4 Work execution order and experimental data analysis

1. Check the correctness of the scheme and the polarity of LED and PD.

2. Using resistance bank R₃ set the current through the LED 5 mA and write down into the table of measurements readings of all devices. Do measurements from 5 mA to 50 mA. If it’s necessary use the microamperemeter shunt.

3. Calculate consumed power P_E and light emission power P_LIGHT for all measurements of current.

4. Calculate energy η_1(EN) and quantum η_2(Q) efficiencies.

5. By obtained data build CVC (I_1(LED) = f(U))and determine R_RES and U_CUT.

6. On one graph plot P_LIGHT, η_1(EN), η_2(Q) versus I_1(LED) dependencies (see sample graph in the protocol).

7. Make conclusions about the optimal mode of work of the LED (maximal power mode, maximal efficiency mode).

6. Write down the results of calculations of electric parameters of the LED, quantum and energy efficiency for the 50 mA current.

5 Control question

1. How does the p-n junction appear and when does it conduct the current and when does not?

2. How does the electric energy transform into the light one in the LED? What is injection and radiative recombination?

3. What are the quantum and the energy efficiency?

4. What parameters can be defined from CVC?

5. How do the LED light properties depend on the current?

7 Content of the report

Laboratory work № 6-9 ι. Homework.

(answer on control questions from p. )

…

Ιι. Laboratory work № 6-9 implementation protocol.

1) Topic:

Studying of light-emitting diode

2) Goal: Studying of electric energy transformation into light one by the LED and measuring its electric and light characteristics.

3) Scheme of laboratory research facility:

B - supply battery mA – miliamperemeter; V – voltmeter; R3 – 1 – 9999 Ω resistors bank; LED – light emitting diode; PD – photodiode; Rsh – shunt resistance μA - microamperemeter

4) Table of measuring instruments:

№	Name	Type	Serial №	Grid limit	Grid unit	Accuracy class
1.	Milliamperemeter	М906		25 mА	1 mА	1 %
2.	Microamperemeter	М906		500 μА	20 μА	1 %
				1000 μА	40 μА
3.	Voltmeter	DT803B		2000 mV	1mV	0,5 %
4.	Resistor bank R3	Р333	-	9999 Ω	1 Ω	0,2 %

Accesories: the LED, the photodiode.

5) Equations for calculation:

1. Electrical power consumed by LED:

;

where I_1(LED) – current through LED, U – forward bias voltage.

2. Light emission power:

;

where I_2(PD) – current through photodiode, S – photodiode sensitivity.

3. LED energy efficiency:

;

where P_LIGHT - light emission power, P_E - electrical power consumed by LED.

4. LED quantum efficiency:

.

where e = 1.6·10^-19 - charge of electron, λ - wavelength of light, h=6.63·10^-34J·s - Planck constant, c = 3·10⁸ m/s - speed of light, P_LIGHT - light emission power, I_1(LED) – current through LED.