FermiLevel Pinning Schottky Barrier Height B 93501044 B

半導體專題實驗 Fermi-Level Pinning & Schottky Barrier Height 蘇璟瑋、王騰漢 B 93501044, B 93505007 電機四 1

Schottky Barrier Ideal Condition In Sperated system ◦ ◦ Thermal equilibrium Φm: The work function of metal (about 2 e. V~6 e. V) ΦS: The work function of n-type semiconductor χ: The electron affinity (qχ=Ec – vacuum level) ΦB 0: Schottkey barrier height (ΦB 0= Φm - χ) 2

Schottky Barrier (cont’d) Ideal Condition (Cont’d) ◦ The work function of metal 3

Schottky Barrier (cont’d) Ideal Condition (Cont’d) ◦ The deviation of Schottky barrier height The interface layer (oxide) Image-force lowering The presence of interface states 4

Schottky Barrier (cont’d) Image-force lowering ◦ Image-force lowering results the distortion of the potential barrier ◦ The effect is very small since the reduction is about 10 -20 m-e. V 5

Fermi-Level Pinning Interface States ◦ Metal / N-type semiconductor Acceptor type Netural level Donor type If the density of bandgap states near is very large, then addition or depletion of electrons to semiconductor doesn’t alter the Fermi level position at the surface and Fermi level is said to 6

Fermi-Level Pinning (cont’d) The Schottky Barrier Height 7

Fermi-Level Pinning (cont’d) The Schottky Barrier Height Acceptor type Netural level Donor type ◦ When surface states → ∞ The Fermi level at the surface is pinned by large amount of surface states at the value above the valence band, and the barrier height is independent of the metal work function and is entirely determined by the surface properties of the semiconductor. (Bardeen limit) ◦ When surface states → 0 Identical to the ideal condition ◦ Generally, the number of surface states is hard to control, so the 8 barrier height is determined by experiment.

Fermi-Level Pinning (cont’d) The Schottky Barrier Height ◦ Metal/ n-type Si based semiconductor Experimental Result Reference: S. M. Sze, Physics of Semiconductor Devices, 3 rd ed. , Wiley, New York 2006, ch. 3 9

Reference ◦ Donald A. Neamen, Semiconductor Physics and Devices – Basic Principles, 3 ed ed. , Mc. GRAW-HILL, 2003, ch 1 ◦ S. M. Sze, Physics of Semiconductor Devices, 3 rd ed. , Wiley, New York 2006, ch. 3 ◦ Jasprit Singh, Semiconductors Devices Basic Principle, Wiley, New York 2001, ch. 6 10