ECE 875: Electronic Devices

transcript

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:

Conductivity effective masses m*/m0 result in:

“Ge-like” surface: 8 equivalent directions

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

Special region at interface also impacts A**:

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

5. diffusion of holes

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

Currents:

Additional models

Specific resistance across SB-type contacts

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

All electrons have KE well above EC

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

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

Thermionic emission:

Thermionic + field emission:

Field emission = tunnelling:

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

Both can influence electron energy relative to EC

Currents:

Additional models

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

Specific contact resistance RC ( cm-2) definition:

1st step

2nd step

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

RC for TE model:

Function of effective barrier height and temperature

RC for TFE model:

Function of effective barrier height and temperature and doping

RC for FE model:

Function of effective barrier height and temperature and doping

Plot of the results of carrying out those derivatives:

(MSM: 2 SB device)

ECE 875: Electronic Devices

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