Error in bandgap measurements of n-type Ge

In summary, the conversation discusses the difficulties encountered while conducting an experiment to measure the bandgap of n-type Ge using the 4-probe method. It was found that switching between the milliammeter and millivoltmeter settings on the instrument caused anomalies in the recorded voltage readings. This could be due to impedance mismatch between the two meters. The solution suggested is to use a constant-current regulator and ensure that the voltmeter is not measuring the voltage drop across the milliammeter. It is also important to understand the instruments being used.
  • #1
joel.martens
16
0
In conducting an experiment to measure the bandgap of n-type Ge using the 4-probe method, heating the sample and measuring the change in voltage across the probes as it cooled, it was necessary to change regularly between the milliammeter and the millivoltmeter setting on the instrument to ensure the current remained constant while voltages were recorded at temperature intervals. It was found that the act of switching to the ammeter and back caused large anomalies in the recorded voltages, specifically it caused the voltage readings to drop considerably lower than the ones taken previously. The voltages should steadily increase as the temperature drops gradually from around 170 dergrees to room temperature, levelling off to almost constant when extrinsic conduction begins to dominate.
Can anyone explain this fault, i was told that it may be that the millivoltmeters impedance doesn't match the milliammeters impedance but i am not familiar enough with impedance and how it relates to the operation of the millivoltmeter / milliameter to understand how this causes the error.
 
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  • #2
Hi Joel-
Use a constant-current regulator for your power source, and two meters, one for current and one for voltage. Make sure the voltmeter is not measuring the voltage drop across the miiliammeter. Correct the milli-amp reading for the current drawn by the voltmeter. Lastly, understand the instruments you are using.
Bob S
 
  • #3


Thank you for sharing your findings on the error in bandgap measurements of n-type Ge. I can offer some insight into the possible cause of this fault.

Firstly, it is important to note that the 4-probe method is a reliable technique for measuring the bandgap of materials. However, in order to obtain accurate results, it is crucial to maintain a constant current throughout the experiment. Any fluctuation in current can significantly affect the voltage readings and lead to errors in the bandgap measurement.

Based on your description, it seems that the act of switching between the milliammeter and millivoltmeter settings on the instrument is causing a change in the current flow. This could be due to differences in the impedance of the two settings, as you mentioned. Impedance is a measure of the resistance to current flow in a circuit, and if there is a mismatch between the impedance of the two settings, it can cause a change in the current flow.

To understand this better, let's consider the operation of the millivoltmeter and milliammeter. The millivoltmeter measures the voltage drop across the sample, while the milliammeter measures the current flowing through the sample. Both of these measurements are affected by the impedance of the instrument. If the impedance of the millivoltmeter is higher than the milliammeter, it can cause a decrease in the current flow when switching between the two settings. This decrease in current can then lead to a decrease in voltage readings, as observed in your experiment.

In order to avoid this error, it is important to ensure that the impedance of the millivoltmeter and milliammeter match. This can be achieved by using instruments with similar impedance values or by using a matching network to adjust the impedance. Additionally, it is important to minimize any disruptions in the current flow, such as switching between settings, to obtain accurate and consistent readings.

I hope this explanation helps to clarify the issue with your experiment. It is always important to carefully consider and control all factors that can affect the accuracy of measurements in scientific experiments. Best of luck with your future experiments.
 

1. What is the reason for error in bandgap measurements of n-type Ge?

There are several factors that can contribute to errors in bandgap measurements of n-type Ge. Some common reasons include impurities in the material, defects in the lattice structure, and surface effects.

2. How does impurities affect bandgap measurements of n-type Ge?

Impurities in the material can act as energy levels within the bandgap, leading to incorrect measurements of the bandgap energy. These impurities can also alter the conductivity and carrier concentration of the material, further affecting the measured bandgap.

3. Can defects in the lattice structure impact bandgap measurements of n-type Ge?

Yes, defects in the lattice structure, such as dislocations or vacancies, can act as energy levels within the bandgap and interfere with accurate measurements. These defects can also affect the electrical and optical properties of the material.

4. How do surface effects influence bandgap measurements of n-type Ge?

The surface of the material can introduce additional energy states within the bandgap, leading to errors in the measured bandgap energy. This effect is often more significant in thin films or nanostructured materials.

5. Are there any methods to reduce error in bandgap measurements of n-type Ge?

Yes, there are several methods to minimize errors in bandgap measurements of n-type Ge. These include using highly pure and defect-free materials, carefully controlling the experimental conditions, and using advanced techniques such as spectroscopic ellipsometry or photoluminescence measurements.

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