OCVD measurement for extraction of minority carrier lifetime in GaSb, GaAs and silicon junctions: simulations and experimentations

Minority carrier lifetime measurement is essential to optimize PV solar cells. The OCVD method allows it into p-n junction. Compare to other techniques widely used like PCD or TRPL, it is really simple and cheap. However it has been scarcely used for III-V materials mainly due to their low lifetime (< 1 μs). We focus on III-V semiconductors because they are good candidates to multijunction solar cells dedicated to CPV. Nevertheless, the OCVD signal must be simulated in order to extract lifetime in these materials. Therefore, we first used TCAD simulation to study design influence (bulk thickness and emitter doping) of silicon and GaAs p-n junctions on OCVD signal. We examined lifetime extraction in a specific region: the bulk. In parallel, we characterized GaSb and GaAs diodes. Experimental I-V and OCVD curves of GaSb p-n junctions have been fitted by TCAD simulation. It allowed to highlight the blocking diode is of major importance. Its blocking time has to be shorter than measured lifetime. Finally, we developed a model under Python based on transient single-diode model. It enables first to simulate OCVD signal, then to fit experimental curve with several fitting variables (τ_OCVD, N_l et R_sh). This modelling allowed to study further the variable influences on the signal and thus improved our knowledge on OCVD behaviour. (author)