11. Read the text “The p-n Junction”. Mark the following sentences as true (t) or false (f).

8. Diffusion is a tendency of charge carriers to move to areas of high density.

9. The free electrons and holes have completely purposeful motions in the lattice.

10. On average the N-type region gains holes and loses electrons and the P-type region gains electrons and loses holes.

11. The region to the left of the junction becomes positively charged and the region to the right of the junction becomes negatively charged.

12. If a silicon crystal is doped with donor atoms at one end and with acceptor atoms at the other end, the crystal will have only N-type regions.

13. In Fig.2 from the text the plane AB is the P-N junction.

14. A hole passing into the N-type region, or an electron passing into the P-type region, becomes a majority charge carrier.

11. Fill in the gaps in the sentences.

1. In the N-type region electrons are in … and in the P-type region holes … .

2. Since the N-type region loses … and gains … and the P-type region loses … and gains …, the region to the left of the junction becomes … and the region to the right of the junction becomes … .

3. If a silicon crystal is doped with … at one end and with … at the other end, the crystal will have both … and there will be … between them.

4. In both regions the probability of a minority charge carrier meeting and recombining with a majority charge carrier is … and the minority charge carrier lifetime is … .

5. The movement of holes and electrons across the junction … current and this is known as … .

18. Refresh the text “The p-n Junction“ in your memory and answer some questions.

1. What is a sign of charge carriers in the N-type and P-type regions?

2. Where do we find majority charge carriers and minority charge carriers?

3. What is the lifetime of them?

4. On average more electrons cross the junction from right to left than from left to right, don’t they?

5. How can you define the process of diffusion?

6. Do you know what the diffusion current is?

7. What will happen if a hole passes in the N-type region or an electron passes into the P-type region?

18. Summarize the text “The p-n Junction” in 150 words using the following plan:

1. The necessary conditions of gaining P-type and N-type regions and a junction between them.

2. A description of processes which take place in a plane of P-N junction.

3. Diffusion.

4. A diffusion current.

20. Translate the text about Semiconductor Device Simulator with a dictionary in writing guessing the meaning of international words. Abstract

We present here a computer program – the Semiconductor Device Simulator which simulates the working of three p-n junction devices - the LED, the solar cell, and the tunnel diode. This program enables students to create the device starting with two pieces of intrinsic semiconductor material, and doping them appropriately to create a p-n junction device of their choice. While creating the device, students can observe the changes in the energy bands and Fermi level as a response to doping. The device once created, can then be incorporated into a circuit where the students can observe the energy bands, the I-V graph, as well as the intensity spectrum of the device in response to the changes in applied voltage and/or incident light. No prior knowledge of higher level mathematics is required to use the program. The program is available for Windows and Macintosh platforms. The flexibility of the program allows it to be used by students over a range of academic levels. We have field tested the program along with associated materials in both high school and university environments. The current version of the program contains modifications based on these field tests.

I. INTRODUCTION The Visual Quantum Mechanics project is developing materials to help students learn quantum physics. The primary audience for these materials is high school or introductory undergraduate students who do not have a background in higher level mathematics or quantum physics. To reach these students we are concentrating on the development of activities which integrate hands-on experiments, computer visualizations, and multimedia materials in addition to the more traditional written materials.

During the first eight months of this project we have concentrated on developing activities with a device that requires knowledge of quantum physics to understand how it works. The ubiquitous light emitting diode (LED) is recognized by almost every student as a small red or green light that indicates that some electronic gadget such as a CD player or computer disk drive is operating. To capitalize on this recognition, we are have designed and tested a series of activities that will enable the students to qualitatively explain how an LED is able to emit light. Since the primary goal of the activities is to enable students to understand the quantum effects in an LED, the students must be able to understand the relationship between the energy bands of the material of an LED and its electrical and spectral characteristics. To understand this relationship the students must learn how the energy bands respond to changes in applied voltage or incident light. Most standard introductory texts do not mention the quantum properties of LEDs or any similar devices. More advanced texts discuss these devices quantitatively, and use relatively few visualization tools. Hence these books and other instructional materials are unsuitable for our intended audiences.

This lacuna in the available instructional materials motivated us to develop a computer program that would enable a user who has no knowledge of higher level mathematics or physics to understand how the electrical and spectral properties of a p-n junction device can be explained using energy bands. Although the original purpose of the program was to explain how an LED worked, we decided that it could be designed to address the operation of any p-n junction device. Also while the program was originally meant for users who do not have a knowledge of semiconductor physics, the program in its current version can be used by students studying solid state physics, semiconductors or electronics at a higher level.