Semiconductor device fundamentals

1. The main reason semiconductor materials are so useful is that the behaviour of a semiconductor can be easily manipulated by the addition of impurities, known as doping. Semiconductor conductivity can be controlled by introduction of an electric field, by exposure to light, and even pressure and heat; thus, semiconductors can make excellent sensors. Current conduction in a semiconductor occurs via mobile or «free» electrons and holes (collectively known as charge carriers). Doping a semiconductor such as silicon with a small amount of impurity atoms, such as phosphorus or boron, greatly increases the number of free electrons or holes within the semiconductor. When a doped semiconductor contains excess holes it is called «p-type», and when it contains excess free electrons it is known as «n-type». The semiconductor material used in devices is doped under highly controlled conditions in a fabrication facility, or fab, to precisely control the location and concentration of p- and n-type dopants. The junctions which form where n-type and p-type semiconductors join together are called p-n junctions.

2. The simplest device made from a p-n junction is the p-n junction diode. At the junction of a p-type and an n-type semiconductor there forms a region called the depletion zone which blocks current conduction from the n-type region to the p-type region, but allows current to conduct from the p-type region to the n-type region. Thus, when the device is forward biased, with the p-side at higher electric potential, the diode conducts current easily; but the current is very small when the diode is reverse biased.

3. Exposing a semiconductor to light can generate electron–hole pairs, which increases the number of free carriers and its conductivity. Diodes optimized to take advantage of this phenomenon are known as photodiodes. Compound semiconductor diodes can also be used to generate light, as in light-emitting diodes and laser diodes.

4. Bipolar junction transistors are formed from two p-n junctions, in either n-p-n or p-n-p configuration. The middle, or base, region between the junctions is typically very narrow. The other regions, and their associated terminals, are known as the emitter and the collector. A small current injected through the junction between the base and the emitter changes the properties of the base-collector junction so that it can conduct current even though it is reverse biased. This creates a much larger current between the collector and emitter, controlled by the base-emitter current.

5. Another type of transistor, the field effect transistor operates on the principle that semiconductor conductivity can be increased or decreased by the presence of an electric field. An electric field can increase the number of free electrons and holes in a semiconductor, thereby changing its conductivity. The field may be applied by a reverse-biased p-n junction, forming a junction field effect transistor, or JFET; or by an electrode isolated from the bulk material by an oxide layer, forming a metal-oxide-semiconductor field effect transistor, or MOSFET. The MOSFET is the most used semiconductor device today.

Notes:

impurity	примесь
to dope	вводить примесь
dopant	примесь
junction diode	плоскостной диод
bias to be forward/reverse biased	смещение иметь прямое/обратное смещение
junction field effect transistor (JFET)	канальный полевой транзистор с p-n переходом
metal-oxide-semiconductor field-effect transistor (MOSFET)	канальный полевой униполярный МОП-транзистор

5. Укажите, какие из данных утверждений соответствуют содержанию текста.

1. The removal of impurities from a semiconductor is called doping.

2. The performance of a semiconductor can be influenced by doping.

3. Junction diodes conduct current easily when they are forward biased.

6. Выберите правильные ответы на вопросы.

1. How do we call semiconductors with excess holes?

(a) p-type semiconductors;

(b) n-type semiconductors.

2. What does a small current base-emitter current injection cause in a junction transistor?

(a) an increase of collector-emitter current;

(b) decrease of collector -emitter current.

7. Прочтите предложения. Выберите правильный вариант перевода.

1. At the junction of a p-type and an n-type semiconductor there forms a region called the depletion zone.

(a) На стыке полупроводников p- и n-типов формируется область, называемая зоной истощения.

(b) Там, на стыке p- и n-полупроводников, образуется область, называемая зоной уменьшения.

2. Exposing a semiconductor to light can generate electron-hole pairs, which increases the number of free carriers and its conductivity.

(a) Воздействие света на полупроводник может приводить к образованию электронно-дырочных пар, что увеличивает количество свободных носителей тока в полупроводнике и его проводимость.

(b) Подвергнув полупроводник свету, можно генерировать электронно-дырочные пары, которые увеличивают количество свободных носителей и его проводимость.

3. When the diode is reverse biased the current is very small.

(a) Когда диод наклонен обратно, ток мал.

(b) При обратном смещении диода ток мал.