Mula Sigiro An OVERVIEW Semiconductor Devices

7/28/2019 Mula Sigiro An OVERVIEW Semiconductor Devices

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A N O V E R V I E W

S e m i c o n d u c t o r s f o r m t h e a c t i v e r e g i o n s o f \ i n t e l l i g e n t " d e v i c e s . T h e f o l l o w i n g g u r e s p r o v i d e a n

o v e r v i e w o f w h y s e m i c o n d u c t o r s a r e i m p o r t a n t , w h a t t h e v a r i o u s d e m a n d s i n s e m i c o n d u c t o r t e c h -

n o l o g i e s a r e , a n d w h i c h s e m i c o n d u c t o r s a r e u s e d f o r v a r i o u s a p p l i c a t i o n s .


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Prof. Jasprit Singh www.eecs.umich.edu/~singh

SEMICONDUCTORTECHNOLOGYMATERIALS, PHYSICS, DEVICES, TECHNOLOGY

The new industrial age is driven by information technology.

Computation, communication and theexploding internet use is driving our new economy.

Semiconductor-based devices are the most critical component ofthe new industrial age.

Why semiconductors?The reasons semiconductor technology dominates are:

Physical properties of semiconductor devicescan be altered rapidly. Response of semiconductor devices to externalinputs can be tailored in a manner that allowsthe devices to implement all needed informationprocessing operations. Semiconductor devicescan be used to implement Boolean logic,amplify signals, generate signals, store andretrieve information, etc.


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ELECTRONICMATERIALS


Electronic materials can be classified into three categories:

METALS SEMICONDUCTORS INSULATORS

Have very lowresistivities

(~106cm). Resistance isdifficult to alter ortailor.

Have resistivities that canbe altered by up to 10orders of magnitude bydoping or external biases.

Have extremely highresistivities.It is difficult to alter theresistivity throughdoping or externalfields.

Highest occupiedenergy band ispartially filled withelectrons.

Highest occupied energyband (valence band) iscompletely filled withelectrons at lowtemperature. Next band(conduction band) is empty.

High bandgapbetween valenceband (filled) andconduction band(empty) is large( 4 eV).

SEMICONDUCTORS: Conductivity of the material can be altered(in times as fast as 1 ps). Optical properties (absorption coefficient, refractive index)can be altered.

USEFULIN: Electronic devices: ON/OFF switches,high gain amplifiers...

Optoelectronic devices: Detectors, modulators,

lasers, light emitting diodes.

because because because

~>


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IMPORTANT SEMICONDUCTORS: DEMANDS

Like other industries, semiconductor technology feels the pressures of cost andperformance. The following show factors that influence cost and performance.

COST PERFORMANCE

Availability of substrate. Only silicon,gallium arsenide, indium phosphideand germanium substrate are widelyavailable.

Electronic devices: High speed switching. High frequency operation. High power operation togenerate microwave power.

High temperature operation. Integration for high densitychips.Ease of doping, contact formation,

insulator incorporation.Only silicon has a high qualityinsulator that can be incorporatedcheaplySi/SiO2.

It is difficult to dope large bandgapsemiconductors.

Optoelectronic devices: Light emission at 1.3 m or1.55 m for communicationapplication.

Light emission in red, green,and blue regimes for display. Short wavelength lightemission for optical storage. Long wavelength detectionfor night vision, thermalimaging. High speed laser diodes. High speed modulators,optical switches.

Availability of reliable technology tofabricate devices and circuits.

Inertia of existing technology. Billionsof dollars have been invested in Sitechnology.


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IMPORTANTSEMICONDUCTORS: ELECTRONICS

High speed low effective mass, superior mobility.High power applications large bandgap.

High temperature applications large bandgap.

Silicon(Si):

ADVANTAGES DISADVANTAGES

The most importantsemiconductor system.MOSFETs, bipolar devicesbased on Si form over 90% ofthe electronic market.

Not as fast as othersemiconductors. Not good forhigh power, high temperatureoperation. Cannot emit light,since it is an indirect gapmaterial.

Silicon-Germanium(Si-Ge):

Can be grown on Si substratesand processed using Sitechnology. Bipolar divices haveperformance rivaling GaAstechnology.

GaAs;GaAs/AlGaAs:

High speed devices fordigital/microwaveapplications. Performance is

superior to silicon.

More expensive than Sitechnology.

InP;InGaAs/InP:

High speed performance issuperior to GaAs basedtechnology. Can be combinedwith longhaul optoelectroniccommunication technology.

Expensive.

GaN/AlGaN

High power/high temperatureapplications.

Not as reliable yet; highcost.

SiC: High power/high temperatureapplications.

Reliability; cost.

Strained system. Needs greatcare in crystal growthconditions.


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IMPORTANTSEMICONDUCTORS: OPTOELECTRONICS

Cosiderations: Correct bandgap (Eg) for light emission/detection at appropriate wavelength.

Substrate availability for high quality growth.

LIGHTSOURCES

IMPORTANT MATERIALSYSTEMS

In1xGax AsyP1y;x = 0.47y for

lattice match to InP

Eg = 1.35 - 0.72y + 0.12y2eV

Lattice matched to InP.

Wide range of emission energies can beaccessed (~0.8 to 1.35 eV). Material technology is quite advanced andcan be exploited for communicationapplications.

GaAs1xPx

AlGaAsEg = 1.43 + 1.25x eV;x < 0.35

COMMENTS

SiC, GaN, ZnS, ZnSe, AlInGaPlarge gap materials which can

emit blue light and beyond.

Lattice matched to GaAs. Technology is quite advanced and can beused for LANs.

Material becomes indirect atx = 0.45. WithNdoping the LED can operate evenif the material is indirect and green lightemission ( = 0.55 m) can be achieved. The versatile material can provide red(GaAs0.6P0.4); orange (GaAs0.35P0.65:N),

and yellow (GaAs0.15P0.85:N) as well.

Important materials for blue lightemission (for displays, memories).

Technology for optical sources is notmature, but rapid progress is being made.


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IMPORTANTSEMICONDUCTORS: OPTOELECTRONICS

DETECTORS

Suitable for both 1.55 m and 1.3 m applications forlong haul applications.

Can be lattice matched to InP substrates.

InGaAsP(Tunable Eg)

Excellent material for long wavelength applications innight vision and thermal imaging. Can be used for 1.55 m and 1.3 m, but the technologyis not as advanced as the InP based technology.

HgCdTe(TunableEg)

AlGaSb(Tunable Eg)

Excellent optical properties. Can be used for long haul communications. Suffers from poor substrate availability, since it has tobe grown on GaSb, whose technology is not matured.

Indirect material with small near the bandedge. Has high imp/imp ratio and can be used in high

Si(Eg = 1.1 eV)

performance avalanche photodiodes for local areanetwork (LAN) applications. Not suitable for long haul communication at = 1.55m or 1.3 m.

Excellent material for long haul communications(at 1.55 m). Can be lattice matched to InP.

InGaAs(Tunable Eg)

Indirect material with small near the bandedge. Has high imp/impratio and can be used for avalanche

Ge(Eg = 0.7 eV)

photodiodes for both local area and long distancecommunications.

Direct gap material. Not suitable for high quality avalanche detectors, since

GaAs(Eg= 1.43 eV)

Not suited for long distance or LAN applications.

imp

~ imp.~


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TOOLSOFTHETRADE

Digital signalprocessing

chips (DSPs)

Data convertersAnalogs to digital (A/D)Digital to analog (D/A)

Chips for wirelesssystems

Digital logicchips

Application-specificintegrated circuits (ASICs)

Networkswitching chips

Microprocessors Programmable logic Memory andstorage chips

Chips for optical

communicationsystems

Microwave systems:

radar, military applicationsHigh power

switches

Information technology depends upon these chips to generate, receive, process, store,and transmit information.

Mula Sigiro An OVERVIEW Semiconductor Devices

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