磷化銦鎵/砷化銦鎵/鍺三接面聚光型太陽能電池之全銅金屬製程之研究

Abstract

對於提升三五族太陽能電池的市場而言，在低成本的條件下改善轉換效率已經成為未來重要的發展趨勢。在本論文中，為了降低生產成本，我們利用較便宜的銅取代傳統的金作為三五族太陽能電池歐姆接觸的主要材料。在研究中，藉由電子束蒸鍍以及濺鍍技術將鈀(15nm)/鍺(150nm)/銅(150nm)結構沉積於N型砷化鎵覆蓋層上作為前接觸電極。經過250℃退火處理30秒後，其最低特徵電阻值為4.4 x 10-6 Ω-cm2。另一方面，沉積鉑(5nm)/鈦(50nm)/鉑(60nm)/銅(150nm)/鉻(10nm)於P型鍺基板上作為背接觸電極。經過310℃退火處理30秒後，其最低特徵電阻值為6.9 x 10-6 Ω-cm2。同時此兩種銅金屬化歐姆接觸結構均可以有效地阻擋銅擴散進入磊晶結構中，且經過週期性的退火處理後仍表現出良好的熱穩定性。最後，成功製作出受光面積為0.254 cm2的全銅金屬化三接面聚光型太陽能電池。在AM1.5，25℃條件下量測，可得轉換效率為23.11%及填充因子為82.48%。且進一步增加聚光倍率至122倍，可得轉換效率為37.21%及填充因子為83.98%。根據以上這些結果，鈀/鍺/銅與鉑/鈦/鉑/銅/鉻的銅金屬化歐姆接觸成功應用在三五族三接面太陽能電池上並具有優異的表現。

The improvement of conversion efficiency of solar cell with reduced cost is important for enhancing III-V solar cell market in the future. In this thesis, we use low cost Cu metal to replace traditional Au metal as the material of ohmic contact of III-V solar cells in order to reduce production cost. In this study, the Pd(15nm)/Ge(150nm)/Cu(150nm) metallization is used as the ohmic metal, the contact metal was deposited on n-GaAs cap layer as front contact using E-gun evaporation, sputtering method and was rapid thermal annealed at 250℃ for 30 sec. The specific contact resistance of Pd(15nm)/Ge(150nm)/Cu(150nm) metallization is about 4.4 x 10-6 Ω-cm2. On the other hand, Pt(5nm)/Ti(50nm)/Pt(60nm)/Cu(150nm)/Cr(10nm) was used as ohmic contact metal on the back side of p-Ge wafer, low specific contact resistance of 6.9 x 10-6 Ω-cm2 was achieved using these copper based contact metals. These two kinds of Cu-metallized ohmic contacts structure can effectively prevent Cu diffusion into the substrate and the epitaxial layers, and showed good thermal stability by repeating annealing treatment. Finally, the fully Cu-metallized InGaP/InGaAs/Ge triple-junction solar cell with 0.254 cm2 was successfully fabricated. The conversion efficiency and fill factor are about 23.11% and 82.48% at AM1.5, 25℃, respectively. When the concentration ratio is further increased to 122X, the conversion efficiency and fill factor become about 37.21% and 83.98%, respectively. Based to the results shown above, Cu-metallization ohmic contact systems, Pd/Ge/Cu and Pt/Ti/Pt/Cu/Cr have been successfully applied to fabricate III-V solar cells and provided excellent solar cell performance.