高增益磷化銦雪崩光二極體及三接面砷化鎵太陽能電池電流匹配之研究

Fabrication of high-multiplication InP avalanche photodiode and current-matched triple-junction GaAs solar cell

劉政杰(Jheng-Jie Liu)

指導教授 ： 何文章

國立臺北科技大學/電資學院/光電工程系研究所/博士(2014年)

摘要

本論文進行具InP/InAlAs異質結構雪崩層之磷化銦分離吸收、漸變、電荷、雪崩層(SAGCM)結構雪崩光二極體及三接面砷化鎵太陽能電池(Triple junction GaAs-based solar cell, 3J-SC)之研製及特性提升探討。
本研究之APD是利用InP及InAlAs異質結構組合之雪崩層，入射光被吸收產生之電洞經InAlAs區域可使其能量增長，讓電洞進入高電場InP雪崩層區時立即發生游離碰撞(Impact-ionization)，進而提升雪崩增益。在元件特性探討，我們進行在常溫(25°C)至低溫(-70°C)下暗電流電壓(Dark I-V)特性、照光電流電壓(Photo I-V)特性、雪崩增益等特性量測分析，及進行電容電壓(C-V)、3dB頻率響應量測分析。所完成之InP-based SAGCM APD，在波長1550 nm、照光1 nW、溫度為25°C及-70°C下，InP-based SAGCM APD最大雪崩增益分別可達到1012及3306。在C-V特性，溫度為25°C下，當偏壓在0.9倍之崩潰電壓(Breakdown Voltage, Vbr)時，電容值約為0.59 pF，此時3-dB截止頻率(f3dB)超過3 GHz。當雪崩增益為20，其最大增益頻寬乘積可達62 GHz。
3J-SC是由GaInP、GaAs及Ge等三個不同能隙材料串聯組成，在磊晶後GaInP及GaAs太陽電池會有電流不匹配產生。因此本論文提出二氧化矽奈米柱抗反射層(SiO2-Nanopillars structure anti-reflection coating, SiO2-Nanopillars ARC)及混合沉積漸變式ARC兩種架構以改善電池間電流不匹配之問題。(a)頂部限流電池之裸3J-SC電流不匹配改進：本論文利用雙層抗反射層(TiO2/SiO2)及搭配SiO2-Nanopillars於雙層抗反射層上，形成具有表面次波長結構SiO2-Nanopillars ARC，它能使空氣與表面結構之間產生有效的梯度折射率，這可以抑制光的反射及降低短波長的反射率，同時也減低光散射，進而增加光捕捉。(b)中間限流電池之裸3J-SC電流不匹配改進：本論文利用旋轉塗佈及真空蒸鍍之混合沉積法形成graded-index TiO2薄膜及SiO2薄膜之三層漸變式抗反射薄膜，並透過商用光學薄膜軟體設計薄膜之厚度，讓中波長的反射率能有效降低且具有寬波段低反射率，進而提高中間電池之電流。最後經由反射率、光電流、EQE分析驗証兩種不同抗反射層結構可改善3J-SC電池間電流不匹配之問題及提升3J-SC總光伏特性。

關鍵字

三接面砷化鎵太陽能電池 ； 磷化銦 ； 雪崩光二極體 ； 電流匹配 ； 漸變式折射率抗反射層

並列摘要

In this thesis, the fabrication and performane characterization of InP-based SAGCM APD with InP/InAlAs hetero-structure avalanche layer and the triple-junction GaAs-based solar cells with the subwavelength nanopillars and graded-Index anti-reflection coating (ARC) were proposed and demonstrated.
The hetero-multiplication region is consisted of an InAlAs energy build-up layer and an InP multiplication layer. InAlAs layer is mainly to make the energy promotion. When the potogenerated holes went into the high electric field InP avalanche region, the impact-ionization was immediately generation. The dark current-voltage (I–V), photo I–V characteristics and multiplication gains of APD were characterized from 25oC to -70oC. The capacitance-voltage (C–V) and 3-dB frequency response are also measured and compared. The maximum multiplication gain of 1012 at 25oC and of 3306 at −70oC were achieved, respectively, when the APD illuminated with an optical power of 1 nW at the wavelength of 1550 nm. Capacitance of 0.59 pF was obtained when biased at 0.9 Vbr and the gain-bandwidth product of 62 GHz also achieved in the propose APD structure.
The epitaxial layers of the triple-junction GaAs-based solar cell were consisted of a GaInP top cell and a GaInAs middle cell. In general, the current mismatched between the GaInP subcell and GaAs subcell was generated after epitaxied growth. To improve current mismatched, two approaches of (a) SiO2-Nanopillars ARC structure and (b) hybrid deposition graded-index ARC two structures were proposed in this study. The experimental results show that (a) for a top cell current limited 3J-SC: using a SiO2-Nanopillars SiO2/TiO2 ARC on 3J-SC, a low and broad band reflective spectrum can achieve, especially exhibited at short wavelength region. Thus, the photocurrent generated in top cell was enhanced as well as the overall performance of 3J-SC was enhanced. (b) For a middle cell current limited 3J-SC: we proposed a hybrid deposition method to fabricated graded-index TiO2/SiO2 thin film to form a triple layer (TL) ARC. Before deposition these thin films, we also simulated the optical reflectance of TL ARC using TFCalcTM optical thin film software to obtain a low reflective band at the middle cell wavelength. Therefore, the photocurrent generated in the middle cell was enhanced due to a low reflectance exhibited at 680-950 nm wavelength band. Finally, the optical reflectance, EQE response, and photovottaic I-V were measured and compared. The results show that the proposed approaches were effectively improved the current mistmatched between the top and middle cell of 3J-SC and enhanced the overall photovoltaic performance of 3J-SCs.

並列關鍵字

Triple junction GaAs-based solar cell ； InP ； Avalanche photodiode ； current match ； Grading Index anti-reflection coating

參考文獻

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