Atomic Force Microscope(AFM)分析

第三章摻入銻(Sb)量子點之光性 PL 量測與 AFM 量測及分析

3.5 Atomic Force Microscope(AFM)分析

由圖3.9 AFM平面圖與圖3.10 AFM 3D圖，我們可以看到不論(a)2.0ML (b)2.2ML (c)2.8ML 各磊晶厚度，均有很明顯的兩群大小不同的量子點。我們將大尺寸的視為InSb-rich，小尺寸的視為InAs-rich，並將兩群量子點區分出來，

詳如表3.1 表3.1

ML 直徑 InAs-rich(小) 直徑 InSb-rich(大) 顆數比總顆數 2.0 15~40nm 180~190顆 ~50nm ~4顆 ~46 184~194 2.2 20~45nm 220~230顆 ~60nm ~20顆 ~12 240~250 2.8 45~55nm 170~190顆 ~65nm ~37顆 ~4.8 207~227

從顆數來看，2.0ML大顆的數目非常少，原因同PL解釋，顆數比差最多。2.2ML 二群顆數皆增加，這是由於2.0ML樣品是為了找出成核時間，導致2.2ML仍有部分量子點形成，另一方面InSb-rich開始由二維轉三維，使大顆量子點增多，顆數比變小。2.8ML小顆數目變少，大顆數目變多，推測是Sb持續加入，產生相分離並取代As位置[39]，故大顆漸漸取代小顆，顆數比最接近。

從直徑來看，隨著磊晶厚度增加，都變大顆。小顆量子點2.0ML與2.2ML，尺寸明顯都不均勻，2.8ML直徑變大但卻較均勻。大顆量子點2.0ML至2.2ML尺寸與密度變化大，這是由於InSb-rich的二維結構已經開始轉三維形成量子點所致。

第四章

摻入氮(N)量子點之電性量測的結果與分析

4.1 電流-電壓(I-V)、電容-電壓(C-V)量測結果

由於樣品基本參數已由本實驗室學長量測完畢，只列出結果如下：

I-V所得參數如下表：

樣品代號(結構) n R Is φ^Bn

tr502(InAs/InGaAs) 1.2 650Ω 9.28*10^-11 0.67v tr507(InAsN/InGaAs) 1.9 1832Ω 2.93*10^-11 0.76v

C-V 所得參數如下表:

樣品代號(結構) N^d V^bi φⁿ φ^Bn Tr502(InAs/InGaAs) 6.4*10¹⁶cm^-3 0.59v 49mev 0.64v Tr507(InAsN/InGaAs) 7.2*10¹⁶cm^-3 0.75v 47mev 0.79v

詳細內容請參考本實驗室學長論文[41]，我們會將相關資料拿來做參考，所有相關電性量測原理亦不再贅述。論文有關結論如下：(1)在無摻氮(N) Tr502 (InAs/InGaAs)樣品中的quantum peak，其quantum emission time 非常短，溫度 18K時仍小於 10-6s，沒有缺陷，由TEM得量子點密度為 3×10¹⁰cm^-2。(2)在摻氮 (N) Tr507(InAsN/InGaAs)樣品，溫度 300K時載子時間常數約 10^--3~10^-5秒，有缺陷能階產生，造成載子空乏。

4.2 導納頻譜(C-f G/f-f)量測量測對應的頻率，做成 Arrhenius plot，如圖 4.2(b)。依照活化能與捕獲截面積明顯分為兩部分，小偏壓活化能為 0.08~0.146 eV 與後面推算的捕捉位能障相

4.3 深層能階暫態頻譜(DLTS)與捕獲位能障(Capture barrier) 率(capture rate)。

(2)將(1)的步驟做四個不同的速率視窗(rate window)，由於在不同速率視窗

σ 是捕捉截面積(capture cross section)，v是平均速率(mean thermal velocity) 取，n是自由載子濃度(free carrier concentration)取摻雜濃度

， 4.4 10× 7cm/ sec

16 3

8 10 / cm×

σ

^∞是與溫度無關的係數，E^σ是捕捉位能障(capture barrier)大小，

KB是波茲曼常數(Boltzmann constant)。

依照上述步驟，求得如圖 4.4(a)不同速率視窗之對應溫度及其捕捉速率與(b) 捕捉位能障，由此判定此樣品有捕捉位能障E^σ=0.151eV。

圖4.3(a)(b)(c)(d)為不同填充偏壓四個速率窗DLTS圖，飽和填充時間隨著載子時間常數變大而愈大，詳細載子時間常數(飽和填充時間估計值)變化如下：

τ=0.86ms(0.7ms)→τ=2.15ms(2ms)→τ=4.3ms(4ms)→τ=8.6ms(8ms)

隨著載子時間常數增加，載子速率變慢，對應溫度變低，即對應的缺陷捕捉載子

4.4 暫態電容(Transient)量測

圖 4.5(a)(b)為-1~-1.5v暫態電容量測，將此暫態電容以指數函數模擬求出對應的時間常數，再對溫度做Arrhenius plot如圖 4.6(a)(b)，在此偏壓下，不論 Emission或Capture活化能均約為 0.07~0.08eV，捕捉載子能力又弱，為自由載子訊號。接著我們將偏壓加深到-1.5~-2v，如圖 4.7(a)(b)量測溫度 120K~140K，

此訊號來源應為缺陷載子，故將其△C(t)/△C(0)取對數座標對時間做圖，如圖 4.8(a)(b)非常近似於線性，顯示暫態電容為指數函數。同理圖 4.9(a)(b)為其 Arrhenius plot，我們發現Emission的活化能為 0.25eV，缺陷濃度同DLTS推估 Nt=2.8×10¹⁵cm^-3，Capture活化能為 0.19eV，Nt=1.8×10¹⁵cm^-3。

4.5 缺陷能帶模擬

由以上電性量測歸納，此缺陷能階位於傳導帶下方約 0.2~0.25eV，缺陷濃度約 1~2.8×10¹⁵cm^-3，並且由於載子空乏造成捕捉位能障高度 0.15eV。為了再次確認，

參考論文[41]我們引用C-V得來的縱深分佈得到空乏區寬度約為 0.25μm。假設缺陷要能造成空乏區寬度 0.25μm與位能障高度 0.15eV，則所需要的缺陷濃度由空

乏區寬度

2

_s 2 t

W E

eN ε

⎡ ⎤

= ⎢ ⎣ ⎦ ⎥

估計為 1.06×10¹⁵cm^-3，恰好符合量測到的缺陷濃度。因此我們做了此缺陷的能帶模擬圖，如圖 4.10，來表示量測到的缺陷參數。

第五章結論

摻入銻量子點經由 PL 與 AFM 的分析，量子點分為兩群，得到銻元素有相分離的現象，此現象導致 InSb-rich 量子點較晚出現，而後量子點隨著磊晶厚度增加而增加。由磊晶結果得知，形成量子點的臨界厚度由 1.68ML(19.9sec)後推約至 2.0ML(24sec)，表示二維轉三維的臨界厚度增加，Sb 延緩量子點形成，此即 Sb 的表面活化效應。由低溫半高寬判定，2.8ML 的 uniformity 最好，其他較差。由變溫 PL 與半高寬知，低溫載子有穿隧現象，高溫載子容易由 InAs-rich 量子點跳到 InSb-rich 量子點，隨著磊晶厚度增加，密度與尺寸變大，此現象於更低溫發生。

無摻氮樣品溫度 18K時載子時間常數仍小於 10^-6秒，沒有缺陷。有摻氮樣品於溫度 300K載子時間常數約 10^--3~10^-5秒，有缺陷能階產生，造成載子空乏。以深層能階暫態頻譜與電容暫態頻譜量測，此缺陷能階位於傳導帶下方約 0.2~0.25eV，隨著偏壓加大能階愈深，為能階分佈很廣的缺陷，缺陷濃度約 1~2.8×10¹⁵cm^-3。此缺陷的暫態電容為可以填充達到飽和的指數函數，推測應該是摻入氮引起的點缺陷。DLTS改變填充偏壓時間與不同速率視窗，求得捕捉位能障高度 0.15eV，再配合縱深分佈的空乏區寬度 0.25μm，要造成此空乏所需要的的缺陷濃度為

1.06×10¹⁵cm^-3。因此電性量測結果有很高的一致性，將其作成缺陷的能帶模擬圖，

如圖 4.10，推測直接將氮摻入量子點會於量子點位置產生缺陷造成載子空乏，使得原本無摻氮量子點非常短的時間常數變長為 10^-3~10^-5秒(室溫)。因此我們相信可以藉由摻入氮元素於量子點來調變所需要的時間常數。

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GaAs GaAs

圖2.1 摻入銻(Sb)量子點系列樣品的能帶與結構圖 InAs QDs doped with Sb

(24s、26s、32.9s) (2.0ML、2.2ML、2.8ML) 0.256Å/sec，485ºC

n-GaAs, 0.3μm, 595ºC Si：3×10¹⁶cm^-3, 3.03Å/s

n⁺-GaAs Substrate n-GaAs 0.3μm, 595ºC Si：3×10¹⁶cm^-3, 3.03Å/s

在同樣長晶條件下

InAs QDs without Sb InAs QDs doped with Sb

19.9s形成量子點，約1.68ML 24s形成量子點，約2.0ML

量子點形成判定是藉由反射式高能電子束繞射(Reflection High-Energy Electron Diffraction, RHEED)圖形

GaAs

圖2.2 摻入氮(N)量子點與其對照樣品的能帶與結構圖 Al

0.3µm GaAs Nd=8×10¹⁶cm^-3

GaAs

In

_0.14

GaAs

0.3µm GaAs

InAs ( QDs )

InAsN

_17%

( QDs )

Nd=8×10¹⁶cm^-3

n⁺-GaAs substrate

In Si

圖2.3 PL量測系統之架構圖

圖2.4 InAsSb ternary alloys X-ray分成InAs-rich與InSb-rich兩群 Ref. Journal of Crystal Growth vol.237–239, p1519–1524, 2002

Laser 532nm

1.3W VNDF

Chopper Focus lens

Vacuum and cooling system

Long-pass filter Ref. Signal

Lock-in Amplifier

Monochromator InGaAs

GPIB Interface

Multi-meter

photodetector

(a)

(b)

(c)

防震系統

圖2.5 (a)AFM懸臂樑及針頭TEM圖(圖片來源Ultrasharp公司網站) (b)凡得瓦力與距離的關係圖

(c)AFM示意圖

(a)

1000 1100 1200 1300 1400 1500 0.0

2.0x10^-3 4.0x10^-3 6.0x10^-3 8.0x10^-3

300K 50K dots-in-well 2.7ML 10mW

int ens ity (a. u.)

wavelength(nm)

(b)

1000 1100 1200 1300 1400 1500 0.0

1.0x10^-2 2.0x10^-2 3.0x10^-2 4.0x10^-2

1mW 100mW dots-in-well 2.7ML 300K

In tensit y(a. u. )

Wavelength(nm)

圖3.1 一般dots-in-well量子點 (a) 變溫PL圖 (b)室溫300K變功率PL圖

1000 1100 1200 1300 1400 1500

Inte nsi ty( a.u .)

Wavelength(nm)

dots-in-well 2.7ML 300K

1mW 100mW

圖3.2 一般dots-in-well量子點室溫300K變功率正規化調整PL圖

InAs-rich InSb-rich

0.52eV

0.734eV 1.424eV 0.83eV

0.24eV

量子點尺寸量子點尺寸

圖 3.3 二群量子點室溫能階模擬圖

900 1000 1100 1200 1300 1400

dots+Sb 2.0ML 25K

Intensity(A.U.)

900 1000 1100 1200 1300 1400 0.0

6.0x10^-2

dots+Sb 2.2ML 25K

intensity (a.u.)

900 1000 1100 1200 1300 1400 0.0

dots+Sb 2.8ML 25K

Wavelength(nm) (a1)2.0ML (b1)2.2ML (c1)2.8ML

900 1000 1100 1200 1300 1400

Intensity(A.U.)

Wavelength(nm)

dots+Sb 2ML 25K

15mW

900 1000 1100 1200 1300 1400

dots+Sb 2.2ML 25K

Intensity (A.U.)

900 1000 1100 1200 1300 1400

dots+Sb 2.8ML 25K

Intensity(A.U.) (a2)2.0ML (b2)2.2ML (c2)2.8ML

900 1000 1100 1200 1300 1400 0.000

0.002 0.004 0.006

dots+Sb 2.0ML 300K

Wavelength(nm)

900 1000 1100 1200 1300 1400 0.0000

0.0005 0.0010 0.0015 0.0020

dots+Sb 2.2ML 300K

intensity (a.u.)

900 1000 1100 1200 1300 1400 0.0000

0.0005 0.0010 0.0015

dots+Sb 2.8ML 300K

Intensity(A.U.) (a1)2.0ML (b1)2.2ML (c1)2.8ML

900 1000 1100 1200 1300 1400

Intensity(A.U.)

Wavelength(nm)

dots+Sb 2ML 300K

7.5mW 750mW

(a2)

900 1000 1100 1200 1300 1400

10mW 90mW

dots+Sb 2.2ML 300K

Wavelength(nm)

Intensity (A.U.)

900 1000 1100 1200 1300 1400

32mW 320mW

dots+Sb 2.8ML 300K

Intensity(A.U.)

Wavelength(nm)

(b2)

(c2)

圖3.5 室溫300K變功率正規化調整PL圖 (a2)2.0ML (b2)2.2ML (c2)2.8ML

間距小

( 密度大 ) 間距大

( 密

度小 )

圖3.6 載子侷限空間分佈耦合機率圖

900 1000 1100 1200 1300 1400

900 1000 1100 1200 1300 1400 0.0

5.0x10^-3 1.0x10^-2 1.5x10^-2 2.0x10^-2

2.5x10^-2

dots+Sb 2.2ML

intensity (a.u.)

900 1000 1100 1200 1300 1400 0.0

dots+Sb 2.8ML

Intensity(A.U.)

(a1)2.0ML (b1)2.2ML (c1)2.8ML

800 900 1000 1100 1200 1300 1400 1500 1600

dots+Sb 2.0ML

Intensity(A.U.)

Wavelength(nm)

25K 70K 115K 150K 180K 200K 250K 275K 300K

(a2)

900 1000 1100 1200 1300 1400 300K

25K 200K

Intensity (A.U.)

Wavelength(nm)

dots+Sb 2.2ML

(b2)

圖3.7 變溫正規化調整PL圖 (a2)2.0ML (b2)2.2ML

950 1000 1050 1100 1150 1200 1250 1300 1350 1400

dots+Sb 2.8ML

Intensity(A.U.)

Wavelength(nm)

150K 120K 80K 60K 40K 25K

(c2)

950 1000 1050 1100 1150 1200 1250 1300 1350 1400

dots+Sb 2.8ML

Intensity(A.U.)

Wavelength(nm)

210K 190K 180K 170K 160K 150K

(c3)

圖3.7 變溫正規化調整PL圖 2.8ML (c2)低溫區(c3)高溫區

0 50 100 150 200 250 300 0.06

0.08 0.10 0.12 0.14

FWHM(eV)

T(K) InAs-rich

ML2.0 ML2.2 ML2.8

0 50 100 150 200 250 300

0.03 0.04 0.05 0.06 0.07

InSb-rich

FWHM(eV)

T(K)

ML2.0 ML2.2 ML2.8

圖3.8 各樣品半高寬隨溫度變化圖 (a)InAs-rich量子點

(b)InSb-rich量子點

(a)

(b)

(c)

圖3.9 AFM平面圖

(a)2.0ML (b)2.2ML (c)2.8ML

(a)

2.0ML

(b)

2.2ML

(c)

2.8ML

圖3.10 AFM 3D圖

(a)2.0ML (b)2.2ML (c)2.8ML

10² 10³ 10⁴ 10⁵ 10⁶ 10⁷ 10⁸

InAsN/InGaAs 300K

C(pF)

InAsN/InGaAs 300K

-2V -1.5V

1000 10000 1000001000000 1E7 1E8 0

50 100 150

InAsN/InGaAs -1.5volt

G/f(pS/Hz) ln( τ T

) (sec-K

)

-1.5V Ea=0.34eV σ=4.16E-16 cm²

-0.5V Ea=0.08eV σ=2.63E-19 cm² -1V Ea=0.13eV σ=1.13E-18 cm² -2V Ea=0.38eV σ=5.74E-16 cm² -2.5V Ea=0.41eV σ=3.10E-16 cm²

圖4.2 (a)變溫G/f-f量測偏壓1.5v (b)各偏壓的Arrhenius plot

(a)

150 200 250 300

-1.0

v=-1~-1.5volt

=0.86ms

∆ C(pF)

T(K)

filling pulse tp 0.05ms

150 200 250 300

-1.0

v=-1~-1.5volt

=2.15ms

∆ C(pF )

T(K)

filling pulse tp 0.05ms

50 100 150 200 250 300

filling pulse tp 0.05ms

v=-1~-1.5volt

=4.3ms

(c)

v=-1~-1.5volt

=8.6ms

∆ C(pF)

T(K)

filling pulse tp 0.05ms

-1 0 1 2 3 4 5 6 7 8 -4.0

-3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0

ln(1-S(t

)/S( ))

t

(ms)

τ=8.6ms C=0.824 s^-1 T=205K τ=4.3ms C=1.468 s^-1 T=215K τ=2.15ms C=2.067 s^-1 T=228K τ=0.86ms C=3.243 s^-1 T=242.5K

(a)

4.0 4.2 4.4 4.6 4.8 5.0

-57.0 -56.5 -56.0 -55.5 -55.0

ln( σ ) (cm

)

1000/T(1/K)

E

_σ

=0.151eV

(b)

圖4.4 (a)不同速率視窗之對應溫度及其捕捉速率 (b)捕捉位能障

(a) (a) -1~-1.5v Emission

(b) -1.5~-1v Capture

(a)

ln( τ T

) (sec-K

)

1000/T(1/K)

ln( τ T

) (se c -K

)

1000/T(1/K)

圖4.6 暫態電容(Transient)量測所得Arrhenius plot (a) -1~-1.5v Emission

(b) -1.5~-1v Capture

(b) (a) -1.5~-2v Emission

(b) -2~-1.5v Capture

0 50 100 150 200 0.01

0.1 1

Emission

C(t)/

C(0)

Time(sec)

120K 125K 130K 135K 140K

(a)

0 10 20 30 40 50

0.01 0.1 1

Capture

δ C(t )/ δ C(0)

Time(sec)

120K 125K (b)

圖4.8 △C(t)/△C(0) (a)Emission (b)Capture

7.0 7.5 8.0 8.5 10

11 12 13

Emission

ln( τ T

) (sec-K

)

1000/T(1/K)

Ea=0.25 eV σ =2.5E-16 cm²

(a)

8.0 8.2 8.4

11.0 11.5 12.0

Ea=0.19eV σ =3.4E-18 cm²

Capture

ln (

T

)(sec-K

)

1000/T (1/K)

(b)

圖4.9 暫態電容(Transient)量測所得Arrhenius plot (a) -1.5~-2v Emission (b) -2 ~-1.5v Capture

圖4.10 缺陷能帶模擬圖

Ec

capture barrier Defect level 0.15eV 0.2~0.25eV

Et Defect concentration

1×10

¹⁵

cm

^-3

Depletion width

0.25μm

在文檔中 InAs/GaAs自聚式量子點掺入銻與氮之特性研究 (頁 27-0)

第三章 摻入銻(Sb)量子點之光性 PL 量測與 AFM 量測及分析

3.5 Atomic Force Microscope(AFM)分析

第四章

摻入氮(N)量子點之電性量測的結果與分析

σ

2

W E

eN ε

⎡ ⎤

= ⎢ ⎣ ⎦ ⎥

第五章 結論

參考文獻

GaAs

GaAs

In

GaAs

InAs ( QDs )

InAsN

( QDs )

300K 50K dots-in-well 2.7ML 10mW

int ens ity (a. u.)

wavelength(nm)

1mW 100mW dots-in-well 2.7ML 300K

In tensit y(a. u. )

Wavelength(nm)

Inte nsi ty( a.u .)

Wavelength(nm)

dots-in-well 2.7ML 300K

1mW 100mW

dots+Sb 2.0ML 25K

dots+Sb 2.2ML 25K

dots+Sb 2.8ML 25K

dots+Sb 2ML 25K

dots+Sb 2.2ML 25K

dots+Sb 2.8ML 25K

dots+Sb 2.0ML 300K

dots+Sb 2.2ML 300K

dots+Sb 2.8ML 300K

dots+Sb 2ML 300K

7.5mW 750mW

10mW 90mW

dots+Sb 2.2ML 300K

32mW 320mW

dots+Sb 2.8ML 300K

間距小

( 密 度 大 ) 間距大

( 密

度 小 )

dots+Sb 2.2ML

dots+Sb 2.8ML

dots+Sb 2.0ML

dots+Sb 2.2ML

dots+Sb 2.8ML

dots+Sb 2.8ML

2.0ML

2.2ML

2.8ML

C(pF)

InAsN/InGaAs 300K

InAsN/InGaAs -1.5volt

G/f(pS/Hz) ln( τ T

) (sec-K

)

v=-1~-1.5volt

=0.86ms

∆ C(pF)

T(K)

v=-1~-1.5volt

=2.15ms

∆ C(pF )

T(K)

v=-1~-1.5volt

=4.3ms

v=-1~-1.5volt

=8.6ms

∆ C(pF)

T(K)

ln(1-S(t

)/S( ))

第三章摻入銻(Sb)量子點之光性 PL 量測與 AFM 量測及分析

第五章結論

( 密度大 ) 間距大

度小 )