Growth of Crystals

167 Pages·1996·12.221 MB·English

by  O. P. Pchelyakov, L. V. Sokolov (auth.), E. I. Givargizov, A. M. Melnikova (eds.)

POCT KPHCTAnnOB
ROST KRISTALLOV
GROWTH OF CRYSTALS
VOLUME 20
Growth of Crystals
Volume 20
Edited by
E. I. Givargizov and A. M. Melnikova
Institute of Crystallography
Russian Academy of Sciences
Moscow, Russia
Translated by
Dennis W. Wester
®
CONSULTANTS BUREAU • NEW YORK AND LONDON
The Library of Congress cataloged the first volume of this title as follows:
Growth of crystals. v. [lJ
New York, Consultants Bureau, 1958-
v. illus., diagrs. 28cm.
Vols. 1, 3- constitute reports of 1s t- Conference on Crystal
Growth, 1956- v. 2 contains interim reports between the 1st and
2nd Conference on Crystal Growth, Institute of Crystallography,
Academy of Sciences, USSR.
"Authorized translation from the Russian" (varies slighty)
Editors: 1958- A. V. Shubnikov and N. N. Sheftal'.
1. Crystal-Growth. 1. Shubnikov, Aleksei Vasil'evich, ed. II.
Sheftal', N. N., ed. III. Consultants Bureau Enterprises, inc., New
York. IV. Soveshchanie po rostu kristallov. V. Akademiia nauk
SSSR. Institut kristallografii.
QD921.R633 548.5 58-1212
ISBN-13: 978-1-4612-8445-1 e-ISBN-13: 978-1-4613-1141-6
DOl: 10.1007/978-1-4613-1141-6 1-6
© 1996 Consultants Bureau, New York
A Division of Plenum Publishing Corporation
233 Spring Street, New York, N.Y. 10013-1578
Softcover reprint of the hardcover 1s t edition 1996
10987654321
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmitted
in any form or by any means, electronic, mechanical, photocopying, microfilming,
recording, or otherwise, without written permission from the Publisher
PREFACE
In keeping with tradition, this collection covers three principal crystallization methods: from the
vapor, solution, and the melt.
The five articles of the first part are concerned with heterostructure formation.
O. P. Pchelyakov and L. V. Sokolov report on controlled growth of nanostructures in the Si-Ge system
using an array of modern analytical tools to follow the process in situ. A different method for growing
quantum-sized Si-Ge structures is used by Mil'vidskii et al., chemical deposition of hydrides from the
vapor. Stresses and misfit dislocations in the resulting heterostructures are thoroughly investigated. The
theoretical work of E. M. Trukhanov examines the formation mechanism of long-range stresses that produce
r -shaped cracks during the growth of thick Ge-Si films. The reasons for the manifestation of macro defects
connected with the generation of twins in HgCdTe films are unraveled by Yu. G. Sidorov et al.
The conditions under which films with a low defect density grow are found. The preparation of highly
oxidized amorphous Nb films and the structures formed during the crystallization of these films are reported
by A. A. Sokol et al.
Growth from solutions is the subject of the four articles in the second part.
The general instability criterion derived by V. V. Voronkov takes into account all possible mechanisms
that limit the accumulation of an impurity in front of a growth step and is applied equally to gaseous
and liquid solutions. According to this criterion, a rectilinear step that became unstable at a certain
supersaturation can again become stable if the supersaturation is further increased. The kinetics of layered
growth of KDP crystals from solutions at various acidities are measured in situ using an interference method
by L. N. Rashkovich and G. T. Moldazhanova. The influence of this same parameter (pH) and the growth
temperature on the actual structure and certain properties of KDP crystals are investigated by V. A.
Kuznetsov et al. The last two articles discuss various effects due to the presence of an unstable impurity
in solution. G. D. Ilyushin and L. N. Dem'yanets use a crystallochemical model that they previously
developed to analyze in detail the successive construction of K-Zr silicates under hydrothermal conditions.
The third part includes a variety of articles that, nevertheless, are centered on the same theme. They
all treat the preparation of a homogeneous material during melt crystallization.
P. P. Fedorov examines common principles and actual methods for the most facile determination of
those starting compositions that would most easily produce homogeneous single crystals of multicomponent
compounds or solid solutions that are needed for practical applications. The theoretical study of V. S.
Yuferev determines the conditions under which the Coriolis force stabilizes and suppresses thermal and
constitutional convection in the melt. However, he finds that there are factors that neutralize the Coriolis
force and examines the influence of these factors. N. A. Verezub et al. calculate the thermal exchange
in the Stockbarger method and determine how heaters should be programmed so that the growth front
remains planar during the whole process. In this instance, the resulting crystals are more homogeneous.
The relationship between the ingot substructure, the stages of establishing this superstructure, and the
crystallographic orientation of the growth direction is found by O. P. Fedorov and E. L. Zhivolub. V. I.
Voronkova and V. K. Yanovskii present a new method for preparing untwinned single crystals of certain
high-temperature 1-2-3 superconductors.
The articles of this collection cover a broad spectrum of current research in Russia and Ukraine.
E. I. Givargizov
A. M. Melnikova
v
CONTENTS
I. HETEROSTRUCTURE FORMATION IN
MOLECULAR-BEAM AND GAS-PHASE EPITAXY
Direct Synthesis of Nanostructures in the Germanium-Silicon System by Molecular-Beam Epitaxy 3
O. P. Pchelyakov and L. V. Sokolov
Het~rostructures and Strained Superlattices in the Ge-Si System: Growth, Structure Defects,
and Electronic Properties 13
M. G. Mil'vidskii, V.1. Vdovin, L. K. Orlov, O. A. Kuznetsov, and V. M. Vorotyntsev
Long-Range Stresses and Their Effects on Growth of Epitaxial Films 29
E. M. Trukhanov
Growth of and Defect Formation in CdxHg1- xT e Films During Molecular-Beam Epitaxy 35
Yu. G. Sidorov, V. S. Varavin, S. A. Dvoretskii, V. 1. Liberman, N. N. Mikhailov,
1. V. Sabinina, and M. V. Yakushev
Structure of Amorphous Nb Oxide Films and Their Crystallization 47
A. A. Sokol, A. R. Marinchev, and V. M. Kosevich
II. GROWTH OF CRYSTALS IN LOW-TEMPERATURE
AND HYDROTHERMAL SOLUTIONS
Morphological Stability of a Linear Step in the Presence of a Mobile Adsorbed Impurity 59
V. V. Voronkov
Growth Kinetics and Bipyramid-Face Morphology of KDP Crystals 69
L. N. Rashkovich and G. T. Moldazhanova
Growth and Certain Properties of KDP Crystals Affected by pH and Temperature 79
V. A. Kuznetsov, E. P. Efremova, T. M. Okhrimenko, and A. Yu. Klimova
KOH-Zr02-SiOrH20 Hydrothermal System: Formation of Potassium Zirconosilicates
and Crystallochemical Correlations Among Them 89
G. D. Ilyushin and L. N. Dem yanets
vii
viii CONTENTS
III. GROWTH OF CRYSTALS FROM THE MELT
Compositions of Congruently Melting Three-Component Solid Solutions Determined
by Finding Acnodes on Ternary-System Fusion Surfaces 103
P. P. Fedorov
Coriolis Force on Melt Convection During Growth of Crystals in a Centrifuge and
Under Weightlessness 117
V. S. Yuferev
Convection-Induced Effects in the Step-Heater Stockbarger Growth of CaF2 Crystals:
Growth-Front Shape 129
N. A. Verezub, M. P. Marchenko, M. N. Nutsubidze, and A. 1. Prostomolotov
Crystallization Front Structure During Growth of Single Crystals from a Melt in Various
Crystallographic Directions 139
O. P. Fedorov and E. L. Zhivolub
Growth, Detwinning, and Properties of YBa2Cu30x and TmBa2Cu30x Single Crystals 153
V. 1. Voronkova and V. K. Yanovskii
I. HETEROSTRUCTURE FORMATION IN
MOLECULAR-BEAM AND GAS-PHASE EPITAXY
DIRECT SYNTHESIS OF NANOSTRUCTURES IN THE
GERMANIUM-SILICON SYSTEM BY MOLECULAR-BEAM EPITAXY
O. P. Pchelyakov and L. V. Sokolov
INTRODUCTION
Direct synthesis, self-organization, or spontaneous formation of semiconducting nanostructures during
molecular-beam epitaxy (MBE) are synonyms that are presently used to describe methods for preparing
heterostructures with isolated nanometer-sized regions in which microstructuring is not applied. These
methods provide new capabilities for fabricating quantum-sized features such as tilted, lateral and serpen
tine superlattices and systems with quantum threads and points [1-5J. Direct synthesis enables systems
with a high density of elements with limitingly small dimensions to be formed. This is in contrast with
selective growth and electron lithography, which are strictly limited to the minimal dimensions of separate
elements [6J.
The structure and morphology of the growth surface and how they change during epitaxy must be
accurately known for the direct synthesis of nanostructures to be successful. Furthermore, the time when
the flux of atoms to the surface of the growing film should be stopped or started must be capable of being
accurately defined. For this, ways of accurately determining the film thickness in situ and precisely timing
complete or a given partial coverage of each next atomic layer must be available. The method by which
such fine measurements are made is reflective high-energy electron diffraction (RHEED). The measured
quantity providing the required information is the specular-beam intensity, Ir, of the electrons reflected
from the film surface. The method is based on the well-known oscillations of Ir under conditions where
the film experiences layered growth.
In the present work we examine certain literature data and report results from new experiments on
the direct synthesis by MBE of heterostructures and nanostructures in the Ge-Si system.
1. EXPERIMENTAL
All original results reported herein were obtained on equipment developed and constructed in the Divi
sion of the Growth and Structure of Semiconducting Crystals and Films in the Institute of Semiconductor
Physics of the Siberian Branch of the Russian Academy of Sciences.
The experimental setup (Fig. 1) includes a growth chamber with crucible molecular-beam sources and
a mobile heater for the Si substrate. This enables the temperature to be raised to 1280°C before epitaxy.
An oil-free pump produces a vacuum of at least 2.10-6 Pa during epitaxy. A gated chamber enables the
substrates to be loaded into the growth chamber without destroying the vacuum. The epitaxy parameters
are monitored using a fast-electron diffractometer equipped with a fluorescent screen, a video system, and
an automated laser ellipsometer. The information produced by the analytical systems is used to form a
signal that controls the position of the source shields. The experimental setup has been described in detail
[7J.
Silicon substrates in the (111) and (001) orientations were used. The substrates were treated be
forehand by chemical-mechanical polishing and oxidation in moist oxygen. An oxidized layer of 100 nm
thickness was removed immediately before epitaxy in HF. Then the substrate was washed in deionized
water, mounted on a special holder, and inserted into the growth chamber. The substrate was finally
3
4 O. P. PCHELYAKOV AND L. V. SOKOLOV
4
2 3
8
Fig. 1. Diagram of experimental MBE apparatus. Substrate (1),
inputs for controlling source heating and screen positions (2, 3),
RHEED gun (4), fluorescent screen (5), television system (6), ellip
someter (7), personal computer (8), controlling signal (9,10).
9 10
thermochemically cleaned under vacuum (details have been published [8]). Depending on the final heating
of Si(111) substrate under vacuum, its surface consisted of terraces with the 7 x 7 structure that were
subdivided by equidistant monatomic steps or step echelons [9J. An atomically pure Ge(l11) surface was
fabricated in order to investigate the homoepitaxial growth of Ge. For this, a buffer layer of Ge 200 nm
thick (growth temperature 450DC) was grown on Si(l11) substrate.
Knudsen cells with crucibles of boron nitride were used to create a Ge beam. The Si vapor source was
a Si plate heated directly by current passage. The growth rate of Ge films and GexSi1- x solid solutions
was 0.01-0.1 nm/sec. The substrate temperature was kept in the range 100-700DC. The Si films were grown
at 600-950DC at a rate of 0.05 nm/sec [8, 1O-12J.
2. FILM SURFACE STRUCTURE
The structure and reconstruction of the growth surface are important factors that determine the
course of adsorption-desorption processes and affect the surface migration of film and impurity atoms and
their incorporation into the growing film. The effects of substrate temperature and film composition on the
structure of the growth surface are presently well known. In particular, we investigated the dynamics of the
surface-structure change of GexSh-x growing on Si(111)7x7 substrate over a wide range of concentrations
x and growth temperatures Tgr [10-12J.
Two structures with a seven-fold period are observed during Ge epitaxy on Si(111). These are Si(l11)
(7x7)Ge and Ge(111)-(7x7)Si. Here the first chemical symbol indicates the material for which the surface
acquires this superstructure; the second, the material that stabilizes this superstructure.
The superstructure Si(111)-(7x7)Ge is formed at high temperatures with small amounts of Ge on the Si
surface. The maximal temperature at which this superstructure is stable during film growth reaches 950DC.
It has been estimated that the fluxes of Ge atoms that are adsorbed and desorbed at this temperature are
equal. If the temperature is further increased, the concentration of surface Ge atoms quickly decreases.
The Ge(111)-(7 x 7)Si superstructure is formed on the surface of Ge islands owing to diffusion of Si
atoms from the substrate. The facts that a surface film of Ge growing at < 350DC, where interdiffusion can
be neglected, had the Ge(111)-(2x8) superstructure whereas subsequent annealing of this film at 600-700DC
produced the Ge(111)-(7x7)Si superstructure confirms this.
In addition to the structures mentioned above, the SiGe(111)-(5x5) superstructure was also observed.
Its presence was ascribed to the presence of a pseudomorphic Ge film. After the pseudomorphism was
relieved, this superstructure converted to the Ge(111)-(7x7)Si structure or the (111)-(2x8) superstructure
characteristic of an atomically clean Ge surface [10, 12J. The phase diagram of surface structures present
O. P. PCHELYAKOV AND L. V. SOKOLOV 5
1000
1x1
-------------
800
1x 1
600
400
200
Fig. 2. Structure-phase diagram of Ge film surface on Si [10].
Diffraction from twins is observed in region I. The diffraction
pattern of the 1 x 1 structure in region II gradually replaces the d,nm
0 1- 2 3 4
continuous diffuse-scattering background.
during the early growth stages of Ge films on Si(111) substrates is plotted in Fig. 2. Our results were later
confirmed by other researchers [13, 14].
The superstructures (2 x 1) and (2 x 8) are initially present on the surface during growth of GexSh-x
films on Si(001) substrates. Facets of the {811} and {311} types are found after islands form [15].
As mentioned above, relief of the pseudomorphism and relaxation of the misfit strains rearranges
the surface of GexSh-x films. This is important in developing preparation methods of quantum-sized
nanostructures. By examining RHEED patterns and the change of the specular-beam intensity, we obtain
data on the change of surface structures and the film thickness at the time the pseudomorphism is relieved
[16, 17]. The critical thickness of the pseudomorphic layer he [16], which is calculated following Frank-van
der Merwe, gives values for different substrate orientations and various crystal-lattice misfit parameters
for any regular change of elastic deformation along the film length. By knowing the film thickness at
which pseudomorphism is relieved and the island structure is formed and being able to measure the film
thickness in situ, quantum-sized island structures can be directly synthesized. These structures consist of
three-dimensional islands, the density and cross section of which are determined by the surface diffusion
length and are dependent on the growth temperature. With respect to electronic properties, such films act
as a system of quantum points in which a zero-dimensional electron (hole) gas is localized.
3. OSCILLATION OF SPECULAR-BEAM INTENSITY
The intensity change Ir of a beam of electrons reflected from the surface of a growing film (Fig. 3)
regularly changes with a periodic change of the number and cross section of two-dimensional (2D) islands.
This occurs where films grow by 2D nucleation [18-23].1
Depending on the diffraction conditions (azimuth, incidence angle, beam coherency and electron en
ergy) , not only the azimuth and shape of the RHEED oscillation signal but also its frequency and phase
change [24]. The behavior of a RHEED signal that was observed during MBE on a fluorescent screen was
investigated in detail both theoretically and experimentally [23-26]. The calculations were confirmed by
the experiments and revealed the following [23-24]: 1) when the zero-order rod of the diffraction pattern
corresponds with an off-Bragg incident angle of the electron beam, Ir correlates with the instantaneous
area of 2D islands or the coverage of the next atomic layer; 2) when the Bragg incident angle occurs, the
intensity of the reflected beam correlates with the step density. 2
1 The periodic change of surface roughness of a film growing by 2D nucleation is also evident in oscillations of the specular
beam parameters (see Fig. 3). These were first detected by us using an automated ellipsometer [20, 21]. Ellipsometry is used
less than RHEED in MBE technology to follow film growth. However, it produces good results since this method is exceedingly
sensitive to changes of surface roughness at the atomic level. The comparison of the oscillations of the electron and light
beams is important in interpreting the measurements.
2The shape of the oscillating specular-beam intensity is different in these two situations (see below, Section 6).