" 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