## Basic/Intro - its both an insulator and a conductor - **Basic Idea**: In simple terms, semiconductors are like **light switches**. When the switch is off, no current flows (they act as an insulator). But when the switch is on, current flows (they act as a conductor). This “switch” behavior makes semiconductors ideal for controlling electrical signals. ### Band Theory Energy ^ | Conduction Band | --------------- | Band Gap | --------------- | Valence Band | +------------------ ![[Pasted image 20240927155233.png]] **Analogy**: Imagine an auditorium with two levels (valence and conduction bands). The ground floor ([[valence band]]) is nearly full of seated people ([[electron]]s). The upper level ([[conduction band]]) is mostly empty. The staircase between levels represents the [[band gap]]. - In [[insulator]], the staircase is extremely tall (large band gap). - In [[conductor]]s, the levels overlap or the staircase is nonexistent. - In [[semiconductor]], the staircase is manageable but requires some effort to climb ([[moderate band gap]]). ![[Pasted image 20240927155243.png]] #### Why need a [[moderate band gap]]? - advantage of [[semiconductor]] lies in controllability - Moderate band : Allows to manipulate electrical properties in ways that aren’t possible with conductors or insulators Usually: a) Conductors always conduct: - They have many free electrons - You can't easily turn their conductivity "off" b) Insulators almost never conduct: - Their electrons are tightly bound - It's very difficult to make them conduct c) Semiconductors are in the "Goldilocks zone": - They don't conduct much naturally - But with a small amount of energy or [[doping]], they can conduct well - Most importantly, ==we can switch them between conducting and non-conducting states== With the [[moderate band gap]] : - large enough that we we can excite electrons from the valence to conduction band → but small enough it does not happen spontaneously, rather control [[conductivity]] through: - Temperature - Light ([[Photoelektrische Effekt|photoelectrical effect]] ) - Electrical field (as in [[transistors]]) - [[Doping]] (adding impurities) Think of it this way: - A conductor is like a light that's always on - An insulator is like a light that's always off - A semiconductor is like a light with a switch ![[Pasted image 20240927160143.png|232]] ##### Practical applications where switching is key: - [[transistors]]: The basis of all modern computing - [[Solar cells]]: Converting light to electricity - [[LED]]s: Converting electricity to light - [[Diode]]s: Controlling the direction of current flow ### Why do I need to switch the flow electricity? ##### 1. Fundamental Concept - **Switching = control of electron flow** - Allows manipulation of electric current in circuits - **Binary states: ON (1) / OFF (0)** - Forms the basis of digital information processing ##### 2. Applications - **Digital: information processing, logic gates, memory** - Enables computation through manipulation of binary data - [[Logic Gates]] (AND, OR, NOT) built from switches (transistors) - Memory stores data as switch states (on/off) - **Analog: signal amplification, power control** - Rapid switching can control signal strength or power delivery - **Power management: device on/off, energy efficiency** - Crucial for battery life and reducing energy consumption ##### 3. Quantum Effects - **[[Quantum Tunneling]]** - Exploits quantum behavior for specialized electronic devices - **[[band gap]] engineering** - Allows precise control of electronic and optical properties #### More Details on how its used in information processing ###### The Fundamental Need for Switching in Computation At its core, computation is about making decisions and processing information. In the world of electronics, we represent information using electrical signals. Switching allows us to control these signals, essentially giving us a way to represent and manipulate information. **Analogy**: Think of electricity like water in a pipe system. Switching is like having valves that can direct the flow of water. Without valves, water would flow everywhere indiscriminately. With valves, we can control where the water goes, just like we control the flow of electricity in a computer. | **Component** | **Description** | **Why Switching is Needed** | **Analogy** | | --------------- | ------------------------------------------------------------------------------------------------------------ | ---------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | **Logic Gates** | Fundamental building blocks of digital circuits, performing logical operations on binary inputs (0s and 1s). | Switches (transistors) control the flow of electricity based on inputs to produce correct output. | Water tanks and pipes: AND gate flows water only if all tanks are full, OR gate flows if any tank is full, NOT gate inverts (full tank = empty output, empty tank = full). | | **RAM** | Temporary data storage actively used by the computer. | Each bit of data is stored in a charged (1) or discharged (0) state using tiny switches (transistors). | A grid of light bulbs: Each bulb represents a 1 (on) or 0 (off), and switching bulbs on/off allows quick changes in data. | | **CPU** | Performs calculations and executes instructions. | Manipulates data by controlling the flow of electricity through various logic gates to execute operations. | A complex network of pipes and valves: Instructions control valve operations, guiding water (electricity) to perform complex tasks. | ###### [[Logic Gates]]: Logic gates are the fundamental building blocks of digital circuits. They perform basic logical operations on binary inputs (0s and 1s). - AND gate: Output is 1 only if all inputs are 1 - OR gate: Output is 1 if at least one input is 1 - NOT gate: Inverts the input (0 becomes 1, 1 becomes 0) **Why switching is needed**: Each of these gates requires the ability to control the flow of electricity based on the inputs. [[transistors]] act as switches to implement this control. **Analogy**: Imagine a series of water tanks connected by pipes, with each tank representing an input or output: - AND gate: Water only flows out if all input tanks are full - OR gate: Water flows out if any input tank is full - NOT gate: If the input tank is full, the output is empty, and vice versa ![[Pasted image 20240927161723.png]] ###### [[RAM]] Random Access Memory (RAM) stores temporary data that the computer is actively using. **Why switching is needed**: Each bit of information in RAM is stored as the state of a tiny switch (usually a capacitor and transistor combination). A charged state might represent a 1, while a discharged state represents a 0. **Analogy**: Picture a massive grid of light bulbs. Each bulb can be on or off, representing a 1 or 0. The ability to switch each bulb on or off individually allows us to store and change information quickly. ![[Pasted image 20240927162116.png]] ##### [[CPU]] Central Processing Units perform calculations and execute instructions. **Why switching is needed**: CPUs operate by executing a series of instructions. Each instruction involves manipulating data, which at the hardware level means controlling the flow of electricity through various logic gates. **Analogy**: Imagine a complex network of pipes and valves (logic gates) where water (electricity) flows. The CPU's instructions are like a sequence of valve operations. By opening and closing valves in specific patterns, we can guide the water to perform complex operations. ![[Pasted image 20240927161723.png]] ]