Russian Society of Scanning Probe Microscopy and Nanotechnology

M.Mynbaeva, A.Titkov, A.Kryganovskii, V.Ratnikov, K.Mynbaev et al., Structural characterization and strain relaxation in porous GaN layers//
Applied Physics Letters 76(8), (2000)
Surface and subsurface structures of porous GaN prepared by anodizing epitaxial GaN layers grown on SiC substrates are investigated by atomic force microscopy. Comparison of the images of the porous GaN surfaces with those taken on planes cleft perpendicular to the surface shows that the pores are formed along the boundaries of columnar structures of the original GaN films. X-ray investigations show that the porous GaN has less residual stresses than the initial GaN epitaxial layers. Use of porous GaN as a buffer layer for growth of low-stress GaN is proposed.

A.V.Ankudinov, A.N.Titkov, T.V.Shubina, S.V.Ivanov, P.S.Kop'ev et al., Cross-sectional atomic force microscopy of ZnMgSSe- and BeMgZnSe-based laser diodes//
Applied Physics Letters 75(17), 2626-28 (1999).
Atomic force microscopy of cleaved facets of ZnSe-based lasers with various active region designs is reported. Different AFM probe friction on the materials forming the laser structures are exploited for imaging their basic layers. Unlike ZnMgSSe-based lasers, the cleaved surface of cladding layers in BeMgZnSe-based structures is atomically flat, which is attributed to hardening of the II-VI materials by Be incorporation. Nanomiter-high steps and undulations are observed at the laser heterointerfaces on cleaved facets. The shape and height of such topographic singularities located in the vicinity of a (Zn,Cd)Se quantum well active region depend on the strain distribution in the laser waveguide.

L.N.Bolotov, A.Nakamura, V.P.Evtikchiev, V.E.Tokranov, A.N.Titkov UHV STM studies of the decapped InAs quantum dots on GaAs(001) surface after desorption of a protective As layer//
Surface and Interface Analysis 27, 533-536 (1999).
The morphology and electronic properties of InAs QDs on the GaAs(001) surface has been studied by UHV STM/S after removal of a preliminary deposited protective As layer. A thermal annealing procedure has been developed, which, applied to a sample with an As cap layer, allows InAs QDs to be opened on the surface of InAs wetting layer (WL) exhibiting a [2x4] reconstruction of As dimers. Scanning tunneling spectroscopy measurements on the decapped surface show that I-V characteristics taken with the tip positioned over single InAs QDs have a smaller voltage width for zero conductivity (dI/dV=o) when compared with those taken over the InAs WL, which are essentially the same as the I-V characteristics for a clean GaAs surface. This observation seems to indicate a weakening of the surface band bending in the area beneath InAs QDs.

I.Grechov, L.Delimova, I.Liniichuk, I.Veselovskii, A.Titkov, M.Dunaevskii et al., Growth mode study of ultrathin HTSC YBCO films on YBaCuNbO buffer//
Physica C 324, 39-46 (1999)
It is known that the critical temperature Tc of ultrathin YBCO films is reduced to values far less than 77K. To improve the superconducting properties of ultrathin YBCO films, we developed a new buffer layer which allowed an increase in the critical temperature of five-unit-cell-thick YBCO films to values above 77K. Using atomic-force microscopy to study the growth modes of ultrathin YBCO films deposited on a SrTiO3 substrate and on a YBaCuNbO buffer layer, we found that ultrathin YBCO films deposited on a SrTiO3 substrate are formed due to 2D nucleation. The growth of ultrathin YBCO films deposited on YBaCuNbO buffer is governed by the step-flow mode. As a consequence of the different growth modes, the ultrathin films deposited on a SrTiO3 substrate and a YBaCuNbO buffer layer have different surface morphologies and superconductive properties. We believe that the step-flow mode makes it possible to improve the ultrathin YBCO folms structure and increase the critical temperature.

V.P.Evtikhiev, V.E.Tokranov, A.K.Kryganovskii, A.M.Boiko, R.A.Suris, A.N.Titkov Characterization of the InAs quantumdots MBE grown on the vicinal GaAs (001) surfaces misoriented to the [010] direction//
Journal of Crystal Growth 201/202, 1154-57 (1999)
Atomic force microscopy is used to study InAs quantum dot arrays grown by MBE on vicinal GaAs (001) surfaces misoriented to the [010] direction by 1, 2, 4 and 6 degrees. For a chosen misorientation direction , it is shown that the vicinal GaAs (001) surface is covered with a net of steppe terraces. The condensation of the network of terraces upon increasing of the misorientation angle leads to the suppression of adatom surface diffusion and makes it possible to achieve higher densities and better unifomity of quantum dots arrays.

А.В.Анкудинов, В.П.Евтихиев, В.Е.Токранов, В.П.Улин, А.Н.Титков Нанорельеф окисленной поверхности скола решетки чередующихся гетерослоев GaAlAs/GaAs//
Физика и техника полупроводников 33(5), 594-598 (1999)
Методом атомно-силовой микроскопии исследована морфология окисленной поверхности скола решетки чередующихся слоев GaAlAs и GaAs. Обнаружено, что поверхность пленки естественного окисла на сколе обладает квазистационарным нанорельефом, отражающим состав слоев гетероструктуры. Области скола над слоями GaAlAs оказываютс выше областей над слоями GaAs на 0.5 нм. Стравливание пленки окисла показывает, что на открывшейся поверхности скола также формируется нанорельеф, однако инвертированный по отношению к рельефу поверхности окисла. Возникновение нанорельефов на поверхности и на нижней границе пленки естественного окисла обьяснено различной глубиной окисления слоев GaAs и GaAlAs и увеличением обьема при окислении.

N.M.Shmidt, V.V.Emtsev, A.K.Kryganovskii, R.N.Kyutt, W.V.Lundin, A.N.Titkov et al., Mosaic structure and Si doping related peculiarities of charge carrier transport in III-V nitrides//
Phys. Stat. Sol. (b) 216, 581-586 (1999).
Studies of the charge carrier transport in undoped moderatevily and heavily Si doped GaN and AlGaN epilayers with different mosaic structure are presented. The epilayer were grown by low-pressure MOCVD on (0001) sapphire substrates. The mosaic (columnar) structure of the epilayer has been characterized by X-ray diffraction and AFM surface topography studies. Application of electrostatic force microscopy (EFM) permitted to reveal irregular potential barriers at the mosaic domain boundaries in undoped layers and their reduction in Si doped layers. For undoped GaN and AlGaN epilayers unconventional transport of electrons and a low RT mobility have been found. We relate the peculiarities in the electron transport in undoped samples with additional carrier scatterring on the potential barriers at domain boundaries. Si doping reduces the potential barriers. Moderate Si doping causes a considerable increase of the electron RT mobility and restores normal mobility dependence on the temperature.

Группа Сканирующей зондовой микроскопии лаборатории Оптики поверхности Физико-Технического института им.А.Ф.Иоффе РАН.

Группа Сканирующей зондовой микроскопии
лаборатории Оптики поверхности
Физико-Технического института им.А.Ф.Иоффе РАН.