From e38ec58774bcbd2756c76deb34446de919effd1c Mon Sep 17 00:00:00 2001
From: Anton Akhmerov <anton.akhmerov@gmail.com>
Date: Wed, 3 Apr 2019 09:13:10 +0000
Subject: [PATCH] exercise 2

---
 src/14_doping_and_devices.md | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/14_doping_and_devices.md b/src/14_doping_and_devices.md
index 074aae71..3059a7c8 100644
--- a/src/14_doping_and_devices.md
+++ b/src/14_doping_and_devices.md
@@ -238,6 +238,14 @@ Let us now work out what happens when the semiconductor is at the border between
 
 ### Exercise 2: Donor ionization
 
+Previously we have assumed that all dopants are ionized.
+Let us examine when this is a good assumption.
+For that we consider a doped semiconductor in the extrinsic regime.
+
+1. Assume that all dopants are ionized, determine the position of the Fermi level.
+2. Write down the concentration of dopants that are not ionized.
+3. Determine at what donor concentration one cannot assume anymore that all donors are ionized in germanium at room temperature.
+
 ### Exercise 3: Performance of a diode
 
 ### Exercise 4: Quantum well heterojunction in detail
-- 
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