Native oxide and optical constant determination of InP lattice-matched quaternary materials using variable angle spectroscopic ellipsometry

Quaternary materials lattice-matched to InP have been examined using variable angle spectroscopic ellipsometry (VASE). The optical constants of InGaAsP and InAlGaAs, lattice-matched to InP with bandgaps of 1.2eV, have been determined. The native oxide layer of the materials was simulated using a weighted Bruggeman effective medium approximation (EMA) approach comprising the known optical constants of the native oxides of the end-point materials. The extracted optical constants from VASE measurements are compared with interpolated values from literature data, in order to assess the effectiveness of such an approach for quaternary alloys. Additionally, the absorption coefficients of InGaAsP and InAlGaAs are compared, the results of which can be used to evaluate the effectiveness of both material systems in high efficiency multijunction (MJ) photovoltaic (PV) devices.