PVMD Ren van Swaaij Delft University of Technology Learning - PowerPoint PPT Presentation

Heterojunctions PVMD René van Swaaij Delft University of Technology

Learning objectives • Why use a heterojunction? 2

Learning objectives • Why use a heterojunction? • Types of heterojunctions 3

Learning objectives • Why use a heterojunction? • Types of heterojunctions • Construct a band diagram of a heterojunction 4

Why go for a heterojunction? Open circuit voltage 5

Why go for a heterojunction? Open circuit voltage 6

Why go for a heterojunction? Saturation current density Open circuit voltage 𝑟 ln 𝐾 ph oc = 𝑙𝑈 𝑊 + 1 𝐾 0 7

Why go for a heterojunction? Saturation current density Open circuit voltage 𝑟 ln 𝐾 ph oc = 𝑙𝑈 𝑊 + 1 𝐾 0 is a material property 10

Electron affinity E vac E F 11

Electron affinity E vac q χ sem E F 12

Electron affinity E vac q φ sem q χ sem E F 13

Electron affinity E vac q φ sem q χ sem Semiconductor Electron affinity (V) Ge 4.13 Si 4.01 GaAs 4.07 E F AlAs 3.50 14

Bandgap alignment: Straddling E vac q χ 1 q χ 2 E C2 E C1 E V1 E V2 15

Bandgap alignment: Staggered E vac q χ 1 q χ 2 E C1 E C2 E V1 E V2 16

Bandgap alignment: Broken gap E vac q χ 1 q χ 2 E C1 E C2 E V1 E V2 17

Bandgap alignment E C2 E C1 Straddling E V1 E V2 E C1 E C2 Staggered E V1 E V2 E C1 E C2 Broken gap E V1 E V2 18

Bandgap alignment E C2 E C1 Straddling E V1 E V2 E C1 E C2 Staggered E V1 E V2 E C1 E C2 Broken gap E V1 E V2 19

Band diagram n type P type E CP E Cn E Cn E VP 20

Band diagram n type P type E CP E Cn E gn E Cn E VP 21

Band diagram n type P type E CP E Cn E gn E gP E Cn E VP 22

Band diagram n type P type E CP E Cn E Fn E gn E gP E FP E Cn E VP 23

Band diagram E vac q φ sP q χ P q φ sn q χ n E CP E Cn E Fn E gn E gP E FP E Cn E VP 24

Band diagram E vac q φ sP q χ P q φ sn q χ n E CP E Cn Δ E C E Fn E gn E gP E FP E Cn Δ E V E VP 25

Band diagram E vac q φ sP q χ P q φ sn q χ n E CP E Cn Δ E C E Fn E Gn E gP E FP E Cn Δ E V E VP 26

Electron affinity rule 33

Electron affinity rule • Assumption : also the case when interface is formed 34

Electron affinity rule • Assumption : also the case when interface is formed • In reality : mixing of materials / lattice mismatch 35

Band diagram E vac q φ sP q χ P q φ sn q χ n E CP E Cn E Fn E gn E gP E FP E Cn E VP 36

Band diagram q φ sP q χ P E vac E CP q φ sn q χ n E gP E Cn E Fn E FP E gn E VP E Vn 37

Band diagram x 0 q φ sP q χ P E vac E CP q φ sn q χ n E gP E Cn E Fn E FP E gn E VP E Vn 38

Band diagram x 0 q φ sP q χ P E vac E CP q φ sn q χ n E gP E Cn E Fn E FP E gn E VP E Vn 39

Band diagram x 0 q φ sP q χ P E vac E CP q φ sn q χ n Δ E C E gP E Cn E Fn E FP E gn E VP Δ E V E Vn 40

Band diagram x 0 q φ sP q χ P E vac E CP q φ sn q χ n qV biP qV bin Δ E C E gP E Cn E Fn E FP E gn E VP Δ E V E Vn 41

Band diagram x 0 qV biP q φ sP q χ P E vac E CP qV bin q φ sn q χ n qV biP qV bin Δ E C E gP E Cn E Fn E FP E gn E VP Δ E V E Vn 42

Band diagram x 0 qV biP qV bi q φ sP q χ P E vac E CP qV bin q φ sn q χ n qV biP qV bin Δ E C E gP E Cn E Fn E FP E gn E VP Δ E V E Vn 43

Band diagram x 0 qV biP qV bi q φ sP q χ P E vac E CP qV bin q φ sn q χ n qV biP qV bin Δ E C E gP E Cn E Fn E FP E gn E vP Δ E V E Vn 47

Band diagram x 0 qV biP qV bi q φ sP q χ P E vac E CP qV bin q  sn q  n qV biP qV bin Δ E C E gP E Cn E Fn E FP E gn E vP Δ E V E Vn 48

Electrostatic characteristics 51

Band diagram x 0 qV biP qV bi Different transport characteristics q φ sP q χ P E vac E CP qV bin q φ sn q χ n qV biP qV bin Δ E C E gP E Cn E Fn E FP E gn E VP Δ E V E Vn 60

Summary • Use heterojunction to change V oc 61

Summary • Use heterojunction to change V oc • Discussed three types of band alignment 62

Summary • Use heterojunction to change V oc • Discussed three types of band alignment • Constructed band diagram 63

PVMD Ren van Swaaij Delft University of Technology Learning - PowerPoint PPT Presentation

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