Kalin, Eugeniy A.

Kokhanenko, Andrey P.

Satdarov, Vadim G.

Voytsekhovskiy, Alexander V.

English

Tomsk State University Repository

ИЗВЕСТИЯ ВЫСШИХ УЧЕБНЫХ ЗАВЕДЕНИЙТ. 56, № 10/3 ФИЗИКА 2013UDC 621.315.592E.A. KALIN*, V.G. SATDAROV*, A.V. VOYTSEKHOVSKIY*, A.P. KOKHANENKO*THE GROWTH OF SiGe NANOSTRUCTURES BY MOLECULAR BEAM EPITAXY1In the paper the method of molecular beam epitaxy (MBE) is considered. MBE allows to receive nanoheterostructures onthe basis of SiGe with Ge quantum dots. Also the results of experiments on synthesis of nanoheterostructures SiGe withGe quantum dots by growth  on the installation MBE «Katun-100» are presented.Keywords: quantum dots, molecular beam epitaxy, germanium, silicon.In recent years, creation of semiconductor structures with new physical properties is the main task ofnanotechnology, with the aim to expand the application of semiconductor materials. Special attention ispaid to the structures on the basis of silicon, as silicon is the basic material of electronics. Low-dimensional semiconductor heterostructures attract more attention. Spatial localization of charge carriersleads to a substantial difference between the electrical and optical properties of low-dimensional struc-tures in comparison with the bulk semiconductors. Among a wide class of semiconductor heterostructuresit is possible to allocate the structure of Si/Ge, which are compatible with the modern silicon technology.This allows to use them both for the improvement of the traditional elements of silicon nano - and mi-croelectronics, and for creation of new electronic and optoelectronic devices. The most promising methodof formation of quantum dots (QDs) is based on the effects of self-organization of semiconductor nanos-tructures in heteroepitaxy systems. There are developed modes of growth of structures, providing suffi-ciently homogeneous in the size of the islands of nanometric scale. For many applications it is necessaryto create heterostructures with quantum dots with different properties, which are determined by such pa-rameters QDs, as their form and lateral size (the size of the plane of the substrate) [1–3].The main method of obtaining Ge/Si nanostructures is a molecular-beam epitaxy. In this case theformation of Ge islands occurs by the Stranski – Krastanov mechanism due to the effects of self-organization at the expense of a mismatch in the permanent crystal lattices (4,2 %). Since during the pro-cess of growth the islands are formed spontaneously, you can control their morphology only by changingthe conditions of synthesis: the temperature of the substrate, the speed of deposition, the amount of de-posited material. In addition, the characteristics of arrays of germanium clusters grown on surfaces withdifferent crystallographic orientation, at the pre-oxidized silicon surface differ significantly.Compared with other technologies used for the synthesis of nanostructures MBE is characterized,first of all, by low growth rate and a relatively low temperature of growth. The advantages of this methodshould include the possibility of sharp interruptions and subsequent renewal of the process of depositionof different materials, which is the most important for the formation of multilayer structures with sharpboundaries between the layers. Receiving perfect nanostructures is promoted by the possibility of theanalysis of the structure, composition and morphology of grown layers in the process of their formationby the method of high energy electron diffraction and electron Auger-spectroscopy [4].The main parameter of the synthesis of nanoheterostructures Si/Ge with Ge quantum dots is thetemperature of the silicon substrate, on which germanium is deposited. In [5] it is shown that during theprocess of formation of structures of Ge/Si (001) by the method of MBE high density of self-organizingclusters can be achieved during the deposition of germanium on the silicon substrate preheated to themoderate temperature (< 550 °C). Decrease of the temperature of formation of the array to the valueslower than 450 °C is required to ensure that the process of growth of heterostructures Ge/Si(001) is com-patible with silicon microelectronic devices production technology. This is another reason to decrease thetemperature of all technological processes starting with the stage of preparation of the silicon surface. Inthis case, the lower the temperature of the silicon substrate during the deposition of germanium, thehigher the density of the clusters with the same amount of Ge deposited. So, for example, at a temperatureof substrate of Tgr = 360 °C during the deposition and effective thickness Ge layer hGe = 8 Å the density ofclusters of Ge in the array reaches 6⋅1011 cm–2, while at Tgr = 530 °С and the same value of hGe the densityof clusters obtained made up only about 2⋅1011 cm–2.The MBE installation «Katun-100» is a complex automated complex with a large number of con-trolled parameters. «Technology» software program, installed on the computer is designed for the process                                                     1 This work was supported in part by State Contracts No. 01201256281 and by the RFBR No. 01201366117.E.A. Kalin, V.G. Satdarov, A.V. Voytsekhovskiy, A.P. Kokhanenko204control and operational control of the basic technological parameters: channels, valves and stepper mo-tors.The presence of high vacuum in the chamber of the growth during MBE allows to use analyticalmethods of the control of the parameters of the surfaces, in particular, the high energy electron diffrac-tion. High energy electron diffraction is a method of study of surface structure, speed of growth, the con-trol of changes of the upper atomic layers (formation of 3D-islands), observation of the topography of thesurface directly during the process of growth.The MBE installation is also equipped with a mass spectrometer, which allows to determine thechemical composition of external atomic layers of solid body and determine the pressure of residual gasesduring the epitaxy. The pressure of residual gases in vacuum chamber with the enabled sources of mate-rial is maintained at a level not higher than the ~ 10–8 Torr. Figure 1 shows diagrams of pressure of resid-ual gases detected with the use of mass spectrometer.Fig. 1. Pressure of residual gases in the epitaxy in searching for leaks. The axes are: y – pressure (mbar),the x – axis the atomic mass.Experimental samples were grown by the method of MBE on the device  «Katun-100» on the sub-strate of Si(100). After a preliminary standard chemical treatment  the substrate were placed in the growthchamber, where annealing at a temperature of 800 ºС in a weak stream Si within 15 minutes was per-formed. Then buffer layer Si a thickness of the order of 100 monolayers at a substrate temperature of500 ºС was grown. The deposition of Ge was carried out at temperatures of substrates 350 and 450 ºС, thegrowth rate v = 3,84 nm/min. The pressure in the growths experiments were not above 5⋅10–8 Torr. Fig-ures 2 and 3 show the experimental samples of Ge/Si quantum dots Ge. The parameters of the experi-ments are given in Table 1.T a b l e  1Parameters of growth of the samplesPatternNo.Temperature ofdeposition of Si,°CRate ofdeposition ofSi, nm/minThickness of thedeposited layer ofSi, nmTemperature ofdeposition Ge, °CRate ofdeposited Ge,nm/minThickness of thedeposited layerof Ge, nm1 500 1,5 90 350 3,84 0,832 500 1,2 72 450 3,84 0,83Fig. 2. AFM image of the sample No. 1. Fig. 3. AFM image of the sample No. 2.From Table 1 and Figs. 1, 2 you can see that the surface density of Ge nanoislands and their lateraldimensions depend very much on the conditions of synthesis.yxThe growth of SiGe nanostructures by molecular beam epitaxy 205REFERENCES1. Шк л я е в  А . А . ,  И ч и к а в а  М .  // УФН. – 2008. – Т. 178. – № 2. – С. 139–1692. Б о л х о в и т я н о в  Ю . Б . ,  П ч е л я к о в  О . П .  // УФН. – 2008. – Т. 178. – № 5. – С. 459–4803. Н о в и к о в  А . В . ,  Я б л о н с к и й  А . Н . ,  П л а т о н о в  В . В . ,  e t  a l .  // ФТП. – 2010. – Т. 44. – № 3. –С. 346–3514. Д у б р о в с к и й  В . Г .  Теоретические основы технологии полупроводниковых наноструктур. – СПб.: СПБГУ,2006. – 347 с.5. А р а п к и н а  Л . В . ,  Юр ь е в  В . А .  // УФН. – 2010. – Т. 180. – № 3. – С. 289–302National Research Tomsk State University, Tomsk, Russia Article submitted July 15, 2013.E-mail: eugeniy.kalin@gmail.com_______________Kalin Eugeniy A., student;Satdarov Vadim G., student;Voytsekhovskiy Alexander V., professor;Kokhanenko Andrey P., professor.

The growth of SiGe nanostructures by molecular beam epitaxy

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The growth of SiGe nanostructures by molecular beam epitaxy

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