Absorption coefficients in AlGaInP lattice-matched to GaAs

•Absorption coefficient of AlGaInP alloys has been obtained down to 100 cm−1.•Indirect and direct gap energies in AlGaInP were determined.•Photocurrent measurements in PINs can be used to extract accurate absorption coefficients.

The absorption coefficient of AlGaInP lattice-matched to GaAs, across the composition range from AlInP to GaInP has been obtained from photocurrent versus wavelength measurements on seven homo-junction AlGaInP PIN diode structures. Due to the sensitivity of the photocurrent measurement technique, values of absorption down to 100 cm−1 have been determined close to the band-gap. From these, the bandgaps in this material system were extracted across the composition range and these corroborate data in the literature that shows the band-gap becoming indirect when the aluminium content, x>0.48.