Characterization of InGaAsP/InP p-i-n Solar Cell Structures Using Modulation Spectroscopy and Secondary Ion Mass Spectrometry

We have investigated two In sub (1-x) G sub (ax) As sub y P sub (1-y)/InP p-i-n multiple quantum (MQW) solar cell structures (with and without gold contacts) with intrinsic (i)-InP spacers and two InP p-i-n control samples (with and without gold contacts) using electroreflectance (ER), piezoreflectance (PZR) and secondary ion mass spectromety (SIMS). From a comparison of the rich ER/PZR spectra from the MQW regions (including the quantum confined Stark effect produced by an external bias) with an envelope function calculation (strain and electric field) we have been able to completely characterize the composition (x,y), strain and well width of the MQWs. From the electric fields originating in the i-InP region of the two InP p-i-n control samples, as determined from the observed Franz-Keldysh oscillations (FKOs), we have evaluated the amount of p-dopant interdiffusion, in agreement with the SIMS. The FKOs from the i-InP region of the MQW samples reveal an unusual effect, i.e., a modulation-doping field (superimposed on the p- i-n field) due to a transfer of charge from the n-InP layer to the nearest InGaAsP quantum well.