transistors

Hope that this isn't too simple for you, but there are good concepts:

http://electronics.howstuffworks.com/diode.htm

If you have specific questions, we can tackle them right here.

I hope you will understand what I write, because English is not my primary language so I don't know translations for technical words.
I don't clearly understand how to calculate recombinational current.
I think I don't understand clearly what is happening in the transistor when we connect it to a voltages. Could anyone describe the flow of the current?

Gee, my connection with this stuff was very minor, and I have forgotten most of what I knew, but I know that:

1 The semiconductors are doped with small amounts of impurities to be p type or n type, which means that the charge carriers are positive or negative respectively.
2. A diode is a p type material pressed against an n type material. A transistor is either pnp or npn.
3. I believe that the diode and transistor effects are the result of some kind of charge depletion phenomenon at the junctions between the different types.

I would be interested if someone could expand on this a bit.

This is gonna be real simple, and overlooks a lot, but I hope it clears up a bit of it for you. A transistor is more or less sort of a switch or valve. There are different types of transistors, but all essentially either, or in combination, turn current flow (voltage) on or off, direct it (or its direction of flow) somewhere, or vary the amount of current flow through a circuit.

For example, a transistor used in an amplification application will be roughly equivalent to a valve, directly influenced by a relatively low source, or control, voltage, proportionately allowing a greater or lesser flow of a relatively higher bias voltage in direct relationship to changes in the control voltage. While transistors themselves are typically very low voltage devices, acted upon by very low voltages (the control voltage), they can be and are used to control how much of an often very much higher, or bias, voltage, provided independently of the control voltage by a separate power supply, will be available to the next device in the chain.

Think of the power supply as a pressure tank which itself is kept at a relatively high pressure by a compressor. The transistor could be thought of as a valve tapping pressure from the storage tank. A relatively little amount of work, or energy, is required to manipulate the valve itself, but manipulation of the valve controls the flow of the greater energy stored in the tank, subject, of course, to the capacity of the tank, the maximum pressure available, and the ability of the compressor to maintain that pressure (the bias voltage) within the tank as the transistor, or exit valve, allows pressure to flow out of the tank in order to perform work (apply energy) elsewhere.