# Doped semiconductor material: identify n- p- type

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1. Oct 14, 2016

### moenste

1. The problem statement, all variables and given/known data
You are given a small slice of doped semiconductor material but you do not know whether it is n-type or p-type Explain with the aid of a diagram the physical principles of an investigation which would enable you to identify the type.

2. The attempt at a solution
I searched on the net for some decent information on this topic, but most of the images are very similar to each other.

Image 1.

Image 2:

As I understand, a doped semiconductor means an inpure semiconductor, that is intentionally made so in order to be used as an n-type or p-type semiconductor.

These two pictures could be used as the answer for the question?

Also, how do doped semiconductors looks like? What's the theory about the pictures?

2. Oct 14, 2016

### lychette

Do you realise that in n-type material the charge carriers would be -ve electrons and that in p-type material the charge carriers would be +ve 'holes' ?
If you could make current flow the materials could you produce an effect that would enable you to see a difference between +ve and -ve charge carriers

3. Oct 14, 2016

### moenste

So the principle of investigation is to see whether there are "holes" in the graph?

4. Oct 14, 2016

### lychette

I would say that you are expected to design some practical investigation.
You are supplied with a sample of material. My first thought is to make some electrical measurements that would reveal the presence of -ve charge carriers or +ve charge carriers......got any ideas?

5. Oct 15, 2016

### moenste

Use the Hall effect?

6. Oct 15, 2016

### lychette

Yes.....you now need to find out the experimental set up.

7. Oct 15, 2016

### moenste

That's the thing, I don't quite understand how does a "small slide of doped semiconductor material" look like.

As I see it, we'll need to use an apparatus that creates magnetic field (like a magnet). Like shown here.

8. Oct 15, 2016

### ehild

When working with semiconductors, I used a simple method to decide if a silicon slice was p type or n type. It worked by producing temperature gradient in the semiconductor wafer.(Wafers of several inches in diameter and 0.3-0.5 mm thick are available from the producers)

You need a sensitive multimeter or a galvanometer. Connect the wafer to the negative input of the meter, and add a pin to the other lead. Warm up the pin and touch it to the wafer.

The figure shows an n type Si, with electrons as free carriers. Near the hot pin, they gain higher velocity and diffuse away. The hot spot becomes positive with respect to the cold part and the pointer of the meter will deflect in positive direction.

9. Oct 15, 2016

### lychette

I know of this technique but never found it reliable...getting good contact with the wafer was unpredictable and trying the probe over the surface can give conflicting readings. When working with semiconductor wafers I found gold wire probes to be most reliable ( most of this work was with gallium arsenide)

10. Oct 15, 2016

### ehild

@lychette: It worked quite well with silicon.

11. Oct 15, 2016

### lychette

OK...may be the way to go for moenste if all that is needed is 'identification'