3 Description of laboratory research facility and methodology of measurements

The experimental setup consists of semiconductor sample connected to the digital multimeter (set as Ohm-meter) and illuminator (see scheme in the protocol below). The sample is placed in the illuminator. Intensity of illumination of the sample is changed by changing the distance between sample and the illuminator lamp.

4 Work execution order and experimental data analysis

1. Put the sample in the illuminator at minimal distance to the lamp and turn on multimeter.

2. Set multimeter scale range as 200 or 2000  and measure resistance of the sample at the absence of illumination (dark resistance).

3. Turn on illumination and measure resistance over each 10 mm of distance between illuminator and the sample. Write results in appropriate columns of your measurement table

4. Measure dark resistance on maximum distance between illuminator and the sample.

5. By known sizes of the sample and measured resistances calculate conductivity  of the sample.

6. By measured distances between illuminator and the sample calculate relative luminosity Ф.

7. Plot conductivity versus luminosity graph.

8. Calculate dark-light conductivity ratios K_min and K_max for minimal and maximal luminosities.

9. Basing on a plot, conclude about type of recombination of charge carriers in the sample.

5 Control questions

1. What is the internal photoeffect?

2. What is photoconductivity?

3. What is intrinsic photoconductivity mechanism?

4. What is the photoconductivity red border?

5. What is extrinsic photoconductivity mechanism?

6. Write down the formula for the photoconductivity of a semiconductor.

7. Write down the formula for the stady-state concentration of nonequilibrium

charge carriers and stationary photoconductivity.

8. What is monopolar photoconductivity? Write down equation for monopolar

photoconductivity.

9. What look may have dependence of photoconductivity of a semiconductor

from light intensity? What conclusions can be made from this dependence?

6 Content of the report

Laboratory work №8-5

I. Homework

(answer on a control questions).

…

II. Laboratory work № 8-5 implementation protocol.

1) Topic:

STUDYING PHOTOCONDUCTIVITY OF HOMOGENEOUS SEMICONDUCTORS

2) Goal :

1. Learning the basic provisions of the theory of the internal photoeffect.

2. Acquaintance with the method of investigation of photoelectric properties of semiconductor.

3. Removal of the lux-ampere characteristics in order to elucidate the mechanism of recombination of nonequilibrium charge carriers.

3) Scheme of laboratory research facility:

1–semiconductor sample; 2 – illuminator; 3 – digital multimeter.

4 ) Table of measuring instruments:

№	Name	Type	Serial №	Grid limit	Grid unit	Accuracy class
1.	Digital multimeter	DT-830B	-	200 Ω	0,1 Ω	0,8%
				2000 Ω	1 Ω	0,8%
2	Ruler	У	-		1 mm	0.5 mm

5) Equations for calculation:

1)	Conductivity of the sample: , where ℓ, x, b – length, width, thickness of the sample; R - resistance of the sample.
2)	Relative luminosity: , where r – distance between illuminator and a sample.
3)	Dark-light conductivity ratio at maximal luminosity: , where - conductivity of the sample at maximal luminosity; - conductivity of the sample at zero luminosity.

6) Table of measurements:

Number of the sample ….; ℓ = … mm; x = … mm; b = … mm

	r, mm	R, Ω	Ф	 ,(Ωm)-1
dark
	20
	30
	40
	50
	60
	70
	80
	90
	100
dark