The principle of upgrading the new Hall effect experiment instrument
Hall effect tester is used to measure important parameters such as carrier concentration, mobility, resistivity and Hall coefficient of semiconductor materials. These parameters are necessary to understand the electrical properties of semiconductor materials, so it is understood and studied. A must-have tool for the electrical properties of semiconductor devices and semiconductor materials.
Upgrade features
1, high precision current source
The accuracy of the output current can reach 2nA. Such a small current can be used for the measurement of semi-insulating materials, that is, the measurement of high-resistance materials.
2, high precision electric meter
Using ultra-high-precision electricity meters, the voltage measurement capability can reach nV level, the upper limit can reach 300V, which is very suitable for measuring low resistance materials.
3, the appearance is simple, simple operation
The shape is light and elegant, and the polarity of the magnet group is also very flexible. The unique liquid nitrogen container design ensures the best stability of the low temperature measurement.
4, IV curve
The current-voltage curve between the four points (A, B, C, D) of the probe is measured by means of a graph, thereby judging whether the ohmic contact of the sample is good or bad.
5, simple and easy to use operation screen
All the settings can be completed by the user in the same operation screen. The experimental results are automatically calculated by the software and displayed on the same screen, which saves the trouble of screen switching. As a result, the body carrier can be obtained at the same time. Important experimental data such as Bulk Carrier Concentration, Sheet Carrier Concentration, Mobility, Resistivity, and Hall Coefficient.
6. Self-developed spring sample holder, specially designed spring probe, its strength enhancement can improve the electrical contact between the probe and the contact point, and improve the reliability of measurement.
Purpose and requirements
1. Understand the principle and method of measuring the magnetic field by the Hall effect;
2. Observe the phenomenon of magnetoelectric effect;
3. Learn the basic method of measuring magnetic field and component parameters with Hall elements
principle
Hall effect
The Hall effect is essentially the result of the deflection of moving charged particles in the magnetic field caused by Lorentz forces. When charged particles (electrons or holes) are confined in a solid material, this deflection results in an accumulation of positive and negative charges in a direction perpendicular to the current and the magnetic field, thereby creating an additional transverse electric field. As shown in Figure 5.1-1, if a current is applied in the direction and a magnetic field is applied in the direction (the vertical paper faces outward), the opposite direction begins to accumulate the opposite charge on both sides of the sample and the electrode. Additional electric field. The direction of the electric field depends on the conductivity type of the sample. Obviously, the electric field prevents the carriers from continuing to shift laterally. When the lateral electric field force of the carrier is equal to the Lorentz force, the accumulation of charge on both sides of the sample reaches equilibrium. So there is
(5.1-1)
Among them is the Hall electric field, which is the average drift velocity of the carriers in the current direction. Here, the carrier amount is the amount of electrons.
Let the width of the sample be the thickness and the carrier concentration be:
(5.1-2)
Available from 5.1-1, 5.1-2:
(5.1-3)
That is, the Hall voltage (and the voltage between the electrodes) is proportional to the product and inversely proportional to the thickness of the sample. The proportional coefficient is called the Hall coefficient, which is an important parameter reflecting the strength of the Hall effect of the material. As long as it is measured (volts) and known (A), (Tesla), it can be calculated as follows (volts/ampere). Tesla):
(5.1-4)
According to the following parameters can be further determined:
(1) discriminating the conductivity type of the semiconductor sample by the sign (or the positive and negative of the Hall voltage);
The method of discrimination is in the direction of the sum shown in Figure 5.1-1. If the measured <0 (that is, the potential of point A' is lower than the potential of point A), it is negative, the sample is of type, and vice versa.
(2) by determining the carrier concentration, ie;
(3) Combine the measurement of conductivity to find the mobility of carriers.
The mobility represents the average drift velocity of the unit electric field download stream, which is an important parameter reflecting the conductivity of the carrier in the semiconductor. The relationship between conductivity and carrier concentration and mobility is as follows:
(5.1-5)
The measured value can be obtained.
In the experiment, the voltage between the two electrodes was measured. Known, the length of the sample is the cross-sectional area of ​​the sample, and the operating current is obtained by Ohm's law. Among them is the electronic power coulomb.
2. Various effects and their elimination
The Hall voltage discussed above is produced under ideal conditions. In fact, while the Hall effect is generated, it is accompanied by various effects, so the experimental measurement does not equal the true Hall voltage value, but Contains additional voltages caused by various effects. The unequal voltage drop as shown in Figure 5.1-2, because the position of the electrode and the Hall voltage is difficult to achieve on an ideal equipotential surface, so when there is current, even if it is not added The magnetic field also produces additional voltage. However, the sign of the additional voltage is only related to the direction of the current, independent of the direction of the magnetic field, so that this additional voltage can be eliminated by changing the direction.
In addition to this, there are various additional effects caused by the thermoelectric effect and the thermomagnetic effect. However, these attached effects are basically related to the direction of the sum, and can be eliminated by the symmetrical measurement method, that is, the direction of the change. That is, after the positive and negative directions of the current and the magnetic field are specified, the sum of the following four groups of different directions is measured, namely:
Then the algebraic mean of the sum, and
(5.1-6)
By the above measurement method, the attached effect can be substantially eliminated, which can be verified by the curve.
3. Introduction to the instrument:
The experimental instrument consists of two parts: a tester and an experimental instrument.
(1) Introduction to the experiment instrument
The experiment instrument consists of two parts (see Figure 5.1-3, Figure 5.1-5).
1 sample holder and electromagnet
The magnet wire wrap is clockwise (the operator faces the experimenter). According to the direction of the winding direction of the wire package and the direction of the excitation current, the direction of the magnetic induction intensity can be determined, and the relationship between the magnitude and the relationship is determined by the mark on the wire package. Generally HB>3.00 Gauss/Amp or Tesla/Amp.
The sample is a semiconductor silicon single wafer that is attached to one end of the sample holder (not touchable by hand). Its geometry is shown in Figure 5.1-4: Thickness: Width, AC electrode spacing.
The sample has three pairs of electrodes, wherein, or, for measuring the Hall voltage; or, for measuring the conductance; and working current electrodes for the sample.
The sample holder has a direction adjustment function and a reading device that adjusts the position of the sample in the magnetic field.
2 three double knife switches
, for, IM commutation switch; for VH, measurement selection switch. The connections of IS, IM, VH, and , are shown in Figure 5.1-3.
(2) Tester introduction:
The tester panel is shown in Figure 5.1-5. The tester consists of two parts:
1 two groups of constant current sources
The "output" is the sample (Hall element) operating current source. "Output" is the excitation current source. The two groups of power supplies are independent of each other, and their output sizes are adjusted by the adjustment knob and the adjustment knob respectively. The value is observed by the same digital ammeter through the "Measure Selection" button. The "Measure Selection" button is pressed and the bar is raised. Connect to the commutation switch in the Hall effect tester and connect to the commutation switch in the Hall effect tester (cannot be connected incorrectly).
2 DC digital voltmeter
VH is the sample Hall voltage measured through the A, A' electrodes. The sample voltage measured through the A and C electrodes is used to calculate the sample conductivity. VH, through the tester on the switch is observed by the same digital voltmeter. When VH and input are zero (the input line is shorted), the voltmeter is zero-adjusted by the zero adjustment knob. When the "-" sign appears before the digit of the display, it indicates that the polarity of the measured voltage is negative. During the experiment, the switch in the Hall effect experiment instrument is connected to the VH and input terminals in the tester.
Content and steps
Instrument adjustment
(1) Connect according to the diagram, check the line, and adjust the sample holder so that the Hall piece is in the middle of the magnetic field;
(2) Turn the adjustment knob counterclockwise to the minimum;
(3) Connect the output and output to the experiment instrument and the commutation switch respectively;
(4) Short-circuit with the wire and input, and zero the display by the zero adjustment knob.
(5) Select and close the positive direction of .
2. Measurement content
(1) Surveying and mapping curve: keep unchanged, adjust according to requirements, respectively measure four different values, and record the data in the table;
(2) Surveying and mapping curve: keep unchanged, and measure different lower four values;
(3) Measure VAC: take, under zero magnetic field (), then VAC = 10;
(4) Determine the conductivity type of the sample: select, forward, and determine the conductivity type of the sample based on the measured symbol
data processing
1. Magnetic induction (Tesla)
H standard online package. Make a curve, find it from the curve, bring it in, and calculate the Hall coefficient;
2. Calculate the carrier concentration n
(m-3), where e is the electron charge coulomb;
3. Draw a curve
Draw a curve on the coordinate paper;
4. Calculate conductivity (A/V) and mobility (m 2 / volt second).
ã€design content】
1. According to the Hall effect, measure the principle of magnetic induction, and use the instrument provided to test the one-dimensional (up and down direction) magnetic distribution on the measurement surface of the model.
Measurement requirements: Depicting the magnetic and digital signals recorded by the magnetic field distribution (BX curve), (designing the table, plotting on the coordinate paper, writing the experimental steps) shows the correspondence between the analog and digital signals.
2. Measure the magnetic field gap and the magnetic field distribution around it.
Measurement requirements: First consider how to pick points, and the measurement results are expressed in tables and curves.
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