### 2.1.4 Summary to: 2.1 General Chemistry and Structure

| Structure and size matter! |  |
Typical Si wafer: | 300 mm, 850 µm thick, perfect single crystal
Solar cell: Si | Single crystalline, bulk. Poly crystalline, large grain, bulk. Polycrystalline, micro grain, "thick" film Polycrystalline, nano grain, thin film. Amorphous (plus H), thin film
|  | Mostly we need single crystals, as perfect (and as large) as possible |
|  | Either in bulk, or thin films |
|  | If thin film, substrates matter. |
| For some applications (solar cell , LCD, ...) polycrystalline or amorphous semiconductors are used. |
|  | "CIGS" or CdTe for solar cells. |
|  | Amorphous or poly-Si for LCD transistor matrix. |
| Important elemental semiconductors are Si and marginally Ge. |  |
Some important Properties | Remarks
Lattice type, lattice constant | Structure independent
Melting point, diffusion constants
Bandgap type and energy
Dielectric constant
Thermal expansion coefficient
Doping range | Structure dependent
Transport of electron / holes (mobility, life time, diffusion length, ..
Unwanted levels in bandgap
|  | Forget Se, C, P, As and B. |
| Compound semiconductors are important. |
|  | Group IV and compounds: SiGe, SiC. |
|  | III-V compounds (Al, Ga, In) - (N, P, As, Sb). Important GaAs, GaxAl1-xAs, GaP, InP, .. |
|  | Chalkogenides AxBy(S, Se, Te)2. Important "CIGS" = CuInxGa1-xSe2. |
|  | "Newcomers" like organic semiconductors, Metal oxides (e.g. TiO2). |
| Properties matter! Some properties are rather independent of the structure (= defects), others can be structure sensitive |
| What counts in the end are products that sell and make a profit! |  |
Integrated circuits, Solar cells, Liquid crystal displays, Micro electronic and mechanical systems, Light emitting diodes, (Diode) Lasers, Sensors, ...
|  | Besides the direct semiconductor products, there are also products that contain semiconductors (PC's, Cars, TV's, any modern machine,...) and products that are needed to make semiconductor products (crystal growers, ovens, plasma etchers, ion implanters, ..). |
Exercise 2.1-1
All Class Exercises to 2.1

© H. Föll (Semiconductor Technology - Script)