MaterialsMaterials Conductive materials – valence band overlaps Conductive materials – valence band overlaps

the conduction bandthe conduction band Non conductive materials – valence band is Non conductive materials – valence band is

separated from conduction band and electrons separated from conduction band and electrons can not easily get to the conduction bandcan not easily get to the conduction band

Semiconductor materials – conduction band is Semiconductor materials – conduction band is close to valence band and electrons can easily close to valence band and electrons can easily jump from the valence band to the conduction jump from the valence band to the conduction band with an energy sourceband with an energy source

SiliconSilicon Silicon is an elementSilicon is an element Silicon is the first or second most abundant Silicon is the first or second most abundant

element on the earthelement on the earth Sand is a form of siliconSand is a form of silicon Silicon is know as a semiconductor Silicon is know as a semiconductor

because under certain conditions it can because under certain conditions it can conduct electricity (electrons)conduct electricity (electrons)

Silicon is the most widely used material for Silicon is the most widely used material for today’s microelectronics today’s microelectronics

Silicon was not the first semiconductor Silicon was not the first semiconductor material used, germanium was first.material used, germanium was first.

Group 4 Group 4

SiliconSilicon From the periodic chart you can see From the periodic chart you can see

that silicon is a group 4 elementthat silicon is a group 4 element Group 4 elements have 4 electrons in Group 4 elements have 4 electrons in

their outer most electron shelltheir outer most electron shell Silicon is the most common material Silicon is the most common material

currently used for solar cellscurrently used for solar cells

Why is silicon an excellent Why is silicon an excellent microelectronics material?microelectronics material?

1.1. It is very abundantIt is very abundant2.2. It can be grown into a single orientation It can be grown into a single orientation

crystalcrystal3.3. It can be made electrically active easilyIt can be made electrically active easily4.4. It can be made to conduct electrons It can be made to conduct electrons

with a small applied potentialwith a small applied potential5.5. It has a naturally forming oxide that It has a naturally forming oxide that

acts as an insulating and diffusion acts as an insulating and diffusion barrierbarrier

Silicon ingot ready to be cut Silicon ingot ready to be cut into wafersinto wafers

Silicon ingot being grownSilicon ingot being grown

Two Two dimensional dimensional schematic schematic of three of three

dimensional dimensional crystalcrystal

Group 3 Group 3 ElementsElements

P type doping P type doping – Positive, – Positive,

electron short, electron short, also called a also called a

holehole

Group 5 Group 5 elementselements

N-type N-type doping – N is doping – N is

negative, negative, electron richelectron rich

Combing n-Combing n-type silicon type silicon and p-type and p-type

silicon gives a silicon gives a pn junctionpn junction

Silicon crystal planes and Silicon crystal planes and Miller IndexMiller Index

Silicon wafers have “flats” Silicon wafers have “flats” to denote what type of to denote what type of

wafer it iswafer it is

The futureThe future• Silicon will continue to play a dominant Silicon will continue to play a dominant

role but other semiconductor materials role but other semiconductor materials will play an increasing role will play an increasing role

• III-V semiconductor materials made III-V semiconductor materials made from group III and group V elements from group III and group V elements are now common ( GaAs, InP, AlN )are now common ( GaAs, InP, AlN )

• II-VI semiconductor materials are being II-VI semiconductor materials are being investigated for special applicationsinvestigated for special applications

• SiC, “diamond like carbon”, and SiGe SiC, “diamond like carbon”, and SiGe are also of interestare also of interest

AssignmentAssignment• Submit a schedule of times you can Submit a schedule of times you can work in the clean roomwork in the clean room• Must be at least a 2 hour time block Must be at least a 2 hour time block • You can work with a friend but each You can work with a friend but each student will be required to build their student will be required to build their own solar cellown solar cell