Gas Immersion Laser Doping: n plus plus Phosphorus Doping on p plus Cz-Si Wafers With a Highly Doped p plus plus Emitter

Interconnecting the two sub-cells in a monolithically integrated 2-terminal perovskite/silicon tandem solar cell architecture is a critical aspect with a crucial impact on the cell's conversion efficiency. Our approach to fabricate the interconnecting layer is to form a tunnel junction (TJ) directly on the silicon sub-cell using Gas Immersion Laser Doping (GILD) technique, to achieve an abrupt doping profile required for tunnelling junctions. We present our in-house developed GILD setup, comprised of two main systems: the reaction chamber and the laser apparatus. The setup is capable of laser doping up to 10x10 cm(2) silicon wafers under a POCl3-rich atmosphere. Surface melting of silicon wafers is accomplished by laser rastering sequences with a Nd:YAG ns pulsed 1064 nm laser coupled to a high speed galvano head. Two types of Cz-Si wafers were laser doped: p-type (100)-oriented monocrystalline Cz-Si wafers and p+ (100)oriented Cz-Si wafers with a p++ emitter. Secondary ion mass spectrometry (SIMS) depth profiling was used to characterize the sample elemental composition. On Cz-Si wafers with a p++ emitter, results show successful surface doping with a flat phosphorus concentration within the 10(19)-10(20) cm(-3) range, followed by an abrupt "shoulder" that sets the maximum melt depth location near 220-330 nm. Boron from the emitter accumulates at the maximum melt depth. This is attributed to the well-known pile-up phenomenon. p-type Cz-Si wafers without an emitter were also successfully doped, although for the same laser processing conditions, they present a higher maximum melt depth. This highlights that the sample properties also affect laser absorption and resultant melting and hence the doping profiles. The results show that laser rastering parameters, such as distance between consecutive laser spots and number of rastering sequences, influence the shape of the phosphorus doping profile, but also alter the underlying boron emitter profile due to pile-up.