奈米物理特論

半導體奈米結構之成長與光電特性

交通大學電子物理系 周武清 教授

大綱:Part I: 半導體奈米結構成長---------

分子束磊晶(MBE, molecular beam epitaxy)半導體奈米結構形貌研究---AFM

Part II: 半導體奈米結構光電特性---PhotoluminescencePart III: 半磁性半導體奈米結構之自旋磁光特性

清華大學物理系奈米物理特論 2008/03/13 上課內容 (I)

有幾種製作半導體奈米結構或量子點的方法?

(a) Microcrystallites in glass(b)Quantum dots fabricated by lithographic techniques(c) Self-organized quantum dots (d) Chemical synthesis

Top down

Bottom up

Stranski-Krastanow (SK)從二維到三維長晶模式(wetting layer, WL)

Volmer-Weber (VW)三維長晶模式

Frank-van der Merwe二維長晶模式

Self assembled (organized) quantum dots, SAQD.

WL

u(H, n 1 , n 2 , ε) = Eml(n 1) + n2 E isl + (H - n 1 - n 2) E ripEml(n1)=∫dn{G+ Δ[Θ(1-n) + Θ(n-1) e -(n-1)/a]} G=Cε2 – ΦAAEisl= gCε2 – ΦAA + E0[ -(2/x2)lne1/2x + α/x + β(n2)/x3/2]

Erip = Eisl (x→∞ ) = gCε2 – ΦAA

Buffer layerEpitaxial layer

u(H, n 1 , n 2 , ε) = Eml(n 1) + n2 E isl + (H - n 1 - n 2)E rip

I. Daruka and A.L. Barabasi, APL 72, 2102 (1998)

Energy Gap vs Lattice Constant(材料)菜色豐富千變萬化

超高真空操作程序與重要性、分子束源種類及調控磊晶速率

如何製作半導體奈米結構?

molecularsource

shutter

substrate

buffer

strain

分子束磊晶術

碲化鋅量子點之表面高低(明暗)形貌直徑約10-30奈米 AFM

O. Leifeld et al., APL74, 994 (1999)

半導體奈米結構之形狀

半導體奈米結構之形狀

PRL64, 1943 (1990)

半導體奈米結構之形狀

H.C. Ko et al., APL70, 3278 (1997)

半導體奈米結構之形狀

APL80, 4232 (2002)

Ref. D. Litvinov et al.APL 81, 640 (2002)

Ref. S.Lee et al., Phys. Rev. Lett. 81, 3479 (1998)

Day2 RT air Day2 RT N2 Day2 LT N2

Day3 RT air Day3 RT N2 Day3 LT N2

Day1CdSe QDs 3 ML

Day 1 Day 2 Day 3 Day 4 Day 5

Dot size vs. Time

6.268.117.680.729.290.7312.5100.54H (nm)D (nm)T (days)

12

day 4

day 1

70 80 90 100

6

8

10

12

Day 4

Day 3

Day 2

Day 1

Hig

ht (n

m)

Diameter (nm)

Vav(t)ρ(t)=const. ρ(t)=const. Rav(t)-3

Mass transfer involves kinetic surface barrier for the atom detach fromthe edge of island Rav(t) ~ t1/3

Therefore, ρ(t) ~ t-1

0 1 2

2x1010

3x1010

dot i

nten

sity

(cm

-2)

days (log scale)

ZnSe CdSe 2.5 MLs

CdSe 2.7 MLsCdSe 3.0 MLs

AFM non-contact mode

Find the WL thickness, 2D to 3D growth transition.

CdSe (3.0 MLs)/ZnSe

u(H, n 1 , n 2 , ε) = Eml(n 1) + n2 E isl + (H - n 1 - n 2)E rip

I. Daruka and A.L. Barabasi, APL 72, 2102 (1998)

2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0 the large dot in this work the small dot in this work ref. 15 ref. 24

ripen growth incoherent 2-D growth

S-Kcoherent growth

dot d

ensi

ty (1

09 c

m-2)

average coverage (MLs)2.6 2.8 3.0 3.2 3.4 3.6 3.8

0

40

80

120

two type of QDs

larger dot

smaller dot

average coverage (MLs)

aver

age

diam

eter

(nm

)

2

4

6

8

10

S-Kcoherent growth

incoherent 2-D growthripen growth

average height (nm)

0 3000 6000 9000 12000

0.0

0.2

3.0 MLs 3.3 MLs 3.5 MLs

perc

enta

ge (%

)

dot volume (nm3)

The importance of size control

Two types of QDs.

Effect of ZnSe partial capping on the ripening dynamics of CdSe quantum dots

Typical AFM images of CdSe QDs samples capped with ZnSelayers of (a) 0, (b) 1, (c) 2, and (d) 3 ML. The temperature forZnSe capping was 260 °C.

Dependence of dot height on time. Curve A dashed dots expresses

Curve B dashed line represents the ripening of a QD which has a faster ripening rate.Curve C solid line describes

Lai et al.APL 90, 083226 (2007)