Multi-band solar cell using strain-balanced quantum well of nitride semiconductors

针对基于两步光子吸收的光电流产生方式，采用了量子阱结构，并将其作为三能级光吸收介质，具有很好的应用前景。首先研究了InGaN/GaAsP应变平衡量子阱结构，势垒小于3 nm的超晶格结构通过两步光子吸收产生光电流，这可能是由于隧道传输有效地分离了载流子而延长了量子限制态下的载流子寿命。这种材料系统非常适合于通过两步光子吸收获得高效率所需的大频带偏移量。应变平衡InGaN/AlN堆栈在晶体质量和光致发光性能方面优于传统的InGaN/GaN堆栈。最后，对氮化物量子阱中载流子的提取进行了研究。

Aiming at the photocurrent generation on the basis of two-step photon absorption, which is a promising way of over 50% efficiency, quantum well structure was employed and its potential as a 3-level light absorbing medium. First, InGaAs/GaAsP strain-balanced quantum wells were investigated and a superlattice structure with the barriers thinner than 3 nm exhibited the photocurrent generation via 2-step photon absorption, probably due to extended carrier lifetime in the quantum confinement state owing to efficient carrier separation by tunneling transport.Next, the strain-balanced stacking technology for InGaN/AlN system was established. This material system is ideal for a obtaining a large band offset which is required for the high efficiency by two-step photon absorption. The strain-balanced InGaN/AlN stack was superior to conventional InGaN/GaN in terms of crystal quality and photoluminescenc property. Finally, the carrier extraction from the nitride quantum wells was examined.