Electrical and photoelectrical properties of a GaAs-based p-i-n structure, grown by MOVPE

A GaAs-based p-i-n junction grown by MOVPE and using the high purity and low dissociation temperature tertiarybutylarsine (TBAs) precursor, was studied. Such a structure is suitable to play the role of a sub-cell in a multi-junction photovoltaic device. Electrical measurements showed excellent properties of the junction; in particular, the forward current-voltage characteristic was detected over ten orders of magnitude, showing: a rectification ratio of about 1010 at 1.2 V, low reverse current and low series resistance. Capacitance measurements confirmed the low contaminant concentration of the unintentionally doped intrinsic region (of the order of 1014 cm-3). A fill factor equal to 0.81, confirming low background doping and indicating low series resistance, has been measured for the illuminated junction. The long wavelength tail of the spectral response, controlled by the diffusion length of the minority carriers (holes) in the n-type base region of the junction, has been fitted, giving a hole diffusion length equal to 2 ?m. The comparison with an identical structure, grown by MOVPE with the use of the traditional arsine precursor, showed that the p-i-n junction here studied has some superior electrical and photoelectrical properties, in particular a lower dark-current. Although the primary use for devices of this kind is as a part of a more complex heterostructure, the p-i-n junction studied in this work also achieves a good projected conversion efficiency as a single junction cell (21.4±1)% at AM1.5g.