Traps in AlGaInP materials and devices lattice matched to GaAs for multi-junction solar cells

Deep levels in solid-source MBE-grown n- and p-type (Al
_0.09
Ga
_0.91
)
_0.51
In
_0.49
P are investigated using deep level transient spectroscopy (DLTS). These results are correlated with background oxygen impurities measured by secondary ion mass spectroscopy and electrical properties using Hall effect. Oxygen impurity concentration is found to depend weakly on substrate offcut conditions in MBE-grown AlGaInP films. This is used to investigate the role of oxygen on deep levels in the n- and p-type samples using (100) GaAs substrates with three different substrate offcut conditions (A, B, and C). The DLTS of n-type AlGaInP reveals deep levels at E
_C
-0.22, E
_C
-0.31, E
_C
-0.69 eV and E
_C
-1.0 eV. The E
_C
-0.69 eV concentration tracked oxygen incorporation while the other levels decreased while the oxygen incorporation increased indicating possible secondary offcut effects. In general, we find a direct correlation between reduced carrier compensation, increased carrier mobility, lower trap concentration and lower oxygen content as a function of systematic changes in substrate offcut conditions.