For Peer Review Only

Page 15 of 29
URL: http://mc.manuscriptcentral.com/tsed Email: [e-mail]
International Journal of Science Education
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60

---

For Peer Review Only
reason we say that they have a 'positive charge'." [Italics added] 
‘Generation of electron-hole pairs’ 
Although the students referred to the process of generation in the explanations they gave to the previous 
items, this phenomenon was studied explicitly in Item 4. Somewhat less than 12% of the students did not 
respond [Level 1], and some 20% did so inadequately [Level 2], although in this case we observed no 
predominant obstacle worthy of comment. 
Almost 27% of the students scored Level 3. Some of them, although they indicated that an electron-hole 
pair appears in the generation process, did not clearly differentiate it from the recombination process: 
Level 3: "In the process of generation there appears an electron-hole pair. It is the process in which a free 
electron passes to occupying a hole left previously by another electron." 
Nearly 42% of the students scored Level 4. An example of the responses was: 
Level 4: "In this process there appears an electron-hole pair in the semiconductor because the electron, on 
receiving the ionization energy, breaks the bond. By becoming free the electron leaves a hole in the bond, and 
thus an electron-hole pair is generated." 
‘Generation of a free electron in a semiconductor by means of doping’ 
Item 5 was targeted at investigating the ideas about doping with donor impurities. We found that around 
18% of the students gave no response [Level 1], and almost 17% were mistaken [Level 2]. We observed that, 
besides confusing donor and acceptor impurities, the students did not understand the doping process properly. 
They thought that it is identical to the electron-hole pair generation process. Thus they think that, when a hole 
is generated by means of doping, a free electron is also obtained. This obstacle is brought out in the following 
explanation: 
Level 2: "By putting donor impurities into it, holes are generated that will also produce free electrons. They are 
generated like in an intrinsic semiconductor." 
Another obstacle detected was that the students think, in analogy to the case in the intrinsic 
semiconductors, that when a semiconductor is doped its temperature increases, and for that reason it 
becomes a good electrical conductor: 
Level 2: "[…] because with doping the temperature rises and thus the resistivity falls." 
We also observed that the students think that doping a semiconductor with donor impurities consists of 
directly introducing electrons. They even assume that the holes are a sort of 'defect' of the semiconductor's 
crystal lattice that has to be corrected by adding donor impurities: 
Level 2: "Doping a semiconductor consists of putting in free electrons to fill up the holes that there are in a 
semiconductor." 
Nearly 22% of the students scored Level 3. The incompleteness of their justifications lay in not sufficiently 
clarifying the characteristics that donor impurities must have: 
Level 3: "Well if to an intrinsic semiconductor you add atoms of another material, with a greater number of 
valence electrons than the atoms of the intrinsic semiconductor, a free electron would be generated." 
About 43% of the students scored Level 4, with appropriate justification of their responses. An example of 
this type of response is the following: 
Level 4: "When we dope a covalent solid of germanium, for example with antimony atoms, we generate more 
free electrons than holes. This happens because antimony has 5 valence electrons and it can only share 4 with 
the germanium atoms that surround it; for that reason one is surplus that will become a free electron." [This 
explanation was accompanied by a two-dimensional diagram of the covalent structure of germanium.] 
‘Obtaining a p-type extrinsic semiconductor’ 
The target of Item 6 was to determine whether the students had understood how a p-type extrinsic 
semiconductor is obtained. Responses were left blank by 10% of the students [Level 1], and about 23%