Question

Silicon and germanium are both semiconducting elements from Group \(4 \mathrm{~A}(14)\) that can be doped to improve their conductivity. Would each of the following form an n-type or a p-type semiconductor: (a) Ge doped with \(\mathrm{P} ;\) (b) \(\mathrm{Si}\) doped with In?

Short answer

Ge doped with P forms an n-type semiconductor. Si doped with In forms a p-type semiconductor.

Step-by-step solution

Define n-type and p-type semiconductors

An n-type semiconductor is one in which the charge carriers are primarily electrons. This happens when a semiconductor is doped with an element that has more valence electrons than the semiconductor. A p-type semiconductor is one in which the charge carriers are primarily 'holes' where electrons are absent. This occurs when a semiconductor is doped with an element that has fewer valence electrons than the semiconductor.

Analyze Ge doped with P

Germanium (Ge) is in Group 14 and has 4 valence electrons. Phosphorus (P) is in Group 15 and has 5 valence electrons. When Ge is doped with P, the extra electron from each P atom provides an additional free electron, thus creating an n-type semiconductor.

Analyze Si doped with In

Silicon (Si) is also in Group 14 and has 4 valence electrons. Indium (In) is in Group 13 and has 3 valence electrons. When Si is doped with In, there will be a deficiency of one electron for each In atom, creating 'holes' in the structure, which leads to the formation of a p-type semiconductor.

Key concepts

n-type semiconductor

N-type semiconductors are created when a pure semiconductor like silicon or germanium is doped with an element that has more valence electrons. Imagine you're adding extra sugar to your coffee; that extra bit of sweetness represents additional electrons in this analogy. These extra electrons become the majority charge carriers and enable electrical conduction.
For example, when germanium (which has 4 valence electrons) is doped with phosphorus (which has 5 valence electrons), the result is an n-type semiconductor. The extra electron from phosphorus becomes free to move around, increasing the overall conductivity.
This type of doping introduces negatively charged carriers (electrons), so it's called 'n-type.' The 'n' stands for 'negative.' Understanding this will help you grasp why the conductivity improves and how the properties of the material change.

p-type semiconductor

On the flip side, p-type semiconductors are created by doping a semiconductor with an element that has fewer valence electrons. Think of it like having a sandwich with missing pieces; these missing pieces represent the 'holes' created in the semiconductor structure.
For example, silicon (which has 4 valence electrons) doped with indium (which has 3 valence electrons) forms a p-type semiconductor. The absence of one electron per indium atom creates 'holes,' which act as positive charge carriers.
These 'holes' move around and carry charge, making the material conductive. This type of doping introduces positively charged carriers (holes), hence 'p-type,' where 'p' stands for 'positive.' Simply put, the 'holes' make it easier for the material to conduct electricity, even though they lack electrons.

doping elements

Doping involves adding small amounts of other elements to a pure semiconductor to modify its electrical properties. It’s like adding a pinch of salt to food—it changes the flavor dramatically.
Elements used for doping are carefully chosen based on the number of valence electrons. For n-type semiconductors, we use elements from Group 15 like phosphorus or arsenic, which have 5 valence electrons. Adding these elements to silicon or germanium (both from Group 14 with 4 valence electrons) introduces extra electrons, enhancing conductivity.
For p-type semiconductors, doping elements from Group 13, like boron or indium, are used. These elements have 3 valence electrons. Adding them to silicon or germanium results in a deficiency of one electron per dopant atom, creating 'holes' that act as positive charge carriers.
The process of doping essentially tailors the semiconductor's electrical properties to suit specific applications in electronic devices.