Ambiguity of the "intrinsic" layer in a PIN diode

Question

I'm having trouble understanding the fundamental makeup of large PIN diodes, specifically those used in radiation detection devices. For example, high purity germanium (HPGe) detectors are often referred to as large PIN diodes, where the intrinsic, depleted region is sensitive. However, in diagrams, the bulk material is usually labeled N-type or P-type. For example, in this description from Mirion:

Figure 7-2: A typical p-i-n junction detector (left) with reverse bias. A cross section of an n-type coaxial detector perpendicular to the cylindrical axis (right).

The detector is called a p-i-n junction detector, but clearly labeled N-type Ge. I chose this example because it's an obvious juxtaposition, but I find similar terminology in many places.

How can I understand this discrepancy in terminology? Is the "intrinsic" region just very lightly doped? Or is it not intentionally doped at all, but the native crystal growth results in a net excess of N-type donors? Or ...?

Answer 1

Ideally, the 'i' layer is undoped, but then the polarization and extent of the depletion region is ill-defined (e.g. is it residually p-type or n-type ? that affects where the depletion region extends from).

So, very lightly doped n-type gives some definition to the depletion region, while not noticeably affecting the ideal performance.

http://britneyspears.ac/physics/pin/pin.htm