Heterojunctions. Heterojunctions

Transcription

1 Heterojuctios Heterojuctios Heterojuctio biolar trasistor SiGe GaAs 4 96, , Ch. 9 3 Defiitios eφ s eχ s lemet Ge, germaium lectro affiity, χ (ev) 4.13 Si, silico 4.01 GaAs, gallium arseide 4.07 C AlAs, alumiium arseide 3.5 F V 4 96, , Ch

2 c 1 c Defiitios c 1 v 1 c v straddlig v 1 staggered v c 1 v 1 c broke ga 4 96, , Ch. 9 5 v ad diagram eφ s eχ eφ s eχ c f Δ C c g g v Δ V f v 4 96, , Ch. 9 6

3 ad diagram Δ c e( χ χ ) eφ s eχ eφ s eχ c f g Δ C g c Δ c + Δ v g g Δ g v Δ V f v 4 96, , Ch. 9 7 ad diagram - juctio ev bi ev bi ev bi eφ s eχ c eφ s eχ ev bi ev bi Δ C g c f f g v v Δ V x x x 0 x x 4 96, , Ch

4 lectrostatics ev bi ev bi ev bi eφ s eχ ev bi eφ s eχ ev bi Δ C g c c f g f v v Δ V ev bi φ φ s [ eχ + ( )] [ eχ + ( )]... Δ v s g + kt l x x x 0 x x F 0 0 v v v 4 96, , Ch. 9 9 g F v lectrostatics oisso equatio: d φ( x) d( x) dx dx ρ ε e ε e ε d lectric field becomes: ( x + x) a ( x x) < oudary coditio ( x x ) ( x > x ) , , Ch

5 lectrostatics lectric flux desity cotiuous across juctio: ε ( x 0) ε ( x 0) x Subsequet itegratio of electric field gives built-i voltage: d a x V bi V bi + V bi edx eax + ε ε... ad for the deletio regio width: W x + x ε ε e d ( d + a ) Vbi ( ε + ε ) a 4 96, , Ch d a ad diagram - juctio eφ s eχ c Δ C eφ s eχ g c f v f Δ V g 4 96, , Ch. 9 v 1 5

6 ad diagram - juctio Δ C c f g ev bi ev bi c f v Δ V g v 4 96, , Ch ad diagram - juctio c f c f g v g -dimesioal electro gas (-DG) V(x) 1 F v 0 z , , Ch

7 ad diagram - juctio with gradig c f c f g v g -dimesioal electro gas (-DG) V(x) v 1 F 0 z , , Ch Curret behaviour i heterojuctios Characteristics of the juctios betwee the differet materials: High recombiatio/geeratio rate. There is a otetial barrier, ϕ b0. At metal-semicoductor juctio: Metal is ifiite good coductor I a - juctio: drift-diffusio model Metal-semicoductor: how may electros ca overcome the otetial barrier 4 96, , Ch

8 Charge trasort eφ s eχ c Δ C eφ s eχ g c f f v Δ V g v Differeces with homojuctios: arrier height ot the same for electros ad holes Oe bad (i this case the coductio bad) similar to a rectifyig metal-semicoductor juctio (ffective mass differet o either side juctio) 4 96, , Ch Curret-voltage relatio eva Geeral curret-voltage relatio: J J S ex 1 kt For a rectifyig metal-semicoductor juctio J S * eφ * 4 A T ex kt, with : A * πmk 3 h ad a - juctio: J S ed L 0 + ed L , , Ch

9 Heterjuctio iolar Trasistor mitter ++ + Collector ase C mitter ++ + Collector ase C 4 96, , Ch C C F C F V V 4 96, , Ch

10 C C F V C V C F V V 4 96, , Ch. 9 1 Miority carrier cocetratio i the base Study trasort equatio (o electric field, o geeratio, ad static equilibrium): ( δ ( x) ) δ ( x) D 0 x τ Solve this differetial equatio with the correct boudary coditios (!)...ff...ff...: δ ( x) 0 x 0 ev ex kt ev ex kt 0 x x 1 sih sih L x sih L 1 ( x x) x x L 4 96, , Ch. 9 10

11 mitter ase Collector (x) (x') 0 0 (x'') C0 x' x x' 0 x 0 x x x'' 0 x' x x'' 4 96, , Ch. 9 3 Small-sigal commo base curret gai α J J + J γ J J C α T J J + J + J R + J δ mitter ijectio efficiecy factor, γ: ratio electro diffusio curret / total diffusio curret ase trasort factor, α T : determies the efficiecy of charge trasort across the base, i other words is a measure for the recombiatio losses i the base Recombiatio factor, δ: measure for the quality of the emitterbase juctio ad gives a idicatio about the recombiatio 4 96, , Ch

12 C C F C F V V 4 96, , Ch. 9 6 ad diagram SiGe HT C C F C F V V V 4 96, , Ch

13 ad diagram HT V b φ b φ e eχ b eφ sb eχ c eφ sc eχ e eφ se Δ C c gb f gc ge Δ V ev h v 4 96, , Ch. 9 8 Curret gai Commo-emitter curret gai: β 0 α0 α 1 0 γαtδ γ 1 γα δ 1 γ T Substitutig for γ: β 0 D D x x 0 0 For the thermal equilibrium carrier cocetratios we have: 0 0 i, i, C, C, V, V, ex ex ( / kt ) ( / kt ) g, g, 4 96, , Ch

14 Curret gai β 0 ~ ex g, kt g, Δ ex kt g Curret gai icreases exoetially with bad ga differece Larger curret gai allows higher base doig Higher base doig allows arrow base width arrow base width imlies a faster device 4 96, , Ch