ECE 875: Electronic Devices Prof. Virginia Ayres Electrical & Computer Engineering Michigan State University ayresv@msu.edu

Lecture 24, 12 Mar 14 Chp 03: metal-semiconductor junction Currents: Thermionic emission model Examples Richardson constant(s) Additional models VM Ayres, ECE875, S14

Start: EC VM Ayres, ECE875, S14

JTE = J s->m + J m->s Total Thermionic Current density: JTE = J s->m + J m->s JTE = = {JTE-sat} JTE-sat = VM Ayres, ECE875, S14

JTE = {JTE-sat} {JTE-sat} = Jdiode = {Jdiode-sat} Metal-semiconductor thermionic current density: JTE = {JTE-sat} {JTE-sat} = Similar in form to pn junction current density: Jdiode = {Jdiode-sat} VM Ayres, ECE875, S14

Example: VM Ayres, ECE875, S14

Answer: VM Ayres, ECE875, S14

VM Ayres, ECE875, S14

VM Ayres, ECE875, S14

VM Ayres, ECE875, S14

VM Ayres, ECE875, S14

Metal-semiconductor junction with Schottky barrier  WD: -- ND+ ND+ WD p+n junction  WD: p+ semiconductor -- NA ND+ ND+ NA VM Ayres, ECE875, S14 WD

Metal-semiconductor junction with Schottky barrier  WD  CD C-V measurement good C-V: ybi => ideal qfBn0 I-V: TE: real qfBn (also photoelectric measurement) qfBn = qfBn0 -Df -- ND+ ND+ WD p+n junction  WD  CD: p+ semiconductor -- NA ND+ ND+ NA VM Ayres, ECE875, S14 WD

Metal-semiconductor junction with Schottky barrier  WD  CD C-V measurement good -- ND+ ND+ WD Intercept: ybi Slope: ND VM Ayres, ECE875, S14

Metal-semiconductor junction with Schottky barrier  WD  CD C-V measurement good C-V: ybi => ideal qfBn0 I-V: TE: real qfBn (also photoelectric measurement) qfBn = qfBn0 -Df -- ND+ ND+ WD Intercept: ybi Slope: ND VM Ayres, ECE875, S14

Example: real ^ VM Ayres, ECE875, S14

VM Ayres, ECE875, S14

VM Ayres, ECE875, S14

intercept VM Ayres, ECE875, S14

VM Ayres, ECE875, S14

Now use this 2nd Df to make a 2nd estimate for ND Try it: Now use this 2nd Df to make a 2nd estimate for ND VM Ayres, ECE875, S14

VM Ayres, ECE875, S14

Lecture 24, 12 Mar 14 Chp 03: metal-semiconductor junction Currents: Thermionic emission model Examples Richardson constant(s) Additional models VM Ayres, ECE875, S14

A = Richardson constant = 120 A/cm2 K2 m* = # m0 With m* = m0 = 9.1 x 10-31 kg, A* = A A = Richardson constant = 120 A/cm2 K2 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