Question

Solid state chemistry: n doping and p doping

Classify the following as n- or p-doped semi conductors:

(A) Ga doped Ge

(B) As doped Si

(C) In_0.40 As_0.60

The answer for A is p-doped. The answer for B is n-doped. and the answer for C is p-doped.
I don't really understand why, is there a period table trend that can help determine this? I would think that Ga doped Ge would be n-doped since Ge has more valence electrons than Ga

Answer 1

A] p - type semi conductor

B] n - type semi conductor

C] p -type semi conductor

The addition of trivalent impurities such as boron, aluminum or gallium to an intrinsic semiconductor creates deficiencies of valence electrons,called "holes". Holes are major carriers here and this is called p - type semi conductor.

The addition of pentavalent impurities such as Arsenic or Phosphorus to an intrinsic semi conductor creates an extra electron in the lattice .Electrons are major carriers here and this is called n - type semi conductor.

In A --- trivalent impurity Ga added to Ge

In B --- pentavalent impurity As added to Si

In C ----

In 0.4 -- 3rd group (3 valence electrons) and As 0.6 --- 5th group (5 valence electrons )

Addition of In creates a deficiency of valence electrons called holes..So it is a p - type one