MetalSemiconductor Contacts There are 2 kinds of metalsemiconductor

Ideal M-S Contact: FM < FS, p-type semiconductor Band diagram instantly after contact formation:

Ideal M-S Contact: FM < FS, n-type Band diagram instantly after contact formation: Equilibrium

Effect of Interface States on FBn • Ideal M-S contact: FBn = FM –

Schottky Barrier Heights: Metal on Si • FBn tends to increase with increasing metal

Schottky Barrier Heights: Silicide on Si Silicide-Si interfaces are more stable than metal-silicon interfaces

The Depletion Approximation The semiconductor is depleted of mobile carriers to a depth W

Electrostatics • Poisson’s equation: • The solution is: EE 130/230 M Spring 2013 Lecture

Depletion Width, W At x = 0, V = -Vbi • W decreases with

Summary: Schottky Diode (n-type Si) metal FM > FS n-type Si Eo c. Si

Summary: Schottky Diode (p-type Si) metal FM < FS p-type Si Eo c. Si

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Metal-Semiconductor Contacts There are 2 kinds of metal-semiconductor contacts: • rectifying “Schottky diode” • non-rectifying “ohmic contact” EE 130/230 M Spring 2013 Lecture 7, Slide 1

Ideal M-S Contact: FM < FS, p-type semiconductor Band diagram instantly after contact formation: Equilibrium band diagram: Schottky Barrier Height: FBp q. Vbi = FBp– (EF – Ev)FB W EE 130/230 M Spring 2013 Lecture 7, Slide 2

Ideal M-S Contact: FM > FS, p-type semiconductor Band diagram instantly after contact formation: Equilibrium band diagram: EE 130/230 M Spring 2013 Lecture 7, Slide 3

Ideal M-S Contact: FM < FS, n-type Band diagram instantly after contact formation: Equilibrium band diagram: EE 130/230 M Spring 2013 Lecture 7, Slide 4

Ideal M-S Contact: FM > FS, n-type Band diagram instantly after contact formation: Equilibrium band diagram: q. Vbi = FBn– (Ec – EF)FB n Schottky Barrier Height: W EE 130/230 M Spring 2013 Lecture 7, Slide 5

Effect of Interface States on FBn • Ideal M-S contact: FBn = FM – c • Real M-S contacts: A high density of allowed energy states in the band gap at the M-S interface “pins” EF to be within the range 0. 4 e. V to 0. 9 e. V below Ec FM FBn EE 130/230 M Spring 2013 Lecture 7, Slide 6

Schottky Barrier Heights: Metal on Si • FBn tends to increase with increasing metal work function EE 130/230 M Spring 2013 Lecture 7, Slide 7

Schottky Barrier Heights: Silicide on Si Silicide-Si interfaces are more stable than metal-silicon interfaces and hence are much more prevalent in ICs. After metal is deposited on Si, a thermal annealing step is applied to form a silicide-Si contact. The term metalsilicon contact includes silicide-Si contacts. EE 130/230 M Spring 2013 Lecture 7, Slide 8

The Depletion Approximation The semiconductor is depleted of mobile carriers to a depth W Þ In the depleted region (0 x W ): r = q (ND – NA) Beyond the depleted region (x > W ): r=0 EE 130/230 M Spring 2013 Lecture 7, Slide 9

Electrostatics • Poisson’s equation: • The solution is: EE 130/230 M Spring 2013 Lecture 7, Slide 10

Depletion Width, W At x = 0, V = -Vbi • W decreases with increasing ND EE 130/230 M Spring 2013 Lecture 7, Slide 11

Summary: Schottky Diode (n-type Si) metal FM > FS n-type Si Eo c. Si FM q. Vbi = FBn – (Ec – EFS)FB FBn Ec EF Depletion width Ev W EE 130/230 M Spring 2013 Lecture 7, Slide 12

Summary: Schottky Diode (p-type Si) metal FM < FS p-type Si Eo c. Si Ec FM EF Ev FBp q. Vbi = FBp– (EF – Ev)FB W EE 130/230 M Spring 2013 Lecture 7, Slide 13 Depletion width