By
By
[Weapon X]

[Weapon Xl]

[Semiconductor Diode Characteristics]
[Semiconductor Diode Characteristics]

Abstract
The purpose of this experiment was to investigate a semiconductor diode’s characteristics and its temperature dependence. The received data showed that the for the diode charters tics part of the experiment, there were close to no errors. While testing the temperature dependency of the diode it was found out of the three different temperatures of Hot Water, Room Temperature and Liquid Nitrogen, the Liquid Nitrogen temperature is the best for the diode. The voltage drop across the diode had a 10% error between the theoretical and the measured.

Introduction
Semiconductor diodes are used in electronics mostly because of its asymmetric conductance. It ideally has zero resistance in one direction and an infinite resistance in the other. The physical structure of a diode consists of a semiconducting material such as silicon or germanium which makes a p-n junction within the diode. A diode function by allowing electric current to pass in one direction which is called the forward bias direction and blocking the current to go in the opposite direction which is called the reverse bias direction. A forward bias state is achieved when the p-type material is made more positive than the n-type material and vice versa. Diodes differ from other circuit elements, as they are said to have a nonlinear relationship between the voltage and the current. Several models are used to represent diodes in circuit analysis. The three most common types are ideal, constant drop and Beers-Moll.
As diodes are known to be a nonlinear elements they can analyzed graphically using a load line. Load line defines a relationship between I and Vab this is shown in Figure 1. The circuit shown in Figure 1 must follow

Vs - IR - Vab = 0 (Kirchhoff’s loop rule)

Figure 1

Procedure 1. Setup a circuit containing a 0-20v power supply with a 1 kilo ohms resistor with a variable resistor, diode (IN4148) and an ammeter (fluke DVM) in series. Connect a parallel fluke DVM to measure the voltage across the diode. For a range of currents measure the voltage across the diode (0.003, 0.010, 0.030, 0.060, 0.1, 1, 2, 3, 6) mA. Do this for both the forward bias direction. Now flip the diode for the reverse bias direction and record the current values for a range of voltage values (-1, -5, -10, -20) V. Record the data and plot the values. This plot is the plot for diode characteristics. (Figure 2)

2. Now replace the power supply with a 1.5V battery and remove the variable resistor. Now plot the loadline with Vs = 1.5 v, R = 1 kilo ohms and Kirchhoff’s loop rule. Find the Voltage when Current equals zero. When voltage equals zero find the current. Now connect the two dots and this is the loadline. Plot the graph of loadline on the above drawn plot. (Figure 2). Measure the Id and Vd from the circuit and find the operating point.

3. Now return the circuit to how it was in part1 and for forward bias direction of the diode measure the voltage across it with using a range of current values (0.1, 0.3, 1, 2, 3) mA while immersing diode in 3 different temperatures. Hot Water (363K), Room Temperature (296 K) and Liquid Nitrogen (77K). Record the values separately for each of the temperatures and plot them on a graph (Figure 3). Find the standard approximation for a current of 2mA

Results and Discussion

Forward Bias | | Load Line | | | Operation Point | Vd(V) | Is(A) | | V | I | | V | I | 0.353 | 0.000003 | | 0 | 1.50E-03 | | 0.61 | 8.43E-04 | 0.407 | 0.00001 | | 1.5 | 0 | | | | 0.456 | 0.00003 | | | | | | | 0.487 | 0.00006 | | | | | | | 0.51 | 0.0001 | | | | | | | 0.561 | 0.0003 | | | | | | | 0.62 | 0.001 | | | | | | | 0.653 | 0.002 | | | | | | | 0.674 | 0.003 | | | | | | | 0.711 | 0.006 | | | | | | |

Figure 2
As we can see the graph in the figure 2 resembles the graph in figure 1 .Thus we can conclude that no significant errors were encountered. The forward bias and the reverse bias graphs cannot be plotted on the same graph as the scales are off. The loadline passes through the measured operating point so the measured values are consistent. The points on figure 2 for the diode characteristics should not be connected as we don’t know the values for the other points. The line facilitates the intersection of the loadline and confirming the location of the operation point.

| | Hot Water (363K) | Room Temp. (296K) | Liquid Nitrogen (77K) | Id(mA) | Id(A) | Vd(V) | Vd(V) | Vd(V) | 0.1 | 0.0001 | 0.495 | 0.51 | 1.008 | 0.3 | 0.0003 | 0.423 | 0.561 | 1.023 | 1 | 0.001 | 0.493 | 0.62 | 1.039 | 2 | 0.002 | 0.536 | 0.653 | 1.05 | 3 | 0.003 | 0.563 | 0.674 | 1.057 | | | | | |

Figure 3
There was a slight error while measuring the data for this part as we can see by referring to the table. The first value for the hot temperature is inconsistent with the rest and thus for current of 0.1mA the values weren’t plotted. .The outlier can be estimated to be less than 0.423 V. The other calculated values were consistent of one another and met the predictions. The overall change in temperature was 286K.

The standard approximation is that for a given current of 2mA there is a voltage drop of 2mV for each 1 degree in temperature. Through the received results we expect voltage drop of 2mV * 286K which equals 0.572 V. The measured drop is 0.514 V, which is within 10% of the theoretically expected.
From this we can conclude that to get the max voltage through the diode the best temperature is found to be 77K out of the temperatures tested.

Conclusion
In the final analysis the experiment was a success as we were successful in attempting to investigate semiconductor diode characteristics and its temperature dependence. The part of the procedure consisting of the diode characteristics for forward bias direction and the loadline showed no significant error as the loadline passed right through the operating point. The temperature dependence had a small error of 10% between the measured and the theoretical voltage drop. We also found the best temperature for a diode in forward bias direction to perform is 77K out of the temperatures tested.

BIBLIOGRAPHY
ECEN 203 Laboratory Manual