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Development of Germanium-Based Wafer-Bonded Four-Junction Solar Cells
摘要： Multijunction solar cells with four junctions are expected to be the next-generation technology for both space and concentrator photovoltaic applications. Most commercial triple-junction solar cells are today grown on germanium, which also forms the bottom subcell. Extending this concept to four junctions with an additional ～1-eV subcell was proven to be challenging. We investigate a new cell concept, which uses direct wafer bonding to combine a metamorphic GaInAs/Ge bottom tandem solar cell with a GaInP/AlGaAs top tandem on GaAs resulting in a monolithic four-junction cell on germanium. This article summarizes results of the cell developments, which have been resulting in a four-junction concentrator cell with 42% ef?ciency. We implemented a new passivated Ge backside technology to enhance the current generation in the Ge junction, and we propose realistic steps to realize solar cells with 45% ef?ciency using this cell architecture.
关键词： photovoltaics,concentrator,photovoltaic cells,germanium,III-V semiconductor materials
更新于2025-09-11 14:15:04
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Oxidation-Induced Changes in the ALD-Al2O3/InAs(100) Interface and Control of the Changes for Device Processing
摘要： InAs crystals are emerging materials for various devices like radio-frequency transistors and infrared sensors. Control of oxidation-induced changes is essential for decreasing amounts of the harmful InAs surface (or interface) defects because it is hard to avoid the energetically favored oxidation of InAs surface parts in device processing. We have characterized atomic-layer-deposition (ALD) grown Al2O3/InAs interfaces, pre-oxidized differently, with synchrotron hard x-ray photoelectron spectroscopy (HAXPES), low-energy electron diffraction, scanning tunneling microscopy, and time-of-flight elastic recoil detection analysis. The chemical environment and core-level shifts are clarified for well-embedded InAs interfaces (12 nm Al2O3) to avoid, in particular, effects of a significant potential change at the vacuum-solid interface. High-resolution As 3d spectra reveal that the Al2O3/InAs interface, which was sputter-cleaned before ALD, includes +1.0 eV shift, whereas As 3d of the pre-oxidized (3×1)-O interface exhibits a shift of -0.51 eV. The measurements also indicate that an As2O3 type structure is not crucial in controlling defect densities. Regarding In 4d measurements, the sputtered InAs interface includes only a +0.29 eV shift, while the In 4d shift around -0.3 eV is found to be inherent for the crystalline oxidized interfaces. Thus, the negative shifts, which have been usually associated with dangling bonds, are not necessarily an indication of such point defects as previously expected. In contrast, the negative shifts can arise from bonding with O atoms. Therefore, specific care should be directed in determining the bulk-component positions in photoelectron studies. Finally, we present an approach to transfer the InAs oxidation results to a device process of high electron mobility transistors (HEMT) using an As-rich III-V surface and In deposition. The approach is found to decrease a gate leakage current of HEMT without losing the gate controllability.
关键词： synchrotron,oxidation,atomic layer deposition,III-V semiconductor,photoelectron,InAs
更新于2025-09-10 09:29:36