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Semiconductor MOS Gates

IP.com Disclosure Number: IPCOM000050404D
Original Publication Date: 1982-Oct-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Fowler, AB: AUTHOR

Abstract

Semiconductors have several useful properties when serving as a field-effect transistor gate.

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This is the abbreviated version, containing approximately 76% of the total text.

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Semiconductor MOS Gates

Semiconductors have several useful properties when serving as a field-effect transistor gate.

The internal work function of the materials employed in the gate of a metal oxide semiconductor field-effect transistor (MOSFET) can be employed to provide a turn-on threshold. The internal work function is roughly equal to the vacuum work function less about one volt. Each semiconductor can be doped n- or p-type (with a few exceptions). Each semiconductor if doped n-type heavily has a barrier of X-1 eV, where X is the electron affinity of the material. If doped p(+), the barrier is X Eg-1, where Eg is the energy gap. The flat band voltage of a silicon n-channel MOS transistor is roughly given by eV(FB)=X - 4 - (E(c)-E(F)) where E(c)-E(F) is the energy difference of the conduction band edge and the Ferm level at the interior. If various semiconductors are used with p+ or n/ / doping, the following flat bands can be expected as listed in Table 1. TABLE 1

n/+/ p/+/

Si 0.00 1.12

Ge 0.12 0.70

A1As -0.5 1.65

A1Sb -0.35 1.25

GaP 0.3 2.55

GaAs 0.1 1.5

GaSb 0.05 0.7

InP 0.3 1.6

InAs 0.9 1.25

InSb 0.6 0.8

ZnS -0.1

ZnSe 0.1

ZnTe 5.76

CdTe 0.3 1.7.

Alloys of these semiconductors can be used to adjust for intermediate desired thresholds which are directly related to the thresholds. The values of X-1 and X+Eg-1 are listed for several semiconductors in Table 2. TABLE 2

X1 X+Eg-1

Ce 3.13 3.79

Si 3.01 4.02

GaAs 3.07 4.47

A1As 2.45-2.85 4.6-5.0

InP 3.38 4.75

A1Sb 2.65 4.25

InAs 3.9 4.16

ZnSe 3.09 5.76 - not relevant - n type only

1

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ZnTe 2.5 4.76 p type only easily

GaSb 3.06 3.74.

The numbers are approximate in some cases and can vary by /- 0.2 eV. They are for 300K. It is also advantageous that the gate be heavily doped material and be co...