Semiconductors - Revision history

Hwang: /* p-n junctions */

2006-07-05T20:59:54Z

p-n junctions

← Older revision		Revision as of 15:59, 5 July 2006
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	[[Image:p_n_junction_depletion_zone.gif]]		[[Image:p_n_junction_depletion_zone.gif]]

	If put a voltage across the semiconductors with the positive voltage on the p-type semiconductor, we will create a '''forward bias'''. The positive voltage will repel the holes, and the negative voltage will repel the electrons, pushing both towards the junction. This movement shrinks the depletion zone, and if our voltage is high enough, the depletion zone will become so thin that electrons will be able to tunnel through it. When this happens, current will be able to flow through the semi-conductors.		If we put a voltage across the semiconductors with the positive voltage on the p-type semiconductor, we will create a '''forward bias'''. The positive voltage will repel the holes, and the negative voltage will repel the electrons, pushing both towards the junction. This movement shrinks the depletion zone, and if our voltage is high enough, the depletion zone will become so thin that electrons will be able to tunnel through it. When this happens, current will be able to flow through the semi-conductors.

	[[Image:p_n_forward_bias.gif]]		[[Image:p_n_forward_bias.gif]]

Hwang: /* Semiconductors */

2006-07-05T20:58:14Z

Semiconductors

← Older revision		Revision as of 15:58, 5 July 2006
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	For example, we can dope silicon (which as four valence electrons) with arsenic (which has 5 valence electrons). The extra electron in the arsenic atom cannot form a covalent bond with the neighboring atoms, and thus is loosely bound and available as a charge carrier. This creates an '''n-type''' semiconductor, which has negative charge carriers.		For example, we can dope silicon (which as four valence electrons) with arsenic (which has 5 valence electrons). The extra electron in the arsenic atom cannot form a covalent bond with the neighboring atoms, and thus is loosely bound and available as a charge carrier. This creates an '''n-type''' semiconductor, which has negative charge carriers.

	We can also dope the silicon with boron or gallium, which have 3 valence electrons. The lack of an electron to complete all four covalent bonds the lattice structure leaves a hole ~~into~~ ~~which~~ an electron ~~can fall~~. This creates a '''p-type''' semiconductor, which has positive charge carriers.		We can also dope the silicon with boron or gallium, which have 3 valence electrons. The lack of an electron to complete all four covalent bonds in the lattice structure leaves a hole that can accept an electron. This creates a '''p-type''' semiconductor, which has positive charge carriers.

	===p-n junctions===		===p-n junctions===

Hwang at 22:12, 20 June 2006

2006-06-20T22:12:05Z

← Older revision		Revision as of 17:12, 20 June 2006
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	Conductors are able to accommodate an electron flow through them because the electrons in the atoms are not tightly bound to their atoms. When an electron leaves its atom, it leaves behind '''hole''', which because of the absence of the electron, is positively charged since the atom started out neutral. This hole can be modeled as a positive charge. As electrons move towards one end of the conductor, they will leave holes at the opposite end, thus creating a "flow" of holes in the direction opposite the electron flow.		Conductors are able to accommodate an electron flow through them because the electrons in the atoms are not tightly bound to their atoms. When an electron leaves its atom, it leaves behind '''hole''', which because of the absence of the electron, is positively charged since the atom started out neutral. This hole can be modeled as a positive charge. As electrons move towards one end of the conductor, they will leave holes at the opposite end, thus creating a "flow" of holes in the direction opposite the electron flow.

	[[Image:conductor_diagram.~~jpg~~]]		[[Image:conductor_diagram.gif]]

	The electrons in insulators are tightly bound to their atoms, so they cannot flow.		The electrons in insulators are tightly bound to their atoms, so they cannot flow.

	[[Image:insulator_diagram.~~jpg~~]]		[[Image:insulator_diagram.gif]]

	==Semiconductors==		==Semiconductors==
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	The electrons will jump into the holes across the border:		The electrons will jump into the holes across the border:

	[[Image:p_n_junction.~~jpg~~]]		[[Image:p_n_junction.gif]]

	and will form the depletion zone:		and will form the depletion zone:

	[[Image:p_n_junction_depletion_zone.~~jpg~~]]		[[Image:p_n_junction_depletion_zone.gif]]

	If put a voltage across the semiconductors with the positive voltage on the p-type semiconductor, we will create a '''forward bias'''. The positive voltage will repel the holes, and the negative voltage will repel the electrons, pushing both towards the junction. This movement shrinks the depletion zone, and if our voltage is high enough, the depletion zone will become so thin that electrons will be able to tunnel through it. When this happens, current will be able to flow through the semi-conductors.		If put a voltage across the semiconductors with the positive voltage on the p-type semiconductor, we will create a '''forward bias'''. The positive voltage will repel the holes, and the negative voltage will repel the electrons, pushing both towards the junction. This movement shrinks the depletion zone, and if our voltage is high enough, the depletion zone will become so thin that electrons will be able to tunnel through it. When this happens, current will be able to flow through the semi-conductors.

	[[Image:p_n_forward_bias.~~jpg~~]]		[[Image:p_n_forward_bias.gif]]

	On the other hand, if we connect the positive voltage to the n-type semiconductor and the negative voltage to the p-type semiconductor, we will create a '''reverse bias'''. The negative voltage will attract the holes, and the positive voltage will attract the electrons. This will pull both holes and electrons away from the junction and widen the depletion zone. Because of this, no current can flow through the semiconductors. (However, if the voltage is high enough, current can still force its way across.)		On the other hand, if we connect the positive voltage to the n-type semiconductor and the negative voltage to the p-type semiconductor, we will create a '''reverse bias'''. The negative voltage will attract the holes, and the positive voltage will attract the electrons. This will pull both holes and electrons away from the junction and widen the depletion zone. Because of this, no current can flow through the semiconductors. (However, if the voltage is high enough, current can still force its way across.)

	[[Image:p_n_reverse_bias.~~jpg~~]]		[[Image:p_n_reverse_bias.gif]]

Hwang at 22:23, 19 June 2006

2006-06-19T22:23:52Z

← Older revision		Revision as of 17:23, 19 June 2006
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	__TOC__		__TOC__
	==Conductors and Insulators==		==Conductors and Insulators==
	Conductors are able to ~~accomodate~~ an electron flow through them because the electrons in the atoms are not tightly bound to ~~thier~~ atoms. When an electron leaves its atom, it leaves behind '''hole''', which because of the absence of the electron, is ~~positivly~~ charged since the atom started out neutral. This hole can be modeled as a positive charge. As electrons move towards one end of the conductor, they will leave holes at the opposite end, thus creating a "flow" of holes in the direction opposite the electron flow.		Conductors are able to accommodate an electron flow through them because the electrons in the atoms are not tightly bound to their atoms. When an electron leaves its atom, it leaves behind '''hole''', which because of the absence of the electron, is positively charged since the atom started out neutral. This hole can be modeled as a positive charge. As electrons move towards one end of the conductor, they will leave holes at the opposite end, thus creating a "flow" of holes in the direction opposite the electron flow.

	[[Image:conductor_diagram.jpg]]		[[Image:conductor_diagram.jpg]]

	The electrons in insulators are tightly bound to ~~thier~~ atoms, so they cannot flow.		The electrons in insulators are tightly bound to their atoms, so they cannot flow.

	[[Image:insulator_diagram.jpg]]		[[Image:insulator_diagram.jpg]]

	==Semiconductors==		==Semiconductors==
	Semiconductors, such as silicon, are somewhere in between a conductor and an insulator. Some electrons in the semi-~~conducor~~ are allowed to flow, especially when ~~relased~~ by heat or light. Semiconductors allow us to build ''non-linear'' devices, such as computers.		Semiconductors, such as silicon, are somewhere in between a conductor and an insulator. Some electrons in the semi-conductor are allowed to flow, especially when released by heat or light. Semiconductors allow us to build ''non-linear'' devices, such as computers.

	We can increase the conductivity of semiconductors by ''doping'', or interspersing atoms with more valence electrons into the lattice structure.		We can increase the conductivity of semiconductors by ''doping'', or interspersing atoms with more valence electrons into the lattice structure.
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	For example, we can dope silicon (which as four valence electrons) with arsenic (which has 5 valence electrons). The extra electron in the arsenic atom cannot form a covalent bond with the neighboring atoms, and thus is loosely bound and available as a charge carrier. This creates an '''n-type''' semiconductor, which has negative charge carriers.		For example, we can dope silicon (which as four valence electrons) with arsenic (which has 5 valence electrons). The extra electron in the arsenic atom cannot form a covalent bond with the neighboring atoms, and thus is loosely bound and available as a charge carrier. This creates an '''n-type''' semiconductor, which has negative charge carriers.

	We can also dope the silicon with boron or ~~galium~~, which have 3 valence electrons. The lack of an electron to complete all four covalent bonds the lattice structure leaves a hole into which an electron can fall. This creates a '''p-type''' semiconductor, which has positive charge ~~charriers~~.		We can also dope the silicon with boron or gallium, which have 3 valence electrons. The lack of an electron to complete all four covalent bonds the lattice structure leaves a hole into which an electron can fall. This creates a '''p-type''' semiconductor, which has positive charge carriers.

	===p-n junctions===		===p-n junctions===

Hwang at 22:23, 19 June 2006

2006-06-19T22:23:02Z

← Older revision		Revision as of 17:23, 19 June 2006
Line 1:		Line 1:
			__TOC__
	==Conductors and Insulators==		==Conductors and Insulators==
	Conductors are able to accomodate an electron flow through them because the electrons in the atoms are not tightly bound to thier atoms. When an electron leaves its atom, it leaves behind '''hole''', which because of the absence of the electron, is positivly charged since the atom started out neutral. This hole can be modeled as a positive charge. As electrons move towards one end of the conductor, they will leave holes at the opposite end, thus creating a "flow" of holes in the direction opposite the electron flow.		Conductors are able to accomodate an electron flow through them because the electrons in the atoms are not tightly bound to thier atoms. When an electron leaves its atom, it leaves behind '''hole''', which because of the absence of the electron, is positivly charged since the atom started out neutral. This hole can be modeled as a positive charge. As electrons move towards one end of the conductor, they will leave holes at the opposite end, thus creating a "flow" of holes in the direction opposite the electron flow.

Hwang at 22:22, 19 June 2006

2006-06-19T22:22:25Z

← Older revision		Revision as of 17:22, 19 June 2006
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	[[Image:p_n_reverse_bias.jpg]]		[[Image:p_n_reverse_bias.jpg]]

	==Diodes==
	Symbol for the diode:[[Image:diode_symbol.jpg]]

	We can take advantage of the properties of a p-n junction to make a '''diode''', which is an electrical component that only allows current flow in one direction. A diode made of silicon needs about 0.7V across it in order to conduct. At about -100V, the diode will fail and the current will force its way though.

	[[Image:diode_N4002_profile.jpg]]

	===Applications of Diodes===
	====Half-Wave Rectifier====
	A half-wave rectifier will cut off half of a sine wave, leaving only the postive or negative side.

	The schematic for a simple retifier:

	[[Image:half_wave_rectifier_schematic.jpg]]

	The graph for half-wave rectifier:

	[[Image:half_wave_rectifier_graph.jpg]]

	====Flyback Diode====
	An approximate model of a DC motor is a resistor and inductor in series. If we suddenly break the ciruit to switch off the motor, the inductor will continue to try and push current though, resulting in a sudden spike in voltage (<math>v=L*di/dt</math>). Mechanically, this is like trying to bring the velocity of a certain moving mass to zero, instantly. We can solve this problem by adding a diode, as shown:

	[[Image:diode_flyback_schematic.jpg]]

	This way, the current can flow through the diode and dissipate in the resistor. Yet, the diode prevents a short circuit from occuring when the switch is closed.

	====Peak Detector===
	We can make a peak detector if we hook up our circuit like this:

	[[Image:peak_detector_schematic.jpg]]

	The graph of the input and output voltages looks like this:

	[[Image:peak_detector_graph.jpg]]

	Each time the input voltage dips, the diode prevents the capacitor from draining.

	There are two problems with this circuit: First, the voltage of the peak must be greater than the voltage drop, or we won't detect anything. Second, the circuit has a very low impedance, and the capacitor drains a lot of current. A better peak detector can be built with op-amps.

Hwang: /* =Peak Detector */

2006-06-19T22:20:07Z

=Peak Detector

← Older revision		Revision as of 17:20, 19 June 2006
Line 70:		Line 70:

	[[Image:peak_detector_graph.jpg]]		[[Image:peak_detector_graph.jpg]]

			Each time the input voltage dips, the diode prevents the capacitor from draining.

	There are two problems with this circuit: First, the voltage of the peak must be greater than the voltage drop, or we won't detect anything. Second, the circuit has a very low impedance, and the capacitor drains a lot of current. A better peak detector can be built with op-amps.		There are two problems with this circuit: First, the voltage of the peak must be greater than the voltage drop, or we won't detect anything. Second, the circuit has a very low impedance, and the capacitor drains a lot of current. A better peak detector can be built with op-amps.

Hwang: /* Applications of Diodes */

2006-06-19T22:17:55Z

Applications of Diodes

← Older revision		Revision as of 17:17, 19 June 2006
Line 61:		Line 61:

	This way, the current can flow through the diode and dissipate in the resistor. Yet, the diode prevents a short circuit from occuring when the switch is closed.		This way, the current can flow through the diode and dissipate in the resistor. Yet, the diode prevents a short circuit from occuring when the switch is closed.

			====Peak Detector===
			We can make a peak detector if we hook up our circuit like this:

			[[Image:peak_detector_schematic.jpg]]

			The graph of the input and output voltages looks like this:

			[[Image:peak_detector_graph.jpg]]

			There are two problems with this circuit: First, the voltage of the peak must be greater than the voltage drop, or we won't detect anything. Second, the circuit has a very low impedance, and the capacitor drains a lot of current. A better peak detector can be built with op-amps.

Hwang: /* Flyback Diode */

2006-06-19T21:34:43Z

Flyback Diode

← Older revision		Revision as of 16:34, 19 June 2006
Line 55:		Line 55:
	[[Image:half_wave_rectifier_graph.jpg]]		[[Image:half_wave_rectifier_graph.jpg]]

	===Flyback Diode===		====Flyback Diode====
	An approximate model of a DC motor is a resistor and inductor in series. If we suddenly break the ciruit to switch off the motor, the inductor will continue to try and push current though, resulting in a sudden spike in voltage (<math>v=L*di/dt</math>). Mechanically, this is like trying to bring the velocity of a certain moving mass to zero, instantly. We can solve this problem by adding a diode, as shown:		An approximate model of a DC motor is a resistor and inductor in series. If we suddenly break the ciruit to switch off the motor, the inductor will continue to try and push current though, resulting in a sudden spike in voltage (<math>v=L*di/dt</math>). Mechanically, this is like trying to bring the velocity of a certain moving mass to zero, instantly. We can solve this problem by adding a diode, as shown:

Hwang: /* Applications of Diodes */

2006-06-19T21:30:40Z

Applications of Diodes

← Older revision		Revision as of 16:30, 19 June 2006
Line 45:		Line 45:
	===Applications of Diodes===		===Applications of Diodes===
	====Half-Wave Rectifier====		====Half-Wave Rectifier====
			A half-wave rectifier will cut off half of a sine wave, leaving only the postive or negative side.

			The schematic for a simple retifier:

			[[Image:half_wave_rectifier_schematic.jpg]]

			The graph for half-wave rectifier:

			[[Image:half_wave_rectifier_graph.jpg]]

			===Flyback Diode===
			An approximate model of a DC motor is a resistor and inductor in series. If we suddenly break the ciruit to switch off the motor, the inductor will continue to try and push current though, resulting in a sudden spike in voltage (<math>v=L*di/dt</math>). Mechanically, this is like trying to bring the velocity of a certain moving mass to zero, instantly. We can solve this problem by adding a diode, as shown:

			[[Image:diode_flyback_schematic.jpg]]

			This way, the current can flow through the diode and dissipate in the resistor. Yet, the diode prevents a short circuit from occuring when the switch is closed.