在本論文中，我們使用了傳輸線模型法(TLM)研究在P型鍺之上使用銀鎵合金結構形成歐姆接觸的可能性，為了得到最低的特徵阻值，尋求最合適的Ga還有最佳的回火溫度和時間，實驗的結果指出當增加銀鎵合金裡鎵的含量到達25％得到較低的特徵阻值，其特徵阻值會降到最低( ρc~1.00×10-4Ω-cm2 )，回火溫度為325℃而回火時間為1分鐘。此外我們將此條件來做變溫量測，量測溫度由70℃增加到120℃時，其特徵電阻隨著溫度上升而增加。
此外，將具有最低特徵阻值的歐姆接觸金屬組成結構(亦即Ag-Ga(25%)) 蒸鍍在三接面太陽能電池的正型電極，來探討Ag-Ga歐姆接觸金屬材料應用於元件上之後的元件特性，如同歐姆接觸金屬蒸鍍在正型鍺基板上的結果，太陽能電池的效率(Eff)、填充因子(FF)、短路電流(Isc)、開路電壓(Voc)皆在最佳歐姆接觸金屬組成的最佳條件下有最好的表現。

In this dissertation, the formation of Ag-Ga alloyed film is adopted by means of the transmission line model method (TLM) to study the feasibility of forming p-type ohmic contact to p-Ge material. We sought for the optimum of the Ga and the suitable annealing temperature and time for the lowest specific contact resistance ρc. Then, we found out that the optimum structure of the Ag and Ga and the suitable annealing temperature and time for the lowest specific contact resistance ρc. Experimental results indicate that when the content of gallium in the silver-gallium, up to 25%, respectively, the lowest value (ρc ~1×10-4 Ω-cm2) of specific contact resistance could be attained where the sample is annealed at 325℃ for one minute. In addition to the room temperature results, the variations of specific contact resistance at the elevated temperatures ranging from 70℃ to 120℃ are also detailed .
Furthermore, the optimum ohmic contact structure Ag-Ga(25%) is selected as the p-type electrode for the InGaP / GaAs / Ge triple-junction (TJ) solar cells. Then, we measured the efficiency (Eff), fill factor (FF), open circuit voltage (Voc) and short circuit current (Isc) of solar cells are measured to obtain the optimum ohmic contact formation condition of Ag-Ga(25%) for the best solar cell performance.

摘要…………...…………………………………………………………….I
Abstract…………………………………………………………...……...II
Acknowledgment……………………………………………………….....III
Content………………………………………………………………........IV
Figure Captions………………………………………………………...VI
List of Tables…………………………………………………………....X
Chapter 1 Introductions……………………………………….…………..1
Chapter 2 Theoretic foundations…………………………….……………3
2.1 Metal and Semiconductor contact theory…………………………….…3
2.2 Transmission Line Model (TLM)…………………………………..….5
2.3 Measurement method……………………………………….……..…...7
2.4 Basic concepts of the solar cell………………………………..………8
2.5 The equivalent circuit analysis of a solar cell…………………………9
2.6 Fundamental solar cell parameters…………………………………….10
Chapter 3 Fabrication process and the electric characteristic of
ohmic contact metals………………….………………………….……...11
3.1 Ge TLM Fabrication Process……………………………………….11
3.1.1 Wafer cleaning process………………………………………………11
3.1.2 Photolithography process………………………………….…………12
3.1.3 Metal deposition…………………………………………..……..…..12
3.1.4 Mesa etching process………………………………………..….…...13
3.2 Results and discussions……………………………………………..…...13
3.2.1 Specific contact resistance………………………………………………14
3.3 Surface morphology ………………………………………………………17


Chapter 4 Characteristics of the InGaP/GaAs/Ge triple -junction solar
cell…………………………………………………………………..……..18
4.1 Processes of fabricated solar cell…………..………..…………………….18
4.2 Current-Voltage (I-V) measurement system…………………………........19
4.3 Characteristics of InGaP/GaAs/Ge TJ solar cell……………………..……19
Chapter 5 Conclusions…………………………………………………...21
References…………………………………………………………………43


Figure Captions
Figure 1.1 Schematic cross-sections of the GaInP/GaAs/Ge triple junction
solar cell……………………………………………………………………22
Figure 2.1 A Schottky barrier formed by contacting an n-type semiconductor
with a metal having a larger work function: band diagram for the metal and
semiconductor before joining……………………………………………...….23
Figure 2.2 Band diagram for the junction at equilibrium…………………….24
Figure 2.3 Ohmic metal-semiconductor contact：Φm＜Φs for an n-type
semiconductor at the equilibrium band diagram for the junction…………..…24
Figure 2.4 Ohmic metal-semiconductor contact：Φm＞Φs for an p-type
semiconductor at the equilibrium band diagram for the junction………….….25
Figure 2.5 Ohmic metal-semiconductor contact：Heavy doped for an n-type
semiconductor at the equilibrium band diagram for the junction…………..…25
Figure 2.6 Ohmic metal-semiconductor contact：Heavy doped for an p-type
semiconductor at the equilibrium band diagram for the junction…………..…26
Figure 2.7 A slab of material with ohmic contacts on the two ends exhibits a
resistance composed of the end -to-end resistance of the material, plus the two
contact resistance……………………………………………………………...26
Figure 2.8 The approaches used to model the ohmic contact of a transmission
line………………………………………………………………………..……27
Figure 2.9 Basic pattern used to experimentally determine contact resistance
parameters. Ohmic contacts are separated by increasing distance……………27
Figure 2.10 Plot of measured resistance as a function of contact separation
yields sheet resistance, contact resistance, and other parameters…………….28
Figure 2.11 Equivalent circuit of a solar cell, including series and shunt
resistances…………………………………………………………………….28
Figure 2.12 Terminal I-V properties of a p-n junction diode in the dark and in
illumination……………………………………………………………………29
Fig. 3.1 Variation of specific contact resistance for Ag (2000nm) metal
deposited on p-type Ge after annealing at different temperatures in H2 ambient
for 1 minute…………………………………..…………………………….30
Fig. 3.2 Variation of specific contact resistance for Ag-Ga(8%) (2000nm)
metal deposited on p-type Ge after annealing at different temperatures in H2
ambient for 1 minute………………………………………………….…….30
Fig. 3.3 Variation of specific contact resistance for Ag-Ga(8%) (2000nm)
metal structure deposited on p-type GaAs after annealing at 325℃ for various
time in H2 ambient………………..…………………………………...…….31
Fig. 3.4 Variation of specific contact resistance for Ag-Ga(15%) (2000nm)
metal deposited on p-type Ge after annealing at different temperatures in H2
ambient for 1 minute…………………………………………….………….31
Fig. 3.5 Variation of specific contact resistance for Ag-Ga(15%) (2000nm)
metal structure deposited on p-type GaAs after annealing at 350℃ for various
time in H2 ambient…………………………………………………..…..…..32
Fig. 3.6 Variation of specific contact resistance for Ag-Ga(25%) (2000nm)
metal deposited on p-type Ge after annealing at different temperatures in H2
ambient for 1 minute…………………………………………………....…..32
Fig. 3.7 Various of specific contact resistance for Ag-Ga(8%) (2000nm) metal
structure deposited on p-type GaAs after annealing at 350℃ for various time in
H2 ambient………………………………………………………….………33
Fig. 3.8 Variation of specific contact resistivity as a function of measuring for
Ag-Ga(8%) as deposited and after annealing at increasing temperature ranging
from 70℃ to 120℃……………………………………………..…………..33
Fig. 3.9 Variation of specific contact resistivity as a function of measuring for
Ag-Ga(15%) as deposited and after annealing at increasing temperature ranging
from 70℃ to 120℃………………………………………………...34
Fig. 3.10 Variation of specific contact resistivity as a function of measuring for
Ag-Ga(25%) as deposited and after annealing at increasing temperature
ranging from 70℃ to 120℃……………………………………………..…34
Fig. 3.11 Variation of the lowest specific contact resistivity as a function of
Ag-Ga structure composed of Ga (8%, 15%, and 25%)……………….......…35
Fig. 3.12 The surface morphology of (Ag-Ga(25%)2000nm) annealed at 325℃
for 1 min………………………………………………………………….…35
Fig. 4.1 Schematic cross-sections of the InGaP / GaAs/Ge triple -junction solar
cell……………………………………………………………………………..36
Fig. 4.2 Schematic of the current-voltage characteristic measurement system
(solar simulator)…………………………………………………………...…..36
Fig. 4.3 Variations of efficiency (η) for Ag-Ga metal structures deposited on
n-type ohmic contact after annealing at different temperature for 1min in H2
ambient under multi-suns………………………………………………....…37
Fig. 4.6 Variation of efficiency for InGaP / GaAs / Ge TJ solar cell with
(Ag-Ga(25%)2000nm) p-type ohmic contact after annealing at different
temperature for 1min in H2 ambient under one sun……………………….....38
Fig. 4.7 Variation of fill factor for InGaP / GaAs / Ge TJ solar cell with
(Ag-Ga(25%)2000nm) p-type ohmic contact after annealing at different
temperature for 1min in H2 ambient under one sun……………………...…..38
Fig. 4.8 Variation of short circuit current for InGaP / GaAs / Ge TJ solar cell
with (Ag-Ga(25%)2000nm) p-type ohmic contact after annealing at different
temperature for 1min in H2 ambient under one sun……………………….…39
Fig. 4.9 Variation of open circuit voltage for InGaP / GaAs / Ge TJ solar cell
with (Ag-Ga(25%)2000nm) p-type ohmic contact after annealing at different
temperature for 1min in H2 ambient under one sun……………………..…39
Fig. 4.10 Variation of efficiency for InGaP / GaAs / Ge TJ solar cell with
(Ag-Ga(25%)2000nm) p-type ohmic contact after annealing at different
temperature for 1min in H2 ambient under multi-suns by Fresnel
lens(16×16cm)………………………………………………..…………….40
Fig. 4.11 Variation of fill factor for InGaP / GaAs / Ge TJ solar cell with
(Ag-Ga(25%)2000nm) p-type ohmic contact after annealing at different
temperature for 1min in H2 ambient under multi-suns by Fresnel
lens(16×16cm)……………………………………………………….……..41
Fig. 4.12 Variation of short circuit current for InGaP / GaAs / Ge TJ solar cell
with (Ag-Ga(25%)2000nm) p-type ohmic contact after annealing at different
temperature for 1min in H2 ambient under multi-suns by Fresnel
lens(16×16cm)……………………………………………………….……..41
Fig. 4.13 Variation of open circuit voltage for InGaP / GaAs / Ge TJ solar cell
with (Ag-Ga(25%)2000nm) p-type ohmic contact after annealing at different
temperature for 1min in H2 ambient under multi-suns by Fresnel
lens(16×16cm)……………………………………………………….……..42


List of Tables
Table 2.1 Work functions of some metals…………………………………….22
Table 2.2 Electron affinity of some semiconductors………………………….23
Table 3.1 The composite structure of the Ag-Ga……………………………..29
Table 4.4 Compare the output parameters with different annealing temperature
for 1min in H2 ambient under one sun……………………………………..37
Table 4.5 Compare the output parameters with different annealing
temperature for 1min in H2 ambient under multi-suns by Fresnel
lens(16×16cm)……………………………………………………...………40

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