" On trying daring ideas with Herb". P.M.Petroff Professor Emeritus Materials Department , University of Cali

1. " On trying daring ideas with Herb".P.M.PetroffProfessor Emeritus Materials Department , University ofCalifornia , Santa Barbara

2. Some coauthored papers and shared students T.Y.Liu,P.M.Petroff, and H.Kroemer, "Luminescence of GaAs-GaAlAsSuperlattices Grown on Silicon Substrates: Effects of SuperlatticeInterfaces”.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/AlAsSuperlattices 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 Growth111, 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) .

3. Tilted superlattices , Serpentine superlattices and Self assembled quantum wires with J.Gaines and M.Miller Conventional quantum wells and superlattices : growth direction is normal to the substrate surface Interfaces are parallel to substrate surface GaAs AlAs InAs

4. THE TILTED SUPERLATTICE WITH INTERFACES PARALLEL TO THE GROWTH DIRECTION Vicinal {100} surface • 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 control • deposition to 0.1 ML! h=2.8Å Periodic steps 1o->80Å 2o->40Å (GaAs)0.5(AlAs)0.5

5. TILTED SUPERLATTICE AND QUANTUM WIRE SUPERLATTICE tgß= |p-1|/tga p=m+n p=1.1 a=2o p=0.9 a=2o (GaAs)m(AlAs)n, with p=m+n≂1 and m or n>0.5 or <0.5

6. Serpentine Superlattice Modeling TEM cross section p=0.9 p=1 p=1.1 ß=-30oß=0oß=60o Flux non uniformity solution: Parabolic quantum well profile with linear variations of p(t)=m+n --> Quantum wires

7. How well does it work? PH YSICAL REVIEW LETTERS 8 JUNE 1992 Not as well as we wanted : Exchange reactions Al->Ga Vicinal surfaces are not perfect It is the constant testing of the assumptions which makes for progress in Science. Daring!

8. MOLECULAR BEAM EPITAXY ON SUBSTRATES WITH LARGE LATTICE MISMATCH e.g.: THE HOLY GRAIL III-V layers ON SI With T.Y. LIU

9. Various solutions to a very old problem Dislocations an F3 F2 a3 a2 F1 Si a1 Si (A) (B) Lattice mismatch and thermal expansion coefficient misfit and threading dislocations Thick buffer layer: Dislocation interactions 1010cm-2 to 107 cm-2 Dislocations are deep levels. Electrons or hole traps are thermally or optically ionized Solutions: Multiple strained layers or strain graded layers: dislocation interactions 1010cm-2 to 107 cm-2 Micro pillars: Image forces 1010cm-2 to 0 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.

10. DISLOCATIONS REMOVAL IN HYBRID HETEROSTRUCTURES P.M.Petroff Materials department , University of California , Santa Barbara an a2 as MBE GaAs Liquid layer GaAs substrate Ga(L) Hybrid MBE-LPE Liquid Phase Epitaxy (LPE) Decouple the substrate from the epitaxial layers during growth Hybrid MBE-LPE growth of hetero-structures with large Lattice mismatch and differential thermal expansion coefficients .

11. Solutions 1 b1 b2 b3 b1 b2 b1 b2 Misfit dislocations sources and dislocation interactions in thick buffer layer or multi-layer samples  dislocation density : 1010cm-2 to 107 cm-2 b1+b2+b3=0

12. Solutions 2-3 Micro-pillars: Image forces Dislocations elimination Dislocation density: 1010cm-2 to 0 cm-2 Lateral epitaxial overgrowth: Dislocation filtering Dislocation density: 1010cm-2 to 104cm-2 Problems: Lithography and regrowth Small areas for devices

13. Solution 4: Fusion 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.

14. Proposed method: Use as a first layer a low melting point layer. (L1 layer: eg. InSb) Melted thin film L2 L1 Ideal case Si (a) (b) ( c) (d) (e) L3 Dislocations Real World Growth (f) (g) (h) (i) L4 • Remelt of L1 layer for liquid • solid equilibrium. • Dislocation climb and image forces • eliminate dislocations in L3. • Cooling to 300K may introduce MD • confined to the layer with lowest shear • modulus??? Cooling (j) (k)

15. 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 !

16. Why LPE does not work for sharp hetero- interfaces GaInSb ternary system e.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.

17. Proposed method: Use as a first layer a low melting point layer ( e.g. InSb) Melted thin film L2 L1 Ideal case Si L3 (a) (b) ( c) (d) (e) Dislocations Real World Growth • Remelt of L2 layer for liquid • solid 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??? L4 Cooling (f) (g) (h) (i) (j) (k)

18. Dislocations dynamics at a liquid solid interface in Si (CZ growth) Dislocations climb and glide to the liquid solid interface Dislocation free solid

19. Proposed method: Use as a first layer a low melting point layer ( e.g. InSb) Melted thin film L2 L1 Ideal case Si L3 (a) (b) ( c) (d) (e) Dislocations Real World Growth • Remelt of L2 layer for liquid • solid equilibrium. • Dislocation climb and image forces • eliminate dislocations in L3. • Cooling to 300K may introduce MD in • layer with lowest shear modulus( InSb • Layer)??? L4 Cooling (f) (g) (h) (i) (j) (k)

21. Misfit strain and thermal strain effects in the substrate decoupled epitaxial film Liquid –Solid surface tension : Complete wetting case F3 F2 F1 Si Si (A) (B) Grow lattice parameter matched layers M3 M3 M2 M2 M1 M1 Si Si (C ) (D) Mismatched layers Finite element calculation, linear elasticity M.Finot et al. J.Appl. Phys. 81, 3457 1997

22. Proposed method: Use as a first layer a low melting point layer ( e.g. InSb) Melted thin film L2 L1 Ideal case Si L3 (a) (b) ( c) (d) (e) Dislocations Real World Growth • Remelt of L2 layer for liquid • solid equilibrium. • Dislocation climb and image forces • eliminate dislocations in L3. • Cooling to 300K may introduce MD in • layer with lowest shear modulus??? L4 Cooling (f) (g) (h) (i) (j) (k)