Defects and Diffusion in Semiconductors

188 Pages·1998·0.67 MB·English

Defects and Diffusion
in Semiconductors
An Annual Retrospective
Editor:
D.J. Fisher
SCITEC PUBLICATIONS
Notes:
Each item in this section of the volume begins with a graphical compilation of relevant diffusion data which
have been reported during the past decade. The plotted data are also tabulated as indicated on the graph. In some
cases, the tabulated data have been obtained by digitizing published graphs and the values may not correspond
exactly with the author's unpublished raw data.
Refers to table N
3N Bulk Diffusion - Quantitative Data
The migration of Ag from epitaxial layers and into (111) samples of Si,
during annealing at temperatures of between 450 and 500C, was studied
by means of secondary ion mass spectrometric depth profiling. It was
found that the diffusivities lay between 8 x 10-16 and 1.6 x 10-15cm2/s
(table N). These values were lower than were expected on the basis of
previous data.
T.C.Nason, G.R.Yang, K.H.Park, T.M.Lu: Journal of Applied Physics,
1991, 70[3], 1392-6
[446-91/92-027]
Indicates volume and page number in
DDF where abstract first appeared
Defects and Diffusion in Semiconductors
An Annual Retrospective
AlAs: Electron Irradiation, Point Defects, and Defect Annealing
Damage accumulation, and subsequent thermally activated annealing reactions, in AlAs
layers on GaAs substrates were studied by using X-ray diffraction techniques. Irradiation
19 2
with 2.5MeV electrons was performed at 4.6K, up to a total dose of 2 x 10 /cm . By
measuring irradiation-induced changes in the lattice parameter, it was possible to obtain
information concerning the properties of interstitial atoms and vacancies in AlAs for the
first time. For instance, the observed value of the lattice expansion was affected by the
defect concentration, c, and the relaxation volumes of interstitials, V, and vacancies, V ;
i v
according to: relative lattice change = c(V + V )/3O, where O was the average atomic
i v
volume. These results exhibited remarkable similarities to those for GaAs. The
irradiation-induced increase in the lattice parameter amounted to some 50% of the change
which was observed in the GaAs substrates. Separation of the defect concentration and
relaxation volume of the Frenkel pair was not possible on the basis of the lattice
parameter data alone. Nevertheless, the increase in lattice constant indicated that
interstitials, which were expected to have a positive relative volume, predominated over
vacancies; which could have smaller negative values of the relaxation volume. By
assuming that the relaxation volume of the Frenkel pair was equal to 1O, the defect
19 3
concentration was deduced to be equal to 10 /cm . A comparison of the relaxation
volumes for GaAs, InP, Si and Ge, indicated that the value of 1O was a maximum value;
which yielded a minimum value for the defect concentration. Because of the observed
absolute magnitude of the relative lattice change, it was concluded that Frenkel pairs in
AlAs were characterized by large distortion fields which could be frozen in, in large
quantities, at low temperatures. A major annealing step occurred near to room
temperature, rather continuous annealing occurred at up to 500K, and a final recovery
stage was found between 700 and 900K. There was no indication of an unusually high
defect mobility, as no significant annealing occurred below 250K. It was suggested that
the broad annealing stage (250 to 500K) might have some fine structure which was not
resolved here but might correspond to the I, II and III stages which were observed in
GaAs (due to the migration of various types of interstitials). Consequently, the final
annealing stage was attributed to the migration of vacancies. The temperature of the final
annealing stage, and previous data, suggested that it was related to the melting point.
127
Be Diffusion AlGaAs Interface Defects
A.Gaber, H.Zillgen, P.Ehrhart, P.Partyka, R.S.Averback: Journal of Applied Physics,
1997, 82[11], 5348-51
[446-162/163-128]
AlGaAs/AlAs: Be Diffusion
Dopant diffusion was investigated via depth-profiling using secondary ion mass
spectrometry of heterostructures which contained Be-doped short-period Al Ga As
x 1-x
superlattices, where x ranged from 0.3 to 0.8, that had been grown by means of molecular
beam epitaxy. Out-diffusion of Be into the undoped GaAs layers was observed only at a
18 3
substrate temperature of 660C, when the Be concentration was 2 x 10 /cm . At a dopant
19 3
concentration of 2 x 10 /cm , a marked increase in diffusion occurred at all growth
19 3 18 3
temperatures. The solubility limits of Be were 10 /cm at x = 0.6, and 2 x 10 /cm at x =
0.8. Secondary ion mass spectrometry profiles revealed that the amount of diffused Be in
the active region was twice as high in samples with a thin (450 to 600nm) p-type cladding
layer.
A.Gaymann, M.Maier, W.Bronner, N.Gruen, K.Koehler: Materials Science and
Engineering B, 1997, 44[1-3], 12-5
[446-157/159-237]
AlGaAs/GaAs: Interdiffusion
Low-temperature growth and rapid thermal annealing were used to intermix Al and Ga
atoms in multiple quantum wells. The intermixed samples were characterized by using
photoluminescence spectroscopy, and observed blue-shifts in photoluminescence energy
were interpreted as being the result of modifications of the quantum-well shape; due to
enhanced Al and Ga interdiffusion in the samples. The enhancement of interdiffusion was
found to depend strongly upon the growth and annealing conditions. A saturation of Al
and Ga interdiffusion was detected.
W.Feng, F.Chen, W.Q.Cheng, Q.Huang, J.M.Zhou: Applied Physics Letters, 1997,
71[12], 1676-8
[446-162/163-128]
AlGaAs: Ion Bombardment and Point Defects
Inductively coupled Ar plasmas were found to produce substantially less ion-induced
damage than did electron cyclotron resonance plasmas having the same average ion
energy. Changes in sheet resistance were attributed mainly to the introduction of deep-
level compensating defects which reduced both carrier density and mobility. It was noted
that p-type material was more susceptible to plasma-induced damage than was n-type
material, and the changes in electrical properties were due mainly to carrier trapping.
J.W.Lee, D.Hays, C.R.Abernathy, S.J.Pearton, W.S.Hobson, C.Constantine: Journal of
the Electrochemical Society, 1997, 144[9], L245-7
[446-162/163-128]
AlGaAs/GaAs: Interface Defects
The binding energy of bi-excitons which were bound to single-island interface defects in
deep quantum-wells was calculated. The use of a variational function led to calculations
128
Point Defects AlGaAs/AlN Dislocations
that were largely analytical. The dependence of the bi-exciton binding energy upon the
defect size and the quantum-well width was considered in detail. Numerical calculations
were carried out for AlGaAs/GaAs quantum wells with defect depths of 1 or 2 mono-
layers. An attempt was made to correlate the present case, of a localized bi-exciton, with
existing results for free 4-particle molecules in various confinement structures and for
various mass ratios.
O.Heller, P.Lelong, G.Bastard: Physical Review B, 1997, 56[8], 4702-9
[446-162/163-129]
AlGaAs, GaAs: Point Defects
The transitions which were associated with magnetic circular dichroism of absorption in
GaAs were investigated by studying the spectrum as a function of stoichiometry in
AlGaAs which had been grown at low temperatures by means of molecular-beam
epitaxy. The principal result was that the spectrum of the singly ionized As antisite could
be explained in terms of the valence-band model. That is, the optical transitions were
from the valence band to the A ground state. A competing, internal transition, model was
1
refuted. The stoichiometry dependence also suggested that the observed diamagnetic
spectrum of the neutral As antisite could be linked to the zero-phonon line of the optical-
absorption spectrum.
A.Prasad, P.Stallinga, X.Liu, E.R.Weber: Physical Review B, 1998, 57[8], R4214-7
[446-162/163-129]
AlGaN: Point Defects
The transition from shallow to deep centers, as a function of pressure or alloying, was
investigated for O and Si donors on the basis of first-principles total-energy calculations.
The stability of the localized deep state (DX center) was found to depend upon
interactions between the impurity, and third-nearest neighbor atoms, which occurred at
different positions in the zincblende and wurtzite phases. Such DX-center formation was
suppressed in the zincblende phase, as well as that of Si donors. The results supported the
identification of O as being the unintentional dopant in n-type GaN, and cast new light on
the driving force for DX formation.
C.G.Van de Walle: Physical Review B, 1998, 57[4], R2033-6
[446-162/163-129]
AlN: Dislocations
Samples which had been plastically deformed, using high stresses at temperatures ranging
from 20 to 800C, were studied by means of transmission electron microscopy. The
activation of 1/3<11•0>(00•1) basal slip, as well as the first type of 1/3<11•0>{¯11•0}
prismatic slip, was observed. Dislocation configurations in the basal plane revealed the
role that was played by Peierls forces acting along the screw orientation. It was easier for
a dislocation to cross-slip in the prismatic plane than to lie, in the basal plane, along an
orientation other than the screw direction. In the basal plane, as well as in the prismatic
plane, no dislocation dissociation could be resolved under weak-beam imaging
conditions. The occurrence of cross-slip was favoured by numerous pinning points on
screw dislocations; thus giving rise to dipole dragging. At temperatures ranging from 20
to 500C, deformation proceeded via dislocation glide in the basal and prismatic planes;
129
Dislocations AlN Dislocations
with frequent cross-slip between these planes. At 800C, a change in the mobility of edge
dislocations on the prismatic plane was detected and was attributed to lattice friction
acting in the (00•1) orientation or to dislocation dissociation out of the glide plane.
M.Audurier, J.L.Demenet, J.Rabier: Philosophical Magazine A, 1998, 77[4], 825-42
[446-162/163-130]
AlN/Si: Dislocations
The growth of hexagonal AlN directly onto (111)Si was studied, as a function of the film
thickness, by means of grazing incidence X-ray diffractometry and high-resolution
electron microscopy. Two epitaxial relationships were observed. One was
(00•1)[2¯1•0] ||(111)[02¯2] , which predominated at deposition temperatures greater than
AlN Si
650C, and (00•1)[10•0] ||(111)[02¯2] . The average in-plane crystallite size was 16.2nm
AlN Si
for a 4nm-thick layer, the in-plane rotation was about 2º, and the dislocations introduced
an average strain distribution of 0.8%. The Si/AlN interface was very sharp, and complete
relaxation (down to about 0.2%) occurred within one bilayer. No long-range order was
observed at the interface; thus implying a low mobility of AlN species, on Si, which
inhibited any structural rearrangement. The in-plane rotations originated from early
stages in the layer growth, and decreased with layer thickness; especially for thicknesses
greater than 25nm.
A.Bourret, A.Barski, J.L.Rouvière, G.Renaud, A.Barbier: Journal of Applied Physics,
1998, 83[4], 2003-9
[446-162/163-130]
AlN: Dislocations and Point Defects
The structures and formation energies of neutral and charged edge dislocations were
investigated by means of density-functional calculations. Stoichiometric structures with
full or open cores were considered, as well as non-stoichiometric structures with Al or N
vacancies along the dislocation core. The formation energies were found to depend
strongly upon the Fermi level, due to the presence of defect levels in the band-gap, and
upon the growth conditions; in the case of non-stoichiometric structures. A structure with
Al vacancies along the dislocation core was predicted to be most stable in n-type material
that was grown under N-rich conditions. On the other hand, a N-vacancy structure was
most stable in p-type material that were grown under Al-rich conditions.
A.F.Wright, J.Furthmüller: Applied Physics Letters, 1998, 72[26], 3467-9
[446-162/163-130]
AlN: Dislocations and Stacking Faults
A study was made of the ability of dislocations to glide in one plane relative to another. It
was noted that, according to the closest-packing criterion, the first type of prismatic plane
appeared to be favoured. Line-energy calculations, which were performed under
anisotropic elasticity conditions, did not permit the detection of preferential activation of
one of the glide planes. The crystallographic structures of basal and first-type prismatic
planes, the core structures of dislocations, and dissociation reactions were investigated,
and configurations were proposed for stacking faults on prismatic planes.
130
Point Defects AlN Stacking Faults
M.Audurier, J.L.Demenet, J.Rabier: Philosophical Magazine A, 1998, 77[4], 843-59
[446-162/163-131]
AlN: Point Defects
The magneto-optical properties of the 0.9eV luminescence were investigated. Zero-
2
phonon lines at 0.943eV were attributed to a transition, within a d configuration, because
of a characteristic 3-fold ground-state splitting in magnetic fields. A g-value of 1.96 and a
3
zero-field splitting of 120µeV were determined for the A (F) ground state. On the basis
2
of the temperature dependence in a magnetic field, the 0.943eV zero-phonon line was
1 3 3+
attributed to the E(D)- A (F) transition of isolated V .
2
P.Thurian, I.Loa, P.Maxim, A.Hoffmann, C.Thomsen, K.Pressel: Applied Physics
Letters, 1997, 71[20], 2993-5
[446-162/163-131]
AlN: Stacking Faults
The growth characteristics and atomic structures of defects were investigated in AlN thin
films which were grown by metal-organic chemical vapor deposition onto the (10•2) r-
plane of a-Al O . The AlN films were monocrystalline, and had an epitaxial relationship,
2 3
(11•0) ||(10•2) , with an in-plane alignment of [00•1] ||[¯10•1] . By using
AlN sapphire AlN sapphire
high-resolution electron microscopy and multi-slice image simulation, the predominant
defects in the AlN thin films were found to be low-energy intrinsic stacking faults of
type-I which lay in the basal plane. This fault, with a 1/6[20•3] resultant displacement
1
vector, could be formed by removing one (00•2) plane and then shearing the remaining
half-crystal by a displacement of 1/3[10•0]. The faults appeared as a single face-centered
cubic stack, ABC, which was inserted into the normal, ... ABAB..., hexagonal sequence.
K.Dovidenko, S.Oktyabrsky, J.Narayan: Journal of Applied Physics, 1997, 82[9], 4296-9
[446-162/163-131]
AlN, GaN, InN: Stacking Faults
The energies of basal-plane stacking faults in wurtzites were determined by using a 1-
dimensional Ising-type model which incorporated effective layer-layer interactions that
were based upon density-functional theory calculations. The stacking-fault energies were
found to be largest for AlN and smallest for GaN. This was consistent with density-
functional results for wurtzite/zincblende energy differences. Estimates were also
obtained for stacking-fault energies in the zincblende structure. The values were negative,
in agreement with the observation that nominal zincblende films typically contained a
large number of stacking faults. A related result was that hexagonal structures with
stacking sequences that repeated after 4 or 6 bilayers had lower energies than zincblende,
for all 3 compounds.
A.F.Wright: Journal of Applied Physics, 1997, 82[10], 5259-61
[446-162/163-131]
AlN/SiC, GaN/SiC: Stacking Faults
The polarity of GaN films and AlN buffer layers, grown onto the (00•1) surface of 6H-
Si
SiC using electron cyclotron resonance plasma-enhanced molecular beam epitaxy, was
131
Stacking Faults AlN/BN Point Defects
investigated by means of convergent-beam electron diffraction and high-resolution
electron microscopy. In the case of the AlN buffer layers, which contained a very high
density of defects, the polarity was determined by using extensive high-resolution
electron microscopy and image simulation. In both cases, the simulations were in good
agreement with the experimental results, and demonstrated that the free surfaces of the
GaN and AlN layers were Ga- and Al-terminated, respectively. Moreover, (¯12•0)
prismatic planar defects which were observed in the AlN layers were identified as being
stacking faults, and analysis of various areas of the specimens confirmed that the layers
were unipolar.
P.Vermaut, P.Ruterana, G.Nouet: Philosophical Magazine A, 1997, 76[6], 1215-34
[446-162/163-132]
AlN, GaN, InN: Stacking Faults
Basal-plane stacking faults in wurtzite-structured materials were studied by using density-
functional pseudopotential calculations. The formation energies followed the trend that
was exhibited by zincblende/wurtzite energy differences in the bulk materials. That is, the
lowest energy was found for GaN and the highest was found for AlN. Type-I stacking
faults had the lowest energy, followed by type-II stacking faults, and finally extrinsic
stacking faults. Another type of intrinsic stacking fault was identified that did not seem to
have been previously observed. Its energy was slightly lower than that of the type-II
faults. There were no localized states in the band-gap. However, stacking faults could
bound a quantum well-like region of zincblende material that was surrounded by the
wurtzite host; thus giving rise to a luminescence line below the wurtzite band-gap.
C.Stampfl, C.G.Van de Walle: Physical Review B, 1998, 57[24], R15052-5
[446-162/163-132]
AlN, GaN: Surface Defects
An investigation was made of the structure of the anion- and cation-terminated (00•1)
surfaces of wurtzite-phase GaN and AlN, using ab initio local-orbital calculations that
were based upon the local-density approximation and the pseudopotential method. All of
the stable surface configurations which were studied differed, in atomic composition and
periodicity, from the ideal bulk-like termination. The calculated total energies were
compared for various p(2 x 2) geometries of GaN and AlN (00•1). Vacancy structures
were found to be the most stable configurations for the anion- and cation-terminated
surfaces. Under metal-rich growth conditions, the predictions favoured the adsorption of
metal atoms at the cation-terminated surface. Anion- and cation-derived dangling-bond
states appeared in the bulk band-gap as a result of the formation of vacancies or the
adsorption of group-III atoms. Flat surfaces of both types were found to be stabilized by
¾ of a monolayer of adsorbed H.
J.Fritsch, O.F.Sankey, K.E.Schmidt, J.B.Page: Physical Review B, 1998, 57[24], 15360-
71
[446-162/163-132]
BN: Point Defects
The electronic structures of Be, Mg and Si in zincblende BN were studied by using the
tight-binding linearized muffin-tin orbitals technique. Calculations were performed by
132
Point Defects BN/CdGeAs Point Defects
2
using 64-atom super-cells which were centered on either a B or a N lattice site. While Be
and Mg impurities were substituted only for B, substitution for both B and N was
considered in the case of Si. In each case, total-energy minimization was used to study
lattice relaxation near to the impurity site, and the nature of the chemical bonding
between the impurity and neighboring atoms of the host crystal was studied in detail. It
was found that Be and Mg, when substituted for B, created delocalized levels which
merged with states at the valence-band edge. These partially occupied levels could result
in p-type conductivity, as observed experimentally. In contrast to the behavior of isolated
Be and Mg impurities in crystalline BN, it was found that Si which was substituted at a B
site introduced delocalized impurity states that overlapped with the conduction-band edge
of the host. These levels could contribute to the n-type conductivity of Si-doped
crystalline BN. When Si was substituted into the anion sub-lattice it introduced sharp,
partially occupied, and highly localized levels within the forbidden gap. Experimentally
observed mixtures of n-type and p-type material could therefore be accounted for by the
presence of impurities of each type. The relaxation of the host lattice near to the Be and
Mg impurities was outward, as was the relaxation near to Si which was substituted at a N
site. Inward relaxation was predicted to occur in the case of Si which was substituted for
B. Total, orbital, and shell-projected densities of states for the impurity, and up to 6 of the
coordination shells nearest to the impurity, were analyzed in detail.
V.A.Gubanov, E.A.Pentaleri, C.Y.Fong, B.M.Klein: Physical Review B, 1997, 56[20],
13077-86
[446-162/163-133]
BN: Point Defects
A study was made of the electronic and structural properties of native defects (N vacancy,
B antisite, substitutional O), in the cubic phase, by using all-electron first-principles total-
energy calculations. It was found that all of the defects introduced a deep state above the
middle of the energy-gap. These defects had C local symmetry. A Jahn-Teller distortion
3v
in the <111> direction was observed for the neutral isolated B antisite. Strong relaxation
was found in the case of the neutral N vacancy. A highly localized orbital in the vacancy
region (F-center precursor) and a resonant orbital in the conduction band appeared before
lattice relaxation. Such relaxation, plus distortion, split the resonant orbital and led to a
half-occupied level close to the conduction band. The results suggested that a strong
electron paramagnetic resonance signal which was detected in cubic material could be
generated by the trapping of 2 electrons by acceptor levels which were introduced by C
doping.
P.Piquini, R.Mota, T.M.Schmidt, A.Fazzio: Physical Review B, 1997, 56[7], 3556-9
[446-162/163-133]
CdGeAs : Point Defects
2
Native acceptor centres were studied by using atomistic simulation techniques. A new set
of interatomic potential parameters was developed which consisted of 2-body and 3-body
terms. It was found that lattice, elastic and dielectric constants were well reproduced by
the atomistic model. The calculated formation energies for vacancies, interstitials and
antisites suggested that intrinsic disorder was dominated by antisites in the cation sub-
lattice, followed by Schottky and Frenkel defects. The acceptor centre which was
133
Point Defects CdGeAs /CdHgTe Ag Diffusion
2
identified by Hall-effect measurements and electron paramagnetic resonance was found
to be related to the delocalized hole that was shared by the four As neighbours which
were bound to CdGe. Calculations for this centre yielded a binding energy of 0.13eV, in
agreement with the experimental value of 0.15eV which was given by Hall-effect
measurements. The calculations also indicated the magnitude of the lattice distortion
which was introduced by this acceptor centre.
R.Pandey, M.C.Ohmer, J.D.Gale: Journal of Physics - Condensed Matter, 1998, 10[25],
5525-33
[446-162/163-134]
1.0E-12
1.0E-13
1.0E-14
)
s
/
2
m
c
( 1.0E-15

D
x = 0.4%
x = 3%
1.0E-16
1.0E-17
14 15 16 17 18 19
104/T(K)
Figure 1
Diffusivity of Hg in Hg Cd Te
x 1-x
CdHgTe: Ag Diffusion and Electromigration
The migration of Ag in Cd Hg Te was studied. In samples with x-values of between
x 1-x
0.55 and 0.8, the Ag-doped material was p-type when diffused at temperatures below
125C. The results showed that the higher the Hg content or hole concentration, the faster
was the Ag diffusivity. The results were explained by assuming that Ag was present as 2
species with opposite charges. One of these was supposed to be predominant but
essentially immobile, while the other species diffused rapidly. These forms equilibrated
within a few seconds at room temperature. This, in turn, could be explained in terms of
Ag-Hg complex formation. It was concluded that, if both forms of Ag were bound to Hg,
then this could explain the marked effect of the Hg content upon the diffusion behavior.
134