ISSN 1063-7850, Technical Physics Letters, 2007, Vol. 33, No. 11, pp. 923–925. © Pleiades Publishing, Ltd., 2007. Original Russian Text © O.A. Neucheva, A.A. Evstrapov, Yu.B. Samsonenko, G.E. Cirlin, 2007, published in Pis’ma v Zhurnal Tekhnichesko œ Fiziki, 2007, Vol. 33, No. 21, pp. 56–62. 923 In recent years, semiconductor crystalline nano- structures—nanowhiskers (NWs)—have received much attention, which is related to wide possibilities of their use in various fields. NWs are already used as probes in atomic force microscopy and for the creation of analytical systems, sensors, and nanochips for detecting biologically active substances [1–3]. In par- ticular, a GaN nanowhisker array was recently used for the creation of a sensor capable of detecting methane in the gas phase [4]. The possibility of integrating NWs into microfluidic chips makes possible the development of new multifunctional devices for analytical instru- mentation and microsynthesis. In view of these prospects, it is important to thor- oughly characterize the synthesized nanostructures. At present, only a few papers are available that report on the investigation of the reflectivity of NWs, which were synthesized from GaN [5] and Zn/ZnO [6]. This Letter presents the results of our investigation of the reflectiv- ity spectra of GaAs nanowhiskers with various struc- tural characteristics and describes the effects of laser radiation on the properties of such NW arrays. We have studied doped GaAs nanowhiskers, which were grown by molecular-beam epitaxy (MBE) on doped GaAs(111)B substrates [7, 8]. The samples had different structural characteristics and features (height, density, vertex shape). In the course of MBE, the buffer GaAs layer and GaAs nanowhiskers were doped with silicon to an electron density of ~10 18 cm –3 (buffer) and 5 × 10 17 cm –3 (NW) in order to obtain n -type conductiv- ity. The diameters of NWs varied from 50 to 80 depend- 2 2 2 2 ing on their height and the MBE growth parameters. The reflectivity spectra were measured using a Hitachi U-3410 spectrophotometer. The results of laser irradia- tion in the visible range on the MW array were studied using confocal laser microscopy (Leica TCS SL), scan- ning electron microscopy (SEM) (CamScan S4-90FE) and acoustooptical spectroscopy (AOC-01). The reflectivity spectra of NWs can be divided into several characteristic groups. The first group is charac- terized by a decrease in the reflectivity with increasing NW height (Fig. 1a). In these spectra, the maxima of reflectivity are observed at 250 and 420 nm, that ism Interaction of Optical Radiation with GaAs Nanowhisker Arrays O. A. Neucheva, . A. Evstrapov*, Yu. B. Samsonenko, and G. E. Cirlin Institute for Analytical Instrumentation, Russian Academy of Sciences, St. Petersburg, 190103 Russia St. Petersburg Physical Engineering Research and Education Center, Russian Academy of Sciences, St. Petersburg, 195220 Russia Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia *e-mail: evstra@iai.rssi.ru; an_evs@mail.ru Received April 12, 2007 Abstract—We have studied the reflectivity spectra of doped GaAs nanowhiskers (NWs) with various morphol- ogies, which were grown by molecular-beam epitaxy. It is established that the character of the reflectivity spec- tra of NWs is determined by the shape of nanocrystals. NWs with droplike and pointlike vertices differently interact with electromagnetic radiation. Laser radiation produces a spectral-selective action on the NW array, which leads to a change in the NW height and induces “caking” of their vertices, thus modifying the reflectivity of the sample. This phenomenon can be used for the creation of local microstructures with preset characteristics in large NW arrays. PACS numbers: 78.67.-n DOI: 10.1134/S1063785007110090 2 2 0.8 3 4 5 6 Energy, eV 1 2 3 4 0.6 0.4 0.2 0.004 0.002 Reflectivity ~ ~ 0 1 μm (‡) (b) Fig. 1. NW arrays with droplike vertices: (a) reflectivity spectra of ( 1 , 2 ) samples with NW heights 15000 and 370 nm, respectively; ( 3 ) GaAs substrate; and ( 4 ) GaAs crystal; (b) SEM image.