" on trying daring ideas with herb". p.m.petroff professor emeritus materials department,...
TRANSCRIPT
" On trying daring ideas with Herb".
P.M.PetroffProfessor Emeritus
Materials Department , University of
California , Santa Barbara
Some coauthored papers and shared students
T.Y.Liu, P.M.Petroff, and H.Kroemer, "Luminescence of GaAs-GaAlAs Superlattices Grown on Silicon Substrates: Effects of Superlattice Interfaces”.J,.Applied Physics.64, 12, 6810 ( 1988)
H. Kroemer, P. M.Petroff, T. L.Liu, "GaAs on Si: State of the Art and Future Prospects”.J.Crystal Growth 95, 96 (1989)
J.M. Gaines, P.M. Petroff, H. Kroemer, R.J. Simes, R. S. Geels and J. English, "MBE Growth of Tilted GaAs/AlAs Superlattices by Deposition of Fractional Monolayers on Vicinal (100) Substrates”J. Vac.Scien.Tech. B6, 4,1378 (1988)
M. Tsuchiya, J. M. Gaines, R. H.Yan, R. J. Simes, P. O. Holtz, L. A. Coldren, and P. M. Petroff "Optical Anisotropy in a Quantum Well Wire Array With Two Dimensional Quantum Confinement". Phys Rev. Lett. 6,466 (1989)
.M.S. Miller, C.E. Pryor, L.A. Samoska, H. Weman, H. Kroemer, and P.M. Petroff, "Serpentine Superlattice in GaAs; Concept and Results”. The Physics of Semiconductors (ed. E.M.Anastassakis and J.D.Joannopoulos, World Scientific Publ.). p.1717 (1990)M.S. Miller, C.E. Pryor, H. Weman, L.A. Samoska, H. Kroemer, and P.M. Petroff, "Serpentine Superlattice: Concept and First Results". J.Cryst Growth 111, 323 (1991) M.S. Miller, H. Weman, C.E. Pryor, M. Krishnamurty, P.M. Petroff, H. Kroemer, and J.L. Merz, "Serpentine Superlattices of AlGaAs Grown on GaAs Vicinal Surfaces” Phys. Rev. Lett. 68, 3464 (1992)
.
Tilted superlattices , Serpentine superlattices and Self assembled quantum wires
with J.Gaines and M.Miller
Conventional quantum wells and superlattices :growth direction isnormal to thesubstrate surfaceInterfaces are parallel to substrate surface
AlAsGaAs
InAs
•Atoms will diffuse to steps.•Steps will move in phase.•Atoms stick to the step edges and do not climb steps.•We are able to controldeposition to 0.1 ML!
Vicinal {100} surface
h=2.8ÅPeriodic steps1o->80Å2o->40Å
(GaAs)0.5(AlAs)0.5
THE TILTED SUPERLATTICE WITH INTERFACES PARALLEL TO THE GROWTH DIRECTION
TILTED SUPERLATTICE AND QUANTUM WIRE SUPERLATTICE
tgß= |p-1|/tga
p=1.1=a 2o
p=m+n
p=0.9a=2o
(GaAs)m(AlAs)n, with p=m+n 1 and m or n>0.5 or <0.5≂
Serpentine Superlattice
Modeling TEM cross section
p=0.9 p=1p=1.1
ß=-30o ß=0o
ß=60o
Flux non uniformity solution:Parabolic quantum well profilewith linear variations of p(t)=m+n--> Quantum wires
It is the constant testing of the assumptions which makes for progress in Science. Daring!
How well does it work?
PH YSICAL REVIEW LETTERS 8 JUNE 1992
Not as well as we wanted :Exchange reactions Al->GaVicinal surfaces are not perfect
MOLECULAR BEAM EPITAXY ON SUBSTRATES WITH LARGE LATTICE MISMATCH
e.g.: THE HOLY GRAIL III-V layers ON SI
With T.Y. LIU
Various solutions to a very old problemDislocations
Thick buffer layer: Dislocation interactions 1010cm-2 to 107 cm-2
Micro pillars: Image forces 1010cm-2 to 0 cm-2
Multiple strained layers or strain graded layers: dislocation interactions 1010cm-2 to 107 cm-2
Lateral Epitaxy Overgrowth (LEO): Dislocation filtering 1010cm-2 to 104cm-2
Wafer fusion: interface defects (dislocations) and interface traps.
Quantum dots as active medium.
Lattice mismatch and thermal expansion coefficient misfit and threading dislocations
€
vb i∑ = 0
Dislocations are deep levels. Electrons or hole traps are thermally or optically ionized Solutions:
a1
F3F2F1a2
Si Si(A) (B)
a3
an
Hybrid MBE-LPE growth of hetero-structures with largeLattice mismatch and differential thermal expansion coefficients .
Decouple the substrate from the epitaxial layers during growth
GaAs
GaAs substrate
Liquid Phase Epitaxy (LPE)
MBE
Hybrid MBE-LPE
as
a2
an
Liquid layer
Ga(L)
P.M.PetroffMaterials department , University of California , Santa Barbara
DISLOCATIONS REMOVAL IN HYBRID HETEROSTRUCTURES
Misfit dislocations sources and dislocation interactions in thick buffer layer or multi-layer samples dislocation density : 1010cm-2 to 107 cm-2
b1b2
b1 b2
b1 b2
b3
€
vb i∑ = 0
b1+b2+b3=0
Solutions 1
Solutions 2-3
Image forces Dislocations eliminationMicro-pillars:
Problems: Lithography and regrowthSmall areas for devices
Lateral epitaxial overgrowth:Dislocation filtering Dislocation density: 1010cm-2 to 104cm-2
Dislocation density: 1010cm-2 to 0 cm-2
Bonded interface
≈105 dislocations /cm2 and interface traps: Yet the laser is working.
The active medium: several layers of quantum dots with large carrier capture cross section and fast and efficient carrier radiative carrier recombination.Problem: Passivation of defects at the fused interface.
Solution 4:Fusion
(j) (k)
Dislocations
Si
Melted thin filmL1 L2
L3
(f) (g) (h) (i)
(a) (b) ( c) (d) (e)
L4•Remelt of L1 layer for liquidsolid equilibrium.•Dislocation climb and image forces eliminate dislocations in L3.• Cooling to 300K may introduce MD confined to the layer with lowest shear modulus???
Proposed method: Use as a first layer a low melting point layer. (L1 layer: eg. InSb)
Ideal case
Real World
Cooling
Growth
Does it work ?
Yes and then No: Liu made a mistake!
In fact we do not know.
Be daring and lets try it again seriously !
Why LPE does not work for sharp hetero- interfaces
GaInSb ternary systeme.g: at 550C, Ga.34In.66Sb (S) <->Ga.1In.9Sb (L)
Liquid<->Solid equilibrium requires to be on the same tie line-> solid will readjust its composition and -> remelt and resolidification of the substrate or epilayer L2.
(j) (k)
(f) (g) (h) (i)
Dislocations
Si
(a) (b) ( c) (d) (e)
Melted thin filmL1 L2
L3
L4 •Remelt of L2 layer for liquidsolid equilibrium.•Dislocation climb and image forces eliminate dislocations in L3. e.g. nanowires grown by VLS• Cooling to 300K may introduce MD in layer with lowest shear modulus???
Proposed method: Use as a first layer a low melting point layer ( e.g. InSb)
Ideal case
Real World
Cooling
Growth
Dislocations dynamics at a liquid solid interface in Si (CZ growth)
Dislocations climb and glideto the liquid solid interface
Dislocation free solid
(j) (k)
(f) (g) (h) (i)
Dislocations
Si
(a) (b) ( c) (d) (e)
Melted thin filmL1 L2
L3
L4 •Remelt of L2 layer for liquidsolid equilibrium.•Dislocation climb and image forces eliminate dislocations in L3.• Cooling to 300K may introduce MD in layer with lowest shear modulus( InSb Layer)???
Proposed method: Use as a first layer a low melting point layer ( e.g. InSb)
Ideal case
Real World
Cooling
Growth
F3F2F1
Si Si(A) (B)
M1M2
M3
Si(C )
Misfit strain and thermal strain effects in the substrate decoupled epitaxial film
M1M2
M3
Si(D)
Finite element calculation, linear elasticity
M.Finot et al. J.Appl. Phys. 81, 3457 1997
Liquid –Solid surface tension : Complete wetting case
Grow lattice parameter matched layers
Mismatched layers
(j) (k)
(f) (g) (h) (i)
Dislocations
Si
(a) (b) ( c) (d) (e)
Melted thin filmL1 L2
L3
L4 •Remelt of L2 layer for liquidsolid equilibrium.•Dislocation climb and image forces eliminate dislocations in L3.• Cooling to 300K may introduce MD in layer with lowest shear modulus???
Proposed method: Use as a first layer a low melting point layer ( e.g. InSb)
Ideal case
Real World
Cooling
Growth