullier-Martins pseudopotentials 29 in the Kleinman-Bylander factorized form 30 and a double-ζ polarized basis set composed of numerical atomic orbitals of finite range. The Brillouin zone has been sampled with (3,15,1) points within the Monkhorst-Pack k-point sampling scheme. The optimized GGA value was used for the lattice constant and it was calculated to be 6.0709Å for bulk ZnTe.…”

“…Scanning tunneling microscopy (STM), with its high spatial resolution and surface sensitivity, has now become a well-established method to investigate at the atomic scale the morphology and local electronic structure of those defects on and near the nonpolar (110) surface of III-V compounds. [1][2][3][4][5] Nevertheless, unlike widely studied III-V surfaces, there are only a few STM analyses so far on wide-gap II-VI materials despite their great technological importance. Following the first STM investigation of CdSe and CdS wurtzite crystals, 6 the measurements were done on the cross-sectional planes of ZnSe/BeTe and ZnSeTe/ZnTe multiple quantum wells.…”