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 8
Why go for a heterojunction? Saturation current density Open circuit voltage 𝑟 ln 𝐾 ph oc = 𝑙𝑈 𝑊 + 1 𝐾 0 9
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
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 27
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 28
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 29
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 30
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 31
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 32
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 44
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 45
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 46
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
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 49
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 50
Electrostatic characteristics 51
Electrostatic characteristics 52
Electrostatic characteristics 53
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 54
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 55
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 56
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 57
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 58
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 59
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
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