Lecture 12 OUTLINE Metalsemiconductor contacts cont IV characteristics

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Lecture #12 OUTLINE • Metal-semiconductor contacts (cont. ) – I-V characteristics Reading: Finish 14.

Lecture #12 OUTLINE • Metal-semiconductor contacts (cont. ) – I-V characteristics Reading: Finish 14. 2 Spring 2007 Semiconductor Devices for Integrated Circuits

Current Flow in a Schottky Diode FORWARD BIAS REVERSE BIAS Spring 2007 • Current

Current Flow in a Schottky Diode FORWARD BIAS REVERSE BIAS Spring 2007 • Current is determined by majority-carrier flow across the MS junction: – Under forward bias, majority-carrier diffusion from the semiconductor into the metal dominates – Under reverse bias, majority-carrier diffusion from the metal into the semiconductor dominates EE 130 Lecture 12, Slide 2

Voltage Drop across the MS Diode • Under equilibrium conditions (VA = 0), the

Voltage Drop across the MS Diode • Under equilibrium conditions (VA = 0), the voltage drop across the semiconductor depletion region is the built-in voltage Vbi. • If VA 0, the voltage drop across the semiconductor depletion region is Vbi - VA. Spring 2007 EE 130 Lecture 12, Slide 3

Depleted Layer Width, W, for VA 0 Last time, we found that At x

Depleted Layer Width, W, for VA 0 Last time, we found that At x = 0, V = - (Vbi - VA) • W increases with increasing –VA • W decreases with increasing ND - (Vbi - VA) Spring 2007 EE 130 Lecture 12, Slide 4

W for p-type Semiconductor At x = 0, V = Vbi + VA •

W for p-type Semiconductor At x = 0, V = Vbi + VA • W increases with increasing VA • W decreases with increasing NA Spring 2007 EE 130 Lecture 12, Slide 5

Thermionic Emission Theory • Electrons can cross the junction into the metal if •

Thermionic Emission Theory • Electrons can cross the junction into the metal if • Thus the current for electrons at a given velocity is: • So, the total current over the barrier is: Spring 2007 EE 130 Lecture 12, Slide 6

Schottky Diode I - V • For a nondegenerate semiconductor, it can be shown

Schottky Diode I - V • For a nondegenerate semiconductor, it can be shown that • We can then obtain • In the reverse direction, the electrons always see the same barrier FB, so • Therefore Spring 2007 EE 130 Lecture 12, Slide 7

Applications of Schottky Diodes • IS of a Schottky diode is 103 to 108

Applications of Schottky Diodes • IS of a Schottky diode is 103 to 108 times larger than that of a pn junction diode, depending on FB. Schottky diodes are preferred rectifiers for lowvoltage, high-current applications. Spring 2007 EE 130 Lecture 12, Slide 8

Summary • In a Schottky contact, charge is stored on either side of the

Summary • In a Schottky contact, charge is stored on either side of the MS junction – The applied bias VA modulates this charge and thus the voltage drop across the semiconductor depletion region Flow of majority carriers into the metal varies exponentially with VA Spring 2007 EE 130 Lecture 12, Slide 9

MetalSemiconductor Interfaces MetalSemiconductor contact Schottky BarrierDiode Ohmic ContactsMetalSemiconductor Interfaces MetalSemiconductor contact Schottky BarrierDiode Ohmic Contacts
MetalSemiconductor Contacts There are 2 kinds of metalsemiconductorMetalSemiconductor Contacts There are 2 kinds of metalsemiconductor
MetalSemiconductor Contacts 1 Introduction 2 Schottky Contacts 3MetalSemiconductor Contacts 1 Introduction 2 Schottky Contacts 3
Lecture 8 OUTLINE MetalSemiconductor Contacts contd Current flowLecture 8 OUTLINE MetalSemiconductor Contacts contd Current flow
Lecture 8 OUTLINE MetalSemiconductor Contacts contd Current flowLecture 8 OUTLINE MetalSemiconductor Contacts contd Current flow
Lecture 8 OUTLINE MetalSemiconductor Contacts contd Current flowLecture 8 OUTLINE MetalSemiconductor Contacts contd Current flow
Lecture 7 OUTLINE Work Function MetalSemiconductor Contacts EnergyLecture 7 OUTLINE Work Function MetalSemiconductor Contacts Energy
Lecture 7 OUTLINE Work Function MetalSemiconductor Contacts EnergyLecture 7 OUTLINE Work Function MetalSemiconductor Contacts Energy