Its combination of low raw material cost, relatively simple processing, and a useful temperature range makes it currently the best compromise among the various competing materials. Silicon used in semiconductor device manufacturing is currently fabricated into boules that are large enough in diameter to allow the production of 300 mm (12 in.) wafers. Germanium (Ge) was a widely used early semiconductor material but its thermal sensitivity makes it less useful than silicon. Today, germanium is often alloyed with silicon for use in very-high-speed SiGe devices; IBM is a major producer of such devices. Gallium arsenide (GaAs) is also widely used in high-speed devices but so far, it has been difficult to form large-diameter boules of this material, limiting the wafer diameter to sizes significantly smaller than silicon wafers thus making mass production of GaAs devices significantly more expensive than silicon. Other less common materials are also in use or under investigation. Silicon carbide (SiC) has found some application as the raw material for blue light-emitting diodes (LEDs) and is being investigated for use in semiconductor devices that could withstand very high operating temperatures and environments with the presence of significant levels of ionizing radiation. IMPATT diodes have also been fabricated from SiC. Various indium compounds (indium arsenide, indium antimonide, and indium phosphide) are also being used in LEDs and solid-state laser diodes. Selenium sulfide is being studied in the manufacture of photovoltaic solar cells. The most common use for organic semiconductors is organic light-emitting diodes. List of common semiconductor devices Two-terminal devices: DIAC Diode (rectifier diode) Gunn diode IMPATT diode Laser diode Light-emitting diode (LED) Photocell Phototransistor PIN diode Schottky diode Solar cell Transient-voltage-suppression diode Tunnel diode VCSEL Zener diode Zen diode Three-terminal devices: Bipolar transistor Darlington transistor Field-effect transistor Insulated-gate bipolar transistor (IGBT) Silicon-controlled rectifier Thyristor TRIAC Unijunction transistor Four-terminal devices: Hall effect sensor (magnetic field sensor) Photocoupler (Optocoupler) Semiconductor device applications All transistor types can be used as the building blocks of logic gates, which are fundamental in the design of digital circuits. In digital circuits like microprocessors, transistors act as on-off switches; in the MOSFET, for instance, the voltage applied to the gate determines whether the switch is on or off. Transistors used for analog circuits do not act as on-off switches; rather, they respond to a continuous range of inputs with a continuous range of outputs. Common analog circuits include amplifiers and oscillators. Circuits that interface