Facet and layer formation of II-VI-semiconductors on GaSe van der Waals terminated Si(111)

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1 Facet and layer formation of II-VI-semiconductors on GaSe van der Waals terminated Si(111) on O 49.4 Epitaxy and growth Bengt Jäckel R. Fritsche, A. Klein, W. Jaegermann Darmstadt University of Technology Department of Materials Science Surface Science Division

2 Contents: Motivation: CdTe / GaSe (3D/2D) - Motivation - A brief introduction to the used substrate - Structural parameters of the II-VI-semiconductors - Experimental results of ZnS, ZnSe and CdS - Conclusions InSe/ MoTe 2 (2D/2D) Quantum-dots Layer-growth II-VI - SC. Combination of classic epitaxy (3D/3D) and v.d. Waals epitaxy (2D/2D) with Si-technology 3D/2D/3D quasi-van der Waals-gap Si 2

3 Si(111):GaSe - Preparation Si(111)-7x7 51eV 3.74Å + ½ GaSelayer Si(111):GaSe 1x1 = 52eV Passivation of all dangling bonds 3

4 II-VI-Semiconductors [111] Cd(S,Se) Wurzite-structure [101] Zn, Cd S, Se Zinc-blende structure substrate-orientation (111) [110] [112] material [110] lattice constants (a=b=c) [A] lattice mismatch to Si [%] bandgap [ev] Silicon 5, ,107 ZnS 5,423-0,14 3,68 ZnSe 5,66 4,2 2,71 CdS 5,83 7,3 2,42 CdSe 6,05 11,4 1,7 increasing decreasing 4

5 Deposition of ZnS at 300 C +0min ZnS +300min ZnS +420min ZnS 660min ZnS 52eV 52eV 52eV 77eV increase of ZnS thickness 77eV closed ZnS-layer 5

6 Type of facets at 400 C 40eV 42eV 44eV 46eV 48eV λ = 150 Å E kin [ ev ] λ1 (33eV ) = λ 2 (50eV ) = 2.14Å 1.73Å 2π L = 2 λ2 a tanα = L * 1 2π λ1 = 1.35 = 1.39 α =

7 Interpretation 3 simple facets in the zinc-blende structure with (111) bottom plane top view: (111) (111)-facets (111) side view: (111) (111) (100)-facets (110)-facets ZnS forms (100)-facets with a (111) bottom plane! 7

8 Deposition of ZnSe at 300 C 5min ZnSe 20min ZnSe 60min ZnSe Formation of epitaxial ZnSe(111) with facets 8

9 Annealing of ZnSe at 400 C 45eV 48eV 52eV 58eV λ = 150 Å E kin [ ev ] λ1 (27eV ) = λ 2 (65eV ) = 2.36Å 1.52Å α = (110)-facets 9

10 ZnS vs ZnSe ZnS - two DB per surface atom (100) - one surface-atome species (Zn or S) - (111) Cation-bottom-plane - (111) Anion-plane ZnSe - one DB per surface atom - two surface atome species (Zn and Se) - (111) Cation-bottom-plane (2x2?) - (111) Anion-plane (100) (111) (110) (111) 54.7 Se Ga Si Zn S Zn Se Se Ga Si 35.2 The growth of QD is maybe possible. 10

11 Deposition of CdS at 150 C +10min 48eV Si:GaSe CdS +20min CdS grows epitaxially on the Si(111):GaSe surface 11

12 Annealing of CdS 450 C 35eV + 10min CdS at 300 C 30eV highly ordered and orientated CdS-film 12

13 Conclusions Similarities: - II-VI-Semiconductors grow in (111) orientation onto Si(111):GaSe - Nucleation occurs only at step-edges and defect-sites - Deposition and annealing can be performed upto 450 C substrate-temperatur Differences: - ZnS forms (100)-facet-planes - ZnSe forms (110)-facets - CdS forms a (111)-orientated film A prediction of layer- or island-growth is not possible, yet! QD- or film- formation is strongly dependent on growthcondition and material 13

14 14

15 ZnSe Conclusions - ZnSe nucleates only at step-edges and defect-sites - ZnSe grow epitaxial in (111)-orientation onto the GaSe:Si(111) surface (one dangling bond per surface-atom) - ZnSe-pyramides are formed with (110)-facets (35.2 ) (only one DB per surface atom) - Anealing at higher temperatures leads to a decrease of faceted-areas and to an increase of flat areas ((111)) - Annealing and deposition is possible upto 450 C (110)-planes a b c 15

16 Annealing of ZnSe at 550 C STM XPS Si-Ga-Se Si-Ga LEED 52eV Decomposition and formation of a Se-rich surface 16

17 ZnS Conclusions - ZnS nucleates only at step-edges and defect-sites - ZnS grow epitaxial in (111)-orientation onto the GaSe:Si(111) surface (one dangling bond per surface-atom) - ZnS-pyramides are formed with (100)-facets (54.7 ) (two DB per surface atom) - Anealing /or higher growth-temperatures leads to an increased crystallinity - Higher temperatures than 450 C lead to ZnS-desorption and to a removal of the GaSe-passivation layer (100)-planes a c b 17

18 Annealing of ZnS at 550 C STM-data XPS Si-Ga-Se Si-Ga 45eV Decomposition of the surface Ga-reconstructions max. 450 C for annealing 18

19 Conclusions ZnS ZnSe Nucleation Orientation step-edges and defect-sites (111)-orientation onto the GaSe:Si(111) surface (one dangling bond per surface-atom) Facets (100)-facets (54.7 ) (two DB per surface atom) (100)-planes (110)-facets (35 ) (only one DB per surface atom) (110)-planes a a b c b c Thermalstability Annealing and deposition is possible upto 450 C CdS and CdSe also form facets on the GaSe:Si(111)-surface 19

20 Offene Frage... Warum sind Facetten ZnS und ZnSe anders? - chemische Bindung an HL oder Stabilität unterschiedlicher OF (Ionenradien) - Terminierung der 100 OF Warum bildet CdS (CdSe) Schicht (auch auf InSe Kristall)?? Warum sind Facetten ZnSe auf Kristall (InSe?) anders als bei HL sind sie doch nicht!!!! beides mal (110) 20