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International Journal of Science Education
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For Peer Review Only
– 
Extrinsic semiconductors are electrically neutral because they are obtained from [neutral] intrinsic semiconductors 
doped with impurities that are also neutral. 
4.3 To understand that: 
– 
The impurities are atoms: donors [pentavalent atoms] contribute free electrons to the semiconductor, and acceptors 
[trivalent atoms] contribute holes to the semiconductor. 
Evidently, the above discussion and reformulation of the learning objectives implies revising a part of the 
initial activities of the teaching sequence. Nevertheless, for reasons of space we will not deal with that here, 
but instead leave it for a future work in which we shall also analyze the sequence's effectiveness with new 
students. 
Finally, we would say that as we are unaware of other studies that have approached the present topic, we 
have been unable to make comparisons to validate our results. We also realize that the present results are not 
generalizable to other educational contexts [they lack external validity], among other reasons, because the 
study was conducted in a specific natural context of educational practice [the sample of students was chosen 
for convenience]. Nonetheless, we believe that the variety of research instruments used [test, personal 
interviews, and student notebooks] and the validation and reliability analyses performed lend sufficient rigour 
to the study. In this sense, we think that it constitutes an important point of reference from which to undertake 
new studies —both in educational contexts similar to ours and in different contexts— which would look deeper 
into the aspects dealt with here, and consequently shed further light on the issue. We hope therefore that there 
will arise new lines of research related to the topic, because at present there are still very few in science 
teaching.