臺灣博碩士論文加值系統

摘要
在本論文中，我們將會先從探討鈀的厚度在鈀/金以及鈀/銀/金沉積在正型鍺當作歐姆接觸金屬結構之影響，為了得到最低的特徵阻值ρc，我們尋求最佳之鈀的金屬厚度還有最佳的回火條件，並且運用傳輸線模型法(TLM)計算出鈀/金金屬材料在正型鍺的特徵阻值。實驗結果顯示，在鍺(30nm)/金(60nm)在350℃兩分鐘的回火條件下，能夠形成此系列之最佳特徵阻值( ρc=6×10-6 Ω-cm2 )。接著，利用相同方式找尋鈀/銀/金金屬材料在正型鍺的特徵阻值，發現當鈀(20nm)/銀(60nm)/金(20nm) 在350℃兩分鐘的回火條件下，也能形成此系列之最佳特徵阻值
( ρc=3.9×10-5 Ω-cm2 )。
緊接著，將具有最低特徵阻值的歐姆接觸金屬組成結構(亦即鈀 (30nm)/金(60nm)以及鈀(20nm)/銀(60nm)/金(20nm)) 蒸鍍在雙接面(GaAs/Ge)太陽能電池當作背電極，來探討鈀/金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。

Abstract
In this dissertation, we discussed the effects of thickness Pd on the Pd / Au and Pd / Ag / Au ohmic contact metallurgical structure deposited on P-Ge material. At first ,we studied the optimum thickness of the Pd layer and the suitable annealing temperature and time for obtaining the lowest specific contact resistance ρc on P-Ge by transmission line model method (TLM).We found out that the optimum metallurgical structure is Pd (30 nm) / Au (60 nm) after annealed at 350 ℃ for 2 minutes. The lowest value ρc=6×10-6 Ω-cm2 of specific contact resistance could be attained. Then, we used the same method to study the optimum thickness of the Pd、Ag and Au layers and the suitable annealing temperature and time for the lowest specific contact resistance ρc. We found out that the optimum metallurgical structure is Pd (20 nm) / Ag (60 nm) / Au (20 nm), in which the lowest specific contact resistance value ρc=3.9×10-5 Ω-cm2 could be attained when the sample is annealed at 350℃ for 2 minutes.
Then, we applied the optimum ohmic contact metallurgical structure Pd (30 nm) /Au (60 nm) and Pd (20 nm) / Ag (60 nm) / Au (20nm), respectively, as the p-type ohmic contact of dual-junction (DJ) solar cells. After that, we measured the efficiency (Eff), fill factor (FF), open circuit voltage (Voc) and short circuit current (Isc) of solar cells. The measured results indicate that solar cells had the best performance when having the ohmic contact fabricated at the optimum conditions.

Content
Abstract(Chinese)...............................I
Abstract(English)..............................II
Acknowledgment.................................IV
Content.........................................V
Figure captions...............................VII
List of Tables................................XIV
Chapter 1 Introductions.........................1
Chapter 2 Theoretic foundations.................4
2.1 Metal and semiconductor contact theory....4
2.2 Transmission Line Model (TLM).............6
2.3 Measurement method........................8
2.4 Basic concepts of the solar cell..........9
2.5 Equivalent circuit analysis of the solar cell...........................................10
2.6 Fundamental solar cell parameters........11
Chapter 3 Fabrication process and electric characteristic of ohmic contact metals.........20
3.1 Ge TLM fabrication process...............20
3.1.1 Wafer cleaning process................20
3.1.2 Photolithography process..............21
3.1.3 Metal deposition......................21
3.1.4 Mesa etching process..................22
3.2 Results and discussions..................22
3.2.1 Analysis system.......................23
3.2.2 Specific contact resistance analysis..23
3.2.2 (a)Pd/Au.............................23
(b)Pd/Ag/Au..........................24
3.2.3 Surface morphology....................25
3.2.4 Energy Dispersive Spectrometer (EDS)analysis.......................................25
Chapter 4 Characteristics of the GaAs/Ge dual-junction solar cell............................42
4.1 GaAs/Ge dual-junction solar cell structure.42
4.2 Dual-junction solar cell fabrication process........................................42
4.2.1 Front surface process..........................................................................42
4.2.2 Back surface process………………………………………………..43
4.3 Current-Voltage (I-V) measurement system ……………………….......44
4.4 Characteristics of the GaAs/Ge dual –junction solar cell……………....44
Chapter 5 Conclusions……………………………………………………...58
References…………………………………………………………………...60

Figure Captions
Figure 1.1 Schematic cross-sections of the GaInP/GaAs/Ge triple junction solar cell………………………………………………………………………...3
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………………………………………………14
Figure 2.2 Band diagram for the junction at equilibrium……………………14
Figure 2.3 Ohmic metal-semiconductor contact: Φm < Φs for an n-type semiconductor at the equilibrium band diagram for the junction……………15
Figure 2.4 Ohmic metal-semiconductor contact: Φm > Φs for a p-type semiconductor at the equilibrium band diagram for the junction……………15
Figure 2.5 Ohmic metal-semiconductor contact: Heavy doped for an n-type semiconductor at the equilibrium band diagram for the junction……………16
Figure 2.6 Ohmic metal-semiconductor contact: Heavy doped for a p-type semiconductor at the equilibrium band diagram for the junction……………16
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……………………………………………………………17
Figure 2.8 The approaches used to model the ohmic contact of a transmission line……………………………………………………………………………17
Figure 2.9 Basic pattern used to experimentally determine contact resistance parameters. Ohmic contacts are separated by increasing distance………18
Figure 2.10 Plot of measure resistance as a function of contact separation yields sheet resistance, contact resistance, and other parameters……………18
Figure 2.11 Equivalent circuit of a solar cell, including series and shunt resistance…………………………………………………………………19
Figure 2.12 Terminal I-V properties of p-n junction diode in the dark and in illumination………………………………………………………………19
Figure 3.1 Electron beam evaporation system………………………………28
Figure 3.2 Variations of specific contact resistivity for Pd (10 nm)/Au (60 nm) metal structure deposited on p-type Ge after annealing at different temperature for various time in pure N2 ambient…………………………………………29
Figure 3.3 Variations of specific contact resistivity for Pd (20 nm)/Au (60 nm) metal structure deposited on p-type Ge after annealing at different temperature for various time in pure N2 ambient…………………………………………29
Figure 3.4 Variations of specific contact resistivity for Pd (30 nm)/Au (60 nm) metal structure deposited on p-type Ge after annealing at different temperature for various time in pure N2 ambient…………………………………………30
Figure 3.5 Variations of specific contact resistivity for Pd (40 nm)/Au (60 nm) metal structure deposited on p-type Ge after annealing at different temperature for various time in pure N2 ambient…………………………………………30
Figure 3.6 Variations of specific contact resistivity for Pd (60 nm)/Au (60 nm) metal structure deposited on p-type Ge after annealing at different temperature for various time in pure N2 ambient…………………………………………31
Figure 3.7 Variations of specific contact resistivity for Pd (30 nm)/Au (60 nm) metal structure deposited on p-type Ge after annealed at different temperature
in pure N2 ambient………………………………………………………31
Figure 3.8 Measured specific contact resistance as a function of annealing time for Pd (30 nm)/Au (60 nm) metal structure deposited on p-type Ge substrate after annealed at 350 ℃ in pure N2 ambient…………………………32
Figure 3.9 Variations of specific contact resistivity for Pd (5 nm)/Ag (60 nm)/Au (20 nm) metal structure deposited on p-type Ge after annealing at different temperature for various time in pure N2 ambient…………………....32
Figure 3.10 Variations of specific contact resistivity for Pd (10 nm)/Ag (60 nm)/Au (20 nm) metal structure deposited on p-type Ge after annealing at different temperature for various time in pure N2 ambient………………33
Figure 3.11 Variations of specific contact resistivity for Pd (20 nm)/Ag (60 nm)/Au (20 nm) metal structure deposited on p-type Ge after annealing at different temperature for various time in pure N2 ambient………………33
Figure 3.12 Variations of specific contact resistivity for Pd (30 nm)/Ag (60 nm)/Au (20 nm) metal structure deposited on p-type Ge after annealing at different temperature for various time in pure N2 ambient………………34
Figure 3.13 Variations of specific contact resistivity for Pd (40 nm)/Ag (60 nm)/Au (20 nm) metal structure deposited on p-type Ge after annealing at different temperature for various time in pure N2 ambient………………34
Figure 3.14 The surface morphology of Pd (30 nm)/Au (60 nm) after annealed at 260 ℃ in pure N2 ambient (500X)………………………………………35
Figure 3.15 The surface morphology of Pd (30 nm)/Au (60 nm) after annealed at 320 ℃ in pure N2 ambient (500X)………………………………………35
Figure 3.16 The surface morphology of Pd (30 nm)/Au (60 nm) after annealed at 350 ℃ in pure N2 ambient(500X)……………………………………36
Figure 3.17 The surface morphology of Pd (30 nm)/Au (60 nm) after annealed at 400 ℃ in pure N2 ambient(500X)……………………………………36
Figure 3.18 The surface morphology of Pd (20 nm)/Ag (60 nm)/Au (20 nm) after annealed at 320 ℃ in pure N2 ambient (500X)………………………37
Figure 3.19 The surface morphology of Pd (20 nm)/Ag (60 nm)/Au (20 nm) after annealed at 350 ℃ in pure N2 ambient (500X)…………………37
Figure 3.20 The surface morphology of Pd (20 nm)/Ag (60 nm)/Au (20 nm) after annealed at 400 ℃ in pure N2 ambient(500X)……………………38
Figure 3.21 Percentage of composition and the associated specific contact resistance as a function of annealing time for Pd (30 nm)/Au (60 nm) metal structure after annealed at 260 ℃ in pure N2 ambient……………………38
Figure 3.22 Percentage of composition and the associated specific contact resistance as a function of annealing time for Pd (30 nm)/Au (60 nm) metal structure after annealed at 320 ℃ in pure N2 ambient……………………39
Figure 3.23 Percentage of composition and the associated specific contact resistance as a function of annealing time for Pd (30 nm)/Au (60 nm) metal structure after annealed at 350 ℃ in pure N2 ambient……………………39
Figure 3.24 Percentage of composition and the associated specific contact resistance as a function of annealing time for Pd (30 nm)/Au (60 nm) metal structure after annealed at 400 ℃ in pure N2 ambient……………………40
Figure 3.25 Percentage of composition and the associated specific contact resistance as a function of annealing time for Pd (20 nm)/Ag (60 nm)/Au (20 nm) metal structure after annealed at 320 ℃ in pure N2 ambient…………40
Figure 3.26 Percentage of composition and the associated specific contact resistance as a function of annealing time for Pd (20 nm)/Ag (60 nm)/Au (20 nm) metal structure after annealed at 350 ℃ in pure N2 ambient…………41
Figure 3.27 Percentage of composition and the associated specific contact resistance as a function of annealing time for Pd (20 nm)/Ag (60 nm)/Au (20 nm) metal structure after annealed at 400 ℃ in pure N2 ambient……41
Figure 4.1 Schematic cross-sections of the GaAs/Ge Dual -junction solar cell…………………………………………………………………………….49
Figure 4.2 Schematic of the current-voltage characteristic measurement
system (solar simulator)……………………...…………………………….….50
Figure 4.3 Light I-V curve and output power of the Pd (10 nm)/Au (60 nm) metal structure after annealed at 350 ℃ for GaAs/Ge Dual -junction solar cell……………………………………………………………………………..51
Figure 4.4 Light I-V curve and output power of the Pd (30 nm)/Au (60 nm) metal structure after annealed at 330 ℃for GaAs/Ge Dual -junction solar cell……………………………………………………………………………..51

Figure 4.5 Light I-V curve and output power of the Pd (30 nm)/Au (60 nm) metal structure after annealed at 350 ℃for GaAs/Ge Dual -junction solar cell……………………………………………………………………………..52
Figure 4.6 Light I-V curve and output power of the Pd (30 nm)/Au (60 nm) metal structure after annealed at 365 ℃for GaAs/Ge Dual -junction solar cell………………………….…………………………………………………52
Figure 4.7 Light I-V curve and output power of the Pd (60 nm)/Au (60 nm) metal structure after annealed at 350 ℃for GaAs/Ge Dual -junction solar cell……………………………………………………………………………..53
Figure 4.8 Light I-V curve and output power of the Pd (20 nm)/Ag (60 nm)/Au (20 nm) metal structure after annealed at 350 ℃for GaAs/Ge Dual -junction solar cell…………………………………………………………………….…53
Figure 4.9 The Jsc versus annealing temperature of Pd (30 nm)/Au (60 nm) for 2 minutes in pure N2 ambient under one-sun………………………………….54
Figure 4.10 The Voc versus annealing temperature of Pd (30 nm)/Au (60 nm) for 2 minutes in pure N2 ambient under one-sun……………………………...54
Figure 4.11 The fill factor versus annealing temperature of Pd (30 nm)/Au (60 nm) for 2 minutes in pure N2 ambient under one-sun…………………………55
Figure 4.12 The efficiency versus annealing temperature of Pd (30 nm)/Au (60 nm) for 2 minutes in pure N2 ambient under one-sun…………………………55
Figure 4.13 The Jsc versus different contact structures after annealed 350℃ for 2 minutes in pure N2 ambient under one-sun………………………………….56
Figure 4.14 The Voc versus different contact structures after annealed 350℃ for 2 minutes in pure N2 ambient under one-sun……………………………..56
Figure 4.15 The fill factor versus different contact structures after annealed 350℃ for 2 minutes in pure N2 ambient under one-sun………………………57
Figure 4.16 The efficiency versus different contact structures after annealed 350℃ for 2 minutes in pure N2 ambient under one-sun………………………57

List of tables
Table 2.1 Work functions of some metals…………………………………13
Table 2.2 Electron affinity of some semiconductors………………………13
Table 3.1 Composite structure of the Pd/Au……………………………27
Table 3.2 Composite structure of the Pd/Ag/Au………………………27
Table 4.1 The different metal condition and annealing condition of the samples applied in DJ solar cell……………………………………………………….47
Table 4.2 Compare the output parameters with different annealing temperature for 2 minutes in pure N2 ambient under one-sun……………………………...47
Table 4.3 Compare the output parameters with different contact structures after annealed 350℃ for 2 minutes in pure N2 ambient under one-sun…………….48

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