ECE 875:Electronic Devices

Prof. Virginia AyresElectrical & Computer EngineeringMichigan State Universityayresv@msu.edu

VM Ayres, ECE875, S14

Chp 03: metal-semiconductor junction

Currents:

Richardson constant(s)

Additional models

Specific resistance across SB-type contact

Lecture 25, 14 Mar 14

m* = # m0

With m* = m0 = 9.1 x 10-31 kg, A* = A

A = Richardson constant = 120 A/cm2 K2

Richardson constant:

VM Ayres, ECE875, S14

Conductivity effective masses m*/m0 result in:

“Ge-like” surface: 8 equivalent directions

VM Ayres, ECE875, S14

In your HW Pr. 08 (b): A* -> A**

If tunnelling is present, it will significantly impact A*: p. 162

fP is probability of thermionic emission over barrier assuming the electrons have a Maxwellian distribution of energies

fp is distorted from a straight percent by amount fQ, which is related to additional quantum mechanical tunneling and reflection

VM Ayres, ECE875, S14

Special region at interface also impacts A**:

VM Ayres, ECE875, S14

vR is is the effective recombination velocityvD is the effective diffusion velocity

5. diffusion of holes

VM Ayres, ECE875, S14

4. diffusion of electrons

3. Jrec

Special region at interface also impacts A**:

vR is is the effective recombination velocityvD is the effective diffusion velocity

VM Ayres, ECE875, S14

Chp 03: metal-semiconductor junction

Currents:

Richardson constant(s)

Additional models

Specific resistance across SB-type contacts

Lecture 25, 14 Mar 14

1. Thermionic emission:enough KE compared with height qBn is critical

2. Tunnelling (WD is critical)

1.5 Thermionic-field emission:enough KE to reach thinner WD critical

Note: device is ON and in forward bias

WD

All electrons have KE well above EC

VM Ayres, ECE875, S14

Current transport processes through Schottky Barriers:

Transport mechanisms;- Thermionic emission- Thermionic + diffusion- Thermionic + tunnelling- Tunnelling

Schottky Barrier (height, width ): Diode I-V

Schottky Barrier (height, thin width): Ohmic I-V

VM Ayres, ECE875, S14

TE

F

Current densities for 3 major transport mechanisms in forward bias are:

Thermionic emission:

Thermionic + field emission:

Field emission = tunnelling:

VM Ayres, ECE875, S14

E00 is the comparison of thermal energy kT to doping written as an energy.

Both can influence electron energy relative to EC

VM Ayres, ECE875, S14

VM Ayres, ECE875, S14

Chp 03: metal-semiconductor junction

Currents:

Richardson constant(s)

Additional models

Specific resistance across SB-type contacts:- TE- FE

Lecture 25, 14 Mar 14

Specific contact resistance RC ( cm-2) definition:

1st step

2nd step

VM Ayres, ECE875, S14

TE

F

Note: easy dJ/dV derivatives for V-functions in red boxes. Harder but not too bad for blue box combination functions

Thermionic emission:

Thermionic + field emission:

Field emission = tunnelling:

Often this approximation is good

VM Ayres, ECE875, S14

RC for TE model:

Function of effective barrier height and temperature

VM Ayres, ECE875, S14

RC for TFE model:

Function of effective barrier height and temperature and doping

VM Ayres, ECE875, S14

RC for FE model:

Function of effective barrier height and temperature and doping

VM Ayres, ECE875, S14

Plot of the results of carrying out those derivatives:

(MSM: 2 SB device)

VM Ayres, ECE875, S14